Resistant Patient-derived Xenograft Research Articles

The SRC-family serves as a therapeutic target in triple negative breast cancer with acquired resistance to chemotherapy

BackgroundResistance to chemotherapy, combined with heterogeneity among resistant tumors, represents a significant challenge in the clinical management of triple negative breast cancer (TNBC). By dissecting molecular pathways associated with treatment resistance, we sought to define patient sub-groups and actionable targets for next-line treatment.MethodsBulk RNA sequencing and reverse phase protein array profiling were performed on isogenic patient-derived xenografts (PDX) representing paclitaxel-sensitive and -resistant tumors. Pathways identified as upregulated in the resistant model were further explored as targets in PDX explants. Their clinical relevance was assessed in two distinct patient cohorts (NeoAva and MET500).ResultsIncreased activity in signaling pathways involving SRC-family kinases (SFKs)- and MAPK/ERK was found in treatment resistant PDX, with targeted inhibitors being significantly more potent in resistant tumors. Up-regulation of SFKs- and MAPK/ERK-pathways was also detected in a sub-group of chemoresistant patients after neoadjuvant treatment. Furthermore, High SFK expression (of either SRC, FYN and/or YES1) was detected in metastatic lesions of TNBC patients with fast progressing disease (median disease-free interval 27 vs 105 months).ConclusionsUpregulation of SFK-signaling is found in a subset of chemoresistant tumors and is persistent in metastatic lesions. Based on pre-clinical results, these patients may respond favorably to treatment targeting SFKs.

Abstract ND02: Discovery of BMS-986365, a ligand-directed androgen receptor degrader (AR LDD) with a dual mechanism-of-action and best-in-class potential, for the treatment of advanced prostate cancer

Abstract The androgen receptor (AR) is a key driver of the cellular processes that contribute to the pathology of prostate cancers at most stages, and drugs that inhibit the activity of this receptor or interfere with androgen biosynthesis have become the cornerstone of treatments for prostate cancer. While both types of therapy have had a significant positive impact on disease progression and overall survival, de novo and acquired resistance remains an impediment to a durable clinical response in patients with metastatic castration-resistant prostate cancer (mCRPC). The mechanisms underlying drug resistance are complex and multifactorial, being attributable to AR overexpression, point mutations in the receptor that alter drug pharmacology, and to the upregulation of receptor-associated coregulators, which render AR less dependent on an activating ligand. Regardless, absolute inhibition of AR signaling remains the objective of contemporary approaches to treat prostate cancer. Recently, there has been specific interest in the development of approaches to eliminate AR proteins using drugs that enable targeted degradation of AR in cancer cells.This puts in context the significance of our discovery of BMS-986365 (also known as CC-94676), a heterobifunctional ligand-directed degrader (LDD) that enables the CRL4CRBN E3 ligase-dependent ubiquitination and degradation of AR (DC50 10 to 40 nM, Ymin 7 to 19%). BMS-986365 is a highly potent and selective AR degrader that induces rapid and deep degradation of both wildtype and mutant forms of the receptor residing in either the cytoplasmic or nuclear compartments of the cell. The drug is ~100-fold more potent than enzalutamide (ENZ) at inhibiting androgen-stimulated transcription of AR target genes, and 10 to 120-fold more potent than ENZ at inhibiting AR-dependent proliferation of multiple prostate cancer cell lines in vitro. In animal models of advanced prostate cancer, BMS-986365 demonstrates on-target activity, degrading AR, suppressing AR signaling, and inhibiting tumor growth. Indeed, tumor volume reductions of 63-92% were achieved by BMS-986365 in validated models of advanced CRPC and therapy resistant patient-derived xenografts, including those with acquired resistance to ENZ. Collectively our preclinical data suggest that the AR degrader BMS-986365 is superior to standard-of-care AR antagonists, such as ENZ, in both preclinical and disease-relevant animal models, and support its clinical development for treatment of prostate cancer. BMS-986365 has advanced into clinical studies where it has demonstrated encouraging clinical activity in patients with mCRPC. Citation Format: Shuichan Xu, Surendra Nayak, John D. Norris, Massimo Ammirante, Emyly Rychak, Suzanne E. Wardell, Toshiya Tsuji, Ken Liu, Joseph Meiring, Joseph R. Piccotti, Deepak Dalvie, Debbie Liao, Raju Kandimalla, Nadia Guerrero, Lisa Sapinoso, Jennifer G. Baker, Yeeun Bae, Joshua Baughman, Brandon Toyama, Celia Fontanillo Fontanillo, Stephen Norris, Evan J. Horn, Veronique Plantevin-Krenitsky, Deborah Mortensen, Brian Cathers, Marie Hong Nguyen, Joshua D. Hensen, Lawrence G. Hamann, Donald P. McDonnell, Rama Krishna Narla, Mark Rolfe. Discovery of BMS-986365, a ligand-directed androgen receptor degrader (AR LDD) with a dual mechanism-of-action and best-in-class potential, for the treatment of advanced prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr ND02.

Abstract 1930: Combination of KRASG12C and FGFR1 inhibitors as a resistance-overcoming therapeutic strategy for maximizing therapeutic impact of KRASG12C inhibitors

