Abstract Diet is a key factor that shapes the gut microbiome, systemic metabolism and immune function. However, how specific macronutrients alter host physiology and tumor-immune interactions relevant to tumor progression and response to immune checkpoint inhibitor (ICI) immunotherapy remains unclear. We therefore sought to investigate how high fat diets (HFDs) varying in macronutrient source and composition influence metabolism, the gut microbiome and anti-tumor immunity. C57BL/6 mice were fed either a standard chow (CD), high fat (HF)/high sugar (HS)-Copha or HF-Lard diet for 2 or 7 weeks prior to inoculation with a syngeneic cancer cell line. These diets notably have differing fatty acid compositions; the copha-based (plant) HFD has more MCFAs compared to the lard-based (animal) HFD that is dominated by LCFAs. Mice on HF-Lard exhibited impaired glucose tolerance and reduced insulin sensitivity compared to CD and HF/HS-Copha after 2 and 7 weeks on diets. However, only mice on HF-Lard longer term had both elevated fasting glucose and insulin. Profiling the gut microbiomes of mice revealed both HFDs rapidly induced gut dysbiosis characterized by reduced diversity, although HF/HS-Copha compared to HF-Lard were enriched with metabolically beneficial species Blautia coccoides, Parabacteroides merdae and Bacteroides acidifaciens. Notably, HF-Lard accelerated the growth of B16-F10 and YUMM3.3-UVR melanomas while both HFDs accelerated the growth of MC38 colorectal adenocarcinomas. Similar results were observed in the short-term study except for B16-F10 where no differences between diets were observed. This suggests the acceleration is independent of obesity though may be influenced by the immunogenicity or intrinsic insulin sensitivity of the tumor. Spectral flow analysis of immune cells across the mesenteric lymph nodes (MLN), spleen, tumor draining LN (tdLN) and tumor revealed divergent immune profiles across diets. Both HFDs had lower plasma cells, cDC1s and CD8 T cells in the tdLN compared to CD. However, HF-Lard mice had higher frequencies of monocytes, and both Th17 cells and RORgt+ Tregs, indicating polarization towards suppressive phenotypes in addition to impaired anti-tumor priming. This was accompanied by enhanced exhaustion across CD8 T cells in the tumors of HF-Lard mice.Together this suggests that HFDs dominated by LCFAs are associated with metabolic dysfunction, and altered microbiome and immune phenotypes, which could contribute to accelerated tumor growth for melanoma. It also highlights that tumor type/genetics are important factors in how the diet-gut axis influences tumor growth. Ongoing work will focus on understanding how specific fat sources and diet durations impact ICI treatment and ultimately inform the design of more specific dietary interventions to enhance the efficacy of treatment. Citation Format: Rebecca C. Simpson, Freya E. Edge, Jordan W. Conway, Hsin-Yi Tseng, Mirei Okada, Inah Camaya, Laura Smith, Akshaya Ramanathan, Oliver K. Fuller, Stewart W. Masson, Jessamy Tiffen, Georgina V. Long, Erin R. Shanahan. The impact of high fat diet on tumor growth is dependent on fatty acid composition and tumor type [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 2882.

Approximately 50% of melanoma patients fail to respond to immune checkpoint blockade (ICB), and acquired resistance hampers long-term survival in about half of initially responding patients. Whether targeting BET reader proteins, implicated in epigenetic dysregulation, can enhance ICB response rates and durability, remains to be determined. Here we show elevated BET proteins correlate with poor survival and ICB responses in melanoma patients. The BET inhibitor IBET151, combined with anti-CTLA-4, overcame innate ICB resistance however, sequential BET inhibition failed against acquired resistance in mouse models. Combination treatment response in the innate resistance model induced changes in tumor-infiltrating immune cells, reducing myeloid-derived suppressor cells (MDSCs). CD4+ and CD8+ T cells showed decreased expression of inhibitory receptors, with reduced TIM3, LAG3, and BTLA checkpoint expression. In human PBMCs in vitro, BET inhibition reduced expression of immune checkpoints in CD4+ and CD8+ T cells, restoring effector cytokines and downregulating the transcriptional driver TOX. BET proteins in melanoma may play an oncogenic role by inducing immune suppression and driving T cell dysfunction. The study demonstrates an effective combination for innately unresponsive melanoma patients to checkpoint inhibitor immunotherapy, yet highlights BET inhibitors' limitations in an acquired resistance context.

