Cyclin-Dependent Kinase 4/6 Inhibitors: Is a Noncanonical Substrate the Key Target?

Targeting STAT3 potentiates CDK4/6 inhibitors therapy in head and neck squamous cell carcinoma

Anti-CDK4/6 therapy has been employed for the treatment for head and neck squamous cell carcinoma (HNSCC) with CDK4/6 hyperactivation, but the response rate is relatively low. In this study, we first showed that CDK4 and CDK6 was over-expressed and conferred poor prognosis in HNSCC. Moreover, in RB-positive HNSCC, STAT3 signaling was activated induced by CDK4/6 inhibition and STAT3 promotes RB deficiency by upregulation of MYC. Thirdly, the combination of Stattic and CDK4/6 inhibitor results in striking anti-tumor effect in vitro and in Cal27 derived animal models. Additionally, phospho-STAT3 level negatively correlates with RB expression and predicts poor prognosis in patients with HNSCC. Taken together, our findings suggest an unrecognized function of STAT3 confers to CDK4/6 inhibitors resistance and presenting a promising combination strategy for patients with HNSCC.

Immunomodulatory effects of CDK4/6 inhibitors

The dysregulation of the cell cycle is one of the hallmarks of cancer. Cyclin-dependent kinase 4 (CDK4) and CDK6 play crucial roles in regulating cell cycle and other cellular functions. CDK4/6 inhibitors have achieved great success in treating breast cancers and are currently being tested extensively in other tumor types as well. Accumulating evidence suggests that CDK4/6 inhibitors exert antitumor effects through immunomodulation aside from cell cycle arrest. Here we outline the immunomodulatory activities of CDK4/6 inhibitors, discuss the immune mechanisms of drug resistance and explore avenues to harness their immunotherapeutic potential when combined with immune checkpoint inhibitors (ICIs) or chimeric antigen receptor (CAR) T-cell therapy to improve the clinical outcomes.

Inhibition of multiple CDKs potentiates colon cancer chemotherapy via p73-mediated DR5 induction

Targeting cyclin-dependent kinases (CDKs) has recently emerged as a promising therapeutic approach against cancer. However, the anticancer mechanisms of different CDK inhibitors (CDKIs) are not well understood. Our recent study revealed that selective CDK4/6 inhibitors sensitize colorectal cancer (CRC) cells to therapy-induced apoptosis by inducing Death Receptor 5 (DR5) via the p53 family member p73. In this study, we investigated if this pathway is involved in anticancer effects of different CDKIs. We found that less-selective CDKIs, including flavopiridol, roscovitine, dinaciclib, and SNS-032, induced DR5 via p73-mediated transcriptional activation. The induction of DR5 by these CDKIs was mediated by dephosphorylation of p73 at Threonine 86 and p73 nuclear translocation. Knockdown of a common target of these CDKIs, including CDK1, 2, or 9, recapitulated p73-mediated DR5 induction. CDKIs strongly synergized with 5-fluorouracil (5-FU), the most commonly used CRC chemotherapy agent, in vitro and in vivo to promote growth suppression and apoptosis, which required DR5 and p73. Together, these findings indicate p73-mediated DR5 induction as a potential tumor suppressive mechanism and a critical target engaged by different CDKIs in potentiating therapy-induced apoptosis in CRC cells. These findings help better understand the anticancer mechanisms of CDKIs and may help facilitate their clinical development and applications in CRC.

Design, synthesis, and anticancer activity of three novel palbociclib derivatives

Cancer is one of the most serious diseases threatening human health, so it is particularly important to develop effective tumor-targeting drugs. As the first CDK4/6 inhibitor, palbociclib effectively inhibits tumor proliferation by blocking the cell cycle to the G1 phase. 10-HCPT is a Topo I inhibitor; however, its clinical application has been greatly limited due to its high toxicity. Based on the successful development of double target inhibitors, three novel palbociclib derivatives (HP-1, HP-2, and HP-3) were designed and synthesized from Palbociclib and 10-HCPT, and their biological activities were investigated. At first, the possible binding sites of the three compounds to Topo I and CDK4/6 were predicted by molecular docking. Then, we evaluated the anti-proliferative effects of the three palbociclib derivatives. In general, human lung cancer cells were more sensitive to HP-1, HP-2, and HP-3, especially NCI-H460. In addition, cell cycle arrest and apoptosis induction were investigated by flow cytometry. The three palbociclib derivatives, especially HP-1, had obvious cell cycle arrest phenomenon on NCI-H460 cells and induced apoptosis of NCI-H460 cells significantly. In the end, it was proved that these three drugs had obvious cyclin-dependent kinase inhibitory activities. In short, all the data showed that HP-1, HP-2, and HP-3 could play anti-cancer roles by acting on dual targets and had the characteristics of high efficiencies and low toxicities, which opened up a new idea for the study of palbociclib derivatives.

Identification of the Potential Correlation between Tumor Protein 73 and Head and Neck Squamous Cell Carcinoma

Background

Head and neck squamous cell carcinomas (HNSC) are common malignant tumors with a high occurrence and poor prognosis. Tumor protein P73 (TP73) plays an integral role in a wide range of human malignancies, but its gene expression profile, prognostic value, and potential mechanisms in HNSC remain to be comprehensively explored.

Objective

This research aimed to elucidate the potential relationship between TP73 and HNSC through bioinformatics analysis.

Methods

The Cancer Genome Atlas (TCGA) database was queried to investigate the regulatory role of TP73 in HNSC. The survival probabilities linked to TP73 mRNA were determined via the Kaplan-Meier analysis using R packages. Subsequently, the association of TP73 with several clinical subgroups and immunological subtypes was studied using a cohort from the TCGA-HNSC. Functional analyses were used to identify the potential signaling pathways enriched by the correlated genes of TP73. The relationship between TP73 and immunological aspects, including immune cells, immune inhibitor genes, immune stimulator genes, and tumor immune microenvironment, were investigated.

Results

This study showed that the protein and mRNA levels of TP73 in HNSC patients were significantly higher than those in normal tissues. Elevated TP73 expression was related to a better survival outcome in HNSC patients. The TP73 gene was an independent prognostic factor for overall survival in HNSC samples. TP73 was mainly involved in DNA replication, ribosome, apoptosis, mismatch repair, and folate biosynthesis. TP73 was found to be positively correlated with the majority of tumor infiltrating immune cells and immunoinhibitory genes in HNSC.

Conclusions

Integrative bioinformatics and statistical analyses displayed that TP73 might serve as a novel marker for the diagnosis and prognosis of HNSC. TP73 modulates immune cells in the tumor microenvironment of HNSC patients, thereby bearing significance for HNSC immunotherapy.