Immune Checkpoint Inhibitor Resistance Research Articles

MIIP downregulates PD-L1 expression through HDAC6 in cutaneous melanoma

PurposeImmune checkpoint inhibitors have improved the objective response rate and survival of melanoma patients. However, there are still many melanoma patients suffering from disease progression due to primary or secondary immune checkpoint inhibitor resistance, as is observed in the failure of anti-PD1/PD-L1 therapy. While the expression of valuable markers, such as TMB, MSI, and PD-L1, could serve as effective predictors of anti-checkpoint inhibitor therapies, tumor cell PD-L1 expression and its regulating mechanism would significantly affect the anti-PD-1 immunotherapy response and efficacy. Therefore, it is urgent to determine the function of PD-1/PD-L1 expression in melanoma and its associated pathways to enhance the efficacy of anti-PD-1 therapies.MethodsA cohort of 133 patients with histologically confirmed melanoma from Tianjin Medical University Cancer Institute & Hospital were included in this study. We performed immunohistochemical staining to detect the expression of Migration and invasion inhibitory protein (MIIP), HDAC6 and PD-L1. Kaplan–Meier and log-rank test were used for survival analysis. As for vitro, Western blot was used in melanoma cell lines to verify the signaling pathway that MIIP regulates PD-L1 expression.ResultsMIIP expression was decreased in melanoma and that the negative expression of MIIP was correlated with worse overall survival. The positive expression of HDAC6, a molecule that is downstream of MIIP, had a positive trend with decreased overall survival. At the same time, the positive expression of PD-L1, a crucial costimulatory molecule, was associated with decreased overall survival. Furthermore, there was a positive association between HDAC6 and PD-L1 protein expression (p < 0.01), and this correlation is more prominent in cutaneous melanoma than acral melanoma. In cutaneous melanoma cell lines, we found that increasing MIIP led to decreased HDAC6, pSTAT3, and PD-L1 expression. Knocking down MIIP led to increased HDAC6, pSTAT3, and PD-L1 expression. Combining the published results, showing that HDAC6 can regulate PD-L1 expression through STAT3, our present data suggest that MIIP inhibits the expression of PD-L1 by downregulating HDAC6 in melanoma. Most importantly, methods for targeting MIIP-HDAC6-PD-L1 pathways, such as treatment with HDAC6 inhibitors, might indicate a new therapeutic approach for enhancing immune checkpoint inhibitor therapies in melanoma.ConclusionsOur findings highlight the immunomodulatory effects of MIIP in the inhibition of PD-L1 expression by downregulating HDAC6 in melanoma. Methods for targeting MIIP-HDAC6-PD-L1 pathways might be new therapeutic approaches for enhancing immune checkpoint inhibitor therapies in melanoma.

Multi-omics analysis of macrophage-associated receptor and ligand reveals a strong prognostic signature and subtypes in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a significant contributor to morbidity and mortality worldwide. The interaction between receptors and ligands is the primary mode of intercellular signaling and plays a vital role in the progression of HCC. This study aimed to identify the macrophage-related receptor ligand marker genes associated with HCC and further explored the molecular immune mechanisms attributed to altered biomarkers. Single-cell RNA sequencing data containing primary and recurrent samples were downloaded from the China National GeneBank. Cell types were first identified to explore differences between immune cells from different sample sources. CellChat analysis was used to infer and analyze intercellular communication networks quantitatively. Three molecular subtypes were constructed based on the screened twenty macrophage-associated receptor ligand genes. Bulk RNA-Seq data were downloaded from The Cancer Genome Atlas and Gene Expression Omnibus databases. After the screening, the minor absolute shrinkage and selection operator (LASSO) regression model was employed to identify key markers. After collecting peripheral blood and clinical information from patients, an enzyme-linked immunosorbent assay (ELISA) was used to detect the correlation between key markers and IL-10, one of the macrophage markers. After developing a new HCC risk adjustment model and conducting analysis, it was found that there were significant differences in immune status and gene mutations between the high-risk and low-risk groups of patients based on macrophage-associated receptor and ligand genes. This study identified SPP1, ANGPT2, and NCL as key biological targets for HCC. The drug-gene interaction network analysis identified wortmannin, ribavirin, and tarnafloxin as potential therapeutic drugs for the three key markers. In a clinical cohort study, patients with immune checkpoint inhibitor (ICI) resistance had significantly higher expression levels of OPN, ANGPT2, NCL, and IL-10 than patients with ICI-responsiveness. These three key markers were positively correlated with the expression level of IL-10. The signature based on macrophage-associated receptor and ligand genes can accurately predict the prognosis of patients with HCC and the sensitivity to immunotherapy. These results may help guide the development of targeted prevention and personalized treatment of HCC.

Janus kinase inhibitor overcomes resistance to immune checkpoint inhibitor treatment in peritoneal dissemination of gastric cancer in C57BL/6J mice.

Cancer immunotherapy aims to unleash the immune system's potential against cancer cells, providing sustained relief for tumors responsive to immune checkpoint inhibitors (ICIs). While promising in gastric cancer (GC) trials, the efficacy of ICIs diminishes in the context of peritoneal dissemination. Our objective is to identify strategies to enhance the impact of ICI treatment specifically for cases involving peritoneal dissemination in GC. The therapeutic efficacy of anti-PD1, CTLA4 treatment alone, or in combination was assessed using the YTN16 peritoneal dissemination tumor model. Peritoneum and peritoneal exudate cells were collected for subsequent analysis. Immunohistochemical staining, flow cytometry, and bulk RNA-sequence analyses were conducted to evaluate the tumor microenvironment (TME). A Janus kinase inhibitor (JAKi) was introduced based on the pathway analysis results. Anti-PD1 and anti-CTLA4 combination treatment (dual ICI treatment) demonstrated therapeutic efficacy in certain mice, primarily mediated by CD8 + T cells. However, in mice resistant to dual ICI treatment, even with CD8 + T cell infiltration, most of the T cells exhibited anexhaustion phenotype. Notably, resistant tumors displayed abnormal activation of the Janus Kinase-Signal Transducer and Activator of Transcription (JAK-STAT) pathway compared to the untreated group, with observed infiltration of macrophages, neutrophils, and Tregs in the TME. The concurrent administration of JAKi rescued CD8 + T cells function and reshaped the immunosuppressive TME, resulting in enhanced efficacy of the dual ICI treatment. Dual ICI treatment exerts its anti-tumor effects by increasing tumor-specific CD8 + T cell infiltration, and the addition of JAKi further improves ICI resistance by reshaping the immunosuppressive TME.

