Pulsed Photothermal Therapy of Solid Tumors as a Precondition for Immunotherapy

Photothermal therapy (PTT) refers to the use of plasmonic nanoparticles to convert electromagnetic radiation in the near infrared region to heat and kill tumor cells. Continuous wave lasers have been used clinically to induce PTT, but the treatment is associated with heat-induced tissue damage that limits usability. Here, the engineering and validation of a novel long-pulsed laser device able to induce selective and localized mild hyperthermia in tumors while reducing the heat affected zone and unwanted damage to surrounding tissue are reported. Long-pulsed PTT induces acute necrotic cell death in heat affected areas and the release of tumor associated antigens. This antigen release triggers maturation and stimulation of CD80/CD86 in dendritic cells in vivo that primes a cytotoxic T cell response. Accordingly, long-pulsed PTT enhances the therapeutic effects of immune checkpoint inhibition and increases survival of mice with bladder cancer. Combined, the data promote long-pulsed PTT as a safe and effective strategy for enhancing therapeutic responses to immune checkpoint inhibitors while minimizing unwanted tissue damage.

Internalization and trafficking of CSPG-bound recombinant VAR2CSA lectins in cancer cells

Proteoglycans are proteins that are modified with glycosaminoglycan chains. Chondroitin sulfate proteoglycans (CSPGs) are currently being exploited as targets for drug-delivery in various cancer indications, however basic knowledge on how CSPGs are internalized in tumor cells is lacking. In this study we took advantage of a recombinant CSPG-binding lectin VAR2CSA (rVAR2) to track internalization and cell fate of CSPGs in tumor cells. We found that rVAR2 is internalized into cancer cells via multiple internalization mechanisms after initial docking on cell surface CSPGs. Regardless of the internalization pathway used, CSPG-bound rVAR2 was trafficked to the early endosomes in an energy-dependent manner but not further transported to the lysosomal compartment. Instead, internalized CSPG-bound rVAR2 proteins were secreted with exosomes to the extracellular environment in a strictly chondroitin sulfate-dependent manner. In summary, our work describes the cell fate of rVAR2 proteins in tumor cells after initial binding to CSPGs, which can be further used to inform development of rVAR2-drug conjugates and other therapeutics targeting CSPGs.

Cancer Cells Employ Nuclear Caspase-8 to Overcome the p53-Dependent G2/M Checkpoint through Cleavage of USP28

Cytosolic caspase-8 is a mediator of death receptor signaling. While caspase-8 expression is lost in some tumors, it is increased in others, indicating a conditional pro-survival function of caspase-8 in cancer. Here, we show that tumor cells employ DNA-damage-induced nuclear caspase-8 to override the p53-dependent G2/M cell-cycle checkpoint. Caspase-8 is upregulated and localized to the nucleus in multiple human cancers, correlating with treatment resistance and poor clinical outcome. Depletion of caspase-8 causes G2/M arrest, stabilization of p53, and induction of p53-dependent intrinsic apoptosis in tumor cells. In the nucleus, caspase-8 cleaves and inactivates the ubiquitin-specific peptidase 28 (USP28), preventing USP28 from de-ubiquitinating and stabilizing wild-type p53. This results in de facto p53 protein loss, switching cell fate from apoptosis toward mitosis. In summary, our work identifies a non-canonical role of caspase-8 exploited by cancer cells to override the p53-dependent G2/M cell-cycle checkpoint.

Ivermectin inhibits HSP27 and potentiates efficacy of oncogene targeting in tumor models

HSP27 is highly expressed in, and supports oncogene addiction of, many cancers. HSP27 phosphorylation is a limiting step for activation of this protein and a target for inhibition, but its highly disordered structure challenges rational structure-guided drug discovery. We performed multistep biochemical, structural, and computational experiments to define a spherical 24-monomer complex composed of 12 HSP27 dimers with a phosphorylation pocket flanked by serine residues between their N-terminal domains. Ivermectin directly binds this pocket to inhibit MAPKAP2-mediated HSP27 phosphorylation and depolymerization, thereby blocking HSP27-regulated survival signaling and client-oncoprotein interactions. Ivermectin potentiated activity of anti-androgen receptor and anti-EGFR drugs in prostate and EGFR/HER2-driven tumor models, respectively, identifying a repurposing approach for cotargeting stress-adaptive responses to overcome resistance to inhibitors of oncogenic pathway signaling.

