DTX-resistant Cells Research Articles

Glucocorticoid Receptor Regulates and Interacts with LEDGF/p75 to Promote Docetaxel Resistance in Prostate Cancer Cells.

Patients with advanced prostate cancer (PCa) invariably develop resistance to anti-androgen therapy and taxane-based chemotherapy. Glucocorticoid receptor (GR) has been implicated in PCa therapy resistance; however, the mechanisms underlying GR-mediated chemoresistance remain unclear. Lens epithelium-derived growth factor p75 (LEDGF/p75, also known as PSIP1 and DFS70) is a glucocorticoid-induced transcription co-activator implicated in cancer chemoresistance. We investigated the contribution of the GR-LEDGF/p75 axis to docetaxel (DTX)-resistance in PCa cells. GR silencing in DTX-sensitive and -resistant PCa cells decreased LEDGF/p75 expression, and GR upregulation in enzalutamide-resistant cells correlated with increased LEDGF/p75 expression. ChIP-sequencing revealed GR binding sites in the LEDGF/p75 promoter. STRING protein-protein interaction analysis indicated that GR and LEDGF/p75 belong to the same transcriptional network, and immunochemical studies demonstrated their co-immunoprecipitation and co-localization in DTX-resistant cells. The GR modulators exicorilant and relacorilant increased the sensitivity of chemoresistant PCa cells to DTX-induced cell death, and this effect was more pronounced upon LEDGF/p75 silencing. RNA-sequencing of DTX-resistant cells with GR or LEDGF/p75 knockdown revealed a transcriptomic overlap targeting signaling pathways associated with cell survival and proliferation, cancer, and therapy resistance. These studies implicate the GR-LEDGF/p75 axis in PCa therapy resistance and provide a pre-clinical rationale for developing novel therapeutic strategies for advanced PCa.

Polysaccharides from Lentinus edodes prevent acquired drug resistance to docetaxel in prostate cancer cells by decreasing the TGF-β1 secretion of cancer-associated fibroblasts.

Prostate cancer is one of the most prevalent lethal diseases among men globally. In the treatment of prostate cancer, the limited therapeutic efficacy of the standard non-hormonal systemic therapy docetaxel (DTX) represents an important challenge. Cancer-associated fibroblasts (CAFs) play a crucial role in resistance to therapy because of their prevalence and functional pleiotropy in tumor environments. Our previous research revealed that MPSSS, a novel polysaccharide extracted from Lentinus edodes, could significantly attenuate the immunosuppressive function of myeloid suppressor cells and CAFs. In this study, we investigated whether MPSSS could potentiate the efficacy of DTX against prostate cancer by inhibiting CAF-induced chemoresistance and elucidated its underlying mechanisms. The sensitivity of PC-3 prostate cancer cells cultured with conditioned medium derived from CAFs (CAF-CM) to DTX was assessed. The resistance effect induced by CAF-CM was abolished when CAFs were pretreated with MPSSS. Bioinformatic analysis of datasets from the Gene Expression Omnibus database revealed the activation of the transforming growth factor β1 (TGF-β1) signaling pathway in DTX-resistant cells. Based on this finding, we demonstrated that treatment with the TGF-β1 receptor inhibitor SB525334 reversed DTX resistance in CAFs, suggesting that TGF-β1 secreted by CAFs was a crucial intermediary in the development of DTX resistance in PC3 cells. Further research revealed that MPSSS decreases the secretion of TGF-β1 by inhibiting the JAK2/STAT3 pathway via Toll-like receptor 4 in CAFs. Overall, MPSSS might be a potential adjuvant treatment for DTX resistance in prostate cancer.

Glucocorticoid Receptor and β-Catenin Interact in Prostate Cancer Cells and Their Co-Inhibition Attenuates Tumorsphere Formation, Stemness, and Docetaxel Resistance.

Therapy resistance hinders the efficacy of anti-androgen therapies and taxane-based chemotherapy for advanced prostate cancer (PCa). Glucocorticoid receptor (GR) signaling mediates resistance to androgen receptor signaling inhibitors (ARSI) and has also been recently implicated in PCa resistance to docetaxel (DTX), suggesting a role in therapy cross-resistance. Like GR, β-catenin is upregulated in metastatic and therapy-resistant tumors and is a crucial regulator of cancer stemness and ARSI resistance. β-catenin interacts with AR to promote PCa progression. Given the structural and functional similarities between AR and GR, we hypothesized that β-catenin also interacts with GR to influence PCa stemness and chemoresistance. As expected, we observed that treatment with the glucocorticoid dexamethasone promotednuclear accumulation of GR and active β-catenin in PCa cells. Co-immunoprecipitation studies showed that GR and β-catenin interact in DTX-resistant and DTX-sensitive PCa cells. Pharmacological co-inhibition of GR and β-catenin, using the GR modulator CORT-108297 and the selective β-catenin inhibitor MSAB, enhanced cytotoxicity in DTX-resistant PCa cells grown in adherent and spheroid cultures and decreased CD44+/CD24- cell populations in tumorspheres. These results indicate that GR and β-catenin influence cell survival, stemness, and tumorsphere formation in DTX-resistant cells. Their co-inhibition could be a promising therapeutic strategy to overcome PCa therapy cross-resistance.

