Combinatorial Treatment with Chlorogenic Acid and Cinnamaldehyde Disrupts Intracellular pH and Metabolic Transport in...

Breast cancer cells exhibit a reversed pH gradient and metabolic plasticity that promote proliferation, invasion, and resistance to therapy. Natural products such as chlorogenic acid (CGA) and cinnamaldehyde (CA) have shown emerging anticancer potential. However, their effects on intracellular pH and metabolic transport systems remain undefined. Therefore, the aim of this study was to characterize these parameters in breast cancer and non-tumorigenic breast cells. This study evaluated the physiochemical properties of CGA and CA using LC-MS, under pH conditions (pH 1.2, 7.4, and 9.0) mimicking the gastrointestinal track (GIT). Additionally, LC-MS-based human liver microsome (HLM) assays with NADPH were used to evaluate susceptibility to CYP-mediated metabolism to evaluate first-pass metabolic stability. Intracellular uptake kinetics were quantified at multiple time points using LC-MS. Following CGA:CA treatment, intracellular pH (pH_i) was measured in cancerous MDA-MB-231 and non-tumorigenic MCF-10A breast cell lines using SNARF-1 targeted ratio-metric fluorescence approach. Expression of OATP1B1, GLUT1, and MCT1 were analyzed by Western and immunofluorescence respectively, to assess potential cellular uptake of CGA:CA through OATP1B1 and their effects on glucose uptake and lactate and proton transport. Physiochemical results demonstrated that the compounds ranged from fully stable (pH 1.2 and 7.4) to completely unstable (pH 9.0). HLM incubation indicated no CYP-mediated hepatic metabolism. Treatment results showed that there was rapid intracellular uptake of CGA and CA in cancer cells and that CGA:CA lowered pH_i in both MDA-MB-231 and MCF-7 cells, while pH_i remained mostly unchanged in MCF-10A cells. Protein analysis revealed that CGA:CA treatment downregulated GLUT1 and MCT1 expression in cancer cells, suggesting impaired glycolytic activity and lactate shuttling. OATP1B1 expression was significantly suppressed in cancer cells, suggesting feedback inhibition of the solute carrier protein. Collectively, these findings indicate that CGA and CA exhibit favorable biochemical stability and disrupt intracellular pH regulation and metabolic transporter expression in breast cancer cells. Importantly, normal cells are not significantly affected. Thus, CGA:CA demonstrates therapeutic potential for breast cancer through pH_i and metabolic modulation.