Mechanisms Of Therapeutic Resistance Research Articles

Strategies to Target Chemoradiotherapy Resistance in Small Cell Lung Cancer.

Background: Small cell lung cancer (SCLC) is a lethal form of lung cancer with few treatment options and a high rate of relapse. While SCLC is initially sensitive to first-line DNA-damaging chemo- and radiotherapy, relapse disease is almost universally therapy-resistant. As a result, there has been interest in understanding the mechanisms of therapeutic resistance in this disease. Conclusions: Progress has been made in elucidating these mechanisms, particularly as they relate to the DNA damage response and SCLC differentiation and transformation, leading to many clinical trials investigating new therapies and combinations. Yet there remain many gaps in our understanding, such as the effect of epigenetics or the tumor microenvironment on treatment response, and no single mechanism has been found to be ubiquitous, suggesting a significant heterogeneity in the mechanisms of acquired resistance. Nevertheless, the advancement of techniques in the laboratory and the clinic will improve our ability to study this disease, especially in patient populations, and identify methods to surmount therapeutic resistance.

Characterization of cell states in biliary tract cancers identifies mechanisms of therapeutic resistance in a phase II trial of DKN-01/nivolumab.

Biliary tract cancers demonstrate profound therapeutic resistance, and broadly effective therapies for refractory disease are lacking. We conducted a single-arm, second-line phase II trial combining DKN-01, a humanized monoclonal antibody targeting Dickkopf-1 (DKK-1), and nivolumab to treat patients with advanced biliary tract cancer ( NCT04057365 ). No objective responses were seen. To identify mechanisms of treatment failure, we analyzed paired pre-treatment and on-treatment biopsies using scRNA-seq and constructed a detailed molecular classification of malignant and immune cells. We annotated five biliary tract cancer malignant cell states: classical, basal, mesenchymal, neural-like, and endothelial-like. Neural-like and endothelial-like states, which drive therapeutic resistance in other cancers, have not previously been described in BTC. Malignant cell states co-varied with distinct immune cell states, revealing diverse mechanisms of myeloid and T-cell mediated immune suppression, including M2 myeloid and terminally exhausted T cell programs that were induced by DKN-01/nivolumab. Here, we provide the first systematic classification of functionally annotated cell states in biliary tract cancer and provide new insight into resistance mechanisms to an immunotherapy combination that can inform the next generation of trials.

Cancer associated variant enrichment CAVE, a gene agnostic approach to identify low burden variants in chronic lymphocytic leukemia

Intratumoral heterogeneity is an important clinical challenge because low burden clones expressing specific genetic alterations drive therapeutic resistance mechanisms. We have developed CAVE (cancer-associated variant enrichment), a gene-agnostic computational tool to identify specific enrichment of low-burden cancer driver variants in next-generation sequencing (NGS) data. For this study, CAVE was applied to TP53 in chronic lymphocytic leukemia (CLL) as a cancer model. Indeed, as TP53 mutations are part of treatment decision-making algorithms and low-burden variants are frequent, there is a need to distinguish true variants from background noise. Recommendations have been published for reliable calling of low-VAF variants of TP53 in CLL and the assessment of the background noise for each platform is essential for the quality of the testing. CAVE is able to detect specific enrichment of low-burden variants starting at variant allele frequencies (VAFs) as low as 0.3%. In silico TP53 dependent and independent analyses confirmed the true driver nature of all these variants. Orthogonal validation using either ddPCR or NGS analyses of follow-up samples confirmed variant identification. CAVE can be easily deployed in any cancer-related NGS workflow to detect the enrichment of low-burden variants of clinical interest.

