Stroma remodeling and reduced cell division define durable response to PD-1 blockade in melanoma.

Although immune checkpoint inhibitors (ICIs) have achieved unprecedented results in melanoma, the biological features of the durable responses initiated by these drugs remain unknown. Here we show the genetic and phenotypic changes induced by treatment with programmed cell death-1 (PD-1) blockade in a genetically engineered mouse model of melanoma driven by oncogenic BRAF. In this controlled system anti-PD-1 treatment yields responses in ~35% of the tumors, and prolongs survival in ~27% of the animals. We identify increased stroma remodeling and reduced expression of proliferation markers as features associated with prolonged response. These traits are corroborated in two independent early on-treatment anti-PD-1 melanoma patient cohorts. These insights into the biological responses of tumors to ICI provide a strategy for identification of durable response early during the course of treatment and could improve patient stratification for checkpoint inhibitory drugs.

Ultraviolet radiation-induced DNA damage is prognostic for outcome in melanoma.

The melanoma genome is dominated by ultraviolet radiation (UVR)-induced mutations. Their relevance in disease progression is unknown. Here we classify melanomas by mutation signatures and identify ten recurrently mutated UVR signature genes that predict patient survival. We validate these findings in primary human melanomas; in mice we show that this signature is imprinted by short-wavelength UVR and that four exposures to UVR are sufficient to accelerate melanomagenesis.

Publisher Correction: Ultraviolet radiation-induced DNA damage is prognostic for outcome in melanoma.

In the version of this article originally published, Extended Data Fig. 3 was incorrect. A duplicate of Extended Data Fig. 4 was uploaded in place of Extended Data Fig. 3. Extended Data Fig. 3 has now been uploaded. The error has been fixed in the PDF and HTML versions of this article.

Resistance to BRAF inhibitors induces glutamine dependency in melanoma cells.

BRAF inhibitors can extend progression-free and overall survival in melanoma patients whose tumors harbor mutations in BRAF. However, the majority of patients eventually develop resistance to these drugs. Here we show that BRAF mutant melanoma cells that have developed acquired resistance to BRAF inhibitors display increased oxidative metabolism and increased dependency on mitochondria for survival. Intriguingly, the increased oxidative metabolism is associated with a switch from glucose to glutamine metabolism and an increased dependence on glutamine over glucose for proliferation. We show that the resistant cells are more sensitive to mitochondrial poisons and to inhibitors of glutaminolysis, suggesting that targeting specific metabolic pathways may offer exciting therapeutic opportunities to treat resistant tumors, or to delay emergence of resistance in the first-line setting.

Ultraviolet radiation accelerates BRAF-driven melanomagenesis by targeting TP53.

Cutaneous melanoma is epidemiologically linked to ultraviolet radiation (UVR), but the molecular mechanisms by which UVR drives melanomagenesis remain unclear. The most common somatic mutation in melanoma is a V600E substitution in BRAF, which is an early event. To investigate how UVR accelerates oncogenic BRAF-driven melanomagenesis, we used a BRAF(V600E) mouse model. In mice expressing BRAF(V600E) in their melanocytes, a single dose of UVR that mimicked mild sunburn in humans induced clonal expansion of the melanocytes, and repeated doses of UVR increased melanoma burden. Here we show that sunscreen (UVA superior, UVB sun protection factor (SPF) 50) delayed the onset of UVR-driven melanoma, but only provided partial protection. The UVR-exposed tumours showed increased numbers of single nucleotide variants and we observed mutations (H39Y, S124F, R245C, R270C, C272G) in the Trp53 tumour suppressor in approximately 40% of cases. TP53 is an accepted UVR target in human non-melanoma skin cancer, but is not thought to have a major role in melanoma. However, we show that, in mice, mutant Trp53 accelerated BRAF(V600E)-driven melanomagenesis, and that TP53 mutations are linked to evidence of UVR-induced DNA damage in human melanoma. Thus, we provide mechanistic insight into epidemiological data linking UVR to acquired naevi in humans. Furthermore, we identify TP53/Trp53 as a UVR-target gene that cooperates with BRAF(V600E) to induce melanoma, providing molecular insight into how UVR accelerates melanomagenesis. Our study validates public health campaigns that promote sunscreen protection for individuals at risk of melanoma.