Abstract INTRODUCTION: Lung cancer is the leading cause of cancer-related deaths worldwide. KRAS is the most frequent mutated driver gen in lung adenocarcinoma (LUAD). KRASG12C inhibitors (G12Ci) have revealed promising results in the clinic, having being approved two G12Ci for the treatment of LUAD patients, which marks the first approved targeted therapy for KRAS-mutant tumors. Nevertheless, these therapies face the same limitation as other targeted therapies, the therapeutic potential of these inhibitors can be impaired by resistance mechanisms. Deciphering resistance mechanisms to G12Ci is of prime relevance to predict which patients may benefit from these therapies and to propose resistance-overcoming therapeutic strategies for maximizing therapeutic impact of these inhibitors. MATERIAL AND METHODS: We generated 10 acquired resistant LUAD cell lines to G12Ci (Sotorasib and Adagrasib), exposing sensitive cells to increasing concentrations of drugs. All the acquired resistant models were characterized at the proteomic (phospho-Array and Western Blot) and transcriptomic (WTS) levels to find signatures that define the resistance.The efficacy of G12Ci was tested in vitro in a panel of 8 cell lines and 7 PDX-derived organoids (PDXDO) models and in vivo in 7 patient-derived xenografts (PDX) models to classify them as resistant, sensitive or partially sensitive. The efficacy of the combination of FGFR1 and G12Ci was tested in vitro in the panel of 10 acquired resistant cell lines but also in the parental cell lines and PDXDOs (sensitive and intrinsic resistant) and in vivo in the intrinsic resistant PDXs. RESULTS AND DISCUSSION: The characterization of 10 acquired resistant cell lines at the proteomic and transcriptomic levels showed differences in the expression and/or activation of Fibroblast Growth Factor Receptors (FGFRs) in more than 50% of them. The combination of KRASG12C and FGFR1 inhibitors in all acquired resistant cell lines showed efficacy, regardless of whether acquired resistance was mediated or not by FGFR1 overexpression/overactivation.In addition, the combination of KRASG12C and FGFR1 inhibitors showed more efficacy than the monotherapies in most intrinsically resistant cell lines, PDXDOs and PDXs models. Finally, we tested the combination with FGFR1i in sensitive or partially responsive models, observing an improvement in efficacy compared to monotherapy with G12Ci. CONCLUSIONS: The activation or overexpression of FGFR1 acts as a mechanism of acquired resistance to KRASG12C inhibitors.-The combination of FGFR and KRASG12C inhibitors is effective as an acquired/intrinsic resistance-overcoming therapeutic strategy in cell lines, PDXDOs and PDXs models.-The combination of FGFR and KRASG12C inhibitors is also synergistic for sensitive models, which could maximize therapeutic impact of KRASG12C inhibitors. Citation Format: Alba Santos, Patricia Plaza, Marta Jimenez, David Gómez-Sánchez, Luis Paz-Ares, Irene Ferrer. Combination of KRASG12C and FGFR1 inhibitors as a resistance-overcoming therapeutic strategy for maximizing therapeutic impact of KRASG12C inhibitors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1930.

Abstract 606: The PLK1 inhibitor, onvansertib, synergizes with paclitaxel in small cell lung cancer

Abstract Background: Small cell lung cancer (SCLC) is an aggressive neuroendocrine tumor with rapid disease progression and poor patient survival. Therapeutic options for SCLC remain a challenge due to limited understanding of both the biology of the disease and the major determinants of treatment response. Key transcription factors associated with unique biological phenotypes of SCLC include ASCL1, NEUROD1, YAP1, and POU2F3. Previously, we demonstrated that onvansertib, a highly specific inhibitor of the PLK1 Ser/Thr kinase, was effective in SCLC preclinical models, leading to its ongoing clinical development for relapsed/refractory SCLC patients (NCT05450965). Here we further explored potential strategies to enhance onvansertib activity by assessing its in vitro and in vivo activity in combination treatments. Methods: Human SCLC cell lines were treated for 72 hr with onvansertib in combination with paclitaxel, lurbinectedin or the ATR inhibitors BAY1895344 and AZD6738. Effect on cell proliferation was analyzed by WST1 and CellTiterGlo assays. In vivo activity of onvansertib in combination with paclitaxel was tested in 3 SCLC patient-derived xenograft (PDX) models either cisplatin-sensitive (TKO5- ASCL1 subtype) or cisplatin-resistant (TKO2-ASCL1 subtype, TKO8-NEUROD1 subtype). Tumor-bearing nude mice were treated with vehicle, onvansertib (50 mg/kg, oral, 4 times/week), paclitaxel (15 mg/kg, IP, once a week) or the combination for 5 weeks. Mice were followed for tumor growth and survival (defined as time to reach tumor volume greater than 2000 mm3). Results: The combination of onvansertib and paclitaxel inhibited cell proliferation synergistically in cell lines from 3 SCLC subtypes (ASCL1, NEUROD1, and YAP1), while the combinations with lurbinectedin or ATR inhibitors were not synergistic. We further examined the combination of onvansertib and paclitaxel in SCLC PDXs. The combination exhibited potent anti-tumor activity, resulting in significantly greater tumor growth inhibition and increase in survival compared to the monotherapies in all 3 PDXs. The combination was well tolerated with no observed body weight loss. While onvansertib and paclitaxel had negligible single agent activity in cisplatin-resistant TK02 PDX and TKO8 PDX models, the combination induced durable complete responses in 25% and 100% of treated mice respectively. Conclusion: The PLK1 inhibitor onvansertib in combination with paclitaxel showed synergy in multiple SCLC cell lines in vitro and potent anti-tumor activity in cisplatin-sensitive and -resistant SCLC PDX models in vivo. Tumor tissue analysis is underway to detail the mechanisms of this interaction. Citation Format: John C. Schmitz, Guojing Zhang, Abbe Pannucci, Tod Smeal, Chu-Chiao Wu, Maya Ridinger, Taofeek K. Owonikoko. The PLK1 inhibitor, onvansertib, synergizes with paclitaxel in small cell lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 606.

Abstract 6912: Pretreatment multiomics in conjunction with preclinical trials on patient-derived xenograft models of cholangiocarcinoma can identify chemotherapy response signatures

Abstract Background Cholangiocarcinoma (CCA) is a heterogeneous malignancy. Platinum-based chemotherapy (Gemcitabine and Cisplatin) has been the standard treatment for over a decade and is the base for the current immunotherapy combinations. Response rates are typically between 20-30%. Herein, we present outcomes of preclinical efficacy trials on CCA PDX models in correlation with baseline multiomics profiling of CCA patient-derived xenograft (PDX) models to identify molecular features associated with response. Methods Tumor samples from twenty-eight CCA PDX were used to isolate RNA and protein to be included in multiomics analysis (Phosphoproteomics, Proteomics, and Transcriptomics). A subset of PDX models were treated with various doses of Gemcitabine and Cisplatin. The Median Efficacy Index (MEI) was calculated as the ratio of the difference in median of delta in tumor volume at the last day of the study between the treatment and the control arms divided by the median of delta in tumor volume of the control at the last day of the treatment (positive= growth, negative=inhibition, and 0=no efficacy). A Hierarchical All-Against-All algorithm was utilized to compare multiomics features to the MEI and pathway analysis completed for identified molecular features. Results After conducting preclinical efficacy trials, the five tested CCA PDX models were classified into sensitive, moderately sensitive, and resistant models based on the MEI on each treatment arm. The top up-regulated genes were identified for Gemcitabine response (SRPK2, GLK2, and RIOK2) and Cisplatin response (NTRK1, PRPF4B, and SRPK2). The top up-regulated genes related to Gemcitabine resistance were NTRK1, PIP5K1C, and CSNK2A2, while those related to Cisplatin resistance were SRPK1, PRPF4B, and CSNK2A1. Conclusion Cholangiocarcinoma multiomics signatures can predict therapeutic response to standard-of-care chemotherapy in preclinical models. Novel mechanisms of Gemcitabine and Cisplatin resistance were identified related to NTRK1, SRPK1 and SRPK2. Resistant signatures will be challenged with the appropriate targeted therapies on the resistant CCA PDX models. Citation Format: Amro M. Abdelrahman, Danielle M. Carlson, Erik Jessen, Dong-Gi Mun, Isaac Lynch, Alessandro Fogliati, Stella Konadu Adjei Antwi, Aushinie Abeynayake, Akhilesh Pandey, Mark J. Truty, Gregory J. Gores, Rory L. Smoot. Pretreatment multiomics in conjunction with preclinical trials on patient-derived xenograft models of cholangiocarcinoma can identify chemotherapy response signatures [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6912.

