Abstract Patient-derived tumor slices (PDS) have been used to evaluate drug sensitivity in multiple human tumor types. Despite this, standardized parameters to establish PDS as a precision medicine tool are lacking. Here we benchmarked proliferation rates and standard deviations from 40 gastrointestinal cancer specimens, defining normal biological variation. Here the mean standard deviation rates in pancreatic duct adenocarcinoma (PDAC), appendiceal cancer, and colorectal adenocarcinomas were 10%, 6%, and 15%, respectively. Using these data, we established threshold criteria set at a z-score of 3 standard deviations in order to distinguish meaningful drug sensitivity to the pan-RAS(On) inhibitor RMC-6236, from that of normal biological variation. This framework enabled classification of PDAC and appendiceal PDS cultures as sensitive or resistant. To benchmark the predictive value of slice assays, we compared RAS-inhibitor activity across matched patient-derived organoids (PDOs) and xenografts (PDXs), and further determined that slice-based assay sensitivity predicted sensitivity and survival outcomes in matching orthogonal tumor models. Citation Format: Kevin Gulay, Rithika Medari, Isabella Ng, Jingjing Zou, Ethan Tabibzadeh, Elias Warren, Brian Wishart, Rebekah White, Herve Tiriac, Andrew Lowy, Jonathan Weitz. Benchmarking human tumor slices from gastrointestinal malignancies for precision cancer therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(8_Suppl):Abstract nr LB483.

Activation of transcription factor NRF2 in pancreatic ductal adenocarcinoma (PDAC) promotes aggressive tumor phenotype and protection from therapy-induced oxidative stress. We postulated that NRF2high PDAC can be selectively targeted by C29h, a prodrug that is activated by the NRF2-induced enzyme NAD(P)H:quinone oxidoreductase-1 (NQO1), which is elevated in human pancreatic tumors. Initial evaluations of C29h alone or together with the standard-of-care chemotherapeutic drug gemcitabine were conducted on NQO1high human and mouse PDAC cell lines and patient-derived organoids. As PDAC is enriched in collagen-containing extracellular matrix (ECM) that activates NRF2 and induces NQO1 expression, we examined the ECM effect on the response to C29h, as well as in vivo tumor control in IKKα-deficient KrasG12D/IkkαΔPEC mice in which NRF2 is strongly activated, immunocompromised Nu/Nu mice orthotopically transplanted with human PDAC cells and C57BL/6n and NOD/SCID mice transplanted with mouse PDAC. C29h led to NQO1-dependent killing of human and mouse PDAC cell lines and organoids and acted additively with gemcitabine. Furthermore, ECM-plated PDAC cells were more susceptible to C29h cytotoxicity than cells grown on plastic. Importantly, C29h treatment induced tumor regression and increased the survival of PDAC-bearing mice and optimal C29h-induced tumor regression was dependent on CD8+ T lymphocytes whose tumoral recruitment was enhanced by drug treatment. This study supports the use of C29h alone or as part of a drug combination as an effective and promising strategy for selective eradication of NRF2high PDAC.

Table S1. List of drugs used in this study.

Table S3. Results of RPPA and transcriptomic analyses.

Supplemental Figure and Table Legends

Patients diagnosed with pancreatic ductal adenocarcinoma (PDAC) have a dismal 5-year survival (∼13%). Thus, new, effective, and ideally, less toxic therapies are desperately needed. Epidemiologic studies have found that patients with PDAC prescribed H1-antihistamines have improved survival. Expression of the histamine H1 receptor (HRH1), a G protein-coupled receptor which is blocked by approved H1-antihistamines, is increased by ∼20-fold in PDAC tumors compared with normal pancreas. Here, we used bioinformatic and molecular biological techniques to identify the cellular localization of HRH1 in the PDAC tumor microenvironment, assess functional responses to HRH1 activation, and define its potential biological roles in PDAC. We found that HRH1 is primarily expressed in cancer cells of PDAC tumors in humans and KPC mice (mice engineered to develop PDAC) and signals via G protein q/11 to increase intracellular Ca2+. HRH1 activation increases migration and invasion by PDAC cancer cells. Orally administered fexofenadine, an H1-antihistamine, was bioavailable in the tumors of KPC mice and yielded smaller pancreatic tumor tissue weights and lower expression of immunomodulatory (interleukin 6 and PD-1) and fibrotic (Col1A1) genes than in vehicle-control KPC mice. Thus, PDAC cancer cells express HRH1, which is functional in vitro and in vivo, suggesting that the repurposing of approved H1-antihistamines may be an efficacious and safe therapeutic approach for patients with PDAC. SIGNIFICANCE STATEMENT: Pancreatic ductal adenocarcinoma (PDAC) has a ∼13% 5-year survival rate, highlighting the need for new therapies. The HRH1 (histamine) receptor, associated with poorer survival, is upregulated in PDAC tumors. This study found that HRH1 is functional in PDAC cells, increasing intracellular Ca2+ via Gq/11 and promoting tumorigenic responses. KPC mice treated with an H1-antihistamine have reduced pancreas weight and lower proinflammatory and fibrotic markers in PDAC tumors. Thus, HRH1 may be a potential target for repurposing approved H1-antihistamines to treat PDAC.

