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SREBP2 is a master regulator of the mevalonate pathway (MVP), a biosynthetic process that drives the synthesis of dolichol, heme A, ubiquinone and cholesterol and also provides substrates for protein prenylation. Here, we identify SREBP2 as a novel substrate for USP28, a deubiquitinating enzyme that is frequently upregulated in squamous cancers. Our results show that silencing of USP28 reduces expression of MVP enzymes and lowers metabolic flux into this pathway. We also show that USP28 binds to mature SREBP2, leading to its deubiquitination and stabilisation. USP28 depletion rendered cancer cells highly sensitive to MVP inhibition by statins, which was rescued by the addition of geranyl-geranyl pyrophosphate. Analysis of human tissue microarrays revealed elevated expression of USP28, SREBP2 and MVP enzymes in lung squamous cell carcinoma (LSCC) compared to lung adenocarcinoma (LADC). Moreover, CRISPR/Cas-mediated deletion of SREBP2 selectively attenuated tumour growth in a KRas/p53/LKB1 mutant mouse model of lung cancer. Finally, we demonstrate that statins synergise with a dual USP28/25 inhibitor to reduce viability of SCC cells. Our findings suggest that combinatorial targeting of MVP and USP28 could be a therapeutic strategy for the treatment of squamous cell carcinomas.

Brain metastases are refractory to therapies that control systemic disease in patients with human epidermal growth factor receptor 2 (HER2+) breast cancer, and the brain microenvironment contributes to this therapy resistance. Nutrient availability can vary across tissues, therefore metabolic adaptations required for brain metastatic breast cancer growth may introduce liabilities that can be exploited for therapy. Here, we assessed how metabolism differs between breast tumors in brain versus extracranial sites and found that fatty acid synthesis is elevated in breast tumors growing in brain. We determine that this phenotype is an adaptation to decreased lipid availability in brain relative to other tissues, resulting in a site-specific dependency on fatty acid synthesis for breast tumors growing at this site. Genetic or pharmacological inhibition of fatty acid synthase (FASN) reduces HER2+ breast tumor growth in the brain, demonstrating that differences in nutrient availability across metastatic sites can result in targetable metabolic dependencies.

Introduction Treatment of patients with metastatic melanoma is hampered by drug-resistance and often requires combination with radiotherapy as last-resort option. However, also after radiotherapy, clinical relapses are common. Methods & results Our preclinical models indicated a higher rate of tumour relapse when melanoma cells were first treated with BRAFV600E inhibition (BRAFi) followed by radiotherapy as compared to the reverse sequence. Accordingly, retrospective follow-up data from 65 stage-IV melanoma patients with irradiated melanoma brain metastases confirmed a shortened duration of local response of mitogen-activated protein kinase (MAPK)-inhibitor–pretreated compared with MAPK-inhibitor–naive intracranial metastases. On the molecular level, we identified JARID1B/KDM5B as a cellular marker for cross-resistance between BRAFi and radiotherapy. JARID1Bhigh cells appeared more frequently under upfront BRAFi as compared with upfront radiation. JARID1B favours cell survival by transcriptional regulation of genes controlling cell cycle, DNA repair and cell death. Conclusion The level of cross-resistance between combined MAPK inhibition and radiotherapy is dependent on the treatment sequence. JARID1B may represent a novel therapy-overarching resistance marker.

