Platelet-derived growth factor (PDGF) and its cognate receptor are widely expressed on melanomas. Coexpression of the growth factor and receptor suggests their role in autocrine or paracrine growth mechanisms. Imatinib mesylate was previously reported to have specific activity in inhibiting select tyrosine kinase receptors, including PDGF and c-Kit. Melanoma cells express abundant levels of the PDGF receptor (PDGFR). Nevertheless, c-Kit expression is progressively lost as the cells take on a more highly metastatic phenotype. To investigate the potential of imatinib mesylate as a therapy for melanoma, we studied its effect on the growth of melanoma cells using an in vivo mouse model. Melanoma cells with high malignant potential (PDGFR-positive, c-Kit-negative) or low malignant potential (PDGFR-positive, c-Kit-positive) were injected subcutaneously into athymic nude mice. Mice were treated with imatinib mesylate (100 mg/kg three times weekly) or with phosphate-buffered saline for 4 to 6 wk. PDGFR-alpha and -beta were expressed on all melanoma cell lines tested. The level of PDGFR expression correlated with the metastatic potential of the melanoma cells: higher levels of PDGFR-alpha were expressed on cells with higher metastatic potential, and higher levels of PDGFR-beta were expressed on cells with lower metastatic potential. There was no significant difference in tumor size between treated and control mice. Immunohistochemical studies demonstrated inhibition of PDGFR phosphorylation on the tumors from mice treated with imatinib mesylate but not from control mice, suggesting that the receptors were functional and that the concentration of drug used was appropriate. Our data demonstrated that imatinib mesylate blocked both PDGFR-alpha and PDGFR-beta in vivo. It did not, however, affect the growth of melanoma cells expressing PDGFR, regardless of whether the cells expressed c-Kit.
Introduction: This study evaluated noninferiority of darbepoetin alfa versus placebo for overall survival (OS) and progression-free survival (PFS) in anemic patients with NSCLC treated to a 12.0-g/dL hemoglobin (Hb) ceiling. Methods: Adults with stage IV NSCLC expected to receive two or more cycles of myelosuppressive chemotherapy and Hb less than or equal to 11.0 g/dL were randomized 2:1 to blinded 500 mg darbepoetin alfa or placebo every 3 weeks. The primary endpoint was OS; a stratified Cox proportional hazards model was used to evaluate noninferiority (upper confidence limit for hazard ratio [HR] < 1.15). Secondary endpoints were PFS and incidence of transfusions or Hb less than or equal to 8.0 g/dL from week 5 to end of the efficacy treatment period. Results: The primary analysis set included 2516 patients: 1680 were randomized to darbepoetin alfa; 836 to placebo. The study was stopped early per independent Data Monitoring Committee recommendation after the primary endpoint was met with no new safety concerns. Darbepoetin alfa was noninferior to placebo for OS (stratified HR ¼ 0.92; 95% confidence interval [CI]: 0.83-1.01) and PFS (stratified HR ¼ 0.95; 95% CI: 0.87-1.04). Darbepoetin alfa was superior to placebo for transfusion or Hb less than or equal to 8.0 g/dL from week 5 to end of the efficacy treatment period (stratified odds ratio ¼ 0.70; 95% CI: 0.57-0.86; p < 0.001). Objective tumor response was similar between the groups (darbepoetin alfa, 36.4%; placebo, 32.6%). Incidence of serious adverse events was 31.1% in both groups. No unexpected adverse events were observed. Conclusions: Darbepoetin alfa dosed to a 12.0-g/dL Hb ceiling was noninferior to placebo for OS and PFS and significantly reduced odds of transfusion or Hb less than or equal to 8.0 g/dL in anemic patients with NSCLC receiving myelosuppressive chemotherapy.
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