Background: Cancer cells notoriously escape radiation therapy, chemotherapy, hormonal therapy, and other anti-cancer therapies. Among various breast cancer subtypes, triple negative breast cancers (TNBCs) are known for their poor clinical outcome and dearth of effective targeted therapies due to the absence of druggable receptors. Cold atmospheric plasma (CAP) holds promise as a cancer-specific treatment agent that selectively kills basal-like/TN breast cancer cells.

Method: In this study, we used plasma-activated media (PAM) to capture and store the multi-modal chemical species of CAP, which significantly expands the treatment scope and flexibility of plasma medicine as a clinical therapeutic approach. The PAM was diluted into different doses and cells were treated for 12 or 24 hours. The effects of PAM on cell viability and ROS levels in 9 different cell lines; normal cells (MCF-10A and HEK-293T), luminal breast cancer cell lines (MCF-7, T47D, HCC70), and TNBC cell lines (MDA-MB-468, SUM-159PT, SUM-149PT, MDA-MB-231), were assessed.

Results: The results showed that TNBC cells were more highly sensitive, in a dose-dependent manner, to PAM treatment. PAM selectively caused apoptosis of TNBC cell lines compared to luminal lines and had little effect on the normal cell lines. It has been hypothesised that the cancer-selective CAP and PAM cytotoxicity is due in part to reactive oxygen (ROS) and nitrogen species (RNS). Constitutive RONS levels, combined with those present in and/or induced by PAM, can combine to push the cells over a cytotoxic threshold. In support of this, we found a tight correlation (R2=0.7502) between the constitutive ROS level of different cell lines used and their response (cell viability) to 100% PAM treatment, and found that ROS levels selectively increased further in the TNBC>luminal>normal cells in response to PAM. We have also identified a strong synergistic molecular partner that further promotes sensitivity and selectivity of PAM for TNBC cells.

Conclusion: We demonstrated that treatment with PAM promotes apoptosis n cell lines representing the most aggressive TNBC subtype. This discovery opens new TNBC-selective opportunities for simultaneous inhibition of diverse (parallel) cancer development factors through synergistic interactions enabled through plasma activated biochemical media.