Development of non-clinical methods for secretion of medicines into human breast milk

Abstract

This Master’s research project mainly investigated whether the chlorophyll metabolite, pheophorbide A (PhA) can be used as a breast cancer resistance protein (BCRP) substrate to screen in vitro for transporter-mediated interaction with and without inhibitor, and whether that could be used to mimic and generalize the mechanism of all BCRP substrate medicines that can be taken up by breastfeeding women by using an uptake assay. PhA is chlorophyll breakdown product and used as a photosensitizer. The best approach is to develop an analysis method using fluorescence intensity to measure cytoplasm concentration of pheophorbide A. However, due to the limitation of equipment, an alternative absorbance-based analysis method was applied to measure cytoplasm concentration. The overall cytoplasm concentration of pheophorbide A was greater in BCPR inhibited MCF-7 cells compared with MCF-7 cells directly treated with PhA due to the lack of PhA efflux via BCRP. The area under the absorbance ratio-time curves up to two hours (AUC_(0-2h)) of PhA treatment is 2.4 times in the inhibitor treated MCF-7 cells compared with untreated cells, and the PhA cytoplasm concentration was 3.7-fold greater in inhibitor treated MCF-7 cells. Pretreatment with known BCRP inhibitor lapatinib at clinically relevant doses according to IC_50 value, significantly increased PhA AUC_(absorbance 0-2 h) by 2.7-fold, whereas the area under PhA cytoplasm concentration-time curve calculated up to two hours (AUC_(cytoplasm 0-2h)) increased by 13.8-fold as in vitro BCRP inhibitors. The results show that uptake using PhA can be potentially used to assess the potential for BCRP-mediated medicine uptake and its mechanism for breastfeeding women.