Phenotype plasticity and altered sensitivity to chemotherapeutic agents in aggressive prostate cancer cells

In 2023, approximately 288,300 new diagnoses of prostate cancer will occur, with 34,700 disease-related deaths. Death from prostate cancer is associated with metastasis, enabled by progression of tumor phenotypes and successful extracapsular extension to reach Batson's venous plexus, a specific route to the spine and brain. Using a mouse-human tumor xenograft model, we isolated an aggressive muscle invasive cell population of prostate cancer, called DU145J7 with a distinct biophysical phenotype, elevated histone H3K27, and increased matrix metalloproteinase 14 expression as compared to the non-aggressive parent cell population called DU145WT. Our goal was to determine the sensitivities to known chemotherapeutic agents of the aggressive cells as compared to the parent population. High-throughput screening was performed with 5,578 compounds, comprising of approved and investigational drugs for oncology. Eleven compounds were selected for additional testing, which revealed that vorinostat, 5-azacitidine, and fimepinostat (epigenetic inhibitors) showed 2.6-to-7.5-fold increases in lethality for the aggressive prostate cancer cell population as compared to the parent, as judged by the concentration of drug to inhibit 50% cell growth (IC50). On the other hand, the DU145J7 cells were 2.2-to-4.0-fold resistant to mitoxantrone, daunorubicin, and gimatecan (topoisomerase inhibitors) as compared to DU145WT. No differences in sensitivities between cell populations were found for docetaxel or pirarubicin. The increased sensitivity of DU145J7 prostate cancer cells to chromatin modifying agents suggests a therapeutic vulnerability occurs after tumor cells invade into and through muscle. Future work will determine which epigenetic modifiers and what combinations will be most effective to eradicate early aggressive tumor populations.

Real-Time Cellular Thermal Shift Assay to Monitor Target Engagement

Determining a molecule's mechanism of action is paramount during chemical probe development and drug discovery. The cellular thermal shift assay (CETSA) is a valuable tool to confirm target engagement in cells for a small molecule that demonstrates a pharmacological effect. CETSA directly detects biophysical interactions between ligands and protein targets, which can alter a protein's unfolding and aggregation properties in response to thermal challenge. In traditional CETSA experiments, each temperature requires an individual sample, which restricts throughput and requires substantial optimization. To capture the full aggregation profile of a protein from a single sample, we developed a prototype real-time CETSA (RT-CETSA) platform by coupling a real-time PCR instrument with a CCD camera to detect luminescence. A thermally stable Nanoluciferase variant (ThermLuc) was bioengineered to withstand unfolding at temperatures greater than 90 °C and was compatible with monitoring target engagement events when fused to diverse targets. Utilizing well-characterized inhibitors of lactate dehydrogenase alpha, RT-CETSA showed significant correlation with enzymatic, biophysical, and other cell-based assays. A data analysis pipeline was developed to enhance the sensitivity of RT-CETSA to detect on-target binding. RT-CETSA technology advances capabilities of the CETSA method and facilitates the identification of ligand-target engagement in cells, a critical step in assessing the mechanism of action of a small molecule.

High-Throughput Cellular Thermal Shift Assay Using Acoustic Transfer of Protein Lysates

Cellular thermal shift assay (CETSA) is a valuable method to confirm target engagement within a complex cellular environment, by detecting changes in a protein's thermal stability upon ligand binding. The classical CETSA method measures changes in the thermal stability of endogenous proteins using immunoblotting, which is low-throughput and laborious. Reverse-phase protein arrays (RPPAs) have been demonstrated as a detection modality for CETSA; however, the reported procedure requires manual processing steps that limit throughput and preclude screening applications. We developed a high-throughput CETSA using an acoustic RPPA (HT-CETSA-aRPPA) protocol that is compatible with 96- and 384-well microplates from start-to-finish, using low speed centrifugation to remove thermally destabilized proteins. The utility of HT-CETSA-aRPPA for guiding structure-activity relationship studies was demonstrated for inhibitors of lactate dehydrogenase A. Additionally, a collection of kinase inhibitors was screened to identify compounds that engage MEK1, a clinically relevant kinase target.

Alpha-Enolase: Emerging Tumor-Associated Antigen, Cancer Biomarker, and Oncotherapeutic Target

Alpha-enolase, also known as enolase-1 (ENO1), is a glycolytic enzyme that “moonlights” as a plasminogen receptor in the cell surface, particularly in tumors, contributing to cancer cell proliferation, migration, invasion, and metastasis. ENO1 also promotes other oncogenic events, including protein-protein interactions that regulate glycolysis, activation of signaling pathways, and resistance to chemotherapy. ENO1 overexpression has been established in a broad range of human cancers and is often associated with poor prognosis. This increased expression is usually accompanied by the generation of anti-ENO1 autoantibodies in some cancer patients, making this protein a tumor associated antigen. These autoantibodies are common in patients with cancer associated retinopathy, where they exert pathogenic effects, and may be triggered by immunodominant peptides within the ENO1 sequence or by posttranslational modifications. ENO1 overexpression in multiple cancer types, localization in the tumor cell surface, and demonstrated targetability make this protein a promising cancer biomarker and therapeutic target. This mini-review summarizes our current knowledge of ENO1 functions in cancer and its growing potential as a cancer biomarker and guide for the development of novel anti-tumor treatments.

