Immunotherapy Resistance by Inflammation-Induced Dedifferentiation

Unveiling the Dynamic Interplay between Cancer Stem Cells and the Tumor Microenvironment in Melanoma: Implications for Novel Therapeutic Strategies

Cutaneous melanoma still represents a significant health burden worldwide, being responsible for the majority of skin cancer deaths. Key advances in therapeutic strategies have significantly improved patient outcomes; however, most patients experience drug resistance and tumor relapse. Cancer stem cells (CSCs) are a small subpopulation of cells in different tumors, including melanoma, endowed with distinctive capacities of self-renewal and differentiation into bulk tumor cells. Melanoma CSCs are characterized by the expression of specific biomarkers and intracellular pathways; moreover, they play a pivotal role in tumor onset, progression and drug resistance. In recent years, great efforts have been made to dissect the molecular mechanisms underlying the protumor activities of melanoma CSCs to provide the basis for novel CSC-targeted therapies. Herein, we highlight the intricate crosstalk between melanoma CSCs and bystander cells in the tumor microenvironment (TME), including immune cells, endothelial cells and cancer-associated fibroblasts (CAFs), and its role in melanoma progression. Specifically, we discuss the peculiar capacities of melanoma CSCs to escape the host immune surveillance, to recruit immunosuppressive cells and to educate immune cells toward an immunosuppressive and protumor phenotype. We also address currently investigated CSC-targeted strategies that could pave the way for new promising therapeutic approaches for melanoma care.

NAD+ metabolism enzyme NNMT in cancer-associated fibroblasts drives tumor progression and resistance to immunotherapy by modulating macrophages in urothelial bladder cancer

BACKGROUND

This study comprehensively investigates the association between the expression of nicotinamide N-methyltransferase (NNMT) and clinical outcomes of urothelial bladder cancer (UBC), as well as the molecular mechanisms by which NNMT in cancer-associated fibroblast (CAF) modulates tumor progression and immunotherapy resistance in UBC.

METHODS

Single-cell transcriptomic analyses, immunohistochemical and immunofluorescence assays were performed on bladder cancer samples to validate the relationship between NNMT expression and clinical outcomes. A series of experiments, including chromatin immunoprecipitation assay, liquid chromatography tandem mass spectrometry assay, and CRISPR‒Cas9 (Clustered Regularly Interspaced Short Palindromic Repeats and CRISPR-associated protein 9) knockout, together with in vivo models, have been established to determine the molecular functions of NNMT in CAFs in UBC.

RESULTS

We demonstrated that elevated expression of the nicotinamide adenine dinucleotide (NAD+) metabolism enzyme NNMT in CAFs (NNMT+ CAFs) was significantly associated with non-response to programmed death-ligand 1 (PD-L1) blockade immunotherapy in patients with UBC and predicted the unfavorable prognosis of UBC in two independent large cohorts. Targeting NNMT using the inhibitor 5-Amino-1-methylquinolinium iodide significantly reduced tumor growth and enhanced the apoptotic effects of the anti-PD-L1 antibody in UBC mouse models. Mechanistically, NNMT+ CAFs recruit tumor-associated macrophages via epigenetic reprogramming of serum amyloid A (SAA) to drive tumor cell proliferation and confer resistance to programmed death-1/PD-L1 blockade immunotherapy.

CONCLUSIONS

NNMT+ CAFs were significantly associated with non-response to PD-L1 blockade immunotherapy in patients with UBC. Elevated NNMT, specifically in CAFs, upregulates SAA expression and enhances the recruitment and differentiation of macrophages in the tumor microenvironment, thereby directly or indirectly promoting tumor progression and conferring resistance to immunotherapies in bladder cancer.

Defining clinically useful biomarkers of immune checkpoint inhibitors in solid tumours

Although more than a decade has passed since the approval of immune checkpoint inhibitors (ICIs) for the treatment of melanoma and non-small-cell lung, breast and gastrointestinal cancers, many patients still show limited response. US Food and Drug Administration (FDA)-approved biomarkers include programmed cell death 1 ligand 1 (PDL1) expression, microsatellite status (that is, microsatellite instability-high (MSI-H)) and tumour mutational burden (TMB), but these have limited utility and/or lack standardized testing approaches for pan-cancer applications. Tissue-based analytes (such as tumour gene signatures, tumour antigen presentation or tumour microenvironment profiles) show a correlation with immune response, but equally, these demonstrate limited efficacy, as they represent a single time point and a single spatial assessment. Patient heterogeneity as well as inter- and intra-tumoural differences across different tissue sites and time points represent substantial challenges for static biomarkers. However, dynamic biomarkers such as longitudinal biopsies or novel, less-invasive markers such as blood-based biomarkers, radiomics and the gut microbiome show increasing potential for the dynamic identification of ICI response, and patient-tailored predictors identified through neoadjuvant trials or novel ex vivo tumour models can help to personalize treatment. In this Perspective, we critically assess the multiple new static, dynamic and patient-specific biomarkers, highlight the newest consortia and trial efforts, and provide recommendations for future clinical trials to make meaningful steps forwards in the field.

Further knowledge and developments in resistance mechanisms to immune checkpoint inhibitors

The past decade has witnessed a revolution in cancer treatment, shifting from conventional drugs (chemotherapies) towards targeted molecular therapies and immune-based therapies, in particular immune-checkpoint inhibitors (ICIs). These immunotherapies release the host's immune system against the tumor and have shown unprecedented durable remission for patients with cancers that were thought incurable, such as metastatic melanoma, metastatic renal cell carcinoma (RCC), microsatellite instability (MSI) high colorectal cancer and late stages of non-small cell lung cancer (NSCLC). However, about 80% of the patients fail to respond to these immunotherapies and are therefore left with other less effective and potentially toxic treatments. Identifying and understanding the mechanisms that enable cancerous cells to adapt to and eventually overcome therapy can help circumvent resistance and improve treatment. In this review, we describe the recent discoveries on the onco-immunological processes which govern the tumor microenvironment and their impact on the resistance to PD-1/PD-L1 checkpoint blockade.

Emerging roles of TBK1 in cancer immunobiology

TANK-binding kinase 1 (TBK1) is a versatile serine/threonine protein kinase with established roles in innate immunity, metabolism, autophagy, cell death, and inflammation. While best known for its role in regulating innate immunity, TBK1 has emerged as a cancer cell-intrinsic immune evasion gene by virtue of its role in modulating cellular responses to inflammatory signals emanating from the immune system. Beyond its effect on cancer cells, TBK1 appears to regulate lymphoid and myeloid cells in the tumor immune microenvironment. In this review, we detail recent advances in our understanding of the tumor-intrinsic and -extrinsic roles and regulation of TBK1 in tumor immunity.

The Complex Role of Thrombin in Cancer and Metastasis: Focus on Interactions with the Immune System

Thrombin, a pleiotropic enzyme involved in coagulation, plays a crucial role in both procoagulant and anticoagulant pathways. Thrombin converts fibrinogen into fibrin, initiates platelet activation, and promotes clot formation. Thrombin also activates anticoagulant pathways, indirectly inhibiting factors involved in coagulation. Tissue factor triggers thrombin generation, and the overexpression of thrombin in various cancers suggests that it is involved in tumor growth, angiogenesis, and metastasis. Increased thrombin generation has been observed in cancer patients, especially those with metastases. Thrombin exerts its effects through protease-activated receptors (PARs), particularly PAR-1 and PAR-2, which are involved in cancer progression, angiogenesis, and immunological responses. Thrombin-mediated signaling promotes angiogenesis by activating endothelial cells and platelets, thereby releasing proangiogenic factors. These functions of thrombin are well recognized and have been widely described. However, in recent years, intriguing new findings concerning the association between thrombin activity and cancer development have come to light, which justifies a review of this research. In particular, there is evidence that thrombin-mediated events interact with the immune system, and may regulate its response to tumor growth. It is also worth reevaluating the impact of thrombin on thrombocytes in conjunction with its multifaceted influence on tumor progression. Understanding the role of thrombin/PAR-mediated signaling in cancer and immunological responses is crucial, particularly in the context of developing immunotherapies. In this systematic review, we focus on the impact of the thrombin-related immune system response on cancer progression.

