Structural diversity of the cardenolide calotropin renders it as a targeted therapy for harnessing TNBC progression through tuning nitric oxide (NO) levels

Abstract

Background: Triple negative breast cancer (TNBC) is the most aggressive breast cancer (BC) subtype. It has the worst prognosis, highest recurrence and metastatic rates. Due to the clinical and molecular heterogeneity of TNBC, there is an emerging need to identify new molecular therapeutic targets. Nitric oxide (NO) has a dual role in cancer depending on its levels. At low concentrations, NO promotes tumor growth, while at high concentrations, NO has an anti-neoplastic function. Natural compounds have emerged as signaling pathways' regulators in various tumors. Cardenolides specifically have potent cytotoxic effects in different cancers as lung and liver cancer. Our group has isolated the cardenolides, Calotropin and 7,8-dehydrocalotropin from Calotropisgigantea (L.) Dryand (Apocyanaceae). Calotropin showed potent cytotoxicy against non-small cell lung cancer, glioblastoma and prostate cancer, but has never been investigated against BC. Our aim was to investigate the anticancer effects of the isolated compounds on MDA-MB-231 TNBC cells by functional characterization and unravel their role in regulating NO levels in BC. Method(s): MDA-MB-231 cells were treated with serial dilutions (1, 5, 10, 20, 60 and 100 lM) of calotropin and 7,8-dehydrocalotropin. Their cytotoxic activities were assessed using MTT for cellular viability and IC50 values were obtained. Cellular migration and colony forming ability were measured using scratch and colony forming assays, respectively. NO production was measured using Greiss reagent. Result(s): Both calotropin and 7,8-dehydrocalotropin were able to decrease cellular viability, migration and colony formation of MDA-MB-231 cells in a dose-dependent manner. Calotropin reduced NO levels in MDA-MB-231 cells. However 7,8-dehydrocalotropin did not have any significant effects in regulating NO. Conclusion(s): Calotropin showed more potent cytotoxicity on MDA-MB-231 cells compared to 7,8-dehydrocalotropin. Calotropin acts as a negative regulator of NO production, whereas 7,8-dehydrocalotropin failed to regulate NO production. This could be attributed to the structural difference between both compounds. Thus calotropin can be developed as a targeted therapy against BC.