Benjamin A. Mooso

Dual EGFR/HER2 Inhibition Sensitizes Prostate Cancer Cells to Androgen Withdrawal by Suppressing ErbB3

Purpose: Patients with recurrent prostate cancer are commonly treated with androgen withdrawal therapy (AWT); however, almost all patients eventually progress to castration resistant prostate cancer (CRPC), indicating failure of AWT to eliminate androgen-sensitive prostate cancer. The overall goal of these studies is to determine whether dual inhibition of the receptor tyrosine kinases epidermal growth factor receptor (EGFR) and HER2 would prolong the effectiveness of this treatment in prostate cancer. Experimental Design: We used androgen-dependent LNCaP cells and its CRPC sublines LNCaP-AI and C4-2. Additional data were collected in pRNS-1-1 cells stably expressing a mutant androgen receptor (AR-T877A), and in nude mice harboring CWR22 tumors. Studies utilized EGFR inhibitors erlotinib and AG1478, and HER2 inhibitors trastuzumab and AG879. Results: Dual EGFR/HER2 inhibition induced apoptosis selectively in androgen-sensitive prostate cancer cells undergoing AWT, but not in the presence of androgens, or in CRPC cells. We show that AWT alone failed to induce significant apoptosis in androgen-dependent cells, due to AWT-induced increase in HER2 and ErbB3, which promoted survival by increasing Akt phosphorylation. AWT-induced ErbB3 stabilized the AR and stimulated PSA, while it was inactivated only by inhibition of both its dimerization partners EGFR and HER2 (prostate cancer cells do not express ErbB4); but not the inhibition of any one receptor alone, explaining the success of dual EGFR/HER2 inhibition in sensitizing androgen-dependent cells to AWT. The effectiveness of the inhibitors in suppressing growth correlated with its ability to prevent Akt phosphorylation. Conclusion: These studies indicate that dual EGFR/HER2 inhibition, administered together with AWT, sensitize prostate cancer cells to apoptosis during AWT. Clin Cancer Res; 17(19); 6218–28. ©2011 AACR.

Nrdp1-mediated regulation of ErbB3 expression by the androgen receptor in androgen-dependent but not castrate-resistant prostate cancer cells.

Patients with advanced prostate cancer (PCa) are initially susceptible to androgen withdrawal (AW), but ultimately develop resistance to this therapy (castration-resistant PCa, CRPC). Here, we show that AW can promote CRPC development by increasing the levels of the receptor tyrosine kinase ErbB3 in androgen-dependent PCa, resulting in AW-resistant cell cycle progression and increased androgen receptor (AR) transcriptional activity. CRPC cell lines and human PCa tissue overexpressed ErbB3, whereas downregulation of ErbB3 prevented CRPC cell growth. Investigation of the mechanism by which AW augments ErbB3, using normal prostate-derived pRNS-1-1 cells, and androgen-dependent PCa lines LNCaP, PC346C, and CWR22 mouse xenografts, revealed that the AR suppresses ErbB3 protein levels, whereas AW relieves this suppression, showing for the first time the negative regulation of ErbB3 by AR. We show that AR activation promotes ErbB3 degradation in androgen-dependent cells, and that this effect is mediated by AR-dependent transcriptional upregulation of neuregulin receptor degradation protein-1 (Nrdp1), an E3 ubiquitin ligase that targets ErbB3 for degradation but whose role in PCa has not been previously examined. Therefore, AW decreases Nrdp1 expression, promoting ErbB3 protein accumulation, and leading to AR-independent proliferation. However, in CRPC sublines of LNCaP and CWR22, which strongly overexpress the AR, ErbB3 levels remain elevated due to constitutive suppression of Nrdp1, which prevents AR regulation of Nrdp1. Our observations point to a model of CRPC development in which progression of PCa to castration resistance is associated with the inability of AR to transcriptionally regulate Nrdp1, and predict that inhibition of ErbB3 during AW may impair CRPC development.