Acquired resistance to immunotherapy and chemoradiation in MYC amplified head and neck cancer

The proto-oncogene MYC encodes a nuclear transcription factor that has an important role in a variety of cellular processes, such as cell cycle progression, proliferation, metabolism, adhesion, apoptosis, and therapeutic resistance. MYC amplification is consistently observed in aggressive forms of several solid malignancies and correlates with poor prognosis and distant metastases. While the tumorigenic effects of MYC in patients with head and neck squamous cell carcinoma (HNSCC) are well known, the molecular mechanisms by which the amplification of this gene may confer treatment resistance, especially to immune checkpoint inhibitors, remains under-investigated. Here we present a unique case of a patient with recurrent/metastatic (R/M) HNSCC who, despite initial response to nivolumab-based treatment, developed rapidly progressive metastatic disease after the acquisition of MYC amplification. We conducted comparative transcriptomic analysis of this patient’s tumor at baseline and upon progression to interrogate potential molecular processes through which MYC may confer resistance to immunotherapy and/or chemoradiation and used TCGA-HNSC dataset and an institutional cohort to further explore clinicopathologic features and key molecular networks associated with MYC amplification in HNSCC. This study highlights MYC amplification as a potential mechanism of immune checkpoint inhibitor resistance and suggest its use as a predictive biomarker and potential therapeutic target in R/M HNSCC.

Dual‐Sensing Nanoreporter for Dynamic and High‐Throughput Monitoring of Immune Checkpoint Inhibitor Responses in Tumor‐Derived Organoids

AbstractHeterogenous immune responses to checkpoint blockade therapy remain a major challenge to early prediction of treatment efficacy. Current methods of evaluating treatment efficacy in tumors are ineffective in accurately monitoring the disease status after immunotherapy early on. This study reports an immune response monitoring strategy that longitudinally reports on two crucial protease activities involved in T cell‐mediated target cell death, granzyme B (GrzB) and downstream caspase 3 (Casp3), during and after immune checkpoint antibody treatment. Specifically, activatable nanoreporters are engineered to sensitively and selectively capture the activity of GrzB and Casp3 enzymes in tumor cells triggered by cytotoxic T cells in real‐time, providing a direct readout of the tumor response to immune checkpoint inhibitors (ICIs). Furthermore, incorporating 3D tumor‐derived organoids and ex vivo cultures on microfluidic devices with nanoreporters enables high‐throughput screening of various ICIs and their combinations in immunocompetent tumor models. These findings suggest that efficient monitoring of dynamic immunological processes in the tumor microenvironment could help uncover mechanisms associated with ICI response or resistance. It is further anticipated that combining the dual‐sensing nanoreporter with tumor‐derived organoid‐on‐chip technology could lead to an early prediction of treatment outcomes with high fidelity and accelerate the development of optimal treatment in immuno‐oncology.

The engineered exosomes targeting ferroptosis: A novel approach to reverse immune checkpoint inhibitors resistance.

Immune checkpoint inhibitors (ICIs) have been extensively used in immunological therapy primarily due to their ability to prolong patient survival. Although ICIs have achieved success in cancer treatment, the resistance of ICIs should not be overlooked. Ferroptosis is a newly found cell death mode characterized by the accumulation of reactive oxygen species (ROS), glutathione (GSH) depletion, and glutathione peroxidase 4 (GPX4) inactivation, which has been demonstrated to be beneficial to immunotherapy and combining ferroptosis and ICIs to exploit new immunotherapies may reverse ICIs resistance. Exosomes act as mediators in cell-to-cell communication that may regulate ferroptosis to influence immunotherapy through the secretion of biological molecules. Thus, utilizing exosomes to target ferroptosis has opened up exciting possibilities for reversing ICIs resistance. In this review, we summarize the mechanisms of ferroptosis improving ICIs therapy and how exosomes regulate ferroptosis through adjusting iron metabolism, blocking the ROS accumulation, controlling ferroptosis defense systems, and influencing classic signaling pathways and how engineered exosomes target ferroptosis and improve ICIs efficiency.

Abstract 7519: Elucidation of the mechanism of acquisition of immune checkpoint inhibitor resistance by chronic inflammation

Abstract Introduction: Eight molecules that are structurally similar to angiopoietin but do not bind to angiopoietin's specific receptor Tie2 were identified and named angiopoietin-like factors (ANGPTL). ANGPTL2, particularly abundantly expressed in adipose tissue, promotes damage repair through tissue remodeling, and contributes to tissue homeostasis; however, in severe obesity, ANGPTL2 is overexpressed, resulting in irreversible tissue remodeling, which induces chronic inflammation and is involved in systemic insulin resistance and diabetes development. On the other hand, it is unclear how systemic chronic inflammation controlled by ANGPTL2 is involved in cancer progression and acquisition of immune checkpoint inhibitor (ICI) resistance. Therefore, we aimed to elucidate the mechanisms in the acquisition of ICI resistance by systemic chronic inflammation from the perspective of ANGPTL2. Materials and Methods: 1. To induce chronic inflammation in adipose tissue, BALB/c mice were fed high-fat-diet (HFD) for 6 weeks. CT26 cells, a mouse colon cancer cell line, were subcutaneously implanted in normal diet (ND) and HFD mice and anti PD-1/PD-L1 antibody was administered intraperitoneally. Immune cell fractions in tumor tissue and bone marrow were analyzed by flow cytometry. 2. CT26 was subcutaneously implanted in WT and systemic ANGPTL2-deficient (Angptl2−/−) mice, and anti PD-1/PD-L1 antibody was administered intraperitoneally. Tumor size and survival time were analyzed. Bone marrow cells were isolated and the immune cell fractions were analyzed by flow cytometry, and the expression of inflammatory cytokines in adipose tissue were also analyzed. 3. Bone marrow cells were isolated from BALB/c mice, and myeloid-derived suppressor cells (MDSCs) were established in vitro by GM-CSF and IL-6. Recombinant ANGPTL2 protein was added, and MDSC differentiation and function were evaluated by flow cytometry and qRT-PCR. Results: 1. HFD mice had larger tumor size and poorer response to ICI treatment compared to ND mice. In tumor microenvironment, MDSCs were increased in HFD mice. HFD mice had significantly increased MDSCs, especially polymorphonuclear MDSCs (PMN-MDSCs) in bone marrow. 2. ICI-treated Angptl2−/− mice showed higher treatment efficacy and prolonged survival compared to WT mice. In bone marrow, MDSCs were reduced in Angptl2−/− mice under ICI treatment. In adipose tissue, the expression of chronic inflammatory markers was increased. 3. In vitro, addition of recombinant ANGPTL2 protein to MDSCs induced differentiation from mouse bone marrow cells did not significantly increase the cell ratio of MDSCs. No changes in the expression of MDSCs markers were observed in qRT-PCR. Conclusions: Chronic inflammation induced by ANGPTL2 promotes MDSCs differentiation and maturation in the bone marrow, which may suppress anti-tumor immunity and contribute to ICI resistance. Citation Format: Shinsei Yumoto, Haruki Horiguchi, Hideo Baba, Yuichi Oike. Elucidation of the mechanism of acquisition of immune checkpoint inhibitor resistance by chronic inflammation [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 7519.

