The development of supportive-care agents for patients with cancer

The development of supportive-care agents for patients with cancer

397 The development of supportive-care agents for patients with cancer Theresa K. Neumann1 and MaryAnn Foote2,* 1 Associate Director, Clinical Resea...

276KB Sizes 3 Downloads 37 Views

397

The development of supportive-care agents for patients with cancer Theresa K. Neumann1 and MaryAnn Foote2,* 1

Associate Director, Clinical Research; 2Director, Medical Writing, Amgen Inc., One Amgen Center Drive, Thousand Oaks, CA 91320-1699, USA Abstract. As the population ages, a dramatic increase in the number of cases of cancer is expected and the need for supportive-care agents, those used to ameliorate some of the side effects of cancer or its treatment, becomes more urgent. At present, supportive-care products are available and new agents are being developed with novel mechanisms of action or modifications of existing agents that improve performance. Because of the urgent need for such products, efficient development is required to deliver useful products to patients as rapidly as possible. This chapter uses actual examples to illustrate the stages of drug development, phase 1 through phase 3. Keywords: biotechnology – medical biotechnology, clinical research – phase 1, clinical research – phase 2, clinical research – phase 3, marketing authorization.

Introduction Patients who have cancer – and particularly those receiving chemotherapy or radiation therapy – frequently have a variety of comorbid conditions. These comorbid conditions may be due to their primary disease (e.g., anemia secondary to malignancy), but often they are the result of chemotherapy or radiation therapy. Common treatment-related conditions include extreme fatigue, pain, alopecia, nausea and vomiting, malnutrition and cachexia, mucositis and stomatitis, anemia, thrombocytopenia, and neutropenia. These manifestations of cancer and/or its therapy are often major contributors to morbidity and mortality from the disease and are known to reduce a patient’s quality of life. Examples of drugs developed to treat cancer-related symptoms or ameliorate side effects from chemotherapy include bisphosphonates, hematopoietic growth factors, and antiemetics. Pamidronate, a bisphosphonate, was approved for the treatment of hypercalcemia of malignancy, but it later showed utility in decreasing skeletal-related events. Hematopoietic growth factors, such as filgrastim (r-metHuG-CSF) and epoetin alfa (rHuEPO), have been shown to correct chemotherapy-induced neutropenia and anemia of cancer, respectively. Ondansetron, an antiemetic, was approved for postoperative nausea and vomiting in adults, but it is also an effective treatment in the prevention and treatment of chemotherapy-induced nausea and vomiting. This chapter will focus on drug development of biotech products and recent development of selective new supportive-care agents and not on the conditions themselves. For more information, interested readers should refer to any one of *Corresponding author: Tel: þ 1 805 447 4925. Fax: þ 1 805 498 5593. E-mail: [email protected] BIOTECHNOLOGY ANNUAL REVIEW VOLUME 9 ISSN 1387-2656 DOI: 10.1016/S1387-2656(03)09011-2

ß 2003 ELSEVIER SCIENCE BV ALL RIGHTS RESERVED

398 the many excellent textbooks that discuss the practical aspects of treating these manifestations [1]. Drug development All new biologics follow the same highly regulated process to attain marketing approval. Drug development has become more global in the past decade, particularly under the aegis of the International Conference on Harmonization (ICH) [2]. With the adoption of the Common Technical Document (CTD), the uniformity of drug applications worldwide will be strengthened. Although the New Drug Application (NDA) and Biologic License Application (BLA) processes have common ground with the European Union’s documents (Clinical Trial Application [CTA] and Marketing Authorisation Application [MAA]), the process in the United States will be used to illustrate the steps in drug and biologic development. Many regulatory documents are required for drug development and are briefly described. Investigational New Drug application A new biologic cannot be tested in humans in the United States without an Investigational New Drug (IND) application. This application requires Food and Drug Administration (FDA) approval to permit the interstate shipment of drug products. The IND process ensures that humans are not exposed to undue risks from investigational products by requiring quality controls in manufacturing; extensive testing in animals; and review of the clinical protocol, investigator’s brochure, and informed consent document by institutional review boards (IRBs); the entire package is reviewed by the FDA. The contents of the IND are listed in Table 1. As the testing of a drug or biologic proceeds through the development process, the IND may be amended; the investigational plan and protocols may be revised; study sites may change; the investigator’s brochure is updated to reflect new and significant information; new protocols are submitted; and manufacturing or product characteristics may change. Serious adverse events reported by patients or their healthcare professional must be communicated to the FDA on a timely basis and in annual IND updates. Table 1. Components of an investigational new drug application. Introduction General investigational plan Investigator’s brochure Clinical protocol(s) Chemistry, manufacturing, and controls Nonclinical pharmacology and toxicology data Previous human experience

399 The initial clinical protocol is a part of the original IND submission and as a program matures, other clinical protocols are filed to the IND. A clinical protocol is a plan for the specific scientific study of a drug or biologic in humans. The goal of a clinical protocol usually is to collect data to support label claims (i.e., prescribing information). Protocols differ by the phase of drug development (phases 1, 2, 3, or postmarketing phases 3b or 4) or by use (compassionate). Not all INDs are held by drug sponsors – Investigator INDs are possible. Other INDs include Treatment INDs and Compassionate-use INDS. These latter INDs are submitted to the FDA to facilitate the availability of investigational drugs for critically ill patients who have failed all other treatment options or for whom no treatments are available. These atypical INDs do not replace the full IND. Instead, they are filed as additions to the original IND submission. New Drug Application/Biologic License Application A new drug cannot be marketed in the United States without an NDA/BLA approval. NDAs were reviewed by the FDA’s Center for Drug Evaluation and Research (CDER), and BLAs were reviewed by the FDA’s Center for Biologics Evaluation and Research (CBER), but new regulations may change this process. Some biologics are reveiwed by CDER, rather than CBER, and some biologics require an NDA rather than a BLA. NDAs and BLAs are huge documents, often containing hundreds of thousands of pages of data. Well-designed clinical development programs that allow determination of safe and efficacious dose and schedule and which typically include a comparative treatment as standard of care are required. Clinical trials submitted as part of the NDA or BLA to gain marketing approval are routinely conducted in a sequential fashion, phase 1 through phase 3 (Table 2). Postmarketing trials (i.e., phase 3b or phase 4) are trials done after gaining regulatory approval to market a product and serve to collect further safety information and assess other potential indications. Table 2. Description of phase 1, 2, and 3 clinical studies. Phase

No. of patients

Purpose

Comments

1

Few, maybe less than 25

2

More, maybe 25–100

Establish preliminary safety risks and obtain pharmacokinetic and pharmacodynamic data Further explore safety, provide data on early indicators of efficacy, provide sufficient data to design phase 3 trials

3

Many, often several hundred to several thousand

Healthy volunteers can be used to test drugs, but patients are usually used to test biologics. Need a proper control group, double-blind drug administration, and proper randomization of patients to treatment groups. Design is crucial because the endpoints supported by the data make up the label and marketing claims.

