Risk of hormone escape in a human prostate cancer model depends on therapy modalities and can be reduced by tyrosine kinase inhibitors

Monitoring PSMA Responses to ADT in Prostate Cancer Patient-Derived Xenograft Mouse Models Using [18F]DCFPyL PET Imaging

PURPOSE

PSMA overexpression has been associated with aggressive prostate cancer (PCa). However, PSMA PET imaging has revealed highly variable changes in PSMA expression in response to ADT treatment ranging from increases to moderate decreases. To better understand these PSMA responses and potential relationship to progressive PCa, the PET imaging agent, [¹⁸F]DCFPyL, was used to assess changes in PSMA expression in response to ADT using genomically characterized LuCaP patient-derived xenograft mouse models (LuCaP-PDXs) which were found to be sensitive to ADT (LuCaP73 and LuCaP136;CS) or resistant (LuCaP167;CR).

METHODS

[¹⁸F]DCFPyL (2-(3-{1-carboxy-5-[(6-[¹⁸F]fluoro-pyridine-3-carbonyl)-amino]-pentyl}-ureido)-pentanedioic acid) was used to assess PSMA in vitro (saturation assays) in LuCaP tumor membrane homogenates and in vivo (imaging/biodistribution) in LuCaP-PDXs. Control and ADT-treated LuCaPs were imaged before ADT (0 days) and 2-, 7-, 14-, and 21-days post-ADT from which tumor:muscle ratios (T:Ms) were determined and concurrently tumor volumes were measured (caliper). After the 21-day imaging, biodistributions and histologic/genomic (PSMA, AR) analysis were done.

RESULTS

[¹⁸F]DCFPyL exhibited high affinity for PSMA and distinguished different levels of PSMA in LuCaP tumors. Post-ADT CS LuCaP73 and LuCaP136 tumor volumes significantly decreased at day 7 or 14 respectively vs controls, whereas the CR LuCaP167 tumor volumes were minimally changed. [¹⁸F]DCFPyL imaging T:Ms were increased 3-5-fold in treated LuCaP73 tumors vs controls, while treated LuCaP136 T:Ms remained unchanged which was confirmed by day 21 biodistribution results. For treated LuCaP167, T:Ms were decreased (~ 45 %) vs controls but due to low T:M values (<2) may not be indicative of PSMA level changes. LuCaP73 tumor PSMA histologic/genomic results were comparable to imaging/biodistribution results, whereas the results for other tumor types varied.

CONCLUSION

Tumor responses to ADT varied from sensitive to resistant among these LuCaP PDXs, while only the high PSMA expressing LuCaP model exhibited an increase in PSMA levels in response to ADT. These models may be useful in understanding the clinical relevance of PSMA PET responses to ADT and potentially the relationship to disease progression as it may relate to the genomic signature.

ErbB-2 signaling in advanced prostate cancer progression and potential therapy

Currently, prostate cancer (PCa) remains the most commonly diagnosed solid tumor and the second leading cause of cancer-related deaths in US men. Most of these deaths are attributed to the development of castration-resistant (CR) PCa. ErbB-2 and ErbB family members have been demonstrated to contribute to the progression of this lethal disease. In this review, we focus on updating the role of ErbB-2 in advanced PCa progression and its regulation, including its regulation via ligand activation, miRNAs and protein phosphorylation. We also discuss its downstream signaling pathways, including AKT, ERK1/2 and STATs, involved in advanced PCa progression. Additionally, we evaluate the potential of ErbB-2, focusing on its protein hyper-phosphorylation status, as a biomarker for aggressive PCa as well as the effectiveness of ErbB-2 as a target for the treatment of CR PCa via a multitude of approaches, including orally available inhibitors, intratumoral expression of cPAcP, vaccination and immunotherapy.

