Myelodysplastic syndromes (MDS) are hematological disorders associated with bone marrow failure and abnormal hematopoietic cell growth, often progressing to acute myeloid leukemia (AML). Current treatments for AML and high-risk MDS are limited in efficacy, highlighting the need for new therapies. Recent studies show ferroptosis induction, alone or with standard chemotherapy, as a promising strategy for treating MDS/AML cells. Here, we report two novel compounds, HA344 and #231, that target both ferroptosis and apoptosis pathways to effectively eradicate MDS/AML cell lines and patient-derived bone-marrow blasts. RNASeq analysis reveals oxidative stress and apoptosis as key pathways activated by these compounds in different AML cell lines. In cellulo click-chemistry experiments coupled to mass spectrometry analysis identified glutathione peroxidase 4 (GPX4) and thioredoxin reductase 1 (TXNRD1) as primary targets of both compounds, inhibiting GPX4 and TXNRD1 in the micromolar range. Mass spectrometry analysis confirms that HA344 and #231 covalently bind GPX4; with however a higher affinity for selenium-containing GPX4 (GPX4-Se) than for sulfur-containing GPX4 (GPX4-S). These findings design HA344 and #231 as potential therapeutic options for MDS/AML treatment.

Abstract The unfolded protein response (UPR) is a stress-adaptation pathway and therapeutic target in cancer, yet its pro-survival versus pro-death outcome is difficult to predict because the three ER sensors, PERK, IRE1α, and ATF6, are highly interconnected. Transcriptomic analyses identified sensor-specific gene signatures associated with patient survival across malignancies, and indicated that low IRE1α activity (low XBP1 signature or higher expression of RIDD targets) correlates with improved outcome. We developed SNUPR (single nuclei analysis of the unfolded protein response), an accessible flow cytometry approach that profiles all three branches in nuclear suspensions. SNUPR reveals marked heterogeneity of UPR activation across cancer cell lines that cannot be inferred from sensor expression. This heterogeneity is derived from differences in the strength and duration of PERK-mediated translational inhibition, which gates downstream translation-dependent IRE1α and ATF6 transcriptional programs. Finally, in multiple myeloma, we show that bortezomib-tolerant cells depend on IRE1α activity for survival, linking UPR state to proteasome-inhibitor resistance and positioning SNUPR to guide branch-selective targeting.

Diffuse large B-cell lymphoma (DLBCL) refers to an aggressive lymphoma that arises from germinal center (GC) B cells, which differentiate into plasma cells to produce high-affinity antibodies. A total of 40% of patients with DLBCL relapse or are refractory to the conventional immunochemotherapy treatment, usually with fatal consequences. DLBCL is characterized by profound alterations in the epigenome, which is correlated with poor survival. The abnormal epigenetic landscape of DLBCL tumors is associated with a blockade in GC exit and differentiation programs, which are regulated by the transcription factor BCL6. This aberrant repression of BCL6 target genes is mediated by (1) increased DNA methylation and (2) the loss of acetylation of lysine 27 of histone 3 through the recruitment of histone deacetylase 3 (HDAC3). Therefore, we investigated the efficacy of the hypomethylating agent 5-azacitidine (5-aza) and a specific HDAC3 inhibitor (HDAC3i) against DLBCL. We found that the treatment of activated B cell-like and GC B cell-like DLBCL cells with 5-aza plus HDAC3i had a potent synergistic antitumor activity in vitro and in vivo, which was superior to the effect of each single drug or 5-aza combined with nonspecific HDACi and, importantly, was not associated with toxicity in normal T cells. We also demonstrated that, compared with that with each drug used as single agents, the combined 5-aza and HDAC3i treatment induced the epigenetic remodeling of DLBCL cells, which resulted in a more potent reexpression of differentiation genes, including XBP1 and ATF4. Our results highlight the importance of specifically targeting multiple layers of the epigenome to maximize the efficacy of epigenetic-based therapies.