Abstract 1744: Chemoresistant non-small cell lung cancer: A resensitizing strategy utilizing antimuscarinics

Abstract Background: Advanced non-small cell lung cancer (NSCLC) remains a leading cause of cancer-related deaths in the United States and worldwide. This is largely due to intrinsic or acquired therapy resistance. The current study investigates the potential of a repurposed antimuscarinic overactive bladder drug to resensitize chemotherapy-resistant NSCLC to chemotherapy-induced apoptosis. Methods: The chemotherapy drug, docetaxel (DTX), resistant human NSCLC cell cultures (A549R) were established to recapitulate the clinical emergence of chemoresistance. These cultures were used to harvest total RNA for RNA-seq and qPCR. DTX-induced apoptosis was measured with crystal violet survival assay, colony formation assay, and TUNEL assay. In vivo experiments were performed by injecting A549R cells into the flanks of immunocompromised mice. Mice were treated with various agents, tumor sizes were monitored, and tumor mass was measured at the end of the experiment. Results: RNA-seq data of DTX-resistant NSCLC (A549R) cells show a 13.5-fold increase in expression of the muscarinic acetylcholine receptor 3 (CHRM3) compared to chemonaive A549 cells which was supported by qPCR analysis (16-fold increase). Oncomine clinical data from TCGA and Bild Lung suggest an increased mortality risk at 3 years is associated with increased CHRM3 expression. In vitro survival experimental results show resensitization of A549R cells to DTX-induced cell death when co-treated with the CHRM3 antagonist, darifenacin. Crystal violet cell survival assays show a 70% reduction in survival when cells are treated with darifenacin + DTX compared to DTX alone. This is supported by colony formation assay results with complete absence of colony growth in the darifenacin + DTX combination therapy group. Furthermore, cells treated with darifenacin + DTX show increased apoptosis measured by TUNEL assay compared to cells treated with DTX alone (% TUNEL positive: DTX alone = 0.9%, darifenacin + DTX = 88%). In vivo tumor measurements of injected A549R cells revealed a 91% decrease in tumor growth in the darifenacin + DTX treated mice compared to the DTX alone treated mice. Conclusion: We show that chemoresistant NSCLC has increased expression of CHRM3 which is associated with poorer clinical outcomes. Furthermore, the currently available antimuscarinic, darifenacin, which is used in the clinic to treat overactive bladder, effectively resensitizes DTX-resistant cells to DTX-induced cell death both in vitro and in vivo. This novel therapy has unique advantages over alternate approaches as it aims to save chemotherapy-eligible patients at multiple levels: 1) to resensitize chemotherapy-resistant tumors, 2) to synergize with chemotherapy for improved efficacy, and 3) to reduce the effective dose of chemotherapy, thus lowering toxic side effects. Funding provided by an INBRE Pilot Grant, and the UI start-up fund (to T.B.) Citation Format: Tyler Bland, Ethan Overfelt. Chemoresistant non-small cell lung cancer: A resensitizing strategy utilizing antimuscarinics [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1744.

Exosomal LOC85009 inhibits docetaxel resistance in lung adenocarcinoma through regulating ATG5-induced autophagy.

This study aims at investigating the role of a neighbor long non-coding RNA (lncRNA) of HDAC4 (LOC85009) in docetaxel (DTX) resistance of lung adenocarcinoma (LUAD). RT-qPCR was used to analyze LOC85009 expression in DTX-resistant LUAD cells. In vitro and in vivo experiments were applied to detect the influence of LOC85009 on LUAD cell growth and xenograft tumor growth. DNA pull down assay, RNA pull down assay, ChIP assay, CoIP assay and RIP assay were performed to identify the direct interactions between factors. LOC85009 was lowly-expressed in DTX-resistant LUAD cells. Functionally, LOC85009 overexpression inhibited DTX resistance and cell proliferation but triggered cell apoptosis. Moreover, we identified that LOC85009 was transferred from LUAD cells to DTX-resistant LUAD cells via exosomes. Exosomal LOC85009 inhibited DTX resistance, proliferation and autophagy while induced apoptosis in DTX-resistant cells. Additionally, we found that LOC85009 sequestered ubiquitin-specific proteinase 5 (USP5) to destabilize upstream transcription factor 1 (USF1) protein, thereby inactivating ATG5 transcription. Exosomal LOC85009 inhibits DTX resistance through regulation of ATG5-induced autophagy via USP5/USF1 axis, suggesting that LOC85009 might be a potential target to reverse DTX resistance in the treatment of LUAD.

Abstract C063: Enolase-1 as a candidate theranostics target for neuroendocrine prostate cancer

Abstract Prostate cancer (PCa) is the second most common cancer in American men, with men of African ancestry (AA) having twice the mortality of men of European ancestry (AA). Although taxane-based chemotherapy is the last line of defense in men with advanced PCa, it ultimately fails due to chemoresistance. The protein-specific membrane antigen (PSMA) has been an effective target for the imaging and therapy of advanced PCa. Specifically, PSMA radioligand therapy (PSMA-RLT) is a theranostics (therapy + diagnostics) option for men with advanced PCa. However, about 30% of men with advanced PCa have limited response to PSMA-RLT due to the presence of neuroendocrine-like PCa (NEPC), which lacks PSMA expression. A promising alternative to PSMA targeting is the glycolytic enzyme enolase (ENO), which localizes to the cell surface in advanced tumors. There are three enolases with similar functions, with ENO-1 and ENO-2 implicated in PCa. Previously, we showed that AA and EA men with PCa show differential serum antibody reactivity to ENO. While circulating serum antibodies from EA-PCa patients recognized ENO in both docetaxel (DTX)-sensitive and -resistant PCa cell lines, sera from AA-PCa men only recognized ENO in DTX-sensitive cells, with loss of immunoreactivity in the resistant cells. Here, we demonstrate, using immunoblotting and specific monoclonal antibodies, that chemosensitive NEPC cells express both ENO-1 and ENO-2; however, DTX-resistant cells only express ENO-1 with a clear loss of ENO-2. This pattern is identical to that produced by the AA-PCa serum antibodies, suggesting the possibility that AA-PCa patients may generate a preferential antibody response to ENO-2, with EA-PCa patients preferentially targeting ENO-1. This differential immunoreactivity may reflect differences between AA and EA PCa patients in tumor immunobiology, consistent with emerging literature. The loss of ENO-2 in chemoresistant PCa cells also generates a metabolic vulnerability due to the loss of ENO redundancy. We hypothesize that ENO-1 is expressed on the surface of NEPC cell lines and can be targeted with small molecule inhibitors (SMIs) that could be used as potential theranostics agents. Current studies are identifying ENO-1 surface expression on NEPC cell lines using monoclonal antibodies as well as AA and EA patient antibodies, via immunofluorescence microscopy, membrane fractionation analysis, and flow cytometry. We also initiated the testing of small molecule inhibitors (SMIs) targeting ENO-1 in chemoresistant NEPC cells. Our long-term goal is to identify an alternative treatment for patients with NEPC by establishing ENO-1 as a novel theranostics target. This could benefit AA-PCa patients, which may not mount a strong antitumor ENO-1 immune response. Citation Format: Krystal R. Santiago, Alfonso M. Duran, Carlos A. Casiano, Frankis G. Almaguel, Bhaskar Das. Enolase-1 as a candidate theranostics target for neuroendocrine prostate cancer [abstract]. In: Proceedings of the 15th AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2022 Sep 16-19; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2022;31(1 Suppl):Abstract nr C063.