Discovery of LHRH and development of LHRH analogs for prostate cancer treatment

The discovery, isolation, elucidation of structure, synthesis, and initial testing of the neuropeptide hypothalamic luteinizing hormone-releasing hormone (LHRH), which regulates reproduction, is briefly described. The design, synthesis, and experimental and clinical testing of agonistic analogs of LHRH is extensively reviewed focusing on the development of new methods for the treatment of prostate cancer. Subsequent development of antagonistic analogs of LHRH is then faithfully recounted with special emphasis on therapy of prostate cancer and BPH. The concepts of targeted therapy to peptide receptors on tumors are re-examined and the development of the cytotoxic analogs of LHRH and their status is reviewed. The endeavor to develop better therapies for prostate cancer, based on LHRH analogs, guided much of our work.

ErbB2 Signaling Increases Androgen Receptor Expression in Abiraterone-Resistant Prostate Cancer

PURPOSE

ErbB2 signaling appears to be increased and may enhance androgen receptor (AR) activity in a subset of patients with castration-resistant prostate cancer (CRPC), but agents targeting ErbB2 have not been effective. This study was undertaken to assess ErbB2 activity in abiraterone-resistant prostate cancer and to determine whether it may contribute to AR signaling in these tumors.

EXPERIMENTAL DESIGN

AR activity and ErbB2 signaling were examined in the radical prostatectomy specimens from a neoadjuvant clinical trial of leuprolide plus abiraterone and in the specimens from abiraterone-resistant CRPC xenograft models. The effect of ErbB2 signaling on AR activity was determined in two CRPC cell lines. Moreover, the effect of combination treatment with abiraterone and an ErbB2 inhibitor was assessed in a CRPC xenograft model.

RESULTS

We found that ErbB2 signaling was elevated in residual tumor following abiraterone treatment in a subset of patients and was associated with higher nuclear AR expression. In xenograft models, we similarly demonstrated that ErbB2 signaling was increased and associated with AR reactivation in abiraterone-resistant tumors. Mechanistically, we show that ErbB2 signaling and subsequent activation of the PI3K/AKT signaling stabilizes AR protein. Furthermore, concomitantly treating CRPC cells with abiraterone and an ErbB2 inhibitor, lapatinib, blocked AR reactivation and suppressed tumor progression.

CONCLUSIONS

ErbB2 signaling is elevated in a subset of patients with abiraterone-resistant prostate cancer and stabilizes AR protein. Combination therapy with abiraterone and ErbB2 antagonists may be effective for treating the subset of CRPC with elevated ErbB2 activity. Clin Cancer Res; 22(14); 3672-82. ©2016 AACR.

ErbB-2 signaling plays a critical role in regulating androgen-sensitive and castration-resistant androgen receptor-positive prostate cancer cells

While androgen deprivation therapy (ADT) reduces tumor burden, autocrine growth factor loops such as human epidermal growth factor receptor 2 (HER2/ErbB-2/neu) have been proposed to contribute to prostate cancer (PCa) survival and relapse. However, the role of ErbB-2 in regulating androgen-sensitive (AS) and castration-resistant (CR) cell proliferation remains unclear. Here, we determined the role of ErbB-2 in PCa progression and survival under steroid-reduced conditions using two independent PCa cell progression models. In AR-positive androgen-independent (AI) PCa cells that exhibit the CR phenotype, ErbB-2 was constitutively activated, compared to corresponding AS PCa cells. In AS LNCaP C-33 cells, androgen-induced ErbB-2 activation through ERK1/2 mediates PCa cell proliferation. Further, the ErbB-2-specific but not EGFR-specific inhibitor suppresses basal and androgen-stimulated cell proliferation and also blocks ERK1/2 activation. ErbB-2 ectopic expression and cPAcP siRNA transfection of LNCaP C-33 cells each increases ErbB-2 tyrosine phosphorylation, correlating with increased AI PSA secretion and cell proliferation. Conversely, trapping ErbB-2 by transfected endoplasmic reticulum-targeting ScFv5R expression vector abolished DHT-induced LNCaP C-33 cell growth. Moreover, inhibition of ErbB-2 but not EGFR in AI LNCaP C-81 and MDA PCa2b-AI PCa cells significantly abolished AI cell growth. In contrast to androgens via ErbB-2/ERK1/2 signaling in AS PCa cells, the inhibition of ErbB-2 abrogated AI cell proliferation by inhibiting the cell survival protein Akt in those AI cells. These results suggest that ErbB-2 is a prominent player in mediating the ligand-dependent and -independent activation of AR in AS and AI/CR PCa cells respectively for PCa progression and survival.