Treatment resistance to melanoma therapeutics on a single cell level

Therapy targeting the BRAF-MEK cascade created a treatment revolution for patients with BRAF mutant advanced melanoma. Unfortunately, 80% patients treated will progress by 5 years follow-up. Thus, it is imperative we study mechanisms of melanoma progression and therapeutic resistance. We created a scRNA (single cell RNA) atlas of 128,230 cells from 18 tumors across the treatment spectrum, discovering melanoma cells clustered strongly by transcriptome profiles of patients of origins. Our cell-level investigation revealed gains of 1q and 7q as likely early clonal events in metastatic melanomas. By comparing patient tumors and their derivative cell lines, we observed that PD1 responsive tumor fraction disappears when cells are propagated in vitro. We further established three anti-BRAF-MEK treatment resistant cell lines using three BRAF mutant tumors. ALDOA and PGK1 were found to be highly expressed in treatment resistant cell populations and metformin was effective in targeting the resistant cells. Our study suggests that the investigation of patient tumors and their derivative lines is essential for understanding disease progression, treatment response and resistance.

Abstract C066: Identifying Transcriptional Drivers of Plasticity in Pancreatic Cancer

Abstract Pancreatic ductal adenocarcinoma (PDAC) remains a deadly disease with few effective treatments. Even with the advent of mutationally-directed therapies targeting the KRAS oncogene, PDAC transcriptional plasticity remains a major mechanism of therapeutic resistance. As a result, there is a desperate need to develop additional strategies to treat this deadly disease. In addition to the canonical genomic alterations in KRAS, TP53, CDKN2A, and SMAD4, PDAC tumors exhibit diverse transcriptional programs, or "cell states," with prognostic implications: PDAC tumors in the “classical state” are more responsive to upfront chemotherapy and have better outcomes, while those in the “basal state” are more aggressive with poorer prognoses. Currently, PDAC cell states are not used to direct therapy. Cell state is an integrative property shaped by both cell-intrinsic (e.g., mutations, epigenetics) and cell-extrinsic (e.g., tumor microenvironment) factors. In our prior work, single-cell analyses of clinical PDAC samples demonstrated notable cell state heterogeneity and plasticity. In addition, longitudinal monitoring of patient-derived organoids showed that cells can shift from classical to basal or coexpressor states as the environment changes, and that these cell states can drastically influence drug response. However, it remains unknown which signaling and transcriptional pathways induce basal or classical states, and whether these gene regulatory networks can be targeted therapeutically. Thus, there is a pressing need to devise scalable methods to determine essential drivers for prognostically relevant cancer cell states.Here, we aim to systematically and unbiasedly identify transcription factors (TFs) that drive basal and classical cell states in PDAC. We have successfully established a high-throughput screening pipeline to 1) over-express all human TF isoforms in a pooled format within a cohort of PDAC models; 2) sort cells using antibodies against state-specific cell surface markers; and 3) perform single-cell RNA sequencing on sorted cells to nominate individual TFs or combinations that induce specific cell state transitions. Preliminary results identify both previously reported (e.g., GATA4) and new TFs that can induce the classical state. By overexpressing TFs individually or in combination, we are able to engineer PDAC cell line models that more faithfully reflect the transcriptional phenotypes observed in patient tumors. Ultimately, we aim to use this approach to construct high-fidelity isogenic but state-variant PDAC models for use both in therapeutic screening and as a substrate for investigating mechanisms governing cancer cell state plasticity. Citation Format: Yuzhou Evelyn Tong, Aswanth Mahalingam, Walaa E Katan, Julia Joung, Alex K Shalek, Peter S Winter, Srivatsan Raghavan. Identifying Transcriptional Drivers of Plasticity in Pancreatic Cancer [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research; 2024 Sep 15-18; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(17 Suppl_2):Abstract nr C066.

Next-generation DC vaccines with an immunogenic trajectory against cancer: therapeutic opportunities vs. resistance mechanisms.

Next-generation DC vaccines with an immunogenic trajectory against cancer: therapeutic opportunities vs. resistance mechanisms.

