SYNERGISTIC ANTITUMOR ACTIVITY OF INTERLEUKIN 1 AND DOXORUBICIN HYDROCHLORIDE AGAINST A375 HUMAN MELANOMA

Abstract

There is great interest in combining Biologic Response Modifiers (BRM) and Chemotherapeutic drugs for the treatment of cancers, both to enhance efficacy and decrease toxicity. Both doxorubicin hydrochloride (Dox) and Interleukin 1 (IL1) inhibited the in vitro proliferation the A375 human melanoma in a dose dependent manner. The 50% inhibitory concentrations were found to be 1 U/ml and 10 U/ml for A375 C6, Insensitive (A375/S) and A375 C5, IL1 resistant (A375/R), cell lines, respectively, using the ³H-thymidine incorporation assay. IL1α and IL1β were found to be equally inhibitory to A375/S. IL1α elicited a cytolytic response against A375/S (60% specific lysis at 3 U/ml); in contrast, Dox at up to 100 μM, was unable to cause lysis of A375/S. Synergistic antiproliferative effects were observed in vitro against both A375/S and A375/R when cells were incubated with the IL1 and Dox combination. One possible mechanism suggested for this antiproliferative synergy was the observed IL1 mediated increase in intracellular Dox concentration. An increase in intracellular Dox concentration, of up to 63%, was seen after exposure of A375/S cells to between 0.3 U/m1 and 3 U/ml of IL1, for as short a duration as 15 minutes. Dox concentration is increased with a longer incubation. The A375 human melanoma was xenografted into athymic nude mice for in vivo therapeutic studies. In vivo the therapeutic combination of Dox (4 mg/kg) and IL1 (1 μg), given simultaneously once every other day, delayed (up to two weeks), the growth of early, day 3, s.c. A375/S tumors, to a greater degree than therapy with either drug alone (p<0.03). The decrease in tumor volumes, when compared to untreated control animal in the IL1:Dox treated mice were maintained throughout the experiment. Although IL1 therapy alone was able to reduce the size of later stage, palpable A375/S tumors (p<0.07), no synergy was observed against these later stage tumors when the DOX:IL1 combination was administered. Tumor pathology after the treatment with 4 mg/kg Dox and/or 5 μg IL1 revealed hemorrhage and necrosis due to IL1 treatment, but not after Dox therapy. The combination of Dox and IL1 had very similar pathological effects to that of IL1 alone with no indication of synergy between the two drugs against the later stage A375/S palpable tumor. This is in agreement with the in vivo findings that IL1 was capable of tumor volume reduction, but Dox was not.