Colorectal cancer (CRC) is the second leading cause of cancer-related deaths globally and the third most frequently diagnosed cancer type, according to the Global Cancer Observatory. While the emergence of immune-checkpoint inhibitors (ICI) in the past decade has transformed cancer treatment paradigms, their efficacy in CRC is limited, particularly in the microsatellite-stable (MSS) subtype, which constitutes 85% of cases. MSS CRC is characterized by a low mutation burden and an immunosuppressive tumor microenvironment (TME), resulting in poor responsiveness to ICIs. Recent studies have identified elevated ALDH1 expression and its enzymatic products in MSS tumors, with retinoic acid (RA) produced by ALDH1 playing a pivotal role in fostering an immunosuppressive TME. This RA-mediated immunosuppression arises not only from tumor cells but also from tumor-associated immune cells, such as M2 macrophages and myeloid-derived suppressor cells (MDSCs), both of which exhibit high ALDH1 activity. Using syngeneic mouse models of MSS CRC, including MC38-CEA and CT26 cell lines, we evaluated the therapeutic potential of combining ABD0171, a selective ALDH1 inhibitor (ALDH1i), with anti-PD-1 therapy. Our findings reveal that ABD0171 significantly enhances the efficacy of anti-PD-1 therapy, leading to improved survival outcomes in MSS CRC models. This synergistic effect is associated with substantial alterations in the TME immune landscape, including an increase in pro-inflammatory M1 macrophages and reductions in both M2 macrophages and regulatory T cells (Tregs). Mechanistically, ALDH1 inhibition significantly reduces intratumoral RA levels, disrupting a key pathway responsible for the differentiation of immunosuppressive macrophages from monocytes. Ongoing studies are exploring the molecular mechanisms underlying these effects. Overall, our work underscores the potential of selective ALDH1 targeting as a strategy to overcome immunotherapy resistance in MSS CRC, offering new therapeutic opportunities for patients with this challenging cancer subtype. Akinchan Kumar, Andrada Constantinescu, Ismail Ceylan, Mileidys Perez-Alea, Bassam Janji. Selective and novel ALDH1 inhibitor enhances immune checkpoint blockade therapy in preclinical models of MSS colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 7306.

Immune checkpoint blockade (ICB) therapies, such as anti-PD-1, have transformed cancer treatment, but many patients do not respond due to a non-inflammatory tumor microenvironment (TME). Here, we investigated the impact of targeting Atypical Chemokine Receptor 2 (ACKR2), which scavenges key chemokines involved in immune cell recruitment, on the improvement of anti-PD-1-based therapy. In a melanoma mouse model, we demonstrated that Ackr2 inhibition increases the release of proinflammatory chemokines CCL5 and CXCL10 and enhances the infiltration of NK cells, activated CD8+ and CD4+ effector T cells while reducing regulatory T cells (Tregs) in the TME. Targeting Ackr2 led to tumor growth inhibition, improved survival, and enhanced response to anti-PD-1 therapy. In BRAF- and NRAS-mutant melanoma patients, low ACKR2 expression or high CCL5/CXCL10 levels correlated with improved survival and higher CD8+ T cell markers. Targeting ACKR2 represents a promising approach for developing combination therapies, particularly for ‘cold’ ICB resistant tumors.

Breast cancer exhibits significant heterogeneity, making the identification of molecular targets critical for the development of effective therapies. In this study, we investigate the expression patterns of the ALDH1A enzyme subfamily- ALDH1A1, ALDH1A2, and ALDH1A3- across diverse molecular subtypes and the tumor microenvironment, with a particular focus on triple-negative breast cancer (TNBC). Notably, ALDH1A3 is predominantly expressed in basal-like tumors and is significantly enriched in epithelial cells. In contrast, ALDH1A1 is uniquely expressed in myeloid cells and cancer-associated fibroblasts (CAFs). This dual expression pattern underscores the critical roles of ALDH1A3 and ALDH1A1 within the tumor microenvironment. We also evaluated the activity of novel ALDH1A inhibitors, specifically ABD0171, which demonstrated selective cytotoxicity in ALDH1A3-expressing basal-like cells and induced apoptosis through activation of the death receptor pathway. Both ABD0171 and its precursor, DIMATE, exhibited potent anti-metastatic effects, likely via inhibition of IL6/JAK/STAT3 signalling, and significantly inhibited tumor growth in preclinical TNBC models. These findings underscore the therapeutic potential of targeting ALDH1A isoforms, particularly ALDH1A3, in aggressive breast cancer subtypes and highlight the importance of considering tumor heterogeneity in the development of targeted therapies. ### Competing Interest Statement MP, GM and IC are shareholders in Advanced Biodesign