Amino acid deprivation in cancer cells with compensatory autophagy induction increases sensitivity to autophagy inhibitors

ABSTRACT Inhibition of autophagy is an important strategy in cancer therapy. However, prolonged inhibition of certain autophagies in established cancer cells may increase therapeutic resistance, though the underlying mechanisms of its induction and enhancement remain unclear. This study sought to elucidate the mechanisms of therapeutic resistance through repeated autophagy inhibition and amino acid deprivation (AD) in an in vitro model of in vivo chronic nutrient deprivation associated with cancer cell treatment. In the human cervical cancer cell line HeLa and human breast cancer cell line MCF-7, initial extracellular AD induced the immediate expression of endosomal microautophagy (eMI). However, repeated inhibition of eMI with U18666A and extracellular AD induced macroautophagy (MA) to compensate for reduced eMI, simultaneously decreasing cytotoxicity. Here, hyperphosphorylated JNK was transformed into a hypophosphorylated state, suggesting conversion of the cell death signal to a survival signal. In a nutrient medium, cell death could not be induced by MA inhibition. However, since LAT1 inhibitors induce intracellular AD, combining them with MA and eMI inhibitors successfully promoted cell death in resistant cells. Our study identified a novel therapeuic approach for promoting cell death and addressing therapeutic resistance in cancers under autophagy-inhibitor treatment.

H3K27-Altered Diffuse Midline Glioma of the Brainstem: From Molecular Mechanisms to Targeted Interventions.

Pediatric high-grade gliomas are a devastating subset of brain tumors, characterized by their aggressive pathophysiology and limited treatment options. Among them, H3 K27-altered diffuse midline gliomas (DMG) of the brainstem stand out due to their distinct molecular features and dismal prognosis. Recent advances in molecular profiling techniques have unveiled the critical role of H3 K27 alterations, particularly a lysine-to-methionine mutation on position 27 (K27M) of the histone H3 tail, in the pathogenesis of DMG. These mutations result in epigenetic dysregulation, which leads to altered chromatin structure and gene expression patterns in DMG tumor cells, ultimately contributing to the aggressive phenotype of DMG. The exploration of targeted therapeutic avenues for DMG has gained momentum in recent years. Therapies, including epigenetic modifiers, kinase inhibitors, and immunotherapies, are under active investigation; these approaches aim to disrupt aberrant signaling cascades and overcome the various mechanisms of therapeutic resistance in DMG. Challenges, including blood-brain barrier penetration and DMG tumor heterogeneity, require innovative approaches to improve drug delivery and personalized treatment strategies. This review aims to provide a comprehensive overview of the evolving understanding of DMG, focusing on the intricate molecular mechanisms driving tumorigenesis/tumor progression and the current landscape of emerging targeted interventions.

Clinical Management of Advanced Prostate Cancer: Where Does Radiopharmaceutical Therapy Fit in the Treatment Algorithm?

Most men with newly appreciated metastatic prostate cancer are optimally treated with a backbone consisting of androgen receptor-directed therapy with or without taxane chemotherapy. Despite improvements in disease outcomes, prostate cancer remains an extremely heterogeneous disease with variable mechanisms of therapeutic resistance. As a result, it remains a leading cause of cancer-related death in men. Radiopharmaceutical therapy has emerged as an alternative, non-androgen receptor-directed treatment modality for metastatic castration-resistant prostate cancer that impacts patient survival and represents a potentially more personalized approach. In this review, we aim to outline the current treatment landscape for metastatic prostate cancer with a focus on radiopharmaceutical therapy, specifically 177Lu-PSMA-617. In addition, we illustrate various clinical challenges with 177Lu-PSMA-617 treatment to date and explore investigative efforts to leverage radiopharmaceutical therapies as part of combination regimens or earlier in the treatment algorithm to further improve patient outcomes. Finally, we introduce ongoing studies of alternative radiopharmaceutical therapies in metastatic prostate cancer that may be incorporated into the treatment algorithm pending further study.