Pancreatic ductal adenocarcinoma (PDA) transcriptomic profiling has identified prognostic subtypes, yet patient-specific first-line therapies remain elusive. Here, we stratified PDA tumors by mRNA translation rates, a frequently dysregulated step in gene expression, using translatome profiling of 27 patient-derived xenografts (PDXs). Unsupervised analysis revealed a distinct tumor subset with low global protein synthesis but sustained translation of Integrated Stress Response (ISR) mRNAs, including ATF4. These ISR-activated cancer cells exhibited broad chemoresistance and apoptosis resistance, yet were auxotrophic for serine due to loss of PHGDH and CBS expression, impairing serine and cysteine biosynthesis. This vulnerability correlated with improved overall survival in patients with low expression of both enzymes. Notably, cancer-associated fibroblasts (CAFs) reprogrammed by ISR-activated cells, shifting from myCAF to iCAF phenotype with reduced collagen synthesis and glycine-to-serine conversion, produced serine and sustained tumor growth in amino acid-depleted environments. Our findings demonstrate the power of translatome profiling to reveal stable, drug-resistant PDA cell states and identify a targetable CAF-tumor metabolic symbiosis, opening new avenues for therapeutic intervention in this highly lethal malignancy.

Abstract Immune checkpoint inhibitors (ICI) have revolutionized cancer treatment, but their efficacy has now reached a plateau. ICIs are the first class of treatment targeting the crosstalk between immune and tumor cells, making it crucial to understand the complex interactions within the tumor microenvironment (TME) to enhance therapeutic responses. The elevated consumption of resources by cancer cells, coupled with limited vascularization, often results in a TME that is deficient in nutrients, leading to competition for resources between cancer and stromal cells. Consequently, targeting tumor metabolism has emerged as a promising strategy to improve the efficacy of ICIs. Through metabolomic analysis, we have identified metabolic alterations in melanoma cells that are resistant to ICIs, specifically an increase in arginine synthesis and upregulation of ASS1, the rate-limiting enzyme in this pathway. By using gain and loss of function models, as well as a pharmacological inhibitor specific for ASS1, we demonstrated that modulations in the expression or activity of ASS1 is associated with translational reprogramming, characterized by an inhibition of the cap-dependent mRNA translation mediated through mTORC1/4EBP1 axis. We also demonstrated that targeting ASS1 in vivo , resensitize tumors initially resistant to ICI. Taken together, our results highlight the interaction between modulations of arginine synthesis pathway, mRNA translation reprogramming, antitumor immunity, and restauration of sensitivity to anti-PD-1. Our work also demonstrates the therapeutic potential of targeting arginine synthesis pathway, and especially ASS1, to offer new treatments to patients suffering from cutaneous melanoma resistant to ICIs.

Melanoma is the most aggressive form of skin cancer, and despite major advances in targeted and immune therapies, durable responses remain limited due to the emergence of resistance mechanisms. Metabolic reprogramming has emerged as a key driver of therapy resistance, allowing tumor cells to adapt to environmental and therapeutic pressures. Here, we identify the maternal embryonic leucine zipper kinase (MELK) as a critical mediator of resistance in melanoma. We demonstrate that MELK stimulates intracellular accumulation of amino acids, leading to activation of mTORC1 signaling and enhanced mitochondrial metabolism and biogenesis. This metabolic shift promotes resistance to immune checkpoint blockade. Importantly, preclinical MELK inhibition sensitizes resistant melanoma cells to immunotherapy, revealing a potential combinatorial strategy to overcome resistance. Our findings establish MELK as a central regulator of metabolic adaptation and therapeutic resistance in melanoma, highlighting its potential as a promising therapeutic target. ### Competing Interest Statement T.P. received consulting honoraria from Almirall, AbbVie, BMS, Incyte, Janssen, Lilly, Novartis, Pfizer, UCB and Vyne Therapeutics; has received grants or honoraria from Almirall, AbbVie, Amgen, BMS, Celgene, Galderma, GSK, Incyte, Janssen, LEO Pharma, Lilly, MSD, Novartis, Pfizer, Sanofi, SUN Pharma, Takeda and UCB; C.R. received consulting fees from BMS, Roche, Pierre Fabre, Novartis, Sanofi, Pfizer, MSD, Merck, Sunpharma, Ultimovacs, Regeneron, Egle, Philogen, MAAT Pharma, IO Biotech; payment honoraria from Pierre Fabre, Sanofi, BMS, MSD, Novartis; supporting for attending meetings from Pierre Fabre, participation on advisory board from BMS, Roche, Pierre Fabre, Novartis, Sanofi, Pfizer, MSD, Merck, Sunpharma, Ultimovacs, Regeneron, EGLE, Philogen, MAAT Pharma. All the other authors declare no conflict of interest. Inserm, https://ror.org/02vjkv261 Université Côte d'Azur, https://ror.org/019tgvf94, Bourses d’Excellence Jeunes Chercheurs 2024 Fondation pour la Recherche Medicale, EQU202003010248 INCA PLBIO, 2020-114 Cancéropôle PACA, https://ror.org/01mwvah42 Agence Nationale de la Recherche, https://ror.org/00rbzpz17, ANR-23-CE14-0023 (TRANSMET)

