Preclinical Melanoma Models Research Articles

Chondroitin Sulfate Proteoglycan 4 (CSPG4) as an Emerging Target for Immunotherapy to Treat Melanoma

Immunotherapies, including checkpoint inhibitor antibodies, have precipitated significant improvements in clinical outcomes for melanoma. However, approximately half of patients do not benefit from approved treatments. Additionally, apart from Tebentafusp, which is approved for the treatment of uveal melanoma, there is a lack of immunotherapies directly focused on melanoma cells. This is partly due to few available targets, especially those expressed on the cancer cell surface. Chondroitin sulfate proteoglycan 4 (CSPG4) is a cell surface molecule overexpressed in human melanoma, with restricted distribution and low expression in non-malignant tissues and involved in several cancer-promoting and dissemination pathways. Here, we summarize the current understanding of the expression and functional significance of CSPG4 in health and melanoma, and we outline immunotherapeutic strategies. These include monoclonal antibodies, antibody–drug conjugates (ADCs), chimeric-antigen receptor (CAR) T cells, and other strategies such as anti-idiotypic and mimotope vaccines to raise immune responses against CSPG4-expressing melanomas. Several showed promising functions in preclinical models of melanoma, yet few have reached clinical testing, and none are approved for therapeutic use. Obstacles preventing that progress include limited knowledge of CSPG4 function in human cancer and a lack of in vivo models that adequately represent patient immune responses and human melanoma biology. Despite several challenges, immunotherapy directed to CSPG4-expressing melanoma harbors significant potential to transform the treatment landscape.

Peripheral-derived regulatory T cells contribute to tumor-mediated immune suppression in a nonredundant manner

Identifying tumor-mediated mechanisms that impair immunity is instrumental for the design of new cancer therapies. Regulatory T cells (Tregs) are a key component of cancer-derived immune suppression; however, these lymphocytes are necessary to prevent systemic autoimmunity in mice and humans, and thus, direct targeting of Tregs is not a clinical option for cancer patients. We have previously demonstrated that excising transcription factor Kruppel-like factor 2 (Klf2) within the T cell lineage blocks the generation of peripheral-derived Tregs (pTregs) without impairing production of thymic-derived Tregs. Using this mouse model, we have now demonstrated that eliminating pTregs is sufficient to delay/prevent tumor malignancy without causing autoimmunity. Cancer-bearing mice that expressed KLF2 converted tumor-specific CD4+ T cells into pTregs, which accumulated in secondary lymphoid organs and impaired further T cell effector activity. In contrast, pTreg-deficient mice retained cancer-specific immunity, including improved T cell infiltration into "cold" tumors, reduced T cell exhaustion in tumor beds, restricted generation of tumor-associated myeloid-derived suppressor cells, and the continued production of circulating effector T cells that arose in a cancer-dependent manner. Results indicate that tumor-specific pTregs are critical for early stages of cancer progression and blocking the generation of these inhibitory lymphocytes safely delays/prevents malignancy in preclinical models of melanoma and prostate cancer.

TYRP1 directed CAR T cells control tumor progression in preclinical melanoma models

Despite therapeutic efficacy observed with immune checkpoint blockade in advanced melanoma, many tumors do not respond to treatment, representing a need for new therapies. Here, we have generated chimeric antigen receptor (CAR) Tcells targeting TYRP1, a melanoma differentiation antigen expressed on the surface of melanomas, including rare acral and uveal melanomas. TYRP1-targeted CAR Tcells demonstrate antigen-specific activation and cytotoxic activity invitro and invivo against human melanomas independent of the MHC alleles and expression. In addition, the toxicity to pigmented normal tissues observed with T lymphocytes expressing TYRP1-targeted TCRs was not observed with TYRP1-targeted CAR Tcells. Anti-TYRP1 CAR Tcells provide a novel means to target advanced melanomas, serving as a platform for the development of similar novel therapeutic agents and as a tool to interrogate the immunobiology of melanomas.