Regulation of eIF4F Translation Initiation Complex by the Peptidyl Prolyl Isomerase FKBP7 in Taxane-resistant Prostate Cancer

PURPOSE

Targeted therapies that use the signaling pathways involved in prostate cancer are required to overcome chemoresistance and improve treatment outcomes for men. Molecular chaperones play a key role in the regulation of protein homeostasis and are potential targets for overcoming chemoresistance.Experimental Design: We established 4 chemoresistant prostate cancer cell lines and used image-based high-content siRNA functional screening, based on gene-expression signature, to explore mechanisms of chemoresistance and identify new potential targets with potential roles in taxane resistance. The functional role of a new target was assessed by in vitro and in vivo silencing, and mass spectrometry analysis was used to identify its downstream effectors.

RESULTS

We identified FKBP7, a prolyl-peptidyl isomerase overexpressed in docetaxel-resistant and in cabazitaxel-resistant prostate cancer cells. This is the first study to characterize the function of human FKBP7 and explore its role in cancer. We discovered that FKBP7 was upregulated in human prostate cancers and its expression correlated with the recurrence observed in patients receiving docetaxel. FKBP7 silencing showed that FKBP7 is required to maintain the growth of chemoresistant cell lines and chemoresistant tumors in mice. Mass spectrometry analysis revealed that FKBP7 interacts with eIF4G, a component of the eIF4F translation initiation complex, to mediate the survival of chemoresistant cells. Using small-molecule inhibitors of eIF4A, the RNA helicase component of eIF4F, we were able to kill docetaxel- and cabazitaxel-resistant cells.

CONCLUSIONS

Targeting FKBP7 or the eIF4G-containing eIF4F translation initiation complex could be novel therapeutic strategies to eradicate taxane-resistant prostate cancer cells.

Abstract 5229: Expression and regulation of chondroitin sulfate in prostate cancer

Increased levels of chondroitin sulfate (CS) glycosaminoglycans (GAGs) in prostate cancer (PC) have been observed for more than three decades. In 1984, De Klerk et al. noted that hyperplastic and cancerous prostate contained elevated levels of CS while other GAGs, like heparin sulfate (HS), were decreased. Chondroitin sulfate-modified proteoglycans (CSPGs), such as versican or tomoregulin (TENB2), have been promoted as PC progression markers. They have been associated with cell attachment to the matrix, the metastatic phenotype, disease progression, and androgen independence. Functionally, pericellular enrichment of CSPGs in the PC microenvironment promotes cell motility. Our team has discovered that human tumors display high levels of a specific highly sulfate type of CS normally restricted to placental and fetal tissue compartment. This "oncofetal" CS (ofCS) GAG can be conveniently detected and targeted using recombinant CS-binding VAR2CSA (rVAR2) lectins, derived from the malaria parasite Plasmodium falciparum. Recently, we identified chondroitin sulfate biosynthesis as being controlled by androgens in PC, modulating expression of the CHST11 and CHST13 carbon-4 GalNAc sulfotransferases. We established that these enzymes are under direct control of the androgen receptor (AR), regulating synthesis of the cancer-associated ofCS-modification on CSPGs. Glycosylation has a key role in many important biologic processes in cancer including cell differentiation. We identified CHST11 to be highly increased in high-risk neuroendocrine prostate cancer (NEPC) both in vitro, in vivo, and in situ. Moreover, cells that expressed neuroendocrine markers showed higher level of sulfation and ofCS. Our work reveals that alterations in GAG signatures regulated by AR might be responsible for progression neuroendocrine differentiation in prostate cancer. The prostate is an abundant secretor of PGs, and tumor-specific alterations in GAG signatures such as ofCS therefore constitute an untapped reservoir of potential biomarkers to be exploited as therapeutic targets.

Citation Format: Nader Al Nakouzi, Chris Kedong Wang, Irina Nelepcu, Coralie Crouzit, Noushin Nabavi, Amal Almami, Htoo Zarni Oo, Thomas Mandel Clausen, Tobias Gustavsson, Ali Salanti, Mads Daugaard. Expression and regulation of chondroitin sulfate in prostate cancer [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 5229.