Confirm efficacy and further characterize safety

400 The remainder of the chapter will discuss the science and decision-making used in the development of support-care agents in oncology and use examples from our experiences. For each drug, we discuss the basic mechanism of action, phase 1 results, phase 2 proof-of-concept studies, and phase 3 comparative studies done to obtain a marketing label. Pegfilgrastim Background information Neutropenia and infection are potential serious complications of cancer chemotherapy, and the risk of infection is directly related to the depth and duration of neutropenia [3]. The severity of neutropenia depends on the intensity of the chemotherapy regimen, as well as on host- and disease-related factors. Fever may be the only manifestation of infection because underlying immunosuppression may obscure the classic signs and symptoms. Delay in initiating subsequent cycles of chemotherapy or decrease in the dose of chemotherapy, or both may be required because of severe neutropenia. Such delay may compromise an otherwise effective chemotherapy. Filgrastim, with properties comparable to the endogenous protein, was licensed for amelioration of chemotherapy-induced neutropenia in 1991. Treatment of severe neutropenia with filgrastim reliably increases neutrophils and can prevent febrile neutropenia. Filgrastim, however, must be injected daily for up to 14 consecutive days. Although filgrastim has been shown to be an effective supportive-care agent, it was thought that a product that could be administered less frequently, ideally once per cycle, would be more acceptable to patients, their caregivers, and healthcare providers and that it might allow for more flexible administration. A drug candidate with a similar safety and efficacy profile, but with a longer half-life, was desirable. Pegfilgrastim is a sustained-duration formulation of filgrastim that has been developed by covalent attachment of a polyethylene glycol (PEG) molecule to the filgrastim molecule (Table 3). Table 3. Comparison of filgrastim and pegfilgrastim (Amgen data on file). Characteristic

Filgrastim

Pegfilgrastim

Number of amino acids Cell source Glycosylation Pegylation Cmax

175 E. coli None No 1.65  0.80 ng/mL for single 75-mg/kg dose 5.5  1.8 for single 75-mg/kg dose 14.3  4.3 (0–24 h, ng/l h) for single 75-mg/kg dose

175 E. coli None Yes 43.6  20 ng/mL for single 30-mg/kg dose 9.50  3.51 for single 30-mg/kg dose 887  336 (0–1, ng/l h) for single 30-mg/kg dose

tmax (h) Area under the curve

401 Pegfilgrastim received marketing approval in the United States in 2002 and is under review for approval in the EU for the amelioration of chemotherapyinduced neutropenia. Mechanism of action Endogenous granulocyte colony-stimulating factor (G-CSF) is usually detectable in serum, and its concentration increases during bouts of infection [4]. G-CSF maintains neutrophil production during steady-state conditions. Filgrastim reduces neutrophil maturation time from five days to one day, leading to the rapid release of mature neutrophils from the bone marrow into the blood, and increases the circulating half-life of neutrophils [5]. Filgrastim enhances neutrophil chemotaxis by increasing the binding of fMLP (formyl-methionylleucyl-phenylalanine) [6] and increases neutrophil superoxide production in response to chemoattractants [7]. Filgrastim has a half-life of 3–4 h and needs to be administered daily [8]. One way to produce a product that is cleared less rapidly is to add a PEG molecule to the product, since PEG-modification of proteins has been shown to sustain the duration of action by reducing renal clearance of the protein and by decreasing rates of cellular uptake and proteolysis [9]. Using information from X-ray crystallography studies of filgrastim [10], it was found that adding a 20-kd PEG molecule to the amino terminal residue did not change the mechanism of action, namely the binding of the molecule to the G-CSF receptor on myeloid cells. Pegfilgrastim has decreased plasma clearance and increased plasma half-life, thus sustaining the duration of the pharmacologic effect. The target product profile for a pegylated form of filgrastim required several important criteria. The ideal candidate molecule needed to provide adequate hematologic support with only a single injection per chemotherapy cycle rather than with up to 14 days of daily injections of filgrastim. This administration schedule would provide convenience to patients, caregivers, and healthcare providers and it would promote compliance. The product could not induce any undesirable side effects that would exceed the safety profile of filgrastim, particularly sustained bone pain. Lastly, the product needed to be given as a subcutaneous injection. After careful preclinical testing of several candidates, the first pegylated form of filgrastim was tested in phase 1 and phase 2 proof-of-concept studies. The clearance mechanism of pegfilgrastim is thought to be mediated by neutrophils bearing the G-CSF receptor. This proposed mechanism of action is based in part on results obtained from a phase 2 study in patients with nonsmall-cell lung cancer in which the pharmacodynamic and pharmacokinetic profiles were compared in the same patients before chemotherapy (i.e., hematologic steady state) and after chemotherapy (myelosuppressive state) [11].

402 Phase 1 studies Phase 1 studies were conducted to establish safety, optimal drug dosage, and potential efficacy, including pharmacodynamic and pharmacokinetic properties [12]. For each cohort, eight normal volunteers received a single subcutaneous injection of pegfilgrastim at doses ranging from 30 to 300 mg/kg. Blood samples for serum drug concentrations, complete blood counts, and CD34 þ cell counts were collected at specified intervals to fully characterize the pharmacodynamic and pharmacokinetic profiles. The safety profile of pegfilgrastim was consistent with the known effects of filgrastim with observed adverse events that included moderate bone pain, headache, and reversible changes in platelet counts, liver enzyme concentrations, and uric acid concentrations with no clinical sequelae. The results of this study confirmed findings that pegfilgrastim exhibits nonlinear pharmacokinetics. As predicted, the serum clearance decreased as the dose increased. The mean terminal half-life was independent of dosage and ranged from 46 to 62 h. The magnitude and duration of absolute neutrophil counts and CD34 þ cell counts was dosage dependent (Table 4) [12]. This study also confirmed the agent was active and warranted further clinical development. Phase 2 studies Once activity was confirmed in volunteers, studies in patients with cancer receiving chemotherapy were necessary. In an open-label, dose-escalation study, 13 patients were randomized to receive a single subcutaneous injection of pegfilgrastim or five daily injections of filgrastim before chemotherapy. After a washout period, the patients received chemotherapy, followed by a single injection of pegfilgrastim or daily injections of filgrastim starting approximately 24 h after completion of chemotherapy. This study was designed to evaluate the safety and pharmacodynamic and pharmacokinetic profiles of several dosages of pegfilgrastim and compare pegfilgrastim with filgrastim both with and without chemotherapy. Table 4. Summary statistics for noncompartmental pharmacokinetic variables, week 1 of cycle 1. Only data from 14 patients are included because one patient had extremely low concentrations. These data have been omitted. Data courtesy of Amgen, Thousand Oaks, California. Variable

Tmax (h)

Cmax (ng/ml)

t1/2 (h)

CL/F (ml/h/kg)

n Mean SD

14 86.1 22.8

14 8.9 5.1

7 32.6 11.8

7 3.7 0.9

Tmax, time to maximum concentration; Cmax, maximum serum concentration; t1/2, terminal half-life; CL/F, relative clearance; SD, standard deviation.