Abstract 3232: LSD1 inhibition transcriptionally reprograms neuroendocrine prostate cancer exposing unique therapeutic vulnerabilities

Abstract Therapeutics have been developed to target castration-resistant prostate cancer (CRPC) classified as adenocarcinoma (CRPC-Adeno). However, an increasing frequency of CRPC-Adeno tumors progress to the highly aggressive and lethal neuroendocrine prostate cancer (NEPC) by acquiring a neuroendocrine (NE) phenotype as a mechanism of therapeutic resistance. This transformation from CRPC-Adeno to NEPC requires distinct epigenetic reprogramming by lysine-specific demethylase 1 (LSD1), which can be exploited for development of novel therapies to target NEPC. LSD1 is upregulated in NEPC and promotes a stem-like transition state through lineage plasticity which enables the cancer cell to undergo NE differentiation. We have shown that LSD1 inhibition reduces the NE program, driving NEPC towards a non-neuroendocrine state through ASCL1 suppression and YAP1 re-expression. This less aggressive non-neuroendocrine state exposes unique vulnerabilities for the development of novel combination therapies to treat this lethal disease. Citation Format: Sumer M. Jasmine, Adel Mandl, Susan L. Dalrymple, Sunghyun Kim, Jennifer Dias, Maria Kleppe, Cassandra Celatka, Amy Tapper, Ilsa Coleman, Peter Nelson, Hugh Rienhoff, Samuel R. Denmeade, W. Nathaniel Brennen. LSD1 inhibition transcriptionally reprograms neuroendocrine prostate cancer exposing unique therapeutic vulnerabilities [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 3232.

Abstract 1852: NCI’s Clinical Proteomic Tumor Analysis Consortium: A proteogenomic cancer analysis program

Abstract The National Cancer Institute’s Clinical Proteomic Tumor Analysis Consortium (NCI’s CPTAC) is a national effort to accelerate the understanding of cancer biology through the integration of large-scale proteome and genome analysis, or proteogenomics. The program which is composed of a Tumor Characterization Program and a Translational Research Program (proteomics.cancer.gov) aims to leverage the investments made in cancer research by understanding the molecular changes by proteogenomically characterizing cancers and accelerating the basic discovery toward clinical impact. All data and analytical tools are made broadly available to the research community through public databases to maximize utility and public benefit.CPTAC teams have characterized a plethora of treatment-naïve tumor types, including colorectal, ovarian, breast, clear cell renal cell carcinoma, uterine corpus endometrial carcinoma, lung adenocarcinoma, lung squamous cell carcinoma, brain (including adult, pediatric, and adolescent and young adult), head and neck squamous cell carcinoma, and pancreatic ductal adenocarcinoma (proteomics.cancer.gov/resources/milestones-and-publications). Ongoing projects include acute myeloid leukemia (AML), cutaneous melanoma, sarcoma, oligodendroglioma, gastric, prostate, liver, and thyroid cancers. In the PTRC Program, CPTAC is partnering with NCI-sponsored clinical trials to support clinically relevant research projects that would elucidate biological mechanisms of therapeutic response, resistance, and/or toxicity in cancers including AML, multiple myeloma, melanoma, and lung cancers. All mass spectrometry-based proteomic, genomic, and imaging data (histopathology and radiology) are made publicly available at the CPTAC Proteomic Data Commons (pdc.cancer.gov), Genomic Data Commons (gdc.cancer.gov), and the Cancer Imaging Archive (cancerimagingarchive.net)/Imaging Data Commons (imaging.datacommons.cancer.gov) respectively. CPTAC is also supporting development of new proteogenomic data analysis tools (proteomics.cancer.gov/resources/computational-tools). In addition, the CPTAC Assay Portal (assays.cancer.gov) is a public resource populated with mass spectrometry-based targeted proteomic assays developed by the consortium for quantitatively measuring proteins of interest, including those discovered through comprehensive tumor characterization. Lastly, well-characterized monoclonal antibodies targeting cancer-specific proteins and peptides are also made available at CPTAC’s Antibody Portal (antibodies.cancer.gov). Citation Format: Mehdi Mesri, Eunkyung An, Xu Zhang, Jasmin Bavarva, Ana I. Robles, Tara Hiltke, Henry Rodriguez. NCI’s Clinical Proteomic Tumor Analysis Consortium: A proteogenomic cancer analysis program [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 1852.