Non-canonical activation of hedgehog in prostate cancer cells mediated by the interaction of transcriptionally active androgen receptor proteins with Gli3

Hedgehog (Hh) is an oncogenic signaling pathway that regulates the activity of Gli transcription factors. Canonical Hh is a Smoothened- (Smo-) driven process that alters the post-translational processing of Gli2/Gli3 proteins. Though evidence supports a role for Gli action in prostate cancer (PCa) cell growth and progression, there is little indication that Smo is involved. Here we describe a non-canonical means for activation of Gli transcription in PCa cells mediated by the binding of transcriptionally-active androgen receptors (ARs) to Gli3. Androgens stimulated reporter expression from a Gli-dependent promoter in a variety of AR + PCa cells and this activity was suppressed by an anti-androgen, Enz, or by AR knockdown. Androgens also upregulated expression of endogenous Gli-dependent genes. This activity was associated with increased intranuclear binding of Gli3 to AR that was antagonized by Enz. Fine mapping of the AR binding domain on Gli2 showed that AR recognizes the Gli protein processing domain (PPD) in the C-terminus. Mutations in the arginine-/serine repeat elements of the Gli2 PPD involved in phosphorylation and ubiquitinylation blocked the binding to AR. β-TrCP, a ubiquitin ligase that recognizes the Gli PPD, competed with AR for binding to this site. AR binding to Gli3 suppressed its proteolytic processing to the Gli3 repressor form (Gli3R) whereas AR knockdown increased Gli3R. Both full-length and truncated ARs were able to activate Gli transcription. Finally, we found that an ARbinding decoy polypeptide derived from the Gli2 C-terminus can compete with Gli3 for binding to AR. Exogenous overexpression of this decoy suppressed Gli transcriptional activity in PCa cells. Collectively, this work identifies a novel pathway for non-canonical activation of Hh signaling in PCa cells and identifies a means for interference that may have clinical relevance for PCa patients.

SEMA3C drives cancer growth by transactivating multiple receptor tyrosine kinases via Plexin B1

Growth factor receptor tyrosine kinase (RTK) pathway activation is a key mechanism for mediating cancer growth, survival, and treatment resistance. Cognate ligands play crucial roles in autocrine or paracrine stimulation of these RTK pathways. Here, we show SEMA3C drives activation of multiple RTKs including EGFR, ErbB2, and MET in a cognate ligand-independent manner via Plexin B1. SEMA3C expression levels increase in castration-resistant prostate cancer (CRPC), where it functions to promote cancer cell growth and resistance to androgen receptor pathway inhibition. SEMA3C inhibition delays CRPC and enzalutamide-resistant progression. Plexin B1 sema domain-containing:Fc fusion proteins suppress RTK signaling and cell growth and inhibit CRPC progression of LNCaP xenografts post-castration in vivo SEMA3C inhibition represents a novel therapeutic strategy for treatment of advanced prostate cancer.

Targeting Binding Function-3 of the Androgen Receptor Blocks Its Co-Chaperone Interactions, Nuclear Translocation, and Activation

The development of new antiandrogens, such as enzalutamide, or androgen synthesis inhibitors like abiraterone has improved patient outcomes in the treatment of advanced prostate cancer. However, due to the development of drug resistance and tumor cell survival, a majority of these patients progress to the refractory state of castration-resistant prostate cancer (CRPC). Thus, newer therapeutic agents and a better understanding of their mode of action are needed for treating these CRPC patients. We demonstrated previously that targeting the Binding Function 3 (BF3) pocket of the androgen receptor (AR) has great potential for treating patients with CRPC. Here, we explore the functional activity of this site by using an advanced BF3-specific small molecule (VPC-13566) that was previously reported to effectively inhibit AR transcriptional activity and to displace the BAG1L peptide from the BF3 pocket. We show that VPC-13566 inhibits the growth of various prostate cancer cell lines, including an enzalutamide-resistant cell line, and reduces the growth of AR-dependent prostate cancer xenograft tumors in mice. Importantly, we have used this AR-BF3 binder as a chemical probe and identified a co-chaperone, small glutamine-rich tetratricopeptide repeat (TPR)-containing protein alpha (SGTA), as an important AR-BF3 interacting partner. Furthermore, we used this AR-BF3-directed small molecule to demonstrate that inhibition of AR activity through the BF3 functionality can block translocation of the receptor into the nucleus. These findings suggest that targeting the BF3 site has potential clinical importance, especially in the treatment of CRPC and provide novel insights on the functional role of the BF3 pocket. Mol Cancer Ther; 15(12); 2936-45. ©2016 AACR.