High-Throughput Detection of Ligand-Protein Binding Using a SplitLuc Cellular Thermal Shift Assay

The confirmation of a small molecule binding to a protein target can be challenging when switching from biochemical assays to physiologically relevant cellular models. The cellular thermal shift assay (CETSA) is an approach to validate ligand-protein binding in a cellular environment by examining a protein's melting profile which can shift to a higher or lower temperature when bound by a small molecule. Traditional CETSA uses SDS-PAGE and Western blotting to quantify protein levels, a process that is both time consuming and low-throughput when screening multiple compounds and concentrations. Herein, we outline the reagents and methods to implement split Nano Luciferase (SplitLuc) CETSA, which is a reporter-based target engagement assay designed for high-throughput screening in 384- or 1536-well plate formats.

Maternal plasma proteomics in a rat model of pregnancy complications reveals immune and pro-coagulant gene pathway activation

PROBLEM

The Brown Norway (BN) rat is a model of T-helper 2 immune diseases, and also a model of pregnancy disorders that include placental insufficiency, fetal loss, and pre-eclampsia-like symptoms. The aim of this study was to investigate the plasma proteomic/cytokine profile of pregnant BN rats in comparison to that of the Lewis (LEW) rat strain.

METHOD OF STUDY

Plasma proteomics differences were studied at day 13 of pregnancy in pooled plasma samples by differential in-gel electrophoresis, and protein identification was performed by mass spectrometry. Key protein findings and predicted cytokine differences were validated by ELISA using plasma from rats at various pregnancy stages. Proteomics data were used for ingenuity pathway analysis (IPA).

RESULTS

In-gel analysis revealed 74 proteins with differential expression between BN and LEW pregnant dams. ELISA studies confirmed increased maternal plasma levels of complement 4, prothrombin, and C-reactive protein in BN compared to LEW pregnancies. LEW pregnancies showed higher maternal plasma levels of transthyretin and haptoglobin than BN pregnancies. Ingenuity pathway analysis revealed that BN pregnancies are characterized by activation of pro-coagulant, reactive oxygen species, and immune-mediated chronic inflammation pathways, and suggested increased interleukin 6 and decreased transforming growth factor-β1 as potential upstream events. Plasma cytokine analysis revealed that pregnant BN dams have a switch from anti- to pro-inflammatory cytokines with the opposite switch observed in pregnant LEW dams.

CONCLUSION

Brown Norway rats show a maternal pro-inflammatory response to pregnancy that likely contributes to the reproductive outcomes observed in this rat strain.

Abstract 1623: Autoantibodies to human endogenous retrovirus K envelope protein (HERV-K ENV) are associated with features of prostate cancer aggressiveness in African American men

Prostate cancer (PCa) is the most commonly diagnosed cancer and the second leading cause of cancer-related deaths in American men. African-American (AA) men are more likely to develop PCa at a younger age and are twice as likely to die from the disease compared to men from other ethnic/racial backgrounds. Even when normalized with equal access to healthcare, socioeconomic status and familial PCa history, AA men still die disproportionately from PCa. Thus, it is paramount to improve the early detection of aggressive PCa. A cancer patient’s humoral immune response to a tumor offers us a minimally invasive opportunity to detect aggressive cancers before a symptomatic tumor emerges. Previous studies indicate that genes associated with immunity and inflammation are significantly upregulated in prostate tumors from AA men compared to European-American (EA) men, suggesting that there are racial differences in the anti-tumor immune response in patients with PCa. This has prompted our laboratory to evaluate the autoantibody repertoire to tumor-associated antigens (TAA) in ethnically diverse patients. Previous studies showed a higher frequency of autoantibodies to the human endogenous retrovirus K (HERV-K) GAG protein in men with late stage PCa. In addition, investigators in this team reported previously an elevated expression of the envelope (ENV) protein in PCa tumors from AA men compared to PCa tumors from EA men. Given the emerging role of HERV-K in human cancers and the potential use of autoantibodies to the ENV and GAG viral proteins as cancer serum biomarkers and immunotherapeutic tools, we investigated the antibody response to the HERV-K ENV in AA and EA men with and without PCa. Using an enzyme-linked immunosorbent assay (ELISA), we detected a significant increase in the frequency of autoantibodies to HERV-K ENV in AA men with PCa compared to EA men with PCa (N=100, p<0.05) and AA men without PCa (N=100, p<0.0001). The frequency of autoantibodies to ENV was also significantly higher in AA men with stage IV (29%, p<0.0001) and AA men with PCa metastasis (40%, p<0.0001) compared to AA men without PCa or EA men with and without PCa. The immunoreactivity of the sera against ENV was confirmed by immunoblotting. To our knowledge this is the first report of an increased autoantibody frequency to HERV-K ENV in PCa patients and the first report of autoantibodies associated with racial differences in PCa. The observation that these autoantibodies are significantly linked to a more aggressive PCa in AA men is also consistent with previous observation of increased upregulation of HERV-K ENV in prostate tumors from AA men. The biological and clinical significance of anti-HERV-K ENV and GAG autoantibodies in PCa, and the racial differences in their frequency and clinical associations, warrant further investigation.