Marked differences in survival from melanoma are noted between men and women that cannot be accounted for by behavioral differences. We and others have provided evidence that this difference may be due to increased expression of immune-related genes from the second X chromosome because of failure of X inactivation. In the present review, we have examined evidence for the contrary view that survival differences are due to weaker immune responses in males. One reason for this may be the loss of Y chromosomes (LOY), particularly in older males. The genes involved may have direct roles in immune responses or be noncoding RNAs that regulate both sex and autosomal genes involved in immune responses or tumor growth. Loss of the KDM6C and KDM5D demethylases appeared to common genes involved. The second factor appears to be the activation of androgen receptors (AR) on melanoma cells that increase their invasiveness and growth. Induction of T-cell exhaustion by AR that limits immune responses against melanoma appeared a common finding. The development of treatments to overcome effects related to gene loss on Y poses challenges, but several avenues related to AR signaling appear worthy of further study in the treatment of metastatic disease.

Abstract Although many studies have uncovered an important role for the receptor-binding protein kinase RIP1 in controlling cell death signaling, its possible contributions to cancer pathogenesis have been little explored. Here, we report that RIP1 functions as an oncogenic driver in human melanoma. Although RIP1 was commonly upregulated in melanoma, RIP1 silencing inhibited melanoma cell proliferation in vitro and retarded the growth of melanoma xenografts in vivo. Conversely, while inducing apoptosis in a small proportion of melanoma cells, RIP1 overexpression enhanced proliferation in the remaining cells. Mechanistic investigations revealed that the proliferative effects of RIP1 overexpression were mediated by NF-κB activation. Strikingly, ectopic expression of RIP1 enhanced the proliferation of primary melanocytes, triggering their anchorage-independent cell growth in an NF-κB–dependent manner. We identified DNA copy-number gain and constitutive ubiquitination by a TNFα autocrine loop mechanism as two mechanisms of RIP1 upregulation in human melanomas. Collectively, our findings define RIP1 as an oncogenic driver in melanoma, with potential implications for targeting its NF-κB–dependent activation mechanism as a novel approach to treat this disease. Cancer Res; 75(8); 1736–48. ©2015 AACR.

<p>Supplementary Figs. S1-S8 and Table S1 Supplementary Materials and Methods - The primers used for qPCR. Supplementary Fig. S1. Quantitation of RIP1 expression in melanocytic tumors. Supplementary Fig. S2. Melanocytes of different origins express lower levels of RIP1 than melanoma cells. Supplementary Fig. S3. Overexpression of RIP1 triggers cell death independently of its kinase domain. Supplementary Fig. S4. NF-kB is constitutively activated in melanoma cells. Supplementary Fig. S5. RIP1 overexpression triggers moderate reduction in melanocyte viability independently of caspases. Supplementary Fig. S6. RIP1 mRNA expression and its gene copy number variations in fresh melanoma isolates. Supplementary Fig. S7. The turnover rates of RIP1 mRNA are comparable between melanoma cells and melanocytes. Supplementary Fig. S8. Overexpression of RIP1 reverses reduction in NF-kB activation and melanoma cell proliferation caused by knockdown of TNFR1. Supplementary Table S1. Summary of melanocytic tumors and their expression levels of RIP1.</p>

Supplementary Experimental Procedures

One of the limitations of immunotherapy is the development of a state referred to as T cell exhaustion (TEx) whereby T cells express inhibitory receptors (IRs) and lose production of effectors involved in killing of their targets. In the present studies we have used the repeated stimulation model with anti CD3 and anti CD28 to understand the factors involved in TEx development and treatments that may reduce changes of TEx. The results show that addition of nicotinamide (NAM) involved in energy supply to cells prevented the development of inhibitory receptors (IRs). This was particularly evident for the IRs CD39, TIM3, and to a lesser extent LAG3 and PD1 expression. NAM also prevented the inhibition of IL-2 and TNFα expression in TEx and induced differentiation of CD4+ and CD8 T cells to effector memory and terminal effector T cells. The present results showed that effects of NAM were linked to regulation of reactive oxygen species (ROS) consistent with previous studies implicating ROS in upregulation of TOX transcription factors that induce TEx. These effects of NAM in reducing changes of TEx and in increasing the differentiation of T cells to effector states appears to have important implications for the use of NAM supplements in immunotherapy against cancers and viral infections and require further exploration in vivo.