Abstract 5993: Temporal dynamics of ferroptosis vulnerability in a resistant cancer cell state

Abstract Once cancer has metastasized it remains incurable as a result of evolved resistance to nearly all systemic therapies. Our group has demonstrated that an endocycling cancer cell state is an underappreciated mechanism of therapeutic resistance in many cancer settings. Cells in this state uncouple DNA replication from cell division to obtain abnormally high genomic content and cell size (over 40x volume). Resulting polyploidy and cellular hypertrophy provide survival advantages such as elevated genomic content, higher oxidative buffer capacity, increased autophagy, and heightened resistance to chemotherapy. Endocycling cancer cells are induced by multiple different classes of chemotherapy and present in vivo at increased frequencies both in metastatic sites and following chemotherapy. We hypothesize elimination of this overlooked resistant cancer cell state is critical for sustained anticancer therapies. Cancer cells, including those in the endocycling cancer cell state, leverage canonical cell cycle and cell death programs to evade apoptosis from external stressors including all classes of chemotherapy. Engaging cell cycle-independent death pathways is an alternative therapeutic strategy that circumvents cancer’s trademark manipulation of the cell cycle1. Ferroptosis is a cell cycle agnostic form of cell death that occurs due to dysregulation of cellular iron and subsequent lipid peroxidation. While ferroptosis is emerging as a vulnerability in resistant cancers, efficacy of ferroptosis induction is highly heterogeneous depending on tissue type, cellular metabolism, and many other factors. We characterized oxidative damage, labile iron, lipid content, and signaling pathways in cells pre- and post-chemotherapy to assess vulnerability to ferroptosis. By inhibiting GPX4, the sole lipophilic antioxidant enzyme, we show induction of ferroptotic cell death across multiple cell lines and chemotherapies with cells in the endocycling state being more susceptible. Importantly, targeting cells in the endocycling cancer cell state (as opposed to untreated cell lines), also affords a more uniform elimination by ferroptosis. Ferroptosis also has a capacity to be immunogenic that may direct anti-cancer immune licensing in addition to direct cytotoxicity. These studies will directly contribute to development of ferroptosis engaging therapeutic strategies for resistant cancer cell states, particularly concerning the timing of intervention. 1Loftus, L.V.; Amend, S.R.; Pienta, K.J. Interplay between Cell Death and Cell Proliferation Reveals New Strategies for Cancer Therapy. Int. J. Mol. Sci. 2022, 23, 4723. https://doi.org/10.3390/ijms23094723 Citation Format: Luke Loftus, Ken Pienta, Sarah Amend. Temporal dynamics of ferroptosis vulnerability in a resistant cancer cell state [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 5993.

Fundamentals and Applications of Focused Ultrasound-Assisted Cancer Immune Checkpoint Inhibition for Solid Tumors.

Despite spectacular clinical successes across several cancer types, immune checkpoint inhibition is effective only in subgroups of patients and suffers from significant systemic toxicities, highlighting the need to understand and locally overcome the mechanisms of therapeutic resistance. Similarly to other therapeutics, immunotherapies face delivery challenges (for example, antibodies need to reach their targets) and immunological barriers that are unique to solid tumors and their microenvironment. Interestingly, focused ultrasound (FUS), with or without microbubbles, which has been shown to enhance gene and drug delivery, notably in oncology, has been recently found to trigger immunological responses. In recent years, there has been a strong emphasis on understanding the biological and immunological effects of FUS for cancer therapy, and FUS is now emerging as an approach that can improve cancer immunotherapy. We herein review: (1) the immunological barriers implicated in ICI resistance; (2) the fundamentals of FUS +/- MB and the current knowledge on leveraging FUS +/- MB bioeffects for improving ICI therapy efficacy; (3) the immune profile of tumor models that have been successfully treated with FUS and ICI; and finally, (4) we discuss the challenges ahead for translating FUS and MB treatments to the clinic, highlighting the exciting perspectives for this new research area.

Current therapeutic landscape and resistance mechanisms to larotrectinib.