Citation Format: Tino W. Sanchez, Shannalee R. Martinez, Greisha Ortiz-Hernandez, Evelyn Sanchez-Hernandez, Christopher Montgomery, Benjamin Becerra, Tiffany Dorsey, Feng Wang-Johanning, Stefan Ambs, Carlos A. Casiano. Autoantibodies to human endogenous retrovirus K envelope protein (HERV-K ENV) are associated with features of prostate cancer aggressiveness in African American men [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 1623.

Targeting the stress oncoprotein LEDGF/p75 to sensitize chemoresistant prostate cancer cells to taxanes

Prostate cancer (PCa) is associated with chronic prostate inflammation resulting in activation of stress and pro-survival pathways that contribute to disease progression and chemoresistance. The stress oncoprotein lens epithelium-derived growth factor p75 (LEDGF/p75), also known as DFS70 autoantigen, promotes cellular survival against environmental stressors, including oxidative stress, radiation, and cytotoxic drugs. Furthermore, LEDGF/p75 overexpression in PCa and other cancers has been associated with features of tumor aggressiveness, including resistance to cell death and chemotherapy. We report here that the endogenous levels of LEDGF/p75 are upregulated in metastatic castration resistant prostate cancer (mCRPC) cells selected for resistance to the taxane drug docetaxel (DTX). These cells also showed resistance to the taxanes cabazitaxel (CBZ) and paclitaxel (PTX), but not to the classical inducer of apoptosis TRAIL. Silencing LEDGF/p75 effectively sensitized taxane-resistant PC3 and DU145 cells to DTX and CBZ, as evidenced by a significant decrease in their clonogenic potential. While TRAIL induced apoptotic blebbing, caspase-3 processing, and apoptotic LEDGF/p75 cleavage, which leads to its inactivation, in both taxane-resistant and -sensitive PC3 and DU145 cells, treatment with DTX and CBZ failed to robustly induce these signature apoptotic events. These observations suggested that taxanes induce both caspase-dependent and -independent cell death in mCRPC cells, and that maintaining the structural integrity of LEDGF/p75 is critical for its role in promoting taxane-resistance. Our results further establish LEDGF/p75 as a stress oncoprotein that plays an important role in taxane-resistance in mCRPC cells, possibly by antagonizing drug-induced caspase-independent cell death.

Abstract B05: Differential autoimmune response to glycolysis and plasminogen antigens from aggressive prostate cancer cells in African American and European American men with prostate cancer

Prostate cancer (PCa) is the most commonly diagnosed cancer and the second leading cause of cancer-related male deaths in the U.S. This cancer is more aggressive in African American (AA) men, who are twice as likely to die from the disease compared to other racial groups. Despite racial disparities in PCa mortality, immunoproteomic studies profiling sera from thousands of men for the presence of autoantibodies to tumor-associated antigens (TAA) have mostly used sera from European or Asian ancestry. These autoantibodies can serve as both cancer biomarkers and potential tools in anti-tumor immunotherapy. In this study we profiled sera of AA and European American (EA) men with (N=157) and without (N=183) PCa against protein lysates from aggressive PCa cell lines using one and two-dimensional Western blotting. Sera from AA-PCa patients showed stronger immunoreactivity to proteins in PC3 cell lysates compared to EA-PCa sera. Common bands of immunoreactivity were observed around 37, 40, 50, 55, 60, and 70 kD from the sera of multiple patients. Several AA-PCa sera showed common immunoreactivity against a 50 kD protein band (16 out of 24, 67%) which was identified by serological proteomic analysis (SERPA) as alpha-enolase (ENO1), an enzyme that participates in both the glycolysis and plasminogen pathways. ELISA using purified ENO1 was conducted on 360 sera and showed significantly elevated frequency in men with PCa compared to non-PCa controls. Interestingly, SERPA analysis of other strongly immunoreactive spots outside the 50 kD region recognized of the other highly reactive PCa sera revealed additional candidate TAAs involved in the glycolysis and plasminogen pathways. These included key glycolytic enzymes GAPDH, fructose bisphosphate aldolase, phosphoglycerate kinase and lactate dehydrogenase, and other members of the plasminogen system such as GRP78 and annexin A2. Autoantibodies to stress survival proteins HSP60 and STIP1 were also identified in multiple PCa sera. We then probed by immunoblotting representative sera recognizing some of these candidate TAAs against a panel of 12 PCa and non-PCa cell lines. Anti-STIP1 sera showed elevated immunoreactivity predominantly in docetaxel-resistant cell lines. In the anti-ENO1 positive sera, we observed a race-related differential immune response, with anti-ENO1 sera from AA-PCa men showing elevated immunoreactivity mostly in metastatic cell lines, and anti-ENO1 sera from EA-PCa men showing uniform immunoreactivity across the entire panel of prostate cell lines. Interestingly, while several anti-ENO1 positive sera from AA-PCa men had increased immunoreactivity to this protein in the metastatic PCa cell lines LNCaP, MDA-PC2b, PC3 and DU145, they lacked reactivity against ENO1 in the docetaxel-resistant PC3-DR and DU145-DR cells, or purified ENO1 used in the ELISA. Anti-ENO1 EA-PCa sera did not display this differential pattern of immunoreactivity. To better understand these differences in anti-ENO1 reactivity, we interrogated the pattern of ENO1 post-translational modifications (PTMs) from PC3, PC3-DR and purified ENO1. Several different acetylated, methylated, phosphorylated, citrullinated, and glycosylated ENO1 PTMs were identified in the PC3 cells that were not present in the PC3-DR cells nor purified ENO1 which might explain the differential reactivity of AA-PCa sera against these three sources of ENO1. Taken together, these data suggest the anti-ENO1 autoantibodies from AA-PCa men may target a modified form of ENO1 that is different from that recognized by EA-PCa men. These discrepancies point to racial differences in immune response to TAAs in prostate tumors, and may have implications for identifying immunobiological factors contributing to PCa health disparities.