Association between warfarin and survival in invasive melanoma: a population-based cohort study

BackgroundWarfarin has been shown to reduce cancer risk via Vitamin K related AXL tyrosine kinase inhibition. Although AXL has been implicated in disease progression and therapy resistance in preclinical melanoma models, there are no clinical studies evaluating the impact of warfarin on melanoma prognosis. Hence, we sought to evaluate the relationship between warfarin and survival in melanoma. MethodsWe conducted a retrospective population-based cohort study of melanoma patients aged ≥ 65 years diagnosed between 2009–2013 from the Surveillance, Epidemiology, and End Results-Medicare database. Patients were grouped according to warfarin therapy 6 months prior and after melanoma diagnosis. Univariable and multivariable Cox proportional hazards models were used to compare overall (OS) and melanoma-specific survival (MSS) between groups. ResultsOverall, 10,778 patients with invasive melanoma were included. 13.2 % were prescribed warfarin, with atrial fibrillation being the most common indication (74.1 %). Warfarin prescription was associated with older age, male sex, and a greater number of comorbidities (all p < 0.001). Patients prescribed warfarin more frequently presented with ulceration, T3 and T4 disease, and stage II disease (all p < 0.05). Warfarin prescription was associated with greater MSS and OS in multivariable models (MSS adjusted hazard ratio [aHR] 0.72, 95 % CI 0.54–0.96, p = 0.02; OS aHR 0.88, 95 % CI 0.79–0.99, p = 0.04). ConclusionsWarfarin was associated with greater MSS and OS among melanoma patients. These findings highlight the potential for Vitamin K related pathways to impact cancer specific activity. Further study of AXL and Vitamin K inhibition will be of significant interest in melanoma, targeted strategies actively under investigation.

1H and 31P Magnetic Resonance Spectroscopic Metabolomic Imaging: Assessing Mitogen-Activated Protein Kinase Inhibition in Melanoma.

The MAPK signaling pathway with BRAF mutations has been shown to drive the pathogenesis of 40-60% of melanomas. Inhibitors of this pathway's BRAF and MEK components are currently used to treat these malignancies. However, responses to these treatments are not always successful. Therefore, identifying noninvasive biomarkers to predict treatment responses is essential for personalized medicine in melanoma. Using noninvasive 1H magnetic resonance spectroscopy (1H MRS), we previously showed that BRAF inhibition reduces lactate and alanine tumor levels in the early stages of effective therapy and could be considered as metabolic imaging biomarkers for drug response. The present work demonstrates that these metabolic changes observed by 1H MRS and those assessed by 31P MRS are also found in preclinical human melanoma models treated with MEK inhibitors. Apart from 1H and 31P MRS, additional supporting in vitro biochemical analyses are described. Our results indicate significant early metabolic correlations with response levels to MEK inhibition in the melanoma models and are consistent with our previous study of BRAF inhibition. Given these results, our study supports the potential clinical utility of noninvasive MRS to objectively image metabolic biomarkers for the early prediction of melanoma's response to MEK inhibition.

Differential impact of genetic deletion of TIGIT or PD-1 on melanoma-specific T-lymphocytes

ABSTRACT Immune checkpoint (IC) blockade and adoptive transfer of tumor-specific T-cells (ACT) are two major strategies to treat metastatic melanoma. Their combination can potentiate T-cell activation in the suppressive tumor microenvironment, but the autoimmune adverse effects associated with systemic injection of IC blockers persist with this strategy. ACT of tumor-reactive T-cells defective for IC expression would overcome this issue. For this purpose, PD-1 and TIGIT appear to be relevant candidates, because their co-expression on highly tumor-reactive lymphocytes limits their therapeutic efficacy within the tumor microenvironme,nt. Our study compares the consequences of PDCD1 or TIGIT genetic deletion on anti-tumor properties and T-cell fitness of melanoma-specific T lymphocytes. Transcriptomic analyses revealed down-regulation of cell cycle-related genes in PD-1KO T-cells, consistent with biological observations, whereas proliferative pathways were preserved in TIGITKO T-cells. Functional analyses showed that PD-1KO and TIGITKO T-cells displayed superior antitumor reactivity than their wild-type counterpart in vitro and in a preclinical melanoma model using immunodeficient mice. Interestingly, it appears that TIGITKO T-cells were more effective at inhibiting tumor cell proliferation in vivo, and persist longer within tumors than PD-1KO T-cells, consistent with the absence of impact of TIGIT deletion on T-cell fitness. Taken together, these results suggest that TIGIT deletion, over PD-1 deletion, in melanoma-specific T-cells is a compelling option for future immunotherapeutic strategies.

A Multimodal Drug-Diet-Immunotherapy Combination Restrains Melanoma Progression and Metastasis.

