Targeting tumor-derived NLRP3 reduces melanoma progression by limiting MDSCs expansion.

Interleukin-1ß (IL-1ß)-mediated inflammation suppresses antitumor immunity, leading to the generation of a tumor-permissive environment, tumor growth, and progression. Here, we demonstrate that nucleotide-binding domain, leucine-rich containing family, pyrin domain-containing-3 (NLRP3) inflammasome activation in melanoma is linked to IL-1ß production, inflammation, and immunosuppression. Analysis of cancer genome datasets (TCGA and GTEx) revealed greater NLRP3 and IL-1ß expression in cutaneous melanoma samples (n = 469) compared to normal skin (n = 324), with a highly significant correlation between NLRP3 and IL-1ß (P < 0.0001). We show the formation of the NLRP3 inflammasome in biopsies of metastatic melanoma using fluorescent resonance energy transfer analysis for NLRP3 and apoptosis-associated speck-like protein containing a CARD. In vivo, tumor-associated NLRP3/IL-1 signaling induced expansion of myeloid-derived suppressor cells (MDSCs), leading to reduced natural killer and CD8+ T cell activity concomitant with an increased presence of regulatory T (Treg) cells in the primary tumors. Either genetic or pharmacological inhibition of tumor-derived NLRP3 by dapansutrile (OLT1177) was sufficient to reduce MDSCs expansion and to enhance antitumor immunity, resulting in reduced tumor growth. Additionally, we observed that the combination of NLRP3 inhibition and anti-PD-1 treatment significantly increased the antitumor efficacy of the monotherapy by limiting MDSC-mediated T cell suppression and tumor progression. These data show that NLRP3 activation in melanoma cells is a protumor mechanism, which induces MDSCs expansion and immune evasion. We conclude that inhibition of NLRP3 can augment the efficacy of anti-PD-1 therapy.

Commonly integrated epigenetic modifications of differentially expressed genes lead to adaptive resistance in cancer.

Aim: To investigate the integrated epigenetic regulation of acquired drug resistance in cancer. Materials & methods: Our gene expression data of five induced drug-tolerant cell models, one resistant cell line and one publicly available drug-resistant dataset were integrated to identify common differentially expressed genes and pathways. ChIP-seq and DNA methylation by HM450K beadchip were used to study the epigenetic profile of differential expressed genes. Results & conclusion: Integrated transcriptomic analysis identified a common 'viral mimicry' related gene signature in induced drug-tolerant cells and the resistant state. Analysis of the epigenetic regulation revealed a common set of down-regulated genes, which are marked and regulated by a concomitant loss of H3K4me3, gain of H3K9me3 and increment of regional DNA methylation levels associated with tumor suppressor genes and apoptotic signaling.

TGF-ß1 and TNF-α differentially regulate Twist1 mediated resistance towards BRAF/MEK inhibition in melanoma.

Resistance to BRAF and MEK inhibition is a common phenomenon in melanoma. Cytokines and transcription factors have been attributed to contribute to the loss of sensitivity towards these inhibitors. Here, we show that transforming growth factor (TGF)-ß1 if combined with PLX4032, a BRAF inhibitor, or GSK1120212, a MEK inhibitor, substantially increased cell death in BRAF-mutant melanoma cell lines. This increase was based on the combined regulatory decrease in Twist1, an antiapoptotic protein. Overexpression or silencing of Twist1 attenuated or aggravated induction of apoptosis through PLX4032 or GSK1120212, respectively. Exposure to tumour necrosis factor (TNF)-α, however, led to increased Twist1 levels and oppositional decrease in cell death if exposed to PLX4032 or GSK1120212. This increase in drug resistance again depended on Twist1 levels. Our studies suggest that Twist1 as a common downstream target of multiple signalling cascades plays a crucial role in mediating drug resistance to BRAF- and MEK-targeted molecular inhibitors.