Abstract 4993: CJRB-101 induces immune responses through the GUT-TME axis in immune cell-driven mechanism in lung cancer models

Abstract Background Live biotherapeutic products (LBPs) are known to enhance immune responses through the GUT-TME axis. Here, we investigate the GUT-TME-related immune cell profiling and signals associated with the anti-cancer effects of CJRB-101. Methods Tumors from NSCLC patients (anti-PD-1 refractory) were transplanted in Hu-CD34-NSG to establish humanized patient-derived xenograft (PDX) models. CJRB-101 was administered at 1x109 CFU (p.o., BID) or combination with anti-PD-1 (10 mpk, i.p., BIW). TME was analyzed using multiplex IHC, flow cytometry and scRNA sequencing. Samples were collected from C3PQ syngeneic mice at multiple timepoints for GUT-TME immune cell profiling. For depletion assay, immune cells were individually depleted during the combination treatment. TLR4-mediated mechanism was evaluated using ex vivo and in vivo assay treated with CJRB-101 or cell membrane of CJRB-101. Results CJRB-101 combined with pembrolizumab effectively suppressed tumor growth in anti-PD-1 resistant PDX models. Further analysis revealed a correlation between the activity of NK cells and angiogenesis inhibition. Abundance of NK/NKT was higher in the CJRB-101 treated group compared to the vehicle group in multiple PDX models. The expression of GZMB and IFNG in NK/NKT cells was significantly higher in the CJRB-101 treated group compared to the vehicle group in YHIM2014 (p<0.001). CJRB-101 treated group showed significantly higher expression of antiangiogenic IL1B (p<0.001) while the expression of pro-angiogenic VEGFA (p=0.002) was lower compared to the vehicle group in YHIM2014 cancer cells. Macrophages in the intestine were increased at Day 3 in the CJRB-101 group compared to anti-PD1, while NK cells, granulocytes, CD3+, CD4+, CD8+ T cells increased at Day 10 in the syngeneic model. Depletion assay confirmed that macrophages, CD8+ T cells and neutrophils were pivotal in the anti-cancer effects of CJRB-101. We observed that TAK242 and MD2 reduced the IL-6 secretion of Raw264.7 in a dose-dependent manner. The cell membrane played a key role in increasing BMDM M1 polarization and repolarization of M2 to M1, and that inhibition of TLR4 resulted in a decrease in BMDM repolarization. TLR inhibition also demonstrated that TGI decreased from 34% to 20% when treated with cell membrane + TAK242 compared to cell membrane monotherapy. Conclusions This study showed that macrophages were the dominant immune population in the early stages then T cells (CD3, CD4, CD8), NK cells and granulocytes became more active in the latter stages of the GUT-TME-axis immune response. In vivo results indicated that anti-cancer efficacy of CJRB-101 is immune-cell driven by TLR4-dependent stimulation of key immune cell populations (macrophages, CD8+ T cells, neutrophils) modulated by the cell membrane of CJRB-101. CJRB-101 is currently undergoing clinical investigation for treatment of patients with advanced NSCLC. Citation Format: Arim Min, Bo-eun Kwon, Seong-san Kang, Sujeong Baek, Junwon Yang, Hyunkyung Park, Jieun Im, Hyunjeong Kim, Jaemin Kim, Jieun Kwon, Dong Kwon Kim, Jii Bum Lee, Hyeonseok Oh, Seung Min Yang, Yu Jin Han, Mi hyun Kim, Heekyung Han, Kwangmin Na, Young Taek Kim, Mi Ran Yun, Jae Hwan Kim, Youngseon Byeon, Young Seob Kim, Min Hee Hong, Sun Min Lim, Kyoung-Ho Pyo, Byoung Chul Cho. CJRB-101 induces immune responses through the GUT-TME axis in immune cell-driven mechanism in lung cancer models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4993.

Abstract 4737: The combination of the BET inhibitor JQ1 and gemcitabine induces regressions in gemcitabine resistant patient-derived xenograft models of pancreatic cancer

Abstract Efforts to develop targeted therapies for drug resistant tumors have been relatively unsuccessful. The 5-year survival for patients with advanced pancreatic cancer is ~3%. Gemcitabine is usually combined with nab-paclitaxel as a standard of care for treatment of locally advanced or metastatic pancreatic ductal adenocarcinoma (PDAC). However, no chemotherapeutic regimens thus far evaluated have been curative. We developed the first PDAC patient-derived xenograft (PDX) models in which resistance against gemcitabine was acquired in vivo. We used RNA-seq and ingenuity pathway analysis to compare expression profiles of paired parent vs gemcitabine resistant PDX models. This comparison suggested a previously unreported mechanism for gemcitabine resistance, involving aberrations of cholesterol biosynthesis and lipid metabolism pathways. We also made the unexpected observation that gemcitabine-resistant PDAC models derived from primary tumors have high levels of 3-hydroxy-3-methylglutaryl-CoA synthase 2 (HMGCS2), an enzyme essential to cholesterol biosynthesis and rate limiting in ketogenesis. Notably, the BET bromodomain inhibitor JQ1 decreases HMGCS2 levels; and BET inhibitors + gemcitabine exert synergistic cytotoxicity in gemcitabine-resistant PDAC cells. We determined that the BET bromodomain inhibitor JQ1 + gemcitabine induces regressions of two in vivo gemcitabine-resistant tumor models which we developed directly from primary human tumor tissue. These mechanism-based studies suggest that inhibiting HMGCS2 represents a novel approach to therapy for PDAC. We propose that combining gemcitabine with agents that decrease levels of HMGCS2 comprises effective treatment for patients with drug resistant PDAC. Citation Format: Aubrey L. Miller, Samuel C. Fehling, Eric Josh Brown, Eric O. Heard, Tracy L. Gamblin, Rebecca B. Vance, Karina J. Yoon. The combination of the BET inhibitor JQ1 and gemcitabine induces regressions in gemcitabine resistant patient-derived xenograft models of pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4737.