Patients diagnosed with pancreatic ductal adenocarcinoma (PDAC) have a dismal 5-year survival (∼13%). Thus, new, effective, and ideally, less toxic therapies are desperately needed. Epidemiologic studies have found that patients with PDAC prescribed H1-antihistamines have improved survival. Expression of the histamine H1 receptor (HRH1), a G protein-coupled receptor which is blocked by approved H1-antihistamines, is increased by ∼20-fold in PDAC tumors compared with normal pancreas. Here, we used bioinformatic and molecular biological techniques to identify the cellular localization of HRH1 in the PDAC tumor microenvironment, assess functional responses to HRH1 activation, and define its potential biological roles in PDAC. We found that HRH1 is primarily expressed in cancer cells of PDAC tumors in humans and KPC mice (mice engineered to develop PDAC) and signals via G protein q/11 to increase intracellular Ca2+. HRH1 activation increases migration and invasion by PDAC cancer cells. Orally administered fexofenadine, an H1-antihistamine, was bioavailable in the tumors of KPC mice and yielded smaller pancreatic tumor tissue weights and lower expression of immunomodulatory (interleukin 6 and PD-1) and fibrotic (Col1A1) genes than in vehicle-control KPC mice. Thus, PDAC cancer cells express HRH1, which is functional in vitro and in vivo, suggesting that the repurposing of approved H1-antihistamines may be an efficacious and safe therapeutic approach for patients with PDAC. SIGNIFICANCE STATEMENT: Pancreatic ductal adenocarcinoma (PDAC) has a ∼13% 5-year survival rate, highlighting the need for new therapies. The HRH1 (histamine) receptor, associated with poorer survival, is upregulated in PDAC tumors. This study found that HRH1 is functional in PDAC cells, increasing intracellular Ca2+ via Gq/11 and promoting tumorigenic responses. KPC mice treated with an H1-antihistamine have reduced pancreas weight and lower proinflammatory and fibrotic markers in PDAC tumors. Thus, HRH1 may be a potential target for repurposing approved H1-antihistamines to treat PDAC.

PURPOSE Mucinous neoplasms of the gastrointestinal tract are characterized by a propensity for metastasis to the peritoneum, resulting in peritoneal mucinous carcinomatosis (PMC). A subset of these tumors, most often originating in the appendix, harbor mutations in the GNAS oncogene. While the natural history of GNAS -mutant PMC varies, patient outcomes are generally poor, as is response to cytotoxic chemotherapy. The purpose of this study was to evaluate the clinical efficacy of single-agent palbociclib, a cyclin-dependent kinase (CDK)4/6 inhibitor, in patients with GNAS -mutant PMC. PATIENTS AND METHODS We enrolled 16 patients with PMC in a single-arm personalized cancer therapy trial. For all patients, tumor tissue and/or circulating tumor DNA genomic profiling using next-generation sequencing and, when possible, PD-L1 expression, tumor mutational burden, and microsatellite instability status was assessed. Twelve of 16 patients had previous disease progression on at least one previous line of chemotherapy. The primary tumor was appendix in 13 patients, unknown in two patients, and pancreas in one patient. Eleven cases were classified as low grade, and five as high grade. RESULTS In 13 of 16 patients, we observed a decrease in carcinoembryonic antigen (CEA), and in six patients, the CEA declined by >50%. As measured by clinical and modified peritoneal RECIST criteria, 50% of evaluable patients had stable disease after 12 months of palbociclib. At a median follow-up of 17.6 months, median survival has not been reached. Clinical response to CDK4/6 inhibition was mirrored in tumors with GNAS mutation and mucinous histology using an ex vivo preclinical platform. CONCLUSION CDK4/6 inhibition with palbociclib had clinical activity in PMC characterized by mutations in GNAS that was superior to that previously reported with cytotoxic chemotherapy. CDK4/6 inhibition is a novel therapeutic strategy worthy of further evaluation in this subgroup of gastrointestinal neoplasms.