The Role of EGFR Family Inhibitors in Muscle Invasive Bladder Cancer: A Review of Clinical Data and Molecular Evidence

PURPOSE Conventional platinum based chemotherapy for advanced urothelial carcinoma is plagued by common resistance to this regimen. Several studies implicate the EGFR family of RTKs in urothelial carcinoma progression and chemoresistance. Many groups have investigated the effects of inhibitors of this family in patients with urothelial carcinoma. This review focuses on the underlying molecular pathways that lead to urothelial carcinoma resistance to EGFR family inhibitors. MATERIALS AND METHODS We performed a PubMed® search for peer reviewed literature on bladder cancer development, EGFR family expression, clinical trials of EGFR family inhibitors and molecular bypass pathways. Research articles deemed to be relevant were examined and a summary of original data was created. Meta-analysis of expression profiles was also performed for each EGFR family member based on data sets accessible via Oncomine®. RESULTS Many clinical trials using inhibitors of EGFR family RTKs have been done or are under way. Those that have concluded with results published to date do not show an added benefit over standard of care chemotherapy in an adjuvant or second line setting. However, a neoadjuvant study using erlotinib before radical cystectomy demonstrated promising results. CONCLUSIONS Clinical and preclinical studies show that for reasons not currently clear prior treatment with chemotherapeutic agents rendered patients with urothelial carcinoma with muscle invasive bladder cancer resistant to EGFR family inhibitors as well. However, EGFR family inhibitors may be of use in patients with no prior chemotherapy in whom EGFR or ERBB2 is over expressed.

Enhancing the effectiveness of androgen deprivation in prostate cancer by inducing Filamin A nuclear localization

As prostate cancer (CaP) is regulated by androgen receptor (AR) activity, metastatic CaP is treated with androgen deprivation therapy (ADT). Despite initial response, patients on ADT eventually progress to castration-resistant CaP (CRPC), which is currently incurable. We previously showed that cleavage of the 280 kDa structural protein Filamin A (FlnA) to a 90 kDa fragment, and nuclear localization of the cleaved product, sensitized CRPC cells to ADT. Hence, treatment promoting FlnA nuclear localization would enhance androgen responsiveness. Here, we show that FlnA nuclear localization induced apoptosis in CRPC cells during ADT, identifying it as a treatment tool in advanced CaP. Significantly, the natural product genistein combined polysaccharide (GCP) had a similar effect. Investigation of the mechanism of GCP-induced apoptosis showed that GCP induced FlnA cleavage and nuclear localization and that apoptosis resulting from GCP treatment was mediated by FlnA nuclear localization. Two main components of GCP are genistein and daidzein: the ability of GCP to induce G2 arrest was due to genistein whereas sensitivity to ADT stemmed from daidzein; hence, both were needed to mediate GCPs effects. FlnA cleavage is regulated by its phosphorylation; we show that ADT enhanced FlnA phosphorylation, which prevented its cleavage, whereas GCP inhibited FlnA phosphorylation, thereby sensitizing CaP cells to ADT. In a mouse model of CaP recurrence, GCP, but not vehicle, impeded relapse following castration, indicating that GCP, when administered with ADT, interrupted the development of CRPC. These results demonstrate the efficacy of GCP in promoting FlnA nuclear localization and enhancing androgen responsiveness in CaP.

Androgen Receptor regulation of Vitamin D receptor in response of castration-resistant prostate cancer cells to 1α-Hydroxyvitamin D5 - a calcitriol analog.

Calcitriol (1,25(OH)(2)D3) is cytostatic for prostate cancer (CaP), but had limited therapeutic utility due to hypercalcemia-related toxicities, leading to the development of low-calcemic calcitriol analogs. We show that one analog, 1-α-Hydroxyvitamin-D5 (1α(OH)D5), induced apoptosis in castration-sensitive LNCaP prostate cancer cells, but unlike calcitriol, did not increase androgen receptor (AR) transcriptional activity. LNCaP-AI, a castrate-resistant (CRCaP) LNCaP subline, was resistant to 1α(OH)D5 in the presence of androgens; however, androgen withdrawal (AWD), although ineffective by itself, sensitized LNCaP-AI cells to 1α(OH)D5. Investigation of the mechanism revealed that the vitamin D receptor (VDR), which mediates the effects of 1α(OH)D5, is downregulated in LNCaP-AI cells compared to LNCaP in the presence of androgens, whereas AWD restored VDR expression. Since LNCaP-AI cells expressed higher AR compared to LNCaP and AWD decreased AR, this indicated an inverse relationship between VDR and AR. Further, AR stimulation (by increased androgen) suppressed VDR, while AR downregulation (by ARsiRNA) stimulated VDR levels and sensitized LNCaP-AI cells to 1α(OH)D5 similar to AWD. Another cell line, pRNS-1-1, although isolated from a normal prostate, had lost AR expression in culture and adapted to androgen-independent growth. These cells expressed the VDR and were sensitive to 1α(OH)D5, but restoration of AR expression suppressed VDR levels and induced resistance to 1α(OH)D5 treatment. Taken together, these results demonstrate negative regulation of VDR by AR in CRCaP cells. This effect is likely mediated by prohibitin (PHB), which was inhibited by AR transcriptional activity and stimulated VDR in CRCaP, but not castrate-sensitive cells. Therefore, in castration sensitive cells, although the AR negatively regulates PHB, this does not affect VDR expression, whereas in CRCaP cells, negative regulation of PHB by the AR results in concomitant negative regulation of the VDR by the AR. These data demonstrate a novel mechanism by which 1α(OH)D5 prolong the effectiveness of AWD in CaP cells.