Comprehensive Evaluation of Multiple Approaches Targeting ABCB1 to Resensitize Docetaxel-Resistant Prostate Cancer Cell Lines.

Docetaxel (DTX) is a mainstay in the treatment of metastatic prostate cancer. Failure of DTX therapy is often associated with multidrug resistance caused by overexpression of efflux membrane transporters of the ABC family such as the glycoprotein ABCB1. This study investigated multiple approaches targeting ABCB1 to resensitize DTX-resistant (DTXR) prostate cancer cell lines. In DU145 DTXR and PC-3 DTXR cells as well as age-matched parental controls, the expression of selected ABC transporters was analyzed by quantitative PCR, Western blot, flow cytometry and immunofluorescence. ABCB1 effluxing activity was studied using the fluorescent ABCB1 substrate rhodamine 123. The influence of ABCB1 inhibitors (elacridar, tariquidar), ABCB1-specific siRNA and inhibition of post-translational glycosylation on DTX tolerance was assessed by cell viability and colony formation assays. In DTXR cells, only ABCB1 was highly upregulated, which was accompanied by a strong effluxing activity and additional post-translational glycosylation of ABCB1. Pharmacological inhibition and siRNA-mediated knockdown of ABCB1 completely resensitized DTXR cells to DTX. Inhibition of glycosylation with tunicamycin affected DTX resistance partially in DU145 DTXR cells, which was accompanied by a slight intracellular accumulation and decreased effluxing activity of ABCB1. In conclusion, DTX resistance can be reversed by various strategies with small molecule inhibitors representing the most promising and feasible approach.

CircCYP24A1 promotes Docetaxel resistance in prostate Cancer by Upregulating ALDH1A3

BackgroundDocetaxel (DTX) is the most widely prescribed first-line chemotherapy for advanced prostate cancer (PCa). Unfortunately, DTX resistance invariably emerges, leading to worse prognosis of PCa. Growing evidence has shown that circRNAs had complex spatiotemporal specificity during the tumor development and oncogenesis. This study was designed to investigate the biological functions and possible molecular mechanisms of circRNAs in DTX resistance of PCa.MethodscircRNAs in established DTX-resistant DU145 cell line were identified by RNA sequencing. Biological function of circCYP24A1 was verified in vitro and in vivo. The potential role of circCYP24A1 in the development of DTX-resistant PCa was investigated via dual-luciferase reporter assays, RIP assays and RNA pull-down assays. Univariate and multivariate logistic regression analyses was used to predict DTX-chemotherapy response based on patients’ clinical and biological information.ResultsCircCYP24A1 was identified to be upregulated in DTX-resistant DU145 cells. Upregulated circCYP24A1 was found to suppress the DTX chemosensitivity in vitro and in vivo. Furthermore, we found that circCYP24A1 promoted DTX resistance in PCa via regulating ALDH1A3 expression by sponging miR-1301-3p and activating PI3K/AKT/mTOR signaling pathway. Statistical analyses elucidated that circCYP24A1 was an independent risk factor to predict DTX response (OR = 0.165; 95% CI: 0.038–0.723; P = 0.017).ConclusionsThis study demonstrated that circCYP24A played an essential role in DTX resistance in PCa, suggesting that circCYP24A1 could be a promising biomarker to predict DTX response and a potential therapeutic target in PCa patients resistant to DTX chemotherapy.

Abstract 301: Repurposing engineered thymoquinone nanoparticles to inhibit drug-resistant prostate cancer

Abstract Despite advanced treatment strategies and therapeutics for prostate cancer (PCa), the metastatic castration-resistant prostate cancer (mCRPC) mechanism remains obscure. Although docetaxel (DTX) and other anti-mitotic chemotherapeutic drug are considered the first line drugs for PCa patients; the resulting side effects and drug resistance increase the demand for an alternative such as natural compounds for effective treatment. However, the natural compounds that achieved remarkable height to overcome drug resistance, their bioavailability and targeted delivery during treatment has become a new challenge. As prostate-specific membrane antigen (PSMA) receptors are expressed on the surface of most PCa cells, we anticipated that these receptors may provide the potential target for effective therapy. Considering these, we employed the natural compound, thymoquinone (TQ)-encapsulated planetary ball-milled nanoparticles (PBM-NPs) formulated with starch (FDA approved, natural polysaccharides) inner core and biocompatible and biodegradable co-polymers poly (ε-caprolactone)/poly (ethylene glycol), functionalized with a PSMA aptamer (A10), which can selectively recognize and bind to PSMA membrane. The functionalities of this strategy were analyzed by targeting A10-TQ-PBM-NP in DTX-resistant cells (C4-2B-R and LNCaP-R), which overexpresses PSMA protein and multidrug resistance (MDR) gene ABCB1, and validated through flow cytometry, immunofluorescence, qRT-PCR, and western blot techniques. The results showed that the aptamer-based nano delivery of a TQ can modulate the cellular and molecular pathways responsible for DTX resistance in PCa cells through the EGFR and ZEB1 dependent mechanism. The A10-TQ-PBM-NPs counteract ATP-binding cassette (ABC)-transporter-mediated chemoresistance in PCa cells. In both cell lines, these NPs rapidly internalized and induced significant cell death at five times lower concentrations than non-conjugated PBM-TQ-NP. Further, A10-TQ-PBM-NPs have high selectivity to the PSMA receptor and downregulated the EGFR dependent pathway, Akt-1, ERK1/2, NF-kB, STAT3, and epithelial-mesenchymal transition (EMT) markers in both C4-2B-R and LNCaP-R cells, thus constraining cell survival, proliferation, and migration. The A10-TQ-PBM-NP bioconjugates also reveal remarkable efficacy and reduced toxicity as measured by body weight loss in the LNCaP-R cells xenograft mice. Altogether, our findings demonstrate that targeting PCa cells with PBM-NPs may reverse the MDR and could be used as potential therapeutic options for patients. Citation Format: Santosh Kumar Singh, Manoj Kumar Mishra, Rajesh Singh. Repurposing engineered thymoquinone nanoparticles to inhibit drug-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 301.