Abstract 3853: T cell ferroptosis attenuates antitumor immune responses in sickle cell disease

Abstract Background: Sickle cell disease (SCD) is the most common inherited blood disorder and arises from homozygosity for the HbS mutation (GAG&amp;gt;GTG: βGlu6Val) leading to the production of abnormal hemoglobin that cause sickle shaped red blood cells (RBCs). Individuals with SCD are at higher risk than the general population for developing hematologic malignancies or solid tumors such as renal medullary carcinoma (RMC). Although relatively rare, RMC is one of the most aggressive kidney cancers and is the third most common kidney cancer among children and young adults who harbor sickle hemoglobinopathies such as SCD or sickle cell trait (SCT) which occurs due to heterozygosity for the HbS mutation. Molecular profiling studies have shown that most cases involve biallelic inactivation of the SMARCB1 gene, either through simultaneous hemizygous loss and translocation or by homozygous loss. The loss of SMARCB1 and subsequent dysregulation of chromatin remodeling are key factors contributing to the development and progression of renal medullary carcinoma. Despite manifesting an inflamed tumor immune microenvironment, RMC consistently demonstrates resistance to conventional immune checkpoint inhibitors (ICI). Ameliorating the efficacy of immunotherapy of RMC is vital for research and potential therapeutic interventions by targeting CD8+ T cells. Methods: CyTOF was performed by using the spleen of WT mice and SCD mouse model. mRNA was isolated from CD8+ T cells of Peripheral Blood Mononuclear Cell (PBMC) collected from healthy donors and SCD patients followed by bulk RNA sequencing. Hi-C was conducted using CD8+ T cells isolated from PBMC of healthy donors and SCD patients. We employed DNA FISH (Fluorescence in Situ Hybridization) to examine alterations in gene architecture within CD8+ T cells under varying conditions. Results: RMC tumors exhibit accelerated tumor growth and reduced numbers of tumor resident CD8+ T cells in SCD mice model compared with WT control. CD8+ T cells in the SCD associated tumor microenvironment (TME) are subjected to ferroptosis by downregulation of SLC7A11; however, SMARCB1 loss promotes the resistance of RMC tumor cells to ferroptosis. Genomic architecture of CD8+ T cells is altered under SCD conditions, potentially contributing to immune dysfunction. Conclusions: Our research has identified significant alterations in the 3D genome architecture of CD8+ T cells in individuals with SCD. These alterations lead to transcriptional inhibition of SLC7A11, resulting in CD8+ T cell ferroptosis and a hindered anti-tumor immune response in RMC. These findings elucidate the mechanistic relationship of SCD with ICI resistance in cancers such as RMC and provide novel avenues for therapeutically sensitizing tumors to immunotherapies in individuals with SCD. Keywords: Sickle Cell Disease, Renal Medullary Carcinoma, SMARCB1, Ferroptosis, Genomic Architecture Alteration, Hi-C, SLC7A11 Citation Format: Zilong Zhao, Benxia Hu, Yalan Deng, Melinda Soeung, Giannicola Genovese, Wenbo Li, Pavlos Msaouel, Liuqing Yang, Chunru Lin. T cell ferroptosis attenuates antitumor immune responses in sickle cell disease [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 3853.

Abstract 108: Tumor-derived complement C3 is overexpressed in STK11 mutant non-small cell lung cancer and contributes to an immunosuppressive tumor microenvironment in a syngeneic mouse model

Abstract Mutations in STK11 that lead to loss of its protein LKB1 occur in 15-20% of non-squamous non-small cell lung cancer (NSCLC) and are frequently co-mutated with oncogenic KRAS mutations. KRAS and STK11 co-mutant NSCLC is associated with poor prognosis, low PD-L1 expression, low T-cell infiltration, and poor response to immune-checkpoint inhibitors (ICI). Loss of LKB1 leads to altered transcriptional programs with the activation of CREB-dependent gene transcription and changes in the tumor microenvironment including recruitment of suppressive myeloid cells. We used the syngeneic Kras mutant murine CMT167 tumor cell line that is wild-type for Tp53 and Stk11 and sensitive to ICI and generated isogeneic Stk11 knockout cell lines (CMT167-Stk11-KO) by CRISPR/Cas-9 deletion. Loss of Stk11 recapitulated LKB1-loss transcriptional signatures and rendered CMT167 tumors resistant to ICI. Single-cell RNA sequencing (10x) of implanted tumors demonstrated significantly less CD8 T-cells and increased neutrophils (PMN) in Stk11-KO versus Stk11-WT tumors. Analysis of differentially expressed genes in the tumor compartment identified increased expression of complement pathway genes including the central mediator C3 in CMT-167-Stk11-KO tumors. Examination of a well characterized clinical cohort of human KRAS-mutant NSCLC patient samples with and without STK11 mutation confirmed the increased expression of complement C3 in STK11-mutant tumors. Analysis of a human NSCLC cell line panel demonstrated that C3 expression was modulated by LKB1. Knockout of C3 in CMT167-Stk11-KO tumor resulted in dramatic inhibition of tumor growth and re-sensitized CMT167-Stk11-KO tumors to ICI treatment in WT mice. Using C3-/- knockout mice, this effect was determined to be reliant on tumor-derived C3 and dependent on adaptive immunity as no difference in growth of CMT167-Stk11-KO tumors occurred in nude mice or in WT mice after CD8 T-cell depletion. We then compared the transcriptome of Stk11-KO tumor cells with and without C3 deletion, and observed that C3 upregulates the expression of Cxcl1, Cxcl2 and Cxcl3 which mediate PMN recruitment and activation. Since these chemokines ligate Cxcr2, we asked whether Cxcr2 mediated tumor growth and ICI resistance in Stk11-KO tumors. While treatment with single-agent Cxcr2 inhibitor and anti-PD-1 therapy had no effect on tumor growth, the combination resulted in significant suppression of tumor growth in vivo. These results support a role for tumor-derived C3 suppressing CD8 T-cell immunity, potentially indirectly through recruitment of PMN or inducing PMN suppressor function. Our results also provide rationale for targeting tumor-derived complement and inhibiting Cxcr2 to enhance ICI efficacy as novel therapeutic approaches in patients with STK11-mutant NSCLC. Citation Format: Sora Suzuki, Catrina Ting, Bojidar Kandar, Te-An Chen, Anm Nazmul Khan, Thejaswini Giridharan, Brahm Segal, Edwin H. Yau. Tumor-derived complement C3 is overexpressed in STK11 mutant non-small cell lung cancer and contributes to an immunosuppressive tumor microenvironment in a syngeneic mouse 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 108.