403 A single subcutaneous injection of pegfilgrastim administered before chemotherapy produced the expected increase in absolute neutrophil count (ANC) and a subsequent rapid decrease in serum drug concentration, while a single subcutaneous injection of pegfilgrastim administered after chemotherapy maintained serum drug concentration longer because of a reduction in ANC, suggesting a neutrophil receptor-mediated mechanism of clearance. This finding suggested that serum pegfilgrastim levels are self-regulating, i.e., as ANC recovered to normal levels, serum concentration of pegfilgrastim decreased. The safety data from this trial suggested no difference in adverse events and, in particular, no difference in the incidence and severity of bone pain. The study provided preliminary evidence that a single injection of pegfilgrastim provides similar hematologic support as filgrastim in patients undergoing chemotherapy. Based on these data, a phase 2 program was initiated in patients with breast cancer. This program would form the basis for the pivotal phase 3 trial and was designed to allow selection of optimal dose and directly compare efficacy with filgrastim. Doxorubicin–docetaxel combination chemotherapy was chosen because it was a promising regimen that produced significant myelosuppression. The duration of severe neutropenia in the absence of growth factor support was reported to be between five and seven days, with an incidence of grade 4 neutropenia approaching 90%. Patients with high-risk stage II, III, and IV breast cancer were enrolled into a randomized, multicenter trial [13]. The key endpoints included duration of grade 4 neutropenia, incidence of febrile neutropenia, pharmacokinetics, and safety. The results of this study showed that a single injection of pegfilgrastim at a dose of 100 mg/kg/cycle was equivalent to filgrastim in supporting neutrophil recovery in patients with breast cancer who were receiving multiple cycles of chemotherapy. Other phase 2 studies comparing filgrastim with pegfilgrastim were conducted in patients with non-Hodgkin’s lymphoma to confirm the efficacy and safety for a broad range of tumor and chemotherapy settings (Amgen data on file). Phase 3 studies In the phase 3 program, the same patient population, chemotherapy regimen, and study endpoints were used as in the phase 2 studies [14,15]. These studies were double-blind, noninferiority trials to test the hypothesis that there was no difference between a single injection of pegfilgrastim administered as 100 mg/kg or as a 6-mg fixed dose and multiple 5-mg/kg injections of filgrastim. ANC profile, time to ANC recovery, and safety were assessed. The results from both trials showed that a single fixed dose or a by-weight dose produced a similar duration of severe neutropenia, ANC profile, and time to ANC recovery compared with daily injections of filgrastim. In addition to ANC recovery, the serum concentrations of pegfilgrastim showed clearance similar to what

404 was described in the nonsmall-cell lung cancer study, which further confirms the cell-mediated clearance. Safety profiles were similar between treatment groups. Results of the weight-based study showed a statistically significant decrease in the overall incidence of febrile neutropenia in favor of pegfilgrastim. A similar trend, not statistically significant possibly due to lower sample size, was noted in the fixed-dose study. Taken together, these trials confirmed that a single injection of pegfilgrastim per chemotherapy cycle was safe and effective in treating chemotherapy-induced neutropenia and that once-per-cycle treatment with sustained-duration pegfilgrastim has significant advantages over standard filgrastim. Summary A clear understanding of the native G-CSF molecule and an ability to use pegylation to extend half-life facilitated the development of pegfilgrastim. Potential benefits of the longer-acting pegfilgrastim molecule to patients with chemotherapy-induced neutropenia include fewer injections, increased patient compliance, and decreased burden on healthcare providers. Darbepoetin alfa Background Anemia is common in patients with cancer, and it is an important contributor to the morbidity associated with cancer and its treatment. Anemia in patients with cancer is usually manifested by fatigue [16]. Anemia in patients with cancer is best managed by treatment of the underlying cause, when possible; however, treatment is often not successful and can exacerbate anemia. Epoetin alfa acts like the endogenous protein and is licensed to treat anemia of cancer, human immunodeficiency virus (HIV) infection, and chronic renal failure, and for perisurgical use. Many studies have been published concerning the treatment of anemia and its sequelae in patients with cancer [17–20]. These studies have shown that treatment with epoetin alfa reduces the requirement for red blood cell transfusions and improves quality of life in patients with a broad range of nonmyeloid tumors and chemotherapeutic agents [17, 18, 21, 22]. Darbepoetin alfa is the recombinant product of a gene produced through site-directed mutagenesis of the erythropoietin gene that increases the glycosylation of the resultant protein. Darbepoetin alfa binds to the erythropoietin receptor and stimulates erythropoiesis by the same mechanism as endogenous erythropoietin and rHuEPO, and it has increased potency due to its extended serum residence time [23]. Darbepoetin alfa is currently approved for marketing in the United States for the amelioration of anemia associated with cancer and its treatment.

405 Mechanism of action Endogenous erythropoietin is the hormone that stimulates the production of red cells from the erythroid precursor cells in the bone marrow. Erythropoietin functions as a growth factor, binding to receptors on erythroid-progenitor cells and stimulating the mitotic activity of erythrocyte burst-forming and colony-forming units and early precursor cells (proerythroblasts) [24]. Although the precise location for the production of erythropoietin in the kidney tubule is not fully understood, it has been suggested that tubular or interstitial cells function as the main site for localization of the hormone and its mRNA [24]. Preliminary work has also identified the liver as the major site (>90%) of erythropoietin production for the fetus [25] and shows that some erythropoietin is produced in the adult human brain, but not enough to have an effect on systemic amounts [26]. The recombinant proteins epoetin alfa and darbepoetin alfa have the same mechanism of action as the endogenous protein, increasing red blood cell count by causing committed erythroid progenitor cells to proliferate and differentiate into normoblasts, thus keeping the body’s red blood cell mass at the optimal level [27–29]. The binding affinity of darbepoetin alfa is lower than that of epoetin alfa or natural erythropoietin, but the longer half-life of darbepoetin has been shown to increase in vivo biologic activity [23, 29]. Phase 1 studies Pharmacokinetic data are available from 15 evaluable patients with a variety of nonmyeloid tumor types who were enrolled into an open-label study [30]. Patients received injections of darbepoetin alfa 2.25 mg/kg/week immediately before receiving chemotherapy, continuing through three cycles of chemotherapy that were given at least three weeks apart. Blood samples were collected for pharmacokinetic analysis periodically during week 1 of chemotherapy cycles 1 and 3. Analyses of the results suggested that the drug is slowly absorbed after subcutaneous injection, reaching a peak concentration approximately 85 h later, and that it had a low relative clearance and long terminal half-life. Mean hemoglobin response (defined as a change from baseline, in the absence of a red blood cell transfusion) was 2.3 g/dl after three cycles of chemotherapy. The mean change in hemoglobin concentrations appeared similar to historical results using epoetin alfa [17, 31] and additional development of darbepoetin alfa was undertaken. Phase 2 studies Phase 2 studies of darbepoetin alfa were initiated to determine dose, schedule, and to compare darbepoetin alfa to epoetin alfa and placebo. Several phase 2 trials have shown a dose response to darbepoetin alfa in patients receiving multicycle chemotherapy for the treatment of solid tumors [32, 33] and in patients