Abstract 2348: Contribution of the GR/LEDGFp75 axis to prostate cancer chemoresistance

Abstract Prostate cancer (PCa) is the second leading cause of cancer deaths in the U.S., disproportionally affecting African American (AA) men. Glucocorticoids (GCs) are administered to PCa patients and have been implicated in therapy resistance. This may be critical to AA men with PCa since they have elevated endogenous GCs levels compared to Caucasian American (CA) men. GCs bind to the glucocorticoid receptor (GR) to exert their actions. The mechanisms of GR-mediated chemoresistance, and its possible contribution to PCa mortality disparities are unknown. We demonstrated that GCs upregulate the chemoresistance-associated protein and transcription co-activator LEDGF/p75 in PCa cells and identified consensus GR binding sites in the promoter region of this protein. Given that both GR and LEDGF/p75 are components of the RNA polymerase II transcription complex, we hypothesized that GR transcriptionally upregulates LEDGF/p75 and then interacts with it to enhance taxane resistance in PCa cells. Pharmacological and genetic inhibition of GR in a panel of docetaxel (DTX)-sensitive and -resistant PCa cells decreased the expression of LEDGF/p75, confirming its status as a candidate GR target gene. However, silencing of LEDGF/p75 had no effects on GR expression. Immunoprecipitation studies revealed that GR and LEDGF/p75 interact in DTX-resistant PCa cells. This interaction was confirmed by confocal microscopy. Immunohistochemical analysis of GR and LEDGF/p75 expression in normal and tumor prostate tissues was performed, and the results are currently being analyzed. Our studies use a mechanistic approach to evaluate the potential contribution of the GR-LEDGF/p75 axis to PCa chemoresistance. Evaluating the co-expression of these proteins in racially diverse PCa tissues may also reveal race-related differential expression, providing insights into the potential contribution of this axis to PCa chemoresistance and mortality disparities. Citation Format: Evelyn S. Sanchez Hernandez, Greisha L. Ortiz Hernandez, Pedro T. Ochoa, Christian R. Gomez, Carlos A. Casiano. Contribution of the GR/LEDGFp75 axis to prostate cancer chemoresistance [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 2348.

Itraconazole Reverts ABCB1-Mediated Docetaxel Resistance in Prostate Cancer.

Docetaxel (DTX) was the first chemotherapeutic agent to demonstrate significant efficacy in the treatment of men with metastatic castration-resistant prostate cancer. However, response to DTX is generally short-lived, and relapse eventually occurs due to emergence of drug-resistance. We previously established two DTX-resistant prostate cancer cell lines, LNCaPR and C4-2BR, derived from the androgen‐dependent LNCaP cell line, and from the LNCaP lineage-derived androgen-independent C4-2B sub-line, respectively. Using an unbiased drug screen, we identify itraconazole (ITZ), an oral antifungal drug, as a compound that can efficiently re-sensitize drug-resistant LNCaPR and C4-2BR prostate cancer cells to DTX treatment. ITZ can re-sensitize multiple DTX-resistant cell models, not only in prostate cancer derived cells, such as PC-3 and DU145, but also in docetaxel-resistant breast cancer cells. This effect is dependent on expression of ATP-binding cassette (ABC) transporter protein ABCB1, also known as P-glycoprotein (P-gp). Molecular modeling of ITZ bound to ABCB1, indicates that ITZ binds tightly to the inward-facing form of ABCB1 thereby inhibiting the transport of DTX. Our results suggest that ITZ may provide a feasible approach to re-sensitization of DTX resistant cells, which would add to the life-prolonging effects of DTX in men with metastatic castration-resistant prostate cancer.

Inhibition of CHRM1 reverts docetaxel resistance in castration‐resistant prostate cancer

