Gavin P. Robertson

Melanoma, particularly in its advanced forms, remains one of the most lethal skin cancers, with limited effective treatments for both common cutaneous subtypes and rarer variants such as acral melanoma. The effects of the extracellular matrix (ECM) and other cancer-cell extrinsic processes on melanoma development remain underexplored. This study identifies growth differentiation factor-15 (GDF-15) as a mechanosensing-regulated driver of melanoma pathogenesis across melanoma types. GDF-15 is shown here to be mechanically induced by ECM rigidity and compressive forces occurring during metastatic progression, leading to significantly elevated levels in both cutaneous and acral melanoma cells. In this study, ECM rigidity was recapitulated using cell-adhesive gelatin methacryloyl (GelMA) hydrogel microparticles (microgels) with tunable stiffness, providing a biomimetic platform to investigate how mechanical cues in the tumor microenvironment regulate GDF-15 expression in melanoma. A previously unrecognized synergy between GDF-15 and inflammatory factors commonly present in tumors was identified and found to promote a disorganized, hyperpermeable vasculature, thereby facilitating tumor nutrient access and impeding effective immune cell infiltration. GDF-15 knockdown reduced the intratumoral hemorrhage phenotype, indicating a causal role. GDF-15 also functions by directly suppressing natural killer (NK) cell-mediated cytotoxicity, revealing a second cooperating mechanism of immune evasion. These effects position GDF-15 as a key node linking mechanical stress, co-operation with inflammatory factors, abnormal vascular development, and immune dysfunction, thereby converging on pathways and processes relevant to melanoma progression and treatment.

Drug-tolerant persister cells use conserved adaptive transcriptional programs

Melanoma, particularly in its advanced forms, remains one of the most lethal skin cancers, with limited effective treatments for both common cutaneous subtypes and rarer variants such as acral melanoma. The effects of the extracellular matrix (ECM) and other cancer-cell extrinsic processes on melanoma development remain underexplored. This study identifies Growth Differentiation Factor-15 (GDF-15) as a novel mechanosensing-regulated driver of melanoma pathogenesis across melanoma types. GDF-15 is shown here to be mechanically induced by ECM rigidity and compressive forces occurring during metastatic progression, leading to significantly elevated levels in both cutaneous and acral melanoma cells. In this study, ECM rigidity was recapitulated using cell-adhesive gelatin methacryloyl (GelMA) hydrogel microparticles (microgels) with tunable stiffness, providing a biomimetic platform to investigate how mechanical cues in the tumor microenvironment regulate GDF-15 expression in melanoma. A previously unrecognized synergy between GDF-15 and inflammatory factors commonly present in tumors was identified and found to promote a disorganized, hyperpermeable vasculature, thereby facilitating tumor nutrient access and impeding effective immune cell infiltration. GDF-15 knockdown reduced the intratumoral hemorrhage phenotype, indicating a causal role. GDF-15 also functions by directly suppressing natural killer (NK) cell-mediated cytotoxicity, revealing a second cooperating mechanism of immune evasion. These effects position GDF-15 as a key node linking mechanical stress, co-operation with inflammatory factors, abnormal vascular development, and immune dysfunction, thereby converging on a pathways and processes not previously described in melanomas. TEASER: Uncovering GDF-15 as a central mediator at the intersection of mechanical rigidity and external force, disorganized vascular hemorrhagic remodeling, co-operation with inflammatory factors, and immune evasion, revealing a previously unrecognized therapeutic vulnerability across both common and rare melanoma subtypes

The p53 pathway plays an important role in role in cancer immunity. Mutation or downregulation of the proteins in the p53 pathway are prevalent in many cancers, contributing to tumor progression and immune dysregulation. Recent findings suggest that the activity of p53 within tumor cells, immune cells, and the tumor microenvironment can play an important role in modulating NK cell–mediated immunity. Consequently, efforts to restore p53 pathway activity are being actively pursued to modulate this form of immunity. This review focuses on p53 activity regulating the infiltration and activation of NK cells in the tumor immune microenvironment. Furthermore, the impact of p53 and its regulation of NK cells on immunogenic cell death within solid tumors and the abscopal effect are reviewed. Finally, future avenues for therapeutically restoring p53 activity to improve NK cell–mediated antitumor immunity and optimize the effectiveness of cancer therapies are discussed.

