Melanoma cell intrinsic GABAA receptor enhancement potentiates radiation and immune checkpoint inhibitor response by promoting direct and T cell-mediated anti-tumor activity

Most metastatic melanoma patients show variable responses to radiotherapy and do not benefit from immune checkpoint inhibitors (ICIs). Improved strategies for combination therapy that leverage potential benefits from radiotherapy and ICI are critical. Genes coding for subunits of GABAARs express functional GABAARs in melanoma cells. By enhancing GABAAR mediated anion transport, benzodiazepines depolarize melanoma cells and impair their viability. In vivo, benzodiazepine alone reduces tumor growth and potentiates radiotherapy and a-PD-L1 anti-tumor activity. Combination of benzodiazepine, radiotherapy, and a-PD-L1 results in near complete regression of treated tumors and a potent abscopal effect, mediated by increased infiltration of polyfunctional CD8+ T cells. Treated tumors show expression of cytokine:cytokine receptor interactions and overrepresentation of p53 signaling. This study identifies an anti-tumor strategy combining radiation and/or immune checkpoint inhibitor with modulation of GABAARs in melanoma using a benzodiazepine. Overall design: B16F10-GP mice were treated with radiation and/or Drug (QH-II-066). Mice receiving rdiation (5 Gy once) were irradiated on right flank only. Mice receiving Drug, QH-II-066 was delivered ip. Mice receiving 5 Gy and Drug were irradiated first and then received drug ip.