TMET-18. Inhibition of stearoyl-CoA desaturase prevents immunosuppressive phenotypic switch of macrophages and reprograms lipid metabolism in melanoma brain metastases

Abstract The 5-year survival rate for metastatic melanoma (MM) is 35% with rates increasing to ~50% with immune checkpoint blockade (ICB) treatment. Unfortunately, melanoma brain metastases (MBM) develop in nearly half of MM patients and often relapse rapidly following ICB treatment. MBM resistance to ICB can be attributed to tumor-associated macrophages (TAM). Transcriptional profiling of MM revealed that TAMs possess a lipidated phenotype suggesting that aberrant lipogenic processes confer ICB resistance. Stearoyl-CoA desaturase (SCD) is a lipogenic enzyme that is overexpressed in MM and may cause TAM lipidation. SCD serves as an attractive target for inhibition and combination with ICB for treating MBM. We hypothesize that SCD overexpression produces lipid-rich tumor cells that trigger a phenotypic switch towards immunosuppressive lipid-laden macrophages (LL-Mø). Clinical correlation analysis was conducted to assess SCD expression with ICB response. scRNA-seq data of MBM were analyzed to assess TAMs exhibiting lipidated phenotype. Phagocytosis and lipid transfer was assessed via macrophage and melanoma co-culture using time-lapse microscopy. In-silico modeling and LC-MS/MS was performed to assess blood brain barrier (BBB) penetrance of two small molecule inhibitors of SCD (SCDi): MTI-301 and MF-438. Clinical correlation analysis of MM patients revealed high SCD expression associated with decreased survival of patients treated with ICB. scRNA-seq analysis of MBM revealed upregulation of de novo lipogenesis and cholesterol uptake transcripts within TAM populations. Time-lapse co-culture studies reveal rapid lipid accumulation in macrophages. In-silico modeling predicted SCDi BBB penetration and was corroborated by LC-MS/MS. MBM are notoriously difficult to treat due to poor drug penetrance into CNS and unique microenvironment. We demonstrate that macrophages reprogram towards immunosuppressive LL-Mø, which can be exploited for anti-tumor targeting. The potential for SCDi to synergize with ICB in MBM may improve patient outcomes. MTI-301 is approved for first-in-human clinical trial starting end of 2025.