CAR-T cell therapy targeting surface expression of TYRP1 to treat cutaneous and rare melanoma subtypes

A major limitation to developing chimeric antigen receptor (CAR)-T cell therapies for solid tumors is identifying surface proteins highly expressed in tumors but not in normal tissues. Here, we identify Tyrosinase Related Protein 1 (TYRP1) as a CAR-T cell therapy target to treat patients with cutaneous and rare melanoma subtypes unresponsive to immune checkpoint blockade. TYRP1 is primarily located intracellularly in the melanosomes, with a small fraction being trafficked to the cell surface via vesicular transport. We develop a highly sensitive CAR-T cell therapy that detects surface TYRP1 in tumor cells with high TYRP1 overexpression and presents antitumor activity in vitro and in vivo in murine and patient-derived cutaneous, acral and uveal melanoma models. Furthermore, no systemic or off-tumor severe toxicities are observed in an immunocompetent murine model. The efficacy and safety profile of the TYRP1 CAR-T cell therapy supports the ongoing preparation of a phase I clinical trial.

Single-cell RNA sequencing in melanoma: what have we learned so far?

Over the past decade, there have been remarkable improvements in the treatment and survival rates of melanoma patients. Treatment resistance remains a persistent challenge, however, and is partly attributable to intratumoural heterogeneity. Melanoma cells can transition through a series of phenotypic and transcriptional cell states that vary in invasiveness and treatment responsiveness. The diverse stromal and immune contexture of the tumour microenvironment also contributes to intratumoural heterogeneity and disparities in treatment response in melanoma patients. Recent advances in single-cell sequencing technologies have enabled a more detailed understanding of melanoma heterogeneity and the underlying transcriptional programs that regulate melanoma cell diversity and behaviour. In this review, we examine the concept of intratumoural heterogeneity and the challenges it poses to achieving long-lasting treatment responses. We focus on the significance of next generation single-cell sequencing in advancing our understanding of melanoma diversity and the unique insights gained from single-cell studies.

SOX10 Loss Sensitizes Melanoma Cells to Cytokine-Mediated Inflammatory Cell Death

The transcription factor, SOX10, plays an important role in the differentiation of neural crest precursors to the melanocytic lineage. Malignant transformation of melanocytes leads to the development of melanoma, and SOX10 promotes melanoma cell proliferation and tumor formation. SOX10 expression in melanomas is heterogeneous, and loss of SOX10 causes a phenotypic switch toward an invasive, mesenchymal-like cell state and therapy resistance; hence, strategies to target SOX10-deficient cells are an active area of investigation. The impact of cell state and SOX10 expression on antitumor immunity is not well understood but will likely have important implications for immunotherapeutic interventions. To this end, we tested whether SOX10 status affects the response to CD8+ T cell-mediated killing and T cell-secreted cytokines, TNFα and IFNγ, which are critical effectors in the cytotoxic killing of cancer cells. We observed that genetic ablation of SOX10 rendered melanoma cells more sensitive to CD8+ T cell-mediated killing and cell death induction by either TNFα or IFNγ. Cytokine-mediated cell death in SOX10-deficient cells was associated with features of caspase-dependent pyroptosis, an inflammatory form of cell death that has the potential to increase immune responses.

IMPLICATIONS

These data support a role for SOX10 expression altering the response to T cell-mediated cell death and contribute to a broader understanding of the interaction between immune cells and melanoma cells.

Lineage Plasticity: The New Cancer Hallmark on the Block

Plasticity refers to the ability of cells to adopt a spectrum of states or phenotypes. In cancer, it is a critical contributor to tumor initiation, progression, invasiveness, and therapy resistance, and it has recently been recognized as an emerging cancer hallmark. Plasticity can occur as a result of cell-intrinsic factors (e.g., genetic, transcriptional, or epigenetic fluctuations), or through cell-extrinsic cues (e.g., signaling from components of the tumor microenvironment or selective pressure from therapy). Over the past decade, technological advances, analysis of patient samples, and studies in mouse model systems have led to a deeper understanding of how such plastic states come about. In this review, we discuss: (i) the definition of plasticity; (ii) methods to measure and quantify plasticity; (iii) the clinical relevance of plasticity; and (iv) therapeutic hypotheses to modulate plasticity in the clinic.

A TCF4-dependent gene regulatory network confers resistance to immunotherapy in melanoma

To better understand intrinsic resistance to immune checkpoint blockade (ICB), we established a comprehensive view of the cellular architecture of the treatment-naive melanoma ecosystem and studied its evolution under ICB. Using single-cell, spatial multi-omics, we showed that the tumor microenvironment promotes the emergence of a complex melanoma transcriptomic landscape. Melanoma cells harboring a mesenchymal-like (MES) state, a population known to confer resistance to targeted therapy, were significantly enriched in early on-treatment biopsies from non-responders to ICB. TCF4 serves as the hub of this landscape by being a master regulator of the MES signature and a suppressor of the melanocytic and antigen presentation transcriptional programs. Targeting TCF4 genetically or pharmacologically, using a bromodomain inhibitor, increased immunogenicity and sensitivity of MES cells to ICB and targeted therapy. We thereby uncovered a TCF4-dependent regulatory network that orchestrates multiple transcriptional programs and contributes to resistance to both targeted therapy and ICB in melanoma.

Drug dependence in cancer is exploitable by optimally constructed treatment holidays

Cancers with acquired resistance to targeted therapy can become simultaneously dependent on the presence of the targeted therapy drug for survival, suggesting that intermittent therapy may slow resistance. However, relatively little is known about which tumours are likely to become dependent and how to schedule intermittent therapy optimally. Here we characterized drug dependence across a panel of over 75 MAPK-inhibitor-resistant BRAFV600E mutant melanoma models at the population and single-clone levels. Melanocytic differentiated models exhibited a much greater tendency to give rise to drug-dependent progeny than their dedifferentiated counterparts. Mechanistically, acquired loss of microphthalmia-associated transcription factor in differentiated melanoma models drives ERK-JunB-p21 signalling to enforce drug dependence. We identified the optimal scheduling of 'drug holidays' using simple mathematical models that we validated across short and long timescales. Without detailed knowledge of tumour characteristics, we found that a simple adaptive therapy protocol can produce near-optimal outcomes using only measurements of total population size. Finally, a spatial agent-based model showed that optimal schedules derived from exponentially growing cells in culture remain nearly optimal in the context of tumour cell turnover and limited environmental carrying capacity. These findings may guide the implementation of improved evolution-inspired treatment strategies for drug-dependent cancers.

Dynamical hallmarks of cancer: Phenotypic switching in melanoma and epithelial-mesenchymal plasticity

Phenotypic plasticity was recently incorporated as a hallmark of cancer. This plasticity can manifest along many interconnected axes, such as stemness and differentiation, drug-sensitive and drug-resistant states, and between epithelial and mesenchymal cell-states. Despite growing acceptance for phenotypic plasticity as a hallmark of cancer, the dynamics of this process remains poorly understood. In particular, the knowledge necessary for a predictive understanding of how individual cancer cells and populations of cells dynamically switch their phenotypes in response to the intensity and/or duration of their current and past environmental stimuli remains far from complete. Here, we present recent investigations of phenotypic plasticity from a systems-level perspective using two exemplars: epithelial-mesenchymal plasticity in carcinomas and phenotypic switching in melanoma. We highlight how an integrated computational-experimental approach has helped unravel insights into specific dynamical hallmarks of phenotypic plasticity in different cancers to address the following questions: a) how many distinct cell-states or phenotypes exist?; b) how reversible are transitions among these cell-states, and what factors control the extent of reversibility?; and c) how might cell-cell communication be able to alter rates of cell-state switching and enable diverse patterns of phenotypic heterogeneity? Understanding these dynamic features of phenotypic plasticity may be a key component in shifting the paradigm of cancer treatment from reactionary to a more predictive, proactive approach.