Dysregulation of epigenetic modifiers is a frequent event in melanoma and underlies many aspects of melanoma biology, including resistance to targeted therapy and immunotherapies. Here, we report that dual targeting of BET and CDK9 proteins have synergistic effects against melanoma cells in vitro and in vivo. The BET inhibitor (IBET151) and CDK9 inhibitor (CDKI73) synergistically killed melanoma cells in vitro independent of their BRAF or NRAS mutation status. The combination of drugs markedly inhibited the growth of human melanoma C002M cells in vitro in three-dimensional spheroids and in vivo in NOD-SCID gamma mice compared with vehicle control and the individual drugs (P < 0.05). Cell death was associated with mitochondrial depolarization, caspase-dependent apoptosis with cleavage of PARP1, and downregulation of anti-apoptotic proteins BCL2, BCLXL, and MCL1. Gene set enrichment analysis revealed downregulation of hallmark gene sets associated with E2F, G2M checkpoint, and c-MYC. Survival analysis showed worse prognosis with high G2M, E2F, or c-MYC gene signatures, suggesting biomarkers of response of BET and CDK9 inhibitors in melanoma. This combination of epigenetic inhibitors targets multiple downstream genes, leading to cell death of melanoma cells in vitro and in vivo, and warrants further investigation for treatment of melanoma in patients not responding to current therapies.

The development of resistance to treatments of melanoma is commonly associated with upregulation of the MAPK pathway and development of an undifferentiated state. Prior studies have suggested that melanoma with these resistance characteristics may be susceptible to innate death mechanisms such as pyroptosis triggered by activation of inflammasomes. In the present studies we have taken cell lines from patients before and after development of resistance to BRAF V600 inhibitors and exposed the resistant melanoma to temozolomide (a commonly used chemotherapy) with and without chloroquine to inhibit autophagy. It was found that melanoma with an inflammatory undifferentiated state appeared susceptible to this combination when tested in vitro and in vivo against xenografts in NSG mice. Translation of the latter results into patients would promise durable responses in patients treated by the combination. The inflammasome and death mechanism involved appeared to vary between melanoma and involved either AIM2, NLRP3 or NLRC4 inflammasomes and gasdermin D or E. These preliminary studies have raised questions as to the selectivity for different inflammasomes in different melanoma and their selective targeting by chemotherapy. They also question whether the inflammatory state of melanoma may be used as biomarkers to select patients for inflammasome targeted therapy.

The treatment of melanoma has been markedly improved by the introduction of targeted therapies and checkpoint blockade immunotherapy. Unfortunately, resistance to these therapies remains a limitation. Novel anticancer therapeutics targeting the MCL1 anti‐apoptotic protein have shown impressive responses in haematological cancers but are yet to be evaluated in melanoma. To assess the sensitivity of melanoma to new MCL1 inhibitors, we measured the response of 51 melanoma cell lines to the novel MCL1 inhibitor, S63845. Additionally, we assessed combination of this drug with inhibitors of the bromodomain and extra‐terminal (BET) protein family of epigenetic readers, which we postulated would assist MCL1 inhibition by downregulating anti‐apoptotic targets regulated by NF‐kB such as BCLXL, BCL2A1 and XIAP, and by upregulating pro‐apoptotic proteins including BIM and NOXA. Only 14% of melanoma cell lines showed sensitivity to S63845, however, combination of S63845 and I‐BET151 induced highly synergistic apoptotic cell death in all melanoma lines tested and in an in vivo xenograft model. Cell death was dependent on caspases and BAX/BAK. Although the combination of drugs increased the BH3‐only protein, BIM, and downregulated anti‐apoptotic proteins such as BCL2A1, the importance of these proteins in inducing cell death varied between cell lines. ABT‐199 or ABT‐263 inhibitors against BCL2 or BCL2 and BCLXL, respectively, induced further cell death when combined with S63845 and I‐BET151. The combination of MCL1 and BET inhibition appears to be a promising therapeutic approach for metastatic melanoma, and presents opportunities to add further BCL2 family inhibitors to overcome treatment resistance.

Melanoma, as for many other cancers, undergoes a selection process during progression that limits many innate and adaptive tumor control mechanisms. Immunotherapy with immune checkpoint blockade overcomes one of the escape mechanisms but if the tumor is not eliminated other escape mechanisms evolve that require new approaches for tumor control. Some of the innate mechanisms that have evolved against infections with microorganisms and viruses are proving to be active against cancer cells but require better understanding of how they are activated and what inhibitory mechanisms may need to be targeted. This is particularly so for inflammasomes which have evolved against many different organisms and which recruit a number of cytotoxic mechanisms that remain poorly understood. Equally important is understanding of where these mechanisms will fit into existing treatment strategies and whether existing strategies already involve the innate killing mechanisms.