miR-148a dependent apoptosis of bladder cancer cells is mediated in part by the epigenetic modifier DNMT1

Urothelial cell carcinoma of the bladder (UCCB) is the most common form of bladder cancer and it is estimated that ∼15,000 people in the United States succumbed to this disease in 2013. Bladder cancer treatment options are limited and research to understand the molecular mechanisms of this disease is needed to design novel therapeutic strategies. Recent studies have shown that microRNAs play pivotal roles in the progression of cancer. miR‐148a has been shown to serve as a tumor suppressor in cancers of the prostate, colon, and liver, but its role in bladder cancer has never been elucidated. Here we show that miR‐148a is down‐regulated in UCCB cell lines. We demonstrate that overexpression of miR‐148a leads to reduced cell viability through an increase in apoptosis rather than an inhibition of proliferation. We additionally show that miR‐148a exerts this effect partially by attenuating expression of DNA methyltransferase 1 (DNMT1). Finally, our studies demonstrate that treating cells with both miR‐148a and either cisplatin or doxorubicin is either additive or synergistic in causing apoptosis. These data taken together suggest that miR‐148a is a tumor suppressor in UCCB and could potentially serve as a novel therapeutic for this malignancy.

Transcription of Nrdp1 by the androgen receptor is regulated by nuclear filamin A in prostate cancer

Prostate cancer (PCa) progression is regulated by the androgen receptor (AR); however, patients undergoing androgen-deprivation therapy (ADT) for disseminated PCa eventually develop castration-resistant PCa (CRPC). Results of previous studies indicated that AR, a transcription factor, occupies distinct genomic loci in CRPC compared with hormone-naïve PCa; however, the cause of this distinction was unknown. The E3 ubiquitin ligase Nrdp1 is a model AR target modulated by androgens in hormone-naïve PCa but not in CRPC. Using Nrdp1, we investigated how AR switches transcription programs during CRPC progression. The proximal Nrdp1 promoter contains an androgen response element (ARE); we demonstrated AR binding to this ARE in androgen-sensitive PCa. Analysis of hormone-naive human prostatectomy specimens revealed correlation between Nrdp1 and AR expression, supporting AR regulation of NRDP1 levels in androgen-sensitive tissue. However, despite sustained AR levels, AR binding to the Nrdp1 promoter and Nrdp1 expression were suppressed in CRPC. Elucidation of the suppression mechanism demonstrated correlation of NRDP1 levels with nuclear localization of the scaffolding protein filamin A (FLNA) which, as we previously showed, is itself repressed following ADT in many CRPC tumors. Restoration of nuclear FLNA in CRPC stimulated AR binding to Nrdp1 ARE, increased its transcription, and augmented NRDP1 protein expression and responsiveness to ADT, indicating that nuclear FLNA controls AR-mediated androgen-sensitive Nrdp1 transcription. Expression of other AR-regulated genes lost in CRPC was also re-established by nuclear FLNA. Thus, our results indicate that nuclear FLNA promotes androgen-dependent AR-regulated transcription in PCa, while loss of nuclear FLNA in CRPC alters the AR-regulated transcription program.

