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CDK4/6 inhibition suppresses p73 phosphorylation and activates DR5 to potentiate chemotherapy and immune checkpoint blockade

ABSTRACT: Targeting cyclin-dependent kinases 4 and 6 (CDK4/6) is a successful therapeutic approach against breast and other solid tumors. Inhibition of CDK4/6 halts cell cycle progression and promotes antitumor immunity. However, the mechanisms underlying the antitumor activity of CDK4/6 inhibitors are not fully understood. We found that CDK4/6 bind and phosphorylate the p53 family member p73 at threonine 86, which sequesters p73 in the cytoplasm. Inhibition of CDK4/6 led to dephosphorylation and nuclear translocation of p73, which transcriptionally activated death receptor 5 (DR5), a cytokine receptor and key component of the extrinsic apoptotic pathway. p73-mediated induction of DR5 by CDK4/6 inhibitors promoted immunogenic cell death (ICD) of cancer cells. Deletion of DR5 in cancer cells in vitro and in vivo abrogated the potentiating effects of CDK4/6 inhibitors on immune cytokine TNF-related apoptosis-inducing ligand (TRAIL), 5-fluorouracil (5-FU) chemotherapy, and anti-PD-1 immunotherapy. Together, these results reveal a previously unrecognized consequence of CDK4/6 inhibition, which may be critical for potentiating the killing and immunogenic effects on cancer cells.

ORGANISM(S): Homo sapiens

PROVIDER: GSE196276 | GEO | 2022/02/09

REPOSITORIES: GEO

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Project description:Immune checkpoint blockade has shown tremendous anti-tumor potential in the clinic. However, these therapies are only effective in a subset of patients, so identification of additional immunomodulatory molecules that enhance the anti-tumor activity of these treatments may expand their clinical utility. In particular, identifying small molecules that complement existing immunotherapies has been relatively unexplored, so we performed a small molecule screen to identify compounds that can enhance co-inhibitory molecule blockade, to improve the anti-tumor adaptive immune response. Our unbiased screen identified inhibitors of cyclin-dependent kinase 4 and 6 (CDK4/6), including the FDA-approved palbociclib, as a class of small molecule compounds that exhibited significant immunostimulatory activity in vitro. In accordance with our in vitro finding of enhanced NFAT signaling, single-cell RNA-sequencing confirmed that in vivo exposure to CDK4/6 inhibitors enhanced NFAT signaling in tumor infiltrating T cells. Moreover, our results revealed that CDK4/6 inhibition up-regulated activation molecules and down-regulated suppressive molecules in these cells. CDK4/6 inhibition also increased the number of T cells with activated TCR (T cell receptor) signaling, as well as factors that are important for signal transduction downstream of TCR signaling. In summary, the impact of CDK4/6i on cell cycle progression and T cell proliferation are balanced favorably towards increased T cell recruitment and enhanced effector cell function, mediated in part by activation of the NFAT family of transcription factors. Further, our results demonstrate that CDK4/6i enhances PD-1 blockade through increased T-cell effector function and inhibition of immune suppressive cytokine production. While prolonged CDK4/6i treatment could be immunosuppressive due to adverse effects on lymphocyte proliferation, properly timed/sequenced CDK4/6i may potentiate the clinical impact of anti-PD-1/PD-L1 antibodies. As palbociclib is FDA-approved and multiple other CDK4/6 inhibitors are in clinical trials, we expect that this hypothesis will undergo rapid testing in humans.

Project description:Cdk4 and Cdk6 are two related kinases that bind D-type cyclins and regulate cell cycle progression. Due to their relevance in cancer, Cdk4/6 inhibitors are currently in advanced clinical trials in multiple tumor types. Cdk4/6 are inhibited by INK4 proteins that exert tumor suppressing functions. To test the significance of this inhibitory mechanism we have generated knock-in mice that express a Cdk6 mutant (Cdk6 R31C) insensitive to INK4-mediated inhibition. Cdk6R/R mice display altered development of the hematopoietic system without resulting in enhanced tumor susceptibility, either in the presence or absence of p53. The presence of the Cdk6 R31C allele results in defective potential of hematopoietic progenitors in adoptive transfer assays or after induced damage. These defects are rescued after complete insensitivity to INK4 inhibitors in Cdk4R/R; Cdk6R/R double mutant mice, and INK4-resistant mice display increased susceptibility to hematopoietic and endocrine tumors. In BCR-ABL-transformed hematopoietic cells, the presence of the Cdk6 R31C allele results in increased binding of p16INK4a to wild-type Cdk4, whereas the double mutant is fully insensitive to INK4 inhibitors resulting in accelerated disease onset. Our observations reveal that Cdk4 and Cdk6 cooperate in tumor development and suggest a role for Cdk6 in buffering INK4 protein levels thus contributing to the development of hematopoietic tumors. The presence of the Cdk4 R24C and Cdk6 R31C alleles results in relevant changes in the expression profiles of cancer cells including deregulation of apoptosis and other processes. p185BCR-ABL1 was used to transform wild-type or double knock-in Cdk4 R24C; Cdk6 R31C fetal livers. Cell lines were isolated as spontaneous immortal and transformed clones after transduction of fetal liver with a p185 BCR-ABL1-transgene. RNA was isolated from asynchronous cultures. Two-condition experiment, Cdk4R-Cdk6R cells versus wild-type cells. Biological replicates: 3 control replicates, 3 transfected replicates.

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CDK4/6 inhibition suppresses p73 phosphorylation and activates DR5 to potentiate chemotherapy and immune checkpoint blockade

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