Abstract 1426: Lipid-mediated epigenetic activation of PPAR-gamma signaling promotes immune-checkpoint resistance in hepatocellular carcinoma

Abstract Background: Although use of immune-checkpoint inhibitors (ICI) has yielded impressive results in cancer patients, resistance to ICI therapies has increasingly been observed, especially in hepatocellular carcinoma (HCC). Materials and Methods: We generated a novel anti-programmed death-ligand 1 (PD-L1) treatment resistant mouse hepatoma cell Hepa1-6 (PD-L1R) by 7-generation of in vivo selection. To dissect tumor cell-intrinsic resistant mechanism, we performed single-cell RNA-sequencing (scRNA-seq) from anti-PD-L1-treated tumors generated from parental or PD-L1R cells. Expression level of target genes was detected by QPCR, western blot and immunohistochemical analyses. Lipid content and fatty acid uptake was examined by Oil Red O and BIODIPY staining. Peroxisome proliferator-activated receptor gamma (PPARγ) promoter methylation level was analyzed by bisulfite pyrosequencing. To investigate the tumor cell-extrinsic factors, we profiled the myeloid and lymphoid lineages by flow cytometry. Results: ScRNA-seq revealed significant gene enrichments in lipid metabolism and PPARγ signaling pathway in PD-L1R tumors, which could be verified in both mRNA and protein levels. Moreover, we observed evident lipid accumulation in the PD-L1R tumors when compared to the parental tumors by Oil Red O staining. Consistently, PD-L1R tumor cells exhibited higher lipid content and enhanced fatty acid uptake in vitro, as demonstrated by BODIPY493/503 and BODIPY-C16 analyses. Of note, palmitic acid could dose-dependently increase Pparg mRNA expression in parental cells to a similar level with the PD-L1R cells, supporting an important role of lipids in inducing PPARγ expression. Pyrosequencing analysis indicated that PD-L1R cells exhibited lower PPARγ methylation level compared with parental cells. Notably, 5-Azacytidine treatment in parental cells significantly reduced the promoter DNA methylation and increased Pparg mRNA expression to similar extent with the PD-L1R tumor cells, thus indicating DNA hypomethylation-driven PPARγ up-regulation. Flow cytometry analysis showed that ICI resistance was associated with lower cytotoxic CD8+ T cells but higher intermediate Th17 cells, myeloid-derived suppressor cells and T regulatory cells in the tumor microenvironment (TME). Conclusions: Our study suggested that lipid exposure may epigenetically up-regulate PPARγ transcription in the development of anti-PD-L1 resistance. Detailed investigation on the crosstalk between aberrant lipid metabolism and immunosuppressive TME is ongoing. Acknowledgment: This study is supported by RGC General Research Fund (14120621 and 14119023), Li Ka Shing Foundation and CUHK Strategic Seed Funding for Collaborative Research Scheme. Citation Format: Zhewen Xiong, Stephen Lam Chan, Jingying Zhou, Xuezhen Zeng, Weiqin Yang, Haoran Wu, Jianquan Cao, Jie-Ting Low, Michael Wing-Yan Chan, Kevin Yuk-Lap Yip, Joseph Jao-Yiu Sung, Alfred Sze-Lok Cheng. Lipid-mediated epigenetic activation of PPAR-gamma signaling promotes immune-checkpoint resistance in hepatocellular carcinoma [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 1426.

Abstract 5305: M9657, a tumor-targeted anti-CD137 agonist, induced significant antitumor immunity in combination with anti-PD-1 antibody

Abstract Background: M9657, a first-in-class tumor-targeted conditional immune agonist, was developed to boost antitumor immune responses in the tumor microenvironment (TME) by targeting CD137. The immune agonism potency of M9657 was validated through in vitro assays and in vivo efficacy studies in syngeneic tumor models using the surrogate antibody FS122m. Combining CD137 agonists and antiPD(L)-1 antibodies presents a novel therapeutic strategy to overcome immune checkpoint inhibitor (ICI) resistance and enhance antitumor activity via complementary mechanisms. Anti-PD-(L)-1 antibodies can reverse the suppressive immune signals, and CD137 agonists can boost T cell activation, improving antigen presentation and cytokine release. Methods: The antitumor immunity of M9657 + pembrolizumab (anti-PD-1 antibody) combination therapy was assessed using in-vitro luciferase and ex-vivo functional assays. In vivo antitumor efficacy was investigated with the M9657 surrogate (FS122m) and anti-mPD-1 in syngeneic tumor models expressing Mesothelin (MSLN). Results: The combination of M9657 and pembrolizumab displayed dose-dependent immune agonism potency and significantly enhanced tumor cell cytotoxicity and CD8+ T cell cytokine release relative to single agent treatments. In various syngeneic tumor models, the combination of FS122m with antimPD1 significantly increased antitumor efficacy relative to monotherapies, with more mice achieving complete tumor regression and prolonged median survival. Tumor-cured mice after combination treatment exhibited resistance to the primary tumor rechallenge, indicating the generation of tumor antigen-specific antitumor immunity and long-term immune protectivity. Conclusion: The combination of M9657 with anti-PD-(L)1 could overcome primary ICI therapy resistance and improve the antitumor efficacy of current anti-PD-(L)1 therapy in the clinic. Our findings support a combination strategy to combine M9657 with anti-PD-(L)1 in a clinical setting, potentially leading to enhanced antitumor immunity and improved patient outcomes. Future studies should investigate the safety and efficacy of this combination therapy in human patients. Sponsored by the healthcare business of Merck KGaA, Darmstadt, Germany (CrossRef Funder ID: 10.13039/100009945) Citation Format: Chunxiao Xu, Sireesha Yalavarthi, Hong Zhang, Uma Mahesh Gundra, Clotilde Bourin, Laura Helming. M9657, a tumor-targeted anti-CD137 agonist, induced significant antitumor immunity in combination with anti-PD-1 antibody [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 5305.