Oncofetal Chondroitin Sulfate Glycosaminoglycans Are Key Players in Integrin Signaling and Tumor Cell Motility

Many tumors express proteoglycans modified with oncofetal chondroitin sulfate glycosaminoglycan chains (ofCS), which are normally restricted to the placenta. However, the role of ofCS in cancer is largely unknown. The function of ofCS in cancer was analyzed using the recombinant ofCS-binding VAR2CSA protein (rVAR2) derived from the malaria parasite, Plasmodium falciparum We demonstrate that ofCS plays a key role in tumor cell motility by affecting canonical integrin signaling pathways. Binding of rVAR2 to tumor cells inhibited the interaction of cells with extracellular matrix (ECM) components, which correlated with decreased phosphorylation of Src kinase. Moreover, rVAR2 binding decreased migration, invasion, and anchorage-independent growth of tumor cells in vitro Mass spectrometry of ofCS-modified proteoglycan complexes affinity purified from tumor cell lines on rVAR2 columns revealed an overrepresentation of proteins involved in cell motility and integrin signaling, such as integrin-β1 (ITGB1) and integrin-α4 (ITGA4). Saturating concentrations of rVAR2 inhibited downstream integrin signaling, which was mimicked by knockdown of the core chondroitin sulfate synthesis enzymes β-1,3-glucuronyltransferase 1 (B3GAT1) and chondroitin sulfate N-acetylgalactosaminyltransferase 1 (CSGALNACT1). The ofCS modification was highly expressed in both human and murine metastatic lesions in situ and preincubation or early intravenous treatment of tumor cells with rVAR2 inhibited seeding and spreading of tumor cells in mice. This was associated with a significant increase in survival of the animals. These data functionally link ofCS modifications with cancer cell motility and further highlights ofCS as a novel therapeutic cancer target.

IMPLICATIONS

The cancer-specific expression of ofCS aids in metastatic phenotypes and is a candidate target for therapy. Mol Cancer Res; 14(12); 1288-99. ©2016 AACR.

Clusterin knockdown sensitizes prostate cancer cells to taxane by modulating mitosis

Clusterin (CLU) is a stress‐activated molecular chaperone that confers treatment resistance to taxanes when highly expressed. While CLU inhibition potentiates activity of taxanes and other anti‐cancer therapies in preclinical models, progression to treatment‐resistant disease still occurs implicating additional compensatory survival mechanisms. Taxanes are believed to selectively target cells in mitosis, a complex mechanism controlled in part by balancing antagonistic roles of Cdc25C and Wee1 in mitosis progression. Our data indicate that CLU silencing induces a constitutive activation of Cdc25C, which delays mitotic exit and hence sensitizes cancer cells to mitotic‐targeting agents such as taxanes. Unchecked Cdc25C activation leads to mitotic catastrophe and cell death unless cells up‐regulate protective mechanisms mediated through the cell cycle regulators Wee1 and Cdk1. In this study, we show that CLU silencing induces a constitutive activation of Cdc25C via the phosphatase PP2A leading to relief of negative feedback inhibition and activation of Wee1‐Cdk1 to promote survival and limit therapeutic efficacy. Simultaneous inhibition of CLU‐regulated cell cycle effector Wee1 may improve synergistic responses of biologically rational combinatorial regimens using taxanes and CLU inhibitors.

Targeting Human Cancer by a Glycosaminoglycan Binding Malaria Protein

Plasmodium falciparum engineer infected erythrocytes to present the malarial protein, VAR2CSA, which binds a distinct type chondroitin sulfate (CS) exclusively expressed in the placenta. Here, we show that the same CS modification is present on a high proportion of malignant cells and that it can be specifically targeted by recombinant VAR2CSA (rVAR2). In tumors, placental-like CS chains are linked to a limited repertoire of cancer-associated proteoglycans including CD44 and CSPG4. The rVAR2 protein localizes to tumors in vivo and rVAR2 fused to diphtheria toxin or conjugated to hemiasterlin compounds strongly inhibits in vivo tumor cell growth and metastasis. Our data demonstrate how an evolutionarily refined parasite-derived protein can be exploited to target a common, but complex, malignancy-associated glycosaminoglycan modification.

