Increased sensitivity of BRCA defective triple negative breast tumors to plumbagin through induction of DNA Double Strand Breaks (DSB)

Rakesh Sathish Nair,Thapasimuthu V Anilkumar,Priya Srinivas,Jedy Jose,Jerald Mahesh Kumar,Satheesh Kumar Sengodan,Sreelatha K Hemalatha,Veena Somasundaram,Revathy Nadhan

doi:10.1038/srep26631

Abstract

We have earlier shown that Plumbagin (PB) can induce selective cytotoxicity to BRCA1 defective ovarian cancer cells; however, the effect of this molecule in BRCA1 mutated breast cancers has not been analyzed yet. Here, we report that reactive oxygen species (ROS) induced by PB resulted in DNA DSB and activates downstream signaling by ATR/ATM kinases and subsequent apoptosis. PB reduces DNA- dependent protein kinase (DNA-PK) expression and inhibits NHEJ (Non Homologous End Joining) activity in BRCA1 defective breast cancer cells. Also, PB induces apoptosis in two different BRCA1 conditional knock out murine models: MMTV-Cre; BRCA1Co/Co and WAP-Cre; BRCA1Co/Co, at 2 mg/kg body weight, but 32 mg/kg of carboplatin (CN) was needed to induce apoptosis in them. This is the first study where two different tissue specific promoter driven transgenic mice models with BRCA1 exon 11 deletions are used for preclinical drug testing. The apoptosis induced by PB in HR (Homologous Recombination) defective triple negative BRCA1 mutant cell lines and in mouse models occur by inducing ROS mediated DNA DSB. The toxicity profile as compared with CN in transgenic mice provides evidence for PB’s safer disposition as a therapeutic lead in breast cancer drug development.

Highlights

BRCA1 germline mutations have been identified in nearly 50% of hereditary breast cancers and 80% of cases with both hereditary breast and ovarian cancers
For anti-proliferative analysis, both HCC1937 and MX1 cells were reconstituted with wild type BRCA1GFP plasmid and cytotoxicity of PB was analyzed by MTT assay
These results corroborate that PB induces cytotoxicity at a lower concentration in BRCA1 defective breast cancer cells in comparison to malignant as well as nonmalignant breast cells expressing wild type BRCA1

Summary

Introduction

BRCA1 germline mutations have been identified in nearly 50% of hereditary breast cancers and 80% of cases with both hereditary breast and ovarian cancers. Results Wild type BRCA1 reconstitution reduces the sensitivity towards PB in BRCA1 mutated breast cancer cells. PB induces ROS, resulting in the expression of antioxidant response element Nrf1/2; defective HR due to absence of wild type BRCA1 might still cause DNA DSB.

Results

Conclusion