Rutaecarpine induces the differentiation of triple-negative breast cancer cells through inhibiting fumarate hydratase

BACKGROUND

Triple-negative breast cancer (TNBC) is one of the most aggressive human cancers and has poor prognosis. Approximately 80% of TNBC cases belong to the molecular basal-like subtype, which can be exploited therapeutically by inducing differentiation. However, the strategies for inducing the differentiation of TNBC remain underexplored.

METHODS

A three-dimensional (3D) morphological screening model based on a natural compound library was used to identify possible candidate compounds that can induce TNBC cell differentiation. The efficacy of rutaecarpine was verified using assays: RT-qPCR, RNA-seq, flow cytometry, immunofluorescence, SCENITH and label-free LC-MS/MS. The direct targets of rutaecarpine were identified through drug affinity responsive target stability (DARTS) assay. A xenograft mice model was also constructed to confirm the effect of rutaecarpine in vivo.

RESULTS

We identified that rutaecarpine, an indolopyridoquinazolinone, induces luminal differentiation of basal TNBC cells in both 3D spheroids and in vivo mice models. Mechanistically, rutaecarpine treatment leads to global metabolic stress and elevated ROS in 3D cultured TNBC cells. Moreover, NAC, a scavenger of ROS, impedes rutaecarpine-induced differentiation of TNBC cells in 3D culture. Finally, we identified fumarate hydratase (FH) as the direct interacting target of rutaecarpine. The inhibition of FH and the knockdown of FH consistently induced the differentiation of TNBC cells in 3D culture.

CONCLUSIONS

Our results provide a platform for differentiation therapy drug discovery using 3D culture models and identify rutaecarpine as a potential compound for TNBC treatment.

The SWI/SNF complex member SMARCB1 supports lineage fidelity in kidney cancer

Lineage switching can induce therapy resistance in cancer. Yet, how lineage fidelity is maintained and how it can be lost remain poorly understood. Here, we have used CRISPR-Cas9-based genetic screening to demonstrate that loss of SMARCB1, a member of the SWI/SNF chromatin remodeling complex, can confer an advantage to clear cell renal cell carcinoma (ccRCC) cells upon inhibition of the renal lineage factor PAX8. Lineage factor inhibition-resistant ccRCC cells formed tumors with morphological features, but not molecular markers, of neuroendocrine differentiation. SMARCB1 inactivation led to large-scale loss of kidney-specific epigenetic programs and restoration of proliferative capacity through the adoption of new dependencies on factors that represent rare essential genes across different cancers. We further developed an analytical approach to systematically characterize lineage fidelity using large-scale CRISPR-Cas9 data. An understanding of the rules that govern lineage switching could aid the development of more durable lineage factor-targeted and other cancer therapies.

Undifferentiated and Dedifferentiated Metastatic Melanomas Masquerading as Soft Tissue Sarcomas: Mutational Signature Analysis and Immunotherapy Response

The distinction between undifferentiated melanoma (UM) or dedifferentiated melanoma (DM) from undifferentiated or unclassifiable sarcoma can be difficult and requires the careful correlation of clinical, pathologic, and genomic findings. In this study, we examined the utility of mutational signatures to identify patients with UM/DM with particular attention as to whether this distinction matters for treatment because the survival of patients with metastatic melanoma has dramatically improved with immunologic therapy, whereas durable responses are less frequent in sarcomas. We identified 19 cases of UM/DM that were initially reported as unclassified or undifferentiated malignant neoplasm or sarcoma and submitted for targeted next-generation sequencing analysis. These cases were confirmed as UM/DM by harboring melanoma driver mutations, UV signature, and high tumor mutation burden. One case of DM showed melanoma in situ. Meanwhile, 18 cases represented metastatic UM/DM. Eleven patients had a prior history of melanoma. Thirteen of 19 (68%) of the tumors were immunohistochemically completely negative for 4 melanocytic markers (S100, SOX10, HMB45, and MELAN-A). All cases harbored a dominant UV signature. Frequent driver mutations involved BRAF (26%), NRAS (32%), and NF1 (42%). In contrast, the control cohort of undifferentiated pleomorphic sarcomas (UPS) of deep soft tissue exhibited a dominant aging signature in 46.6% (7/15) without evidence of UV signature. The median tumor mutation burden for DM/UM vs UPS was 31.5 vs 7.0 mutations/Mb (P < .001). A favorable response to immune checkpoint inhibitor therapy was observed in 66.6% (12/18) of patients with UM/DM. Eight patients exhibited a complete response and were alive with no evidence of disease at the last follow-up (median 45.5 months). Our findings support the usefulness of the UV signature in discriminating DM/UM vs UPS. Furthermore, we present evidence suggesting that patients with DM/UM and UV signatures can benefit from immune checkpoint inhibitor therapy.

Molecular Evaluation of the Impact of Polymorphic Variants in Apoptotic (Bcl-2/Bax) and Proinflammatory Cytokine (TNF-α/IL-8) Genes on the Susceptibility and Progression of Myeloproliferative Neoplasms: A Case-Control Biomarker Study

The regulation of apoptosis (the programmed cell death) is dependent on the crucial involvement of BCL2 and BAX. The Bax-248G>A and Bcl-2-938 C>A polymorphic variations in the promoter sequences of the Bax and Bcl-2 gene have been recently associated with low Bax expression, progression to advanced stages, treatment resistance, and shortened overall survival rate in some hematological malignancies, including chronic myeloid leukemia (CML) and other myeloproliferative neoplasms. Chronic inflammation has been linked to various stages of carcinogenesis wherein pro-inflammatory cytokines play diverse roles in influencing cancer microenvironment leading to cell invasion and cancer progression. Cytokines such as TNF-α and IL-8 have been implicated in cancer growth in both solid and hematological malignancies with studies showing their elevated levels in patients. Genomic approaches have in recent years provided significant knowledge with the regard to the association of certain SNPs (single nucleotide polymerphisms) either in a gene or its promoter that can influence its expression, with the risk and susceptibility to human diseases including cancer. This study has investigated the consequences of promoter SNPs in apoptosis genes Bax-248G>A (rs4645878)/Bcl-2-938C>A (rs2279115) and pro-inflammatory cytokines TNF-α rs1800629 G>A/IL-8 rs4073 T>A on the risk and susceptibility towards hematological cancers. The study design has 235 individuals both male and female enrolled as subjects that had 113 cases of MPDs (myeloproliferative disorders) and 122 healthy individuals as controls. The genotyping studies were conducted through ARMS PCR (amplification-refractory mutation system PCR). The Bcl-2-938 C>A polymorphism showed up in 22% of patients in the study, while it was observed in only 10% of normal controls. This difference in genotype and allele frequency between the two groups was significant (p = 0.025). Similarly, the Bax-248G>A polymorphism was detected in 6.48% of the patients and 4.54% of the normal controls, with a significant difference in genotype and allele frequency between the groups (p = 0.048). The results suggest that the Bcl-2-938 C>A variant is linked to an elevated risk of MPDs in the codominant, dominant, and recessive inheritance models. Moreover, the study indicated allele A as risk allele which can significantly increase the risk of MPDs unlike the C allele. In case of Bax gene covariants, these were associated with an increased risk of MPDs in the codominant inheritance model and dominant inheritance model. It was found that the allele A significantly enhanced the risk of MPDs unlike the G allele. The frequencies of IL-8 rs4073 T>A in patients was found to be TT (16.39%), AT (36.88%) and AA (46.72%), compared to controls who were more likely to have frequencies of TT (39.34%), AT (37.70%) and AA (22.95%) as such, respectively. There was a notable overrepresentation of the AA genotype and GG homozygotes among patients compared to controls in TNF-α polymorphic variants, with 6.55% of patients having the AA genotype and 84% of patients being GG homozygotes, compared to 1.63% and 69%, respectively in controls. The data from the current study provide partial but important evidence that polymorphisms in apoptotic genes Bcl-2-938C>A and Bax-248G>A and pro-inflammatory cytokines IL-8 rs4073 T>A and TNF-α G>A may help predict the clinical outcomes of patients and determine the significance of such polymorphic variations in the risk of myeloproliferative diseases and their role as prognostic markers in disease management using a case-control study approach.