Acetyl-CoA carboxylase 1 controls a lipid droplet-peroxisome axis and is a vulnerability of endocrine-resistant ER+ breast cancer.

Targeting aromatase deprives ER+ breast cancers of estrogens and is an effective therapeutic approach for these tumors. However, drug resistance is an unmet clinical need. Lipidomic analysis of long-term estrogen-deprived (LTED) ER+ breast cancer cells, a model of aromatase inhibitor resistance, revealed enhanced intracellular lipid storage. Functional metabolic analysis showed that lipid droplets together with peroxisomes, which we showed to be enriched and active in the LTED cells, controlled redox homeostasis and conferred metabolic adaptability to the resistant tumors. This reprogramming was controlled by acetyl-CoA-carboxylase-1 (ACC1), whose targeting selectively impaired LTED survival. However, the addition of branched- and very long-chain fatty acids reverted ACC1 inhibition, a process that was mediated by peroxisome function and redox homeostasis. The therapeutic relevance of these findings was validated in aromatase inhibitor-treated patient-derived samples. Last, targeting ACC1 reduced tumor growth of resistant patient-derived xenografts, thus identifying a targetable hub to combat the acquisition of estrogen independence in ER+ breast cancers.

ELK1/MTOR/S6K1 Pathway Contributes to Acquired Resistance to Gefitinib in Non-Small Cell Lung Cancer.

The development of acquired resistance to small molecule tyrosine kinase inhibitors (TKIs) targeting epidermal growth factor receptor (EGFR) signaling has hindered their efficacy in treating non-small cell lung cancer (NSCLC) patients. Our previous study showed that constitutive activation of the 70 kDa ribosomal protein S6 kinase 1 (S6K1) contributes to the acquired resistance to EGFR-TKIs in NSCLC cell lines and xenograft tumors in nude mice. However, the regulatory mechanisms underlying S6K1 constitutive activation in TKI-resistant cancer cells have not yet been explored. In this study, we recapitulated this finding by taking advantage of a gefitinib-resistant patient-derived xenograft (PDX) model established through a number of passages in mice treated with increasing doses of gefitinib. The dissociated primary cells from the resistant PDX tumors (PDX-R) displayed higher levels of phosphor-S6K1 expression and were resistant to gefitinib compared to cells from passage-matched parental PDX tumors (PDX-P). Both genetic and pharmacological inhibition of S6K1 increased sensitivity to gefitinib in PDX-R cells. In addition, both total and phosphorylated mechanistic target of rapamycin kinase (MTOR) levels were upregulated in PDX-R and gefitinib-resistant PC9G cells. Knockdown of MTOR by siRNA decreased the expression levels of total and phosphor-S6K1 and increased sensitivity to gefitinib in PDX-R and PC9G cells. Moreover, a transcription factor ELK1, which has multiple predicted binding sites on the MTOR promoter, was also upregulated in PDX-R and PC9G cells, while the knockdown of ELK1 led to decreased expression of MTOR and S6K1. The chromatin immunoprecipitation (ChIP)-PCR assay showed the direct binding between ELK1 and the MTOR promoter, and the luciferase reporter assay further indicated that ELK1 could upregulate MTOR expression through tuning up its transcription. Silencing ELK1 via siRNA transfection improved the efficacy of gefitinib in PDX-R and PC9G cells. These results support the notion that activation of ELK1/MTOR/S6K1 signaling contributes to acquired resistance to gefitinib in NSCLC. The findings in this study shed new light on the mechanism for acquired EGFR-TKI resistance and provide potential novel strategies by targeting the ELK1/MTOR/S6K1 pathway.

Targeting Mitochondrial Apoptotic Priming State to Personalize Therapy for Relapsed Acute Myeloid Leukemia

Despite of remarkable changes in therapeutic landscape of AML in past 5 years, relapsed AML patients still succumb to disease. In majority of patients, the common cause of death ultimately is the emergence multi-drug resistance at relapse. Using patient-derived xenograft (PDX) as our models, we investigated the basis of multi-drug resistance and methods for identifying drug sensitivity in relapsed AML. We hypothesized that there is differential activation of drug-induced mitochondrial apoptotic signaling between treatment-naïve and relapsed myeloblasts. To study mechanisms of drug resistance in AML, we developed PDX models (n=18 models) of in vivo acquired resistance to single agents (BCL-2/MCL-1 inhibitor, FLT3 inhibitor, SMAC mimetics and BRD-4 inhibitor) of distinct mechanisms, which caused board chemoresistance across all models. We tested whether multidrug resistance is associated with reduction in apoptotic signaling, using BH3 profiling, a method for measurement of mitochondrial sensitivity to apoptosis via exposure to synthetic BH3 domain peptides, on matched pre- and post-resistant PDXs. Using BH3 profiling, we found that a reduction in mitochondrial apoptotic priming consistently accompanied the acquisition of multidrug resistance irrespective of the mechanism of drug action and genetic status of PDX models. Next we created pharmacologic sensitivity landscape for 22 AML PDX models by exposing splenic myeloblasts isolated after confirmed engraftment (>70% circulating hCD45+ blasts) to drug a drug panel (n=40) for 14 hours. We first demonstrate that ex vivo drug-induced mitochondrial sensitivity singling measured via dynamic BH3 profiling (DBP) segregates PDXs according to prior treatment. By using unsupervised hierarchical clustering we found that AML PDXs developed from treatment naïve patients clustered together and showed greater apoptotic priming responses to a larger number of targeted agents than PDXs from R/R patients, which also formed discrete clusters. We replicated drug-response patterns from PDX models in primary and relapsed AML patients by analyzing ex vivo sensitivity responses to >500 drugs across relapse and diagnosis patients (Malani et al, 2021 and Tyner et al, 2018). We show that human AML patients at relapse also broadly lose sensitivity to agents in a similar pan-resistant manner as PDX models. Using unbiased whole transcriptomic analysis of naïve and resistant PDXs (n=78 samples), we found common pathways of resistance where positive enrichment was observed for cytokine-cytokine receptor interactions, xenobiotics biodegradation, metabolic pathways, Hippo signaling, and Ras signaling in resistant compared to treatment-naïve PDXs. Conversely, mechanisms relating to DNA repair and replication, such as base excision repair, mismatch repair, and homologous recombination, were negatively enriched. Moreover, pathways associated with specific drug resistance were also observed. One of the known multi-drug resistance mechanisms to chemotherapy drugs in AML is increased expression of efflux pumps from the superfamily of ATP binding cassette. We found enrichment in ABC transporter family pathway signatures in all 3 PDX models, DFAM-61786, DFAM-15354, and DFAM-61345, resistant to quizartinib, birinapant, and JQ-1 and validated higher drug-efflux activity in quizartinib and birinapant resistant model using calcein-AM efflux assay. We finally tested whether DBP could predict in vivo response of patient myeloblasts in PDX models. We tested in vivo sensitivity to 5 drugs of disparate mechanisms of action: birinapant and LCL-161 (SMAC mimetics), JQ-1 (BRD-4 inhibitor), venetoclax (BCL-2 antagonist), and quizartinib (FLT-3 inhibitor) in 4-9 different PDX models each. Using ex vivo DBP assay, we identified drugs that prime not only treatment naïve PDXs but also R/R PDXs. We identified persistent in vivo activity in a drug-specific manner, with BH3 mimetics and HDAC inhibitors showing overlapping activity across different drug-resistant models. Overall, we demonstrate that acquired resistance to targeted therapy in AML is accompanied by common mechanism of reduction in mitochondrial priming along with drug-specific resistance mechanisms. Further, we find that, even in the context of a multiply-resistant PDX model, DBP can still identify therapeutic vulnerabilities that can be efficaciously exploited in vivo.