Citation Format: Tino W. Sanchez, Guangyu Zhang, Jitian Li, Liping Dai, Rowaid Kellow, Saied Mirshahidi, Nathan R. Wall, Clayton Yates, Colwick Wilson, Susanne Montgomery, Jian-Ying Zhang, Carlos Casiano. Differential autoimmune response to glycolysis and plasminogen antigens from aggressive prostate cancer cells in African American and European American men with prostate cancer. [abstract]. In: Proceedings of the Ninth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2016 Sep 25-28; Fort Lauderdale, FL. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2017;26(2 Suppl):Abstract nr B05.

Using Serological Proteome Analysis to Identify Serum Anti-Nucleophosmin 1 Autoantibody as a Potential Biomarker in European-American and African-American Patients With Prostate Cancer

BACKGROUND

The prostate-specific antigen (PSA) testing has been widely implemented for the early detection and management of prostate cancer (PCa). However, the lack of specificity has led to overdiagnosis, resulting in many possibly unnecessary biopsies and overtreatment. Therefore, novel serological biomarkers with high sensitivity and specificity are of vital importance needed to complement PSA testing in the early diagnosis and effective management of PCa. This is particularly critical in the context of PCa health disparities, where early detection and management could help reduce the disproportionately high PCa mortality observed in African-American men. Previous studies have demonstrated that sera from patients with PCa contain autoantibodies that react with tumor-associated antigens (TAAs).

METHODS

The serological proteome analysis (SERPA) approach was used to identify tumor-associated antigens (TAAs) of PCa. In evaluation study, the level of anti-NPM1 antibody was examined in sera from test cohort, validation cohort, as well as European-American (EA) and African-American (AA) men with PCa by using immunoassay.

RESULTS

Nucleophosmin 1 (NPM1) as a 33 kDa TAA in PCa was identified and characterized by SERPA approach. Anti-NPM1 antibody level in PCa was higher than in benign prostatic hyperplasia (BPH) patients and healthy individuals. Receiver operating characteristic (ROC) curve analysis showed similar high diagnostic value for PCa in the test cohort (area under the curve (AUC):0.860) and validation cohort (AUC: 0.822) to differentiate from normal individuals and BPH. Interestingly, AUC values were significantly higher for AA PCa patients. When considering concurrent serum measurements of anti-NPM1 antibody and PSA, 97.1% PCa patients at early stage were identified correctly, while 69.2% BPH patients who had elevated PSA levels were found to be anti-NPM1 negative. Additionally, anti-NPM1 antibody levels in PCa patients at early stage significantly increased after surgery treatment.

CONCLUSION

This intriguing data suggested that NPM1 can elicit autoantibody response in PCa and might be a potential biomarker for the immunodiagnosis and prognosis of PCa, and for supplementing PSA testing in distinguishing PCa from BPH. Prostate 76:1375-1386, 2016. © 2016 Wiley Periodicals, Inc.