Association between Fluoxetine Use and Overall Survival among Patients with Cancer Treated with PD-1/L1 Immunotherapy

Checkpoint inhibitors can be a highly effective antitumor therapy but only to a subset of patients, presumably due to immunotherapy resistance. Fluoxetine was recently revealed to inhibit the NLRP3 inflammasome, and NLRP3 inhibition could serve as a target for immunotherapy resistance. Therefore, we evaluated the overall survival (OS) in patients with cancer receiving checkpoint inhibitors combined with fluoxetine. A cohort study was conducted among patients diagnosed with lung, throat (pharynx or larynx), skin, or kidney/urinary cancer treated with checkpoint inhibitor therapy. Utilizing the Veterans Affairs Informatics and Computing Infrastructure, patients were retrospectively evaluated during the period from October 2015 to June 2021. The primary outcome was overall survival (OS). Patients were followed until death or the end of the study period. There were 2316 patients evaluated, including 34 patients who were exposed to checkpoint inhibitors and fluoxetine. Propensity score weighted Cox proportional hazards demonstrated a better OS in fluoxetine-exposed patients than unexposed (HR: 0.59, 95% CI 0.371-0.936). This cohort study among cancer patients treated with checkpoint inhibitor therapy showed a significant improvement in the OS when fluoxetine was used. Because of this study's potential for selection bias, randomized trials are needed to assess the efficacy of the association of fluoxetine or another anti-NLRP3 drug to checkpoint inhibitor therapy.

Localized immune surveillance of primary melanoma in the skin deciphered through executable modeling

While skin is a site of active immune surveillance, primary melanomas often escape detection. Here, we have developed an in silico model to determine the local cross-talk between melanomas and Langerhans cells (LCs), the primary antigen-presenting cells at the site of melanoma development. The model predicts that melanomas fail to activate LC migration to lymph nodes until tumors reach a critical size, which is determined by a positive TNF-α feedback loop within melanomas, in line with our observations of murine tumors. In silico drug screening, supported by subsequent experimental testing, shows that treatment of primary tumors with MAPK pathway inhibitors may further prevent LC migration. In addition, our in silico model predicts treatment combinations that bypass LC dysfunction. In conclusion, our combined approach of in silico and in vivo studies suggests a molecular mechanism that explains how early melanomas develop under the radar of immune surveillance by LC.

T cell immunotherapies engage neutrophils to eliminate tumor antigen escape variants

Cancer immunotherapies, including adoptive T cell transfer, can be ineffective because tumors evolve to display antigen-loss-variant clones. Therapies that activate multiple branches of the immune system may eliminate escape variants. Here, we show that melanoma-specific CD4+ T cell therapy in combination with OX40 co-stimulation or CTLA-4 blockade can eradicate melanomas containing antigen escape variants. As expected, early on-target recognition of melanoma antigens by tumor-specific CD4+ T cells was required. Surprisingly, complete tumor eradication was dependent on neutrophils and partly dependent on inducible nitric oxide synthase. In support of these findings, extensive neutrophil activation was observed in mouse tumors and in biopsies of melanoma patients treated with immune checkpoint blockade. Transcriptomic and flow cytometry analyses revealed a distinct anti-tumorigenic neutrophil subset present in treated mice. Our findings uncover an interplay between T cells mediating the initial anti-tumor immune response and neutrophils mediating the destruction of tumor antigen loss variants.

The molecular and functional landscape of resistance to immune checkpoint blockade in melanoma

Resistance to immune checkpoint inhibitor therapies in melanoma is common and remains an intractable clinical challenge. In this study, we comprehensively profile immune checkpoint inhibitor resistance mechanisms in short-term tumor cell lines and matched tumor samples from melanoma patients progressing on immune checkpoint inhibitors. Combining genome, transcriptome, and high dimensional flow cytometric profiling with functional analysis, we identify three distinct programs of immunotherapy resistance. Here we show that resistance programs include (1) the loss of wild-type antigen expression, resulting from tumor-intrinsic IFNγ signaling and melanoma de-differentiation, (2) the disruption of antigen presentation via multiple independent mechanisms affecting MHC expression, and (3) immune cell exclusion associated with PTEN loss. The dominant role of compromised antigen production and presentation in melanoma resistance to immune checkpoint inhibition highlights the importance of treatment salvage strategies aimed at the restoration of MHC expression, stimulation of innate immunity, and re-expression of wild-type differentiation antigens.

The cancer epigenome: Non-cell autonomous player in tumor immunity

Dysregulation of the tumor-intrinsic epigenetic circuit is a key driver event for the development of cancer. Accumulating evidence suggests that epigenetic and/or genetic drivers stimulate intrinsic oncogenic pathways as well as extrinsic factors that modulate the immune system. These modulations indeed shape the tumor microenvironment (TME), allowing pro-oncogenic factors to become oncogenic, thereby contributing to cancer development and progression. Here we review the epigenetic dysregulation arising in cancer cells that disseminates throughout the TME and beyond. Recent CRISPR screening has elucidated key epigenetic drivers that play important roles in the proliferation of cancer cells (intrinsic) and inhibition of antitumor immunity (extrinsic), which lead to the development and progression of cancer. These epigenetic players can serve as promising targets for cancer therapy as a dual (two-in-one)-targeted approach. Considering the interplay between cancer and the immune system as a key determinant of immunotherapy, we discuss a novel lineage-tracing technology that enables longitudinal monitoring of cancer and immune phenotypic heterogeneity and fate paths during cancer development, progression, and therapeutic interventions.

S-adenosylmethionine blocks tumorigenesis and with immune checkpoint inhibitor enhances anti-cancer efficacy against BRAF mutant and wildtype melanomas

Despite marked success in treatment with immune checkpoint inhibitor (CPI), only a third of patients are responsive. Thus, melanoma still has one of the highest prevalence and mortality rates; which has led to a search for novel combination therapies that might complement CPI. Aberrant methylomes are one of the mechanisms of resistance to CPI therapy. S-adenosylmethionine (SAM), methyl donor of important epigenetic processes, has significant anti-cancer effects in several malignancies; however, SAM's effect has never been extensively investigated in melanoma. We demonstrate that SAM modulates phenotype switching of melanoma cells and directs the cells towards differentiation indicated by increased melanogenesis (melanin and melanosome synthesis), melanocyte-like morphology, elevated Mitf and Mitf activators' expression, increased antigen expression, reduced proliferation, and reduced stemness genes' expression. Consistently, providing SAM orally, reduced tumor growth and progression, and metastasis of syngeneic BRAF mutant and wild-type (WT) melanoma mouse models. Of note, SAM and anti-PD-1 antibody combination treatment had enhanced anti-cancer efficacy compared to monotherapies, showed significant reduction in tumor growth and progression, and increased survival. Furthermore, SAM and anti-PD-1 antibody combination triggered significantly higher immune cell infiltration, higher CD8+ T cells infiltration and effector functions, and polyfunctionality of CD8+ T cells in YUMMER1.7 tumors. Therefore, SAM combined with CPI provides a novel therapeutic strategy against BRAF mutant and WT melanomas and provides potential to be translated into clinic.

Escape from NK cell tumor surveillance by NGFR-induced lipid remodeling in melanoma

Metastatic disease is a major cause of death for patients with melanoma. Melanoma cells can become metastatic not only due to cell-intrinsic plasticity but also due to cancer-induced protumorigenic remodeling of the immune microenvironment. Here, we report that innate immune surveillance by natural killer (NK) cells is bypassed by human melanoma cells expressing the stem cell marker NGFR. Using in vitro and in vivo cytotoxic assays, we show that NGFR protects melanoma cells from NK cell-mediated killing and, furthermore, boosts metastasis formation in a mouse model with adoptively transferred human NK cells. Mechanistically, NGFR leads to down-regulation of NK cell activating ligands and simultaneous up-regulation of the fatty acid stearoyl-coenzyme A desaturase (SCD) in melanoma cells. Notably, pharmacological and small interfering RNA-mediated inhibition of SCD reverted NGFR-induced NK cell evasion in vitro and in vivo. Hence, NGFR orchestrates immune control antagonizing pathways to protect melanoma cells from NK cell clearance, which ultimately favors metastatic disease.

