Aberrant estrogen receptor (ERα) signaling mediates detrimental effects of tamoxifen including drug resistance and endometrial hyperplasia. ERα36, an alternative isoform of ERα, contributes to these effects. We have demonstrated that CK2 modulates ERα expression and function in breast cancer (BCa). Here, we assess if CX-4945 (CX), a clinical stage CK2 inhibitor, can disrupt ERα66 and ERα36 signaling in BCa. Using live cell imaging, we assessed the antiproliferative effects of CX in tamoxifen-sensitive and tamoxifen-resistant BCa cells in monolayer and/or spheroid cultures. CX-induced alterations in ERα66 and ERα36 mRNA and protein expression were assessed by RT-PCR and immunoblot. Co-immunoprecipitation was performed to determine the differential interaction of ERα isoforms with HSP90 and CK2 upon CX exposure. CX caused concentration-dependent decreases in proliferation in tamoxifen-sensitive MCF-7 and tamoxifen-resistant MCF-7 Tam1 cells and significantly repressed spheroid growth in 3D models. Additionally, CX caused dramatic decreases in endogenous or exogenously expressed ERα66 and ERα36 protein. Silencing of CK2β, the regulatory subunit of CK2, resulted in destabilization and decreased proliferation, similar to CX. Co-immunoprecipitation demonstrated that ERα66/36 show CK2 dependance for interaction with molecular chaperone HSP90. Our findings show that CK2 functions regulate the protein stability of ERα66 and ERα36 through a mechanism that is dependent on CK2β subunit and HSP90 chaperone function. CX may be a component of a novel therapeutic strategy that targets both tamoxifen-sensitive and tamoxifen-resistant BCa, providing an additional tool to treat ERα-positive BCa.

Background: The outgrowth of castration-resistant prostate cancer (CRPC) dictates patient morbidity and mortality. Recurrence of prostate cancer (PC) following androgen-deprivation therapy (ADT) often occurs due to constitutively active androgen receptor (AR) splice variants (AR-Vs), primarily AR-V7. Therefore, safe and effective therapies enabling the suppression of both full-length AR (AR-FL) and AR-Vs are urgently needed. The natural compound dimethyl sulfoxide (DMSO) has negligible cytotoxicity at concentrations below 5% and has anticancer potential. DMSO has been broadly used in biomedical research as a solvent for pharmaceuticals, as a cryoprotectant for cells, and as a topical treatment to suppress pain and inflammation. We investigated the effect of low-dose DMSO on AR expression, cell viability, and metastatic ability in PC cell lines expressing both AR-FL and AR-V7 (e.g., 22Rv1) and those expressing only AR-FL (e.g., C4-2B). Methods: MTT cell viability assays were performed to measure DMSO-induced cytotoxicity. Wound-healing assays were conducted to monitor the effect of DMSO on the migratory phenotype of cancer cells. Western blot analyses were performed to study the efficacy of DMSO in suppressing the protein levels of AR-FL and AR-V7, and expression of heterogeneous nuclear ribonucleoprotein H1 (hnRNPH1) was measured as a possible mechanism. Results: At concentrations of 0.1–1% (v/v), DMSO treatment showed minimal cytotoxicity, whereas the highest concentration used (2.5%) showed approximately 20% cytotoxicity at 96 h. Interestingly, however, DMSO treatment at concentrations of 1.0 and 2.5% significantly inhibited the migration of PC cells. Treatment with DMSO led to a dose-dependent inhibition of both AR-FL and AR-V7. Notably, in 22Rv1 cells, DMSO potently downregulated the expression of hnRNPH1, a splicing factor often associated with AR expression and signaling. Conclusions: Our findings suggest that low concentrations of DMSO may have potential as an effective anticancer agent, both at the initial and later stages when PC cells become castration resistant.