Current therapeutic landscape and resistance mechanisms to larotrectinib.

Abstract B040: Trispecific killer engagers against IGF1R and fetal form of insulin receptor induce human natural killer cell mediated killing of hormone receptor positive breast cancer in vitro and in vivo

Abstract Patients with hormone receptor-positive (HR+) breast cancers frequently recur with metastatic disease 5-20 years after the initial diagnosis and completion of chemotherapy and prolonged treatment with hormonal therapy. Thus, patients with metastatic HR+ breast cancer need new therapeutic options. A potential mechanism of therapeutic resistance in HR+ patients is the presence of slow-growing, well-differentiated cancer cells that result in clinically detectable metastases after a prolonged latency. One way to eliminate these cancer cells is with immunotherapy (IT). Unfortunately HR+ breast cancers have not responded to current T-cell based IT. The objective of this study is to target HR+ breast cancers using a natural killer (NK) cell based approach that targets cell surface receptors in HR+ breast cancer. The type I IGF receptor (IGF1R) is expressed on HR+ breast cancers and its expression is tightly related to ER function. Endocrine therapy resistance is associated with increased expression of the A-isoform or fetal form of IR (IR-A) and depend on IR signaling. We hypothesized that a drug that would target NK cells to IGF1R or IR-A expressing HR+ cells will be effective in killing them. We generated IGF1R or IR-A specific Tri specific Killer Engagers (TriKE) that leverage expression of IGF1R and IR-A on HR+ cells to cause NK directed death. The IGF1R TriKE consists of humanized single domain antibody (VHH) sequence of a CD16 nanobody to engage and activate NK cells, a humanized VHH of a nanobody against IGF1R to target HR+ breast cancer cells, and an IL-15 molecule between them to drive NK cell expansion and survival. The IGF1R TriKE did not bind embryonal fibroblasts from IGF1R knock out mice (R- cells) but bound R-/IGF1R cells (R- cells engineered to express human IGF1R) and to IGF1R+ MCF-7 and T47D breast cancer cells indicating specific binding to IGF1R on cells. It did not cause downregulation of IGF1R levels in multiple HR+ breast cancer cells and did not inhibit signaling via IGF1R. It specifically induced NK cell degranulation, measured by surface CD107a expression and intracellular IFNγ, against IGF1R+ target breast cancer cells (MCF-7, T-47D, ZR-75-1) in a functional assay compared to the anti-IGF1R nanobody. It did not induce degranulation of NK cells against IGF1R negative cells suggesting that the functionality was specific for IGF1R expressing targets. The IGF1R TriKE enhanced cell killing of HR+ breast cancer cells as measured by cytotoxicity assays. IGF1R TriKE combined with human NK cells inhibited tumor growth of MCF-7 tumors in NSG mice compared to control groups. Human NK cells persisted in peripheral blood three weeks after final NK infusion based on flow cytometry assessment. The IR-A TriKE incorporated a novel engineered non-immunoglobulin IR-A specific peptide binder. Our preliminary data show that the IR-A TriKE degranulated NK cells against breast cancer cells overexpressing IR-A. These data indicate that this strategy could be an effective treatment for HR+ metastatic breast cancer and make them responsive to IT. Citation Format: Courtney Baar, Emily Chiu, Yvette Soignier, Behiye Kodal, Jeffrey S Miller, Martin Felices, Deepali Sachdev. Trispecific killer engagers against IGF1R and fetal form of insulin receptor induce human natural killer cell mediated killing of hormone receptor positive breast cancer in vitro and in vivo [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Breast Cancer Research; 2023 Oct 19-22; San Diego, California. Philadelphia (PA): AACR; Cancer Res 2024;84(3 Suppl_1):Abstract nr B040.

ABC transporter expression to predict therapeutic effect of enfortumab vedotin in urothelial cancer.