Phenotype Switching and the Melanoma Microenvironment; Impact on Immunotherapy and Drug Resistance

Melanoma, a highly heterogeneous tumor, is comprised of a functionally diverse spectrum of cell phenotypes and subpopulations, including stromal cells in the tumor microenvironment (TME). Melanoma has been shown to dynamically shift between different transcriptional states or phenotypes. This is referred to as phenotype switching in melanoma, and it involves switching between quiescent and proliferative cell cycle states, and dramatic shifts in invasiveness, as well as changes in signaling pathways in the melanoma cells, and immune cell composition in the TME. Melanoma cell plasticity is associated with altered gene expression in immune cells and cancer-associated fibroblasts, as well as changes in extracellular matrix, which drive the metastatic cascade and therapeutic resistance. Therefore, resistance to therapy in melanoma is not only dependent on genetic evolution, but it has also been suggested to be driven by gene expression changes and adaptive phenotypic cell plasticity. This review discusses recent findings in melanoma phenotype switching, immunotherapy resistance, and the balancing of the homeostatic TME between the different melanoma cell subpopulations. We also discuss future perspectives of the biology of neural crest-like state(s) in melanoma.

Early contribution of germline and nevi genetic alterations to a rapidly-progressing cutaneous melanoma patient: a case report

BACKGROUND

Cutaneous melanoma is the skin cancer with the highest mutational burden and metastatic rate. Early genetic alterations and biomarkers of distant progression are a point of interest. In addition to germline-susceptibility loci, almost 30% of melanomas arise from precursor benign nevi lesions, providing a source for malignant transformation.

CASE PRESENTATION

Patient#009 developed a cutaneous melanoma over a nevus, followed by progression to regional and distant metastases in months, unresponsive to targeted therapy. To search for the genetic contribution to this rapid progression, a longitudinal analysis was performed through WES of germline, nevi, primary tumor, and a metastatic lymph node. Differential SNP/INDEL and CNV gene alterations, with functional impact on key pathways and cancer hallmarks in each step of evolution, were discerned. Tumor-associated nevus was, for the first time, split into two sections, distant and adjacent to the primary tumor, to study its heterogeneity. Shared SNP alterations, with stable allele fraction from germline to metastasis were detected, mainly affecting DNA repair genes and promoting genome instability. Early somatic alterations, shared by nevi and primary and metastatic tumors, included BRAF^V600E and focal copy-loss of several genes, acquiring additional cancer hallmarks. Phylogenetic analyses revealed that these common somatic alterations would provide a "bridge", allowing progression from a benign to a malignant state. Distant and adjacent nevi were rich in alterations, presenting differential SNP and CNV alterations. Upon tumor transformation, a marked increase in CNV over SNP alterations was determined. Both the number of SNP and CNV-affected genes, including known driver genes, increased throughout progression, although TMB levels remained lower than expected for melanoma. Typical alterations in BRAF^V600E tumors related to intrinsic resistance to targeted therapy were found, including BRAF amplification and loss of PTEN, CDKN2A/B, and TP53 surveillance genes. Finally, numerous metastatic alterations were detected, further promoting tumor progression.

CONCLUSIONS

In this patient, longitudinal WES analysis revealed a sequential and cumulative pattern of genetic alterations, where germline and nevi somatic events contributed early to its rapid clinical progression. In this case report, we found tumor-associated nevi as genetically heterogeneous precursor entities, in which potential prognostic biomarkers should be studied prospectively.

Molecular underpinnings of exceptional response in primary malignant melanoma of the esophagus to anti-PD-1 monotherapy

BACKGROUND

Accumulating data suggest that mucosal melanoma, well known for its poor response to immune checkpoint blockade (ICB) and abysmal prognosis, is a heterogeneous subtype of melanoma with distinct genomic and clinical characteristics between different anatomic locations of the primary lesions. Primary malignant melanoma of the esophagus (PMME) is a rare, highly aggressive disease with a poorer prognosis compared with that of non-esophageal mucosal melanoma (NEMM). In this study, we retrospectively analyzed the efficacy of anti-programmed death (PD)-1 in patients with PMME and explored its molecular basis.

METHODS

The response and survival of patients with PMME and NEMM under anti-PD-1 monotherapy were retrospectively analyzed. To explore the molecular mechanisms of the difference in therapeutic efficacy between PMME and NEMM, we performed genomic analysis, bulk RNA sequencing, and multiplex immunohistochemistry staining.

RESULTS

We found that PMME (n=28) responded better to anti-PD-1 treatment than NEMM (n=64), with a significantly higher objective response rate (33.3% (95% CI 14.3% to 52.3%) vs 6.6% (95% CI 0.2% to 12.9%)) and disease control rate (74.1% (95% CI 56.4% to 91.7%) vs 37.7% (95% CI 25.2% to 50.2%)). Genomic sequencing analysis revealed that the genomic aberration landscape of PMME predominated in classical cancer driver genes, with approximately half of PMME cases harboring mutations in BRAF, N/KRAS, and NF1. In contrast, most NEMM cases were triple wild-type. Transcriptome analysis revealed that, compared with NEMM, PMME displayed more significant proliferation and inflammatory features with higher expression of genes related to antigen presentation and differentiation, and a less immunosuppressive signature with lower expression of inhibitory immune checkpoints and dedifferentiation-related genes. The multiplex immunohistochemical analysis also demonstrated higher CD8⁺ T-cell infiltration in PMME than in NEMM.

CONCLUSIONS

PMME is an outlier of mucosal melanoma showing a malicious phenotype but a particularly high response rate to ICB because of its distinct molecular characteristics. Patient stratification based on anatomic origin can facilitate clinical decision-making in patients with mucosal melanoma following the verification of our results in future prospective studies.

Emerging Challenges to Cellular Therapy of Cancer

ABSTRACT

Cellular immunotherapy of cancer in the form of chimeric antigen receptor-modified T-cell therapy has become a standard treatment for lymphoid and more recently plasma cell malignancies. Although their successes in these cancers represent a breakthrough for adoptive cell therapy, there are several challenges to their continued growth in the field of cancer medicine. In this review, we discuss the progress made thus far toward achieving "off-the-shelf" accessibility of cell therapies that has the potential to greatly offset the costs associated with the current practice of making patient-specific products. We also review the innovations under investigation that attempt to make cellular therapy applicable to solid tumors as well.

The epigenome and the many facets of cancer drug tolerance

The use of chemotherapeutic agents and the development of new cancer therapies over the past few decades has consequently led to the emergence of myriad therapeutic resistance mechanisms. Once thought to be explicitly driven by genetics, the coupling of reversible sensitivity and absence of pre-existing mutations in some tumors opened the way for discovery of drug-tolerant persisters (DTPs): slow-cycling subpopulations of tumor cells that exhibit reversible sensitivity to therapy. These cells confer multi-drug tolerance, to targeted and chemotherapies alike, until the residual disease can establish a stable, drug-resistant state. The DTP state can exploit a multitude of distinct, yet interlaced, mechanisms to survive otherwise lethal drug exposures. Here, we categorize these multi-faceted defense mechanisms into unique Hallmarks of Cancer Drug Tolerance. At the highest level, these are comprised of heterogeneity, signaling plasticity, differentiation, proliferation/metabolism, stress management, genomic integrity, crosstalk with the tumor microenvironment, immune escape, and epigenetic regulatory mechanisms. Of these, epigenetics was both one of the first proposed means of non-genetic resistance and one of the first discovered. As we describe in this review, epigenetic regulatory factors are involved in most facets of DTP biology, positioning this hallmark as an overarching mediator of drug tolerance and a potential avenue to novel therapies.