The goal of this project was to demonstrate that subpopulations of cells in tumors can uniquely fluctuate in size in response to environmental conditions created during drug treatment, thereby acting as a dynamic "rheostat" to create a favorable tumor environment for growth. The cancer modeling used for these studies was subpopulations of melanoma cells existing in cultured and tumor systems that differed in aldehyde dehydrogenase (ALDH) activity. However, similar observations were found in other cancer types in addition to melanoma, making them applicable broadly across cancer. The approach was designed to show that either ALDH^high and ALDH^low subpopulations rapidly epigenetically transition between stem-cell-like high into nonstem-like low production states to create an environment during drug treatment that would enable optimal cellular proliferation and tumor expansion to facilitate drug resistance. The controlled experiments showed proportional changes in each cell population to reach an evolutionarily stable equilibrium mediated by the needed levels of ALDH enzyme activity. Mechanistically, cell population size changes served to functionally move the aldehyde and the resulting reactive oxygen species (ROS) levels to those compatible with optimal cellular proliferation with population fluctuations dependent on the levels of drug induced tumor stress. This is the first report documenting fluctuations in the sizes of cell populations in tumors to cooperatively assist in drug resistance development.

Aldehyde dehydrogenases (ALDHs) are a family of enzymes that aid in detoxification and are overexpressed in several different malignancies. There is a correlation between increased expression of ALDH and a poor prognosis, stemness, and resistance to several drugs. Several ALDH inhibitors have been generated due to the crucial role that ALDH plays in cancer stem cells. All of these inhibitors, however, are either ineffective, very toxic, or have yet to be subjected to rigorous testing on their effectiveness. Although various drug-like compounds targeting ALDH have been reported in the literature, none have made it to routine use in the oncology clinic. As a result, new potent, non-toxic, bioavailable, and therapeutically effective ALDH inhibitors are still needed. In this study, we designed and synthesized potent multi-ALDH isoform inhibitors based on the isatin and indazole pharmacophore. Molecular docking studies and enzymatic tests revealed that among all of the synthesized analogs, compound 3 is the most potent inhibitor of ALDH1A1, ALDH3A1, and ALDH1A3, exhibiting 51.32%, 51.87%, and 36.65% inhibition, respectively. The ALDEFLUOR assay further revealed that compound 3 acts as an ALDH broad spectrum inhibitor at 500 nM. Compound 3 was also the most cytotoxic to cancer cells, with an IC₅₀ in the range of 2.1 to 3.8 µM for ovarian, colon, and pancreatic cancer cells, compared to normal and embryonic kidney cells (IC₅₀ 7.1 to 8.7 µM). Mechanistically, compound 3 increased ROS activity due to potent multi-ALDH isoform inhibition, which increased apoptosis. Taken together, this study identified a potent multi-isoform ALDH inhibitor that could be further developed as a cancer therapeutic.

Telomerase activation is a crucial step in melanomagenesis, often occurring because of ultraviolet radiation (UVR)‐induced mutations at the telomerase gene (TERT) promoter and rendering TERT transcription in response to the activated Raf‐MAP kinase pathway by BRAF^V600E mutation. Due to the excessively long telomeres in mice, this process does not occur during melanomagenesis in mouse models. To investigate the impact of telomere dysfunction on melanomagenesis, Braf^V600E was induced in generations 1 and 4 (G1 and G4) of Tert^−/− mice. Our findings revealed that, regardless of UVR exposure, melanoma development was delayed in G4 mice, which had shorter telomeres compared to G1 and wild‐type C57BL/6J (G0) mice. Moreover, many G4 tumors displayed an accumulation of excessive DNA damage, as evidenced by increased γH2A.X staining. Tumors from UVR‐exposed mice exhibited elevated p53 protein expression. Cultured tumor cells isolated from G4 mice displayed abundant chromosomal fusions and rearrangements, indicative of telomere dysfunction in these cells. Additionally, tumor cells derived from UVB‐exposed mice exhibited constitutively elevated expression of mutant p53 proteins, suggesting that p53 was a target of UVB‐induced mutagenesis. Taken together, our findings suggest that telomere dysfunction hampers melanomagenesis, and targeting telomere crisis‐mediated genomic instability may hold promise for the prevention and treatment of melanoma.