Abstract Concomitant mutations in KRAS and GNAS have been linked to mucinous histology in gastrointestinal neoplasms of the appendix, colon, and pancreas (IPMN). Upon progression, these tumors are characterized by metastasis which favors the peritoneal surface, resulting in mucinous carcinomatosis peritonei (MCP). Recently we have described a novel technique which allows for long term culture and drug intervention of human MCP tumors ex-vivo. With evidence of durable clinical benefit of CDK4-6 inhibition in a single patient with chemo refractory MCP of appendiceal origin, we sought to further investigate anti-tumor responses using CDK4-6 inhibition in ex-vivo tumor slices, in order to identify candidates for a personalized clinical therapy trial. Here, in a comparison of ex-vivo patient tumor slices from 18 individual donors, treatment using CDK4-6 inhibitors revealed a significant reduction in cancer cell specific proliferation in mucinous GNAS-mut tumors compared to non-mucinous cancers. Anti-tumor responses of CDK4-6 were determined to be tumor-cell intrinsic, as CDK4-6 inhibition blocked proliferation of stromal cells in the TME independently of patient tumor mutational and mucin status. Based on these finding a personalized clinical trial was conducted where we report that 13 of 16 patients (81%) enrolled with MCP treated with palbociclib had at least a 10% decrease in CEA, as compared to historical chemotherapy responses rates reported from 14-30%. These results indicate that CDK4/6 inhibition is a novel and efficacious treatment for patients with MCP. Citation Format: Jonathan Weitz, Daisuke Nishizaki, Jay Patel, Isabella Ng, Siming Sun, Dana Ramms, Jingjing Zou, Joel Baumgartner, Kaitlyn Kelly, Hitendra Patel, Rebekah White, Jula Veerapong, Peter Vu, Silvio Gutkind, Herve Tiriac, Shumei Kato, Andrew Lowy. An ex-vivo organotypic culture platform of mucinous carcinomatosis peritonei identifies CDK4-6 inhibition as a novel treatment [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 6777.

Figure Legends for Supp Fig. 1 and Supp. Fig 2

Supplemental Figure 1: Expression of Vav3 DH domain inhibits the growth of AR-expressing cells only, and does not decrease total levels of FL-AR, AR-V7, Vav3 or Vav2. Supplemental Figure 2: Disruption of coactivator interactions with FL-AR or AR-V7 increases cell death through apoptosis.

ARTICLES DISCUSSED Delgadillo-Silva, L. F., Akhtar, M. N., Tasoz, E., Ninov, N. Simultaneous calcium imaging and glucose stimulation in living zebrafish to investigate in vivo beta-cell function. Journal of Visualized Experiments. (175), e62347 (2021). Felix-Martinez, G. J.,Nicolas-Mata, A., Godinez-Fernandez, J. R. Computational reconstruction of pancreatic islets as a tool for structural and functional analysis. Journal of Visualized Experiments. (181), e63352 (2022). Huber, M. K. et al. Observing islet function and islet-immune cell interactions in live pancreatic tissue slices. Journal of Visualized Experiments. (170), e62207 (2021). Park, I.,Kim, P. Stabilized longitudinal in vivo cellular-level visualization of the pancreas in a murine model with a pancreatic intravital imaging window. Journal of Visualized Experiments. (171), e62538 (2021). Stozer, A. et al. Confocal laser scanning microscopy of calcium dynamics in acute mouse pancreatic tissue slices. Journal of Visualized Experiments. (170), e62293 (2021). Zhou, X. et al. Establishment of a mouse severe acute pancreatitis model using retrograde injection of sodium taurocholate into the biliopancreatic duct. Journal of Visualized Experiments. (182), e63129 (2022).

Pancreatic ductal adenocarcinoma (PDAC) is an insidious disease with a low 5-year survival rate. PDAC is characterized by infiltration of abundant tumor-associated macrophages (TAM), which promote immune tolerance and immunotherapeutic resistance. Here we report that macrophage spleen tyrosine kinase (Syk) promotes PDAC growth and metastasis. In orthotopic PDAC mouse models, genetic deletion of myeloid Syk reprogrammed macrophages into immunostimulatory phenotype, increased the infiltration, prolifer-ation, and cytotoxicity of CD8+ T cells, and repressed PDAC growth and metastasis. Furthermore, gemcitabine (Gem) treatment induced an immunosuppressive microenvironment in PDAC by promoting protumorigenic polarization of macrophages. In contrast, treatment with the FDA-approved Syk inhibitor R788 (fostamatinib) remod-eled the tumor immune microenvironment, "re-educated" protu-morigenic macrophages towards an immunostimulatory phenotype and boosted CD8+ T-cell responses in Gem-treated PDAC in orthotopic mouse models and an ex vivo human pancreatic slice culture model. These findings illustrate the potential of Syk inhibi-tion for enhancing the antitumor immune responses in PDAC and support the clinical evaluation of R788 either alone or together with Gem as a potential treatment strategy for PDAC.Significance: Syk blockade induces macrophage polariza-tion to an immunostimulatory phenotype, which enhances CD8+ T-cell responses and improves gemcitabine efficacy in pancreatic ductal adenocarcinoma, a clinically challenging malignancy.