BackgroundChemotherapy remains the major treatment option for castration‐resistant prostate cancer (CRPC). Docetaxel (DTX)‐based chemotherapy provides significant survival benefit in patients with CRPC. However, the clinical utility of DTX is compromised when resistance is encountered. Therefore, a more thorough understanding of mechanisms underlying DTX resistance may potentially improve survival in patients with CRPC. The objective of this study is to investigate the role and mechanism of cholinergic receptor muscarinic 1 (CHRM1) activation upon chemotherapy resistance in PC and the efficacy of the CHRM1 antagonist dicyclomine (Dic) in treating DTX‐resistant PC. The hypothesis is that CHRM1 is essential for developing chemotherapy resistance in PC cells and driving survival and growth of DTX‐resistant PC cells.MethodsThe CHRM1 expression levels and their association with DTX resistance were determined in PC clinical specimens and cultured cells. Human PC cells subjected to stable knockdown or overexpression of CHRM1 were evaluated for their response to DTX by cell proliferation, colony and tumorsphere formation, and TUNEL assays. Synergistic growth inhibition by combination treatment with DTX and Dic was assessed by cell viability and tumorgenicity assays.ResultsCHRM1 expression was elevated under DTX treatment in CRPC 22Rv1 and DU145 cells, which was paralleled by higher CHRM1 expression in these cells after acquiring resistance to DTX (22Rv1DTXR and DU145DTXR). Immunohistochemical analyses revealed higher CHRM1 protein levels in longitudinally collected tumor tissues post‐ versus pre‐chemotherapy from a PC patient cohort. Enforced expression of CHRM1 increased DTX IC50 by up to 5‐fold, along with reduced cell apoptosis marker c‐PARP1 expression, in 22Rv1 and DU145 cells. Conversely, silencing of CHRM1 in 22Rv1DTXR cells decreased cell proliferation, invasion, and colony and tumorsphere formation. CHRM1 inactivation with Dic in combination with DTX resulted in more cell death of both DTX‐sensitive (22Rv1 and DU145) and ‐resistant (22Rv1DTXR, DU145DTXR and PC‐3DTXR) cells compared to either treatment alone. Further, Dic restored DTX sensitivity to suppress the growth of DTX‐resistant cells and xenograft tumors (22Rv1DTXR and PC‐3DTXR). Mechanistically, CHRM1 activation upregulated phosphoprotein levels of ERK, JNK and p38, which all are key players in the MAPK pathway and potential mediators driving chemoresistance in cancer cells, while Dic treatment reduced their phosphorylation levels in 22Rv1DTXR and DU145DTXR cells.ConclusionOur results suggest that CHRM1 contributes to the development of DTX resistance in CRPC, which can be reversed by genetic or pharmacologic inactivation of CHRM1, providing new insights into developing a CHRM1‐targeted therapeutic strategy for overcoming DTX‐based chemotherapy resistance in CRPC.

Exosomal Circ-XIAP Promotes Docetaxel Resistance in Prostate Cancer by Regulating miR-1182/TPD52 Axis.

BackgroundExosomal circular RNAs (circRNAs) are involved in the pathogenesis of prostate cancer (PCa) and chemotherapy resistance. This research aimed to explore the function and molecular mechanism of circRNA X-linked inhibitor of apoptosis (circ-XIAP) in docetaxel (DTX) resistance of PCa.MethodsThe expression of circ-XIAP, microRNA-1182 (miR-1182), tumor protein D52 (TPD52) was measured by quantitative real-time polymerase chain reaction (qRT-PCR). Exosomes were detected with transmission electron microscopy (TEM). Cluster of differentiation 63 (CD63), cluster of differentiation 9 (CD9) and TPD52 protein levels were detected by Western blot (WB). FIfty percent inhibitory concentration (IC50) of DTX and cell viability were determined using Cell Counting Kit-8 (CCK-8) assay. Colony formation assay was applied to assess colony-forming ability. Cell cycle distribution and apoptosis were analyzed by flow cytometry. Transwell assay was used for measuring cell migration and invasion. Dual-reporter luciferase assay was performed to confirm the interaction between miR-1182 and circ-XIAP or TPD52. The role of circ-XIAP in vivo was confirmed via the mice xenograft model.ResultsCirc-XIAP and TPD52 were upregulated and miR-1182 was downregulated in DTX-resistant PCa tissue specimens and cell lines. Circ-XIAP was also overexpressed in exosomes from DTX-resistant cells and could be transmitted via exosomes. Circ-XIAP knockdown enhanced DTX sensitivity by suppressing DTX-resistant cell proliferation, migration and invasion and inducing cell cycle arrest and apoptosis. Circ-XIAP directly targeted miR-1182, and the effects of circ-XIAP knockdown were reversed by downregulating miR-1182 in DTX-resistant cells. TPD52 was the target of miR-1182, and its upregulation weakened the promotive effect of miR-1182 on DTX sensitivity. Importantly, circ-XIAP depletion inhibited tumor growth and increased DTX sensitivity in vivo.ConclusionExosomal circ-XIAP promoted DTX resistance of PCa by regulating miR-1182/TPD52 axis, providing a promising therapeutic target for PCa chemotherapy.

Abstract 4688: Interaction of LEDGF/p75 with oncogenic transcription factors in docetaxel resistant prostate cancer cells

Abstract Prostate Cancer (PCa) progression leads to an advanced stage called metastatic castration PCa (mCRPC), for which currently there is no cure in spite of advances in treatment with new generation anti-androgen drugs and chemotherapy with taxanes such as docetaxel (DTX). Our group demonstrated previously that the stress oncoprotein Lens Epithelium Derived Growth Factor of 75 kD (LEDGF/p75) is upregulated in clinical prostate tumors and contributes to DTX-resistance in mCRPC cells. However, little is known about the molecular mechanisms by which LEDGF/p75 promotes taxane resistance. The C-terminus of LEDGF/p75 contains a domain called the Integrase Binding Domain (IBD), which in T cells is responsible for tethering the HIV-integrase complex to transcriptionally active chromatin. In non-PCa cells, the LEDGF/p75 IBD interacts with transcription complexes, such as Menin-MLL and the c-MYC binding protein JPO2, to promote cell survival. However, the relevance of these and others protein-protein interactions (PPIs) in the context of PCa chemoresistance has never been explored. This study was designed to test the hypothesis that interactions between LEDGF/p75, the c-MYC binding protein JPO2, Menin and MLL in DTX-resistant mCRPC cells contribute to chemoresistance. We demonstrated by immunoblotting a significant co-upregulation of JPO2, c-MYC, Menin, MLL, and LEDGF/p75 in the DTX-resistant PC3-DR and DU145-DR cell lines, compared to the parental, drug sensitive cells. We also observed nuclear co-localization of these proteins by immunofluorescence microscopy and confocal microscopy. Using an immunoprecipitation approach, we confirmed that endogenous JPO2, c-MYC, Menin, and MLL co-immunoprecipitate with LEDGF/p75 in the DTX-resistant PCa cell lines. We are extending these studies to other known interacting partners of LEDGF/p75 to determine if they are also upregulated in DTX-resistant PCa cells and interact with this protein in the chemoresistance context. In addition, we have initiated studies to evaluate the effects of pharmacologic and genetic inhibition of LEDGF/p75 and its interacting partners on sensitization of DR cells to DTX. We predict that targeting LEDGF/p75 PPIs will disrupt transcriptional activity contributing to DTX resistance. Our goals are to establish the contribution of these PPIs to LEDGF/p75-mediated transactivation of DTX resistance-associated genes, and target these interactions to overcome PCa chemoresistance. Citation Format: Greisha L. Ortiz Hernandez, Evelyn S. Sanchez-Hernández, Carlos A. Casiano. Interaction of LEDGF/p75 with oncogenic transcription factors in docetaxel resistant prostate cancer cells [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4688.