The genetic landscape of cancer cells can lead to specific metabolic dependencies for tumor growth. Dietary interventions represent an attractive strategy to restrict the availability of key nutrients to tumors. In this study, we identified that growth of a subset of melanoma was severely restricted by a rationally designed combination therapy of a stearoyl-CoA desaturase (SCD) inhibitor with an isocaloric low-oleic acid diet. Despite its importance in oncogenesis, SCD underwent monoallelic codeletion along with PTEN on chromosome 10q in approximately 47.5% of melanoma, and the other SCD allele was methylated, resulting in very low-SCD expression. Although this SCD-deficient subset was refractory to SCD inhibitors, the subset of PTEN wild-type melanoma that retained SCD was sensitive. As dietary oleic acid could potentially blunt the effect of SCD inhibitors, a low oleic acid custom diet was combined with an SCD inhibitor. The combination reduced monounsaturated fatty acids and increased saturated fatty acids, inducing robust apoptosis and growth suppression and inhibiting lung metastasis with minimal toxicity in preclinical mouse models of PTEN wild-type melanoma. When combined with anti-PD1 immunotherapy, the SCD inhibitor improved T-cell functionality and further constrained melanoma growth in mice. Collectively, these results suggest that optimizing SCD inhibitors with diets low in oleic acid may offer a viable and efficacious therapeutic approach for improving melanoma treatment. Significance: Blockade of endogenous production of fatty acids essential for melanoma combined with restriction of dietary intake blocks tumor growth and enhances response to immunotherapy, providing a rational drug-diet treatment regimen for melanoma.

Epigenetic Reprogramming Potentiates ICAM1 Antibody Drug Conjugates in Preclinical Models of Melanoma.

Therapeutic benefits and underlying biomechanism(s) of antibody drug conjugates (ADC) in combination with other targeted therapeutics are largely unknown. Here, the synergy between ADC and epigenetic drug decitabine (DAC), a clinically approved DNA methylation inhibitor, in multiple preclinical models of melanoma specifically investigated. Mechanistically, the underlying biomechanisms of how DAC cooperatively worked with ICAM1 antibody conjugated DNA topoisomerase I inhibitor DXd (I1-DXd) is elucidated. DAC treatment significantly enhanced anti-tumor efficacy of I1-DXd by upregulating antigen expression, enhancing antibody internalization and potentiating tumor sensitivity by epigenetically reprogramming of melanoma. Meanwhile, I1-DXd/DAC combination also exerted regulatory effects on tumor microenvironment (TME) by enhancing tumor infiltration of innate and adaptive immune cells and improving penetration of ADCs with a boosted antitumor immunity. This study provides a rational ADC combination strategy for solid tumor treatment.

Multiple Endocrine Neoplasia Type 1 Regulates TGFβ-Mediated Suppression of Tumor Formation and Metastasis in Melanoma.

Over the past few decades, the worldwide incidence of cutaneous melanoma, a malignant neoplasm arising from melanocytes, has been increasing markedly, leading to the highest rate of skin cancer-related deaths. While localized tumors are easily removed by excision surgery, late-stage metastatic melanomas are refractory to treatment and exhibit a poor prognosis. Consequently, unraveling the molecular mechanisms underlying melanoma tumorigenesis and metastasis is crucial for developing novel targeted therapies. We found that the multiple endocrine neoplasia type 1 (MEN1) gene product Menin is required for the transforming growth factor beta (TGFβ) signaling pathway to induce cell growth arrest and apoptosis in vitro and prevent tumorigenesis in vivo in preclinical xenograft models of melanoma. We further identified point mutations in two MEN1 family members affected by melanoma that led to proteasomal degradation of the MEN1 gene product and to a loss of TGFβ signaling. Interestingly, blocking the proteasome degradation pathway using an FDA-approved drug and RNAi targeting could efficiently restore MEN1 expression and TGFβ transcriptional responses. Together, these results provide new potential therapeutic strategies and patient stratification for the treatment of cutaneous melanoma.

Fasting mimicking diet reduces anti-OX40/anti PD-L1 and anti-PD-1/anti-CTLA-4 cardiovascular side effects in preclinical melanoma models.

Fasting mimicking diet reduces anti-OX40/anti PD-L1 and anti-PD-1/anti-CTLA-4 cardiovascular side effects in preclinical melanoma models.

Syringeable Near-Infrared Light-Activated In Situ Immunogenic Hydrogel Boosts the Cancer-Immunity Cycle to Enhance Anticancer Immunity.

