Introduction: Treating drug-resistant sarcomas remain a major challenge. The present study aimed to identify a novel therapy for drug-resistant sarcomas based on a metabolic errors involving argininosuccinate synthetase1 (ASS1).

Methods: We assessed the expression of ASS1 and P-glycoprotein (P-gp) in osteosarcoma (KHOS), doxorubicin (Dox)-resistant osteosarcoma (KHOSR2), epithelioid sarcomas (ES-X and VAESBJ), alveolar soft part sarcoma (ASPS-KY), and each clinical specimen. Each cell was cultured in arginine-containing and arginine-free media. Cell growth was assessed using an XTT assay and flow cytometry. We analyzed the induction of autophagy in arginine-free medium. Moreover, we assessed the expression of P-gp in after suppressing ASS1 in Dox-sensitive cells (MCF-7, KHOS) and in after transfecting the ASS1 into Dox-resistant cells (ES-X, VAESBJ, ASPS-KY and KHOSR2).

Results: The expression of ASS1 was reduced in Dox-resistant sarcoma cells. Immunohistochemistry (IHC) and real-time PCR showed that there was interestingly an inverse relationship between the expression of ASS1 and the expression of P-gp. The inhibition of cellular proliferation with G1-arrest was shown to lead to autophagy with arginine deprivation. In addition, the combination of autophagy inhibitor plus arginine deprivation was more effective than arginine deprivation alone. In cells in which the expression of ASS1 was suppressed, the expression of P-gp was upregulated in comparison to negative controls.

Discussion: These results indicate that the reduced expression of ASS1 expression in Dox-resistant sarcomas may contribute to drug resistance. ASS1 deficiency is a potential target for novel drug therapies. The combination of arginine deprivation therapy and an autophagy inhibitor may have anti-tumor effects in refractory sarcomas.

Significance: As the induction of autophagy by the deprivation arginine may have a pro-survival role in patients with ASS1-deficient sarcomas, the combination of arginine deprivation therapy with autophagy modulators might potentiate anti-tumor effects in patients with drug-resistant sarcomas.

Citation Format: Eisuke Kobayashi, Youngji Kim, Daisuke Kubota, Yoshiyuki Suehara, Akira Kawai, Shigehisa Kitano. Reduced argininosuccinate synthetase expression in refractory sarcomas: impacts on therapeutic potential and drug resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 449. doi:10.1158/1538-7445.AM2017-449