406 with cancer who were not receiving chemotherapy but were nevertheless anemic [34]. Results from another phase 2 study suggest that darbepoetin alfa can be administered as infrequently as once every three weeks and still maintain hemoglobin concentrations [35]. The initial studies with darbepoetin alfa suggested the possibility of developing schedules that result in a more rapid benefit to a greater proportion of patients with anemia who are receiving chemotherapy [32, 36]. Dose loading may be both more efficacious and more cost effective. In one study, 127 patients were randomized to receive either epoetin alfa 40,000 U with escalations to 60,000 U for nonresponders, or darbepoetin alfa at 4.5 mg/kg/week until hemoglobin concentration  12 g/dl, followed by doses of 1.5, 3.0, or 4.5 mg/kg/week on a variety of schedules [33]. Overall, after four weeks of treatment, mean change in hemoglobin was 80% greater in the groups receiving darbepoetin alfa than in the group receiving epoetin alfa. By the end of the study, the mean change in hemoglobin was 30% greater in patients receiving darbepoetin alfa compared with patients receiving epoetin alfa. Loading doses of darbepoetin alfa for four weeks followed by a lower dose and/or a less frequent administration schedule (every two weeks or every three weeks) appear to be safe and may decrease the time to response and increase the proportion of patients benefiting from therapy compared with current approaches using rHuEPO. Phase 3 studies A phase 3, multicenter, double-blind, placebo-controlled study evaluated darbepoetin alfa compared with placebo in anemic patients with cancer receiving chemotherapy [37]. Endpoints were red blood cell transfusions and hemoglobin concentration, adverse events, antibody formation to darbepoetin alfa, hospitalizations, Functional Assessment of Cancer Therapy (FACT) Fatigue score, and disease outcome. Three hundred fourteen patients with lung cancer receiving chemotherapy were randomly assigned to receive darbepoetin alfa or placebo administered weekly for 12 weeks. Darbepoetin alfa reduced the proportion of patients requiring a transfusion and the number of RBC units transfused, increased the proportion of patients with a hemoglobin response, and the proportion of patients with improvement in the FACT Fatigue score. A trend towards fewer hospitalization days for patients receiving darbepoetin alfa was seen. Patients receiving darbepoetin alfa had a longer median progression-free and overall survival. Adverse events were comparable between the groups. No antibodies to darbepoetin alfa were detected. Based on these data, darbepoetin alfa received marketing approval for treatment of patients with cancer receiving chemotherapy. Summary The development of darbepoetin alfa is an example of drug development based on knowledge of the physical properties of the recombinant and native

407

Fig. 1. Biochemical and biological properties of rHuEPO and rHuEPO analogs containing four and five N-linked carbohydrate chains [23]. Used with permission of British Journal of Cancer.

proteins (Fig. 1). Using this knowledge of the physical properties of the longacting darbepoetin alfa, it is possible to examine various doses and schedules to optimize treatment of the anemia of cancer for individual patients. Potential benefits may include reduced number of injections and faster amelioration of anemia. Keratinocyte Growth Factor Background Chemotherapy and radiotherapy, alone or in combination, kill rapidly proliferating tumor cells and, consequently, often damage rapidly dividing normal cells of the gastrointestinal tract. Damage or destruction of the normal cells in the gastrointestinal tract causes mucositis that can be a dose-limiting side effect of chemotherapy and/or radiotherapy. Mucositis compromises the integrity of the protective mucosal barrier and may limit a patient’s ability to speak, eat, or swallow. Existing oral mucositis treatment focuses on alleviating symptoms, which requires substantial healthcare resources. This increase in resources is particularly true in the setting of bone marrow or stem cell transplantation [38–40]. Treatments that address the pathogenesis of oral mucositis rather than symptomatic relief could improve the health-related quality of life of patients with cancer who are receiving mucositis-inducing treatment. Keratinocyte growth factor (KGF) is a natural ligand for the KGF receptor that is found on nearly all epithelial cells, including those lining the digestive tract. KGF stimulates the proliferation and differentiation of the epithelium, including that of the gastrointestinal tract. Recombinant human forms of KGF (rHuKGF) are under development. Because rHuKGF increases the proliferation of the epithelium, the increased thickness may provide protection from the damaging effects of radiation and chemotherapy.

408 Mechanism of action Keratinocyte growth factor, a member of the fibroblast growth factor (FGF) family, was originally isolated from cultured human embryonic fibroblasts [41, 42]. Unlike other members of this family, however, KGF exhibits strict specificity of action for epithelial cells and has no direct effects on other types of cells [43, 44]. KGF stimulates cell proliferation, as evidenced by incorporation of 3 H-thymidine into the DNA of epithelial cells [43, 45–49]. Early preclinical testing of rHuKGF showed that systemic administration in animals caused the proliferation and thickening of epithelial tissues throughout the gastrointestinal tract [50]. In addition, pretreatment with rHuKGF appeared to markedly reduce damage to the mucosal lining of the oral and lower gastrointestinal tracts in animals given chemotherapy or radiation [51] (Fig. 2). Theoretically rHuKGF has the potential to stimulate epithelial tumors, but there are no data to support this theory. Phase 1 studies Phase 1 studies were done in healthy volunteers and patients with cancer. Dose-escalation studies in healthy volunteers used a single intravenous dose or daily dosing for three consecutive days at dosages up to 20 mg/kg/day. After intravenous administration at both 10 and 20 mg/kg/day, serum rHuKGF concentrations declined rapidly (i.e., by 50- to 100-fold) after the initial 30 min and reached a plateau between 1 and 6 h [52] (Table 5). After the plateau, a terminal half-life of approximately 3 h was seen. No accumulation was evident after three days of dosing, and the pharmacokinetics of rHuKGF were dose linear over the range of dosages. The biologic activity was measured using buccal Table 5. Summary of pharmacokinetic variables in normal human volunteers on days 1 and 3. rHuKGF was administered intravenously for three days. Numbers are reported as mean (SD). Data courtesy of Amgen Inc., Thousand Oaks, California. Parameter

V0 (mL/kg) AUC (pg h/mL) t1/2 (h) CL (mL/h/kg) Vss (mL/kg)

rHuKGF 20 mg/kg/day Day 1 (n ¼ 6)

Day 3 (n ¼ 5)

89.1 (42.6) 36,700 (11,900) 3.31 (0.59) 596 (194) 1890 (51)

79.9 (41.8) 41,900 (2000) 6.21 (2.69) 558 (222) 1620 (1110)

AUC, area under the curve, 0–1; CL, clearance; t1/2, half-life associated with terminal phase; V0, volume of distribution at time 0; Vss, volume of distribution at steady state.

