Reversal of multidrug resistance by valinomycin is overcome by CCCP

Network analysis, sequence and structure dynamics of key proteins of coronavirus and human host, and molecular docking of selected phytochemicals of nine medicinal plants

The novel coronavirus of 2019 (nCoV-19) has become a pandemic, affecting over 205 nations with over 7,410,000 confirmed cases which has resulted to over 418,000 deaths worldwide. This study aimed to identify potential therapeutic compounds and phytochemicals of medicinal plants that have potential to modulate the expression network of genes that are involve in SARS-CoV-2 pathology in human host and to understand the dynamics key proteins involved in the virus-host interactions. The method used include gene network analysis, molecular docking, and sequence and structure dynamics simulations. The results identified DNA-dependent protein kinase (DNA-PK) and Protein kinase CK2 as key players in SARS-CoV-2 lifecycle. Among the predicted drugs compounds, clemizole, monorden, spironolactone and tanespimycin showed high binding energies; among the studied repurposing compounds, remdesivir, simeprevir and valinomycin showed high binding energies; among the predicted acidic compounds, acetylursolic acid and hardwickiic acid gave high binding energies; while among the studied anthraquinones and glycosides compounds, ellagitannin and friedelanone showed high binding energies against 3-Chymotrypsin-like protease (3CL^pro), Papain-like protease (PL^pro), helicase (nsp13), RNA-dependent RNA polymerase (nsp12), 2'-O-ribose methyltransferase (nsp16) of SARS-CoV-2 and DNA-PK and CK2alpha in human. The order of affinity for CoV proteins is 5Y3E > 6NUS > 6JYT > 2XYR > 3VB6. Finally, medicinal plants with phytochemicals such as caffeine, ellagic acid, quercetin and their derivatives could possibly remediate COVID-19.Communicated by Ramaswamy H. Sarma.

New insights into the P-glycoprotein-mediated effluxes of rhodamines

Multidrug resistance (MDR) in tumour cells is often caused by the overexpression of the plasma drug transporter P-glycoprotein (P-gp). This protein is an active efflux pump for chemotherapeutic drugs, natural products and hydrophobic peptides. Despite the advances of recent years, we still have an unclear view of the molecular mechanism by which P-gp transports such a wide diversity of compounds across the membrane. Measurement of the kinetic characteristics of substrate transport is a powerful approach to enhancing our understanding of their function and mechanism. The aim of the present study was to further characterize the transport of several rhodamine analogues, either positively charged or zwitterionic. We took advantage of the intrinsic fluorescence of rhodamines and performed a flow-cytometric analysis of dye accumulation in the wild-type drug sensitive K562 that do not express P-gp and its MDR subline that display high levels of MDR. The measurements were made in real time using intact cells. The kinetic parameter, ka = VM/km, which is a measure of the efficiency of the P-gp-mediated efflux of a substrate was similar for almost all the rhodamine analogues tested. In addition these values were compared with those determined previously for the P-gp-mediated efflux of anthracycline. Our conclusion is that the compounds of these two classes of molecules, anthracyclines and rhodamines, are substrates of P-gp and that their pumping rates at limiting low substrate concentration are similar. The findings presented here are the first to show quantitative information about the kinetic parameters for P-gp-mediated efflux of rhodamine analogues in intact cells.

The medicinal chemistry of multidrug resistance (MDR) reversing drugs

Multidrug resistance (MDR) is a kind of resistance of cancer cells to multiple classes of chemotherapic drugs that can be structurally and mechanistically unrelated. Classical MDR regards altered membrane transport that results in lower cell concentrations of cytotoxic drug and is related to the over expression of a variety of proteins that act as ATP-dependent extrusion pumps. P-glycoprotein (Pgp) and multidrug resistance protein (MRP1) are the most important and widely studied members of the family that belongs to the ABC superfamily of transporters. It is apparent that, besides their role in cancer cell resistance, these proteins have multiple physiological functions as well, since they are expressed also in many important non-tumoural tissues and are largely present in prokaryotic organisms. A number of drugs have been identified which are able to reverse the effects of Pgp, MRPI and sister proteins, on multidrug resistance. The first MDR modulators discovered and studied in clinical trials were endowed with definite pharmacological actions so that the doses required to overcome MDR were associated with unacceptably high side effects. As a consequence, much attention has been focused on developing more potent and selective modulators with proper potency, selectivity and pharmacokinetics that can be used at lower doses. Several novel MDR reversing agents (also known as chemosensitisers) are currently undergoing clinical evaluation for the treatment of resistant tumours. This review is concerned with the medicinal chemistry of MDR reversers, with particular attention to the drugs that are presently in development.

A method for studying plasma membrane transport with intact cells using computerized fluorometry

A new method is presented for measuring rapid efflux of fluorescent compounds from monolayer cells. Cells grown on a glass coverslip were loaded with a fluorescent substrate. Thereafter, the coverslip was installed outside the light path in a stirred and thermostated cuvette of a fluorometer. The efflux was recorded by measuring the changes of fluorescence in the extracellular medium. The method was used to study the kinetics of active and passive plasma membrane transport of the P-glycoprotein substrates rhodamine 123 and daunorubicin. The method has advantages over other methods: (1) no radioactively labeled substrate is needed, (2) fluorescence of the transported substrate is not compromised by the cells, (3) changes in the extracellular concentration of the substrate can be monitored continuously and therefore a substantial improvement of the kinetic resolution is obtained, and (4) the measurement setup is relatively simple and a standard fluorometer can be used. From the efflux data, cellular transport parameters could be calculated, such as passive permeation coefficients and active transport rates.

Positively cooperative sites for drug transport by P-glycoprotein with distinct drug specificities

In this paper, we show that P-glycoprotein contains two distinct sites for drug binding and transport, and that, unexpectedly, these sites interact in a positively cooperative manner. The kinetics of transport of rhodamine 123 and Hoechst 33342 in isolated P-glycoprotein-rich plasma membrane vesicles from Chinese hamster ovary CH(R)B30 cells were followed by continuous fluorescence monitoring. Each substrate stimulated P-glycoprotein-mediated transport of the other. Colchicine and quercetin stimulated rhodamine 123 transport and inhibited Hoechst 33342 transport. In contrast, anthracyclines such as daunorubicin and doxorubicin stimulated Hoechst 33342 transport and inhibited rhodamine 123 transport. Vinblastine, actinomycin D, and etoposide inhibited transport of both dyes. The results are consistent with a functional model of P-glycoprotein containing at least two positively cooperative sites (H site and R site) for drug binding and transport. This model is consistent with earlier observations of competitive and non-competitive effects of P-glycoprotein substrates and chemosensitizers. Such a two-site model may be fundamental to multidrug transport by P-glycoprotein, and it may be a feature common to other ATP-dependent transporters belonging to the ATP-binding cassette superfamily.