Most of the classical drugs used today to destroy cancer cells lead to the development of acquired resistance in those cells by limiting cellular entry of the drugs or exporting them out by efflux pumps. As a result, higher doses of drugs are usually required to kill the cancer cells affecting normal cells and causing numerous side effects. Accumulation of the therapeutic level of drugs inside the cancer cells is thus required for an adequate period of time to get drugs' complete therapeutic efficacy minimizing the side effects on normal cells. In order to improve the efficacy of chemotherapeutic drugs, nanoparticles of carbonate apatite and its strontium (Sr(2+))-substituted derivative were used in this study to make complexes with three classical anticancer drugs, methotrexate, cyclophosphamide and 5-flurouracil. The binding affinities of these drugs to apatite were evaluated by absorbance and HPLC analysis and the therapeutic efficacy of drug-apatite complexes was determined by cell viability assay. Carbonate apatite demonstrated significant binding affinity towards methotrexate and cyclophosphamide leading to more cellular toxicity than free drugs in MCF-7 and 4T1 breast cancer cells. Moreover, Sr(2+) substitution in carbonate apatite with resulting tiny particles less than 100 nm in diameter further promoted binding of methotrexate to the nanocarriers indicating that Sr(2+)-substituted apatite nanoparticles have the high potential for loading substantial amount of anti-cancer drugs with eventual more therapeutic effectiveness.
Treatment of breast cancer, the second leading cause of female deaths worldwide, with classical drugs is often accompanied by treatment failure and relapse of disease condition. Development of chemoresistance and drug toxicity compels compromising the drug concentration below the threshold level with the consequence of therapeutic inefficacy. Moreover, amplification and over-activation of proto-oncogenes in tumor cells make the treatment more challenging. The oncogene, ROS1 which is highly expressed in diverse types of cancers including breast carcinoma, functions as a survival protein aiding cancer progression. Thus we speculated that selective silencing of ROS1 gene by carrier-mediated delivery of siRNA might sensitize the cancer cells to the classical drugs at a relatively low concentration. In this investigation we showed that intracellular delivery of c-ROS1-targeting siRNA using pH-sensitive inorganic nanoparticles of carbonate apatite sensitizes mouse breast cancer cells (4T1) to doxorubicin, but not to cisplatin or paclitaxel, with the highest enhancement in chemosensitivity obtained at 40 nM of the drug concentration. Although intravenous administrations of ROS1-loaded nanoparticles reduced growth of the tumor, a further substantial effect on growth retardation was noted when the mice were treated with the siRNA- and Dox-bound particles, thus suggesting that silencing of ROS1 gene could sensitize the mouse breast cancer cells both in vitro and in vivo to doxorubicin as a result of synergistic effect of the gene knockdown and the drug action, eventually preventing activation of the survival pathway protein, AKT1. Our findings therefore provide valuable insight into the potential cross-talk between the pathways of ROS1 and doxorubicin for future development of effective therapeutics for breast cancer.