Targeting the Divergent Roles of STK3 Inhibits Breast Cancer Cell Growth and Opposes Doxorubicin-Induced Cardiotoxicity In Vitro.

Breast cancer (BCa) is the most prevalent type of cancer in women. Several therapies used in the treatment of breast cancer are associated with clinically important rates of cardiovascular toxicity during or after treatment exposure, including anthracyclines. There is a need for new BCa therapeutics and treatments that mitigate chemotherapy-induced cardiotoxicity in BCa. In this study, we examine the effects of Serine/Threonine Kinase 3 (STK3) inhibition in the context of BCa therapy and cardioprotection from doxorubicin. STK3 (also known as MST2) is a key member of the Hippo Tumor-Suppressor Pathway, which regulates cell growth and proliferation by inhibiting YAP/TAZ co-transcription factors. Canonically, STK3 should restrict BCa growth; however, we observed that STK3 is amplified in BCa and associated with worse patient outcomes, suggesting a noncanonical pro-tumorigenic role. We found BCa cell lines have varying dependence on STK3. SUM52PE cells had the highest expression and dependence on STK3 in genetic and pharmacological assays. MCF-7 and MDA-MB-231 were less sensitive to STK3 targeting in standard proliferation assays, but were STK3 dependent in colony formation and matrigel invasion assays. In contrast, STK3 inhibition mitigated the toxic effects of doxorubicin in H9C2 rat cardiomyocytes by increasing YAP expression. Importantly, STK3 inhibition in BCa cells did not interfere with the therapeutic effects of doxorubicin. Our studies highlight STK3 is a potential molecular target for BCa with dual therapeutic effects: suppression of BCa growth and progression, and chemoprotection in cardiomyocytes.

Non-canonical role of Hippo tumor suppressor serine/threonine kinase 3 STK3 in prostate cancer.

Serine/threonine kinase 3 (STK3) is an essential member of the highly conserved Hippo tumor suppressor pathway that regulates Yes-associated protein 1 (YAP1) and TAZ. STK3 and its paralog STK4 initiate a phosphorylation cascade that regulates YAP1/TAZ inhibition and degradation, which is important for regulated cell growth and organ size. Deregulation of this pathway leads to hyperactivation of YAP1 in various cancers. Counter to the canonical tumor suppression role of STK3, we report that in the context of prostate cancer (PC), STK3 has a pro-tumorigenic role. Our investigation started with the observation that STK3, but not STK4, is frequently amplified in PC. Additionally, high STK3 expression is associated with decreased overall survival and positively correlates with androgen receptor (AR) activity in metastatic castrate-resistant PC. XMU-MP-1, an STK3/4 inhibitor, slowed cell proliferation, spheroid growth, and Matrigel invasion in multiple models. Genetic depletion of STK3 decreased proliferation in several PC cell lines. In a syngeneic allograft model, STK3 loss slowed tumor growth kinetics in vivo, and biochemical analysis suggests a mitotic growth arrest phenotype. To further probe the role of STK3 in PC, we identified and validated a new set of selective STK3 inhibitors, with enhanced kinase selectivity relative to XMU-MP-1, that inhibited tumor spheroid growth and invasion. Consistent with the canonical role, inhibition of STK3 induced cardiomyocyte growth and had chemoprotective effects. Our results indicate that STK3 has a non-canonical role in PC progression and that inhibition of STK3 may have a therapeutic potential for PC that merits further investigation.

NUAK family kinase 2 is a novel therapeutic target for prostate cancer.

Current advancements in prostate cancer (PC) therapies have been successful in slowing PC progression and increasing life expectancy; however, there is still no curative treatment for advanced metastatic castration resistant PC (mCRPC). Most treatment options target the androgen receptor, to which many PCs eventually develop resistance. Thus, there is a dire need to identify and validate new molecular targets for treating PC. We found NUAK family kinase 2 (NUAK2) expression is elevated in PC and mCRPC versus normal tissue, and expression correlates with an increased risk of metastasis. Given this observation and because NUAK2, as a kinase, is actionable, we evaluated the potential of NUAK2 as a molecular target for PC. NUAK2 is a stress response kinase that also plays a role in activation of the YAP cotranscriptional oncogene. Combining pharmacological and genetic methods for modulating NUAK2, we found that targeting NUAK2 in vitro leads to reduction in proliferation, three-dimensional tumor spheroid growth, and matrigel invasion of PC cells. Differential gene expression analysis of PC cells treated NUAK2 small molecule inhibitor HTH-02-006 demonstrated that NUAK2 inhibition results in downregulation of E2F, EMT, and MYC hallmark gene sets after NUAK2 inhibition. In a syngeneic allograft model and in radical prostatectomy patient derived explants, NUAK2 inhibition slowed tumor growth and proliferation rates. Mechanistically, HTH-02-006 treatment led to inactivation of YAP and the downregulation of NUAK2 and MYC protein levels. Our results suggest that NUAK2 represents a novel actionable molecular target for PC that warrants further exploration.