PARP1 inhibitor olaparib (Lynparza) exerts synthetic lethal effect against ligase 4-deficient melanomas
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Małgorzata Czyż1, Monika Toma2, Anna Gajos-Michniewicz1, Kinga Majchrzak1, Grazyna Hoser3, Janusz Szemraj4, Margaret Nieborowska-Skorska5, Phil Cheng6, Daniel Gritsyuk5, Mitchell Levesque6, Reinhard Dummer6, Tomasz Sliwinski2, Tomasz Skorski5
1Department of Molecular Biology of Cancer, Medical University of Lodz, 92-215 Lodz, Poland
2Department of Molecular Genetics, University of Lodz, 90-236 Lodz, Poland
3Department of Flow Cytometry, Medical Center for Postgraduate Education, 01-813 Warsaw, Poland
4Department of Medical Biochemistry, Medical University of Lodz, 92-215 Lodz, Poland
5Department of Microbiology and Immunology, Temple University Lewis Katz School of Medicine, Philadelphia, PA 19140, USA
6Department of Dermatology, Faculty of Medicine, University Hospital Zürich, and University of Zürich, CH-8952, Zürich, Switzerland
Tomasz Skorski, email: email@example.com
Tomasz Sliwinski, email: firstname.lastname@example.org
Keywords: melanoma, PARP1 inhibitor, synthetic lethality
Received: June 03, 2016 Accepted: September 16, 2016 Published: September 27, 2016
Cancer including melanoma may be ‘‘addicted” to double strand break (DSB) repair and targeting this process could sensitize them to the lethal effect of DNA damage. PARP1 exerts an important impact on DSB repair as it binds to both single- and double- strand breaks. PARP1 inhibitors might be highly effective drugs triggering synthetic lethality in patients whose tumors have germline or somatic defects in DNA repair genes. We hypothesized that PARP1-dependent synthetic lethality could be induced in melanoma cells displaying downregulation of DSB repair genes. We observed that PARP1 inhibitor olaparib sensitized melanomas with reduced expression of DNA ligase 4 (LIG4) to an alkylatimg agent dacarbazine (DTIC) treatment in vitro, while normal melanocytes remained intact. PARP1 inhibition caused accumulation of DSBs, which was associated with apoptosis in LIG4 deficient melanoma cells. Our hypothesis that olaparib is synthetic lethal with LIG4 deficiency in melanoma cells was supported by selective anti-tumor effects of olaparib used either alone or in combination with dacarbazine (DTIC) in LIG4 deficient, but not LIG4 proficient cells. In addition, olaparib combined with DTIC inhibited the growth of LIG4 deficient human melanoma xenografts. This work for the first time demonstrates the effectiveness of a combination of PARP1 inhibitor olaparib and alkylating agent DTIC for treating LIG4 deficient melanomas. In addition, analysis of the TCGA and transcriptome microarray databases revealed numerous individual melanoma samples potentially displaying specific defects in DSB repair pathways, which may predispose them to synthetic lethality triggered by PARP1 inhibitor combined with a cytotoxic drug.
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