Dual Screen for Efficacy and Toxicity Identifies HDAC Inhibitor with Distinctive Activity Spectrum for BAP1-Mutant Uveal Melanoma

Our plain-English summary of Dual Screen for Efficacy and Toxicity Identifies HDAC Inhibitor with Distinctive Activity Spectrum for BAP1-Mutant Uveal Melanoma, by J.N. Kuznetsoff, D.A. Owens, A. Lopez, et al (Molecular Cancer Research, 2021).

The study

• Authors: J.N. Kuznetsoff, D.A. Owens, A. Lopez, D.A. Rodriguez, N.T. Chee, S. Kurtenbach, D. Bilbao, E.R. Roberts, C.H. Volmar, C. Wahlestedt, S.P. Brothers, J.W. Harbour
• Journal: Molecular Cancer Research
• Published: 2021;19(2):215-222
• Cited by: 31 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Drug screens leading to successful targeted therapies in cancer have been mainly based on cell viability assays identifying inhibitors of dominantly acting oncogenes. In contrast, there has been little success in discovering targeted therapies that reverse the effects of inactivating mutations in tumor-suppressor genes. BAP1 is one such tumor suppressor that is frequently inactivated in a variety of cancers, including uveal melanoma, renal cell carcinoma, and mesothelioma. Because BAP1 is an epigenetic transcriptional regulator of developmental genes, we designed a two-phase drug screen involving a cell-based rescue screen of transcriptional repression caused by BAP1 loss, followed by an in vivo screen of lead compounds for rescue of a BAP1-deficient phenotype with minimal toxicity in Xenopus embryos. The first screen identified 9 compounds, 8 of which were HDAC inhibitors. The second screen eliminated all except one compound due to inefficacy or toxicity. The resulting lead compound, quisinostat, has a distinctive activity spectrum, including high potency against HDAC4, which was recently shown to be a key target of BAP1. Quisinostat was further validated in a mouse model and found to prevent the growth of BAP1-mutant uveal melanomas. This innovative strategy demonstrates the potential for identifying therapeutic compounds that target tumor-suppressor mutations in cancer. IMPLICATIONS: Few drugs have been identified that target mutations in tumor suppressors. Using a novel 2-step screening approach, strategy, we identified quisinostat as a candidate for therapy in BAP1-mutant uveal melanoma. HDAC4 is implicated as a key target in uveal melanoma and perhaps other BAP1-mutant cancers.

©2020 American Association for Cancer Research.

In plain English

This laboratory study did not involve asbestos or people with mesothelioma. It concerned uveal melanoma, an eye cancer, and the gene BAP1, which the authors note is also mutated in mesothelioma and other cancers. The authors looked for drugs that reverse the effects of losing BAP1. Using tumor data and uveal melanoma cell lines with reduced BAP1, they found only 4 genes lowered in all three systems and chose GLO1 as a marker. A library of 1280 pharmacologically active compounds gave 11 initial hits. Only ouabain held up, and it was set aside because of possible heart side effects. A library of 180 epigenetic compounds gave 8 hits, all HDAC inhibitors. In frog embryos with Bap1 reduced by a targeting agent, some candidates failed to rescue development and CUDC-907 was severely toxic. Quisinostat rescued development with no detectable toxicity in control embryos. In mice carrying human uveal melanoma cells, quisinostat markedly reduced the growth of two BAP1-mutant lines but not of a BAP1-normal line. The authors concluded that quisinostat is a potential targeted therapy for BAP1-mutant uveal melanoma.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory drug-screening study: a cell-based screen, then a frog (Xenopus) embryo screen for efficacy and toxicity, then a mouse xenograft experiment
• Who was studied: The study used several systems at the University of Miami. Human uveal melanoma cell lines 92.1 and Mel202 were engineered to knock down BAP1, and clones with more than 85% depletion were used. Patient-derived lines MM28 and MP46 had BAP1 mutations, and line MP41 did not. The study also used RNA data from 80 uveal melanoma samples in The Cancer Genome Atlas and 300 Xenopus embryos from 3 females. Bap1 in the embryos was reduced with a bap1-targeting morpholino. Immunodeficient mice were given tumor cell grafts. The number of mice is not stated in the text.
• Exposure: No asbestos exposure was studied. The exposures were drug compounds. In cells, the authors used the LOPAC1280 library (10 uM) and an in-house library of 180 epigenetic compounds (1 uM). Candidate compounds were then tested in frog embryos. Mice received quisinostat at 10 mg/kg body weight by intraperitoneal injection on Mondays and Thursdays.
• Main results:
  • Only 4 genes (GLO1, EDARADD, DAPL1 and BAP1 itself) were differentially expressed in all 3 systems examined. GLO1 showed the largest change and was used for screening.
  • The LOPAC1280 library gave 11 initial hits. Only ouabain passed dose-response validation, an overall hit rate of 0.08% for this library. It was not considered viable because of potential cardiac side effects.
  • The 180-compound epigenetic library gave 8 hits, all HDAC inhibitors. All 8 passed dose-response validation, a hit rate of 4.4%.
  • In Xenopus embryos, CUDC-907 caused severe toxicity in both control and BAP1-deficient embryos. Pracinostat and AR-42 showed no toxicity but also no rescue.
  • In Xenopus embryos, quisinostat rescued the BAP1-deficient phenotype in the nanomolar range. It showed no detectable toxicity in control embryos, even at micromolar concentrations.
  • Combining quisinostat with the MEK inhibitor trametinib produced only a modest additive effect.
  • In mice, quisinostat markedly reduced tumor growth over a 2-month period in both BAP1-mutant lines (MM28 and MP46). It did not affect growth of the BAP1-wildtype line (MP41).
• The authors' conclusion: The authors concluded that quisinostat is a potential targeted therapy in BAP1-mutant uveal melanoma. They also concluded that their multi-step screening approach has potential value for finding such compounds.

Topics

Medical terms in this study, explained in our Lexicon: BAP1, Carcinoma, Mesothelioma.

Related studies

• Analysis of BAP1 Germline Gene Mutation in Young Uveal Melanoma Patients — C.M. Cebulla, E.M. Binkley, et al. (2015)
• Ocular melanoma and the BAP1 hereditary cancer syndrome: implications for the dermatologist — L.M. Martorano, R.R. Winkelmann, et al. (2014)
• Germline BAP1-positive patients: the dilemmas of cancer surveillance and a proposed interdisciplinary consensus monitoring strategy — P. Star, A. Goodwin, et al. (2018)
• Prevalence and Preliminary Validation of Screening Criteria to Identify Carriers of Germline BAP1 Mutations — M.G. Zauderer, G. Jayakumaran, et al. (2019)
• Histomorphologic spectrum of BAP1 negative melanocytic neoplasms in a family with BAP1-associated cancer susceptibility syndrome — Z. Marušić, M. Buljan, et al. (2015)
• CDKN2A and BAP1 germline mutations predispose to melanoma and mesothelioma — M. Betti, A. Aspesi, et al. (2016)

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