Melanoma, particularly in its metastatic form, remains highly lethal. Despite advancements in treatment, nearly half of melanoma patients experience therapeutic failure due to resistance. Consequently, the development of new antimelanoma drugs is critical for those unresponsive to current therapies. Here, we report the discovery of a potent antimelanoma scaffold and a promising inhibitor of glycogen synthase kinase 3 beta (GSK3β) through a drug-to-target approach. A phenotypic screening of arylbiamidine derivatives identified lead compound 35, N-(N-(benzo[d]thiazol-2-yl)carbamimidoyl)pyrazine-2-carboximidamide, which exhibited the highest in vitro potency against melanoma cell lines and nanomolar inhibition of oncogenic GSK3β (IC50 = 73.8 nM). Moreover, compound 35 demonstrated a favourable pharmacological profile, significantly reducing tumour growth in vivo in an A375 xenograft mouse model.

We demonstrate that exposure to the AB5 subtilase cytotoxin (SubAB) induces the unfolded protein response (UPR) in human peripheral blood mononuclear cells, concomitant with a proinflammatory response across distinct cell subsets. Notably, SubAB selectively induces type-I interferon (IFN) expression in plasmacytoid dendritic cells, acting synergistically with Toll-like receptor 7 stimulation. The induction of type-I IFN in response to SubAB relies on stimulator of interferon genes (STING) activation, coupled with protein synthesis inhibition mediated by protein kinase R-like endoplasmic reticulum kinase (PERK) and phosphorylation of the eukaryotic translation initiation factor 2 subunit-alpha. By impeding mRNA translation through the integrated stress response, SubAB precipitates the downregulation of the negative innate signaling feedback regulator Tax1-binding protein 1. This downregulation is necessary to unleash TANK-binding kinase 1 signaling associated with STING activation. These findings shed light on how UPR-inducing conditions may regulate the immune system during infection or pathogenesis.

We demonstrate that exposure to the AB5 subtilase cytotoxin (SubAB) induces the unfolded protein response (UPR) in human peripheral blood mononuclear cells, concomitant with a pro-inflammatory response across distinct cell subsets. Notably, SubAB selectively induces type-I interferon (IFN) expression in plasmacytoid dendritic cells, acting synergistically with Toll-like receptor 7 stimulation. The induction of type-I IFN in response to SubAB relies on stimulator of interferon genes (STING) activation, coupled with protein synthesis inhibition mediated by protein kinase R-like endoplasmic reticulum kinase and phosphorylation of the eukaryotic translation initiation factor 2 subunit-alpha. By impeding mRNA translation through the integrated stress response, SubAB precipitates the downregulation of the negative innate signaling feedback regulator Tax1-binding protein 1. This downregulation is necessary to unleash TANK-binding kinase 1 signaling associated with STING activation. These findings shed new light on how UPR-inducing conditions may regulate the immune system during infection or pathogenesis.