Abstract D117: Differential reactivity and cell migration inhibitory functions of autoantibodies to Enolase 1 from African American and European American men with prostate cancer

Abstract Prostate cancer (PCa) is the second leading cause of cancer-related deaths in the U.S., with African American (AA) men showing a higher mortality than European American (EA) men. While biological determinants contributing to PCa health disparities remain to be clearly established, there is growing evidence of differences in immunobiology between AA and EA patients with PCa. We demonstrated previously, using immunoproteomic profiling of anti-tumor autoantibody responses in AA and EA patients with PCa, that the glycolytic enzyme enolase 1 (ENO1) is the target of an autoantibody response in subsets of these patients. AA patient sera showed immunoreactivity to ENO1 in a panel of PCa cell lines, as detected by immunoblotting, with lack of reactivity in docetaxel (DTX)-resistant PC3 and DU145 cells. By contrast, anti-ENO1 sera from EA patients and a monoclonal anti-ENO1 antibody (MoAB-ENO1) showed immunoreactivity across the same cell line panel, including DTX-resistant cells. We also noted differences in anti-ENO1 reactivity in ELISA and immunoblots of PCa cell lysates between AA-PCa and EA-PCa patients, suggesting a race-related generation of autoantibodies to different ENO1 variants. ENO1 is a surface protein in cancer cells with roles in plasminogen activation, cell migration, and metastasis. Thus, we explored if anti-ENO1 autoantibodies from AA and EA PCa patients exerted different anti-cancer effects against DTX-sensitive and DTX-resistant PCa cells. Using cell migration assays, we observed that anti-ENO1 sera from EA patients and MoAB-ENO1 reduced the migration of DTX-resistant PC3 and DU145 cells but not that of DTX-sensitive cells. This inhibitory effect was intrinsic to the autoantibodies since purified IgG fraction produced similar results. Further, these inhibitory effects were reversed by pre-absorption of anti-ENO1 sera and purified IgG with recombinant human ENO1. Intriguingly, anti-ENO1 sera from AA patients lacked the same inhibitory effects on the migration of DTX-resistant cells, consistent with their lack of immunoreactivity to ENO1 in these cells. In addition, we observed that MoAB-ENO1, which behaves similar to the anti-ENO1 EA sera, decreased viability without evident cell death, measured by MTT assays and imaging analysis, in both DTX-sensitive and DTX-resistant cells, with a more robust effect on the latter. Together, these results suggest that anti-ENO1 autoantibodies from EA-PCa patients may exert a protective effect by decreasing the migration and proliferation of chemoresistant PCa cells. By contrast, anti-ENO1 autoantibodies from AA PCa patients may lack these protective effects, which could contribute to increased cancer cell migration and metastasis. Further studies are needed to dissect the molecular basis for this race-related differential anti-ENO1 immunoreactivity in PCa patients, and exploit the immunotherapeutic potential of anti-ENO1 antibodies for the treatment of chemoresistant PCa. Citation Format: Carlos Diaz-Osterman, Tino Sanchez, Carlos A Casiano. Differential reactivity and cell migration inhibitory functions of autoantibodies to Enolase 1 from African American and European American men with prostate cancer [abstract]. In: Proceedings of the Twelfth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2019 Sep 20-23; San Francisco, CA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2020;29(6 Suppl_2):Abstract nr D117.

Abstract D116: Glucocorticoid receptor interacts with beta-catenin to promote stemness and therapy resistance in prostate cancer cells

