MECHANISM OF THE ANTITUMOR EFFECT OF BIOCHEMOTHERAPY IN MELANOMA - PRELIMINARY-RESULTS

During the conduct of a biochemotherapy trial in which cisplatin, vinblastine and dacarbazine (CVD) were administered concurrently with interleukin-2 (IL-2) plus interferon-alpha2a (IFN-alpha2a) (biochemotherapy) in advanced melanoma, we performed a series of laboratory studies in an attempt to understand better the mechanism of anti-tumour effect of the regimen. We initially hypothesized that CVD enhanced the antitumour effect of the biotherapy. However, in the first 10 patients studied, of whom eight were responders, we observed no lymphokine-associated killer cell (LAK) and minimal natural killer (NK) cell activities. This prompted us to change our initial hypothesis. Based on the work of others which showed a marked synergism between IL-1alpha and cisplatin, apparently mediated by H2O2 derived from tumour-infiltrating macrophages, we reasoned that the biotherapy could enhance the cytotoxicity of the CVD regimen. To evaluate macrophage function, we measured serum neopterin levels in eight responders and seven non-responders. An increase of six or more times above baseline levels was observed in seven out of eight responders but in only two of seven non-responders (P = 0.041). We also examined the level of DNA inter-strand cross-link in peripheral blood mononuclear cells in four responders and four responders, as a means to evaluate the DNA repair process. A DNA cross-link index greater-than-or-equal-to 0.75 was observed in all four responders but only in one non-responder (P = 0.14). Our preliminary results suggest that concurrent biochemotherapy may exert its predominant anti-tumour effect by direct cytotoxicity and that macrophages may be involved in this process.