Abstract 6558: Thymoquinone and epicatechin ameliorate the anticancer properties of tafuramycin-A against naïve and resistant breast cancer cells
Authors: Alshehri Ohoud Y. , Henidi Hanan A. , Alabbasi Fahad A. , El-Deeb Ibrahim M. , Halwani Majed A. , Al-Abd Ahmed M. 
Published: September 2020

Abstract
Tafuramycin-A (TAF) is naturally occurring duocarmycin-SA derivative with known DNA alkylating and/or intercalating potential. On the other hand, TAF possesses excessive and non-specific toxic properties. Epicatechin (EPI) and thymoquinone (TQ) are naturally occurring compounds with a wide range of biological activities, such as anticancer and chemomodulatory potentials. Herein, we temporally assessed the anti-breast cancer properties of TAF alone and in combination with EPI or TQ against naïve (MCF-7, MDA-MB-231 and T47D cells) and resistant breast cancer cells (MCF-7Adr). TAF alone showed very potent cell-killing properties against both naïve and resistant breast cancer cell lines in a time-dependent manner with IC50's ranging from 17 - 190 nM, 2 - 19 nM and 1 - 2 nM after 24 h, 48 h, and 72 h exposures, respectively. To a lesser extent, TQ alone showed moderate cytotoxic properties against all cell lines in a time-dependent manner with IC50's ranging from 4.4 - 18.9 µM, 2.8 - 16.5 µM and 2.1 - 22.7 µM after 24 h, 48 h, and 72 h exposures, respectively. EPI was the weakest in comparison to the previous two agents with IC50's above 100 µM in all cell lines in all durations of exposure. Except 24 h exposure of MDA-MB-231 cells, equitoxic combinations of TAF with TQ showed antagonistic interaction in all cells under investigation with combination indices ranging from 2 - 9.3, 1.3 - 3.7, 1.4 - 3.2 and 0.6 - 3.7 in MCF-7, MCF-7Adr, T47D, and MDA-MB-231 cells, respectively. Combination of TAF with 10 µM EPI did not induce any prominent enhancement in TAF cytotoxic properties. Cell cycle analysis using DNA content flow cytometry showed moderate S-phase and G2/M-phase partial arrest in response to treatment with TAF, TQ and their combinations. While treatment with EPI induced significant arrest in G0/G1-phase which is similar to its reported antiproliferative activity. Further analysis for the differential apoptosis/necrosis cell death using annexin-V/FITC with PI counterstain and coupled with flow cytometric analysis showed significant necrosis induction of TAF alone against breast cancer cells under investigation. Yet, a combination of TAF with TQ or EPI decreased the percentage of necrosis induced by TAF alone; however, it induced significant apoptosis cell death. Yet, the explanation for shifting breast cancer cell death from necrosis to apoptosis due to a combination of TAF with TQ or EPI is currently under molecular investigation and might constitute a high potential in utilizing TAF for the treatment of breast cancer.
Citation Format: Ohoud Y. Alshehri, Hanan A. Henidi, Fahad A. Alabbasi, Ibrahim M. El-Deeb, Majed A. Halwani, Ahmed M. Al-Abd. Thymoquinone and epicatechin ameliorate the anticancer properties of tafuramycin-A against naïve and resistant breast cancer cells [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6558.