Abstract Prostate cancer (PCa) is the most commonly diagnosed male cancer, with men of African ancestry showing a disproportionately high incidence and mortality. There is increasing evidence that glucocorticoid signaling through glucocorticoid receptor (GR) is amplified in African American men due to cumulative life stress, and that GR signaling is a key driver of resistance to androgen-targeted therapy, radiotherapy, and taxane chemotherapy in advanced PCa. Recent studies indicate that GR also promotes in PCa cells the formation of tumorspheres, a property of cancer stem cells (CSC); however, the mechanisms remain unclear. CSCs are intrinsically resistant to therapies due to their low-frequency, expression of transporters and efflux pumps, quiescent cell cycle and metabolic profile. Our previous studies demonstrated that docetaxel (DTX)-resistant PCa cells exhibit increased capacity for CSC-like properties, suggesting that these properties contribute to chemoresistance. Like GR, beta-catenin is overexpressed in metastatic and therapy-resistant tumors, and is considered a key regulator of cancer stemness and androgen-targeted therapy resistance. Thus, we hypothesized that GR may interact with beta-catenin in PCa cells to support stemness and chemoresistance. Using whole-cell and nuclear co-immunoprecipitation, we demonstrated the interaction between GR and beta-catenin in several DTX-sensitive and -resistant PCa cell line pairs. Pharmacological inhibition of GR using the selective inhibitor CORT-108297 with concomitant inhibition of beta-catenin using the small molecule inhibitor MSAB significantly enhanced DTX cytotoxicity in resistant PCa cells grown in both adherent and spheroid cultures. The BET bromodomain inhibitor JQ1, an antagonist of enhancer-mediated GR upregulation, also significantly reduced tumorsphere formation and stemness in DTX-resistant PCa cells. In order to gain insights into transcriptomic profiles activated by GR signaling that may contribute to stemness and therapy resistance, we performed RNA sequencing in a racially diverse panel of PCa cell lines (MDA-PCa-2b, VCaP, 22RV1, and PC3) treated with and without dexamethasone, a potent glucocorticoid. We observed that the African American cell line MDA-PCa-2b yielded the largest number of differentially regulated genes, perhaps due to the ability of dexamethasone to signal through both AR and GR in this particular cell line. RNAseq data is currently being mined and validated in cellular models treated with glucocorticoids or androgens, in the presence or absence of anti-GR or anti-androgen inhibitors, in order to identify GR-regulated genes. Our results offer novel insights into mechanisms by which GR signaling may influence tumorsphere formation and stemness, and suggest that combinatorial targeting of GR and beta-catenin could be a promising therapeutic strategy to overcome PCa therapy resistance and consequently reduce PCa mortality and its racial disparities. Citation Format: Shannalee R Martinez, Evelyn S Sanchez-Hernandez, Xin Chen, Alfonso M Duran, Charles H Wang, Carlos A Casiano. Glucocorticoid receptor interacts with beta-catenin to promote stemness and therapy resistance in prostate cancer cells [abstract]. In: Proceedings of the Twelfth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2019 Sep 20-23; San Francisco, CA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2020;29(6 Suppl_2):Abstract nr D116.

Repurposing antimuscarinics to treat lethal chemoresistant prostate and lung cancers.

e15636 Background: Advanced non-small cell lung cancer (NSCLC) and prostate cancer (PCa) remain leading causes of cancer-related deaths in the United States and worldwide. The current study investigates the ability of antimuscarinics to resensitize chemotherapy resistant NSCLC and PCa to chemotherapy-induced apoptosis. Methods: The chemotherapy drug docetaxel (DTX) resistant human NSCLC and PCa cell cultures were established to recapitulate clinical emergence of chemoresistance. These cultures were used to harvest total RNA and protein for qPCR and Western blot analyses, respectively. DTX’s ability to induce apoptosis was measured with crystal violet survival assay and TUNEL assay. Results: DTX-resistant NSCLC (A549R) and PCa (DU145R) cells show increased expression of the muscarinic acetylcholine receptors 1 and 3 (CHRM1 / CHRM3). Treatment of these DTX-resistant cells with the CHRM1 antagonist dicyclomine (Dic) or the CHRM3 antagonist darifenacin (Dari) resensitize these cells to DTX-induced cell death. This treatment repurposes Dic and Dari, which are currently used in the clinic to treat irritable-bowel syndrome and overactive bladder, respectively. Decreased cell survival was observed with crystal violet survival assay, which led to increased cell death at a lower concentration of DTX compared to cells treated with DTX alone (A549R [DTX IC50]: DTX = No response, Dic + DTX = 5.2 nM, Dari + DTX = 2.2 nM / DU145R [DTX IC50]: DTX = No response, Dic + DTX = 4.2 nM, Dari + DTX = 1.4 nM). Furthermore, cells treated with Dic + DTX or Dari + DTX show increased apoptosis measured by TUNEL assay compared to cells treated with DTX alone (A549R [TUNEL positive %]: DTX = 0.9%, Dic + DTX = 22.2%, Dari + DTX = 88.2% / DU145R [TUNEL positive %]: DTX = 3.6%, Dic + DTX = 96.4%, Dari + DTX = 90.1%). Conclusions: We show that chemoresistant NSCLC and PCa have high expression of CHRM1 and CHRM3 and that antimuscarinics effectively resensitize these lethal forms of cancer to chemotherapeutics. Our data support the rationale of repurposing these therapies to treat chemoresistant NSCLC and PCa, allowing quick entry into a Phase II clinical trial and further translation into clinical practice, in a more cost-effective and less financially risky way, to benefit cancer patients.

TUBB3 Reverses Resistance to Docetaxel and Cabazitaxel in Prostate Cancer.

Recent studies have reported that TUBB3 overexpression is involved in docetaxel (DTX) resistance in prostate cancer (PCa). The aim of this study was to clarify the role of TUBB3 in DTX and cabazitaxel (CBZ) resistance, and cross-resistance between DTX and CBZ in PCa. We analyzed the effect of TUBB3 knockdown on DTX and CBZ resistance and examined the interaction between TUBB3 and PTEN. We also investigated the role of phosphoinositide 3-kinases (PI3K) inhibitor (LY294002) in DTX and CBZ resistance. TUBB3 expression was upregulated in DTX-resistant and CBZ-resistant cells. TUBB3 knockdown re-sensitized DTX-resistant cells to DTX and CBZ-resistant cells to CBZ. Additionally, TUBB3 knockdown re-sensitized DTX-resistant cell lines to CBZ, indicating that TUBB3 mediates cross-resistance between DTX and CBZ. Knockdown of TUBB3 enhanced PTEN expression, and PTEN knockout enhanced TUBB3 expression. LY294002 suppressed TUBB3 expression in DTX-resistant and CBZ-resistant cell lines. LY294002 re-sensitized DTX-resistant cell lines to DTX and CBZ-resistant cell lines to CBZ. These results suggest that TUBB3 is involved in DTX resistance and CBZ resistance. A combination of LY294002/DTX and that of LY294002/CBZ could be potential strategies for PCa treatment.