Abstract 1303: In vivo analysis of EGFR family signalling as a bypass mechanism in prostate cancer

Background: Prostate cancers (PCa) rely on androgenic ligands and the androgen receptor (AR) for their growth and survival, making AR inhibition a predominant therapeutic strategy for these tumors. Some prostate tumors however fail this therapy due to ‘bypass’ mechanisms that emerge as a result of prolonged AR targeting. This in vivo study attempted to assess the expression and activation of the epidermal growth factor receptor (EGFR) family (whose role is well-documented in PCa) in response to androgen deprivation therapy (ADT). Methods: Nude mice were implanted (s.c.) with CWR22 tumors (human-patient-derived, androgen-dependent ‘AD’) and its castration-resistant (‘CR’) subline CWR22-Rv1 (relapsed CWR22). Androgen deprivation (i.e. AR inhibition) was achieved by surgical or ‘sham’ castration of mice. Tumors were analyzed (immunohistochemistry/immunoblot) for EGFR/ErbB2/ErbB3/AR proteins and proliferative/apoptotic markers. Results: Castration caused significant tumor regression in AD but not CR tumors. in vitro viability assays demonstrated that castration (mimicked by using charcoal-stripped serum, ‘css’) did not slow down CR cells to the same degree as it did AD cells. At baseline, intratumoral EGFR protein was unchanged in R22 tumors, ErbB2 levels decreased and ErbB3 protein increased in Rv1 tumors. Castration increased ErbB3 but not EGFR or ErbB2 proteins in CWR22 tumors. Phosphorylated forms of these receptors were generally difficult to detect but there was more phosphorylated ErbB3 protein in Rv1 tumors. Downstream of the EGFR family, there was less phosphorylated Erk but not Akt protein in CWR22-Rv1 tumors. Castration decreased Erk protein in AD tumors but increased it in CR tumors. Immunohistochemical quantification revealed that cytoplasmic EGFR and ErbB3 proteins were elevated in CR tumors but reduced in AD tumors. Castration greatly decreased Ki-67 staining in AD but not in CR tumors while the number of TUNEL-positive nuclei and intensity of PARP staining decreased in castrated CR but not in AD tumors. ErbB3 and AR proteins were significantly correlated with DNA damage and proliferation in CWR22 tumors but only nuclear AR levels and proliferation were significantly correlated in CR tumors. Conclusions: We conclude that androgen deprivation therapy may alter EGFR and ErbB3 protein levels and localization in androgen-dependent and castration-resistant tumors. The EGFR family is typically activated at the cell surface hence their presence and activity there, in response to castration, may initiate signalling pathways encouraging tumor cell proliferation and survival. Citation Format: Maitreyee K. Jathal, Thomas M. Steele, Salma Siddiqui, Benjamin A. Mooso, Leandro S. D’Abronzo, Christiana M. Drake, Paramita M. Ghosh. In vivo analysis of EGFR family signalling as a bypass mechanism in prostate cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1303.

Abstract 5051: Androgen receptor-mediated regulation of p14ARF transcription in prostate tumor cells

The p14ARF tumor suppressor is often deleted or silenced in malignancies. Prostate tumors are an exception, where p14 expression is elevated. To understand this phenomenon, we assessed the expression of p53 pathway members, which are most effected by p14ARF. The expression of androgen receptor (AR), a pivotal prostate cancer regulator, which is also affected by p14arf and MDM2 was analyzed as well. The studies used archival prostate tumor tissues obtained from prostatectomies performed at the Veterans Affairs-Northern California Health Care System in Mather California between 1996 and 2002 to better define the relationship between these interrelated networks. A prostate tumor tissue array consisting of 78 tumors of differing stages and grades was constructed to evaluate correlations between multiple parameters. Immunohistochemical studies assessed expression of the proliferation marker Ki67, p53, MDM2, MDM4, p14ARF, and the AR in the nuclear and cytoplasmic compartments of tumor and adjacent cells. p53, MDM4, p14ARF and AR were detected in nuclear and cytoplasmic compartments of tumor and non-tumor cells, but were predominantly nuclear. MDM2 expression was primarily cytoplasmic in tumor cells. Multivariate analysis of the immunohistochemical markers identified a strong correlation between expression of p14ARF and AR. Studies utilizing the prostate CWR22 xenograft and LNCaP cell line models revealed that castration or androgen deprivation resulted in reduced p14arf levels and that this effect correlated with a precipitous decline in E2F1-3a levels. In a reciprocal analysis, RB ablation enhanced p14ARF transcription, arguing that the E2F/RB pathway mediates AR-dependent p14ARF expression. However, we also identified an AR binding site located ∼40 KB upstream of the p14ARF gene. Chromatin immunoprecipitation (ChIP) studies showed that in prostate cells this site was bound by AR. ChIP studies also revealed E2F1 and E2F3 were present at the p14ARF promoter. Together, the studies argue p14ARF is a direct transcriptional target of AR and that AR and E2F collaborate to promote p14ARF expression. . Citation Format: Maria Mudryj, Salma Siddiqui, Stephen J. Libertini, Alan P. Lombard, Benjamin Mooso, Leandro D9Abronzo, Frank Melgoza, Alexander Borowsky, Christiana Drake, LiHong Qi, Paramita M. Ghosh. Androgen receptor-mediated regulation of p14ARF transcription in prostate tumor cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5051. doi:10.1158/1538-7445.AM2015-5051