Targeting oncogenic transcription factors in skin malignancies: An update on cancer stemness and therapeutic outcomes

The skin is the largest organ of the human body and prone to various diseases, including cancer; thus, provides the first line of defense against exogenous biological and non-biological agents. Skin cancer, a complex and heterogenic process, with steep incidence rate often metastasizes due to poor understanding of the underlying mechanisms of pathogenesis and clinical challenges. Indeed, accumulating evidence indicates that deregulation of transcription factors (TFs) due to genetic, epigenetic and signaling distortions plays essential role in the development of cutaneous malignancies and therapeutic challenges including cancer stemness features and reprogramming. This review highlights the recent developments exploring underlying mechanisms how deregulated TFs (e.g., NF-κB, AP-1, STAT etc.,) orchestrates cutaneous onco-pathogenesis, reprogramming, stemness and poor clinical outcomes. Along this line, bioactive drugs, and their derivatives from natural and or synthetic origin has gained attention due to their multitargeting potential, potentially safer and effective therapeutic outcome for human malignancies. We also discussed therapeutic importance of targeting aberrantly expressed TFs in skin cancers with bioactive natural products and or synthetic agents.

PI3K/AKT signaling allows for MAPK/ERK pathway independency mediating dedifferentiation-driven treatment resistance in melanoma

BACKGROUND

Current therapeutic management of advanced melanoma patients largely depends on their BRAF mutation status. However, the vast heterogeneity of the tumors hampers the success of therapies targeting the MAPK/ERK pathway alone. Dissecting this heterogeneity will contribute to identifying key players in the oncogenic progression to tailor more effective therapies.

METHODS

We performed a comprehensive molecular and phenotypic characterization of a panel of patient-derived BRAF^V600E-positive melanoma cell lines. Transcriptional profiling was used to identify groups of coregulated genes whose expression relates to an increased migratory potential and a higher resistance.

RESULTS

A decrease in sensitivity to MAPK/ERK pathway inhibition with vemurafenib or trametinib corresponded with an increasing quiescence and migratory properties of the cells. This was accompanied by the loss of transcriptional signatures of melanocytic differentiation, and the gain of stem cell features that conferred highly-resistant/mesenchymal-like cells with increased xenobiotic efflux capacity. Nevertheless, targeting of the implicated ABC transporters did not improve the response to vemurafenib, indicating that incomplete BRAF inhibition due to reduced drug uptake is not a main driver of resistance. Rather, indifference to MAPK/ERK pathway inhibition arose from the activation of compensatory signaling cascades. The PI3K/AKT pathway in particular showed a higher activity in mesenchymal-like cells, conferring a lower dependency on MAPK/ERK signaling and supporting stem-like properties that could be reverted by dual PI3K/mTOR inhibition with dactolisib.

CONCLUSIONS

In case of MAPK/ERK independency, therapeutic focus may be shifted to the PI3K/AKT pathway to overcome late-stage resistance in melanoma tumors that have acquired a mesenchymal phenotype. Video Abstract.

Tumor-intrinsic SIRPA promotes sensitivity to checkpoint inhibition immunotherapy in melanoma

Checkpoint inhibition immunotherapy has revolutionized cancer treatment, but many patients show resistance. Here we perform integrative transcriptomic and proteomic analyses on emerging immuno-oncology targets across multiple clinical cohorts of melanoma under anti-PD-1 treatment, on both bulk and single-cell levels. We reveal a surprising role of tumor-intrinsic SIRPA in enhancing antitumor immunity, in contrast to its well-established role as a major inhibitory immune modulator in macrophages. The loss of SIRPA expression is a marker of melanoma dedifferentiation, a key phenotype linked to immunotherapy efficacy. Inhibition of SIRPA in melanoma cells abrogates tumor killing by activated CD8+ T cells in a co-culture system. Mice bearing SIRPA-deficient melanoma tumors show no response to anti-PD-L1 treatment, whereas melanoma-specific SIRPA overexpression significantly enhances immunotherapy response. Mechanistically, SIRPA is regulated by its pseudogene, SIRPAP1. Our results suggest a complicated role of SIRPA in the tumor ecosystem, highlighting cell-type-dependent antagonistic effects of the same target on immunotherapy.

Could SIRPA expression predict response to anti-PD-1 immunotherapy?

Immune checkpoint inhibitors (ICIs) offer significant promise for patients with melanoma; however, many patients succumb to de novo or acquired ICI resistance. In this issue of Cancer Cell, Zhou et al. propose a mechanism for signal-regulatory protein α1 (SIRPα) expression and describe how its loss may contribute to immunotherapy resistance.

Alcohol as a Non-UV Social-Environmental Risk Factor for Melanoma

Although cancer mortality has declined among the general population, the incidence of melanoma continues to rise. While identifying high-risk cohorts with genetic risk factors improves public health initiatives and clinical care management, recognizing modifiable risk factors such as social-environmental risk factors would also affect the methods of patient outreach and education. One major modifiable social-environmental risk factor associated with melanoma is ultraviolet (UV) radiation. However, not all forms of melanoma are correlated with sun exposure or occur in sun-exposed areas. Additionally, UV exposure is rarely associated with tumor progression. Another social-environmental factor, pregnancy, does not explain the sharply increased incidence of melanoma. Recent studies have demonstrated that alcohol consumption is positively linked with an increased risk of cancers, including melanoma. This perspective review paper summarizes epidemiological data correlating melanoma incidence with alcohol consumption, describes the biochemical mechanisms of ethanol metabolism, and discusses how ethanol and ethanol metabolites contribute to human cancer, including melanoma.

Identification of an endogenous retroviral signature to predict anti-PD1 response in advanced clear cell renal cell carcinoma: an integrated analysis of three clinical trials

Background

Endogenous retrovirus (ERV) elements are genomic footprints of ancestral retroviral infections within the human genome. Previous studies have demonstrated that dysregulated ERV transcription level is associated with immune cell infiltration in cancers, but the association between ERV expression and programmed cell death protein 1 (PD-1) blockade response is currently unraveled for solid cancers, such as advanced clear cell renal cell carcinoma (ccRCC).

Methods

ERV mRNA profiles were obtained from three clinical trials of ccRCC where the patients were treated with anti-PD-1 (CM-009, CM-010, CM-025, and TCGA-KIRC data). Patients treated with nivolumab were divided into training and test cohort, while the TCGA-KIRC cohort was used as an external validation. Univariate Cox regression analysis and least absolute shrinkage and selection operator regression were used to establish the signature. Immune cell infiltration analysis and gene set enrichment analysis were performed to explore potential biological mechanisms.

Results

An ERV signature was established based on nine ERV expression patterns. In the training cohort, the median overall survival in the low- and high-risk group was 45.2 and 19.6 months [hazard ratio (HR) = 0.49, 0.32-0.75, p < 0.001], respectively. The results were confirmed in the test (HR = 0.41, 0.20-0.83, p = 0.013), and in the TCGA-KIRC cohort (HR = 0.55, 0.34-0.90, p = 0.017). Moreover, in the CM-025 cohort, the low-risk group that received nivolumab had a more favorable survival compared with those that received the mTOR inhibitor everolimus, while no significant differences were observed in the high-risk group. CD8+ T cells were enriched in the low-risk group, while immune suppressive pathways were suppressed.

Conclusion

The newly identified ERV signature is not only a prognostic, but also a predictive biomarker for advanced ccRCC patients who received anti-PD-1 therapy, which can guide personalized treatment in cancer patients in the future.

Identification of Age-Associated Transcriptomic Changes Linked to Immunotherapy Response in Primary Melanoma

Melanoma is a lethal form of skin cancer. Immunotherapeutic agents such as anti-PD-1 (pembrolizumab and nivolumab) and anti-CTLA-4 (ipilimumab) have revolutionized melanoma treatment; however, drug resistance is rapidly acquired. Several studies have reported an increase in melanoma rates in older patients. Thus, the impact of ageing on transcriptional profiles of melanoma and response to immunotherapy is essential to understand. In this study, the bioinformatic analysis of RNA seq data of old and young melanoma patients receiving immunotherapy identifies the significant upregulation of extra-cellular matrix and cellular adhesion genes in young cohorts, while genes involved in cell proliferation, inflammation, non-canonical Wnt signaling and tyrosine kinase receptor ROR2 are significantly upregulated in the old cohort. Several Treg signature genes as well as transcription factors that are associated with dysfunctional T cell tumor infiltration are differentially expressed. The differential expression of several genes involved in oxidative phosphorylation, glycolysis and glutamine metabolism is also observed. Taken together, this study provides novel findings on the impact of ageing on transcriptional changes in melanoma, and novel therapeutic targets for future studies.

