Cisplatin-induced increase in heregulin 1 and its attenuation by the monoclonal ErbB3 antibody seribantumab in bladder cancer

Cisplatin-based combination chemotherapy is the foundation for treatment of advanced bladder cancer (BlCa), but many patients develop chemoresistance mediated by increased Akt and ERK phosphorylation. However, the mechanism by which cisplatin induces this increase has not been elucidated. Among six patient-derived xenograft (PDX) models of BlCa, we observed that the cisplatin-resistant BL0269 express high epidermal growth factor receptor, ErbB2/HER2 and ErbB3/HER3. Cisplatin treatment transiently increased phospho-ErbB3 (Y1328), phospho-ERK (T202/Y204) and phospho-Akt (S473), and analysis of radical cystectomy tissues from patients with BlCa showed correlation between ErbB3 and ERK phosphorylation, likely due to the activation of ERK via the ErbB3 pathway. In vitro analysis revealed a role for the ErbB3 ligand heregulin1-β1 (HRG1/NRG1), which is higher in chemoresistant lines compared to cisplatin-sensitive cells. Additionally, cisplatin treatment, both in PDX and cell models, increased HRG1 levels. The monoclonal antibody seribantumab, that obstructs ErbB3 ligand-binding, suppressed HRG1-induced ErbB3, Akt and ERK phosphorylation. Seribantumab also prevented tumor growth in both the chemosensitive BL0440 and chemoresistant BL0269 models. Our data demonstrate that cisplatin-associated increases in Akt and ERK phosphorylation is mediated by an elevation in HRG1, suggesting that inhibition of ErbB3 phosphorylation may be a useful therapeutic strategy in BlCa with high phospho-ErbB3 and HRG1 levels.

Abstract 2650: Targeting the DNA-binding domain of the androgen receptor in castration-resistant prostate cancer

Background: The androgen receptor (AR), which plays a major role in prostate cancer (PCa), consists of a C-terminal ligand-binding domain (LBD), a hinge domain, a DNA-binding domain (DBD), and an N-terminal domain (NTD). Current AR antagonists and AR signaling inhibitors (ASIs), used in androgen deprivation therapy (ADT) and to prevent disease progression, often fail due to production of alternatively spliced AR variants (AR-Vs) that lack the LBD but retain the DBD, which is essential to AR transcriptional activity. This project examines a series of novel compounds designed to inhibit AR-DNA interaction and study how these compounds affect castration-resistant PCa (CRPC).

Methods: Compounds potentially targeting the DBD were used to predict direction and position of compounds when docked to the AR. MTT assays, flow cytometry, immunoblots, qRT-PCR, luciferase assay, and immunofluorescence were used to test compounds on AR and PCa. Drug Affinity Responsive Target Stability (DARTS) tested potential binding of the compounds to the AR. Studies in intact mice were used to determine toxicity of the compounds and the maximum tolerated dose.

Results: Of 48 compounds synthesized, C15 had the highest and most consistent efficacy overall. C15 decreased metabolic activity in 22Rv1 and CWR-R1 cells that express AR-Vs and in C4 and C4-2 that do not express AR-Vs. Further, C15 had a reduced effect in AR-null PC3 cells and minimal effect in normal human dermal fibroblast (NHDF) cells. In C4-2 and 22Rv1, C15 significantly reduced PSA mRNA and AR transcriptional activity, and in C4-2, C15 significantly reduced TMPRSS2 and Nrdp1 mRNA levels. C08 and C15 reduced pronase-induced AR proteolysis only when the AR DBD is present. Furthermore, C15 reduces AR binding at the PSA enhancer, but DHT stimulation may weaken this binding inhibition and reduction in AR transcriptional activity. However, combining C15 with an AR inhibitor targeting the LBD (enzalutamide, darolutamide, apalutamide) restores the full inhibitory potential and even reduces metabolic activity and AR transcriptional activity further than either drug alone in both C4-2 and 22Rv1s. No toxicity in intact mice was observed with C15 with the highest dose tested being 50 mg/kg.

