Androgen receptor signalling impairs docetaxel efficacy in castration-resistant prostate cancer.

Androgen receptor (AR) signalling drives neoplastic growth and therapy resistance in prostate cancer. Recent clinical data show that docetaxel combined with androgen deprivation therapy improves outcome in hormone-sensitive disease. We studied whether testosterone and AR signalling interferes with docetaxel treatment efficacy in castration-resistant prostate cancer (CRPC). We found that testosterone supplementation significantly impaired docetaxel tumour accumulation in a CRPC model, resulting in decreased tubulin stabilisation and antitumour activity. Furthermore, testosterone competed with docetaxel for uptake by the drug transporter OATP1B3. Irrespective of docetaxel-induced tubulin stabilisation, AR signalling by testosterone counteracted docetaxel efficacy. AR-pathway activation could also reverse long-term tumour regression by docetaxel treatment in vivo. These results indicate that to optimise docetaxel efficacy, androgen levels and AR signalling need to be suppressed. This study lends evidence for continued maximum suppression of AR signalling by combining targeted therapeutics with docetaxel in CRPC.

Tumor heterogeneity, aggressiveness, and immune cell composition in a novel syngeneic PSA-targeted Pten knockout mouse prostate cancer (MuCaP) model.

BACKGROUND: Prostate cancer is recognized as a heterogeneous disease demanding appropriate preclinical models that reflect tumor complexity. Previously, we established the PSA-Cre;PtenLoxP/LoxP genetic engineered mouse model (GEMM) for prostate cancer reflecting the various stages of tumor development. Prostate tumors in this Pten KO model slowly develop, requiring more than 10 months. In order to enhance its practical utility, we established a syngeneic panel of cell lines derived from PSA-Cre targeted Pten KO tumors, designated the mouse prostate cancer (MuCap) model. METHODS: Four different MuCaP epithelial cell lines were established from three independent primary Pten KO mouse prostate tumors. Tumorigenic capacity of the MuCaP cell lines was determined by subcutaneous inoculation of these cell lines in immunocompetent mice. Response to PI3K-targeted therapy was validated in ex vivo tissue slices of the established MuCaP tumors. RESULTS: The MuCaP cell lines were all tumorigenic in immunocompetent mice after subcutaneous inoculation. Interestingly, these syngrafted tumors represented different tumor growth rates and morphologies. Treatment with the specific PI3K inhibitor GDC0941 resulted in responses very similar between syngeneic MuCaP and primary Pten KO prostate tumors. Finally, immunoprofiling of the different syngeneic MuCaP tumors demonstrated differential numbers of tumor infiltrating lymphocytes and distinct immune gene profiles with expression of CD8, INFy, and PD1 being inversely related to tumor aggressiveness. CONCLUSIONS: Collectively, we present here a well-defined MuCaP platform of in vitro and in vivo mouse prostate cancer models that may support preclinical assessment of (immune)-therapies for prostate cancer.

Understanding taxanes in prostate cancer; importance of intratumoral drug accumulation.

BACKGROUND: Resistance to docetaxel is common in metastatic castration-resistant prostate cancer (mCRPC) and may be caused by sub-therapeutic intratumoral drug concentrations. Cabazitaxel demonstrated survival benefit in docetaxel-pretreated and docetaxel-refractory patients. In this study, we investigated whether the superior antitumor activity of cabazitaxel in mCRPC is explained by higher intratumoral cabazitaxel levels. Since recent studies suggest a reduced efficacy of docetaxel following treatment with novel androgen receptor (AR)-targeted agents, we also investigated taxane efficacy in an enzalutamide-resistant tumor model. METHODS: Intratumoral concentrations of docetaxel and cabazitaxel were correlated with antitumor activity in docetaxel-naïve, docetaxel-resistant, and enzalutamide-resistant patient-derived xenografts (PDXs) of prostate cancer. RESULTS: Intratumoral drug levels were negatively related to intrinsic and acquired resistance to docetaxel. Also, the observed stronger antitumor activity of cabazitaxel was associated with increased cumulative exposure and higher intratumoral of cabazitaxel concentrations in all PDXs. CONCLUSIONS: The superior antitumor activity of cabazitaxel in docetaxel- and enzalutamide-resistant tumors can be partly attributed to higher intratumoral drug concentrations. Especially for patients who are intrinsically resistant to docetaxel resulting from suboptimal intratumoral docetaxel concentrations, cabazitaxel may be the preferred chemotherapeutic agent. Prostate 76:927-936, 2016. © 2016 Wiley Periodicals, Inc.

Loss of SLCO1B3 drives taxane resistance in prostate cancer.