ABSTRACTAggressive breast cancer subtypes, particularly triple-negative breast cancer (TNBC), lack effective targeted therapies, requiring novel approaches. This study focuses on the aldehyde dehydrogenase 1A (ALDH1A) subfamily, comprising ALDH1A1, ALDH1A2, and ALDH1A3, and their roles in tumor biology and the tumor microenvironment. Comprehensive transcriptomic and single-cell analyses revealed subtype- and cell-specific expression patterns of ALDH1A isoforms, withALDH1A3predominantly expressed in epithelial cancer cells of basal-like tumors, whileALDH1A1andALDH1A2were expressed in stromal and immune-associated subpopulations. Guided by these findings, we developed ABD0171, a selective ALDH1A3 inhibitor that demonstrated potent isoform-specific activity. ABD0171 effectively disrupted key pathways in TNBC cellsin vitro, including IL6/JAK/STAT3, tPA and Src/FAK, and exhibited superior selectivity, robust antitumor and antimetastatic effects, and a favorable safety profilein vivo. These results establish ALDH1A3 as a promising therapeutic target and validate ABD0171 as a candidate to address current challenges in aggressive breast cancers.

Harmine is a dual-specificity tyrosine-regulated kinase 1A (DYRK1A) inhibitor that displays a number of biological and pharmacological properties. Also referred to as ACB1801 molecule, we have previously reported that harmine increases the presentation of major histocompatibility complex (MHC)-I-dependent antigen on melanoma cells. Here, we show that ACB1801 upregulates the mRNA expression of several proteins of the MHC-I such as Transporter Associated with antigen Processing TAP1 and 2, Tapasin and Lmp2 (hereafter referred to as MHC-I signature) in melanoma cells. Treatment of mice bearing melanoma B16-F10 with ACB1801 inhibits the growth and weight of tumors and induces a profound modification of the tumor immune landscape. Strikingly, combining ACB1801 with anti-PD1 significantly improves its therapeutic benefit in B16-F10 melanoma-bearing mice. These results suggest that, by increasing the MHC-I, ACB1801 can be combined with anti-PD1/PD-L1 therapy to improve the survival benefit in cancer patients displaying a defect in MHC-I expression. This is further supported by data showing that i) high expression levels of TAP1, Tapasin and Lmp2 was observed in melanoma patients that respond to anti-PD1; ii) the survival is significantly improved in melanoma patients who express high MHC-I signature relative to those expressing low MHC-I signature; and iii) high expression of MHC-I signature in melanoma patients was correlated with increased expression of CD8 and NK cell markers and overexpression of proinflammatory chemokines involved in the recruitment of CD8+ T cells.

Triple-negative subtype of breast cancer (TNBC) is hallmarked by frequent disease relapse and shows highest mortality rate. Although PD-1/PD-L1 immune checkpoint blockades have recently shown promising clinical benefits, the overall response rate remains largely insufficient. Hence, alternative therapeutic approaches are warranted. Given the immunosuppressive properties of CD73-mediated adenosine release, CD73 blocking approaches are emerging as attractive strategies in cancer immunotherapy. Understanding the precise mechanism regulating the expression of CD73 is required to develop effective anti-CD73-based therapy. Our previous observations demonstrate that the transcription factors driving epithelial-to-mesenchymal transition (EMT-TF) can regulate the expression of several inhibitory immune checkpoints. Here we analyzed the role of the EMT-TF SNAI1 in the regulation of CD73 in TNBC cells. We found that doxycycline-driven SNAI1 expression in the epithelial -like TNBC cell line MDA-MB-468 results in CD73 upregulation by direct binding to the CD73 proximal promoter. SNAI1-dependent upregulation of CD73 leads to increased production and release of extracellular adenosine by TNBC cells and contributes to the enhancement of TNBC immunosuppressive properties. Our data are validated in TNBC samples by showing a positive correlation between the mRNA expression of CD73 and SNAI1. Overall, our results reveal a new CD73 regulation mechanism in TNBC that participates in TNBC-mediated immunosuppression and paves the way for developing new treatment opportunities for CD73-positive TNBC.