409

Fig. 2. Biologic activity of rHuKGF can be quantified by measuring the proliferation of epithelial cells. Antibodies to BrdUrd (Accurate Chemical & Scientific Corporation, Westbury, NY) bind to Ki67-stained cells (Ki67 is a nuclear marker found in proliferating epithelial cells). The effect of rHuKGF on surviving intestinal crypts of mice after irradiation and bone marrow transplantation. Panel A, no rHuKGF; panel B, rHuKGF for three days before irradiation. C Farrell, personal communication.

mucosa biopsy samples to evaluate the presence of mitotic activity and Ki67 immunohistochemistry, biomarkers of proliferation. At dosages of 10 and 20 mg/kg/day, a statistically significant increase in mitotic figures was evident, and Ki67 staining was significant at dosages of 5–20 mg/kg/day. A phase 1 study was done in patients with metastatic colorectal cancer who were receiving high-dose chemotherapy with autologous stem cell transplantation. rHuKGF serum concentration declined rapidly after an intravenous bolus administration of 60 mg/kg/day (i.e., approximately 50-fold over the initial 30 min) [53]. Serum concentration reached a plateau between 1 and 4 h after administration and then declined further, with a terminal half-life of approximately 3–4 h. rHuKGF was detectable in the serum up to 36 h after administration. These phase 1 studies show that rHuKGF is well tolerated and biologically active only when administered at dosages  10 mg/kg/day for three days as an intravenous infusion.

Phase 2 studies Since the mucositis is difficult to grade and has a large subjective component, it will be necessary to have readily measurable endpoints in clinical studies and to train the investigators to a uniform standard for grading mucositis. Several phase 2 studies were done with patients with cancer receiving chemotherapy and/or radiotherapy, using doses and schedules chosen based on phase 1 acute

410 toxicity data and preliminary evidence of efficacy [54, 55]. The phase 2 program included studies in patients with hematologic malignancies who were receiving stem cell transplantation and in patients with advanced colorectal or head-andneck cancer. In one phase 2, randomized, placebo-controlled study, rHuKGF reduced the duration of grade 3/4 oral mucositis and improved the quality of life of patients with hematologic malignancies who were receiving autologous stem cell transplants [55]. Patients administered 60 mg/kg rHuKGF three days before and three days after transplantation had a significant reduction in the duration of grade 3/4 oral mucositis, required fewer days of intravenously administered opioid analgesics, and had improved health-related quality-of-life assessments (i.e., ability to swallow, eat, drink, talk, and sleep) than patients who received placebo. Transient, asymptomatic increases in serum amylase and lipase occurred more frequently in rHuKGF-treated patients than in patients receiving placebo. Another phase 2, randomized, placebo-controlled study was done in patients with advanced colorectal cancer [54]. Patients were randomly assigned to receive two cycles of either rHuKGF 40 mg/kg/day or placebo by intravenous bolus on days 1–3, followed by chemotherapy. Incidence of grade 2–4 mucositis was 78% in placebo patients compared with 32% of rHuKGF-treated patients. Other endpoints including duration of mucositis were reduced in patients receiving rHuKGF (3.4 days) compared with patients receiving placebo (10.2 days). Asymptomatic increases in serum amylase and lipase were seen in patients receiving rHuKGF, but without sequelae. These studies supported the hypothesis that rHuKGF acts on the pathogenesis of oral mucositis and can prevent mucositis and associated symptoms in patients receiving mucositis-inducing chemotherapy. Phase 3 studies Based on promising phase 2 results, a phase 3 trial in the setting of stem cell transplantation is underway. This trial will attempt to confirm the promising phase 2 results. Summary The development of rHuKGF is an example of how knowledge of the pathogenesis of a comorbid condition lead to a specifically targeted therapy to attempt to prevent the underlying cause of this toxicity. To date, phase 1 and phase 2 studies have shown that rHuKGF has biologic activity with acceptable acute toxicity. Large randomized studies, however, will determine the magnitude of the benefit and determine whether there are any chronic toxicities.

411 Osteoprotogerin Background Bone is a common site for metastasis for patients with breast, lung, prostate, or renal cancers [56–58]. Lytic bone lesions, caused primarily by increased osteoclastic activity, can lead to pathologic fractures, spinal collapse, hypercalcemia, and pain. A medicine that could inhibit the activity of osteoclasts could have clinical utility in preventing these sequelae. Osteoprotegerin (OPG) (meaning ‘‘to protect bone’’) is a member of the tumornecrosis factor receptor (TNFR) superfamily and acts to reduce bone resorption by inhibiting differentiation and activation of osteoclasts. OPG is an endogenous protein; a recombinant product (rHuOPG) in early clinical development. Several nonbiologic approaches have been used to treat bone metastasis, these include the bisphosphonates, a class of compounds based on the naturally occurring pyrophosphates. These small-molecule drugs have been used to reduce skeletal-related events and bone pain [59]. Bisphosphonates act by complexing with bone mineral. They prevent tumor cells from adhering to the bone, prevent or restrict osteoclast-mediated bone resorption, and inhibit matrix metalloproteinases. These compounds may inhibit angiogenesis and reduce the level of growth factors involved in bone resorption. A recently approved bisphosphonate called zoledronic acid has been shown to be significantly superior to the standard, pamidronate in the treatment of hypercalcemia of malignancy. In a randomized, double-blind trial comparing intravenous zoledronic acid with intravenous pamidronate in patients with hypercalcemia of malignancy, patients receiving zoledronic acid had a significantly higher response rate in the correction of serum calcium, a faster onset of effect, and longer duration of action. Zolendronic acid was well tolerated at a single dose of 4 mg. One advantage of zolendronic acid over other marketed products is that the medicine is administered as a 5-min infusion compared with the 2-h infusions required for pamidronate [60]. Mechanism of action Bone resorption can be inhibited by three mechanisms: reducing the activation frequency of basic multicellular units, reducing the bone resorptive activity of mature osteoclasts, or increasing the rate of osteoclastic apoptosis. OPG reduces the terminal differentiation of osteoclasts and thus affects the pool of mature osteoclasts and also reduces the activity of mature osteoclasts [61]. OPG is important in bone metabolism and has been shown to be a potent inhibitor of bone resorption in vivo, acting as a decoy receptor to bind and inactivate OPG ligand [62] (Fig. 3). OPG ligand is required for osteoclast differentiation [61, 63]. Additionally, OPG opposes the bone resorptive activity of parathyroid hormone, PTH, interleukin (IL-1), and (TNF) [64], the main mediators of