Abstract 4270: ErbB inhibitors in bladder cancer cell lines: Effectiveness in cells that express high levels but low activity of the ErbB receptors.

Background: Various studies demonstrated increased expression of EGF-receptor (EGFR/HER1/ErbB1) and related receptors ErbB2/HER2/Neu, ErbB3/HER3 and ErbB4/HER4 in bladder cancer. Despite this, clinical trials using drugs inhibiting EGFR (erlotinib), ErbB2 (trastuzumab) or dual EGFR/ErbB2 inhibitors (lapatinib) were all deemed ineffective. Since ErbB receptors require dimerization with other members of this family, each of which regulate cell growth and survival, we hypothesized that all four receptors must be simultaneously suppressed to achieve lasting effects. Here we compare the effects of erlotinib, trastuzumab and lapatinib to a novel pan-ErbB inhibitor dacomitinib in four bladder cancer cell lines expressing high and low levels of these receptors. Methods: The bladder cancer cell lines T24, TCCSUP, J82 and HTB-2FT4 were used to evaluate the efficacy of erlotinib (Tarceva), trastuzumab (Herceptin), lapatinib (Tykerb, GW572016) and dacomitinib (PF00299804). Cell growth was estimated by MTT or crystal-violet staining. Protein expression was determined by western blotting and apoptosis was determined by flow cytometry after seventy-two hour incubation with the indicated treatment. Results: Comparison of the T24, TCCSUP, J82 and HTB-2FT4 bladder cancer cells with C4-2 (prostate) and MCF-7 (breast) cells showed that all but the HTB-2FT4 bladder cancer cells expressed high levels of EGFR and ErbB3 but not ErbB2, while HTB-2FT4 cells expressed only EGFR and TCCSUP cells had higher ErbB levels than T24. Interestingly, ErbB2 and ErbB3 are readily activated by EGF in T24 cells compared to TCCSUP. MTT demonstrated the efficacy of dacomitinib and erlotinib, primarily EGFR inhibitors, compared to lapatinib, primarily an ErbB2 inhibitor with anti-EGFR activity at higher concentrations, while the ErbB2 inhibitor, trastuzumab, had little effect. The trastuzumab and erlotinib combination performed worse than erlotinib alone in T24 cells; hence trastuzumab studies were not pursued further. Crystal-violet staining after treatment with erlotinib, lapatinib and dacomitinib indicated higher efficacy of dacomitinib after seven days in the T24 and TCCSUP cell lines. MTT and flow cytometry showed that lapatinib was ineffective alone but, in combination with dacomitinib, significantly decreased cell viability in TCCSUP cells. In contrast, combining erlotinib, lapatinib and dacomitinib proved most effective in T24 cells. Conclusions: We demonstrate that all ErbB receptors must be simultaneously inhibited to prevent proliferation of both high and low ErbB expressing bladder lines. Inhibition of ErbB2 alone had a deleterious effect, likely due to ErbB2 inhibition stimulating the activation of the other ErbB receptors. While high levels of ErbB kinases sensitized cells to the inhibitors, the drugs were more effective in cells that had lower activation of the receptors. Citation Format: Benjamin A. Mooso, Ralph W. deVere White, Paramita M. Ghosh. ErbB inhibitors in bladder cancer cell lines: Effectiveness in cells that express high levels but low activity of the ErbB receptors. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4270. doi:10.1158/1538-7445.AM2013-4270