Resistance to PRMT5-targeted therapy in mantle cell lymphoma

AbstractMantle cell lymphoma (MCL) is an incurable B-cell non-Hodgkin lymphoma, and patients who relapse on targeted therapies have poor prognosis. Protein arginine methyltransferase 5 (PRMT5), an enzyme essential for B-cell transformation, drives multiple oncogenic pathways and is overexpressed in MCL. Despite the antitumor activity of PRMT5 inhibition (PRT-382/PRT-808), drug resistance was observed in a patient-derived xenograft (PDX) MCL model. Decreased survival of mice engrafted with these PRMT5 inhibitor–resistant cells vs treatment-naive cells was observed (P = .005). MCL cell lines showed variable sensitivity to PRMT5 inhibition. Using PRT-382, cell lines were classified as sensitive (n = 4; 50% inhibitory concentration [IC50], 20-140 nM) or primary resistant (n = 4; 340-1650 nM). Prolonged culture of sensitive MCL lines with drug escalation produced PRMT5 inhibitor–resistant cell lines (n = 4; 200-500 nM). This resistant phenotype persisted after prolonged culture in the absence of drug and was observed with PRT-808. In the resistant PDX and cell line models, symmetric dimethylarginine reduction was achieved at the original PRMT5 inhibitor IC50, suggesting activation of alternative resistance pathways. Bulk RNA sequencing of resistant cell lines and PDX relative to sensitive or short-term–treated cells, respectively, highlighted shared upregulation of multiple pathways including mechanistic target of rapamycin kinase [mTOR] signaling (P < 10-5 and z score > 0.3 or < 0.3). Single-cell RNA sequencing analysis demonstrated a strong shift in global gene expression, with upregulation of mTOR signaling in resistant PDX MCL samples. Targeted blockade of mTORC1 with temsirolimus overcame the PRMT5 inhibitor–resistant phenotype, displayed therapeutic synergy in resistant MCL cell lines, and improved survival of a resistant PDX.

Oxidative phosphorylation is a metabolic vulnerability of endocrine therapy and palbociclib resistant metastatic breast cancers

Resistance to endocrine treatments and CDK4/6 inhibitors is considered a near-inevitability in most patients with estrogen receptor positive breast cancers (ER + BC). By genomic and metabolomics analyses of patients’ tumours, metastasis-derived patient-derived xenografts (PDX) and isogenic cell lines we demonstrate that a fraction of metastatic ER + BC is highly reliant on oxidative phosphorylation (OXPHOS). Treatment by the OXPHOS inhibitor IACS-010759 strongly inhibits tumour growth in multiple endocrine and palbociclib resistant PDX. Mutations in the PIK3CA/AKT1 genes are significantly associated with response to IACS-010759. At the metabolic level, in vivo response to IACS-010759 is associated with decreased levels of metabolites of the glutathione, glycogen and pentose phosphate pathways in treated tumours. In vitro, endocrine and palbociclib resistant cells show increased OXPHOS dependency and increased ROS levels upon IACS-010759 treatment. Finally, in ER + BC patients, high expression of OXPHOS associated genes predict poor prognosis. In conclusion, these results identify OXPHOS as a promising target for treatment resistant ER + BC patients.

Species-Deconvolved Proteomics for In Situ Investigation of Tumor-Stroma Interactions after Treatment of Pancreatic Cancer Patient-Derived Xenografts with Combined Gemcitabine and Paclitaxel.

Tumor-stroma interactions are critical in pancreatic ductal adenocarcinoma (PDAC) progression and therapeutics. Patient-derived xenograft (PDX) models recapitulate tumor-stroma interactions, but the conventional antibody-based immunoassay is inadequate to discriminate tumor and stromal proteins. Here, we describe a species-deconvolved proteomics approach embedded in IonStar that can unambiguously quantify the tumor (human-derived) and stromal (mouse-derived) proteins in PDX samples, enabling unbiased investigation of tumor and stromal proteomes with excellent quantitative reproducibility. With this strategy, we studied tumor-stroma interactions in PDAC PDXs that responded differently to Gemcitabine combined with nab-Paclitaxel (GEM+PTX) treatment. By analyzing 48 PDX animals 24 h/192 h after treatment with/without GEM+PTX, we quantified 7262 species-specific proteins under stringent cutoff criteria, with high reproducibility. For the PDX sensitive to GEM+PTX, the drug-dysregulated proteins in tumor cells were involved in suppressed oxidative phosphorylation and the TCA cycle, and in the stroma, inhibition of glycolytic activity was predominant, suggesting a relieved reverse Warburg effect by the treatment. In GEM+PTX-resistant PDXs, protein changes suggested extracellular matrix deposition and activation of tumor cell proliferation. Key findings were validated by immunohistochemistry (IHC). Overall, this approach provides a species-deconvolved proteomic platform that could advance cancer therapeutic studies by enabling unbiased exploration of tumor-stroma interactions in the large number of PDX samples required for such investigations.