Abstract 6699: Delineating germline, tumor and extrinsic factors driving mucosal melanoma (MM) risk and response to immune checkpoint inhibitor (ICI) treatment

Abstract Introduction MM is a rare melanoma subtype with distinct biology, low immunogenicity and tumor mutational burden, and subsequently lower response rates to ICIs. The biology of MM is poorly understood. We sought to prospectively, uniformly, and comprehensively profile a cohort of MM patients to determine the interplay of molecular variation, germline predisposition, immunity, gut, mucosal and tumor microbiome and modifiable risk factors on ICI response and resistance in advanced MM. Methods Patients (pts) with MM treated with standard-of-care ICI as any treatment line presenting to MD Anderson are being prospectively enrolled for longitudinal collection for molecular, microbiome, and lifestyle factor profiling. Planned analyses include: whole genome sequencing of normal and tumor tissue, RNA sequencing, and T cell receptor sequencing from fresh tumor samples; germline sequencing and genotype analyses; NanoString Digital Spatial Profiling (DSP) from formalin-fixed paraffin embedded (FFPE) specimens; whole genome shotgun, microbiome profiling and 16S rRNA gene sequencing (16S) of fecal specimens and affected mucosal and tumor sites (swabs); participant lifestyle and patient reported outcomes (PROs) assessments. Fresh tissue is collected and used to develop PDX models and cell lines. Results 98 pts have been enrolled to date; 83 (85%) Caucasians, 8 (8%) Hispanic, 4 (4%) Asians. 67 (68%) females. Median age at MM diagnosis is 64 years (range 32-91 years). MM primary sites include 24 (24%) naso-oral, 29 (30%) urogenital, 26 (27%) anorectal, 7 (7%) conjunctival and 12 (12%) other. Clinical somatic mutation testing was performed in 76 (76%) pts and common mutations were KIT (n = 12, 16%), NRAS (n = 8, 11%) and BRAF V600 or non-V600 (n = 9, 12%). At data cut-off (November 2023), 18 (18%) pts deceased. Median follow-up from first diagnosis to last visit/death was 16 months (range 1-178 months). Sample collections at data cut-off include: blood samples (n = 95; 219 samples); fecal specimens (n = 50; 97 samples); mucosal swabs (tumor/tumor adjacent/oral cavity; n = 38; 101 samples); fresh frozen tumor/normal (n = 38; 55 samples), fresh tumor/normal (n = 28; 36 samples) and FFPE tumor (n = 21; 37 samples) tissue. PROs and dietary assessments have been collected from 47 pts. Fresh tissue for PDX model and cell line development has been collected from 11 pts. Conclusion This is an ongoing prospective study that is expected to drive insights into the tumor/microenvironment/host interactions and factors regulating immunogenicity to predict response and resistance to ICIs in a rare and understudied melanoma subtype. Interrogation of the role of the gut microbiome and its modifiable determinants will lead to the investigation of new therapeutic strategies to modulate the microbiome to improve treatment outcomes in MM. Data will be presented from initial cohort analyses. Citation Format: Florentia Dimitriou, Priyadharsini Nagarajan, Sabitha Prabhakaran, Neus Bota, Mark Knafl, Randy A. Chu, Ashish V. Damania, Pranoti V. Sahasrabhojane, Yasmine Hoballah, Jillian S. Losh, Nadim J. Ajami, Scott E. Woodman, Jennifer A. Wargo, Andrew Futreal, Jennifer L. McQuade. Delineating germline, tumor and extrinsic factors driving mucosal melanoma (MM) risk and response to immune checkpoint inhibitor (ICI) 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 6699.

Abstract 6558: Ultra-sensitive ctDNA detection predicts response to immune checkpoint inhibition in advanced melanoma patients

Abstract Immune checkpoint inhibition (ICI) provides clinical benefit to a subset of cancer patients. Monitoring circulating tumor DNA (ctDNA) in peripheral blood may allow clinicians to predict ICI response or resistance earlier than imaging and track response more frequently. In this study, melanoma patients receiving ICI were profiled using an ultra-sensitive, tumor-informed ctDNA detection platform, and the findings were correlated with clinical outcome. In this retrospective study, 188 plasma samples were collected from 23 advanced melanoma patients receiving immune checkpoint inhibitor (ICI) treatment, spanning a period of up to 40 months. Levels of ctDNA were then profiled using the NeXT Personal® assay. NeXT Personal is a liquid biopsy platform that utilizes whole-genome sequencing of tumor and normal samples to create a customized panel for each patient, encompassing up to 1,800 genetic somatic variants. This enables the detection of molecular residual disease (MRD) down to a limit of detection (LOD) of 1-3 parts per million (PPM). We subsequently compared the results obtained through NeXT Personal with RECIST-defined measurements and clinical outcomes. Ultra-sensitive ctDNA detection was achieved across a wide dynamic range, spanning from 2.3 PPM to over 130,000 PPM (median LOD = 2 PPM). A significant number of detections were attained at low PPM levels, with 30% (31/105) occurring below 100 PPM and 25% (26/105) occurring below 50 PPM. 94% (17/18) of baseline samples were ctDNA+ among patients without recent second-line therapy, including all patients who progressed. All ctDNA+ detections aligned with imaging results that indicated the presence of tumor. Likewise, all plasma timepoints corresponding to complete responses (CR) assessed via RECIST were ctDNA-. Early increase in ctDNA from baseline to treatment cycle 3 significantly predicted PFS (log-rank 0.003; Wald p=0.01, HR=8.35, 95% CI 1.62-43.15). Survival was predicted by both imaging CR (log-rank p=0.018) and ctDNA clearance (log-rank p=0.003). Molecular progression, defined as a 20% increase in ctDNA, significantly predicted OS (log-rank p=0.023), whereas imaging PD status did not predict OS (log-rank p=0.09). We achieved detection of ctDNA with an LOD down to 1.3 PPM in this cohort, with nearly a third of detections occurring below 100 PPM, suggesting the importance of an ultra-sensitive ctDNA approach even in late stage patients. Our findings suggest that ctDNA changes arepredictive of ICI response in late stage melanoma. These results highlight the potential for patient-specific ctDNA monitoring to inform patient management and for clincal trial design. Citation Format: Christoffer Gebhardt, Laura Keller, Isabel Heidrich, Julian Koett, Glenn Geidel, Daniel J. Smit, Ronald Simon, Stefan W. Schneider, Jason Pugh, Charles W. Abbott, Sean Boyle, Richard O. Chen, Klaus Pantel. Ultra-sensitive ctDNA detection predicts response to immune checkpoint inhibition in advanced melanoma patients [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 6558.