Conclusion: Our preliminary data demonstrate that C15 directly binds to the DBD of the AR and potently inhibits CRPC cells, including those that express AR-Vs missing the LBD. Although increased DHT levels may weaken C15’s inhibition of the AR DBD, addition of a LBD-targeting AR inhibitor improves the inhibitory potential of both drugs. Based on these results, we conclude that C15 may hold great clinical potential as it successfully inhibits CRPC by targeting the AR DBD with minimal toxicity, and it can improve the effects of standard-of-care LBD-targeting AR inhibitors by reducing AR-V-induced resistance.

Citation Format: Thomas M. Steele, Elisabeth A. Messner, Maria Malvina Tsamouri, Salma Siddiqui, Brian Bennion, Ruiwu Liu, Paramita Ghosh. Targeting the DNA-binding domain of the androgen receptor in castration-resistant prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2650.

Comparative Cancer Cell Signaling in Muscle-Invasive Urothelial Carcinoma of the Bladder in Dogs and Humans

Muscle-invasive urothelial carcinoma (MIUC) is the most common type of bladder malignancy in humans, but also in dogs that represent a naturally occurring model for this disease. Dogs are immunocompetent animals that share risk factors, pathophysiological features, clinical signs and response to chemotherapeutics with human cancer patients. This review summarizes the fundamental pathways for canine MIUC initiation, progression, and metastasis, emerging therapeutic targets and mechanisms of drug resistance, and proposes new opportunities for potential prognostic and diagnostic biomarkers and therapeutics. Identifying similarities and differences between cancer signaling in dogs and humans is of utmost importance for the efficient translation of in vitro research to successful clinical trials for both species.

The p14ARF tumor suppressor restrains androgen receptor activity and prevents apoptosis in prostate cancer cells

Prostate cancer (PCa) is characterized by a unique dependence on optimal androgen receptor (AR) activity where physiological androgen concentrations induce proliferation but castrate and supraphysiological levels suppress growth. This feature has been exploited in bipolar androgen therapy (BAT) for castrate resistant malignancies. Here, we investigated the role of the tumor suppressor protein p14ARF in maintaining optimal AR activity and the function of the AR itself in regulating p14ARF levels. We used a tumor tissue array of differing stages and grades to define the relationships between these components and identified a strong positive correlation between p14ARF and AR expression. Mechanistic studies utilizing CWR22 xenograft and cell culture models revealed that a decrease in AR reduced p14ARF expression and deregulated E2F factors, which are linked to p14ARF and AR regulation. Chromatin immunoprecipitation studies identified AR binding sites upstream of p14ARF. p14ARF depletion enhanced AR-dependent PSA and TMPRSS2 transcription, hence p14ARF constrains AR activity. However, p14ARF depletion ultimately results in apoptosis. In PCa cells, AR co-ops p14ARF as part of a feedback mechanism to ensure optimal AR activity for maximal prostate cancer cell survival and proliferation.

Dacomitinib, but not lapatinib, suppressed progression in castration-resistant prostate cancer models by preventing HER2 increase

BACKGROUND

Despite overexpression of the ErbB (EGFR/HER2/ErbB3/ErbB4) family in castration-resistant prostate cancer (CRPC), some inhibitors of this family, including the dual EGFR/HER2 inhibitor lapatinib, failed in Phase II clinical trials. Hence, we investigated mechanisms of lapatinib resistance to determine whether alternate ErbB inhibitors can succeed.

METHODS

The CWR22 human tumour xenograft and its CRPC subline 22Rv1 and sera from lapatinib-treated CRPC patients from a previously reported Phase II trial were used to study lapatinib resistance. Mechanistic studies were conducted in LNCaP, C4-2 and 22Rv1 cell lines.

RESULTS

Lapatinib increased intratumoral HER2 protein, which encouraged resistance to this treatment in mouse models. Sera from CRPC patients following lapatinib treatment demonstrated increased HER2 levels. Investigation of the mechanism of lapatinib-induced HER2 increase revealed that lapatinib promotes HER2 protein stability, leading to membrane localisation, EGFR/HER2 heterodimerisation and signalling, elevating cell viability. Knockdown of HER2 and ErbB3, but not EGFR, sensitised CRPC cells to lapatinib. At equimolar concentrations, the recently FDA-approved pan-ErbB inhibitor dacomitinib decreased HER2 protein stability, prevented ErbB membrane localisation (despite continued membrane integrity) and EGFR/HER2 heterodimerisation, thereby decreasing downstream signalling and increasing apoptosis.