Prostate cancer (PrCa) is the second most common malignancy in men. More than 50% of advanced prostate cancers display the TMPRSS2-ERG fusion. Despite extensive cancer genome/transcriptome data, little is known about the impact of mutations and altered transcription on regulatory networks in the PrCa of individual patients. Using patient-matched normal and tumor samples, we established somatic variations and differential transcriptome profiles of primary ERG-positive prostate cancers. Integration of protein-protein interaction and gene-regulatory network databases defined highly diverse patient-specific network alterations. Different components of a given regulatory pathway were altered by novel and known mutations and/or aberrant gene expression, including deregulated ERG targets, and were validated by using a novel in silico methodology. Consequently, different sets of pathways were altered in each individual PrCa. In a given PrCa, several deregulated pathways share common factors, predicting synergistic effects on cancer progression. Our integrated analysis provides a paradigm to identify druggable key deregulated factors within regulatory networks to guide personalized therapies.

Building molecular correlates of drug resistance in cancer and exploiting them for therapeutic intervention remains a pressing clinical need. To identify factors that impact drug resistance herein we built a model that couples inherent cell-based response toward drugs with transcriptomes of resistant/sensitive cells. To test this model, we focused on a group of genes called metastasis suppressor genes (MSGs) that influence aggressiveness and metastatic potential of cancers. Interestingly, modeling of 84 000 drug response transcriptome combinations predicted multiple MSGs to be associated with resistance of different cell types and drugs. As a case study, on inducing MSG levels in a drug resistant breast cancer line resistance to anticancer drugs caerulomycin, camptothecin and topotecan decreased by more than 50-60%, in both culture conditions and also in tumors generated in mice, in contrast to control un-induced cells. To our knowledge, this is the first demonstration of engineered reversal of drug resistance in cancer cells based on a model that exploits inherent cellular response profiles.

The mechanism of action of NME2, a widely accepted metastasis-suppressor gene, is poorly understood. Recently we found that NME2 directly regulates transcription of the c-MYC proto-oncogene. This prompted a genome-wide study to ascertain whether NME2 exerts its anti-metastatic action through transcriptional regulation. Chromatin-immunoprecipitation followed by massively parallel sequencing (ChIPseq) along with transcriptome profiling uncovered a network of genes involved in intercellular contact, focal adhesion and actin assembly under direct transcriptional control of NME2. In line with this, NME2-depleted cells displayed increased focal adhesion points and altered actin stress fiber organization. Our findings demonstrate that NME2 regulates transcription of a key focal adhesion factor vinculin and its localization within adhesion foci. NME2-depleted A549 lung cancer cells showed higher invasiveness in vitro and seeded more metastases in vivo. Consistent with these findings, expression of several NME2-transcriptional target genes related closely to advanced tumor stages with metastatic proclivity, and NME2 levels predicted patient survival.

Previous studies have analyzed patterns of transcription, transcription factor (TF) binding or mapped nucleosome occupancy across the genome. These suggest that the three aspects are genetically connected but the cause and effect relationships are still unknown. For example, physiologic TF binding studies involve many TFs, consequently, it is difficult to assign nucleosome reorganization to the binding site occupancy of any particular TF. Therefore, several aspects remain unclear: does TF binding influence nucleosome (re)organizations locally or impact the chromatin landscape at a more global level; are all or only a fraction of TF binding a result of reorganization in nucleosome occupancy and do all TF binding and associated changes in nucleosome occupancy result in altered gene expression? With these in mind, following characterization of two states (before and after induction of a single TF of choice) we determined: (i) genomic binding sites of the TF, (ii) promoter nucleosome occupancy and (iii) transcriptome profiles. Results demonstrated that promoter-proximal TF binding influenced expression of the target gene when it was coupled to nucleosome repositioning at or close to its binding site in most cases. In contrast, only in few cases change in target gene expression was found when TF binding occurred without local nucleosome reorganization.

