Cancer is a disease which results when the cellular changes cause the uncontrolled cell growth and cell division. While breast cancer is the most common cancer amongst women, Triple negative breast cancer (TNBC) is one of its subtypes which is characterized by the absence of estrogen receptor (ER) and progesterone receptor (PR) as well as the absence of overexpression of human epidermal growth factor receptor-2 (Her2). Hence, it is unresponsive to hormonal and HER-2 targeted antibody therapy. TNBC is also characterized by poor overall survival time, predominantly due to unavailability for specific therapy and certain patients initially responding to the cytotoxic drugs exhibit high rates of systemic relapse in the early stages and decreased overall survival times. This may be due to the drug resistance arising from the overexpression of the drug-efflux pumps of ATP-binding cassette(ABC) transporter family which includes MDR associated transporter P-glycoprotein (MDR-1) or MDR- associated protein (MRP) and so, there is an immediate requirement for development of novel model for analysis of mechanisms to bypass MDR in TNBC.
P-glycoprotein, which is a glycosylated transmembrane protein, encoded by the MDR1 gene is highly expressed in healthy human organs and is the best studied drug efflux pump of ABC transporters family. It protects against xenobiotics and its overexpression in cancers results in reduced accumulation of anti-cancer drugs and leads to resistance of many available chemotherapeutics. Hence, inclusion of a P-gp inhibitor along with the therapeutic agent was found to be efficacious in overall survival and relapse rate. These inhibitors like Verapamil, are known to block the pumping action of P-gp. Cell mortality was also found to increase when the anti-cancer drugs were used in combination with P-gp inhibitors.
In this study, Rhodamine-6-G is used as a P-gp substrate which is also a fluorescent dye binding to the inner membrane of mitochondria and produces fluorescent images of mitochondria with high resolution and low background noise. This binding decreases the mitochondrial enzymatic activity in turn inhibiting the oxidative phosphorylation and causing reduce in number of active mitochondria. Hence, this leads to cell suffocation or death due to prohibition of respiratory chain.
The negatively charged citrate capped gold nanoparticles are used as carriers for the cationic R-6G dyes. These nanoparticles exhibit excitation of free electrons known as localized surface plasmon resonance (LSPR) giving rise to optical absorption and scattering. The LSPR bands of the R-6G dye-AuNp composite systems overlap with each other. The gold nanoparticles decrease the fluorescence power and fluorescence quantum yield and increases the absorbance and absorbed power of R-6G. Also, the dye induces the gold nanoparticles aggregates formation at different dilutions. The nanoparticles are preferred as they remain lodged in the tumor core for longer period of time due to enhanced permeation caused by vasculature and lymphatic leakage resulting from abnormal blood vessel growth. This effect was termed as Enhanced permeability and retention effect (EPR).
In this study, gold nanoparticles are being used to analyze if they could decrease the efflux of P-gp substrates which is R-6G in this case and also if it there is increase in efficiency of these agents in MDR cancer. The cell lines used in this study, MDA MB 231 were purchased from ATCC which was derived from the metastatic site of mammary gland with adenocarcinoma disease.