Abstract Pancreatic ductal adenocarcinoma (PDAC) is a lethal cancer with a low survival rate. Recently, new drugs that target KRASG12D, a common mutation in PDAC, have been developed. We studied one of these compounds, MRTX1133, and found it was specific and effective at low nanomolar concentrations in patient-derived organoid models and cell lines harboring KRASG12D mutations. Treatment with MRTX1133 upregulated the expression and phosphorylation of EGFR and HER2, indicating that inhibition of ERBB signaling may potentiate MRTX1133 antitumor activity. Indeed, the irreversible pan-ERBB inhibitor, afatinib, potently synergized with MRTX1133 in vitro, and cancer cells with acquired resistance to MRTX1133 in vitro remained sensitive to this combination therapy. Finally, the combination of MRTX1133 and afatinib led to tumor regression and longer survival in orthotopic PDAC mouse models. These results suggest that dual inhibition of ERBB and KRAS signaling may be synergistic and circumvent the rapid development of acquired resistance in patients with KRAS mutant pancreatic cancer. Significance: KRAS-mutant pancreatic cancer models, including KRAS inhibitor–resistant models, show exquisite sensitivity to combined pan-ERBB and KRAS targeting, which provides the rationale for testing this drug combination in clinical trials.

Perineural invasion (PNI) is the phenomenon whereby cancer cells invade the space surrounding nerves. PNI occurs frequently in epithelial malignancies, but is especially characteristic of pancreatic ductal adenocarcinoma (PDAC). The presence of PNI portends an increased incidence of local recurrence, metastasis and poorer overall survival. While interactions between tumor cells and nerves have been investigated, the etiology and initiating cues for PNI development is not well understood. Here, we used digital spatial profiling to reveal changes in the transcriptome and to allow for a functional analysis of neural-supportive cell types present within the tumor-nerve microenvironment of PDAC during PNI. We found that hypertrophic tumor-associated nerves within PDAC express transcriptomic signals of nerve damage including programmed cell death, Schwann cell proliferation signaling pathways, as well as macrophage clearance of apoptotic cell debris by phagocytosis. Moreover, we identified that neural hypertrophic regions have increased local neuroglial cell proliferation which was tracked using EdU tumor labeling in KPC mice, as well as frequent TUNEL positivity, suggestive of a high turnover rate. Functional calcium imaging studies using human PDAC organotypic slices confirmed nerve bundles had neuronal activity, as well as contained NGFR+ cells with high sustained calcium levels, which are indicative of apoptosis. This study reveals a common gene expression pattern that characterizes solid tumor-induced damage to local nerves. These data provide new insights into the pathobiology of the tumor-nerve microenvironment during PDAC as well as other gastrointestinal cancers.

Supplementary Figure from An Ex Vivo Organotypic Culture Platform for Functional Interrogation of Human Appendiceal Cancer Reveals a Prominent and Heterogenous Immunological Landscape

Abstract Appendiceal neoplasms are rare and often clinically present with peritoneal metastasis. While surgical tumor resection is effective for some types of primary appendiceal cancers, patients with metastatic disease have poor prognostic outcomes. Models to study appendix cancer biology are limited, given that 1) no mouse models exist and 2) reliable in vitro models are unavailable. As such, we have developed an ex-vivo organotypic slice model to examine cellular interactions between tumor cells and their local microenvironment. Tumor specimens from human appendiceal cancer patients were cut using a vibratome to make 200 μm organotypic slices. Slices were cultured on transwell inserts and tested for changes in morphological, cellular and functional characteristics over a seven-day period. Organotypic slices maintained their cellular composition in regard to the proportion of epithelial, immune cells and fibroblasts. Live cell [Ca2+]i imaging of long term cultured slices confirmed that immune cells remain functionally active when stimulated with extracellular ATP. Lasty, using tumor biopsies from human donors, we have identified a diverse immunological profile of appendiceal tumors not previously identified. Our study illustrates a novel approach for studying the pathophysiology of appendiceal cancer, a notoriously difficult disease to model. Citation Format: Jonathan Weitz, Tatiana Hurtado de Mendoza, Herve Tiriac, Joel Baumgartner, Kaitlyn Kelly, Jula Veerapong, Andrew Lowy. A novel ex-vivo organotypic culture platform for functional interrogation of human appendiceal neoplasms [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 289.