Abstract 7036: Integrative biomarker profiling for predicting immunotherapy outcomes in gynecologic cancers

Abstract Immunotherapy with immune checkpoint inhibitors (ICI) has proven effective for various solid tumors, such as those in the lungs, urinary tract, and skin. However, its efficacy in gynecologic (GYN) cancers has been limited, with response rates of 11-17% in recurrent cases. Only a minority of patients with DNA mismatch repair deficiencies exhibit favorable responses to PD-1 inhibitors. The predictability of PD-L1 expression in GYN cancers remains inconsistent. Our research aimed to identify and prioritize biomarkers and mechanisms linked to ICI resistance in GYN oncology, targeting those who could benefit from these treatments.We gathered clinical and pathological data from 49 patients with ovarian, endometrial, and cervical cancers at various stages, all treated with ICI. We performed comprehensive analyses, including transcriptome-based immune cell abundance estimation, signaling pathway enrichment, and correlation with ICI treatment responses and survival outcomes. Our previous work highlighted TGF-β and CD47's roles in immunotherapy resistance, facilitating an immunosuppressive environment within our GYN cancer cohort. Moreover, we conducted a stoichiometry constraint-based genome-scale metabolic model and computed correlation-grouped metabolic activity scores (cgScore) using metabolic enzyme gene expression as constraints. Among 1533 metabolic reactions, pyruvate transport and folate metabolism stood out as the most upregulated in responders versus those who progressed.Upon identifying several promising biomarkers, we used logistic regression classifiers to decipher the predictive value of each. Our model included clinical-demographic (age, BMI, cancer type, stage) and molecular-genomic features (immune marker gene expression, TopTGF-β score, immune cell abundance from transcriptomic deconvolution, and the top 2 cgScores). Analysis divided into training and testing sets highlighted features such as stage, BMI, eosinophils, CD274, CD47, and the pyruvate transport reaction as significant predictors of ICI response. The model achieved an 80% accuracy rate on the test set, confirmed by permutation importance from scikit-learn. We also used a Regularized Cox model to link predictors with progression-free survival, emphasizing the roles of BMI, plasma cells, CD276, pyruvate transport reaction, and folate metabolism. In conclusion, there are immunological and metabolic markers have the potential to serve as predictive indicators for ICI treatment response and survival in GYN cancers. Understanding these predictors can profoundly influence clinical decision-making in immunotherapy, ultimately leading to enhanced patient outcomes and personalized treatment approaches. Citation Format: Gideon Idumah, Lin Li, Haider Mahdi, Ying Ni. Integrative biomarker profiling for predicting immunotherapy outcomes in gynecologic cancers [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 7036.

Abstract 6857: Evolution of myeloid-mediated mechanisms of immunotherapy resistance at single-cell resolution with prostate cancer progression

Abstract Background: Patients with metastatic castration-resistant prostate cancer (mCRPC) are largely refractory to immune checkpoint inhibitors (ICIs). This resistance is, in part, attributed to the presence of immunosuppressive myeloid cells in tumors. However, attempts to target these cells broadly, such as CSF1R antagonism, have thus far failed clinically primarily due to their heterogeneous nature. Thus, we hypothesized that a more comprehensive understanding of immunosuppressive myeloid subsets and their molecular mechanisms at the single-cell level is critical to enhance the effectiveness of immunotherapy. Methods: We performed single-cell profiling of patient biopsies with either localized, metastatic hormone-sensitive prostate cancer, or mCRPC. We then reverse translated these findings in a syngeneic mouse model of CRPC, where we performed multi-omic single-cell assessment and conducted studies to assess tumor efficacy and gain mechanistic insights. Results: We identified a specific subset of tumor-associated macrophages with elevated hypoxia signatures, including higher SPP1 transcript levels (SPP1hi-TAMs). These macrophages become significantly more abundant as the disease advances, expressing elevated immunosuppressive molecular programs. Notably, CSF1R transcripts were significantly reduced in SPP1hi-TAMs, suggesting their potential role in the clinical ineffectiveness of CSF1R blockade. In a syngeneic mouse CRPC model, we identified an analogous macrophage subset through single-cell profiling and flow cytometry. These macrophages possess the ability to suppress T cell activity in co-culture. Consistent with these findings, adoptive transfer of Spp1hi-TAMs into CRPC promoted ICI resistance and worsened survival in vivo. Importantly, these macrophages proved resistant to anti-CSF1R treatment, underscoring the need to target their immunosuppressive signals as a potential therapeutic approach. Pathway analysis revealed enrichment of gene signatures associated with adenosine signaling in SPP1hi-TAMs both in patients and in mice, implicating this pathway as their immunosuppressive mechanism. Indeed, blocking adenosine signaling using antibodies or pharmacologic inhibitors resulted in a significant reduction in T cell suppression mediated by Spp1hi-TAMs in culture. Furthermore, pharmacologic blockade of adenosine receptors in vivo significantly decreased tumor growth and enhanced the responsiveness of tumor cells to ICI therapies. Conclusions: Our studies demonstrate that SPP1hi-TAMs become prevalent as the disease progresses. They are resistant to CSF1R blockade and play a key role in mediating immunotherapeutic resistance in vivo by activating adenosine signaling pathways. These findings highlight the potential of the associated signals as promising targets for therapeutic intervention. Citation Format: Aram Lyu, Zenghua Fan, Diamond Luong, Ali Setayesh, Alec Starzinski, Laura Valderrábano, Eliezer Van Allen, Lawrence Fong. Evolution of myeloid-mediated mechanisms of immunotherapy resistance at single-cell resolution with prostate cancer progression [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 6857.

