Phase I study of continuous-infusion recombinant macrophage colony-stimulating factor in patients with metastatic melanoma.

Macrophage colony-stimulating factor (M-CSF) is a lineage-specific, homodimeric growth factor that supports the proliferation and maturation of bone marrow progenitors and the survival and function of mononuclear/macrophage cells. In vitro studies have demonstrated antitumor activity of macrophage colony-stimulating factor-treated monocytes against melanoma target cells. A Phase I study was conducted by administering the glycosylated form of the protein to patients with metastatic melanoma as two 7-day continuous i.v. infusions separated by a 2-week rest. Cohorts of three patients per dose level received escalating doses of 10-160 microgram/kg/day. Safety, clinical, and biological effects were evaluated. The infusions were well tolerated with occasional maximum grade 2 nonhematological toxicity. Rapidly reversible thrombocytopenia was the major hematological adverse effect. Its etiology may in part be explained by proliferation and activation of monocyte/macrophage cells in bone marrow samples. Evidence for a biological effect on tumors was suggested by the delayed, complete disappearance of multiple lesions in one patient and a decrease in the size of one marker lesion in a second patient with a mixed response. Fasting serum cholesterol levels decreased during the infusions and may represent an additional therapeutic application for this growth factor.