693 Background: Enfortumab vedotin (EV) is an antibody-drug conjugate consisting of anti-Nectin-4 antibody and is approved for metastatic urothelial cancer. Predictors of therapeutic benefit of EV have not been established since nectin-4 expression varies widely with the course of treatment. ATP Binding Cassette (ABC) transporters which export the administered anti-cancer drugs out of the cells have been postulated as one of the mechanisms of therapeutic resistance to EV. In this study, we evaluated the expression of Nectin-4 and ABC transporters in primary biopsy tissues, primary radical resection tissues, and metastatic sites from urothelial cancer patients and evaluated their association with prognosis after EV therapy. Methods: We studied 16 patients who received enfortumab vedotin for metastatic urothelial cancer. Biopsy of primary tissue, radical surgery of primary tumor, and resection of metastatic sites was performed in 16, 7, and 4 patients, respectively. In these specimens, the expression of nectin-4 and ABC transporters was evaluated by immunostaining. Among ABC transporters, we evaluated MDR1 (ABCB1), MRP1 (ABCC1), and BCRP (ABCG2) since they have been reported to be associated with anticancer drug resistance. Staining intensity on the cell membrane was classified into 0 to 3 according to the evaluation criteria of HER2. We investigated the relationship between the expression of nectin-4 and ABC transporters and survival after EV therapy. Results: Nectin-4 was positive in all patients (score 3 in 12 patients, score 1 in 4 patients) in primary biopsy. All patients tested negative for MDR1. MRP1 was positive in 11 (score 2 in 2 patients and score 1 in 9 patients), and BCRP was positive in 14 (score 2 in 10 patients, score 1 in 4 patients). Nectin-4 expression decreased in radical surgery tissues and metastatic sites. On the other hand, ABC transporter expression remained unchanged or rather increased in radical surgery tissues and metastatic sites (Table). Patients with both MRP1 and BCRP expression in the primary biopsy specimen (n=8) had significantly worse PFS and OS after EV therapy while nectin-4 expression in the primary biopsy specimen was not associated with survival. Conclusions: Patients with ABC transporter expression had a poor prognosis after EV therapy, although nectin-4 expression in primary biopsies was not associated with prognosis. Nectin-4 expression tended to decrease, while the ABC transporter remained unchanged or enhanced as the disease progressed. [Table: see text]

Abstract A100: KRAS inhibition targets and depends on pro-oncogenic HuR in PDAC cells

Abstract The Kirsten rat sarcoma viral oncogene homolog (KRAS) mutation is found in more than 90% of patients with pancreatic ductal adenocarcinomas (PDACs), making it a prime target for therapeutic drug development. HuR (ELAVL1) has been extensively studied in the context of PDAC and also plays a key role in PDAC progression and chemoresistance. In recent years, researchers have shed light on the specific role of the HuR protein in PDAC and its relationship with KRAS signaling. Using in KRASG12D – mutant patient derived models, cell lines derived from GEMM models, and conventional cell lines, we found that HuR CRISPR knock out lines showed more than 80-fold resistance to MRTX1133 (a KRAS inhibitor targeted against G12D mutation) compared to wild type cells. Furthermore, western blot and immunofluorescence studies demonstrated that therapeutic inhibition of KRAS, inhibited HuR protein expression and subcellular localization in as early as 3 hours post-treatment. Furthermore, HuR protein levels decreased post-treatment even under nutrient starvation. Herein, we show that the presence of HuR is necessary for the efficacy of KRAS targeting and Kras inhibition can rapidly degrade HuR protein levels and its active subcellular localization. Mechanistic studies determining the molecular interaction between HuR and KRAS and KRAS related proteins and mRNAs are underway. Taken together with ongoing studies, we are exploring the importance of HuR as a key downstream target of KRAS’ oncogenic activity and if the loss of HuR may be a potent, PDAC therapeutic resistance mechanism. Understanding the interplay between KRAS and HuR could offer a novel strategy to disrupt the oncogenic KRAS signaling cascade and overcome the potential inherent resistance of KRAS-mutant PDACs to promising, KRAS-targeted therapies. Citation Format: Hen Halamish, Michaela Bush, Alexander Smith, Rosalie Sears, Jonathan Brody. KRAS inhibition targets and depends on pro-oncogenic HuR in PDAC cells [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Pancreatic Cancer; 2023 Sep 27-30; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84(2 Suppl):Abstract nr A100.