Generation 2.5 antisense oligonucleotides targeting the androgen receptor and its splice variants suppress enzalutamide-resistant prostate cancer cell growth

PURPOSE

Enzalutamide (ENZ) is a potent androgen receptor (AR) antagonist with activity in castration-resistant prostate cancer (CRPC); however, progression to ENZ-resistant (ENZ-R) CRPC frequently occurs with rising serum PSA levels, implicating AR full-length (ARFL) or variants (AR-Vs) in disease progression.

EXPERIMENTAL DESIGN

To define functional roles of ARFL and AR-Vs in ENZ-R CRPC, we designed 3 antisense oligonucleotides (ASO) targeting exon-1, intron-1, and exon-8 in AR pre-mRNA to knockdown ARFL alone or with AR-Vs, and examined their effects in three CRPC cell lines and patient-derived xenografts.

RESULTS

ENZ-R-LNCaP cells express high levels of both ARFL and AR-V7 compared with CRPC-LNCaP; in particular, ARFL levels were approximately 12-fold higher than AR-V7. Both ARFL and AR-V7 are highly expressed in the nuclear fractions of ENZ-R-LNCaP cells even in the absence of exogenous androgens. In ENZ-R-LNCaP cells, knockdown of ARFL alone, or ARFL plus AR-Vs, similarly induced apoptosis, suppressed cell growth and AR-regulated gene expression, and delayed tumor growth in vivo. In 22Rv1 cells that are inherently ENZ-resistant, knockdown of both ARFL and AR-Vs more potently suppressed cell growth, AR transcriptional activity, and AR-regulated gene expression than knockdown of ARFL alone. Exon-1 AR-ASO also inhibited tumor growth of LTL-313BR patient-derived CRPC xenografts.

CONCLUSIONS

These data identify the AR as an important driver of ENZ resistance, and while the contributions of ARFL and AR-Vs can vary across cell systems, ARFL is the key driver in the ENZ-R LNCaP model. AR targeting strategies against both ARFL and AR-Vs is a rational approach for AR-dependent CRPC.

Targeting CDC25C, PLK1 and CHEK1 to overcome Docetaxel resistance induced by loss of LZTS1 in prostate cancer

Docetaxel is used as a standard treatment in patients with metastatic castration-resistant prostate cancer. However, a large subset of patients develops resistance. Understanding resistance mechanisms, which are largely unknown, will allow identification of predictive biomarkers and therapeutic targets. We established resistant IGR-CaP1 prostate cancer cell lines for different doses of Docetaxel. We investigated gene expression profiles by microarray analyses in these cell lines and generated a signature of 99 highly differentially expressed genes potentially implicated in chemoresistance. We focused on the role of the cell cycle regulator LZTS1, which was under-expressed in the Docetaxel-resistant cell lines, its inhibition resulting from the promoter methylation. Knockdown of LZTS1 in parental cells with siRNA showed that LZTS1 plays a role in the acquisition of the resistant phenotype. Furthermore, we observed that targeting CDC25C, a partner of LZTS1, with the NSC663284 inhibitor specifically killed the Docetaxel-resistant cells. To further investigate the role of CDC25C, we used inhibitors of the mitotic kinases that regulate CDC25C. Inhibition of CHEK1 and PLK1 induced growth arrest and cell death in the resistant cells. Our findings identify an important role of LZTS1 through its regulation of CDC25C in Docetaxel resistance in prostate cancer and suggest that CDC25C, or the mitotic kinases CHEK1 and PLK1, could be efficient therapeutic targets to overcome Docetaxel resistance.

Abstract 4062: Clusterin downregulation sensitize prostate cancer cells to taxane by modulating mitosis

Clusterin (CLU) is a stress-activated molecular chaperone closely linked to treatment resistance and cancer progression. CLU is a novel therapeutic anti-cancer target with both preclinical and phase II clinical proof of concept using the antisense OGX-011 inhibitor; phase III clinical trials of combination docetaxel + OGX-011 are underway.

Cytotoxic chemotherapy drugs like taxane are believed to gain selectivity by targeting cells that are in mitosis. When cultured cancer cells are treated with taxane, only cells that enter mitosis are killed or rendered senescent. Quiescent cells or cycling cells that do not reach mitosis during drug exposure are spared. In this sense, sentisizing cells to taxane can occur through mitosis regulation.