Abstract Background: Dysregulation of epigenetic modifiers is a frequent event in melanoma and underlies many aspects of melanoma biology including resistance to targeted and immunotherapies. Here we report that dual targeting of BET and CDK9 proteins have synergistic effect in melanoma cells in vitro and in vivo. Methods: Cell viability was measured by Cell titre glow and colony forming assays. Annexin V/PI staining was performed to assess apoptosis. Apoptotic, anti-apoptotic, pro-survival signalling proteins were probed by immunoblotting. Genome wide expression analysis were performed by RNA-seq analysis of sensitive cell lines. Live-dead staining and apoptosis were performed in 3D spheroid models. In vivo studies were carried out on the YUMM1.1 mouse model in C57BL/6 syngeneic mice. Results: We report that BET and CDK9 inhibitor iBET151 and CDKI73 synergistically killed melanoma cells independent of their genetic background compared to single inhibitors. Combination index (CI) was calculated by calcusyn software also showed strong synergism (<0.3). However, these drugs did not kill human dermal fibroblast suggestive of a cancer cell specific effect. There was a time dependent increase in cell death that was associated with downregulation of anti-apoptotic proteins BCL2 and MCL1 and the oncogene c-MYC. These findings in 2D models were corroborated in 3D spheroid models. Gene Set Enrichment Analysis (GSEA) revealed that HALLMARK G2M CHECKPOINT, HALLMARK E2F TARGETS, HALLMARK MYC TARGETS were negatively enriched in the combination treatment (Normalized enrichment score =<-2.5). The in-vivo studies on the anti-PD1 resistant mouse melanoma cell line YUMM 1.1. showed that iBET151 and CDKI73 combination had marked effects on tumour growth compared to vehicle control and the individual drugs (p<0.05). Conclusion: Our findings have revealed that this novel combination of two epigenetic inhibitors targets multiple downstream genes associated with cell cycle, oncogenesis and, apoptotic pathways which augments cell death compared to effects of the single drugs. Overall, the findings warrant further investigation of key targets involved in the responses and the extent to which effects of CDK9 inhibition is due to effects on chromatin modelling. The combination would appear promising to consider for future clinical trial in melanoma patients not responding to current therapies. Citation Format: Abdullah Al Emran, Hsin-Yi Tseng, Dilini Gunatilake, Stuart Cook, Jessamy Tiffen, Stuart Gallagher, Peter Hersey. BET and CDK9 protein inhibitors: Novel epigenetic therapy to synergistically kill human melanoma cells [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr LB-177.

The development of changes in T cells, referred to as T cell exhaustion, has been suggested as a cause of primary or acquired resistance to immunotherapy by immune checkpoint blockade (ICB). A limited number of studies, largely performed on tumor infiltrating lymphocytes (TILs), has provided evidence in support of this hypothesis, but whether similar changes occur in circulating blood lymphocytes has received little attention. In the present study, a comprehensive analysis of peripheral blood leukocytes from 42 patients taken over the course of treatment with anti-PD-1 was undertaken. The patients included those grouped as responders (who did not progress), primary non-responders (primary resistance) and those with acquired resistance (who initially responded then subsequently progressed). Analysis included surface markers of exhaustion, production of cytokines following in vitro stimulation, and assessment of transcription factor levels associated with T cell exhaustion. There were differences in innate cell populations between responders and non-responders at baseline and maintained throughout therapy. Frequencies of total and classical CD14(+)CD16(-) monocytes were higher and the major subset of NK cells (CD16(hi)CD56(+)) was significantly smaller in the primary resistance group compared with responders. However, differences in peripheral blood expression of exhaustion markers were not evident between the treatment groups. T cell exhaustion markers were expressed in practically all patients and the major observation was an increase in CD39 on CD4 T cells during treatment. The results confirm the association of Eomes transcription factor with T cell exhaustion but levels of expression and the ratio with T-bet over Eomes did not differ between the patient groups. Thus, peripheral blood expression of T cell exhaustion markers does not distinguish between responders and non-responders to anti-PD-1 therapy. CD4 T cell expression of IFN gamma also differed in pre-treatment samples, indicating that predictors of response unrelated to exhaustion may be present in peripheral blood. The association of response with innate cell populations and CD4 T cell responses requires further study.