BACKGROUND: Both taxanes, docetaxel and cabazitaxel, are effective treatments for metastatic castration-resistant prostate cancer (mCRPC). However, resistance to taxanes is common. Our objective was to investigate mechanisms of taxane resistance in prostate cancer. METHODS: Two docetaxel-resistant patient-derived xenografts (PDXs) of CRPC were established (PC339-DOC and PC346C-DOC) in male athymic nude mice by frequent intraperitoneal administrations of docetaxel. Next-generation sequencing was performed on PDX tissue pre- and post-docetaxel resistance and gene expression profiles were compared. [(14)C]-docetaxel and [(14)C]-cabazitaxel uptake assays in vitro and cytotoxicity assays were performed to validate direct involvement of transporter genes in taxane sensitivity. RESULTS: Organic anion-transporting polypeptide (SLCO1B3), an influx transporter of docetaxel, was significantly downregulated in PC346C-DOC tumours. In accordance with this finding, intratumoural concentrations of docetaxel and cabazitaxel were significantly decreased in PC346C-DOC as compared with levels in chemotherapy-naive PC346C tumours. In addition, silencing of SLCO1B3 in chemo-naive PC346C resulted in a two-fold decrease in intracellular concentrations of both taxanes. Overexpression of SLCO1B3 showed higher sensitivity to docetaxel and cabazitaxel. CONCLUSIONS: The SLCO1B3 determines intracellular concentrations of docetaxel and cabazitaxel and consequently influences taxane efficacy. Loss of the drug transporter SLCO1B3 may drive taxane resistance in prostate cancer.

No Evidence for the Involvement of Leiomodin-1 Antibodies in the Pathogenesis of Onchocerciasis-Associated Epilepsy.

Nodding syndrome has been suggested to be triggered by neurotoxic leiomodin-1 auto-antibodies cross-reacting with Onchocerca volvulus. Here, we screened serum and CSF samples of persons with nodding syndrome and other forms of onchocerciasis-associated epilepsy (OAE) and African and European controls for leiomodin-1 antibodies by a cell-based assay (CBA) and Western blot (WB). These samples were also investigated for the presence of auto-antibodies cross-reacting with rat brain tissue by immunohistochemistry (IHC). Additionally, IHC was used to detect the leiomodin-1 protein in post-mortem brain samples of persons with OAE who died. Leiomodin-1 antibodies were detected by CBA in 6/52 (12%) and by WB in 23/54 (43%) persons with OAE compared to in 14/61 (23%) (p = 0.113) and 23/54 (43%) (p = 0.479) of controls without epilepsy. Multivariable exact logistic regression did not show an association between O. volvulus infection or epilepsy status and the presence of leiomodin-1. Leiomodin-1 antibodies were not detected in 12 CSF samples from persons with OAE or in 16 CSF samples from persons with acute-onset neurological conditions, as well as not being detected in serum from European controls. Moreover, the leiomodin-1 protein was only detected in capillary walls in post-mortem brain tissues and not in brain cells. IHC on rat brain slides with serum samples from persons with OAE or controls from persons with or without O. volvulus infection revealed no specific staining pattern. In conclusion, our data do not support OAE to be an autoimmune disorder caused by leiomodin-1 antibodies.

High Efficacy of Combination Therapy Using PI3K/AKT Inhibitors with Androgen Deprivation in Prostate Cancer Preclinical Models.

BACKGROUND: The phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K)/AKT pathway is frequently activated during prostate cancer (PCa) progression through loss or mutation of the phosphatase and tensin homolog (PTEN) gene. Following the androgen receptor (AR) pathway, it is the second major driver of PCa growth. OBJECTIVE: To assess efficacy of novel PI3K/AKT-targeted therapies in PCa models, as a single agent and in combination with androgen deprivation. DESIGN, SETTING, AND PARTICIPANTS: Twelve human PCa cell lines were tested in vitro for sensitivity to the AKT inhibitor AZD5363 and the PI3K beta/delta inhibitor AZD8186. The combination of AZD5363 and AZD8186 with castration was evaluated in vivo in PTEN-negative versus PTEN-positive patient-derived xenografts. Tumors and plasma were collected for biomarker analysis. OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS: In vitro growth inhibition was determined by methylthiazolyldiphenyl-tetrazolium bromide assay. In vivo efficacy was monitored by caliper measurements of subcutaneous tumor volume. PI3K/AKT and AR pathway activity was analyzed by Western blot, enzyme-linked immunosorbent assay, and real-time polymerase chain reaction. RESULTS AND LIMITATIONS: AZD5363 and AZD8186 inhibited in vitro growth of 10 of 12 and 7 of 12 PCa cell lines, respectively, with increased sensitivity under androgen depletion. In vivo, AZD5363 and AZD8186 as single agents significantly inhibited growth of PTEN-negative PC346C xenografts compared to placebo by 60% and 66%, respectively. Importantly, combination of either agent with castration resulted in long-lasting tumor regression, which persisted after treatment cessation. Expression of AR-target genes kallikrein-related peptidase 3 (KLK3, also known as PSA); transmembrane protease, serine 2 (TMPRSS2); and FK506 binding protein 5 (FKBP5) was upregulated after PI3K/AKT inhibition. Neither compound inhibited tumor growth in the PTEN-positive PC310 model. CONCLUSIONS: Combination with hormonal therapy improved efficacy of PI3K/AKT-targeted agents in PTEN-negative PCa models. Upregulation of AR-target genes upon PI3K/AKT inhibition suggests a compensatory crosstalk between the PI3K-AR pathways. These data strongly advocate for further clinical evaluation. PATIENT SUMMARY: Inactivation of the PTEN gene is a common event promoting prostate cancer (PCa) progression. This preclinical study illustrates the potent anticancer activity of novel PTEN-targeted drugs on PCa models, particularly in combination with hormonal therapy.