Abstract 1102: Establishing the cytotoxic benefit of Tumor Treating Fields on radiation sensitive and acquired radiation resistant glioblastoma patient derived xenograft pairs

Abstract Background: Glioblastoma (GBM) is the most common malignant primary brain tumor with very poor prognosis. The current standard of care for GBM consists of maximal safe tumor resection, chemotherapy (temozolomide) and radiotherapy followed by adjuvant temozolomide and Tumor Treating Fields (TTFields). Unfortunately, GBM displays both inherent and acquired resistance to temozolomide and radiation and is incurable. While TTFields have been found to broadly induce endoplasmic reticulum stress, autophagy, cell membrane permeability, DNA replication stress, anti-mitotic and anti-migratory effects, it is unclear how well TTFields impact radiation resistant GBM. To better understand the cytotoxic benefit of TTFields on acquired radiation resistant GBM, we tested patient-derived xenograft (PDX) brain tumor initiating cells (BTICs) that had been selected for radiation resistance and compared them to their radiation sensitive parent. Methods: PDX were developed with subcutaneous implantation of patient GBM cells into immunodeficient (nu/nu) mice. Acquired radiation resistant PDXs were generated through in vivo selection (6-8 passages) using six fractions of 2 Gray of radiation over two weeks. PDX BTICs were cultured on laminin-coated cover slips under serum free conditions. Cytotoxicity was measured on both the two-dimensional sham control and two-dimensional TTFields treatment conditions over the course of 72 hours and analyzed with crystal violet staining for both imaging and absorbance quantification. PamStation 12 Kinomic data and RNA-seq (Illumina) data was generated for each PDX. Results: Crystal violet quantification and representative imaging indicated that TTFields inhibit cell growth in both parental and acquired radiation resistant PDX-derived BTICs. There is an observed TTFields sensitivity response from the acquired radiation resistant PDX, indicating that TTFields treatment does have a cytotoxic effect on acquired radiation resistant models (seen over four reproducible experiments). Baseline kinomic and transcriptomic differences between the PDX lines suggest potential TTFields sensitivity signatures. Conclusions: Ongoing studies are focused on validation of this cytotoxic effect on larger cohort of both acquired and inherent radiation resistant PDX cells. We plan to measure TTFields -treatment induced kinomic alterations to identify downstream signaling pathways associated with TTFields treatment response, as well as the development of acquired TTFields resistant GBM PDX cells. Citation Format: Taylor L. Schanel, Amber B. Jones, Andee M. Beierle, Hasan Alrefai, Lauren C. Nassour, Patricia H. Hicks, Joshua C. Anderson, Anita B. Hjelmeland, Christopher D. Willey. Establishing the cytotoxic benefit of Tumor Treating Fields on radiation sensitive and acquired radiation resistant glioblastoma patient derived xenograft pairs [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 1102.

Abstract 5011: Targeting kinome reprogramming in ESR1 fusion-driven breast cancer

Abstract Background: Transcriptionally active ESR1 gene fusions (ESR1-TAF) are a potent cause of estrogen receptor alpha-positive (ERα+) breast cancer endocrine therapy (ET) resistance. These ESR1-TAF are gain-of-function mutations, exhibiting estrogen-independent cell growth, motility and ET resistance. They are not directly druggable because the ERα C-terminal ligand binding domain (LBD) encoding sequence is replaced with a translocated in-frame partner gene sequence. Herein we utilized proteomic approaches to develop novel targeted therapies against ESR1-TAF driven tumorigenesis. Methods: ESR1 fusion cDNA constructs were expressed in ERα+ breast cancer cell lines (T47D and MCF7). Cell growth was assayed by an Alamar blue assay. A mass spectrometry (MS)-based Kinase Inhibitor Pulldown Assay (KIPA) was employed to identify druggable kinases that are commonly upregulated by diverse ESR1-TAFs. A panel of 22 ERα+ patient-derived xenograft (PDX) models were profiled using proteomics and phosphoproteomics to identify models with sensitivity to RET kinase inhibition. Results: KIPA detected an increased abundance of a receptor tyrosine kinase, RET, in T47D cells expressing ESR1-TAFs in an estrogen-independent manner, compared to stable cell lines expressing transcriptionally inactive fusions as well as wild-type ERα protein. Interestingly, RET was also increased when constitutive activating ERα LBD point mutants, Y537S and D538G, were expressed in breast cancer cells. Inhibition of the RET kinase in vitro by repurposing pralsetinib, an FDA-approved RET inhibitor for advanced thyroid and non-small-cell lung cancers, demonstrated a significant reduction in the growth of cells expressing ESR1-TAFs and ERα LBD mutants. These data nominate RET kinase as a common therapeutic vulnerability for ESR1-TAF expressing breast cancers. Proteomic profiling of 22 biologically heterogenous ERα+ PDX tumors defined targetable pathways and predicted tumor subsets that were responsive to RET inhibition therapy. Organoids and xenografts from the pan-ET resistant WHIM18 PDX (that expresses the ESR1-YAP1 TAF) were inhibited by pralsetinib to a similar extent as the CDK4/6 inhibitor palbociclib. These data provide key preclinical rationale for the consideration of RET inhibition for the treatment of ESR1-TAF-driven ET-resistant breast cancer. Interestingly, the growth of WHIM37 PDX (that expresses ERα D538G) that had low level of RET and high level of GFRα-1, the co-receptor of RET, was also suppressed by pralsetinib. This data suggests that either RET or GFRα-1 is a predictive biomarker for RET inhibitor efficacy. Conclusions: Kinome analysis of ESR1 translocated breast tumors using KIPA followed by drug sensitivity studies nominated RET as a new therapeutic target for ET-resistant ERα+ breast cancer. Citation Format: Xuxu Gou, Beom-Jun Kim, Meenakshi Anurag, Jonathan T. Lei, Meggie N. Young, Matthew V. Holt, Diana Fandino, Craig T. Vollert, Purba Singh, Mohammad A. Alzubi, Anna Malovannaya, Lacey E. Dobrolecki, Michael T. Lewis, Shunqiang Li, Matthew J. Ellis, Charles E. Foulds. Targeting kinome reprogramming in ESR1 fusion-driven breast cancer. [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 5011.

