Sensitivity of Mesothelioma Cells to PARP Inhibitors Is Not Dependent on BAP1 but Is Enhanced by Temozolomide in Cells With High-Schlafen 11 and Low-O6-methylguanine-DNA Methyltransferase Expression

Our plain-English summary of Sensitivity of Mesothelioma Cells to PARP Inhibitors Is Not Dependent on BAP1 but Is Enhanced by Temozolomide in Cells With High-Schlafen 11 and Low-O6-methylguanine-DNA Methyltransferase Expression, by D. Rathkey, M. Khanal, J. Murai, et al (Journal of Thoracic Oncology, 2020).

The study

• Authors: D. Rathkey, M. Khanal, J. Murai, J. Zhang, M. Sengupta, Q. Jiang, B. Morrow, C.N. Evans, R. Chari, P. Fetsch, H.J. Chung, L. Xi, M. Roth, A. Filie, M. Raffeld, A. Thomas, Y. Pommier, R. Hassan
• Journal: Journal of Thoracic Oncology
• Published: 2020;15(5):843-859
• Cited by: 65 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Introduction: BRCA1-associated protein-1 (BAP1), a nuclear deubiquitinase thought to be involved in DNA double-strand break repair, is frequently mutated in mesothelioma. Because poly(adenosine diphosphate-ribose) polymerase inhibitors (PARPIs) induce synthetic lethality in BRCA1/2 mutant cancers, we evaluated whether BAP1 inactivating mutations confer sensitivity to PARPIs in mesothelioma and if combination therapy with temozolomide (TMZ) would be beneficial.

Methods: A total of 10 patient-derived mesothelioma cell lines were generated and characterized for BAP1 mutation status, protein expression, nuclear localization, and sensitivity to the PARPIs, olaparib, and talazoparib, alone or in combination with TMZ. BAP1 deubiquitinase (DUB) activity was evaluated by ubiquitin with 7-amido-4-methylcoumarin assay. BAP1 knockout mesothelioma cell lines were generated by CRISPR-Cas9. Because Schlafen 11 (SLFN11) and O6-methylguanine-DNA methyltransferase also drive response to TMZ and PARPIs, we tested their expression and relationship with drug response.

Results: BAP1 mutations or copy-number alterations, or both were present in all 10 cell lines. Nonetheless, four cell lines exhibited intact DUB activity and two had nuclear BAP1 localization. Half maximal-inhibitory concentrations of olaparib and talazoparib ranged from 4.8 μM to greater than 50 μM and 0.039 μM to greater than 5 μM, respectively, classifying them into sensitive (two) or resistant (seven) cells, independent of their BAP1 status. Cell lines with BAP1 knockout resulted in the loss of BAP1 DUB activity but did not increase sensitivity to talazoparib. Response to PARPI tended to be associated with high SLFN11 expression, and combination with temozolomide increased sensitivity of cells with low or no MGMT expression.

Conclusions: BAP1 status does not determine sensitivity to PARPIs in patient-derived mesothelioma cell lines. Combination of PARPI with TMZ may be beneficial for patients whose tumors have high SLFN11 and low or no MGMT expression.

Published by Elsevier Inc.

In plain English

This laboratory study tested whether mesothelioma cells with defects in the BAP1 gene respond better to PARP inhibitor drugs (olaparib and talazoparib). It was done in cells, not patients. The authors grew 10 cell lines from ascites or pleural fluid of patients with mesothelioma treated at the US National Cancer Institute, and also used established mesothelioma and breast cancer cell lines. All 10 patient-derived lines had BAP1 mutations or copy-number changes, yet four still showed working BAP1 enzyme activity. Of the nine lines included in the sensitivity analysis, two were sensitive and seven resistant, and sensitivity did not follow BAP1 status. Removing BAP1 from cells, or adding it, did not change talazoparib sensitivity. All three lines lacking a protein called SLFN11 were resistant. Adding the chemotherapy drug temozolomide produced strong synergy in the two sensitive lines, which had low or no MGMT protein. The authors concluded that BAP1 did not determine sensitivity, and that patients with MGMT-negative, SLFN11-positive tumors might benefit from the combination. They said a larger sample is needed. Asbestos exposure was not studied.