412

Fig. 3. Proposed mechanism of action of OPG (osteoprotegerin). OPG ligand (OPGL) is produced by osteoblasts in response to bone resorptive agents such as parathyroid hormone (PTH), vitamin D, interleukin (IL)-1b, and tumor necrosis factor (TNF)-a. OPGL, either on cell surfaces or in solution, interacts with its receptor, osteoclast differentiation and activation receptor (ODAR), on osteoclast precursors to promote differentiation or on mature osteoclasts to cause activation. OPG binds to and inactivates OPGL either in solution or on exposed cell surfaces. In the absence of OPG, OPGL binds to ODAR to increase osteoclast numbers and to increase bone resorption. Used with permission of Amgen Inc., Thousand Oaks, California.

cancer-related bone diseases. OPG and OPG ligand are present in the systemic circulation of adult humans [65] and have been found to regulate the differentiation of osteoclasts from precursors in human peripheral blood [66]. Recombinant human OPG (rHuOPG) has been shown to be bone antiresorptive in postmenopausal women [67]. Phase 1 studies Several phase 1 studies are underway to characterize the safety and potential efficacy of targeted rHuOPG therapy in patients with lytic bone metastases or to examine several routes of administration in healthy postmenopausal women. Phase 2 and phase 3 studies Because phase 1 studies have not been completed, no phase 2 or phase 3 studies actively studying rHuOPG administration to patients with cancer are being done. Summary The early development of rHuOPG illustrates that the drug development process is orderly and proceeds in a stepwise fashion. The potential hope for rHuOPG as a viable biologic to provide amelioration of symptoms related to bone metastasis is an exciting area of research. More research is needed to fully understand the utility of this drug in this supportive-care setting.

413 Discussion The need for supportive-care agents to treat patients with cancer continues. As the population ages, a dramatic increase in the number of cases of cancer is expected. It has been estimated that by 2020, 20 million new patients will be diagnosed with cancer [68]. These data illustrate the need for the continual development of improved therapeutic and supportive-care agents. At present, supportive-care products are available to treat a number of comorbid conditions associated with cancer and morbidities associated with cancer treatments. New agents are being developed with novel mechanisms of action or modifications of existing agents that improve performance. Because of the urgent need for such products, efficient development is required to deliver useful products to patients as rapidly as possible. Although we have discussed several examples of successfully developed or promising supportive-care products, many agents entering clinical development will not be successful. An example of this is megakaryocyte growth and development factor (MGDF). In preclinical studies [69–71], this product increased platelet counts with mechanism similar to the endogenous protein, thrombopoetin. Initial clinical studies showed increased platelet counts confirming the preclinical studies [72–74]. The rare but potentially serious adverse events of antibody formation to MGDF leading to severe and potentially chronic thrombocytopenia, however, terminated the clinical program. Analysis of all aspects of this drug development suggests that the ideal candidate for a platelet mobilizer would be one that mimics the endogenous protein but does induce antibody formation. We hope that the examples provided in this chapter will be useful to investigators as they develop the next generation of supportive-care products. Acknowledgments Dr Neumann and Dr Foote are employees of Amgen Inc., the manufacturer of Epogen, Neupogen, Neulasta, and Aranesp; and the developer of rHuKGF, PEG-rHuMGDF, and OPG. References 1. 2. 3. 4. 5.

Cancer: Principles and Practice of Oncology, 6th ed. In: VT DeVita, S Hellman and SA Rosenberg (eds). Philadelphia, PA, Lippincott Williams & Wilkins. 2001. International Conference on Harmonisation, www.ich.org (accessed 2 May 2002). Bodey GP, Buckley M, Sathe YS, et al. Quantitative relationships between circulating leukocytes and infection in patients with acute leukemia. Ann Intern Med 1966;64:328–340. Cebon J, Layton JE, Maher D and Morstyn G. Endogenous haemopoietic growth factors in neutropenia and infection. Br J Haematol 1994;86:265–274. Lord BI, Bronchud MH, Owens S, et al. The kinetics of human granulopoiesis following treatment with granulocyte colony-stimulating factor in vivo. Proc Natl Acad Sci USA 1989;86:9499–9503.