Abstract 2682: Targeting phosphoglycerate dehydrogenase (PHGDH) in combination with tamoxifen reduces hormone receptor positive breast cancer growth in vivo

Abstract Breast cancer afflicts thousands of individuals every year and is clinically diagnosed in various subtypes, including hormone receptor positive (HR+ BC). Significant strides have been made in treating HR+ BC through the development of endocrine therapies, such as tamoxifen, fulvestrant, and aromatase inhibitors. While these have improved the survival outcomes of these patients, many eventually relapse and, ultimately succumb to metastatic endocrine resistant disease. Subsequent work has identified various cellular pathways contributing to endocrine resistance, including alterations in cellular metabolism. We previously demonstrated that de novo serine synthesis (SSP) is increased in endocrine resistant cell types and genetic disruption of SSP enzymes impacts tamoxifen sensitivity. Further, elevated transcript expression is inversely correlated with survival outcomes in HR+ BC patients treated with tamoxifen. From this, we aimed to assess whether pharmacological targeting of SSP activity in combination with tamoxifen affects the growth of HR+ BC in vivo. We confirmed the presence of ER-alpha in three distinct patient derived xenograft (PDX) models and found varying levels of both phosphoglycerate dehydrogenase (PHGDH) and phosphoserine aminotransferase (PSAT1), which are the first and second enzymatic steps in the SSP pathway, respectively. In our efficacy studies, we initially found differential sensitivity to tamoxifen administration across the PDX models. While treatment with a PHGDH inhibitor (PHGDHi) had no anti-tumor activity against an endocrine-sensitive PDX, it moderately reduced the growth of endocrine resistant PDX tumors. Notably, combinatorial treatment resulted in a substantial decrease in tumor growth in all three models compared to single agents alone. Together, these data suggest that targeting of SSP activity in combination with endocrine therapies may be a promising therapeutic strategy in HR+ BC. Citation Format: Brian F. Clem, Yoannis Imbert-Fernandez, Belinda Petri, Carolyn Klinge. Targeting phosphoglycerate dehydrogenase (PHGDH) in combination with tamoxifen reduces hormone receptor positive breast cancer growth in vivo [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 2682.

Abstract 2961: HLA-G-TCB (RG6353), a T cell bispecific antibody for the treatment of solid tumors in monotherapy and combination with immunomodulator agents

Abstract T-cell bispecific antibodies (TCB) represent a class of therapeutic agents that specifically activate T cells to attack and kill tumor cells. TCBs have demonstrated efficacy in the clinic and are also approved. TCB mediated efficacy in solid tumors, however, has been more challenging to demonstrate. HLA-G-TCB specifically targets human leukocyte antigen G (HLA-G) on tumor cells and cluster of differentiation 3 epsilon chain (CD3ε) expressed on T cells. HLA-G is expressed in a broad range of solid tumor indications and its role in mediating immune suppression makes it an attractive cancer immunotherapy target. Anti-tumor activity of HLA-G-TCB was demonstrated in vitro using different HLA G positive tumor cell lines. T-cell activation, IFN𝛾; secretion, and cytotoxicity induced by HLA G-TCB were shown to be dose dependent and correlating to the HLA G density on cell surface and the percentage of HLA G positive cells. Administration of HLA-G TCB as monotherapy (5mg/kg) to hematopoietic stem cell-humanized NSG mice (Humice) bearing SKOV3 HLA-G tumors resulted in strong tumor growth inhibition resulting in tumor-free animals (7 out of 8). Additionally, in a patient derived xenograft (PDX) tumor model with physiological (low/patchy) HLA-G expression, a significant dose-dependent efficacy ranging from 10-90% was achieved in monotherapy (0.05-5 mg/kg). Treatment of Humice bearing PDX tumors with a combination of HLA-G-TCB and a co-stimulatory immunomodulator resulted in remarkable anti-tumor activity resulting in tumor eradication in 100% of the mice treated with the combination (8 out of 8). A strong synergistic effect was also observed in checkpoint inhibitor resistant PDX tumor model, also resulting in tumor-free mice (5 out of 8) treated with a combination of HLA-G TCB and an immunomodulatory bispecific antibody. In line with the mode of action of TCBs, tumor growth inhibition was accompanied by increased cytokine secretion (including IFN𝛾;), tumoral T cell infiltration and activation as reflected by increased expression of T cell activation markers including CD69, CD25 and Granzyme B. Evaluation of HLA-G expression on tumor cell lines upon IFN𝛾; stimulation in vitro and in PDX tumors treated with HLA-G TCB revealed that HLA-G expression can be upregulated upon IFN𝛾; stimulation and TCB treatment respectively and may positively impact the anti-tumor activity of HLA-G-TCB in vivo. These promising preclinical findings reflect the potential and support the clinical evaluation of HLA-G TCB in treating patients with solid tumors in monotherapy and in combination. HLA-G TCB (RG6353) is being advanced to the clinic in BP44068, an open-label, multicenter, phase 1 study to evaluate safety, pharmacokinetics, and preliminary anti-tumor activity in patients with unresectable and/or metastatic HLA-G expressing solid tumors. Citation Format: Meher Majety, Carina Hage, Alexander Bujotzek, Anneliese Schneider, Martin Lechmann, Nitya Nair, Stefan Zimmerman, Anthony Morel, Christian Klein, Pablo Umana. HLA-G-TCB (RG6353), a T cell bispecific antibody for the treatment of solid tumors in monotherapy and combination with immunomodulator agents [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 2961.

Abstract 393: Determinants of birinapant efficacy in triple negative breast cancer

Abstract Background: Triple-Negative Breast Cancer (TNBC) is an aggressive subtype of breast cancer with few targeted therapies, limiting patients to harsh systemic treatments and resulting in the lowest 5-year survival rate of all breast cancer subtypes. This survival rate plummets after metastasis to another site, making it crucial to identify new therapeutic options for TNBC patients to prevent recurrence and metastasis. The small molecule therapy birinapant, a secondary mitochondrial activator of caspases (SMAC) mimetic, represents a potential new avenue for TNBC treatment. Birinapant initiates apoptotic signaling through targeting of Inhibitor of Apoptosis (IAP) proteins in the Tumor Necrosis Factor Receptor (TNFR) extrinsic apoptosis signaling pathway, leading to the formation of a death complex, caspase activity, and apoptosis. We have found that approximately 25% of TNBC patient-derived xenograft (PDX) and xenograft-derived organoid (PDxO) models are exquisitely sensitive to birinapant treatment. However, the majority of our TNBC patient-derived lines remain resistant through unknown means. We seek to understand the parameters for birinapant response and the mechanism of inherent resistance in TNBC using our patient-derived TNBC models. Approach and Results: Preliminary Western blot experiments revealed that treatment of birinapant-sensitive and resistant PDX tumors in vivo and PDxOs in vitro with birinapant causes degradation of cIAP1 and cIAP2, but only causes apoptosis in birinapant-sensitive lines. Therefore, there may be a disruption of necessary downstream apoptotic signaling in the birinapant-resistant lines. Through follow-up Western blot experiments we determined that at baseline, birinapant-resistant PDxOs do not lack the TNFR extrinsic apoptosis proteins required for apoptosis signaling after IAP degradation, nor is there an abundance of these proteins in the birinapant-sensitive PDxOs. Furthermore, to determine if TNFR extrinsic apoptosis signaling is impaired in birinapant-resistant PDxOs, we treated birinapant-resistant and -sensitive PDxOs with the TNF-a cytokine, which is known to enhance extrinsic apoptosis signaling in the presence of birinapant. Treatment with TNF-a and birinapant did not induce apoptosis in the birinapant-resistant PDxOs, suggesting that the extrinsic apoptosis signaling pathway may be the culprit of resistance in these patient-derived lines. Discussion: Follow-up experiments will address whether an inability to execute extrinsic apoptosis through other death receptor pathways explains birinapant resistance in these models. This work will allow us to uncover what predisposes TNBC patients to be resistant or sensitive to birinapant, and determine how this may be harnessed therapeutically to improve outcomes for TNBC patients. This project was funded in part with federal funds under HHSN261201500003I and U54CA224076. Citation Format: Elisabeth A. Brown, Chieh-Hsiang Yang, Emilio Cortes-Sanchez, Zhengtao Chu, Jeevan Govindharajulu, Ralph Parchment, James Doroshow, Apurva Srivastava, Alana Welm. Determinants of birinapant efficacy in triple negative breast cancer [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 393.