[Pertuzumab and solid tumors: perspectives]

Over the past decade, trastuzumab was the only available monoclonal anti-HER2 antibody for the treatment of HER2 positive breast and gastric cancer. Recently, pertuzumab added to docetaxel and trastuzumab showed dramatic overall survival improvement in first line treatment of HER2 positive metastatic breast cancer. Pertuzumab is the first approved monoclonal antibody in a new class of drugs called dimerization inhibitors. This agent was also approved in association with trastuzumab for neoadjuvant HER2-positive breast cancer treatment. However, pertuzumab development was not confined to breast cancer and in the present review, we will focus on biological rational, preclinical data and clinical trial results of pertuzumab in solid tumors excluding breast cancer.

Enhanced anticancer activity of a combination of docetaxel and Aneustat (OMN54) in a patient-derived, advanced prostate cancer tissue xenograft model

The current first‐line treatment for advanced metastatic prostate cancer, i.e. docetaxel‐based therapy, is only marginally effective. The aim of the present study was to determine whether such therapy can be improved by combining docetaxel with Aneustat (OMN54), a multivalent botanical drug candidate shown to have anti‐prostate cancer activity in preliminary in vitro experiments, which is currently undergoing a Phase‐I Clinical Trial. Human metastatic, androgen‐independent C4‐2 prostate cancer cells and NOD‐SCID mice bearing PTEN‐deficient, metastatic and PSA‐secreting, patient‐derived subrenal capsule LTL‐313H prostate cancer tissue xenografts were treated with docetaxel and Aneustat, alone and in combination. In vitro, Aneustat markedly inhibited C4‐2 cell replication in a dose‐dependent manner. When Aneustat was combined with docetaxel, the growth inhibitions of the drugs were essentially additive. In vivo, however, the combination of docetaxel and Aneustat enhanced anti‐tumor activity synergistically and very markedly, without inducing major host toxicity. Complete growth inhibition and shrinkage of the xenografts could be obtained with the combined drugs as distinct from the drugs on their own. Analysis of the gene expression of the xenografts using microarray indicated that docetaxel + Aneustat led to expanded anticancer activity, in particular to targeting of cancer hallmarks that were not affected by the single drugs. Our findings, obtained with a highly clinically relevant prostate cancer model, suggest, for the first time, that docetaxel‐based therapy of advanced human prostate cancer may be improved by combining docetaxel with Aneustat.

First‐line, docetaxel‐based therapy of advanced prostate cancer is only marginally effective.

The efficacy of docetaxel combined with Aneustat was determined in a metastatic xenograft model.

Anti‐tumor activity was synergistically and markedly enhanced without major host toxicity.

Gene expression analysis indicated docetaxel + Aneustat led to expanded anticancer activity.

Docetaxel‐based therapy of advanced prostate cancer may be improved by combining docetaxel with Aneustat.

Effect of androgen blockade on HER-2 and matrix metalloproteinase-2 expression on bone marrow micrometastasis and stromal cells in men with prostate cancer

INTRODUCTION

HER-2 has been associated with castrate resistant prostate cancer and matrix metalloproteinase-2 (MMP-2) in the dissemination and invasion of tumor cells as well as activating angiogenesis. We present an immunocytochemical study of the effect of androgen blockade on the expression of HER-2 and MMP-2 in bone marrow micrometastasis and the surrounding stromal cells in men with prostate cancer.

METHODS AND PATIENTS

A cross-sectional study of men with prostate cancer. Touch preps were obtained from bone marrow biopsies of men with prostate cancer, before and after radical prostatectomy and during androgen blockade. Micrometastasis detected with anti-PSA immunocytochemistry underwent processing with anti-HER-2 and anti-MMP-2 immunocytochemistry. Patients were defined as HER-2 positive or negative, MMP-2 negative or an MMP-2 pattern described as border or central and stromal MMP-2 defined as positive or negative. The expression of the biomarkers was compared before and after primary treatment and during androgen blockade in relation to the serum PSA at the time of sampling and duration of androgen blockade.