Melanoma is a highly plastic tumor characterized by dynamic interconversion of different cell identities depending on the biological context. For example, melanoma cells with high expression of the H3K4 demethylase KDM5B (JARID1B) rest in a slow-cycling, yet reversible persister state. Over time, KDM5Bhigh cells can promote rapid tumor repopulation with equilibrated KDM5B expression heterogeneity. The cellular identity of KDM5Bhigh persister cells has not been studied so far, missing an important cell state-directed treatment opportunity in melanoma. Here, we have established a doxycycline-titratable system for genetic induction of permanent intratumor expression of KDM5B and screened for chemical agents that phenocopy this effect. Transcriptional profiling and cell functional assays confirmed that the dihydropyridine phenoxyethyl 4-(2-fluorophenyl)-2,7,7-trimethyl-5-oxo-1,4,5,6,7,8-hexa-hydro-quinoline-3-carboxylate (termed Cpd1) supports high KDM5B expression and directs melanoma cells towards differentiation along the melanocytic lineage and to cell cycle-arrest. The high KDM5B state additionally prevents cell proliferation through negative regulation of cytokinetic abscission. Moreover, treatment with Cpd1 promoted the expression of the melanocyte-specific tyrosinase gene specifically sensitizing melanoma cells for the tyrosinase-processed antifolate prodrug 3-O-(3,4,5-trimethoxybenzoyl)-(-)-epicatechin (TMECG). In summary, our study provides proof-of-concept for a new dual hit strategy in melanoma, in which persister state-directed transitioning limits tumor growth and plasticity and primes melanoma cells towards lineage-specific elimination.

Natural products (NPs) are an important inspirational source for developing drugs and chemical probes. In 1999, the group of Ōmura reported the constitutional elucidation of zelkovamycin. Although largely unrecognized so far, this NP displays structural similarities as well as differences to the argyrin NP family, a class of peptidic NPs with promising anticancer activities and diverse mode‐of‐action at the molecular level. By a combination of structure elucidation experiments, the first total synthesis of zelkovamycin and bioassays, the zelkovamycin configuration was determined and its previously proposed molecular structure was revised. The full structure assignment proves zelkovamycin as an additional member of the argyrins with however unique OXPHOS inhibitory properties. Zelkovamycin may therefore not only serve as a new starting point for chemical inhibitors of the OXPHOS system, but also guide customized argyrin NP isolation and biosynthesis studies., Zelkovamycin is an argyrin natural product. By a combination of structural elucidation methodologies, total synthesis and bioassays, the exact molecular structure of zelkovamycin was assigned and revised and its OXHPOS inhibitory properties revealed.

9548 Background: The field of liquid biopsy provides a promising alternative to standard tissue biopsies. Previous work has shown that plasma circulating cell-free DNA (ctDNA) can reflect the heterogeneous spectrum of mutations in cancer including metastatic melanoma. Our project aimed to establish and statistically validate plasma-based assays for tumour load and therapy monitoring in melanoma. Methods: On a large cohort of stage III and stage IV melanoma patients (N = 96) who received signalling targeted or immune checkpoint inhibitors we showed that the most common oncogenic drivers of this disease such as the BRAFV600E, NRASQ61 and the TERTC250T and TERTC228T promoter mutations (termed TERTprom) can be analysed in ctDNA with highly sensitive droplet digital PCR technology (detection of mutant ctDNA down to 0.01% analytical sensitivity). Results: Our research has demonstrated that ctDNA (irrespective of the genotype) significantly correlates with tumour stage (P < 0.05). Using receiver operating characteristics (ROC) analyses thresholds were established for risk stratification and response prediction. Elevated ctDNA at baseline was a significant predictor of disease progression compared to elevated LDH or S100 in multivariable cox proportional hazards model (Hazard ratio [HR] 7.43, P = 0.05). During therapy, patients with low ctDNA load (below the ROC threshold) had significantly better radiological outcomes and prolonged progression free survival (PFS) compared to patients with high ctDNA load (P < 0.0001). Our findings were confirmed on an independent cohort of metastatic melanoma patients (N = 35) treated with immune checkpoint inhibitors, where also during therapy low ctDNA load correlated with prolonged PFS (P = 0.003). An added benefit of ctDNA was demonstrated in about 80% of the patients, where ctDNA analyses preceded the radiological diagnosis of response or relapse. Progression was detected in plasma ctDNA in average 3.5 months earlier as compared to routine imaging techniques. Finally, we demonstrated that the occurrence of NRASQ61 mutation in BRAFV600-inhibitor treated patients at therapy baseline was associated with treatment failure. The sub-clonal NRASQ61 mutation at therapy baseline was an independent predictor of shorter PFS (HR 2.69, P = 0.02) as compared to BRAFV600E patients without the NRASQ61 mutation at therapy baseline. Conclusions: In sum, our results support the value of ctDNA as a sensitive biomarker for real-time therapy monitoring and early detection of disease progression.

