Targeting the TLK1-Nek1-Mediated Activation of YAP1 Attenuates PD-L1 and Anti-Inflammation Set for Prostate Cancer Immunoevasion

Our recent studies on the activation of the TLK1B>NEK1>YAP1 axis following ADT/ARSI have revealed the outlines of an innate immunity integration response that includes PD-L1 expression and alterations in cGAS-pSTING and pSTAT1/3, which drive the immunoevasion of PCa cells after prolonged treatment with ARSI and can thus contribute to CRPC progression. These observations are consistent with the general assessment that human PCa is immunologically ‘cold’ and unresponsive in the long term to ICB treatments aimed at combating mCRPC once it is established. Here, we utilized a TLK1 inhibitor (J54) and a PD-L1 monoclonal antibody to suppress tumor growth in a syngeneic PCa model (TC2 in C57/Bl6 mice), in addition to Enzalutamide (ENZ). Remarkably, the combinations of ENZ+J54 or Atez+J54 resulted in durable suppression of tumor growth, partly explained by a strong antitumor immune response. These observations were further generalized using a genetic model (TRAMPxNEK1+/- mice), in which we occasionally observed progression to genuine PRAD with age. In cases when it did progress, there was clear evidence of a strong immunoreactive response, spatially discernible with VISIUM (10XG) of PEFF prostate sections. We also defined the mechanism of YAP-dependent expression of PD-L1 using a number of common PCa cell lines, OE plasmids for YAP-wt and inactive Y407F mutant, Luc reporters containing proximal and distal regulatory elements of the PD-L1 gene, and occupancy of those same elements by YAP/TEAD by ChIP.