CONCLUSIONS

Targeting the EGFR axis using the irreversible pan-ErbB inhibitor dacomitinib is a viable therapeutic option for CRPC.

Abstract 4842: Overcoming EGFR and ERK-mediated resistance to enzalutamide in castration-resistant prostate cancer

The present project was undertaken to determine whether the activation of the EGFR family (EGFR/ErbB2/ErbB3/ErbB4) and its downstream signaling effector ERK1/2 plays a role in enzalutamide resistance and whether treatment with ErbB or ERK inhibitors overcome this resistance. C4-2B (enzalutamide sensitive) and 22Rv1 (partially enzalutamide resistant) cell lines cultured for prolonged periods in enzalutamide, developed resistance to this drug (C4-2B/MDVR and 22Rv1/MDVR, respectively). Whole genome comparison of enza-resistant to parental lines demonstrated that the ErbB signaling network was significantly upregulated in the enza-resistant lines. Comparison of various enza-sensitive and resistant lines demonstrated a strong correlation between phosphorylation at EGFR(Y1068) and enza resistance. Inhibition of EGFR, but not that of ErbB2 or ErbB3 prevented cell viability. The EGFR inhibitors erlotinib and dacomitinib, but not the ErbB2 inhibitor lapatinib, suppressed viability in combination with enzalutamide. We hypothesized that enza-resistant tumors expressing higher levels of EGFR would be more responsive to erlotinib. To test this hypothesis, we compared the effects of erlotinib and enzalutamide, individually or in combination, in organelles from PDX tumors expressing high or low EGFR levels. Significantly, tumors expressing high EGFR, but not those expressing low EGFR, were responsive to the combination. Finally, we investigated the cause for greater efficacy with erlotinib compared to lapatinib in PCa. Comparison of the effects of different ligands revealed that while both lapatinib and erlotinib inhibited EGFR phosphorylation, only erlotinib but not lapatinib was able to inhibit EGF-induced ERK phosphorylation. This indicated an important role for ERK in the mediation of EGFR ligand induced enzalutamide resistance. Continuous culture of enza-sensitive C4 cells in enzalutamide resulted in the development of ERK phosphorylation in these PTEN-null cells that normally do not express phosphorylated ERK, and the newly ERK phosphorylated cells also were more susceptible to erlotinib as well. In support of a role for ERK in mediating the effects of EGFR activation in enza-resistant cells, inhibition of EGFR but not ErbB2 or ErbB3 inhibited ERK phosphorylation, and the ERK inhibitor ulitertinib inhibited viability of enza-resistant lines. We conclude that enzalutamide treatment causes an increase in EGFR ligands that result in the phosphorylation of EGFR at Y1068, which further resulted in phosphorylation of ERK. EGFR inhibitors that prevent ERK phosphorylation were effective in suppressing viability of enza-resistant CRPC cells, whereas ErbB2 inhibitors that did not affect ERK phosphorylation were unable to affect cell viability. These results demonstrate why certain ErbB inhibitors failed to affect enza-resistant CRPC tumors but provide encouragement for others.

Citation Format: Thomas M. Steele, Maitreyee K. Jathal, Salma Siddiqui, Sisi Qin, Clifford G. Tepper, Ralph W. deVere White, Manish Kohli, Liewei Wang, Allen C. Gao, Paramita M. Ghosh. Overcoming EGFR and ERK-mediated resistance to enzalutamide in castration-resistant prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4842.

