Abstract
Loss of argininosuccinate synthetase (ASS) expression in melanoma makes these tumor cells vulnerable to arginine deprivation. Pegylated arginine deiminase (ADI-PEG20) which degrades arginine to citrulline and ammonia has been used clinically and partial responses and stable disease have been noted with minimal toxicity. In order to improve the therapeutic efficacy of ADI-PEG20, we have combined ADI-PEG20 with a DNA damaging agent, cisplatin. We have shown that the combination of the two drugs together significantly improved the therapeutic efficacy when compared to ADI-PEG20 alone or cisplatin alone in 4 melanoma cell lines, regardless of their BRAF mutation. In-vivo study also exhibited the same effect as in-vitro with no added toxicity to either agent alone. The underlying mechanism is complex, but increased DNA damage upon arginine deprivation due to decreased DNA repair proteins, FANCD2, ATM, and CHK1/2 most likely leads to increased apoptosis. This action is further intensified by increased proapoptotic protein, NOXA, and decreased antiapoptotic proteins, SURVIVIN, BCL2 and XIAP. The autophagic process which protects cells from apoptosis upon ADI-PEG20 treatment also dampens upon cisplatin administration. Thus, the combination of arginine deprivation and cisplatin function in concert to kill tumor cells which do not express ASS without added toxicity to normal cells.