Introduction Melanoma progression is often associated with the growth of anatomically critical metastases that require immediate therapy response, e.g. in the brain. In such situations, systemic drugs are often sequentially combined with radiotherapy. However, there is a lack of clinical and preclinical studies that systematically examine the potential effects of therapy-timing on treatment efficacy and radio-cross-resistance in melanoma. Material and methods We established an experimental platform comprising cell culture and mouse xenograft models that allows predicting the outcome of different BRAF V600E inhibitor-radiotherapy sequences. Retrospectively collected clinical follow up data of 65 stage IV melanoma patients with brain metastases were analysed for their intracranial response after radiotherapy depending on the sequence of co-administered MAPK inhibition. Results and discussions Our models indicated a higher rate of tumour relapse when melanoma cells were first treated with BRAF V600E inhibition followed by radiotherapy as compared to the reverse sequence. We identified the H3K4 demethylase JARID1B/KDM5B as a cellular marker for cross-resistance between BRAF V600E inhibition and radiotherapy. JARID1B high cells appeared more frequently in vitro and in vivo under upfront BRAF V600E inhibition as compared to upfront radiation. Accordingly, retrospective follow-up data from irradiated melanoma brain metastases confirmed a shortened duration of response of MAPK inhibitor-pretreated compared to MAPK inhibitor-naive metastases. Mechanistically, JARID1B favours cell survival by transcriptional regulation of genes controlling cell cycle, DNA repair, and cell death. Conclusion Our preclinical results and the clinical follow up of patients support a higher rate of tumour relapse when melanomas are treated with upfront MAPK inhibition as compared to upfront radiation. JARID1B may represent a novel therapy-overarching resistance marker that could guide future therapy sequencing.

Introduction Melanoma is an aggressive tumour with a median survival of only 6–12 month after occurrence of metastasis. In detail, one key factor of drug resistance mechanism in melanoma pathogenesis is cell heterogeneity. A defined cell subpopulation of slow cycling cells marked by a high histone demethylase JARID1B expression are therapy resistant and are most likely responsible for tumour repopulation. Moreover, cells with a slow cycling phenotype are described to modulate metabolism under targeted therapy. Therefore, the aim of my thesis is to characterise metabolic ‘hubs’ within metabolic landscaping analysis of melanoma cells. Material and methods We induced JARID1Blow and JARID1Bhigh phenotypes in WM3734 melanoma cells via shRNA-mediated knockdown and Doxycyclin-inducible Tet3G-Overexpression and prepared for a subpopulation-specific LC-HRMS based metabolomics landscaping analysis. Additionally, we investigated if chemical H3K4 demethylase inhibition could be used to specifically target the JARID1B-driven malignant metabolic phenotype in melanoma cells. Results and discussions JARID1Bhigh expressing melanoma cells show upregulated metabolites of glutathione-redox-system and pentose phosphate pathway. Moreover, several upregulated metabolites in JARID1Bhigh melanoma cells confirm existing data stating that those tumour cells do not follow the Warburg effect, but rather depend on mitochondrial OXPHOS to gain ATP and maintain a multi-resistant phenotype. Furthermore, a treatment with H3K4 demethylase inhibitors modulates the detected active metabolic pathways in melanoma cells functionally and also impairs cell proliferation and invasion capacity. Conclusion Our present metabolic landscaping analysis unravelled heterogeneous metabolic profiles in melanoma pointing to a possible relevance for therapy resistance of distinct melanoma cell subpopulations. In detail, we could profile the metabolome of multi-drug resistant JARID1Bhigh melanoma cells including their underlying enzymatic hubs. To overcome drug resistance in future, such hubs could be either directly targeted or indirectly by inhibiting their epigenetic regulators.