Obatoclax, a BH3 Mimetic, Enhances Cisplatin-Induced Apoptosis and Decreases the Clonogenicity of Muscle Invasive Bladder Cancer Cells via Mechanisms That Involve the Inhibition of Pro-Survival Molecules as Well as Cell Cycle Regulators

Several studies by our group and others have determined that expression levels of Bcl-2 and/or Bcl-xL, pro-survival molecules which are associated with chemoresistance, are elevated in patients with muscle invasive bladder cancer (MI-BC). The goal of this study was to determine whether combining Obatoclax, a BH3 mimetic which inhibits pro-survival Bcl-2 family members, can improve responses to cisplatin chemotherapy, the standard of care treatment for MI-BC. Three MI-BC cell lines (T24, TCCSuP, 5637) were treated with Obatoclax alone or in combination with cisplatin and/or pre-miR-34a, a molecule which we have previously shown to inhibit MI-BC cell proliferation via decreasing Cdk6 expression. Proliferation, clonogenic, and apoptosis assays confirmed that Obatoclax can decrease cell proliferation and promote apoptosis in a dose-dependent manner. Combination treatment experiments identified Obatoclax + cisplatin as the most effective treatment. Immunoprecipitation and Western analyses indicate that, in addition to being able to inhibit Bcl-2 and Bcl-xL, Obatoclax can also decrease cyclin D1 and Cdk4/6 expression levels. This has not previously been reported. The combined data demonstrate that Obatoclax can inhibit cell proliferation, promote apoptosis, and significantly enhance the effectiveness of cisplatin in MI-BC cells via mechanisms that likely involve the inhibition of both pro-survival molecules and cell cycle regulators.

Abstract 868: The pan-ErbB inhibitor dacomitinib but not the dual EGFR/ErbB2 inhibitor labatinib disrupts membrane localization of the EGFR family of receptor tyrosine kinases

Introduction: Despite ample evidence for the overexpression/overactivation of the epidermal growth factor receptor (EGFR) family, the dual EGFR/ErbB2 inhibitor lapatinib failed in patients with castration-resistant prostate cancer (CRPC). Our preclinical data show that the pan-ErbB inhibitor dacomitinib succeeds where lapatinib fails by decreasing membrane-localized EGFR family protein expression. Experimental Procedures: Nude mice were implanted with CWR22 tumors (human-patient-derived, androgen-dependent) and its CRPC subline 22Rv1 (relapsed CWR22). Mice were castrated or left intact and gavaged daily with 100 mg/kg lapatinib or vehicle. Tumors were analyzed for EGFR/ErbB2/ErbB3/androgen receptor (AR) proteins by both immunohistochemistry in paraffin-embedded tumor sections and Western blots in tumor lysates. Observations were validated in human-derived androgen-dependent and CRPC cell lines treated with lapatinib or dacomitinib by immunoblots and by immunofluorescence. Results: Intratumoral EGFR and ErbB2 (but not ErbB3) increased in intact, lapatinib-treated 22Rv1 tumor-bearing mice compared to placebo-treated ones. Elevated EGFR/ErbB2 was also observed in vitro in lapatinib-treated LNCaP, C4-2, PC-346C cells compared to vehicle-treated cells. EGFR phosphorylation increased from 1/5 intact, lapatinib-treated Rv1 tumors (20%) to 3/5 castrated, lapatinib-treated 22Rv1 tumors (60%). Lapatinib caused an increase in cytoplasmic EGFR and ErbB2 in LNCaP (androgen-dependent) and 22Rv1 (CRPC) cells. Low, physiological doses of dacomitinib overcame lapatinib resistance by suppressing cell viability and this effect was heightened by EGFR family knockdown or when AR activity was simultaneously inhibited. High-magnification microscopy revealed that dacomitinib possibly exerted its effects by decreasing the presence of membrane-localized EGFR, ErbB2 and ErbB3 proteins in comparison to lapatinib. Conclusions: We hypothesize that increased EGFR/ErbB2 heterodimerization is one cause of lapatinib resistance. Activated EGFR family proteins are typically localized in the plasma membrane and dacomitinib, by disrupting this membrane-localization, decreases cell viability. Future studies will attempt to refine the mechanism by which lapatinib and dacomitinib induce changes in RTK localization and how this may impact therapeutic response and prostate tumor progression.

Citation Format: Maitreyee K. Jathak, Thomas M. Steele, Salma Siddiqui, Benjamin A. Mooso, Leandro S. D'Abronzo, Christiana M. Drake, Paramita M. Ghosh. The pan-ErbB inhibitor dacomitinib but not the dual EGFR/ErbB2 inhibitor labatinib disrupts membrane localization of the EGFR family of receptor tyrosine kinases [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 868.

