Androgens modify therapeutic response to cabazitaxel in models of advanced prostate cancer.

BACKGROUND: Disruption of the phenotypic landscape via epithelial-mesenchymal transition (EMT) enables prostate cancer cells to metastasize and acquire therapeutic resistance. Our previous studies demonstrated that cabazitaxel (CBZ) (second-generation Food and Drug Administration-approved taxane chemotherapy), used for the treatment of castration-resistant prostate cancer (CRPC), causes reversal of EMT to mesenchymal-epithelial transition (MET) and reduces expression of kinesin motor protein KIFC1 (HSET). The present study examined the effect of sequencing CBZ chemotherapy mediated MET on prostate tumor redifferentiation overcoming therapeutic resistance in models of advanced prostate cancer. METHODS: To examine the impact of androgens on the antitumor effect of CBZ, we used human prostate cancer cell lines with different sensitivity to androgens and CBZ, in vitro, and two human prostate cancer xenograft models in vivo. Tumor-bearing male mice (with either the androgen-sensitive LNCaP or the CRPC 22Rv1 xenografts) were treated with CBZ (3 mg/kg) alone, or in combination with castration-induced androgen-deprivation therapy (ADT) for 14 days. RESULTS: Cell viability assays indicate that the presence of 5α-dihydrotestosterone (1 nM) confers resistance to CBZ in vitro. CBZ treatment in vivo induced MET in LNCaP-derived tumors as shown by increased E-cadherin and decreased N-cadherin levels. Sequencing CBZ after ADT improves tumor response in androgen-sensitive LNCaP, but not in CRPC 22Rv1 xenografts. Mechanistic dissection revealed a novel association between the androgen receptor and HSET in prostate cancer cells that is inhibited by CBZ in an androgen-dependent manner. CONCLUSIONS: Our findings provide new insights into the phenotypic reprogramming of prostate cancer cells to resensitize tumors to CBZ action. This evidence is of translational significance in treatment sequencing (CBZ and ADT) towards improved therapeutic benefit in patients with lethal CRPC.

TGF-ß receptor I inhibitor enhances response to enzalutamide in a pre-clinical model of advanced prostate cancer.

BACKGROUND: Prostate cancer progression is navigated by the androgen receptor (AR) and transforming-growth factor-ß (TGF-ß) signaling. We previously demonstrated that aberrant TGF-ß signaling accelerates prostate tumor progression in a transgenic mouse model of prostate cancer via effects on epithelial-mesenchymal transition (EMT), driving castration-resistant prostate cancer (CRPC). METHODS: This study examined the antitumor effect of the combination of TGF-ß receptor I (TßRI) inhibitor, galunisertib, and FDA-approved antiandrogen enzalutamide, in our pre-clinical model. Age-matched genotypically characterized DNTGFßRII male mice were treated with either galunisertib and enzalutamide, in combination or as single agents in three "mini"-trials and the effects on tumor growth, phenotypic EMT, and actin cytoskeleton were evaluated. RESULTS: Galunisertib in combination with enzalutamide significantly suppressed prostate tumor growth, by increasing apoptosis and decreasing cell proliferation of tumor cell populations compared to the inhibitor as a monotherapy (P < 0.05). The combination treatment dramatically reduced cofilin levels, actin cytoskeleton regulator, compared to single agents. Treatment with galunisertib targeted nuclear Smad4 protein (intracellular TGF-ß effector), but had no effect on nuclear AR. Consequential to TGF-ß inhibition there was an EMT reversion to mesenchymal-epithelial transition (MET) and re-differentiation of prostate tumors. Elevated intratumoral TGF-ß1 ligand, in response to galunisertib, was blocked by enzalutamide. CONCLUSION: Our results provide novel insights into the therapeutic value of targeting TGF-ß signaling to overcome resistance to enzalutamide in prostate cancer by phenotypic reprogramming of EMT towards tumor re-differentiation and cytoskeleton remodeling. This translational work is significant in sequencing TGF-ß blockade and antiandrogens to optimize therapeutic response in CRPC.

Cell death under epithelial-mesenchymal transition control in prostate cancer therapeutic response.