Abstract 6510: BPI-511966,a potent and selective HPK1 inhibitor with robust single-agent efficacy for cancer immunotherapy

Abstract Although immune checkpoint inhibitors (ICIs) have become the standard treatment for many types of cancers, a large proportion of patients fail to respond to ICIs. Hematopoietic progenitor kinase 1 (HPK1) has been validated as a negative intracellular immune checkpoint that constrains T-cell activation. Genetic or pharmacological ablation of HPK1 induces a robust anti-cancer immune response in vivo, highlighting the potential of HPK1 as a next-generation target for cancer immunotherapy. Herein, we reported the discovery of BPI-511966, a highly potent ATP-competitive HPK1 inhibitor. The compound strongly inhibited HPK1 kinase with an IC50 of 2.3 nM at physiologically relevant ATP concentration (1 mM) and reduced phosphorylation of SLP-76, a substrate adaptor of HPK1, in Jurkat T cells in vitro, with an IC50 value of 11 nM. Development of an optimal HPK1 inhibitor requires not only high potency for target engagement but also high selectivity to spare other kinases that are essential for T cell activation. BPI-511966 showed &amp;gt;100-fold higher IC50 (364 nM) against MAP4K3/GLK, an HPK1 homology kinase promoting T-cell activation, and also demonstrated weak inhibition in a panel of other immune-related kinases. The remarkable potency and selectivity of BPI-511966 translate into robust T cell-enhancing efficacy in vitro. Treatment with BPI-511966 promoted both IL-2 and IFN-γ production by Jurkat T cell and human PBMC in a dose-dependent manner. The on-target action of BPI-511966 was validated in HPK1-KO Jurkat T cells, in which no significant impacts on SLP-76 phosphorylation and IL-2 secretion were observed. In vivo, single dose escalation of BPI-511966 in mice leads to dose-proportional increases in drug exposure, accompanied by inhibition of SLP-76 phosphorylation in peripheral CD3+ T cells. Furthermore, repeated oral administration of BPI-511966 as a single agent significantly suppressed CT-26 tumor growth in immune-competent mice (92% TGI), correlating with increased infiltration of CD45+ CD8+ cells and enhanced cytokine production in tumor. Notably, the efficacy of BPI-511966 is abrogated in immune-compromised mice, suggesting its vital role in promoting anti-cancer immunity. In summary, this study presents a novel, highly potent, and selective HPK1 inhibitor BPI-511966. The robust single-agent activity of BPI-511966 makes it a promising small molecule I/O agent to address ICI resistance as monotherapy or in combination. Citation Format: Yong Zhang, Xiaoguan Zhu, Wenmao Wu, Zhifang Xia, Zhengyao Zou, Han Han, Cheng Yang, Haibo Chen, Tianyi Ma, Xiaoyun Liu, Jing Guo, Hao Wu, Hong Lan, Lieming Ding, Jiabing Wang, Quan Zhou. BPI-511966,a potent and selective HPK1 inhibitor with robust single-agent efficacy for 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 6510.

Abstract 2415: Resistance to immune checkpoint inhibitor (ICI) therapy in metastatic melanoma is revealed by deep circulating tumor DNA tracking in concert with tumor immune profiling

Abstract Monitoring clinically actionable and emerging mutations in circulating tumor DNA (ctDNA) may be crucial for guiding treatment, but adoption has been slow due to the narrow scope and reproducibility of current approaches. Here, we investigate melanoma patients receiving ICI over several years, beginning with extensive tumor mutational and immune profiling followed by deep, whole-exome ctDNA monitoring.Here, 66 plasma samples from 23 advanced stage melanoma patients that were collected throughout ICI treatment (up to 40 months) were profiled using the NeXT Liquid Biopsy® platform (NeXT LB). NeXT LB monitors exome-wide ctDNA by leveraging a patient’s tumor, PBMCs and plasma samples, detecting both tumor-derived and emerging mutations. In addition to ctDNA tracking, we also used the ImmunoID NeXT Platform® to immunologically profile tumor tissue; including gene expression quantification, HLA profiling (typing, mutation, and loss of heterozygosity), T-cell receptor and tumor microenvironment profiling, and neoantigen prediction. ctDNA dynamics and tumor immunity were correlated with clinical outcome. Patients who progressed had lower tumor mutational burden (TMB, Mann-Whitney (MW); p=0.03), and lower neoantigen burden (MW; p=0.04). Responding tumors were enriched for interferon gamma and inflammatory signaling (Wald; adjusted p&amp;lt;0.01) and myeloid dendritic cells (MW; p=0.01), as measured by baseline RNA expression profiling. With an average coverage of 2260X SD +/-157, plasma samples yielded from 4 to 4081 variants. The number of on-treatment tumor variants detected in plasma predicted increased OS hazard (HR=2.95, Wald p=0.03; Kaplan-Meier (KM) p=0.0003) and progression hazard (HR=1.74, Wald p=0.04; KM p=0.0003). Overall, 10% (4277) of all variants were novel mutations observed only in the plasma. Novel variants were less likely to emerge in genes conferring sensitivity to ICI therapy (mixed-model; p&amp;lt;0.001). Dynamic shifts in allelic fraction between baseline and the first available on-treatment timepoint predicted increased OS hazard (HR=3.02, Wald p=0.05) and progression hazard (HR=2.90, Wald p=0.02). In ctDNA clonal phylogenies, 100% of BRAF and NRAS mutations belonged to the dominant clone. By combining immune and ctDNA features, a multivariable model predicted resistance to ICI treatment (log-likelihood p=0.002; c-index=0.89). Using a single liquid biopsy platform, we profiled tumor immunity and tracked existing and emerging ctDNA variants over the course of ICI treatment. We demonstrate that, even though counts of on-treatment ctDNA variants were sufficient for significant survival models, deep profiling of both tumor immunity and ctDNA dynamics provided deeper understanding of ICI resistance. Subsequent studies will determine if ctDNA-guided intervention can improve clinical outcomes. Citation Format: Charles W. Abbott, Laura Keller, Isabel Heidrich, Julian Kött, Glenn Geidel, Daniel J. Smit, Ronald Simon, Stefan Schneider, Jason Pugh, Sean M. Boyle, Richard O. Chen, Klaus Pantel, Christoffer Gebhardt. Resistance to immune checkpoint inhibitor (ICI) therapy in metastatic melanoma is revealed by deep circulating tumor DNA tracking in concert with tumor immune profiling [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 2415.

