Phase I study of R24 in patients with metastatic melanoma including evaluation of immunologic parameters

R24 is a mouse IgG3 monoclonal antibody with specificity for the disialoganglioside GD3. Most human melanomas have substantial surface GD3; in addition, a significant proportion of T lymphocytes display surface GD3. In a phase I study, we have investigated the toxicity and effect on selected immunological parameters of three dose levels of R24 given intravenously daily for five days (10 mg/m2/d, 30 mg/m2/d and 50 mg/m2/d) to patients with advanced melanoma. R24 administration neither consistently diminished nor augmented expression of delayed type hypersensitivity (DTH) skin reactions to anergy panel antigens or to a contact allergen dinitrofluorobenzene. R24 was infrequently found on tumor cells, or on lymphocytes from DTH biopsies, despite measurable serum levels of R24. The 30 mg/m2/d dose of R24 produced a statistically significant drop in peripheral blood lymphocytes on treatment Day 5. Likewise, on Day 5 there was a modest but statistically significant decrement in the proportion of circulating cells which were R24+. While there was one mixed response, there were no complete or partial tumor regressions in the R24 treated patients; there was no evident clinical benefit from the R24 therapy. The toxicity of the R24 at the higher dose levels can be very substantial. One patient, on the highest dose level, died on the 4th day of R24 treatment; in the absence of a plausible alternative explanation, a relationship of the death to the administered R24 must be considered. A precipitous drop in serum albumin coincident with R24 administration was found in all cases; this effect has not been previously reported with R24.