In this study, we show that CLU downregulation enhances cytotoxicity of the new generation taxane cabazitaxol. Treatment of PC3 human prostate cancer cells with cabazitaxol induces G2/M arrest followed by mitotic death. Downregulation of CLU accelerated these G2/M associated events and resulted in reduced cabazitaxol EC50 and clonogenic survival upon cabazitaxol treatment. To investigate the mechanisms that allow CLU deficient cells to respond to taxane and examine whether this response is linked to a role of CLU in the control of cell cycle progression, we knocked down CLU expression in PC3 and LNCaP cells and found an accumulation of cells in G2/M phase and a reduction in cell growth. The screening of different cell cycle effectors after CLU downregulation in different cell lines and xenografts shows that CLU specifically regulates Cdc25C, while the two other Cdc25 isoforms, A and B, are not affected. Interestingly Cdc25C is a key regulator of mitosis initiation and exit. Importantly, we show that Cdc25C and CLU expression negatively correlate in prostate cancer cell lines, xenografts and human biopsies. When CLU is down regulated, Cdc25C transcription increased resulting in protein accumulation; as a consequence, cells showed G2/M blockage and slower mitotic progression. Accordingly, we suggest that down regulation of CLU alters sensitivity to taxane by modulating exit from mitosis, which is controlled by Cdc25C.

Citation Format: Nader Al Nakouzi, Eliana Beraldi, Stuart Shepherd, Yohann Loriot, Soojin Kim, Lauren Leichmann, Amina Zoubeidi, Martin E Gleave. Clusterin downregulation sensitize prostate cancer cells to taxane by modulating mitosis. [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 4062. doi:10.1158/1538-7445.AM2013-4062

Abstract 956: Role of the cell cycle regulator LZTS1 in docetaxel resistance of prostate cancer cells and overcoming the docetaxel resistance by cell cycle pharmacological inhibitors

Background: Docetaxel is the standard treatment for metastatic castration-resistant prostate cancer (CRPC) since 2004 and overall survival benefit in CRPC has been demonstrated in docetaxel-treated patients. In spite of this benefit, a drug resistance is eventually observed in all patients, leaving few therapeutic options. Therefore, it is crucial to identify predictive markers that enable selection of patients who will respond to treatment.

Methods: Three docetaxel-resistant prostate cancer cell lines (LNCaP, PC3 and IGR-CaP1) were obtained by continuous exposure to Docetaxel. A high-density genomic profiling by cDNA microarrays (Agilent technologies) was performed to compare sensitive and chemoresistant cell lines and a signature of 99 highly differentially expressed genes (with Fold Change >5) potentially implicated in chemoresistance was generated.

Results: We focused on the role of the cell cycle regulator LZTS1, which was strongly under-expressed in all the docetaxel-resistant cell lines. This underexpression was due to a stretch of 20 highly methylated CpGs in the region encompassing the exon 1 of the LZTS1 promoter in resistant cells. Knockdown of LZTS1 in IGR-CaP1 parental cells with siRNA showed that LZTS1 plays an important role in the acquisition of the resistant phenotype. Importantly, immunohistochemical staining showed a loss of LZTS1 expression in 33% of diagnostic biopsies obtained from patients with metastatic CRPC. Furthermore, we observed that targeting Cdc25C, a partner of LZTS1, with the Cdc25 pharmacological inhibitor NSC 663284 killed specifically the docetaxel-resistant cells. There are currently no CDC25C inhibitors tested in clinical trials, therefore we are currently investigating the role of other kinases that are involved in the G2/M checkpoint and in the regulation of CDC25C. Importantly, inhibitors of these kinases are currently being assessed in clinical trials. We wish to determine if targeting CDC25C and/or other kinases could kill docetaxel-resistant cells and if the use of such inhibitors could be a promising strategy to overcome docetaxel resistance in prostate cancer.

Conclusion: High-density microarray genomic analyses comparing chemo-resistant versus sensitive prostate cancer cell lines were used to identify signatures of genes and microRNAs, and signaling pathways potentially implicated in Docetaxel resistance.

Our findings identify an important role of LZTS1 in docetaxel resistance in prostate cancer through its regulation of CDC25C. It could also provide the framework for formulation of novel combined therapies that may improve taxane therapy efficacy or prevent chemoresistance in men with prostate cancer.