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 (in vitro) cell-line study, including BAP1 knockout and overexpression experiments and an analysis of public cancer cell-line drug databases
• Who was studied: 10 mesothelioma cell lines derived from ascites or pleural fluid of patients treated at the National Cancer Institute, Bethesda, Maryland. Established mesothelioma cell lines (H2052, H2452, H28) and a breast cancer cell line (HCC1937) were also used. NCI-Meso52 was left out of the drug-sensitivity analysis.
• Exposure: Drugs, not asbestos: the PARP inhibitors olaparib and talazoparib, alone or combined with temozolomide (for the combination tests, talazoparib was fixed at 0.1 micromolar)
• Main results:
  • All 10 patient-derived cell lines had inactivating BAP1 mutations, copy-number abnormalities, or both.
  • Despite these alterations, four patient-derived lines (NCI-Meso17, NCI-Meso18, NCI-Meso19, NCI-Meso52) had BAP1 enzyme (deubiquitinase) activity and were considered functionally BAP1-positive.
  • Nuclear BAP1 was seen in two patient-derived lines (NCI-Meso19 and NCI-Meso52) and in the established lines HCC1937 and H2052.
  • In the patient-derived lines, IC50 values ranged from 4.8 to greater than 50 micromolar for olaparib and from 0.039 to greater than 5 micromolar for talazoparib.
  • The nine lines included in the sensitivity analysis split into two sensitive and seven resistant lines. Of three lines with active BAP1 among them, one (NCI-Meso17) was sensitive and two (NCI-Meso18, NCI-Meso19) were resistant.
  • Knocking out BAP1 in HCC1937, H2052 and NCI-Meso19 did not make them sensitive to talazoparib: IC50s stayed above 5 micromolar.
  • Overexpressing BAP1 in H2452, NCI-Meso17 and NCI-Meso21 did not change talazoparib sensitivity compared with empty-vector controls.
  • In the public GDSC database of about 900 cancer cell lines, BAP1 expression and BAP1 mutation status correlated poorly with PARP inhibitor sensitivity (Pearson's r less than 0.1).
  • All three SLFN11-negative patient-derived lines were resistant to PARP inhibitors, and all sensitive lines were SLFN11-positive.
  • With talazoparib plus temozolomide, the two sensitive lines (NCI-Meso17, NCI-Meso21), which were MGMT-deficient or MGMT-low, showed strong synergism (combination index less than 0.3).
  • Among the four MGMT-positive resistant lines tested with the combination, NCI-Meso16 and NCI-Meso19 showed no synergism at any concentration.
  • The other two MGMT-positive resistant lines, NCI-Meso29 and NCI-Meso63 (both SLFN11-positive), showed reduced survival only at higher temozolomide concentrations.
• The authors' conclusion: The authors concluded that BAP1 is not a determinant of mesothelioma cell response to PARP inhibitors. They also concluded that patients with MGMT-negative and SLFN11-positive tumors might benefit from temozolomide plus PARP inhibitor therapy.
• Limitations the authors state:
  • The authors said the SLFN11 and combination findings are initial observations that need validation in a larger sample.
  • The authors said mechanistic studies, such as SLFN11 knockout cell lines, are needed to understand the combination's effect.
  • One of the 10 patient-derived lines (NCI-Meso52) was excluded from the sensitivity analysis because its IC50 results varied, possibly because of slow growth.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Lung cancer, Mesothelioma.

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

Related studies

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• Response to Letter to the Editor by Yang et al — R. Hassan, M. Sengupta, et al. (2020)
• The value of BRCA-1-associated protein 1 expression and cyclin-dependent kinase inhibitor 2A deletion to distinguish peritoneal malignant mesothelioma from peritoneal location of carcinoma in effusion cytology specimens — W. Althakfi, S. Gazzo, et al. (2020)
• Synthetic lethality in malignant pleural mesothelioma with PARP1 inhibition — G. Srinivasan, G.S. Sidhu, et al. (2017)
• Enhanced apoptosis by pemetrexed and simvastatin in malignant mesothelioma and lung cancer cells by reactive oxygen species-dependent mitochondrial dysfunction and Bim induction — K.E. Hwang, Y.S. Kim, et al. (2014)
• Inhibition of EZH2 methyltransferase decreases immunoediting of mesothelioma cells by autologous macrophages through a PD-1-dependent mechanism — M. Hamaidia, H. Gazon, et al. (2019)

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