Trogocytosis of CAR molecule regulates CAR-T cell dysfunction and tumor antigen escape

Chimeric antigen receptor (CAR) T-cell therapy has demonstrated clinical response in treating both hematologic malignancies and solid tumors. Although instances of rapid tumor remissions have been observed in animal models and clinical trials, tumor relapses occur with multiple therapeutic resistance mechanisms. Furthermore, while the mechanisms underlying the long-term therapeutic resistance are well-known, short-term adaptation remains less understood. However, more views shed light on short-term adaptation and hold that it provides an opportunity window for long-term resistance. In this study, we explore a previously unreported mechanism in which tumor cells employ trogocytosis to acquire CAR molecules from CAR-T cells, a reversal of previously documented processes. This mechanism results in the depletion of CAR molecules and subsequent CAR-T cell dysfunction, also leading to short-term antigen loss and antigen masking. Such type of intercellular communication is independent of CAR downstream signaling, CAR-T cell condition, target antigen, and tumor cell type. However, it is mainly dependent on antigen density and CAR sensitivity, and is associated with tumor cell cholesterol metabolism. Partial mitigation of this trogocytosis-induced CAR molecule transfer can be achieved by adaptively administering CAR-T cells with antigen density-individualized CAR sensitivities. Together, our study reveals a dynamic process of CAR molecule transfer and refining the framework of clinical CAR-T therapy for solid tumors.

Management Challenges of Extrapulmonary Nontuberculous Mycobacterial Infection: A Single-Center Case Series and Literature Review.

Extrapulmonary nontuberculous mycobacterial (NTM) disease remains largely enigmatic, yet these mycobacteria are increasingly acknowledged as important opportunistic pathogens in humans. Traditionally, NTM infections have been identified across various anatomical locations, with the respiratory system being the most affected and best understood. Historically, extrapulmonary NTM infection was predominantly associated with HIV/AIDS, with Mycobacterium avium lymphadenopathy being the most commonly reported. Today, however, because of the expanding utilization of immunosuppressive therapies and the demographic shift towards an aging population, an increasing number of NTM infections are expected and seen. Hence, a heightened index of suspicion is essential, necessitating a multifaceted approach to identification and drug sensitivity testing to improve treatment outcomes. In extrapulmonary NTM management, expert consultation is strongly recommended to determine the most efficacious treatment regimen, as individualized, patient-tailored therapies are often required. Furthermore, the economic burden of NTM disease is considerable, accompanied by high rates of hospitalization. To optimize the management of these intricate infections, there is an urgent need for comprehensive data on incidence, prevalence, and outcomes. This case-based series delves into the intricate nature of extrapulmonary NTM infections, focusing on both rapid and slow-growing NTM species, and explores therapeutic options, resistance mechanisms, and host-related immunological factors.

Emerging Therapeutic Targets and Drug Resistance Mechanisms in Immunotherapy of Hematological Malignancies.

CAR-T cell therapy has revolutionized the treatment of hematological malignancies with high remission rates in the case of ALL and NHL. This therapy has some limitations such as long manufacturing periods, persistent restricted cell sources and high costs. Moreover, combination regimens increase the risk of immune-related adverse events, so the identification new therapeutic targets is important to minimize the risk of toxicities and to guide more effective approaches. Cancer cells employ several mechanisms to evade immunosurveillance, which causes resistance to immunotherapy; therefore, a very important therapeutic approach is to focus on the development of rational combinations of targeted therapies with non-overlapping toxicities. Recent progress in the development of new inhibitory clusters of differentiation (CDs), signaling pathway molecules, checkpoint inhibitors, and immunosuppressive cell subsets and factors in the tumor microenvironment (TME) has significantly improved anticancer responses. Novel strategies regarding combination immunotherapies with CAR-T cells are the most promising approach to cure cancer.