Citation Format: Sophie Cotteret, Nader Al Nakouzi, Catherine Gaudin, Frederic Commo, Shanna Rajpar, Sandra Lejuste, Nicolas Martin, Karim Fizazi, Anne Chauchereau. Role of the cell cycle regulator LZTS1 in docetaxel resistance of prostate cancer cells and overcoming the docetaxel resistance by cell cycle pharmacological inhibitors. [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 956. doi:10.1158/1538-7445.AM2013-956

Abstract 3386: Mechanisms of resistance to enzalutamide in LNCaP models

Background

MDV3100 is a potent androgen receptor (AR) antagonist with activity in castration resistant prostate cancer (CRPC); however, progression to MDV3100-resistant (MDV-R) CRPC frequently occurs with rising serum PSA levels suggesting reactivation of AR pathway. We sought to identify AR-based mechanisms of resistance.

Methods

We treated human CRPC LNCAP-derived xenografts with MDV3100 and assessed androgen receptor (AR) levels and localization as well as genomic alterations versus controls. We also generated by selection MDV3100-R LNCaP-derived sub-lines to study mechanisms of resistance to MDV3100.

Results

Serum and tumoral PSA levels were consistently increased in resistant xenogratfs as compared with sensitive xenografts along with AR nuclear localization. MDV3100 did not induce any new mutation in the DNA binding domain and any AR DNA gene amplification. AR full-length (ARfl) and AR-V7 splicing variant were both highly expressed in RNA sequencing compared to CRPC LNCaP xenografts. However, it was no enrichment of AR-V7 versus ARfl in LNCaP MDV-R xenografts. Interestingly, AR was found in the nucleus and constitutively binding to DNA on androgen response element on PSA enhancer as measured by Chromatin immunoprecipitation in MDV-R cell lines compared to CRPC cell lines. These data were translated by increase of AR responsive genes at both mRNA and protein levels.

Conclusions

MDV-R LNCaP cells exhibited AR overexpression without any significant genomic alterations. While MDV3100 induces both ARfl and AR-V7 levels, no enrichment of AR-V7 was detected. Immunofluorescence, CHIP and qPCR studies suggest that ARfl overexpression remains a significant mechanism of resistance to MDV3100 similar to resistance from chronic androgen depletion.

Citation Format: Yohann Loriot, Alexander Wyatt, Nader Al Nakouzi, Eliana Beraldi, Paul Toren, Ka Mun Nip, Martin Gleave, Amina Zoubeidi. Mechanisms of resistance to enzalutamide in LNCaP models. [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 3386. doi:10.1158/1538-7445.AM2013-3386

Note: This abstract was not presented at the AACR Annual Meeting 2013 because the presenter was unable to attend.

A unique galectin signature in human prostate cancer progression suggests galectin-1 as a key target for treatment of advanced disease

Galectins, a family of glycan-binding proteins, influence tumor progression by modulating interactions between tumor, endothelial, stromal, and immune cells. Despite considerable progress in identifying the roles of individual galectins in tumor biology, an integrated portrait of the galectin network in different tumor microenvironments is still missing. We undertook this study to analyze the "galectin signature" of the human prostate cancer microenvironment with the overarching goal of selecting novel-molecular targets for prognostic and therapeutic purposes. In examining androgen-responsive and castration-resistant prostate cancer cells and primary tumors representing different stages of the disease, we found that galectin-1 (Gal-1) was the most abundantly expressed galectin in prostate cancer tissue and was markedly upregulated during disease progression. In contrast, all other galectins were expressed at lower levels: Gal-3, -4, -9, and -12 were downregulated during disease evolution, whereas expression of Gal-8 was unchanged. Given the prominent regulation of Gal-1 during prostate cancer progression and its predominant localization at the tumor-vascular interface, we analyzed the potential role of this endogenous lectin in prostate cancer angiogenesis. In human prostate cancer tissue arrays, Gal-1 expression correlated with the presence of blood vessels, particularly in advanced stages of the disease. Silencing Gal-1 in prostate cancer cells reduced tumor vascularization without altering expression of other angiogenesis-related genes. Collectively, our findings identify a dynamically regulated "galectin-specific signature" that accompanies disease evolution in prostate cancer, and they highlight a major role for Gal-1 as a tractable target for antiangiogenic therapy in advanced stages of the disease.

