Clinical, molecular, metabolic, and immune features associated with oxidative phosphorylation in melanoma brain metastases

Targeting Translation and the Cell Cycle Inversely Affects CTC Metabolism but Not Metastasis

Melanoma brain metastasis (MBM) is significantly associated with poor prognosis and is diagnosed in 80% of patients at autopsy. Circulating tumor cells (CTCs) are "seeds" of metastasis and the smallest functional units of cancer. Our multilevel approach has previously identified a CTC RPL/RPS gene signature directly linked to MBM onset. We hypothesized that targeting ribogenesis prevents MBM/metastasis in CTC-derived xenografts. We treated parallel cohorts of MBM mice with FDA-approved protein translation inhibitor omacetaxine with or without CDK4/CDK6 inhibitor palbociclib, and monitored metastatic development and cell proliferation. Necropsies and IVIS imaging showed decreased MBM/extracranial metastasis in drug-treated mice, and RNA-Seq on mouse-blood-derived CTCs revealed downregulation of four RPL/RPS genes. However, mitochondrial stress tests and RT-qPCR showed that omacetaxine and palbociclib inversely affected glycolytic metabolism, demonstrating that dual targeting of cell translation/proliferation is critical to suppress plasticity in metastasis-competent CTCs. Equally relevant, we provide the first-ever functional metabolic characterization of patient-derived circulating neoplastic cells/CTCs.

Lipid droplets are a metabolic vulnerability in melanoma

Melanoma exhibits numerous transcriptional cell states including neural crest-like cells as well as pigmented melanocytic cells. How these different cell states relate to distinct tumorigenic phenotypes remains unclear. Here, we use a zebrafish melanoma model to identify a transcriptional program linking the melanocytic cell state to a dependence on lipid droplets, the specialized organelle responsible for lipid storage. Single-cell RNA-sequencing of these tumors show a concordance between genes regulating pigmentation and those involved in lipid and oxidative metabolism. This state is conserved across human melanoma cell lines and patient tumors. This melanocytic state demonstrates increased fatty acid uptake, an increased number of lipid droplets, and dependence upon fatty acid oxidative metabolism. Genetic and pharmacologic suppression of lipid droplet production is sufficient to disrupt cell cycle progression and slow melanoma growth in vivo. Because the melanocytic cell state is linked to poor outcomes in patients, these data indicate a metabolic vulnerability in melanoma that depends on the lipid droplet organelle.

Melanoma central nervous system metastases: An update to approaches, challenges, and opportunities

Brain metastases are the most common brain malignancy. This review discusses the studies presented at the third annual meeting of the Melanoma Research Foundation in the context of other recent reports on the biology and treatment of melanoma brain metastases (MBM). Although symptomatic MBM patients were historically excluded from immunotherapy trials, efforts from clinicians and patient advocates have resulted in more inclusive and even dedicated clinical trials for MBM patients. The results of checkpoint inhibitor trials were discussed in conversation with current standards of care for MBM patients, including steroids, radiotherapy, and targeted therapy. Advances in the basic scientific understanding of MBM, including the role of astrocytes and metabolic adaptations to the brain microenvironment, are exposing new vulnerabilities which could be exploited for therapeutic purposes. Technical advances including single-cell omics and multiplex imaging are expanding our understanding of the MBM ecosystem and its response to therapy. This unprecedented level of spatial and temporal resolution is expected to dramatically advance the field in the coming years and render novel treatment approaches that might improve MBM patient outcomes.

Emerging Studies of Melanoma Brain Metastasis

PURPOSE OF REVIEW

Among solid tumors, melanoma has the highest propensity for brain dissemination. Although newer treatment approaches have resulted in excellent control or elimination of brain metastasis in many patients, they remain the cause of significant morbidity and mortality. Here, we review recent preclinical and clinical studies to detail current understanding of the incidence, prognosis, biological characteristics, and treatments for melanoma brain metastases.

RECENT FINDINGS

Clinical trials tailored to this patient population have demonstrated prolonged disease control with immune checkpoint inhibitors. Emerging clinical challenges include radiation necrosis and perilesional edema, phenomena that are rarely seen in other organs. Recent preclinical studies have resulted in improved understanding of the tumor microenvironment in the brain, providing insights into additional treatment approaches. The biological basis of brain tumor homing and survival within the central nervous system remain understudied. Additional preclinical and clinical studies will enhance our ability to prevent and treat brain metastases.

The microenvironment of brain metastases from solid tumors

Brain metastasis (BrM) is an area of unmet medical need that poses unique therapeutic challenges and heralds a dismal prognosis. The intracranial tumor microenvironment (TME) presents several challenges, including the therapy-resistant blood-brain barrier, a unique immune milieu, distinct intercellular interactions, and specific metabolic conditions, that are responsible for treatment failures and poor clinical outcomes. There is a complex interplay between malignant cells that metastasize to the central nervous system (CNS) and the native TME. Cancer cells take advantage of vascular, neuronal, immune, and anatomical vulnerabilities to proliferate with mechanisms specific to the CNS. In this review, we discuss unique aspects of the TME in the context of brain metastases and pathways through which the TME may hold the key to the discovery of new and effective therapies for patients with BrM.

Emergent immunotherapy approaches for brain metastases

Brain metastases from solid tumors are increasing in incidence, especially as outcomes of systemic therapies continue to extend patients’ overall survival. The long-held notion that the brain is an immune sanctuary has now been largely refuted with increasing evidence that immunotherapy can induce durable responses in brain metastases. Single agent immune checkpoint inhibition with anti-CTLA4 and anti-PD1 antibodies induces durable responses in 15%–20% in melanoma brain metastases as long as patients are asymptomatic and do not require corticosteroids. The combination of anti-CTLA4 with anti-PD-1 antibodies induces an intracranial response in over 50% of asymptomatic melanoma patients, and much lower rate of otherwise durable responses (20%) in symptomatic patients or those on steroids. Data in other cancers, such as renal cell carcinoma, are accumulating indicating a role for immunotherapy. Emerging immunotherapy approaches will have to focus on increasing response rates, decreasing toxicity, and decreasing steroid dependency. The path to those advances will have to include a better understanding of the mechanisms of response and resistance to immunotherapy in brain metastases, the use of novel agents such as anti-LAG3 checkpoint inhibitors, targeted therapy (oncogene directed or TKIs), and possibly surgery and SRS to improve the outcomes of patients with brain metastases.

Re-thinking therapeutic development for CNS metastatic disease

There has been unprecedented progress in the development of systemic therapies for patients with metastatic melanoma over the last decade. There is now tremendous potential and momentum to further and markedly reduce the impact of this disease. However, developing more effective treatments for metastases to the CNS remains a critical challenge for patients with melanoma. Melanoma patients with active CNS metastases have largely been excluded from both early-phase and registration trials for all currently approved targeted and immune therapies for this disease. While this exclusion has generally been justified in clinical research due to concerns about poor prognosis, lack of CNS penetration of agents and/or risk of toxicities, recent post-approval trials have shown the feasibility, safety and clinical benefit of clinical investigation in these patients. These trials have also identified key areas for which more effective strategies are needed. In parallel, recent translational and preclinical research has provided insights into novel immune, molecular and metabolic features of melanoma brain metastases that may mediate the aggressive biology and therapeutic resistance of these tumors. Together, these advances suggest the need for new paradigms for therapeutic development for melanoma patients with CNS metastasis.