PD04-09 COMBINATION TREATMENT WITH HSP70/STUB1 MODULATOR AND ENZALUTAMIDE YIELDS SYNERGISTIC ACTIVITY IN ADVANCED PROSTATE CANCER

You have accessJournal of UrologyCME1 Apr 2023PD04-09 COMBINATION TREATMENT WITH HSP70/STUB1 MODULATOR AND ENZALUTAMIDE YIELDS SYNERGISTIC ACTIVITY IN ADVANCED PROSTATE CANCER Pengfei Xu, Joy C. Yang, Bo Chen, Christopher Nip, Shu Ning, Allen C. Gao, Hao Shao, Jason Gestwicki, Christopher P. Evans, and Chengfei Liu Pengfei XuPengfei Xu More articles by this author , Joy C. YangJoy C. Yang More articles by this author , Bo ChenBo Chen More articles by this author , Christopher NipChristopher Nip More articles by this author , Shu NingShu Ning More articles by this author , Allen C. GaoAllen C. Gao More articles by this author , Hao ShaoHao Shao More articles by this author , Jason GestwickiJason Gestwicki More articles by this author , Christopher P. EvansChristopher P. Evans More articles by this author , and Chengfei LiuChengfei Liu More articles by this author View All Author Informationhttps://doi.org/10.1097/JU.0000000000003228.09AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail Abstract INTRODUCTION AND OBJECTIVE: Ubiquitin proteasome system is suppressed in enzalutamide resistant prostate cancer cells and that the HSP70/STUB1 machinery is involved in androgen receptor (AR) and AR variant protein stabilization. Targeting HSP70 could be a valuable strategy to overcome the resistance of androgen receptor signaling inhibitors (ARSI) in advanced prostate cancer. In this study, we tested novel HSP70/STUB1modulators in enzalutamide resistant cells and patient-derived prostate cancer cell models. METHODS: Expression of AR-V7, HSP70 and STUB1 were determined by qRT-PCR and western blot. Expression of HSP70 and STUB1 was down-regulated using specific siRNA. HSP70/STUB1 and AR-V7 interaction was determined by co-immunoprecipitation and dual immunofluorescence. Tumor organoids were established from the patient derived xenografts (PDX) and the viability was stained by LIVE/DEAD™ Cell Imaging Kit. The effects of HSP70 inhibitors on enzalutamide sensitivity were examined in cell line model and patient-derived cell models. RESULTS: A novel HSP70 inhibitor JG98 significantly suppressed drug resistant C4-2B MDVR and CWR22Rv1 cell growth and enhanced enzalutamide treatment (p<0.001). JG98 also suppressed the PDX derived organoid growth and induced organoid death in a dose dependent manner (p<0.001). Mechanistically, JG98 suppressed AR/AR-V7 expression in resistant cells and promoted STUB1 entering into the nucleus and bound to AR-V7. Knockdown of STUB1 diminished the anti-cancer effect and AR-V7 inhibition by JG98. A more potent HSP70 inhibitor JG231 was developed from JG98. JG231 significantly improved the drug solubility and showed better pharmacokinetic characteristics than JG98. Moreover, JG231 effectively suppressed the cell growth and enhanced enzalutamide treatment in resistant cells and PDX derived prostate cancer cells (p<0.001). CONCLUSIONS: The HSP70/STUB1 machinery involved in AR/AR-V7 regulation and enzalutamide resistance. Targeting HSP70 by novel HSP70/STUB1 modulators overcome the ARSI resistance and improve their therapy. Source of Funding: This work was supported in part by grants NIH/NCI R37CA249108 (C, Liu) and R01CA251253 (C, Liu) © 2023 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 209Issue Supplement 4April 2023Page: e145 Advertisement Copyright & Permissions© 2023 by American Urological Association Education and Research, Inc.MetricsAuthor Information Pengfei Xu More articles by this author Joy C. Yang More articles by this author Bo Chen More articles by this author Christopher Nip More articles by this author Shu Ning More articles by this author Allen C. Gao More articles by this author Hao Shao More articles by this author Jason Gestwicki More articles by this author Christopher P. Evans More articles by this author Chengfei Liu More articles by this author Expand All Advertisement PDF downloadLoading ...

Targeting mTOR to overcome resistance to hormone and CDK4/6 inhibitors in ER-positive breast cancer models

Resistance to therapy remains a major obstacle in cancer management. Although treatment with hormone and CDK4/6 inhibitors is successful in luminal breast cancer, resistance to these treatments is frequent, highlighting the need for novel therapeutic strategies to delay disease progression and improve patient survival. Here, we assessed the mechanisms of acquired resistance using T47D and MCF-7 tamoxifen- and palbociclib-resistant cell-line variants in culture and as xenografts, and patient-derived cells (PDCs) obtained from sensitive or resistant patient-derived xenografts (PDXs). In these models, we analyzed the effect of specific kinase inhibitors on survival, signaling and cellular aggressiveness. Our results revealed that mTOR inhibition is more effective than PI3K inhibition in overcoming resistance, irrespective of PIK3CA mutation status, by decreasing cell proliferation and tumor growth, as well as reducing cell migration and stemness. Moreover, a combination of mTOR and CDK4/6 inhibitors may prevent pathway reactivation downstream of PI3K, interfering with the survival of resistant cells and consequent tumor escape. In conclusion, we highlight the benefits of incorporating mTOR inhibitors into the current therapy in ER + breast cancer. This alternative therapeutic strategy not only enhances the antitumor response but may also delay the emergence of resistance and tumor recurrence.