Abstract 4395: The cMYC-associated transcription factor JPO2 is upregulated in taxane resistant prostate cancer cells and interacts with the stress oncoprotein LEDGF/p75

Abstract Prostate Cancer (PCa) progression leads to an advanced stage called metastatic castration PCa (mCRPC), for which currently there is no cure in spite of advances in treatment with new generation androgen deprivation drugs and chemotherapy with taxanes such as docetaxel (DTX). Our group demonstrated previously that the stress oncoprotein Lens Epithelium Derived Growth Factor of 75 kD (LEDGF/p75) is upregulated in clinical prostate tumors and contributes to DTX-resistance in mCRPC cells. However, little is known about the molecular mechanisms by which LEDGF/p75 promotes taxane resistance. The C-terminus of LEDGF/p75 contains a domain called the Integrase Binding Domain (IBD), which in T cells is responsible for tethering the HIV-integrase complex to transcriptionally active chromatin. In cancer cells, the LEDGF/p75 IBD interacts with oncogenic transcription complexes, such as Menin-MLL and the cMYC binding protein JPO2, to promote cell survival. However, the relevance of these protein-protein interactions (PPIs) in PCa and chemoresistance has never been explored. This study is designed to characterize the interaction between LEDGF/p75 and JPO2 in the DTX-resistant mCRPC cell lines PC3-DR and DU145-DR, and determine if this interaction contributes to drug resistance. Also, we want to target this interaction with repurposed HIV-based small molecule inhibitors (SMI’s) of LEDGF/p75, which target the IBD, to abrogate this resistance. We demonstrated by immunoblotting a significant 2-fold co-upregulation of JPO2 and LEDGF/p75 in the DTX-resistant PCa cells. We also observed the nuclear co-localization of these proteins by immunofluorescence microscopy. Using an immunoprecipitation approach, we confirmed that endogenous JPO2 and LEDGF/p75 co-immunoprecipitate in the DTX-resistant PCa cells. In addition, we initiated studies to evaluate SMIs originally designed to target the interaction between LEDGF/p75 and HIV-IN, for their efficacy in sensitizing resistant cells to DTX. After screening over 100 candidate inhibitors, we selected a set of SMIs which demonstrated a 20-30% decrease in viability in DTX-resistant cells when used alone, and 40-60% when used in combination with DTX. Studies are in progress to determine if these SMIs bind to LEDGF/p75 and inhibit its interaction with JPO2 and other oncoproteins. We predict that targeting LEDGF/p75 PPIs with HVI-based SMIs will disrupt transcriptional activity contributing to DTX resistance. Our goals are to establish the contribution of PPIs to LEDGF/p75-mediated transactivation of stress oncoproteins, and target these interactions to overcome PCa chemoresistance. Citation Format: Greisha L. Ortiz Hernandez, Shannalee Martinez, Evelyn Sanchez-Hernandez, Leslimar Rios-Colon, Christina Cajigas-DuRoss, Tino Sanchez, Nouri Neamati, Carlos A. Casiano. The cMYC-associated transcription factor JPO2 is upregulated in taxane resistant prostate cancer cells and interacts with the stress oncoprotein LEDGF/p75 [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 4395.

Abstract LB-260: Role of the glucocorticoid receptor/beta-catenin interaction in prostate cancer stem cell survival and chemoresistance

Abstract Prostate cancer (PCa) is the second leading cause of cancer deaths in U.S. men, disproportionately affecting African American men and certain Hispanic/Latino populations. Patients with advanced PCa are treated with androgen deprivation therapy (ADT) and docetaxel (DTX)-based chemotherapy with effective but transient results due to therapy resistance. While the role of glucocorticoid receptor (GR) in promoting ADT resistance has been well characterized, comparatively little is known about its contribution to PCa stemness and chemoresistance. Our group demonstrated recently that DTX-resistance is associated with upregulation of a stemness transcriptomic program and enhanced cancer stem cell (CSC) properties in PCa cells. We also demonstrated that GR signaling upregulates the DTX-resistance associated proteins Clusterin and LEDGF/p75 in a panel of PCa cells. The proto-oncogene β-catenin promotes CSC survival in many cancers, including PCa, and several studies have demonstrated a crosstalk between AR and β-catenin signaling pathways contributing to ADT resistance. Given the structural similarities between AR and GR and the importance of GR in therapy resistance, this study was designed to investigate the interaction between GR and β-catenin and its contribution to CSC survival and DTX resistance. Using a panel of PCa cell lines including PC3, DU145, 22rv1, and their corresponding DTX-resistant cell lines, we showed by quantitative immunoblotting that GR is upregulated and β-catenin is activated in PC3 and 22rv1 DTX-resistant cells compared to sensitive cells. Co-immunoprecipitation studies revealed interaction between endogenous GR and β-catenin in these cells. We next assessed the effect of the potent GR ligand dexamethasone (Dex) on CSC maintenance, and observed that Dex treatment of PC3 cells increased tumorsphere number and expression of established CSC markers measured by multicolor flow cytometry. To identify potential GR target genes that could mediate the acquisition of CSC properties and DTX resistance, we performed RNA-sequencing analysis in four different Dex-treated and -untreated PCa cell lines. This analysis revealed several candidate GR target genes differentially regulated in a cell-type dependent manner. To determine the effects of the GR/β-catenin interaction on downstream GR target genes and β-catenin target genes, we performed immunoblotting of specific candidate target genes on lysates from cells treated with Dex alone or in combination with COR-10829 (selective GR inhibitor, and MSAB (β-catenin inhibitor). Interestingly, we also observed that the dual blockade of GR and β-catenin markedly reduced tumorsphere formation in DTX-resistant cells, a phenomenon not observed with either GR or β-catenin inhibition alone. In summary, our findings revealed a novel interaction between GR and β-catenin in PCa cells, and suggest that co-targeting the GR/β-catenin signaling axis in advanced PCa patients could be a potential strategy to overcome therapy resistance. Citation Format: Shannalee R. Martinez, Carlos J. Diaz Osterman, Xin S. Chen, Charles Wang, Lubo Zhang, Carlos A. Casiano. Role of the glucocorticoid receptor/beta-catenin interaction in prostate cancer stem cell survival and chemoresistance [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 LB-260.