Immunoseroproteomic Profiling in African American Men with Prostate Cancer: Evidence for an Autoantibody Response to Glycolysis and Plasminogen-Associated Proteins

African American (AA) men suffer from a disproportionately high incidence and mortality of prostate cancer (PCa) compared with other racial/ethnic groups. Despite these disparities, African American men are underrepresented in clinical trials and in studies on PCa biology and biomarker discovery. We used immunoseroproteomics to profile antitumor autoantibody responses in AA and European American (EA) men with PCa, and explored differences in these responses. This minimally invasive approach detects autoantibodies to tumor-associated antigens that could serve as clinical biomarkers and immunotherapeutic agents. Sera from AA and EA men with PCa were probed by immunoblotting against PC3 cell proteins, with AA sera showing stronger immunoreactivity. Mass spectrometry analysis of immunoreactive protein spots revealed that several AA sera contained autoantibodies to a number of proteins associated with both the glycolysis and plasminogen pathways, particularly to alpha-enolase (ENO1). The proteomic data is deposited in ProteomeXchange with identifier PXD003968. Analysis of sera from 340 racially diverse men by enzyme-linked immunosorbent assays (ELISA) showed higher frequency of anti-ENO1 autoantibodies in PCa sera compared with control sera. We observed differences between AA-PCa and EA-PCa patients in their immunoreactivity against ENO1. Although EA-PCa sera reacted with higher frequency against purified ENO1 in ELISA and recognized by immunoblotting the endogenous cellular ENO1 across a panel of prostate cell lines, AA-PCa sera reacted weakly against this protein by ELISA but recognized it by immunoblotting preferentially in metastatic cell lines. These race-related differences in immunoreactivity to ENO1 could not be accounted by differential autoantibody recognition of phosphoepitopes within this antigen. Proteomic analysis revealed differences in the posttranslational modification profiles of ENO1 variants differentially recognized by AA-PCa and EA-PCa sera. These intriguing results suggest the possibility of race-related differences in the antitumor autoantibody response in PCa, and have implications for defining novel biological determinants of PCa health disparities.

The significance of autoantibodies to DFS70/LEDGFp75 in health and disease: integrating basic science with clinical understanding

Antinuclear autoantibodies (ANAs) displaying the nuclear dense fine speckled immunofluorescence (DFS-IIF) pattern in HEp-2 substrates are commonly observed in clinical laboratory referrals. They target the dense fine speckled autoantigen of 70 kD (DFS70), most commonly known as lens epithelium-derived growth factor p75 (LEDGFp75). Interesting features of these ANAs include their low frequency in patients with systemic autoimmune rheumatic diseases (SARD), elevated prevalence in apparently healthy individuals, IgG isotype, strong trend to occur as the only ANA specificity in serum, and occurrence in moderate to high titers. These autoantibodies have also been detected at varied frequencies in patients with diverse non-SARD inflammatory and malignant conditions such as atopic diseases, asthma, eye diseases, and prostate cancer. These observations have recently stimulated vigorous research on their clinical and biological significance. Some studies have suggested that they are natural, protective antibodies that could serve as biomarkers to exclude a SARD diagnosis. Other studies suggest that they might be pathogenic in certain contexts. The emerging role of DFS70/LEDGFp75 as a stress protein relevant to human acquired immunodeficiency syndrome, cancer, and inflammation also points to the possibility that these autoantibodies could be sensors of cellular stress and inflammation associated with environmental factors. In this comprehensive review, we integrate our current knowledge of the biology of DFS70/LEDGFp75 with the clinical understanding of its autoantibodies in the contexts of health and disease.

DFS70/LEDGFp75: An Enigmatic Autoantigen at the Interface between Autoimmunity, AIDS, and Cancer

Clinical and diagnostic laboratories often encounter patient sera containing antinuclear antibodies (ANAs) that produce a nuclear dense fine speckled immunofluorescence pattern on HEp-2 cells. These autoantibodies usually target the dense fine speckled protein of 70 kDa (DFS70), commonly known as lens epithelium-derived growth factor p75 (LEDGFp75). Anti-DFS70/LEDGFp75 autoantibodies have recently attracted much interest because of their relatively common occurrence in sera from patients with positive ANA tests with no clinical evidence of systemic autoimmune rheumatic disease (SARD). Their presence has been documented primarily in patients with diverse non-SARD inflammatory conditions and “apparently healthy” individuals. While there is circumstantial evidence that depending on the context these autoantibodies could play protective, pathogenic, or sensor roles, their significance remains elusive. DFS70/LEDGFp75 has emerged during the past decade as a stress transcription co-activator relevant to HIV integration, cancer, and inflammation. It is not clear, however, what makes this protein the target of such a common autoantibody response. We suggest that a better understanding of DFS70/LEDGFp75 biology is key to elucidating the significance of its associated autoantibodies. Here, we discuss briefly our current understanding of this enigmatic autoantigen and potential scenarios leading to its targeting by the immune system.

