Potential use of the PARP inhibitor rucaparib to enhance cervical cancer treatment

Background: Cervical cancer (CC) is the fourth most common cancer in women worldwide. In the UK, peak age of CC is 30–35 years and 10-years survival is ~63%. Standard treatment for locally advanced CC is chemoradiotherapy (CTRT) with cisplatin (weekly 40 mg/m2 × 5). However, cisplatin-induced kidney toxicity results in discontinuation of the treatment. The poly(ADP-ribose) polymerase inhibitors (PARPi) targeting homologous recombination repair deficient breast and ovarian cancers are clinically used although, chemo-radio sensitising property of PARPi has widened their therapeutic application. Here we investigate the potential of the PARPi rucaparib to increase the therapeutic index of CTRT by reducing kidney toxicity and increasing cisplatin and radiation cytotoxicity.
Methods: 1) Cytotoxicity of cisplatin (0.1 μM) and radiation/IR and in combination with rucaparib (1 μM) was assessed in HeLa cells by clonogenic assay. 2) The maximum tolerated dose (MTD) of cisplatin 10–20 mg/kg i.p. (day 1 X1) causing acute kidney toxicity (AKT) in 5 days was determined in wild type CD1 female mice. 3) Low dose of rucaparib (1 mg/kg i.p. days 1–5) was given with the MTD of cisplatin (10 mg/kg i.p. day 1) to test any reduction of cisplatin-induced AKT. For toxicity study, mice were monitored for piloerection, hunching and body weight loss. Pathological examination was done with FFPE kidney tissues for H&E, PAS staining and AKT biomarker Lipocalin-2 by IHC. Mechanism of cisplatin-induced PARP activation (PAR levels) by oxidative stress (4HNE) was studied by IHC. Regions of kidney sections from IHC data was quantified by Leica Aperio ImageScopeTM.
Results: 1) The effect of CTRT at 2 Gy IR in HeLa cell was potentiated ~1.3-fold by rucaparib. 2) The MTD of cisplatin causing AKT was 10 mg/kg (human equivalent dose 30 mg/m2). Compared to saline, cisplatin increased Lipocalin-2 expression at the kidney’s cortex regions (cortex: ~19 fold vs. medulla: ~2 fold), PAR level was also found significantly elevated at the cortex (cortex: ~9 fold vs. medulla: ~1.5 fold). Whereas, 4-HNE was higher at kidney’s medulla regions (medulla: ~2 fold vs. cortex: ~1.25 fold). Compared to cisplatin treatment, rucaparib 1 mg/kg reduced PAR levels (cortex: ~5.5 fold, medulla: ~1.7 fold) and cisplatin-induced AKT measured with the reduction in Lipocalin-2 (cortex: ~6 fold, medulla: ~4 fold). Rucaparib did not affect cisplatin-induced oxidative stress and 4-HNE levels were not significantly altered.
Conclusion: Rucaparib showed chemo-radio sensitisation in CC cell line HeLa. In mice treated with cisplatin there was an increase in oxidative stress throughout the kidney but PARP hyperactivation and toxicity was observed primarily in the kidney cortex. Rucaparib protected from cisplatin induced AKT. Combination of rucaparib with conventional CTRT can contribute new therapeutic strategies in CC treatment.