Abstract 823: Integration of microRNA and gene expression signatures from several models of Docetaxel-resistant prostate cancer cell lines

Background: Docetaxel is the standard treatment for metastatic castration-resistant prostate cancer (CRPC) since 2004 and overall survival benefit in CRPC has been demonstrated in docetaxel-treated patients. In spite of this benefit, a drug resistance is eventually observed in all patients, leaving few therapeutic options. Therefore, it is crucial to identify predictive markers that enable selection of patients who will respond to treatment. Methods: Three docetaxel-resistant prostate cancer cell lines (LNCaP, PC3 and IGR-CaP1) were obtained by continuous exposure to Docetaxel. A high-density genomic profiling by cDNA microarrays (Agilent technologies) was performed to compare sensitive and chemoresistant cell lines. The differential expression levels of 377 microRNAs between resistant and sensitive parental cell lines were measured by Taqman Low Density Array (TLDA, Applied Biosystems technology). Each determination was generated from biological replicates in the absence of drug. Results: A gene expression signature of 583 genes was generated by the bootstrap method (Fold change>2 for each doses of Docetaxel, P value <10-5) in IGR-CaP1 cells. Based on the hypothesis of a biological effect due to increasing drug, a second microarray expression profile was identified using a 5-parameters logistic regression model. This analysis led to the identification of 486 genes associated with resistance to increasing doses of docetaxel (with a P value ≤ 10-5 and a fold change between the first and the last dose of drug ≤ 2). 45 genes were common in the two analyses. A 65 miRs expression profile of docetaxel resistance was determined in all three cell lines using two reference miRs. Interestingly, we identified the under-expression of three clusters of miRs in the resistant cells. In particular, the under-expression of the miR 141-200c cluster was inversely correlated to the over-expression of its target genes Jagged1 (JAG1) and dll1(DLL1), which were identified in the gene expression signature. JAG1 and DLL1 are ligands for Notch receptors, thus we are currently exploring the role of the miR-200c/ZEB1/JAG1 axis and the Notch signalling pathway in mechanisms of Docetaxel resistance. Conclusion: High-density microarray genomic and microRNA profiling analyses comparing chemo-resistant versus sensitive prostate cancer cell lines were used to identify signatures of genes and microRNAs, and signaling pathways potentially implicated in Docetaxel resistance. Ultimately, integration of data from gene and microRNA expression will allow the identification of biomarkers to select patients that could benefit from Docetaxel chemotherapy. It could also provide the framework for formulation of novel therapies that may improve taxane therapy efficacy in men with prostate cancer.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 823. doi:1538-7445.AM2012-823

Stemness markers characterize IGR-CaP1, a new cell line derived from primary epithelial prostate cancer

Deciphering molecular pathways involved in the early steps of prostate oncogenesis requires both in vitro and in vivo models derived from human primary tumors. However the few recognized models of human prostate epithelial cancer originate from metastases. To date, very few models are proposed from primary tumors and immortalizing normal human prostate cells does not recapitulate the natural history of the disease. By culturing human prostate primary tumor cells onto human epithelial extra-cellular matrix, we successfully selected a new prostate cancer cell line, IGR-CaP1, and clonally-derived subclones. IGR-CaP1 cells, that harbor a tetraploid karyotype, high telomerase activity and mutated TP53, rapidly induced subcutaneous xenografts in nude mice. Furthermore, IGR-CaP1 cell lines, all exhibiting negativity for the androgen receptor and PSA, express the specific prostate markers alpha-methylacyl-CoA racemase and a low level of the prostate-specific membrane antigen PSMA, along with the prostate basal epithelial markers CK5 and CK14. More importantly, these clones express high CD44, CD133, and CXCR4 levels associated with high expression of α2β1-integrin and Oct4 which are reported to be prostate cancer stemness markers. RT-PCR data also revealed high activation of the Sonic Hedgehog signalling pathway in these cells. Additionally, the IGR-CaP1 cells possess a 3D sphere-forming ability and a renewal capacity by maintaining their CSC potential after xenografting in mice. As a result, the hormone-independent IGR-CaP1 cellular clones exhibit the original features of both basal prostate tissue and cancer stemness. Tumorigenic IGR-CaP1 clones constitute invaluable human models for studying prostate cancer progression and drug assessment in vitro as well as in animals specifically for developing new therapeutic approaches targeting prostate cancer stem cells.