Determinants of resistance and response to melanoma therapy.

Metastatic melanoma is among the most enigmatic advanced cancers to clinically manage despite immense progress in the way of available therapeutic options and historic decreases in the melanoma mortality rate. Most patients with metastatic melanoma treated with modern targeted therapies (for example, BRAFV600E/K inhibitors) and/or immune checkpoint blockade (for example, anti-programmed death 1 therapy) will progress, owing to profound tumor cell plasticity fueled by genetic and nongenetic mechanisms and dichotomous host microenvironmental influences. Here we discuss the determinants of tumor heterogeneity, mechanisms of therapy resistance and effective therapy regimens that hold curative promise.

Age-Related Increases in IGFBP2 Increase Melanoma Cell Invasion and Lipid Synthesis.

Unlabelled: Aged patients with melanoma (>65 years old) have more aggressive disease relative to young patients (<55 years old) for reasons that are not completely understood. Analysis of the young and aged secretome from human dermal fibroblasts identified >5-fold levels of IGF-binding protein 2 (IGFBP2) in the aged fibroblast secretome. IGFBP2 functionally triggers upregulation of the PI3K-dependent fatty acid biosynthesis program in melanoma cells.

Systematic analysis of the transcriptional landscape of melanoma reveals drug-target expression plasticity.

Metastatic melanoma originates from melanocytes of the skin. Melanoma metastasis results in poor treatment prognosis for patients and is associated with epigenetic and transcriptional changes that reflect the developmental program of melanocyte differentiation from neural crest stem cells. Several studies have explored melanoma transcriptional heterogeneity using microarray, bulk and single-cell RNA-sequencing technologies to derive data-driven models of the transcriptional-state change which occurs during melanoma progression.

Disrupting cellular memory to overcome drug resistance.

Gene expression states persist for varying lengths of time at the single-cell level, a phenomenon known as gene expression memory. When cells switch states, losing memory of their prior state, this transition can occur in the absence of genetic changes. However, we lack robust methods to find regulators of memory or track state switching.

Diverse clonal fates emerge upon drug treatment of homogeneous cancer cells.

Even among genetically identical cancer cells, resistance to therapy frequently emerges from a small subset of those cells. Molecular differences in rare individual cells in the initial population enable certain cells to become resistant to therapy; however, comparatively little is known about the variability in the resistance outcomes. Here we develop and apply FateMap, a framework that combines DNA barcoding with single-cell RNA sequencing, to reveal the fates of hundreds of thousands of clones exposed to anti-cancer therapies.

Age-related increases in IGFBP2 increase melanoma cell invasion and lipid synthesis.

Unlabelled: Aged melanoma patients (>65 years old) have more aggressive disease relative to young patients (<55 years old) for reasons that are not completely understood. Analysis of the young and aged secretome from human dermal fibroblasts identified >5-fold levels of insulin-like growth factor binding protein 2 (IGFBP2) in the aged fibroblast secretome. IGFBP2 functionally triggers upregulation of the PI3K-dependent fatty acid biosynthesis program in melanoma cells through increases in FASN.

Dasatinib Resensitizes MAPK Inhibitor Efficacy in Standard-of-Care Relapsed Melanomas.

Resistance to combination BRAF/MEK inhibitor (BRAFi/MEKi) therapy arises in nearly every patient with melanoma, despite promising initial responses. Achieving cures in this expanding BRAFi/MEKi-resistant cohort represents one of the greatest challenges to the field; few experience additional durable benefit from immunotherapy and no alternative therapies exist. To better personalize therapy in cancer patients to address therapy relapse, umbrella trials have been initiated whereby genomic sequencing of a panel of potentially actionable targets guide therapy selection for patients; however, the superior efficacy of such approaches remains to be seen.

ClampFISH 2.0 enables rapid, scalable amplified RNA detection in situ.

RNA labeling in situ has enormous potential to visualize transcripts and quantify their levels in single cells, but it remains challenging to produce high levels of signal while also enabling multiplexed detection of multiple RNA species simultaneously. Here, we describe clampFISH 2.0, a method that uses an inverted padlock design to efficiently detect many RNA species and exponentially amplify their signals at once, while also reducing the time and cost compared with the prior clampFISH method.

Stromal changes in the aged lung induce an emergence from melanoma dormancy.

Disseminated cancer cells from primary tumours can seed in distal tissues, but may take several years to form overt metastases, a phenomenon that is termed tumour dormancy. Despite its importance in metastasis and residual disease, few studies have been able to successfully characterize dormancy within melanoma. Here we show that the aged lung microenvironment facilitates a permissive niche for efficient outgrowth of dormant disseminated cancer cells-in contrast to the aged skin, in which age-related changes suppress melanoma growth but drive dissemination.