Abstract C10: Immunoseroproteomic profiling of autoantibodies to tumor-associated autoantigens in African American and Caucasian men with prostate cancer

Cancer-associated serum autoantibodies are generally considered as “sensors” of molecular events associated with tumorigenesis, and thus constitute promising biomarkers for cancer detection and management, as well as tools for the identification of novel oncoproteins. Immunoseroproteomics is a standard approach for the identification of serum autoantibodies reacting with tumor-associated antigens (TAA) in human cancer populations. This approach entails using one- and two-dimensional gel electrophoresis of proteins from aggressive PCa cell lines, coupled with immunoblotting and mass spectrometry, to characterize the anti-TAA antibody repertoire in a given patient. Immunoseroproteomics has been applied mostly to cancer patients of European and Asian ancestry, and has not been used in African American (AA) patients with PCa. AA men show a disproportionately high incidence and mortality of PCa, compared to other ethnic groups, and display more aggressive tumors developing at a younger age. Recent epidemiological studies suggest that after adjusting for socioeconomic and health care-related factors, these disparities still persist, pointing to biological factors as contributors to these disparities. Growing evidence indicates that genes associated with immune function and autoimmunity are dysregulated in prostate tumors from AA men compared to Caucasian (CC) men. This prompted us to initiate a comprehensive analysis and comparison of the anti-TAA autoantibody response in AA and CC men with PCa by immunoproteomics. We hypothesized that this immune response might be augmented in AA patients with PCa, and that it could be used to identify novel blood biomarkers for early screening and management of the disease in AA men. In initial studies, we screened by immunoblotting of aggressive PCa cell lysates randomly selected serum samples from AA (n=10) and CC (n=13) men) with PCa. The initial results indicated that the autoantibody response in the AA cohort was much more robust in terms of autoantibody frequency and strength of reactivity than the response in CC patients. We used selected AA sera to identify novel TAA by immunoseroproteomics. Our initial analysis identified alpha enolase, fumarate hydratase, and annexin A1 as candidate TAAs in PCa. These proteins have been implicated in PCa in previous studies. Additional validation will be achieved by determining the frequency of the autoantibody response and the expression of these and other identified TAAs in PCa tissue microarrays. We are currently expanding our immunoseroproteomics analysis to sera from larger cohorts of AA and CC men (n>200 per group) with and without PCa, stratified by age and cancer stage. Our immunoproteomics approach will aid in the customization of TAA arrays for autoantibody profiling, leading to the identification of promising biomarkers for early PCa detection and monitoring tumor progression in the AA population. This approach may also reveal immune determinants underlying PCa health disparities.

Citation Format: Tino W. Sanchez, Saied Mirshahidi, Nathan R. Wall, Colwick Wilson, Susanne Montgomery, Carlos A. Casiano. Immunoseroproteomic profiling of autoantibodies to tumor-associated autoantigens in African American and Caucasian men with prostate cancer. [abstract]. In: Proceedings of the Sixth AACR Conference: The Science of Cancer Health Disparities; Dec 6–9, 2013; Atlanta, GA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2014;23(11 Suppl):Abstract nr C10. doi:10.1158/1538-7755.DISP13-C10

Abstract 775: Targeting the stress survival oncoprotein LEDGF/p75 to overcome prostate cancer resistance to taxane therapy

Prostate cancer (PCa) is the second leading cause of cancer-related deaths in men in the U.S. It presents a significant health burden among African American men, who tend to develop more aggressive, chemoresistant tumors and experience higher mortality rates compared to men from other ethnic groups. Eliminating these mortality disparities will require innovative therapies for the chemoresistant form of the disease. Our group has shown previously that the stress survival protein lens epithelium-derived growth factor p75 (LEDGF/p75) is overexpressed in PCa cells and clinical tumors, and promotes resistance to the taxane drug docetaxel (DTX). This study was designed to evaluate the hypothesis that LEDGF/p75 overexpression promotes taxane chemoresistance in PCa by antagonizing drug-induced caspase-independent cell death, and that targeting this protein with small inhibitory RNAs (siRNAs) or small molecule inhibitors will restore tumor cell sensitivity. We observed that acquisition of DTX-resistance in metastatic PCa cell lines (PC3 and DU145) is associated with increased expression of LEDGF/p75. Exposure of these cell lines to increasing concentrations of the taxanes DTX, paclitaxel (PTX), and cabazitaxel (CTX), and to the non-taxane drug TRAIL for up to 72 hours revealed that DTX-resistant cells also displayed increased resistance to PTX and CTX, compared to sensitive cells, but not to TRAIL. This was assessed by viability and clonogenic assays, and microscopic examination. To determine if this resistance was associated with overexpression of LEDGF/p75, we knocked down the protein with siRNAs. This knockdown attenuated resistance to the taxanes, but had no effects on TRAIL-induced cell death. We then explored if LEDGF/p75-induced taxane resistance was associated with preservation of the structural integrity of this protein. Immunoblotting analysis revealed that LEDGF/p75 was cleaved into distinct fragments by caspases during TRAIL-induced apoptosis, leading to its inactivation. However, LEDGF/p75 remained intact during treatment with taxanes, suggesting that these drugs do not induce caspase-mediated cleavage and inactivation of this protein. To determine if LEDGF/p75 is a druggable target for overcoming taxane chemoresistance in PCa cells, we repositioned a panel of small molecule inhibitors originally designed to inhibit the interaction of the C-terminal region of this protein with HIV-1 integrase. Screening of 130 inhibitors for their cytotoxic properties in DTX-resistant and sensitive prostate cancer cells, we identified a number of inhibitors that induced cell death directly, or when combined with DTX, re-sensitized the resistant cells to the drug. These promising results provide novel insights into mechanisms by which LEDGF/p75 promotes chemoresistance in PCa cells, and have implications for the development of innovative strategies to overcome this resistance.