RESULTS

191 men participated, 35 men before surgery and 43 after surgery; there were no significant differences in HER-2 expression between groups, there was no MMP-2 expression centrally or stromal expression of MMP-2. In men with androgen blockade, HER-2 expression was significantly higher; there was a trend for increasing HER-2 expression up to 5 years; central MMP-2 expression significantly increased after 3 years, while stromal MMP-2 significantly increased after 6 years. MMP-2 expression both in micrometastasis and stroma was significantly associated with HER-2 expression. Expression of MMP-2 at the border of the micrometastasis was not associated with HER-2 expression and occurred in the absence of androgen blockade.

CONCLUSIONS

Androgen blockade decreases serum PSA by eliminating HER-2 negative prostate cancer cells. However, there is early selection of HER-2 positive cancer cells which leads to androgen independence and to increased expression of MMP-2 activity in the micrometastasis. The increased MMP-2 activity in the micrometastasis increases the expression of MMP-2 in the surrounding stromal cells and thus could promote angiogenesis and tumor growth resulting in macrometastatic androgen independent disease.

Constitutively active androgen receptor variants upregulate expression of mesenchymal markers in prostate cancer cells

Androgen receptor (AR) signaling pathway remains the foremost target of novel therapeutics for castration-resistant prostate cancer (CRPC). However, the expression of constitutively active AR variants lacking the carboxy-terminal region in CRPC may lead to therapy inefficacy. These AR variants are supposed to support PCa cell growth in an androgen-depleted environment, but their mode of action still remains unresolved. Moreover, recent studies indicate that constitutively active AR variants are expressed in primary prostate tumors and may contribute to tumor progression. The aim of this study was to investigate the impact of constitutively active AR variants on the expression of tumor progression markers. N-cadherin expression was analyzed in LNCaP cells overexpressing the wild type AR or a constitutively active AR variant by qRT-PCR, Western blot and immunofluorescence. We showed here for the first time that N-cadherin expression was increased in the presence of constitutively active AR variants. These results were confirmed in C4-2B cells overexpressing these AR variants. Although N-cadherin expression is often associated with a downregulation of E-cadherin, this phenomenon was not observed in our model. Nevertheless, in addition to the increased expression of N-cadherin, an upregulation of other mesenchymal markers expression such as VIMENTIN, SNAIL and ZEB1 was observed in the presence of constitutively active variants. In conclusion, our findings highlight novel consequences of constitutively active AR variants on the regulation of mesenchymal markers in prostate cancer.

An update on the use of degarelix in the treatment of advanced hormone-dependent prostate cancer

Androgen deprivation therapy remains the mainstay of medical treatment for advanced prostate cancer. Commonly, this is achieved with medical androgen deprivation rather than surgical intervention as the permanence and psychological effects of the latter are unacceptable for most patients. Degarelix is a third generation antagonist of luteinizing hormone-releasing hormone (LHRH, also termed gonadotropin-releasing hormone) for the first-line treatment of androgen-dependent advanced prostate cancer. Degarelix acts directly on the pituitary receptors for LHRH, blocking the action of endogenous LHRH. The use of degarelix eliminates the initial undesirable surge in gonadotropin and testosterone levels, which is produced by agonists of LHRH. Degarelix is the most comprehensively studied and widely available LHRH antagonist worldwide. Clinical trials have demonstrated that degarelix has a long-term efficacy similar to the LHRH agonist leuprolide in achieving testosterone suppression in patients with prostate cancer. Degarelix, however, produces a faster suppression of testosterone and prostate-specific antigen (PSA), with no testosterone surges or microsurges, and thus prevents the risk of clinical flare in advanced disease. Recent clinical trials demonstrated that treatment with degarelix results in improved disease control when compared with an LHRH agonist in terms of superior PSA progression-free survival, suggesting that degarelix likely delays progression to castration-resistant disease and has a more significant impact on bone serum alkaline phosphatase and follicle-stimulating hormone. Degarelix is usually well tolerated, with limited toxicity and no evidence of systemic allergic reactions in clinical studies. Degarelix thus represents an important addition to the hormonal armamentarium for therapy of advanced androgen-dependent prostate cancer.