Enhancing PD-L1 Degradation by ITCH during MAPK Inhibitor Therapy Suppresses Acquired Resistance

MAPK inhibitor (MAPKi) therapy in melanoma leads to accumulation of tumor-surface PD-L1/2, which may evade antitumor immunity and accelerate acquired resistance. Here, we discover that the E3 ligase ITCH binds, ubiquitinates, and down-regulates tumor-surface PD-L1/L2 in MAPKi-treated human melanoma cells, thereby modulating activation of co-cultured T cells. During MAPKi therapy in vivo, tumor cell-intrinsic ITCH knockdown in murine melanoma induced tumor-surface PD-L1, reduced intratumoral cytolytic CD8+ T cells, and accelerated acquired resistance only in immune-proficient mice. Conversely, tumor cell-intrinsic ITCH over-expression reduced MAPKi-elicited PD-L1 accumulation, augmented cytolytic CD8+ T-cell infiltration, and suppressed acquired resistance in BrafMUT, NrasMUT, and Nf1MUT murine melanoma and KrasMUT pancreatic cancer models. CD8+ T-cell depletion and tumor cell-intrinsic PD-L1 over-expression nullified the ability of ITCH over-expression to suppress MAPKi-resistance, supporting in vivo the ITCH­–PD-L1­–T-cell regulatory axis demonstrated in human cancer cell lines. Moreover, we identified a small-molecular ITCH activator which suppressed acquired MAPKi-resistance in vivo. Thus, MAPKi-elicited tumor-surface PD-L1 accelerates acquired-resistance, and degrading PD-L1 by activating ITCH may be a combinatorial approach to promote antitumor T-cell immunity and durable responses. This dataset contains the scRNAseq and scTCR-seq data of intratumoral CD45+ cells in murine melanoma model (NILER1-4, Nras mutant) under MEKi treatment and scRNAseq data of dissociated tumors in BRAFmut murine melanoma model (YUMMER1.7) under MEKi treatment