Effective anticancer immunity depends on properly activating multiple stepwise events in the cancer-immunity cycle. An immunologically "cold" tumor microenvironment (TME) engenders immune evasion and refractoriness to conventional checkpoint blockade immunotherapy. Here, we combine nanoparticle formulations and an in situ formed hydrogel scaffold to treat accessible tumors locally and to stimulate systemic immunity against metastatic tumor lesions. The nanoparticles encapsulate poly(ε-caprolactone)-derived cytotoxic chemotherapy and adjuvant of Toll-like receptor 7/8 through a reactive oxygen species (ROS)-cleavable linker that can be self-activated by the coassembled neighboring photosensitizer following near-infrared (NIR) laser irradiation. Further development results in syringeable, NIR light-responsive, and immunogenic hydrogel (iGEL) that can be implanted peritumorally and deposited into the tumor surgical bed. Upon NIR laser irradiation, the generated ROS induces iGEL degradation and bond cleavage in the polymer-drug conjugates, triggering the immunogenic cell death cascade in cancer cells and spontaneously releasing encapsulated agents to rewire the cancer-immunity cycle. Notably, upon application in multiple preclinical models of melanoma and triple-negative breast cancer, which are aggressive and refractory to conventional immunotherapy, iGEL induces durable remission of established tumors, extends postsurgical tumor-free survival, and inhibits metastatic burden. The result of this study is a locally administrable immunogenic hydrogel for triggering host systemic immunity to improve immunotherapeutic efficacy with minimal off-target side effects.

Quantifying in vivo collagen reorganization during immunotherapy in murine melanoma with second harmonic generation imaging.

Increased collagen linearization and deposition during tumorigenesis can impede immune cell infiltration and lead to tumor metastasis. Although melanoma is well studied in immunotherapy research, studies that quantify collagen changes during melanoma progression and treatment are lacking. We aim to image in vivo collagen in preclinical melanoma models during immunotherapy and quantify the collagen phenotype in treated and control mice. Second-harmonic generation imaging of collagen was performed in mouse melanoma tumors in vivo over a treatment time course. Animals were treated with a curative radiation and immunotherapy combination. Collagen morphology was quantified over time at an image and single-fiber level using CurveAlign and CT-FIRE software. In immunotherapy-treated mice, collagen was reorganized toward a healthy phenotype, including shorter, wider, curlier collagen fibers, with modestly higher collagen density. Temporally, collagen fiber straightness and length changed late in treatment (days 9 and 12), while width and density changed early (day 6) compared with control mice. Single-fiber collagen features calculated in CT-FIRE were the most sensitive to the changes among treatment groups compared with bulk collagen features. Quantitative second-harmonic generation imaging can provide insight into collagen dynamics in vivo during immunotherapy, with key implications in improving immunotherapy response in melanoma and other cancers.

Liposomal Phenylephrine Nanoparticles Enhance the Antitumor Activity of Intratumoral Chemotherapy in a Preclinical Model of Melanoma.

Intratumoral injection of anticancer agents has limited efficacy and is not routinely used for most cancers. In this study, we aimed to improve the efficacy of intratumoral chemotherapy using a novel approach comprising peri-tumoral injection of sustained-release liposomal nanoparticles containing phenylephrine, which is a potent vasoconstrictor. Using a preclinical model of melanoma, we have previously shown that systemically administered (intravenous) phenylephrine could transiently shunt blood flow to the tumor at the time of drug delivery, which in turn improved antitumor responses. This approach was called dynamic control of tumor-associated vessels. Herein, we used liposomal phenylephrine nanoparticles as a "local" dynamic control strategy for the B16 melanoma. Local dynamic control was shown to increase the retention and exposure time of tumors to intratumorally injected chemotherapy (melphalan). C57BL/6 mice bearing B16 tumors were treated with intratumoral melphalan and peri-tumoral injection of sustained-release liposomal phenylephrine nanoparticles (i.e., the local dynamic control protocol). These mice had statistically significantly improved antitumor responses compared to melphalan alone (p = 0.0011), whereby 58.3% obtained long-term complete clinical response. Our novel approach of local dynamic control demonstrated significantly enhanced antitumor efficacy and is the subject of future clinical trials being designed by our group.

Abstract 4034: Lag3 blockade enhances the anti-tumor effect of dual GITR agonism and PD-1 blockade in a preclinical melanoma model

