Antitumoral Activity of a CDK9 PROTAC Compound in HER2-Positive Breast Cancer.

Cyclin-dependent kinases (CDKs) are a broad family of proteins involved in the cell cycle and transcriptional regulation. In this article, we explore the antitumoral activity of a novel proteolysis-targeting chimera (PROTAC) compound against CDK9. Breast cancer cell lines from different subtypes were used. Transcriptomic mapping of CDKs in breast cancer demonstrated that the expression of CDK9 predicted a detrimental outcome in basal-like tumors (HR = 1.51, CI = 1.08-2.11, p = 0.015) and, particularly, in the luminal B subtype with HER2+ expression (HR = 1.82, CI = 1.17-2.82, p = 0.0069). The novel CDK9 PROTAC, THAL-SNS-032, displayed a profound inhibitory activity in MCF7, T47D, and BT474 cells, with less effect in SKBR3, HCC1569, HCC1954, MDA-MB-231, HS578T, and BT549 cells. The three cell lines with HER2 overexpression and no presence of ER, SKBR3, HCC1569, and HCC1954 displayed an EC50 three times higher compared to ER-positive and dual ER/HER2-positive cell lines. BT474-derived trastuzumab-resistant cell lines displayed a particular sensitivity to THAL-SNS-032. Western blot analyses showed that THAL-SNS-032 caused a decrease in CDK9 levels in BT474, BT474-RH, and BT474-TDM1R cells, and a significant increase in apoptosis. Experiments in animals demonstrated an inverse therapeutic index of THAL-SNS-032, with doses in the nontherapeutic and toxic range. The identified toxicity was mainly due to an on-target off-tumor effect of the compound in the gastrointestinal epithelium. In summary, the potent and efficient antitumoral properties of the CDK9 PROTAC THAL-SNS-032 opens the possibility of using this type of compound in breast cancer only if specifically delivered to cancer cells, particularly in ER/HER2-positive and HER2-resistant tumors.

Transcriptional inhibition by CDK7/9 inhibitor SNS-032 abrogates oncogene addiction and reduces liver metastasis in uveal melanoma.

BACKGROUND: Life of patients with uveal melanoma (UM) is largely threatened by liver metastasis. Little is known about the drivers of liver organotropic metastasis in UM. The elevated activity of transcription of oncogenes is presumably to drive aspects of tumors. We hypothesized that inhibition of transcription by cyclin-dependent kinase 7/9 (CDK7/9) inhibitor SNS-032 diminished liver metastasis by abrogating the putative oncogenes in charge of colonization, stemness, cell motility of UM cells in host liver microenvironment. METHODS: The effects of SNS-032 on the expression of the relevant oncogenes were examined by qRT-PCR and Western blotting analysis. Proliferative activity, frequency of CSCs and liver metastasis were evaluated by using NOD-SCID mouse xenograft model and NOG mouse model, respectively. RESULTS: The results showed that CDK7/9 were highly expressed in UM cells, and SNS-032 significantly suppressed the cellular proliferation, induced apoptosis, and inhibited the outgrowth of xenografted UM cells and PDX tumors in NOD-SCID mice, repressed the cancer stem-like cell (CSC) properties through transcriptional inhibition of stemness-related protein Krüppel-like factor 4 (KLF4), inhibited the invasive phonotypes of UM cells through matrix metalloproteinase 9 (MMP9). Mechanistically, SNS-032 repressed the c-Myc-dependent transcription of RhoA gene, and thereby lowered the RhoA GTPase activity and actin polymerization, and subsequently inhibited cell motility and liver metastasis. CONCLUSIONS: In conclusion, we validate a set of transcription factors which confer metastatic traits (e.g., KLF4 for CSCs, c-Myc for cell motility) in UM cells. Our results identify SNS-032 as a promising therapeutic agent, and warrant a clinical trial in patients with metastatic UM.

A SIX1 degradation inducer blocks excessive proliferation of prostate cancer.

Prostate cancer (PC) remains a great medical challenge due to its high incidence and the development of castration resistance in patients treated with androgen deprivation therapy. Deubiquitinases, the enzymes that specifically hydrolyze ubiquitin chains on their substrates, were recently proposed as a serious of critical therapeutic targets for cancer treatment. Our previous study has been reported that the ubiquitin specific peptidase 1 (USP1) functionally acts as a deubiquitinase of sine oculis homeobox homolog 1 (SIX1) and contributes to the proliferation and castration resistance of PC. The stabilization of SIX1 by USP1 partially depends on the status of glucose-regulated protein 75 (GRP75). In this study, we aimed to identify a SIX1 degradation inducer via inhibiting the USP1-SIX1 axis. we screened a range of kinase inhibitors and showed that SNS-032 is the best candidate to trigger the ubiquitinated degradation of SIX1. SNS-032 not only restrains activity of the USP1-SIX1 axis and cell cycle progression, but also results in apoptosis of PC cells. Moreover, the combination of SNS-032 and enzalutamide synergistically induces apoptosis and downregulates expression of USP1, SIX1, and AR/AR-V7 in AR-V7 highly expressed 22Rv1 cells. Overall, our findings may develop a novel and effective strategy to overcome castration resistance in PC for the identification of a SIX1 degradation inducer via targeting the USP1-SIX1 axis.

Cyclin-dependent kinase 7/9 inhibitor SNS-032 induces apoptosis in diffuse large B-cell lymphoma cells.

Approximately 40% of patients with diffuse large B-cell lymphoma (DLBCL) are refractory or relapse to standard chemotherapy, and most of them are activated B cell-like DLBCLs (ABC-DLBCL) and germinal center B cell-like DLBCLs (GCB-DLBCL). SNS-032, a novel and selective CDK7/9 inhibitor, that the first phase clinical trials approved by US FDA for cancer treatment have been completed. In this study, we investigated the anti-tumor effect of SNS-032 in ABC- and GCB-DLBCL subtypes. We report that SNS-032 induced growth inhibition and cell apoptosis in both DLBCL cells in vitro, and inhibited the growth of both DLBCL xenografts in nude mice. Mechanistically, SNS-032 inhibited RNA polymerase II, which led to transcriptional-dependent suppression of NF-κB signaling pathway and its downstream targets involved in cell survival; SNS-032 also downregulates BCL-2 and c-MYC in both mRNA and protein levels. Significantly, these findings provide pre-clinical evidence for application of targeting the CDK7/9 in DLBCL.