Abstract 61: Enhancing arginine deprivation therapy in melanoma by combining with cisplatin

Proceedings: AACR 101st Annual Meeting 2010‐‐ Apr 17‐21, 2010; Washington, DC We have previously shown that arginine deprivation using pegylated arginine deiminase (ADI-PEG20) has activity in melanoma patients whose tumors do not express argininosuccinate synthetase (ASS). However, not all ASS-negative patients respond to treatment, and relapse does occur. In our laboratory, we have found that there are two major mechanisms of resistance to ADI-PEG20: 1) induction of ASS expression upon arginine deprivation and 2) the ability of ASS-negative cells to undergo autophagy and hence evade apoptosis. These cells often have high level of anti-apoptotic proteins such as Bcl-2. To overcome resistance to ADI-PEG20, one can add an agent to either accelerate cell death before cells are rescued by induction of ASS expression or channel cells directly to apoptosis instead of autophagy. Cisplatin is known to induce apoptosis via the mitochondria pathway while ADI-PEG20 can also induce apoptosis through nutritional stress via the same pathway. Therefore combination of these two agents should intensify the apoptotic signal. We have investigated this possibility using a panel of six melanoma cell lines (A375, A2058 and SK-Mel-2 from ATCC; Mel-1220, Mel-F, and Mel-114 established in our laboratory). We have found that the combination of cisplatin (0.1 ug/ml) with ADI-PEG20 (0.05 ug/ml) can effectively induce cell death in all melanoma cell lines tested. The growth inhibition increased from 30-40% with ADI-PEG20 alone to 60-70% with combination in the ATCC cell lines (p < 0.001), and from 35% to 50% in our own cell lines (p =< 0.05). When treated with cisplatin alone at the same dosage, the growth inhibition was only 10-20% for all these cell lines. This combination also increased the percentage of cells undergoing apoptosis. When compared with cisplatin alone treatment, the percentage of cells with caspase activation increased from 5% (0.5 ug/ml of cisplatin) to 29% (combination with ADI-PEG20 at 0.05 ug/ml), or from 20% (1 ug/ml of cisplatin) to 75% (combination with ADI-PEG20 at 0.05 ug/ml) in A375. The increase of cell death was less (12-15% to 25-30%) in Mel-1220 and Mel-F which have high levels of Bcl-2 protein. This combination treatment is not schedule-dependent. In our study of the combination treatment, we found that the combination led to more DNA damage than cisplatin alone in Mel-1220 as revealed by γ-H2AX immunofluorescence. This combination also increased the expression of pro-apoptotic protein Noxa, and resulted in decrease of anti-apoptotic protein Survivin in Mel-1220 and A375. No apparent changes were detected for Bcl-2, Mcl-1, and XIAP. Interestingly, tBid formation was also observed in the combination treatment in A375 and SK-Mel-2 which also indicates the enhancement of apoptotic signal when cisplatin and ADI-PEG20 were combined. From these data, the combination of cisplatin and ADI-PEG20 should be a more effective treatment for melanomas which lack ASS expression. Supported by NIH grant 1RO1CA109578. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 61.