The prognostic and therapeutic implications of distinct patterns of argininosuccinate synthase 1 (ASS1) and arginase-2 (ARG2) expression by cancer cells and tumor stroma in non-small-cell lung cancer

Alexandra Giatromanolaki, Adrian L. Harris, Michael I. Koukourakis

Arginine (Arg) is essential for cancer cell growth and also for the activation of T cells. Thus, therapies aiming to reduce Arg utilization by cancer may prove detrimental for the immune response. We examined the expression of two major enzymes involved in arginine depletion and replenishment, namely arginase ARG2 and argininosuccinate synthase ASS1, respectively, in a series of 98 NSCLCs. Their association with immune infiltrates and the postoperative outcome were also studied. ARG2 was expressed mainly by cancer-associated fibroblasts (CAFs) (58/98 cases; 59.2%), while ASS1 by cancer cells (75/98 cases; 76.5%). ASS1 and ARG2 expression patterns were not related to hypoxia markers. Auxotrophy, implied by the lack of expression of ASS1 in cancer cells, was associated with high angiogenesis (p < 0.02). ASS1 expression by cancer cells was associated with a high density of iNOS-expressing tumor-infiltrating lymphocytes (iNOS+TILs). ARG2 expression by CAFs was inversely related to the TIL-density and linked with poorer prognosis (p = 0.02). Patients with ASS1 expression by cancer cells had a better prognosis especially when CAFs did not express ARG2 (p = 0.004). ARG2 and ASS1 enzymes are extensively expressed in NSCLC stroma and cancer cells, respectively. Auxotrophic tumors have a poor prognosis, potentially by utilizing Arg, thus reducing Arg-dependent TIL anti-tumor activity. ASS1 expression in cancer cells would allow Arg fueling of iNOS+TILs and enhance anti-tumor immunity. However, upregulation of ARG2 in CAFs may divert Arg from TILs, allowing immune escape. Identification of these three distinct phenotypes may be useful in the individualization of Arg-targeting therapies and immunotherapy.