Abstract 4676: Overcoming EGFR-induced resistance to enzalutamide in castration-resistant prostate cancer

Background: The androgen receptor (AR) remains a major therapeutic target in patients with castration-resistant prostate cancer (CRPC). Enzalutamide, an AR inhibitor that is FDA-approved for patients with CRPC, prevents ligand induced AR transcriptional activity, but some initial responders eventually become resistant to the drug. The expression and activity of the EGFR/ErbB family of receptor tyrosine kinases also increases in CRPC patients. The present work was undertaken to determine whether the activation of EGFR family (EGFR/ErbB2/ErbB3/ErbB4) may be responsible for enzalutamide resistance and whether treatment with receptor tyrosine kinase inhibitors would overcome this effect.

Methods: Human-patient-derived androgen-dependent and CRPC prostate tumor cells were grown in 10% Fetal Bovine Serum (FBS). Protein expression and phosphorylation status of the EGFR family were determined by immunoblotting techniques. MTT assays were used to determine the viability of cells treated with enzalutamide, lapatinib (HER2/EGFR inhibitor), erlotinib (EGFR inhibitor), or dacomitinib (pan-ErbB inhibitor). A Luciferase Assay kit (Roche) was used to determine AR transcriptional activity. Lapatinib was obtained from LC Laboratories while erlotinib and dacomitinib were obtained from Selleck Chemicals. Enzalutamide was kindly provided by Medivation Inc.

Results: In viability assays, erlotinib and dacomitinib were more effective than lapatinib in sensitizing CRPC cells to enzalutamide. Enzalutamide suppressed AR transcriptional activity, either alone or in combination with lapatinib, erlotinib, or dacomitinib. Erlotinib, lapatinib, and dacomitinib equally inhibited EGFR and ErbB3 phosphorylation. However, in EGF stimulated cells, erlotinib and dacomitinib—but not lapatinib—suppressed ERK 1/2 phosphorylation at Tyr202/Thr204, indicating a stark difference in downstream inhibition and potentially proliferation.

Conclusions: The above results indicate that ERK 1/2 may play an important role in reducing the efficacy of enzalutamide by itself and in combination with lapatinib. Furthermore, lapatinib's inability to prevent ERK phosphorylation upon EGF stimulation may play a role in its ineffectiveness in prostate cancer. Our preliminary preclinical data indicate that co-administration of enzalutamide with an EGFR targeted inhibitor may be a suitable therapeutic approach towards overcoming enzalutamide resistance in vitro. We are testing whether ERK 1/2 or MEK may be effective in reducing this ERK specific enzalutamide resistance. These strategies may potentially prolong enzalutamide sensitivity in CRPC patients.

Citation Format: Thomas M. Steele, Maitreyee K. Jathal, Salma Siddiqui, Paramita M. Ghosh. Overcoming EGFR-induced resistance to enzalutamide in castration-resistant 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 4676.

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.

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 3335: Increased ErbB3 and EGFR activity mediate lapatinib resistance in prostate cancer

Virtually all patients undergoing standard-of-care androgen deprivation therapy (ADT) for recurrent prostate cancer (PCa) will develop castration-resistant prostate cancer (CRPC). Despite overexpression of the epidermal growth factor receptor (EGFR) family - especially EGFR, ErbB2 and ErbB3 - in all stages of PCa progression, the dual-kinase EGFR/ErbB2 inhibitor lapatinib (GW572016) failed in Phase 2 trials in hormone-naïve and CRPC patients. Here, we investigated mechanisms of lapatinib resistance using the CWR22 (‘R22’, hormone-naïve) and CWR22-Rv1 (‘Rv1’, CRPC) models of PCa progression.

R22 or Rv1 tumors were implanted (s.c.) in male athymic nu/nu mice, castrated or left intact and treated daily with vehicle or 100mg/kg lapatinib (oral gavage). Tumors were collected at the study’s end and analyzed (Western Blot/WB, immunohistochemistry/IHC).

With Ki67 staining, compared to R22 tumors, Rv1 tumors were more proliferative and unaffected by castration or lapatinib. R22 tumors regressed after castration but not lapatinib. As in human patients, lapatinib resistance was observed in hormone-naïve R22 and CRPC Rv1 tumors thus validating our experimental model.