Beyond mismatch repair deficiency? Pre-treatment neutrophil-to-lymphocyte ratio is associated with improved overall survival in patients with recurrent endometrial cancer treated with immunotherapy

OBJECTIVE

To determine the association of pre-treatment neutrophil-to-lymphocyte ratio (NLR) with progression-free survival (PFS) and overall survival (OS) for patients with recurrent endometrial cancer (EC) treated with immunotherapy.

METHODS

Recurrent EC patients treated with immunotherapy alone or in combination from 2016 to 2021 were included. Demographics, pre-treatment laboratory results, pathologic data, response at first radiographic assessment, and cancer outcomes were obtained from the medical record. Kaplan-Meier curves were generated to compare PFS and OS stratified by NLR.

RESULTS

The 106 patients included in the study were stratified by NLR <6 (n = 77, 72.6%) or NLR ≥6 (n = 29, 27.3%). Most had endometrioid pathology (59%), widely metastatic disease, and 36.8% had received ≥2 treatment lines before initiating immunotherapy. Mismatch repair deficiency (dMMR) was noted in 52 (49.1%) tumors. Most dMMR patients (94.3%) were treated with single-agent pembrolizumab, and most MMR proficient patients (78.7%) were treated with lenvatinb plus pembrolizumab. In the overall cohort, 40.2% (partial response (PR) 29.9%, complete response (CR) 10.4%) of patients with a NLR <6 responded at first radiographic assessment, compared to 31% (PR 27.5%, CR 3.4%) of patients with NLR ≥6 (p 0.691). Kaplan-Meier curves stratified by NLR <6 vs. ≥6 showed no difference in PFS. However, NLR <6 was associated with improved OS (p < 0.05). In the NLR < 6 group, the probability of survival at one year was 69% (95% CI: 58%, 82%), compared to 41% (95% CI: 26%, 67%) for the NLR > 6 group.

CONCLUSIONS

Pre-treatment NLR <6 was associated with improved OS for recurrent EC patients treated with immunotherapy. NLR holds promise as a predictive biomarker for survival after immunotherapy treatment for patients with recurrent EC.

Innate immune receptor signaling induces transient melanoma dedifferentiation while preserving immunogenicity

Background

Immune-stimulatory agents, like agonists of the innate immune receptor RIG-I, are currently tested in clinical trials as an intratumoral treatment option for patients with unresectable melanoma, aiming to enhance anti-tumor T cell responses. Switching of melanoma toward a dedifferentiated cell state has recently been linked to T cell and therapy resistance. It remains to be determined whether RIG-I agonists affect melanoma differentiation, potentially leading to T cell resistance.

Methods

Patient metastases-derived melanoma cell lines were treated with the synthetic RIG-I agonist 3pRNA, and effects on tumor cell survival, phenotype and differentiation were determined. Transcriptomic data sets from cell lines and metastases were analyzed for associations between RIG-I (DDX58) and melanoma differentiation markers and used to define signaling pathways involved in RIG-I-driven dedifferentiation. The impact of 3pRNA-induced melanoma dedifferentiation on CD8 T cell activation was studied in autologous tumor T cell models.

Results

RIG-I activation by 3pRNA induced apoptosis in a subpopulation of melanoma cells, while the majority of tumor cells switched into a non-proliferative cell state. Those persisters displayed a dedifferentiated cell phenotype, marked by downregulation of the melanocytic lineage transcription factor MITF and its target genes, including melanoma differentiation antigens (MDA). Transition into the MITF^low/MDA^low cell state was JAK-dependent, with some cells acquiring nerve growth factor receptor expression. MITF^low/MDA^low persisters switched back to the proliferative differentiated cell state when RIG-I signaling declined. Consistent with our in vitro findings, an association between melanoma dedifferentiation and high RIG-I (DDX58) levels was detected in transcriptomic data from patient metastases. Notably, despite their dedifferentiated cell phenotype, 3pRNA-induced MITF^low/MDA^low persisters were still efficiently targeted by autologous CD8 tumor-infiltrating T lymphocytes (TILs).

Conclusions

Our results demonstrate that RIG-I signaling in melanoma cells drives a transient phenotypic switch toward a non-proliferative dedifferentiated persister cell state. Despite their dedifferentiation, those persisters are highly immunogenic and sensitive toward autologous TILs, challenging the concept of melanoma dedifferentiation as a general indicator of T cell resistance. In sum, our findings support the application of RIG-I agonists as a therapeutic tool for the generation of long-term clinical benefit in non-resectable melanoma.

Cancer evolution: special focus on the immune aspect of cancer

Cancer is an evolutionary disease. Intra-tumor heterogeneity (ITH), which describes the diversity within individual tumors, sets the foundation for evolution. The fitness of tumor cells is determined by their microenvironment, which exerts intense selection pressure that generally favors cells with survival and proliferation advantages. It has been revealed that host immunity dramatically influences the evolutionary trajectory of cancer. As technologies advance, a refined map of the immune system's involvement in cancer evolution has gradually come to our knowledge. Here we specifically view cancer through the lens of evolutionary immunological biology. We will cover the neoplastic evolution under immunosurveillance, including how the host immunity shapes the tumor evolutionary trajectory and how progressive tumors modulate the host immunity to survive. A comprehensive understanding of the interplay between cancer evolution and cancer immunity provides clues to combating cancer strategically.

BRAF Inhibitor Resistance Confers Increased Sensitivity to Mitotic Inhibitors

Single agent and combination therapy with BRAF^V600E/K and MEK inhibitors have remarkable efficacy against melanoma tumors with activating BRAF mutations, but in most cases BRAF inhibitor (BRAFi) resistance eventually develops. One resistance mechanism is reactivation of the ERK pathway. However, only about half of BRAFi resistance is due to ERK reactivation. The purpose of this study is to uncover pharmacological vulnerabilities of BRAFi-resistant melanoma cells, with the goal of identifying new therapeutic options for patients whose tumors have developed resistance to BRAFi/MEKi therapy. We screened a well-annotated compound library against a panel of isogenic pairs of parental and BRAFi-resistant melanoma cell lines to identify classes of compounds that selectively target BRAFi-resistant cells over their BRAFi-sensitive counterparts. Two distinct patterns of increased sensitivity to classes of pharmacological inhibitors emerged. In two cell line pairs, BRAFi resistance conferred increased sensitivity to compounds that share the property of cell cycle arrest at M-phase, including inhibitors of aurora kinase (AURK), polo-like kinase (PLK), tubulin, and kinesin. Live cell microscopy, used to track mitosis in real time, revealed that parental but not BRAFi-resistant melanoma cells were able to exit from compound-induced mitotic arrest through mitotic slippage, thus escaping death. Consistent with the key role of Cyclin B1 levels in regulating mitosis at the spindle checkpoint in arrested cells, we found lower Cyclin B1 levels in parental compared with BRAFi-resistant melanoma cells, suggesting that inability to down-regulate Cyclin B1 expression levels may explain the increased vulnerability of resistant cells to mitotic inhibitors. Another BRAFi-resistant cell line showed increased sensitivity to Chk1/2 inhibitors, which was associated with an accumulation of DNA damage, resulting in mitotic failure. This study demonstrates that BRAFi-resistance, in at least a subset of melanoma cells, confers vulnerability to pharmacological disruption of mitosis and suggests a targeted synthetic lethal approach for overcoming resistance to BRAF/MEK-directed therapies.