Abstract 2915: Targeting complement factor H renders STK11-mutant lung adenocarcinoma sensitive to anti-PD-1 therapy in mice

Abstract STK11 mutations occurs in 15-20% of lung adenocarcinoma (LUAD) and is associated with KRAS mutations, poor survival and resistance to immune checkpoint inhibitors (ICI). We observed tumor cell lines and primary human STK11-mutant LUAD upregulates of expression of C3 and complement factor H (FH). Deletion of C3 in STK11 knock-out tumor cells resulted in reduced FH expression. FH is a co-factor of Factor I, which converts C3b to proteolytically inactive iC3b thereby limiting activation of the alternative pathway (AP) C3 convertase. FH binds to proteoaminoglycans on the cell membrane and protects cells from AP complement-dependent cytotoxicity. With increased C3 generation by STK11-mutant tumor cells, we reasoned that systemic or tumor-derived FH protects tumor cells from complement attack. We hypothesized that tumor-derived C3 would promote STK11-mutant LUAD growth in immune intact mice by promoting immune evasion and would drive ICI resistance. Based on the expected tumor-protective effects of FH, we also hypothesized that anti-FH antibodies would control tumor growth and render tumor more sensitive to ICI. We evaluated growth of subcutaneously administered CMT167-STK11KO with and without C3 deletion (CMT167-STK11KO is murine KRASG12V LUAD with CRISPR/Cas9 deletion of STK11). Deletion of C3 in CMT167-STK11KO (CMT167-STK11KO/C3KO) resulted in dramatic inhibition of tumor growth and in sensitivity to anti-PD-1 therapy in vivo. In contrast, deletion of C3 in STK11-KO tumors had no effect on tumor growth in nude mice or following CD8 depletion in WT mice. These findings support a role of tumor-derived C3 in evasion of T cell anti-tumor immunity and as an obstacle to anti-PD-1 therapy. GT103 is a therapeutic antibody that binds tumor cell-attached CFH, causes complement activation, kills tumor cells, initiates a shift from a pro- to an anti-tumor immune microenvironment, and is currently being evaluated in a Phase 1b-2 clinical trial in combination with pembrolizumab (NCT05617313). We observed that single agent GT103 or anti-PD-1 has limited efficacy in CMT167-STK11KO tumor in WT mice. However, the combination of GT103 and anti-PD-1 was very effective in limiting tumor growth. Our results support a role of tumor-derived C3 in suppressing CD8 T-cell immunity and in driving ICI resistance and that the addition of GT103 renders STK11-KO tumors sensitive to anti-PD-1 in mice. These studies establish rationale for evaluating this combination in patients with STK11-mutant LUAD. Citation Format: Sora Suzuki, Anm Nazmul Khan, Thejaswini Giridharan, Catrina Ting, Ryan Bushey, Elizabeth Gottlin, Michael Campa, Edward F. Patz, Edwin H. Yau, Brahm Segal. Targeting complement factor H renders STK11-mutant lung adenocarcinoma sensitive to anti-PD-1 therapy in mice [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 2915.

MCL1 inhibition targets Myeloid Derived Suppressors Cells, promotes antitumor immunity and enhances the efficacy of immune checkpoint blockade

Immune checkpoint inhibitors (ICIs) are now the first-line treatment for patients with advanced melanoma. Despite promising clinical results, many patients fail to respond to these therapies. BH3 mimetics, a novel class of small molecule inhibitors that bind and inhibit anti-apoptotic members of the BCL2 family proteins such as BCL2 or MCL1, have been very successful in treating hematologic malignancies. However, there are limited studies on the immunomodulatory role of the BH3 mimetics. Several factors contribute to ICI resistance including myeloid-derived suppressor cells (MDSCs) that exert immunosuppressive effects through direct and indirect inhibition of antitumor immunity. Thus, targeting MDSCs to enhance antitumor immunity has the potential to enhance the efficacy of ICIs. In this study, we show that the MCL1 inhibitor S64315 reduces melanoma tumor growth in an immune cell-dependent manner in mice. Specifically, S64315 enhances antitumor immunity by reducing MDSC frequency and by promoting the activity of CD8+T cells. Additionally, human MDSCs are 10 times more sensitive to S64315 than cutaneous melanoma lines. Further, we found that a higher expression of MCL1 is associated with poor survival for patients treated with anti-PD-1. Finally, combining S64315 and anti-PD-1 significantly slowed tumor growth compared to either agent alone. Together, this proof-of-concept study demonstrates the potential of combining an MCL1 inhibitor with anti-PD-1 in the treatment of melanoma. It justifies the further development of next generation MCL1 inhibitors to improve efficacy of ICIs in treating malignant melanoma.

Immunotherapy of Human Melanoma: Past, Present, Future.

Immunotherapy with immune checkpoint inhibitors (ICIs) is a promising therapeutic schedule in advanced solid cancers. In this review, clinical trials from highly reputable journals are interpreted for safety and efficacy evaluation of the common anti-programmed death-1 (PD-1) inhibitor nivolumab and/or the most known anti-cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) inhibitor ipilimumab in advanced melanoma. Current progress in the field of melanoma immunotherapy is the focus of this review. Solo nivolumab and combo nivolumab-ipilimumab show higher responses compared to solo ipilimumab or chemotherapy. BRAF and programmed death-ligand 1 (PDL1) expression states are seemingly not reliable biomarkers of response to ICI therapy in melanoma. Solo ipilimumab and particularly a combination of nivolumab-ipilimumab show higher adverse events (AEs) compared with solo nivolumab or chemotherapy. Besides, ICI therapy is safer in mucosal melanoma, but its efficacy is higher in the cutaneous subtype. Patients receiving combination regimens who are experiencing serious AEs can discontinue such regimens until recovery and still maintain clinical benefits. To conclude, combo nivolumab-ipilimumab represents more therapeutic advantages compared with solo nivolumab or ipilimumab, but the rate of AEs is higher for combination regimens. Resistance to combo nivolumab-ipilimumab demands the application of novel approaches to go with ICIs in melanoma immunotherapy. Immunogenic agents, alternative immune checkpoints, vaccination, oncolytic viruses, extracellular vesicles (EVs) and fecal microbiome transplantation (FMT) are novel strategies in patients developing ICI resistance.