Senescence as an immune tolerance breaker: Inhibitors of mitotic kinases TTK (Mps1) and AURKA induce pro-immunogenic senescence that primes the tumor microenvironment for immunotherapy via cGAS-STING signaling

Therapy-induced senescence (TIS) is a common outcome of diverse conventional and emerging anti-cancer treatments, including chemotherapy, radiation, and small-molecule inhibitors. TIS is characterized by stable growth arrest and the Senescence-Associated Secretory Phenotype (SASP), which involves the increased secretion of various molecules, including pro-inflammatory and immune-modulating factors. As cancer immunotherapies become increasingly widespread, understanding the impact of TIS on the tumor microenvironment (TME) and immunotherapy responses is critically important. Here, we investigated the TIS induced by mitotic kinase inhibitors, including Aurora kinase A and Monopolar spindle 1 kinase (Mps1, also known as TTK), in various tumor models in vitro and in vivo. Transcriptional and secretome profiling revealed a significant increase in inflammation/immune gene expression and in the secretion of various immune-related mediators and chemokines in a therapy-induced senescence state. We also found that the addition of a senolytic agent, the BCL2/xL inhibitor navitoclax, which induces cell death in senescent cells, did not abrogate SASP but rather altered it to promote a pro-immunogenic phenotype that recruits and activates cytotoxic T cells. Our investigation of the molecular mechanism driving pro-immunogenic mitotic inhibition-induced TIS revealed the formation of micronuclei linked with the activation of the cGAS-STING pathway, which, in turn, activated STAT1 and interferon-regulated transcriptional programs. In addition to secreting pro-immunogenic factors, mitotic inhibition-induced senescent tumor cells exhibited increased surface expression of MHC-I, indicating enhanced immunogenicity that facilitated their killing by the CD8 T cells. In vivo, mitotic kinase inhibition significantly enriched the TME with activated CD8+ T cells and NK cells. Depletion studies confirmed the critical role of these cells in anti-tumor effects. Treatments combining mitotic inhibitors with immunotherapy, such as the TTK inhibitor OSU13 with anti-PD-1 immune checkpoint blockade, or the AURKA inhibitor alisertib with either T- or NK-cell therapy, resulted in enhanced tumor control and prolonged survival in murine models. These findings suggest that senescence and inflammatory phenotype caused by mitotic kinase inhibition can be harnessed to promote effector cell engagement in immune-cold tumors, thereby enhancing responsiveness to immune therapies.