Citation Format: Leslimar Rios Colon, Catherine Elix, Anamika Basu, Tino W. Sanchez, Nouri Neamati, Carlos A. Casiano. Targeting the stress survival oncoprotein LEDGF/p75 to overcome prostate cancer resistance to taxane therapy. [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 775. doi:10.1158/1538-7445.AM2014-775

Design and discovery of flavonoid-based HIV-1 integrase inhibitors targeting both the active site and the interaction with LEDGF/p75

HIV integrase (IN) is an essential enzyme for the viral replication. Currently, three IN inhibitors have been approved for treating HIV-1 infection. All three drugs selectively inhibit the strand transfer reaction by chelating a divalent metal ion in the enzyme active site. Flavonoids are a well-known class of natural products endowed with versatile biological activities. Their β-ketoenol or catechol structures can serve as a metal chelation motif and be exploited for the design of novel IN inhibitors. Using the metal chelation as a common pharmacophore, we introduced appropriate hydrophobic moieties into the flavonol core to design natural product-based novel IN inhibitors. We developed selective and efficient syntheses to generate a series of mono 3/5/7/3'/4'-substituted flavonoid derivatives. Most of these new compounds showed excellent HIV-1 IN inhibitory activity in enzyme-based assays and protected against HIV-1 infection in cell-based assays. The 7-morpholino substituted 7c showed effective antiviral activity (EC50=0.826 μg/mL) and high therapeutic index (TI>242). More significantly, these hydroxyflavones block the IN-LEDGF/p75 interaction with low- to sub-micromolar IC50 values and represent a novel scaffold to design new generation of drugs simultaneously targeting the catalytic site as well as protein-protein interaction domains.

Synthesis, docking, and biological studies of phenanthrene β-diketo acids as novel HIV-1 integrase inhibitors

In the present study we report the synthesis of halogen-substituted phenanthrene β-diketo acids as new HIV-1 integrase inhibitors. The target phenanthrenes were obtained using both standard thermal- and microwave-assisted synthesis. 4-(6-Chlorophenanthren-2-yl)-2,4-dioxobutanoic acid (18) was the most active compound of the series, inhibiting both 3'-end processing (3'-P) and strand transfer (ST) with IC50 values of 5 and 1.3 μM, respectively. Docking studies revealed two predominant binding modes that were distinct from the binding modes of raltegravir and elvitegravir, and suggest a novel binding region in the IN active site. Moreover, these compounds are predicted not to interact significantly with some of the key amino acids (Q148 and N155) implicated in viral resistance. Therefore, this series of compounds can further be investigated for a possible chemotype to circumvent resistance to clinical HIV-1 IN inhibitors.

Design of cell-permeable stapled peptides as HIV-1 integrase inhibitors

HIV-1 integrase (IN) catalyzes the integration of viral DNA into the host genome, involving several interactions with the viral and cellular proteins. We have previously identified peptide IN inhibitors derived from the α-helical regions along the dimeric interface of HIV-1 IN. Herein, we show that appropriate hydrocarbon stapling of these peptides to stabilize their helical structure remarkably improves the cell permeability, thus allowing inhibition of the HIV-1 replication in cell culture. Furthermore, the stabilized peptides inhibit the interaction of IN with the cellular cofactor LEDGF/p75. Cellular uptake of the stapled peptide was confirmed in four different cell lines using a fluorescein-labeled analogue. Given their enhanced potency and cell permeability, these stapled peptides can serve as not only lead IN inhibitors but also prototypical biochemical probes or "nanoneedles" for the elucidation of HIV-1 IN dimerization and host cofactor interactions within their native cellular environment.

Design and synthesis of 3-carbamoylbenzoic acid derivatives as inhibitors of human apurinic/apyrimidinic endonuclease 1 (APE1)

Apurinic/apyrimidinic (AP) endonuclease 1 (APE1) is a multifaceted protein with an essential role in the base excision repair (BER) pathway. Its implication in tumor development, progression, and resistance has been confirmed in multiple cancers, making it a viable target for intensive investigation. In this work, we designed and synthesized different classes of small-molecule inhibitors of the catalytic endonuclease function of APE1 that contain a 3-carbamoylbenzoic acid scaffold. Further structural modifications were made with the aim of increasing the activity and cytotoxicity of these inhibitors. Several of our compounds were shown to inhibit the catalytic endonuclease function of APE1 with potencies in the low-micromolar range in vitro, and therefore represent novel classes of APE1 inhibitors worthy of further development.

