P-glycoprotein (P-gp) is a drug transporter that effluxes chemotherapeutic drugs and is implicated in the development of resistance of cancer cells to chemotherapeutic drugs. To date, no drug has been approved to inhibit P-gp and restore chemotherapy efficacy. Moreover, majority of the reported inhibitors have high molecular weight and complex structures, making it difficult to understand the basic structural requirement for P-gp inhibition. In this study, two structurally simple, low molecular weight piperine analogs Pip1 and Pip2 were designed and found to better interact with P-gp than piperine in silico. A one step, acid-amine coupling reaction between piperic acid and 6,7-dimethoxytetrahydroisoquinoline or 2-(3,4-dimethoxyphenyl)ethylamine afforded Pip1 and Pip2, respectively. In vitro testing in drug resistant P-gp overexpressing KB (cervical) and SW480 (colon) cancer cells showed that both analogs, when co-administered with vincristine, colchicine or paclitaxel were able to reverse the resistance. Moreover, accumulation of P-gp substrate (rhodamine 123) in the resistant cells, a result of alteration of the P-gp efflux, was also observed. These investigations suggest that the natural product analog – Pip1 ((2E,4E)-5-(benzo[d][1,3]dioxol-5-yl)-1-(6,7-dimethoxy-3,4-dihydroisoquinolin-2(1 H)-yl)penta-2,4-dien-1-one) – is superior to piperine and could inhibit P-gp function. Further studies are required to explore the full potential of Pip1 in treating drug resistant cancer.
A major impediment for cancer chemotherapy is the development of multidrug-resistance (MDR). Continuous use of chemotherapeutic drugs during cancer therapy induces the expression of PGlycoprotein (P-gp, MDR1), an ATP dependant transporter, which in turn reduces the intracellular accumulation of chemotherapeutic drugs leading to MDR. Extensive research over the years has identified several potential P-gp inhibitors, both synthetic as well as natural origin, to overcome the MDR during cancer chemotherapy. In this review, we discuss the cellular pathways involved and transcription factors regulating the expression of P-gp. A number of phytochemicals are reported to inhibit P-gp activity and MDR1 expression; the structure-activity relationship (SAR) among the phytochemicals for P-gp inhibition and the effect of these phytochemicals on cellular signaling pathways regulating P-gp expression are discussed in detail. Moreover, structural biology and mutagenesis studies on P-gp along with docking studies throw light on the structural requirements for P-gp inhibition. Insight provided in the review about the phytochemicals molecular mechanism and SAR could catalyze the design of potent P-gp inhibitors in the future and could help to overcome MDR in cancer chemotherapy.
Understanding the molecular mode of action of natural product is a key step for developing drugs from them. In this regard, this study is aimed to understand the molecular-level interactions of chemical constituents of Clerodendrum colebrookianum Walp., with anti-hypertensive drug targets using computational approaches. The plant has ethno-medicinal importance for the treatment of hypertension and reported to show activity against anti-hypertensive drug targets-Rho-associated coiled-coil protein kinase (ROCK), angiotensin-converting enzyme, and phosphodiesterase 5 (PDE5). Docking studies showed that three chemical constituents (acteoside, martinoside, and osmanthuside β6) out of 21 reported from the plant to interact with the anti-hypertensive drug targets with good glide score. In addition, they formed H-bond interactions with the key residues Met156/Met157 of ROCK I/ROCK II and Gln817 of PDE5. Further, molecular dynamics (MD) simulation of protein-ligand complexes suggest that H-bond interactions between acteoside/osmanthuside β6 and Met156/Met157 (ROCK I/ROCK II), acteoside and Gln817 (PDE5) were stable. The present investigation suggests that the anti-hypertensive activity of the plant is due to the interaction of acteoside and osmanthuside β6 with ROCK and PDE5 drug targets. The identified molecular mode of binding of the plant constituents could help to design new drugs to treat hypertension.
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