Tumor-infiltrating lymphocytes for adoptive cell therapy: recent advances, challenges, and future directions

INTRODUCTION

Adoptive cell therapy (ACT) with tumor-infiltrating lymphocytes (TILs) is a highly personalized type of cancer immunotherapy. TIL-based ACT exploits naturally occurring TILs, derived from the patients' tumor. This treatment has shown consistent clinical responses in melanoma, and recent results point toward a potential use in multiple cancer diagnoses. However, several limitations have restricted the clinical development and adaptation of TIL-based ACT.

AREAS COVERED

In this review, we present the principles of TIL-based ACT and discuss the most significant limitations for therapeutic efficacy and its widespread application. The topics of therapeutic resistance (both innate and acquired), treatment-related toxicity, and the novel research topic of metabolic barriers in the tumor microenvironment (TME) are covered.

EXPERT OPINION

There are many ongoing areas of research focusing on improving clinical efficacy and optimizing TIL-based ACT. Many strategies have shown great potential, particularly strategies advancing TIL efficacy (such as increasing and harnessing ex vivo the sub-population of tumor-reactive TILs) and manufacturing processes. Novel approaches can help overcome current limitations and potentially result in TIL-based ACT entering the mainstream of cancer therapy across tumor types.

Mechanisms of immune activation and regulation: lessons from melanoma

Melanoma, a skin cancer that develops from pigment cells, has been studied intensively, particularly in terms of the immune response to tumours, and has been used as a model for the development of immunotherapy. This is due, in part, to the high mutational burden observed in melanomas, which increases both their immunogenicity and the infiltration of immune cells into the tumours, compared with other types of cancers. The immune response to melanomas involves a complex set of components and interactions. As the tumour evolves, it accumulates an increasing number of genetic and epigenetic alterations, some of which contribute to the immunogenicity of the tumour cells and the infiltration of immune cells. However, tumour evolution also enables the development of resistance mechanisms, which, in turn, lead to tumour immune escape. Understanding the interactions between melanoma tumour cells and the immune system, and the evolving changes within the melanoma tumour cells, the immune system and the microenvironment, is essential for the development of new cancer therapies. However, current research suggests that other extrinsic factors, such as the microbiome, may play a role in the immune response to melanomas. Here, we review the mechanisms underlying the immune response in the tumour and discuss recent advances as well as strategies for treatment development.

Cancer Cell Phenotype Plasticity as a Driver of Immune Escape in Melanoma

Immunotherapies blocking negative immune checkpoints are now approved for the treatment of a growing number of cancers. However, even in metastatic melanoma, where sustained responses are observed, a significant number of patients still do not respond or display resistance. Increasing evidence indicates that non-genetic cancer cell-intrinsic alterations play a key role in resistance to therapies and immune evasion. Cancer cell plasticity, mainly associated with the epithelial-to-mesenchymal transition in carcinoma, relies on transcriptional, epigenetic or translational reprogramming. In melanoma, an EMT-like dedifferentiation process is characterized by the acquisition of invasive or neural crest stem cell-like features. Herein, we discuss recent findings on the specific roles of phenotypic reprogramming of melanoma cells in driving immune evasion and resistance to immunotherapies. The mechanisms by which dedifferentiated melanoma cells escape T cell lysis, mediate T cell exclusion or remodel the immune microenvironment will be detailed. The expanded knowledge on tumor cell plasticity in melanoma should contribute to the development of novel therapeutic combination strategies to further improve outcomes in this deadly metastatic cancer.

PRMT7 ablation stimulates anti-tumor immunity and sensitizes melanoma to immune checkpoint blockade

Despite the success of immune checkpoint inhibitor (ICI) therapy for cancer, resistance and relapse are frequent. Combination therapies are expected to enhance response rates and overcome this resistance. Herein, we report that combining PRMT7 inhibition with ICI therapy induces a strong anti-tumor T cell immunity and restrains tumor growth in vivo by increasing immune cell infiltration. PRMT7-deficient B16.F10 melanoma exhibits increased expression of genes in the interferon pathway, antigen presentation, and chemokine signaling. PRMT7 deficiency or inhibition with SGC3027 in B16.F10 melanoma results in reduced DNMT expression, loss of DNA methylation in the regulatory regions of endogenous retroviral elements (ERVs) causing their increased expression. PRMT7-deficient cells increase RIG-I and MDA5 expression with a reduction in the H4R3me2s repressive histone mark at their gene promoters. Our findings identify PRMT7 as a regulatory checkpoint for RIG-I, MDA5, and their ERV-double-stranded RNA (dsRNA) ligands, facilitating immune escape and anti-tumor T cell immunity to restrain tumor growth.

Immunomodulatory role of thrombin in cancer progression

Coagulation proteases and the generation of thrombin are increased in tumors. In addition, chemotherapeutic agents commonly used to treat malignant cancers can exacerbate cancer-associated thromboses. Thrombin can modify tumor cell behavior directly through the activation of protease-activated receptors (PAR) or indirectly by generating fibrin matrices. In addition to its role in generating fibrin to promote hemostasis, thrombin acts directly on multiple effector cells of the immune system impacting both acute and chronic inflammatory processes. Thrombin-mediated release of interleukin-6, tumor necrosis factor-α, and monocyte chemoattractant protein-1 leads to the accumulation of multiple tumor-infiltrating immunosuppressive cell populations including myeloid derived suppresser cells, M2-like macrophages, and T regulatory cells. Ablation of PAR-1 from the tumor microenvironment, but not the tumor, has been shown to dramatically reduce tumor growth and metastasis in multiple tumor models. Thrombin-activated platelets release immunosuppressive cytokines including transforming growth factor-β that can inhibit natural killer cell activity, helping tumor cells to evade host immunosurveillance. Taken together, there is strong evidence that thrombin influences cancer progression via multiple mechanisms, including the tumor immune response, with thrombin emerging as a target for novel therapeutic strategies for cancer.

LCOR mediates interferon-independent tumor immunogenicity and responsiveness to immune-checkpoint blockade in triple-negative breast cancer

Ligand-dependent corepressor (LCOR) mediates normal and malignant breast stem cell differentiation. Cancer stem cells (CSCs) generate phenotypic heterogeneity and drive therapy resistance, yet their role in immunotherapy is poorly understood. Here we show that immune-checkpoint blockade (ICB) therapy selects for LCORlow CSCs with reduced antigen processing/presentation machinery (APM) driving immune escape and ICB resistance in triple-negative breast cancer (TNBC). We unveil an unexpected function of LCOR as a master transcriptional activator of APM genes binding to IFN-stimulated response elements (ISREs) in an IFN signaling-independent manner. Through genetic modification of LCOR expression, we demonstrate its central role in modulation of tumor immunogenicity and ICB responsiveness. In TNBC, LCOR associates with ICB clinical response. Importantly, extracellular vesicle (EV) Lcor-messenger RNA therapy in combination with anti-PD-L1 overcame resistance and eradicated breast cancer metastasis in preclinical models. Collectively, these data support LCOR as a promising target for enhancement of ICB efficacy in TNBC, by boosting of tumor APM independently of IFN.

Combined tumor and immune signals from genomes or transcriptomes predict outcomes of checkpoint inhibition in melanoma

Immune checkpoint blockade (CPB) improves melanoma outcomes, but many patients still do not respond. Tumor mutational burden (TMB) and tumor-infiltrating T cells are associated with response, and integrative models improve survival prediction. However, integrating immune/tumor-intrinsic features using data from a single assay (DNA/RNA) remains underexplored. Here, we analyze whole-exome and bulk RNA sequencing of tumors from new and published cohorts of 189 and 178 patients with melanoma receiving CPB, respectively. Using DNA, we calculate T cell and B cell burdens (TCB/BCB) from rearranged TCR/Ig sequences and find that patients with TMBhigh and TCBhigh or BCBhigh have improved outcomes compared to other patients. By combining pairs of immune- and tumor-expressed genes, we identify three gene pairs associated with response and survival, which validate in independent cohorts. The top model includes lymphocyte-expressed MAP4K1 and tumor-expressed TBX3. Overall, RNA or DNA-based models combining immune and tumor measures improve predictions of melanoma CPB outcomes.