Investigating the role of metal chelation in HIV-1 integrase strand transfer inhibitors

HIV-1 integrase (IN) has been validated as an attractive target for the treatment of HIV/AIDS. Several studies have confirmed that the metal binding function is a crucial feature in many of the reported IN inhibitors. To provide new insights on the metal chelating mechanism of IN inhibitors, we prepared a series of metal complexes of two ligands (HL1 and HL2), designed as representative models of the clinically used compounds raltegravir and elvitegravir. Potentiometric measurements were conducted for HL2 in the presence of Mg(II), Mn(II), Co(II), and Zn(II) in order to delineate a metal speciation model. We also determined the X-ray structures of both of the ligands and of three representative metal complexes. Our results support the hypothesis that several selective strand transfer inhibitors preferentially chelate one cation in solution and that the metal complexes can interact with the active site of the enzyme.

Design of HIV-1 integrase inhibitors targeting the catalytic domain as well as its interaction with LEDGF/p75: a scaffold hopping approach using salicylate and catechol groups

HIV-1 integrase (IN) is a validated therapeutic target for antiviral drug design. However, the emergence of viral strains resistant to clinically studied IN inhibitors demands the discovery of novel inhibitors that are structurally as well mechanistically different. Herein, we describe the design and discovery of novel IN inhibitors targeting the catalytic domain as well as its interaction with LEDGF/p75, which is essential for the HIV-1 integration as an IN cofactor. By merging the pharmacophores of salicylate and catechol, the 2,3-dihydroxybenzamide (5a) was identified as a new scaffold to inhibit the strand transfer reaction efficiently. Further structural modifications on the 2,3-dihydroxybenzamide scaffold revealed that the heteroaromatic functionality attached on the carboxamide portion and the piperidin-1-ylsulfonyl substituted at the phenyl ring are beneficial for the activity, resulting in a low micromolar IN inhibitor (5p, IC(50)=5 μM) with more than 40-fold selectivity for the strand transfer over the 3'-processing reaction. More significantly, this active scaffold remarkably inhibited the interaction between IN and LEDGF/p75 cofactor. The prototype example, N-(cyclohexylmethyl)-2,3-dihydroxy-5-(piperidin-1-ylsulfonyl) benzamide (5u) inhibited the IN-LEDGF/p75 interaction with an IC(50) value of 8 μM. Using molecular modeling, the mechanism of action was hypothesized to involve the chelation of the divalent metal ions inside the IN active site. Furthermore, the inhibitor of IN-LEDGF/p75 interaction was properly bound to the LEDGF/p75 binding site on IN. This work provides a new and efficient approach to evolve novel HIV-1 IN inhibitors from rational integration and optimization of previously reported inhibitors.

Synthesis, biological evaluation and 3D-QSAR studies of 3-keto salicylic acid chalcones and related amides as novel HIV-1 integrase inhibitors

HIV-1 integrase is one of the three most important enzymes required for viral replication and is therefore an attractive target for anti retroviral therapy. We herein report the design and synthesis of 3-keto salicylic acid chalcone derivatives as novel HIV-1 integrase inhibitors. The most active compound, 5-bromo-2-hydroxy-3-[3-(2,3,6-trichlorophenyl)acryloyl]benzoic acid (25) was selectively active against integrase strand transfer, with an IC(50) of 3.7 μM. While most of the compounds exhibited strand transfer selectivity, a few were nonselective, such as 5-bromo-3-[3-(4-bromophenyl)acryloyl]-2-hydroxybenzoic acid (15), which was active against both 3'-processing and strand transfer with IC(50) values of 11±4 and 5±2 μM, respectively. The compounds also inhibited HIV replication with potencies comparable with their integrase inhibitory potencies. Thus, 5-bromo-2-hydroxy-3-[3-(2,3,6-trichlorophenyl)acryloyl]benzoic acid (25) and 5-bromo-3-[3-(4-bromophenyl)acryloyl]-2-hydroxybenzoic acid (15) inhibited HIV-1 replication with EC(50) values of 7.3 and 8.7 μM, respectively. A PHASE pharmacophore hypothesis was developed and validated by 3D-QSAR, which gave a predictive r(2) of 0.57 for an external test set of ten compounds. Phamacophore derived molecular alignments were used for CoMFA and CoMSIA 3D-QSAR modeling. CoMSIA afforded the best model with q(2) and r(2) values of 0.54 and 0.94, respectively. This model predicted all the ten compounds of the test set within 0.56 log units of the actual pIC(50) values; and can be used to guide the rational design of more potent novel 3-keto salicylic acid integrase inhibitors.

Design and synthesis of novel dihydroquinoline-3-carboxylic acids as HIV-1 integrase inhibitors

Previously, we discovered linomide analogues as novel HIV-1 integrase (IN) inhibitors. Here, to make possible structure-activity relationships, we report on the design and synthesis of a series of substituted dihydroquinoline-3-carboxylic acids. The crystal structure of the representative compound 2c has also been solved. Among the eight new analogues, 2e showed a potency in inhibiting IN strand transfer catalytic activity similar to the reference diketo acid inhibitor L-731,988 (IC(50)=0.9 microM vs. 0.54 microM, for 2e and L-731,988, respectively). Furthermore, none of the compounds showed significant cytotoxicity in two tested cancer cell lines. These compounds represent an interesting prototype of IN inhibitors, potentially involved in a metal chelating mechanism, and further optimization is warranted.