Hendrickson, Andrea Wahner

Background: Poly (ADP-ribose) polymerases (PARPs) are a highly conserved family of enzymes whose main function is to preserve genomic integrity following DNA damage. PARP inhibitors (PARPi) are increasingly used in cancers with deficiencies in homologous recombination. Clinical trials in breast and ovarian cancers have led to several FDA approvals in recent years, and their use in clinical practice is continuing to rise. It is thus necessary to assess their adverse event (AE) profile. Method: Literature search was performed using Ovid MEDLINE, EMBASE, CENTRAL, and Scopus (inception through October 26, 2018). Eligible studies were phase 3, randomized, controlled trials that compared single agent PARPi to placebo or standard treatment. Number of patients treated and AEs reported were recorded. Observed incidence of AE was reported with 95% CI. Heterogeneity was evaluated using Cochran Q statistic and I2 statistics quantified the proportion of heterogeneity not due to chance. Results: Databases revealed 869 references. Of these, 6 were eligible: 2 in breast cancer (OlympiAD, EMBRACA) and 4 in ovarian cancer (NOVA, ARIEL3, SOLO1, SOLO2). PARPi included niraparib (NOVA), olaparib (OlympiAD, SOLO1, SOLO2), rucaparib (ARIEL3), and talazoparib (EMBRACA). Of 1,685 patients who received PARPi, incidence of any AE, regardless of grade, was 98.5% (95% CI, 97.2–99.2%). Common AEs were: nausea (incidence rate, 68.9% and 95% CI, 58.7%–77.5%), fatigue (56.3%, 45.3%–66.8%), anemia (46.3%, 37.2%–55.8%), vomiting (33.7%, 29.5%–38.3%), neutropenia (24.7%, 15.3%–37.4%), headache (23.9%, 19.9%–28.4%), and reduced appetite (21.7%, 19.3%–24.3%). Myeloid neoplasms were rare (1.2%, 0.7%–1.9%). Incidence of grade 3 or higher AE was 44.3% (30.2%–59.5%) and often related to myelosuppression, specifically anemia (24.7%, 15.3%–37.4%), neutropenia (10.7%, 6.6%–16.9%), and thrombocytopenia (5.0%, 1.7%–14.0%). Incidence of serious AE was 24.3% (19.4%–29.9%); dose interruption occurred in 53.3% (41.2%–65.0%) and dose reduction occurred in 39.2% (23.6%–57.4%). 10% (7.4%–13.6%) of patients discontinued therapy due to AE. Death due to AE was rare; less than 1% (0.4%, 0.2%–0.8%) in all trials. Conclusion: Myelosuppression and gastrointestinal toxicities were the most commonly reported AE in 6 randomized phase 3 trials of PARPi for breast and ovarian cancers. Therapy was rarely discontinued due to AE. It remains to be seen whether these results will be reflected in clinical practice.

Background: Paclitaxel-treated patients can suffer from years of peripheral neuropathy with pain, numbness, and tingling. Promising preclinical data with poly (ADP-ribose) polymerase (PARP) inhibitors led us to explore this class of agents to palliate this neuropathy. Methods: We relied on a completed trial that tested the antineoplastic effects of veliparib (NCT01012817). Data from patients who had been enrolled on NCT01012817, who previously received paclitaxel, and who had completed a validated pain assessment instrument were evaluated for improvement in their pain scores. Results: All 34 eligible patients were women, and all had a metastatic gynecological malignancy. On a 10-point scale (higher numbers indicative of worse pain), the average baseline score was 3.6 (range: 0-7). Seven patients (21%; 95% confidence interval: 9%-38%) manifested a drop in pain score (1 score lower than baseline followed by at least one consecutive value also below baseline). Of note, no patients initiated other therapy for neuropathy while on NCT01012817. Conclusion: The PARP inhibitors merit further study for chemotherapy-induced peripheral neuropathy. For patients suffering from peripheral neuropathy, these putative palliative effects might prompt earlier consideration of a PARP inhibitor as part of cancer treatment.

Abstract Resistance is one the main reason for overall decrease in survival of cancer patient treated with cisplatin in different types of cancer. Cisplatin kills cancer cells by various mechanisms, but mainly through formation of inter- and intra stand crosslinks of DNA. Different types of translesion polymerase including Polymerase kappa (POLK) are involved in repair of DNA lesions. We observed high expression levels of POLK in cisplatin resistant bladder and ovarian cancer cells compared to parental cells. Due to its low proof-reading activity POLK can incorporate 8-oxo-dGTP into DNA. The MTH1 protein (Nudix hydrolase- NUDT1) sanitizes oxidized dNTP pools to prevent incorporation of damaged bases during DNA replication. Recently we have generated MTH1 inhibitors that damage the DNA and induce cancer specific cell death through incorporation of more oxidized dNTPs. We found cisplatin resistant bladder cancer cells (NTUB1/P) were more sensitive to MTH1 inhibitors in comparison to parental NTUB1 cells. As POLK is involved in incorporation of 8-oxo-dGTP into DNA, we hypothesized that high expression levels of POLK in cisplatin resistant cells make them more sensitive to MTH1 inhibitors as more 8-oxo-dGTP would be incorporated into DNA, resulting in more DNA damage and cell death in comparison to parental cells. Indeed, we observes higher induction of cleaved-PARP, γH2AX, cleaved-Caspase 3 and more annexin v positive cells in cisplatin resistant NTUB1/P cells in comparison to parental NTUB1 cells upon treatment with MTH1 inhibitors. MTH1 inhibitor also significantly delays the NTUB1/P xenograft tumor growth in comparison to vehicle treatment in immunosuppressive mice. Knocking down POLK in cisplatin resistant NTUB1/P cells by siRNA resulted in decreased incorporation of 8-oxo-dGTP and sensitivity to MTH1 inhibitors compared to non target control cells. Overexpression of POLK in NTUB1 and NTUB1/P cells results in further sensitization to MTH1 inhibitors. In conclusion elevated levels of POLK in cisplatin resistance cells determines increased sensitivity towards MTH1 inhibitors. Thus MTH1 inhibitors can be a potential promising therapy for the treatment of cisplatin resistant tumors in patients. Citation Format: Kumar Sanjiv, Helge Gad, Sean Rudd, Rachel Hurley, Patric Herr, José Manuel Calderón Montaño, Oliver Mortusewicz, Tobias Koolmeister, Sylvain Jaques, Estefanía Burgos Morón, Andreas Hoglund, Te-Chang Lee, Martin Scobie, Scott Kaufmann, John Weroha, Ulrika Warpman Berglund, Andrea Wahner Hendrickson, Thomas Helleday. Polymerase kappa determines the sensitivity of MTH1 inhibitors to cisplatin-resistant cell. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1260.