Abstract Immune checkpoint blockade (ICB) therapies, specifically anti PD-1 and anti CTLA-4, have resulted in tremendous success in the clinic. However, a substantial number of patients still relapse due to either inherent or acquired resistance to ICB therapies. In this scenario, activation of T cell co-stimulation pathways along with ICB emerges as a promising strategy to improve anti-tumor responses. Engagement of Glucocorticoid induced TNFR Related protein (GITR) costimulatory molecule, leads to enhanced activation of cytotoxic T cells while destabilizing suppressive T regulatory cells in the tumor microenvironment. Additionally, combining GITR agonism with PD-1 blockade improves the anti-tumor response in a murine model of advanced melanoma resistant to ICB, positioning GITR as an attractive immunotherapeutic target. In this study, we evaluated the therapeutic efficacy of combining blockade of the immune checkpoint LAG3 with GITR agonism for treating ICB-resistant advanced melanoma, using the B16 model. The combination of LAG3 blockade with GITR agonism was well tolerated, leading to better tumor control and improved survival. Our data revealed increased B cell infiltration and activation within tumors and draining lymph nodes (LNs) of treated mice. B cell depletion diminished the anti-tumor effect of the combination therapy, suggesting that B cells play an active role in controlling tumor growth. Spleens from treated mice exhibited increased lymphocytic hyperplasia, along with more and larger germinal centers. B cell receptor sequencing revealed an increased clonality and reduced entropy. Treating B cells with GITR agonism and LAG3 blockade in vitro led to increased activation and proliferation, suggesting a direct effect of these therapies on B cells. Furthermore, adding LAG3 blockade to the dual combination of GITR agonism and PD-1 blockade resulted in superior tumor control and increased B cell activity in the draining LNs. Collectively, our findings suggest that the humoral response significantly contributes to the anti-tumor responses elicited by ICB when combined with GITR agonism. This triple combination therapy (LAG3 blockade + PD1 blockade + GITR agonism) holds promise as a safe and potent therapeutic strategy to overcome ICB resistance. Further investigation into the mechanism of action by which GITR agonism leads to enhanced B cell responses when combined with ICB is warranted in order to design more effective therapies for cancer treatment. Citation Format: Rachana R. Maniyar, Yuval Elhanati, Levi Mangarin, Yacine Marouf, Ashley Ahmed, Benjamin Greenbaum, Jedd Wolchok, Taha Merghoub. Lag3 blockade enhances the anti-tumor effect of dual GITR agonism and PD-1 blockade in a preclinical melanoma model [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 4034.

Abstract 1658: CFT1946, a potent, selective BRAF V600X mutant-specific degrader demonstrates superior activity as a single agent to clinically approved BRAF inhibitors and standard of care combinations in preclinical models of BRAF V600X melanoma, CRC, NSCLC, and brain metastasis

Abstract Activating mutations in BRAF at residue V600 (typically V600E) lead to dysregulation of the MAPK pathway and occur in approximately 8% of all human cancers including 60% of melanoma, up to 12% of colorectal cancer (CRC), and 4% of NSCLC. Currently approved BRAF inhibitors (BRAFi) are selective for BRAF V600X mutant proteins and are typically used in combination with MEK inhibitors (MEKi) in melanoma and NSCLC, or anti-EGFR antibodies such as cetuximab in CRC. However, their activity is limited by primary or acquired resistance often mediated by RAF dimer-inducing mechanisms. Furthermore, progression of BRAF V600X melanoma after BRAFi/MEKi treatment frequently involves brain metastasis, and currently approved BRAFi have relatively poor brain penetration. CFT1946 is a potent, orally bioavailable, cereblon-based BiDACTM degrader that selectively degrades BRAF V600X mutant protein and is currently under investigation in a Phase I clinical trial. CFT1946 has the potential to overcome limitations of clinically approved BRAFi, as degradation of BRAF V600X should abrogate RAF dimer-driven resistance and paradoxical activation. Indeed, we have previously demonstrated that CFT1946 is efficacious in an A375 BRAF V600E/NRAS Q61K xenograft model of BRAFi resistant melanoma. Here we substantially expand our preclinical characterization of CFT1946 across multiple models of BRAF V600X-driven cancers including BRAF V600X-driven CRC and NSCLC, additional BRAFi-resistant melanoma models, and a brain metastatic melanoma model. Single agent CFT1946 outperformed the SOC encorafenib + cetuximab combination in a panel of BRAF-V600X CRC xenograft models. Pathway analysis in BRAF V600X CRC models revealed that CFT1946 suppresses EGFR-mediated MAPK pathway reactivation, a mechanism known to diminish the impact of approved BRAF inhibitors in this indication. CFT1946 also demonstrated regression in a BRAF-V600X NSCLC PDX model where the SOC dabrafenib + trametinib showed only modest tumor growth inhibition. Consistent with our previous results in the A375 melanoma model, single agent CFT1946 showed superior activity versus the SOC dabrafenib + trametinib combination in all additional melanoma models tested, with complete regression achieved using a CFT1946 + trametinib combination in a PDX model bearing a BRAF-V600E kinase duplication that showed minimal response to dabrafenib + trametinib. Finally, using an A375 intracranial model, treatment with CFT1946 gave robust, dose dependent efficacy and survival advantage over encorafenib. The promising activity of CFT1946 in a broad range of BRAF V600X preclinical models supports its ongoing clinical investigation in BRAF V600 mutant solid tumors (NCT05668585). Citation Format: Bridget Kreger, Jacob R. Stephenson, Mathew E. Sowa, Samantha A. Perino, Laura L. Poling, Eunju Hurh, Michael J. Thomenius, Yanke Liang, Stewart L. Fisher, Roy M. Pollock. CFT1946, a potent, selective BRAF V600X mutant-specific degrader demonstrates superior activity as a single agent to clinically approved BRAF inhibitors and standard of care combinations in preclinical models of BRAF V600X melanoma, CRC, NSCLC, and brain metastasis [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 1658.

