Combinatory Effect of Jerantinine A and Chemotherapeutic Agent in Regulating Spliceosome in Breast Cancer Stem Cells and Non-Stem Breast Cancer Cells

Background: Breast cancer is the second most common cancer and is afflicting women globally. Current standard regimen of chemotherapy includes 2 main classes of drug anthracycline (e.g., doxorubicin) and taxane (e.g., paclitaxel). Two main issues are associated with these drugs: toxicity and recurrence. The former issue warrants for search of novel compounds which preferably synergize with the existing chemotherapeutic agents. Whereas the latter prompts researchers to test their anticancer compounds against breast cancer stem cells (BCSCs), which is the culprit behind tumorigenesis. In a preliminary study, an indole alkaloid compound named Jerantinine A (JA) was found to have anticancer effect on breast cancer cells. The effect was mediated by disruption of splicing in the cancer cells. The key spliceosome component involved was splicing factor 3b subunit 1 (SF3b1). Aim: In current study, we further investigated whether JA had similar inhibitory effect on BCSCs. Also, if such inhibitory effect was mediated by SF3b1 too. Lastly, we explored the drug combination effect of doxorubicin and JA. Methods: Cell proliferative assay was used to determine viability of BCSCs, which would indicate the inhibitory effect of JA. On the other hand, quantitative polymerase chain reaction (qPCR) was used in detection of disrupted spliceosome activity, especially that associated with SF3b1. With respect to drug combination effect, the Chou and Talalay method was used in the relevant analysis. Results: Results showed that JA had inhibitory effect on BCSCs in vitro. Such effect was mediated by SF3b1, as shown by accumulation of 4 associated unspliced premRNAs (e.g., RIOK3, BRD2, DNAJB1, CDKN1B) in quantitative-PCR (qPCR). Lastly, based on the combined index (CI) and drug reduction index (DRI), we concluded that JA not only could synergize with doxorubicin but also sensitized BCSCs to the effect of doxorubicin. Conclusion: There was a main caveat, which was the ratio of JA against doxorubicin; only at certain ratios did the combinatory effect therefor hold promising. Nonetheless, our findings provided basis for future studies to look further into the potential of JA in alleviating cardiotoxicity issue of doxorubicin and the roles of spliceosome in breast cancer.