The expression of CD47 on the cancer cell surface transmits “don’t eat me” signalling that not only inhibits phagocytosis of cancer cells by phagocytes but also impairs anti-cancer T cell responses. Here we report that oncogenic activation of ERK plays an important role in transcriptional activation of CD47 through nuclear respiratory factor 1 (NRF-1) in melanoma cells. Treatment with BRAF/MEK inhibitors upregulated CD47 in cultured melanoma cells and fresh melanoma isolates. Similarly, melanoma cells selected for resistance to the BRAF inhibitor vemurafenib expressed higher levels of CD47. The increase in CD47 expression was mediated by ERK signalling, as it was associated with rebound activation of ERK and co-knockdown of ERK1/2 by siRNA diminished upregulation of CD47 in melanoma cells after exposure to BRAF/MEK inhibitors. Furthermore, ERK1/2 knockdown also reduced the constitutive expression of CD47 in melanoma cells. We identified a DNA fragment that was enriched with the consensus binding sites for NRF-1 and was transcriptionally responsive to BRAF/MEK inhibitor treatment. Knockdown of NRF-1 inhibited the increase in CD47, indicating that NRF-1 has a critical role in transcriptional activation of CD47 by ERK signalling. Functional studies showed that melanoma cells resistant to vemurafenib were more susceptible to macrophage phagocytosis when CD47 was blocked. So these results suggest that NRF-1-mediated regulation of CD47 expression is a novel mechanism by which ERK signalling promotes the pathogenesis of melanoma, and that the combination of CD47 blockade and BRAF/MEK inhibitors may be a useful approach for improving their therapeutic efficacy.

BACKGROUND:Exposure to non-pathogenic Streptococcus pneumoniae and vaccination are inversely associated with asthma. Studies in animal models demonstrate that airway administration of S. pneumoniae (live or killed), or its vaccines or components, suppresses the characteristic features of asthma in mouse models of allergic airway disease (AAD). These components could be developed into immunoregulatory therapies. S. pneumoniae components are recognized by Toll-like receptors (TLR) 2 and TLR4, and both induce inflammatory cell responses through the adaptor protein myeloid differentiation primary response gene 88 (MyD88). The involvement of TLR2, TLR4 and MyD88 in the pathogenesis of AAD and asthma is incompletely understood, and has not been studied in S. pneumoniae-mediated suppression of AAD. We investigated the role of TLR2, TLR4 and MyD88 in the development of AAD and S. pneumoniae-mediated suppression of AAD. METHODS AND FINDINGS:OVA-induced AAD and killed S. pneumoniae-mediated suppression of AAD were assessed in wild-type, TLR2-/-, TLR4-/-, TLR2/4-/- and MyD88-/- BALB/c mice. During OVA-induced AAD, TLR2, TLR4 and MyD88 were variously involved in promoting eosinophil accumulation in bronchoalveolar lavage fluid and blood, and T-helper type (Th)2 cytokine release from mediastinal lymph node T cells and splenocytes. However, all were required for the induction of airways hyperresponsiveness (AHR). In S. pneumoniae-mediated suppression of AAD, TLR2, TLR4 and MyD88 were variously involved in the suppression of eosinophilic and splenocyte Th2 responses but all were required for the reduction in AHR. CONCLUSIONS:These results highlight important but complex roles for TLR2, TLR4 and MyD88 in promoting the development of OVA-induced AAD, but conversely in the S. pneumoniae-mediated suppression of AAD, with consistent and major contributions in both the induction and suppression of AHR. Thus, TLR signaling is likely required for both the development of asthma and the suppression of asthma by S. pneumoniae, and potentially other immunoregulatory therapies.

Direct treatments of cancer such as chemotherapy, radiotherapy and targeted therapy have been shown to depend on recruitment of the immune system for their effectiveness. Recent studies have shown that development of resistance to direct therapies such as BRAF inhibitors in melanoma is associated with suppression of immune responses. We point to emerging data that implicate activation of the polycomb repressive complex 2 (PRC2) and its catalytic component-enhancer of zeste homolog 2 (EZH2)-in progression of melanoma and suppression of immune responses. EZH2 appears to have an important role in differentiation of CD4 T cells and particularly in the function of T regulatory cells, which suppress immune responses to melanoma. We review mechanisms of EZH2 activation at the genomic level and from activation of the MAP kinase, E2F or NF-kB2 pathways. These studies are consistent with activation of EZH2 as a common mechanism for induction of immune suppression in patients failing direct therapies and suggest EZH2 inhibitors may have a role in combination with immunotherapy and targeted therapies to prevent development of immunosuppression.