414 6. Colgan SP, Gasper PW, Thrall MA, Boone TC, Blancquaert AMB and Bruyninckx WJ. Neutrophil function in normal and Chediak-Higashi syndrome cats following administration of recombinant canine granulocyte colony-stimulating factor. Exp Hematol 1992;20:1229–1234. 7. Weisbart RH and Golde DW. Physiology of granulocyte and macrophage colony-stimulating factors in host defense. Hematol Oncol Clin North Am 1989;3:401–409. 8. Roskos LK, Cheung EN, Vincent M, Foote MA and Morstyn G. Pharmacology of filgrastim (r-metHuG-CSF): filgrastim (r-metHuG-CSF) in clinical practice. In: G Morstyn, TM Dexter and MA Foote (eds). New York, Marcel Dekker Inc. 1998:51–71. 9. Delgado C, Francis GE and Fisher D. The uses and properties of PEG-linked proteins. Crit Rev Ther Drug Carrier Syst 1992;9:249–304. 10. Osslund T and Boone TC. Biochemistry and structure of filgrastim (r-metHuG-CSF): filgrastim (r-metHuG-CSF) in clinical practice. In: G Morstyn, TM Dexter and MA Foote (eds). New York, Marcel Dekker Inc. 1998:41–49. 11. Johnston E, Crawford J, Blackwell S, et al. Randomized, dose-escalation study of SD/01 compared with daily filgrastim in patients receiving chemotherapy. J Clin Oncol 2000;18:2522–2528. 12. Molineux G, Kinstler O, Briddell B, et al. A new form of filgrastim with sustained duration in vivo and enhanced ability to mobilize PBPC in both mice and humans. Exp Hematol 1999;27:1724–1734. 13. Holmes FA, Jones SE, O’Shaughnessy J, et al. Comparable efficacy and safety profiles of once-per-cycle pegfilgrastim and daily injection filgrastim in chemotherapy-induced neutropenia: a multicenter dose-finding study in women with breast cancer. Ann Oncol 2002;13:903–909. 14. Holmes FA, O’Shaughnessy JA, Vukelja S, et al. Blinded, randomized, multicenter study to evaluate single administration pegfilgrastim once per cycle versus daily filgrastim as an adjunct to chemotherapy in patients with high-risk stage II or stage III/IV breast cancer. J Clin Oncol 2002;20:727–731. 15. Green M, Koelbl H, Baselga J, et al. A randomized, double-blind, phase 3 study of fixed-dose, single-administration pegfilgrastim vs daily filgrastim in patients receiving myelosuppressive chemotherapy. Ann. Oncol. 2003; 14:9–35. 16. Miaskowski C and Portenoy RK. Update on the assessment and management of cancerrelated fatigue. Principles Practice Supportive Oncol Updates 1998;1:1–10. 17. Glaspy J, Bukowski R, Steinberg D, et al. Impact of therapy with epoetin alfa on clinical outcomes in patients with nonmyeloid malignancies during cancer chemotherapy in community oncology practice. Procrit study group. J Clin Oncol 1997;15:1218–1234. 18. Demetri GD, Kris M, et al., for the Procrit Study Group. Quality-of-life benefit in chemotherapy patients treated with epoetin alfa is independent of disease response or tumor type: results from a prospective oncology study. J Clin Oncol. 1998;16:3412–3425. 19. Littlewood TJ, Bajetta E, Nortier JWR, Vercammen E and Rapoport B. Effects of epoetin alfa on hematologic parameters and quality of life in cancer patients receiving nonplatinum chemotherapy: results of a randomized, double-blind, placebo-controlled trial. J Clin Oncol 2001;19:2865–2874. 20. Gabrilove JL, Cleeland CS, Livingston RB, Sarokhan B, Winer E and Einhorn LH. Clinical evaluation of once-weekly dosing of epoetin alfa in chemotherapy: improvements in hemoglobin and quality of life are similar to three-times-weekly dosing. J Clin Oncol 2001;19:2875–2882. 21. Abels RI and Rudnick SA. Erythropoietin: evolving clinical applications. Exp Hematol 1991;19:842–850. 22. Cascinu S, Fedeli A, Del Ferro E, Luzi Fedeli S and Catalano G. Recombinant human erythropoietin treatment in cisplatin-associated anemia: a randomized double-blind trial with placebo. J Clin Oncol 1994;12:1058–1062.

415 23. Egrie JC and Browne JK. Development and characterization of novel erythropoiesis stimulating protein (NESP). Br J Cancer 2001;84:3–10. 24. Erslev A. Erythropoietin coming of age. N Engl J Med 1987;316:101–103. 25. Nathan DG. Regulation of erythropoiesis. N Engl J Med 1987;296:685–687. 26. Marti HH, Wenger RH, Rivas LA, et al. Erythropoietin gene expression in human, money, and murine brain. Eur J Neurosci 1996;8:666–676. 27. Krantz SB. Erythropoietin. Blood 1991;77:419–434. 28. Lacombe C and Mayeux P. Biology of erythropoietin. Haematologica 1998;83:724–732. 29. Macdougall IC. Novel erythropoiesis stimulating protein. Semin Nephrol 2000;20:375–381. 30. Heatherington AC, Schuller and Mercer AJ. Pharmacokinetics of novel erythropoieis stimulating protein (NESP) in cancer patients: preliminary report. Br J Cancer 2001;84:11–16. 31. Abels RI. Use of recombinant human erythropoietin in the treatment of anemia in patients who have cancer. Semin Oncol 1992;19:29–35. 32. Glaspy J, Jadeja Singh J, Justice G, et al. A dose-finding and safety study of novel erythropoiesis stimulating protein (NESP) for the treatment of anaemia in patients receiving multicycle chemotherapy. Br J Cancer 2001;84:17–23. 33. Glaspy JA, Jadeja JS, Justice G, et al. Darbepoetin alfa given every 1–2 weeks alleviates anaemia associated with cancer chemotherapy. Br J Cancer 2002;87:268–276. 34. Smith RE, Jaiyesimi IA, Meza LA, et al. Novel erythropoiesis stimulating protein (NESP) for the treatment of anaemia of chronic disease associated with cancer. Br J Cancer 2001;84:24–30. 35. Kotasek D, The ARANESP 980291 Study Group, Berg R, Poulsen E and Colowick A. Randomized, double-blind, placebo controlled phase I/II dose finding study of ARANESPTM administered once every three weeks in solid tumor patients. Blood 2000;96:294a–295a (abstract). 36. Hedenus M, Hansen S, Dewey C, et al. A randomized, blinded, placebo-controlled, phase II, dose-finding study of novel erythropoiesis stimulating protein (NESP) in patients with lymphoproliferative malignancies. Proc ASCO 2001;20:393a (abstract 1569). 37. Vansteenkiste J, Pirker R, Massuti B, et al. Double-blind, placebo-controlled, randomized, phase 3 trial of darbepoetin alfa in lung cancer patients receiving chemotherapy. J Natl Cancer Inst 2002;94:1211–1220. 38. Sonis ST, Oster G, Fuchs H, et al. Oral mucositis and the clinical and economic outcomes of hematopoietic stem-cell transplantation. J Clin Oncol 2001;19:2201–2205. 39. Ruescher TJ, Sodeifi A, Scrivani SJ, Kaban LB and Sonis ST. The impact of mucositis on a-hemolytic streptococcal infection in patients undergoing autologous bone marrow transplantation for hematologic malignancies. Cancer 1998;82:2275–2281. 40. Horowitz MM, Oster G, Fuchs H, et al. Oral mucositis assessment scale (OMAS) as a predictor of clinical and economic outcomes in bone marrow transplant patients. Blood 1999;94:399a (abstract). 41. Finch PW, Rubin JS, Miki T, Ron D and Aaronson SA. Human KGF is FGF-related with properties of a paracine effector of epithelial cell growth. Science 1989;245:752–775. 42. Rubin J, Osada H, Finch P, Taylor W, Rudifoff S and Aaronson S. Purification and characterization of a newly identified growth factor specific for epithelial cells. Proc Natl Acad Sci USA 1989;86:802–806. 43. Rubin JS, Bottaro DP, Chedid M, et al. Keratinocyte growth factor. Cell Biol Int 1995;19: 399–404. 44. Rubin JS, Bottaro DP, Chedid M, et al. Keratinocyte growth factor as a cytokine that mediates mesenchymal-epithelial interactions. EXS 1995;74:191–214. 45. Ulich TR, Yi ES, Cardiff R, et al. Keratinocyte growth factor is a growth factor for mammary epithelium in vivo. The mammary epithelium of lactating rats is resistant to the proliferative action of keratinocyte growth factor. Am J Pathol 1994;114:862–868.

