Genome-wide CRISPR/Cas9 screen identified MCL1 as a senolytic target for clearing palbociclib-induced senescent and PD-L1-positive cells in colorectal cancer.

Colorectal cancer (CRC) is the most prevalent digestive system malignancy worldwide. The development of targeted therapeutics specifically effective for CRC is currently in dire need. Preclinical studies showed that CDK4/6 inhibitor palbociclib suppressed the growth of CRC, but whether this effect is durable is unclear. In this study, we aimed to evaluate the roles of palbociclib-induced senescence and find a new strategy to maximize its effectiveness in CRC treatment. Animal and cellular experiments revealed that palbociclib-induced senescence and the senescence-associated secretory phenotype (SASP) caused drug resistance, anti-apoptosis, PD-L1 upregulation and inhibition of CD8+ T cells' function. Using CRISPR/Cas9 screening, we identified MCL1 as a senolytic target to eliminate palbociclib-induced senescent CRC cells in the presence of palbociclib. Mechanically, palbociclib-induced senescent cells upregulated ZHX2 and its transcriptional target MCL1, rendered their resistance to apoptosis and T cell-mediated cytotoxicity, whereases combining palbociclib with MCL1 inhibitor markedly induced apoptosis in senescent cells by activating both extrinsic and intrinsic apoptotic pathways. Lastly, we proposed a seno-therapy consisting of a palbociclib pre-treatment plus a combination treatment of palbociclib and MCL1 inhibitor and found it effectively inhibited tumor growth and improved the survival of CRC xenografted mice. Besides its senolytic effect, seno-therapy also reduced PD-L1-positive cells and enhancing the cytotoxic functions of CD8+ T cells. In conclusion, co-targeting CDK4/6 and MCL1 efficiently eliminates palbociclib-induced senescent CRC cells and offers a promising CDK4/6 inhibitor-based strategy for CRC treatment, ensuring prolonged tumor suppression and reducing the risk of progression or recurrence.