Abstract 1217: Defining the anti-tumor activity and immune effects of the RASMULTI(ON) inhibitor RMC-7977 in preclinical models of NRAS-mutant melanoma

Abstract Introduction: Mutations in the small GTPase NRAS are the second most common oncogenic driver in cutaneous melanoma, being found in ~25% of cases. Targeted therapy strategies are currently lacking for NRAS-mutant melanoma. Here, we characterized the anti-tumor activity and immune effects of RMC-7977, a RASMULTI(ON) preclinical tool compound, representative of the investigational agent RMC-6236, in preclinical mouse and human models of NRAS-mutant melanoma. Methods: The in vitro potency of RMC-7977 was determined using mouse and human NRAS-mutant melanoma cell lines. Recovery of signaling was quantified by Western Blot and receptor tyrosine kinase (RTK) arrays. In vivo anti-tumor activity of RMC-7977 was determined in two syngeneic mouse melanoma models (SW1 NRASG13D and NRAS#5 NRASQ61R), and tumor immune infiltrate quantified using multiplexed IHC and flow cytometry. Mechanisms of resistance were defined using RNA-seq. Results: RMC-7977 had good activity in vitro against human cancer cell lines and in mouse models of NRAS-mutant melanoma. Time-course studies demonstrated RMC-7977 rapidly inhibited phospho-ERK signaling, which then began to recover after 8 hr of treatment. There was also evidence of adaptive receptor tyrosine kinase signaling by 48 hr. In syngeneic mouse models of NRAS-mutant melanoma, RMC-7977 led to a rapid inhibition of tumor growth, increased expression of tumor MHC class I and PD-L1 and an increase in CD4+ and CD8+ T cell infiltrate into tumors. Therapeutic escape was associated with decreased CD4+ and CD8+ T cell infiltration and increased numbers of immunosuppressive MDSCs. Cells collected from tumors resistant to RMC-7977 in vivo did not show any shift in sensitivity to the inhibitor when re-challenged in vitro, suggesting that the resistance observed in vivo resulted from mechanisms specific to the tumor microenvironment, for example adaptive RTK signaling or immune escape. RNA-seq and IHC analysis suggested that resistance was associated with decreased MHC expression and antigen presentation, as well as reduced co-stimulation of T cells. Combination studies of RMC-7977 with anti-PD-1 are ongoing to identify potential synergistic interactions in these preclinical models. Conclusion: RMC-7977 has anti-tumor activity in syngeneic mouse models of NRAS-mutant melanoma, associated with a robust immune response. Citation Format: Larissa A. Carvalho, Manali S. Phadke, Keiran S. M. Smalley. Defining the anti-tumor activity and immune effects of the RASMULTI(ON) inhibitor RMC-7977 in preclinical models of NRAS-mutant melanoma [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 1217.

Abstract 671: G-protein coupled receptor (GPCR) screening library identifies sertindole, an antipsychotic, as potential therapeutic option to target GNAQ mutation Q209L in uveal melanoma