416 46. Alaride ET, Rubin JS, Young P, Chedid M, Aaronson SA and Chuha GR. Keratinocyte growth factor functions in epithelial induction during seminal vesicle development. Proc Natl Acad Sci USA 1994;91:1074–1078. 47. Pierce GF, Yanagihara D, Klopchin K, et al. Stimulation of all epithelial elements during skin regeneration by keratinocyte growth factor. J Exp Med 1994;179:831–840. 48. Ulich TR, Yi ES, Longmuir K, et al. Keratinocyte growth factor is a growth factor for type II pneumocytes in vivo. J Clin Invest 1994;93:1298–1306. 49. Yi ES, Yin S, Harclerode DL, et al. Keratinocyte growth and development factor induces pancreatic ductal epithelial proliferation. Am J Pathol 1994;145:88–95. 50. Housley RM, Morris CM, Boyle W, et al. Keratinocyte growth factor induces proliferation of hepatocytes and epithelial cells throughout the rat gastrointestinal tract. J Clin Invest 1994;94:1764–1777. 51. Farrell CL, Bready JV, Rex KL, et al. Keratinocyte growth factor protects mice from chemotherapy and radiation-induced gastrointestinal injury and mortality. Cancer Res 1998;58:933–939. 52. Serdar C, Heard R, Prathikanti R, et al. Safety, pharmacokinetics and biologic activity of rHuKGF in normal volunteers: results of a placebo-controlled randomized, double-blind, phase I study. Blood 1997;90:761 (abstract). 53. Meropol NJ, Gutheil J, Pelley K, et al. Keratinocyte growth factor (KGF) as a mucositis protectant: a randomized phase 1 trial. Proceed ASCO 2000;19:603a (abstract). 54. Clarke SJ, Abdi E, Davis ID, et al. Recombinant human keratinocyte growth factor (rHuKGF) prevents chemotherapy-induced mucositis in patients with advanced colorectal cancer: a randomized phase II trial. Proc ASCO 2001:383a (abstract). 55. Spielberger RT, Stiff P, Emmanouilides C, et al. Efficacy of recombinant human keratinocyte grow factor (rHuKGF) in reducing mucositis in patients with hematologic malignancies undergoing autologous peripheral blood progenitor cell transplantation (auto-PPPCT) after radiation-based conditioning: results of a phase 2 trial. Proc ASCO 2001;20:7a (abstract). 56. Viadana E, Cotter R, Pickren JW and Bross IDJ. An autopsy study of metastatic sites of breast cancer. Cancer Res 1973;33:179–181. 57. Urwin GH, Percieival RC, Harris S, et al. Generalised increase in bone resorption in carcinoma of the prostate. Br J Urol 1985;57:721–723. 58. Coleman RE and Rubens RD. The clinical course of bone metastases from breast cancer. Br J Cancer 1987;55:61–66. 59. Van de Pluijm G, Sijmons B, Vloedgraven H, et al. Monitoring metastatic behavior of human tumor cells in mice with species-specific polymerase chain reaction: elevated expression of angiogenesis and bone resorption stimulators by breast cancer in bone metastases. J Bone Miner Res 2001;16:1077–1091. 60. Major P, Lortholary A, Hon J, et al. Zoledronic acid is superior to pamidronate in the treatment of hypercalcemia of malignancy: a pooled analysis of two randomized, controlled clinical trials. J Clin Oncol 2001;19:558–567. 61. Simonet WS, Lacey DL, Dunstan CR, et al. Osteoprotegerin: a novel secreted protein involved in the regulation of bone density. Cell 1997;89:309–319. 62. Lacey DL, Timms E, Tan H-L, et al. Osteoprotegerin (OPG) ligand is a cytokine that regulates osteoclast differentiation and activation. Cell 1998;93:165–176. 63. Kong Y-Y, Yoshida H, Sarosi I, et al. OPGL is a key regulator of osteoclastogenesis, lymphocyte development and lymph node organogenesis. Nature 1999;397:315–323. 64. Morony S, Capparelli C, Lee R, et al. A chimeric form of osteoprotegrin inhibits hypercalcemia and bone resorption induced by IL-1b, TNFa, PTHrP, and 1, 25-dihydroxy vitamin D3. J Bone Min Res 1999;14:1478–1485. 65. Yano K, Tsuda E, Washida N, et al. Immunological characterization of circulating osteoprotegerin/osteoclastogenesis inhibitory factor: increased serum concentrations in postmenopausal women. J Bone Miner Res 1999;14:518–527.

417 66. Shalhoub V, Faust J, Boyle WJ, et al. Osteoprotegerin and osteoprotegerin ligand effects on osteoclast formation from human peripheral blood mononuclear cell precursors. J Cell Biol 1999;72:251–261. 67. Bekker PJ, Holloway D, Nakanishi A, Arrighi M, Leese PT and Dunstan CR. The effect of a single dose of osteoprotegerin in postmenopausal women. J Bone Miner Res 2001;16:348–360. 68. Sikora K. Emerging molecular therapies: principles of molecular oncology. In: MH Bronchud, MA Foote, WP Peters and MO Robinson (eds). Totowa, NJ, Humana Press. 2000:411–420. 69. Bartley TD, Bogenberger J, Hunt P, et al. Identification and cloning of a megakaryocyte growth and development factor that is a ligand for the cytokine receptor Mpl. Cell 1994;77:1117–1124. 70. Ulich TR, del Castillo J, Yin S, et al. Megarkaryocyte growth and development factor ameliorates carboplatin-induced thrombocytopenia in mice. Blood 1995;86:971–976. 71. Hokom MM, Lacey D, Kinstler OB, et al. Pegylated megakaryocyte growth and development factor abrogates the lethal thrombocytopenia associated with carboplatin and irradiation in mice. Blood 1995;86:4486–4492. 72. Basser RL, Rasko JE, Clarke K, et al. Thrombopoietic effects of pegylated recombinant human megakaryocyte growth and development factor (PEG-rHuMGDF) in patients with advanced cancer. Lancet 1996;348:1279–1281. 73. Basser RL, Rasko JEJ, Clarke K, et al. Randomized, blinded, placebo-controlled phase 1 trial of pegylated recombinant human megakaryocyte growth and development factor with filgrastim after dose-intensive chemotherapy in patients with advanced cancer. Blood 1997;89:3118–3128. 74. Fanucchi M, Glaspy J, Crawford J, et al. Effects of polyethylene glycol-conjugated recombinant human megakaryocyte growth and development factor on platelet counts after chemotherapy for lung cancer. N Engl J Med 1997;336:404–409.

Note Added in Proof Pegfilgrastim received marketing approval in the EU in September 2002 for use in chemotherapy-induced neutropenia.