First we asked why Rv1 tumors proliferated rapidly. Rv1 tumors expressed 2-fold more ErbB3 than R22 tumors (WB). We previously showed that ErbB3 overexpression increased proliferation (Chen et al., Canc. Res, 70(14):5994-6003, 2010) - hence we attribute the rapid growth of Rv1 tumors to high ErbB3. Castration reduced EGFR, phosphorylated Akt and Erk in R22 but not in Rv1 tumors - decreased activation of these kinases may mediate the effects of castration on tumor growth. Rv1 tumors expressed alternately-spliced variants of androgen receptor (AR) that cause castration-resistance and less PSA than R22 tumors.

Next, we asked why EGFR/ErbB2 inhibition failed in Rv1 tumors, despite EGFR's prominence in this tumor type. Lapatinib reduced intratumoral PSA levels in intact R22 mice but increased it in Rv1 mice. Lapatinib also increased EGFR and phosphorylated Akt in intact Rv1 but not R22 tumors. We hypothesize that, in Rv1 tumors, increased EGFR induces Akt phosphorylation which, we have shown earlier, regulates AR transcriptional activity and increases PSA expression. In contrast, in castrated Rv1 mice, lapatinib also increased ErbB3 levels. In Rv1 tumors, castration increased nuclear ErbB3 whereas in R22 tumors it increased cytoplasmic ErbB3 (IHC).

Our results indicate that lapatinib may have failed in castrated Rv1 mice due to increased overall ErbB3 but in castrated R22 tumors due to increased cytoplasmic ErbB3. Regardless, the result is heightened ErbB3-related activity, which may cause increased proliferation and eventual drug failure. A pan-ErbB drug which also inhibits ErbB3, e.g. dacomitinib, can successfully overcome EGFR/ErbB2 resistance, as demonstrated in vitro.

Citation Format: Maitreyee K. Jathal, Thomas M. Steele, Benjamin A. Mooso, Leandro S. D'Abronzo, Salma Siddiqui, Christiana Drake, Paramita M. Ghosh. Increased ErbB3 and EGFR activity mediate lapatinib resistance in prostate cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3335. doi:10.1158/1538-7445.AM2014-3335

Delayed hepcidin response explains the lag period in iron absorption following a stimulus to increase erythropoiesis

INTRODUCTION

The delay of several days between an erythropoietic stimulus and the subsequent increase in intestinal iron absorption is commonly believed to represent the time required for body signals to programme the immature crypt enterocytes and for these cells to migrate to the villus. Recent data however suggest that signals from the body to alter absorption are mediated by circulating hepcidin and that this peptide exerts its effect on mature villus enterocytes.

METHODS

We have examined the delay in the absorptive response following stimulated erythropoiesis using phenylhydrazine induced haemolysis and correlated this with expression of hepcidin in the liver and iron transporters in the duodenum.

RESULTS

There was a delay of four days following haemolysis before a significant increase in iron absorption was observed. Hepatic hepcidin expression did not decrease until day 3, reaching almost undetectable levels by days 4 and 5. This coincided with the increase in duodenal expression of divalent metal transporter 1, duodenal cytochrome b, and Ireg1.

CONCLUSION

These results suggest that the delayed increase in iron absorption following stimulated erythropoiesis is attributable to a lag in the hepcidin response rather than crypt programming, and are consistent with a direct effect of the hepcidin pathway on mature villus enterocytes.

The effect of social learning intervention on metabolic control of insulin-dependent diabetes mellitus in adolescents

This paper reports the results of an experimental study modeled after a study conducted by Kaplan et al. The hypothesis tested was: Adolescents who receive a social learning intervention (SLI) will show greater improvement in metabolic control of their diabetes than will adolescents who receive only traditional diabetes instruction. Thirty-four adolescents between the ages of 12 and 16 who attended a midwestern camp were randomly divided into two groups. Both groups attended a daily 1-hour teaching session about diabetes. Later each day, the experimental group received an SLI consisting of role modeling to help the subjects circumvent peer pressure. To determine metabolic control, HbA1 values were determined before and 3 1/2 months after the intervention. The control group showed no significant difference in HbA1 values, while the experimental group showed a decrease in metabolic control.