Prostate cancer is a widespread problem among men, with >160 000 new cases in 2017 alone. Androgen deprivation therapy is commonly used in prostate cancer treatment to block androgens required for cancer growth, but disease relapse after androgen deprivation therapy is both common and severe. Changes in androgen receptor signaling from androgen deprivation therapy have been linked to therapeutic resistance and tumor progression. Resistant cells can become reprogrammed to undergo epithelial-mesenchymal transition, a phenotypic switch from benign, epithelial cells to a mobile cell with mesenchymal traits. In these cells, attachment to their epithelial cell layer is no longer required for survival. Anoikis is a form of cell death that occurs when detachment from other cells and the basement membrane occurs. Epithelial cells have been shown to undergo epithelial-mesenchymal transition, avoid anoikis induction and progress to a metastatic phenotype. In prostate cancer progression to advanced disease, epithelial-mesenchymal transition induction (characterized by loss of epithelial cellular attachment protein E-cadherin) correlates with a higher Gleason score, tumor progression, increased metastasis and higher biochemical recurrence. The concept of interfacing epithelial-mesenchymal transition with anoikis in the tumor microenvironment landscape will be discussed here, with focus on the significance of the functional exchange between the two processes in therapeutic targeting of advanced disease. The current evidence on the impact of loss of cell-cell contact, acquisition of chemoresistance, immune escape and metastatic spread in advanced tumors in response to transforming growth factor-ß on prostate cancer metastasis will be also discussed. The signaling cross-talk between transforming growth factor-ß and androgen receptor signaling will be interrogated as a new therapeutic platform for the development of combination strategies to impair prostate cancer metastasis.

Kinesin Facilitates Phenotypic Targeting of Therapeutic Resistance in Advanced Prostate Cancer.

Understanding the mechanisms underlying resistance is critical to improving therapeutic outcomes in patients with metastatic castration-resistant prostate cancer (mCRPC). Previous work showed dynamic interconversions between epithelial-mesenchymal transition (EMT) to mesenchymal-epithelial transition (MET) defines the phenotypic landscape of prostate tumors, as a potential driver of emergence of therapeutic resistance. In this study, we use in vitro and in vivo preclinical MDA PCa PDX models of resistant human prostate cancer to determine molecular mechanisms of cross-resistance between anti-androgen therapy and taxane chemotherapy, underlying the therapeutically resistant phenotype. Transcriptomic profiling revealed that resistant and sensitive prostate cancer C4-2B cells have a unique differential gene signature response to cabazitaxel. Gene pathway analysis showed that sensitive cells exhibit increase in DNA damage, while resistant cells express genes associated with protein regulation in response to cabazitaxel. These PDX specimens are from patients who have metastatic lethal CRPC, treated with androgen-deprivation therapy (ADT), antiandrogens and chemotherapy including 2nd line taxane chemotherapy, cabazitaxel. Immunohistochemistry revealed high expression of E-cadherin and low expression of vimentin resulting in re-differentiation toward an epithelial phenotype. Furthermore, the mitotic kinesin-related protein (HSET) involved in microtubule binding and the SLCO1B3 transporter (implicated in cabazitaxel intracellular transport), associated with resistance in these prostate tumors. Combinational targeting of kinesins (ispinesib) with cabazitaxel was more effective than single monotherapies in inducing cell death in resistant prostate tumors. Implications: Our findings are of translational significance in identifying kinesin as a novel target of cross-resistance, towards enhancing therapeutic vulnerability and improved clinical outcomes in patients with advanced prostate cancer.

Aberrant TGF-ß Signaling Drives Castration-Resistant Prostate Cancer in a Male Mouse Model of Prostate Tumorigenesis.

The androgen receptor (AR) plays a critical role as a driver of castration-resistant prostate cancer (CRPC). Our previous studies demonstrated that disruption of transforming growth factor-ß (TGF-ß) signaling via introduction of dominant-negative transforming growth factor-ß type II receptor (DNTGFßRII) in the prostate epithelium of transgenic adenocarcinoma of the prostate mice accelerated tumor. This study investigated the consequences of disrupted TGF-ß signaling on prostate tumor growth under conditions of castration-induced androgen deprivation in the preclinical model of DNTGFßRII. Our results indicate that in response to androgen deprivation therapy (ADT) the proliferative index in prostate tumors from DNTGFßRII mice was higher compared with prostate tumors from TGFßRII wild-type (WT) mice, whereas there was a reduced incidence of apoptosis in tumors from DNTGFßRII. Protein and gene expression profiling revealed that tumors from DNTGFßRII mice exhibit a strong nuclear AR localization among the prostate tumor epithelial cells and increased AR messenger RNA after ADT. In contrast, TGFßRII WT mice exhibited a marked loss in nuclear AR in prostate tumor acini (20 weeks), followed by a downregulation of AR and transmembrane protease serine 2 messenger RNA. There was a significant increase in nuclear AR and activity in prostate tumors from castrate DNTGFßRII compared with TGFßRII WT mice. Consequential to aberrant TGF-ß signaling, ADT enhanced expression and nuclear localization of Smad4 and ß-catenin. Our findings support that under castrate conditions, aberrant TGF-ß signaling leads to AR activation and ß-catenin nuclear localization, an adaptation mechanism contributing to emergence of CRPC. The work defines a potentially significant new targeting platform for overcoming therapeutic resistance in CRPC.