Tumor metastasis refers to spread of a tumor from site of its origin to distant organs and causes majority of cancer deaths. Although >30 metastasis suppressor genes (MSGs) that negatively regulate metastasis have been identified so far, two issues are poorly understood: first, which MSGs oppose metastasis in a tumor type, and second, which molecular function of MSG controls metastasis. Herein, integrative analyses of tumor-transcriptomes (n = 382), survival data (n = 530) and lymph node metastases (n = 100) in lung cancer patients identified nonmetastatic 2 (NME2) as a key MSG from a pool of >30 metastasis suppressors. Subsequently, we generated a promoter-wide binding map for NME2 using chromatin immunoprecipitation with promoter microarrays (ChIP-chip), and transcriptome profiling. We discovered novel targets of NME2 which are involved in focal adhesion signaling. Importantly, we detected binding of NME2 in promoter of focal adhesion factor, vinculin. Reduced expression of NME2 led to enhanced transcription of vinculin. In comparison, NME1, a close homolog of NME2, did not bind to vinculin promoter nor regulate its expression. In line, enhanced metastasis of NME2-depleted lung cancer cells was found in zebrafish and nude mice tumor models. The metastatic potential of NME2-depleted cells was remarkably diminished upon selective RNA-i-mediated silencing of vinculin. Together, we demonstrate that reduced NME2 levels lead to transcriptional de-repression of vinculin and regulate lung cancer metastasis.

G-quadruplex motifs constitute unusual DNA secondary structures formed by stacking of planar hydrogen-bonded G-tetrads. Recent genome-wide bioinformatics and experimental analyses have suggested the interesting possibility that G-quadruplex motifs could be cis-regulatory elements. Here, we identified a characteristic potential G-quadruplex-forming sequence element within the promoter of human thymidine kinase 1 (TK1). Our NMR, UV and CD spectroscopy and gel electrophoresis data suggested that this sequence forms a novel intramolecular G-quadruplex with two G-tetrads in K+ solution. The results presented here indicate the role of this G-quadruplex motif in transcription of TK1 in cell-based reporter assays. Specific nucleotide substitutions designed to destabilize the G-quadruplex motif resulted in increased promoter activity, supporting direct involvement of the G-quadruplex motif in transcription of TK1. These studies suggest that the G-quadruplex motif may be an important target for controlling critical biological processes, such as DNA synthesis, mediated by TK1.

Guanine-rich DNA of a particular sequence adopts four-stranded structural forms known as G-quadruplex or G4 DNA. Though in vitro formation of G4 DNA is known for several years, in vivo presence of G4 DNA was only recently noted in eukaryote telomeres. Recent bioinformatics analyses showing prevalence of G4 DNA within promoters of human and related species seems to implicate G4 DNA in a genome-wide cis-regulatory role. Herein we demonstrate that G4 DNA may present regulatory sites on a genome-wide scale by showing widespread effect on gene expression in response to the established intracellular G4 DNA-binding ligands. This is particularly relevant to genes that harbor conserved potential G4 DNA (PG4 DNA) forming sequence across human, mouse and rat promoters of orthologous genes. Genes with conserved PG4 DNA in promoters show co-regulated expression in 79 human and 61 mouse normal tissues (z-score > 3.5; P < 0.0001). Conservation of G4 DNA across related species also emphasizes the biological importance of G4 DNA and its role in transcriptional regulation of genes; shedding light on a relatively novel mechanism of regulation of gene expression in eukaryotes.

Regulatory influence of the G-quadruplex or G4 motif present within the nuclease hypersensitive element (NHE) in the promoter of c-MYC has been noted. On the other hand, association of NM23-H2 to the NHE leads to c-MYC activation. Therefore, NM23-H2 interaction with the G4 motif within the c-MYC NHE presents an interesting mechanistic possibility. Herein, using luciferase reporter assay and chromatin immunoprecipitation we show NM23-H2 mediated c-MYC activation involves NM23-H2-G4 motif binding within the c-MYC NHE. G4 motif complex formation with recombinant NM23-H2 was independently confirmed using fluorescence energy transfer, which also indicated that the G4 motif was resolved to an unfolded state within the protein-bound complex. Taken together, this supports transcriptional role of NM23-H2 via a G4 motif.