Tumors often face energy deprivation due to mutations, hypoxia, and nutritional deficiencies within the harsh tumor microenvironment (TME), and as an effect of anticancer treatments. This metabolic stress triggers adaptive reprogramming of mRNA translation, which in turn adjusts metabolic plasticity and associated signaling pathways to ensure tumor cell survival. Emerging evidence is beginning to reveal the complex interplay between metabolism and mRNA translation, shedding light on the mechanisms that synchronize ribosome assembly and reconfigure translation programs under metabolic stress. This review explores recent advances in our understanding of the coordination between metabolism and mRNA translation, offering insights that could inform therapeutic strategies targeting both cancer metabolism and translation, with the aim of disrupting cancer cell plasticity and survival.

CLEC12B is a C-type lectin receptor involved in the inhibition of natural killers-mediated cytotoxicity. We have previously shown that CLEC12B is predominantly expressed on melanocytes, inhibits melanin production and pigmentation as well as proliferation of melanoma. To date, the role of CLEC12B in skin immunity is unknown. Upon phosphorylation of its immunoreceptor tyrosine-based inhibitory motif, we demonstrate that CLEC12B increases the production of innate chemokines from human melanocytes through the activation of the signal transducer and activator of transcription 1 (STAT-1)/interferon regulatory factor 1 (IRF-1)-mediated IFNγ pathway, resulting in chemoattraction of immune cells. We have demonstrated CLEC12B to potentiate the effect of IFNγ in primed melanocytes. Furthermore, CLEC12B recognizes cutaneous (Staphylococcus aureus and Escherichia coli) but not gut (Listeria monocytogenes) bacteria and is capable of modulating their chemokine responses. Finally, we have shown that CLEC12B senses motifs present on human melanocytes and fibroblasts but not keratinocytes. Together, these results demonstrate that CLEC12B plays an important function in the human skin, bridging innate and adaptative immunity. This mechanism is of great interest as IFNγ and cellular recruitment are key initial steps involved in inflammation of many skin pathologies, making this receptor an interesting therapeutic target.

The unfolded protein response (UPR) is a key stress resistance pathway that has become a key potential target for improving the efficacy of cancer chemotherapy. The UPR involves the activation of three ER-resident stress sensors: PERK, IRE-1 and ATF6 with different signalling outcomes leading to cell death or survival. These cell-fate decisions are difficult to predict and are the result of the complex interaction of PERK, IRE-1 and ATF6 downstream events that have differences in their dynamics and their interplay. These characteristics of the UPR are still poorly defined due to lack of methods to monitor their activation simultaneously at single-cell level. We developed SNUPR (Single Nuclei analysis of the Unfolded Protein Response), an accessible technique that allows the profiling of the three UPR branches in nuclear suspensions by flow cytometry, and applied it to study UPR dynamics in a cancer-specific context. By performing transcriptomic analysis, we found that ER-stress sensor specific gene signatures correlate with patient survival in several blood malignancies, and by using SNUPR, we detected high heterogeneity during UPR activation in vitro in different human cancer cell lines, which could not be have been predicted by the level of expression of the sensors. Our SNUPR analyses further indicate that this heterogeneity is explained by variations in the intensity and duration of ER stress-induced protein synthesis inhibition via PERK, acting as upstream regulator of both the IRE-1/XBP1 and ATF6 dependent transcriptional programs. We extend the relevance of these observations by demonstrating that IRE-1/XBP1s pathway plays a critical role in bortezomib resistance of multiple myeloma cells and patients. We present here SNUPR, that can be used to monitor UPR dynamics with single-cell resolution and identified clinical contexts in which targeting a specific UPR branch could be detrimental or help circumventing chemotherapy resistance. ### Competing Interest Statement The authors have declared no competing interest.

PDF - 155K, (A) Mel501 melanoma cells stably transfected with a shRNA against p53 were treated 24h with metformin (at the indicated concentrations) or PBS, lysed and analysed by Western-blot with N-Cadherin, p53, Sparc and Slug antibodies. HSP90 was used for loading control. (B)Invasion assay in coated Boyden chambers with Mel501 melanoma cells stably transfected with a shRNA against p53, treated 24h with metformin (at the indicated concentrations) or PBS.

PDF - 430K, (A) Upper panel, invasion assay in coated Boyden chambers with HMVII melanoma cells (mutated for p53) treated 24h after with metformin (at the indicated concentrations) or PBS for 24h.

PGC-a regulates c-MYC and ODC1 expression