Abstract

Background

Approximately 50% of epithelial ovarian cancers (EOC) harbor defect in the homologous recombination pathway of DNA repair (HRD) and are sensitive to platinum / PARP inhibitors (PARPi). However, HR competent (HRC) tumours are chemo resistant; combination modalities are proposed to compromise HR function and restore chemo response.

We propose a mechanism whereby mechanical/ pharmacological reactive oxygen species (ROS) induction which is modulated by NRF2 activation and therefore requires BRCA1 trapping, will lead to functional HR loss (HRD) and restore chemoresponse. We studied the effect of mahanine, a ROS generating molecule in ovarian cancer cell lines and primary cultures as a pilot project.

Method

We showed ROS generation with mahanine in dose dependant mannaer in PA1 cell line.. Primary cultures were developed from ascites (PCAST) from consecutive patients of EOC (WT1 and PAX8 positive on immunocytochemistry) undergoing primary surgery; all patients received 6 cycles of platinum based chemotherapy subsequently. MTT cytotoxicity assay was performed using increasing dosage of mahanine.

Results

: Clinicopathological features of 8 patients and IC50 of mahanine in ascetic fluid cultures is presented: 

Serial no

Stage and histology

Platinum resistance at 6 months

IC 50

mahanine

PCAST-1

IIIC HGCS

no

34.7 ± 0.02

PCAST-3

IVC HGSC

yes

19.6 ± 0.5

PCAST-4

IIIC HGSC

no

28.5 ± 0.08

PCAST-6

IIIB (Clear cell)

no

23.2± 0.02

PCAST-12

IIIC (HGSC)

no

23.2 ± 0.01

PCAST-14

IIIC (HGSC)

yes

22.3 ± 0.02 

PCAST-15

IIIC (HGSC)

no

30 ± 0.5

PCAST-16

IVB (HGSC)

no

27.4 ± 0.15

Conclusion

ROS generating agent mahanine shows cytotoxicity in primary cells in EOC; we propose to present  future work in HRD and HRC EOC and mechanistic studies to show ROS-NFR2-BRCA1 interaction with a view to devise novel combination strategies with PARPi in HRC. Surgical ROS generating strategies will be explored in ongoing studies