Abstract Background: Uveal melanoma is a rare but aggressive intraocular malignancy with limited therapeutic options. A hallmark genetic alteration associated with uveal melanoma is the mutation of the GNAQ gene, particularly the Q209L substitution in the Gαq protein, which contributes to oncogenic signaling and tumor progression. The GNAQ gene encodes for a Gαq protein that plays a critical role in signal transduction pathways involving G protein-coupled receptors (GPCRs). The Q209L substitution results in a gain-of-function mutation, leading to the chronic activation of downstream signaling pathways. This persistent signaling activity contributes to the uncontrolled growth of uveal melanoma cells. As G protein-coupled receptors (GPCRs) play a crucial role in this process, screening libraries of GPCR inhibitors has been explored as a potential therapeutic avenue. These libraries comprise a vast array of compounds with the potential to block or modulate GPCR activity. Identifying specific inhibitors that can effectively interfere with the oncogenic signaling cascades triggered by the mutated Gαq protein is a critical step in developing targeted therapies for uveal melanoma. Methods: GPCR library high throughput screening employed isogenic cell lines expressing wild type or mutant (Q209L) GNAQ. This process utilized IP-One assays to identify compounds affecting Gq-coupled receptors by detecting inositol monophosphate accumulation. Subsequently, promising hits were evaluated for their impact on inhibiting the growth and proliferation of uveal melanoma cells. Further analysis involved Western blotting to assess their potential in promoting autophagy and apoptosis, inhibiting downstream signaling pathways, and a migration assay. Finally, ROS generation was assessed using flow cytometry. Results: Using isogenic cell lines expressing GNAQ gene wild type and the Q209L mutant, a high-throughput screening of GPCR libraries identified sertindole among 5 hits. Sertindole showed a dose-dependent inhibition of Q209L-mutated uveal melanoma cells, significantly reducing cell viability, proliferation, and migration. It also suppressed key signaling pathways, including the critical MAPK pathway, and activated autophagy and apoptosis, likely via ROS generation. These findings suggest sertindole's multifaceted approach in suppressing cancer in uveal melanoma. Conclusion: Our study highlights the potential therapeutic value of sertindole in GNAQ Q209L-mutated uveal melanoma. Further research is needed to evaluate the efficacy of sertindole in preclinical mouse models of uveal melanoma. Citation Format: Shelby Rheinschmidt, Taylor Bargenquast, Sydney Adamson, Trason Thode, Alexis Weston, Tithi Ghosh Halder, Serina Ng, Harini Tulasi, Brian Durbin, Justin Moser, Mohan Kaadige, Raffaella Soldi, Sunil Sharma. G-protein coupled receptor (GPCR) screening library identifies sertindole, an antipsychotic, as potential therapeutic option to target GNAQ mutation Q209L in uveal melanoma [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 671.

Abstract 3961: Impact of CD8 resident memory T cells on antitumor immunity and response to cancer immunotherapy

Abstract CD8+ resident memory T (TRM) cells expressing the CD103 integrin accumulate in human lung tumors and are associated with a favorable prognosis. We have previously demonstrated that a high density of CD103+CD8+ T cells in human lung tumors is a biomarker of response to immune checkpoint blockade (ICB) immunotherapy. However, a large fraction of human tumors is only weakly infiltrated by CD8+ TRM cells, and the reason of this TRM desert is not explained. Therefore, defining the molecular signals that give rise and maintain TRM cells within the tumor microenvironment (TME) and the mechanisms that potentiate antitumor TRM functions are important challenges. Data obtained in pre-clinical mouse colorectal cancer and melanoma models demonstrate that knocking-out CD103 impairs antitumor T-cell immunity and response to ICB and therapeutic peptide vaccine. Moreover, immunization of melanoma-bearing mice with the cancer vaccine results in a dramatic decrease in the percentage of CD103+ TRM cells among CD8+ tumor-infiltrating T lymphocytes (TIL). Algorithm analyses applied to spectral cytometry data of TIL support the conclusion that upon activation with the peptide vaccine a TRM subset gives rise to tumor-specific effector T cells. The mechanisms associated with the decrease in CD103 expression on CD8+ T cells and lead to a TRM differentiation shift will be presented as well as the key role of TGF-b in CD8+CD103+ TRM formation and persistence in the TME. Our data demonstrate that tumor CD8+CD103+ TRM are capable of mounting a potent antitumor immunity and suggest that a fine balance between diverse signals in the tumor ecosystem is required to induce their differentiation and thereby optimize response to cancer immunotherapy. Citation Format: Stephanie Corgnac, Isabelle DAMEI, Fathia Mami-Chouaib. Impact of CD8 resident memory T cells on antitumor immunity and response to cancer immunotherapy [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 3961.

Abstract 3733: Gut microbiota-dependent bile acidtaurodeoxycholic acid, TDCAfacilitates anti-tumor immune responses by modulating cytotoxic CD8 T cell immunity