The specific functions of sensory systems depend on the tissue-specific expression of genes that code for molecular sensor proteins that are necessary for stimulus detection and membrane signaling. Using the Next Generation Sequencing technique (RNA-Seq), we analyzed the complete transcriptome of the trigeminal ganglia (TG) and dorsal root ganglia (DRG) of adult mice. Focusing on genes with an expression level higher than 1 FPKM (fragments per kilobase of transcript per million mapped reads), we detected the expression of 12984 genes in the TG and 13195 in the DRG. To analyze the specific gene expression patterns of the peripheral neuronal tissues, we compared their gene expression profiles with that of the liver, brain, olfactory epithelium, and skeletal muscle. The transcriptome data of the TG and DRG were scanned for virtually all known G-protein-coupled receptors (GPCRs) as well as for ion channels. The expression profile was ranked with regard to the level and specificity for the TG. In total, we detected 106 non-olfactory GPCRs and 33 ion channels that had not been previously described as expressed in the TG. To validate the RNA-Seq data, \(\textit {in situ}\) hybridization experiments were performed for several of the newly detected transcripts. To identify differences in expression profiles between the sensory ganglia, the RNA-Seq data of the TG and DRG were compared. Among the differentially expressed genes (> 1 FPKM), 65 and 117 were expressed at least 10-fold higher in the TG and DRG, respectively. Our transcriptome analysis allows a comprehensive overview of all ion channels and G protein-coupled receptors that are expressed in trigeminal ganglia and provides additional approaches for the investigation of trigeminal sensing as well as for the physiological and pathophysiological mechanisms of pain.

PURPOSE Circulating cell-free tumor DNA (ctDNA) reflects the heterogeneous spectrum of tumor-specific mutations, especially in systemic disease. We validated plasma-based assays that allow the dynamic quantitative detection of ctDNA as a prognostic biomarker for tumor load and prediction of therapy response in melanoma. MATERIALS and METHODS We analyzed plasma-derived ctDNA from a large training cohort (n = 96) of patients with advanced-stage melanoma, with assays for the BRAFV600E and NRASQ61 driver mutations as well as TERTC250T and TERTC228T promoter mutations. An independent patient cohort (n = 35) was used to validate the utility of ctDNA monitoring under mitogen-activated protein kinase–targeted or immune checkpoint therapies. RESULTS Elevated plasma ctDNA level at baseline was an independent prognostic factor of disease progression when compared with serum S100 and lactate dehydrogenase levels in multivariable analyses (hazard ratio [HR], 7.43; 95% CI, 1.01 to 55.19; P = .05). The change in ctDNA levels during therapy correlated with treatment response, where increasing ctDNA was predictive for shorter progression-free survival (eg, for BRAFV600E ctDNA, HR, 3.70; 95% CI, 1.86 to 7.34; P < .001). Increasing ctDNA levels predicted disease progression significantly earlier than did routine radiologic scans ( P < .05), with a mean lead time of 3.5 months. NRAS-mutant ctDNA was detected in a significant proportion of patients with BRAF-mutant tumors under therapy, but unexpectedly also at baseline. In vitro sensitivity studies suggested that this represents higher-than-expected intratumoral heterogeneity. The detection of NRASQ61 ctDNA in baseline samples of patients with BRAFV600E mutation who were treated with mitogen-activated protein kinase inhibitors significantly correlated with shorter progression-free survival (HR, 3.18; 95% CI, 1.31 to 7.68; P = .03) and shorter overall survival (HR, 4.08; 95% CI, 1.57 to 10.58; P = .01). CONCLUSION Our results show the potential role of ctDNA measurement as a sensitive monitoring and prediction tool for the early assessment of disease progression and therapeutic response in patients with metastatic melanoma.