Reciprocal Regulation of BRN2 and NOTCH1/2 Signaling Synergistically Drives Melanoma Cell Migration and Invasion.

Phenotypic plasticity drives cancer progression, impacts treatment response, and is a major driver of therapeutic resistance. In melanoma, a regulatory axis between the MITF and BRN2 transcription factors has been reported to promote tumor heterogeneity by mediating switching between proliferative and invasive phenotypes, respectively. Despite strong evidence that subpopulations of cells that exhibit a BRN2/MITF expression profile switch to a predominantly invasive phenotype, the mechanisms by which this switch is propagated and promotes invasion remain poorly defined.

Genetic screening for single-cell variability modulators driving therapy resistance.

Cellular plasticity describes the ability of cells to transition from one set of phenotypes to another. In melanoma, transient fluctuations in the molecular state of tumor cells mark the formation of rare cells primed to survive BRAF inhibition and reprogram into a stably drug-resistant fate. However, the biological processes governing cellular priming remain unknown.

Myeloid-Derived Suppressor Cells Are a Major Source of Wnt5A in the Melanoma Microenvironment and Depend on Wnt5A for Full Suppressive Activity.

Metastatic dissemination remains a significant barrier to successful therapy for melanoma. Wnt5A is a potent driver of invasion in melanoma and is believed to be secreted from the tumor microenvironment (TME). Our data suggest that myeloid-derived suppressor cells (MDSC) in the TME are a major source of Wnt5A and are reliant upon Wnt5A for multiple actions.

sFRP2 Supersedes VEGF as an Age-related Driver of Angiogenesis in Melanoma, Affecting Response to Anti-VEGF Therapy in Older Patients.

Purpose: Angiogenesis is thought to be critical for tumor metastasis. However, inhibiting angiogenesis using antibodies such as bevacizumab (Avastin), has had little impact on melanoma patient survival. We have demonstrated that both angiogenesis and metastasis are increased in older individuals, and therefore sought to investigate whether there was an age-related difference in response to bevacizumab, and if so, what the underlying mechanism could be.

Changes in Aged Fibroblast Lipid Metabolism Induce Age-Dependent Melanoma Cell Resistance to Targeted Therapy via the Fatty Acid Transporter FATP2.

Older patients with melanoma (>50 years old) have poorer prognoses and response rates to targeted therapy compared with young patients (<50 years old), which can be driven, in part, by the aged microenvironment. Here, we show that aged dermal fibroblasts increase the secretion of neutral lipids, especially ceramides. When melanoma cells are exposed to the aged fibroblast lipid secretome, or cocultured with aged fibroblasts, they increase the uptake of lipids via the fatty acid transporter FATP2, which is upregulated in melanoma cells in the aged microenvironment and known to play roles in lipid synthesis and accumulation.

How the ageing microenvironment influences tumour progression.

Most cancers arise in individuals over the age of 60. As the world population is living longer and reaching older ages, cancer is becoming a substantial public health problem. It is estimated that, by 2050, more than 20% of the world's population will be over the age of 60 - the economic, healthcare and financial burdens this may place on society are far from trivial.

Paradoxical Role for Wild-Type p53 in Driving Therapy Resistance in Melanoma.

Metastatic melanoma is an aggressive disease, despite recent improvements in therapy. Eradicating all melanoma cells even in drug-sensitive tumors is unsuccessful in patients because a subset of cells can transition to a slow-cycling state, rendering them resistant to most targeted therapy. It is still unclear what pathways define these subpopulations and promote this resistant phenotype.

Normal Aging and Its Role in Cancer Metastasis.

Metastasis is the most common cause of death, with treatments failing to provide a durable response. Aging is a key prognostic factor in many cancers. Emerging data suggest that normal age-related changes in the tumor microenvironment can contribute to metastatic progression.

Remodeling of the Collagen Matrix in Aging Skin Promotes Melanoma Metastasis and Affects Immune Cell Motility.

Physical changes in skin are among the most visible signs of aging. We found that young dermal fibroblasts secrete high levels of extracellular matrix (ECM) constituents, including proteoglycans, glycoproteins, and cartilage-linking proteins. The most abundantly secreted was HAPLN1, a hyaluronic and proteoglycan link protein.

Age-Related Changes in HAPLN1 Increase Lymphatic Permeability and Affect Routes of Melanoma Metastasis.

Older patients with melanoma have lower rates of sentinel lymph node (LN) metastases yet paradoxically have inferior survival. Patient age correlated with an inability to retain Technetium radiotracer during sentinel LN biopsy in more than 1,000 patients, and high Technetium counts correlated to better survival. We hypothesized that loss of integrity in the lymphatic vasculature due to extracellular matrix (ECM) degradation might play a role.