Abstract Gut microbiota are critical for effective immune checkpoint blockade therapy (ICT) for cancer. However, the underlying mechanisms by which gut microbiota and/or microbiota-derived metabolites augment antitumor response are largely unknown. Here, we utilized a preclinical melanoma (B16-F10) model and treated groups of mice (Jackson, C57BL/6J, female, 6-8 wks, n=14-26 per group) with seven distinct antibiotic treatments to induce unique gut microbiomes and metabolomes. Mice were then treated with ICT (anti-PD-1 and anti-CTLA-4), resulting in markedly heterogeneous tumor phenotypes (tumor volume and weight) as dictated by the specific antibiotic treatment. Using machine learning (e.g. random forest classifier), we identified metabolite candidates most strongly associated with ICT response (i.e. tumor volume and weight).One metabolite candidate, the bile acid taurodeoxycholic acid, TDCA, had previously been identified by my group as associated with anti-PD-1/anti-CTLA-4 response in human melanoma patients (PMID 28923537). Administration of TDCA alone is sufficient to overcome antibiotic-induced ICT hyporesponsiveness in mice. Utilizing both in vitro/ex vivo immune cell assays and in vivo preclinical models, we have validated that TDCA treatment directly boosted the antitumor cytotoxic CD8+ T cell responses (i.e. IFN-gamma production, anti-tumor cytotoxicity, tumor growth, etc.) without affecting innate immune responses. Bulk RNAseq of CD8 T cell analysis indicated that TDCA modulate CD8 T cell function through IFN pathway. Together, our findings suggest that the gut microbial metabolite TDCA could promote immunotherapy efficacy through regulation of CD8+ T cell immunity and has the potential to be utilized as a novel therapeutic agent to enhance ICT efficacy. Citation Format: Wenng li, Hesuiyuan Wang, Laura Coughlin, Nicole Poulides, Priscilla Del Valle, Jake Lichterman, Xiaowei Zhan, Chen Liao, Suzette N. Palmer, Xin Li, Andrew Y. Koh. Gut microbiota-dependent bile acidtaurodeoxycholic acid, TDCAfacilitates anti-tumor immune responses by modulating cytotoxic CD8 T cell immunity [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 3733.

Abstract 7472: Melanoma-intrinsic expression of signal-regulatory protein alpha (SIRPα) confers tumor cells resistance to anti-tumor adaptive immunity

Abstract Introduction: Melanoma patient survival rates have significantly improved recently owing to the development of both targeted therapies and immunotherapies. However, there are still around 50% of patients relapse. The limited response to immunotherapies and global rise in melanoma incidence, with around 290,000 cases newly diagnosed each year, highlight the need for identifying new biomarkers, modulatory pathways, and risk factors for melanoma development. Earlier studies have characterized that aberrant expression of CD47 (a.k.a. “don’t eat me” signal) is one of the mechanisms that tumors exploit to avoid innate immune surveillance. CD47 blockade has been demonstrated to restore myeloid effector function by reinvigorating phagocytosis of tumor cells, which further enhances anti-tumor T cell responses. However, melanoma tumors are resistant to CD47 blockade. Interestingly, we and others have discovered that human and mouse melanoma cells express high levels of SIRPα, the receptor for CD47, which is typically expressed in myeloid compartments. Experimental Procedure: To investigate the role of tumor SIRPα, we designed gRNAs to CRISPR out the SIRPα N-terminal region, where it interacts with CD47, in B16 melanoma and generated SIRPα+/+ (WT) and SIRPα-/- (KO) B16 tumors. We conducted multiple in vitro and in vivo experiments to investigate whether tumor SIRPα played a role in tumor growth and modulated anti-tumor immunity. The preclinical tumor model we used is B16-F10 melanoma and the murine strains we used are the immune-competent (C57BL/6j; B6) and the immune-deficient (RAGnull) mice. For phenotypic and functional assessments, we performed analysis using flow cytometry, immunohistochemistry (IHC) and single cell RNA-sequencing (scRNA-seq) derived from live-sorted CD45+ tumor infiltrating lymphocytes (TILs) of SIRPα-WT and SIRPα-KO B16 tumors. Summary of Unpublished Data Our preliminary data in a preclinical B16-F10 melanoma model revealed that surface SIRPα expression is necessary for optimal B16-F10 melanoma growth in immune-competent mice, but not in immune-deficient RAGnull mice, suggesting a potential crosstalk between tumor SIRPα and the host adaptive immune system. Intriguingly, we found that selective SIRPα deletion in melanoma cells results in a significant increase of immune infiltrates within melanoma tumors that further suppresses tumor growth. Concluding Remarks: SIRPα is required for optimal melanoma development by suppressing anti-tumor adaptive immunity. Ethics Approval: All mice were maintained in microisolator cages and treated in accordance with the NIH and American Association of Laboratory Animal Care regulations. All mouse procedures and experiments for this study were approved by the Weill Cornell Medicine Institutional Animal Care and Use Committee. Citation Format: Chien-Huan Weng, Chana Schochet, Linda Hamadene, Shabnam Eghbali, Sébastien Monette, Levi Mangarin, Cailian Liu, Fadi Samaan, Jedd D. Wolchok, Taha Merghoub. Melanoma-intrinsic expression of signal-regulatory protein alpha (SIRPα) confers tumor cells resistance to anti-tumor adaptive immunity [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 7472.