Effect of PARP inhibitors on sensitivity of lung and breast cancer cells to trans-platinum as compared to cis-platinum.

Abstract

e22115 Background: Poly(ADP-ribose) polymerase inhibitors (PARP-i) represent promising strategy in treatment of cisplatin resistant lung cancer and triple-negative breast cancer. We compared PARP inhibition by 3-aminobenzamide (3-AB) or NU1025, on activity of cis- and trans-platinum on NSCLC cells (A549) and breast cancer cells (MDA-MB-361), and correlated with p53 and ERCC1 status. Methods: Cell cycle distribution was determined by FACS-flow and PI-staining, while morphological changes were followed by light microscopy. ERCC1 siRNA transfection was performed by HiperFect reagent, and mRNA was analyzed by qRT-PCR. Protein expression levels were determined by Western blot. PARP-inhibition was quantified as NAD(P)H depletion using colorimetric XTT assay. Results: Trans-platinum compound with planar ammine ligands, trans-[PtCl2(4-acetylpyridine)2] showed cytotoxic activity comparable to cis-platin and exhibited enhanced action in combination with PARP-i. 3-AB enhanced the activity of trans more efficient comparing to cis-platinum in MDA-MB-361 cells. At equitoxic concentrations corresponding to IC50 values in A549 cells, cis-platin and trans-platinum compound differently affected cell survival in combination with PARP-i. XTT assay confirmed efficient inhibition of PARP activity at 200 μM NU1025 and 2 mM 3-AB in both cell lines. ERCC1 silencing in p53 proficient A549 cells, alone or in combination with NU1025, almost completely diminished resistance to trans-[PtCl2(4-acetylpyridine)2], decreasing cell survival to 50 % following 24 h action and more than 85 % following 48 h treatment, comparing to siRNA/NU1025 treated control. By contrast, sensitivity to cisplatin was much less altered. Simultaneous alteration of ERCC1 and PARP itself did not affect cell cycle progression, but prolonged sub-G1 fraction by trans-platinum as well as G2-M fraction by cis-platin. Conclusions: PARP-inhibition enhanced tumor cell sensitivity to trans-platinum drug, stronger than cis-platinum. Knockdown of ERCC1 further increases sensitivity to platinum drugs, irrelevant to p53 status. Trans-platinum complexes should be further explored as good candidates for combining with PARP-i.