Polyadenosine diphosphate-ribose polymerase (PARP) inhibition as a means of protecting the inner ear from cisplatin (CDDP)-mediated ototoxicity without affecting antitumor efficacy in vitro.

Abstract

e13501 Background: Hearing loss can be the dose limiting toxicity of CDDP. In the treatment of germ cell tumors (GCT) or adjuvant therapy of non-small cell lung cancer (NSCLC), CDDP cannot be replaced without loss of efficacy. Inhibition of PARP, an enzyme of the base excision repair pathway, is a novel anti-neoplastic principle. PARP-activation has been identified to induce cell death following inner ear trauma. We evaluated PARP-inhibition by pirenzepin as a means to protect the ear from CDDP. Methods: In an in vitro culture model, inner ears were treated continuously with 1.4 μM CDDP. Ears were obtained from heterozygous and homozygous PARP-knock out mice and wild-type controls at postnatal day 7. The number of preserved hair cell stereocilia bundles was counted by fluorescence microscopy after labeling with phalloidin. Cytotoxicity of CDDP and the effect of pirenzepin were assessed by MTS-assays and flow cytometry using the cell lines 2102EP, NT2 (both GCT) and NCI-H460 (NSCLC). Results: In wild-type mice, only 45% of the inner and 30% of the outer hair cells were preserved following CDDP-exposure compared to untreated controls. In heterozygous PARP-knock out mice, 90% and 80% of the hair cells survived CDDP exposure. The fractions of surviving hair cells in the homozygous knock out mice were 70% and 50%, respectively, the difference was significant (p<0.05). Protection of 60-80% hair cells could be achieved by pirenzepin in wild-type mice with the maximum protective effect at intermediate dose levels. Pirenzepin alone did not affect growth in any cell line. Cytotoxicity of CDDP as measured by IC50 determination in MTS assay or by flow-cytometric assessment of vital cells was not affected by pirenzepin. Conclusions: PARP-activation seems to play a relevant role in CDDP-induced ototoxicity. Thus, PARP-inhibition appears to be a promising means to protect hearing under CDDP therapy, especially since PARP-inhibition did not diminish sensitivity of GCT and NSCLC cell lines to CDDP, even though no synergistic effect could be observed. Author Disclosure Employment or Leadership Position Consultant or Advisory Role Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration ProteoSys AG ProteoSys AG