Mediated Multidrug Resistance Reversal Research Articles

Reversal of Chemoresistance via Staged Liberation of Chemodrug and siRNA in Hierarchical Response to ROS Gradient.

P-glycoprotein (P-gp)-mediated multidrug resistance (MDR) often leads to the failure of antitumor chemotherapy, and codelivery of chemodrug with P-gp siRNA (siP-gp) represents a promising approach for treating chemoresistant tumors. To maximize the antitumor efficacy, it is desired that the chemodrug be latently released upon completion of siP-gp-mediated gene silencing, which however, largely remains an unmet demand. Herein, core-shell nanocomplexes (NCs) are developed to overcome MDR via staged liberation of siP-gp and chemodrug (doxorubicin, Dox) in hierarchical response to reactive oxygen species (ROS) concentration gradients. The NCs are constructed from mesoporous silica nanoparticles (MSNs) surface-decorated with cRGD-modified, PEGylated, ditellurium-crosslinked polyethylenimine (RPPT), wherein thioketal-linked dimeric doxorubicin (TK-Dox2) and photosensitizer are coencapsulated inside MSNs while siP-gp is embedded in the RPPT polymeric layer. RPPT with ultrahigh ROS-sensitivity can be efficiently degraded by the low-concentration ROS inside cancer cells to trigger siP-gp release. Upon siP-gp-mediated gene silencing and MDR reversal, light irradiation is performed to generate high-concentration, lethal amount of ROS, which cleaves thioketal with low ROS-sensitivity to liberate the monomeric Dox. Such a latent release profile greatly enhances Dox accumulation in Dox-resistant cancercells (MCF-7/ADR) in vitro and in vivo, which cooperates with the generated ROS to efficiently eradicate MCF-7/ADR xenograft tumors.

Pregnane steroid glycosides with multidrug resistance reversal activity from the stems of Marsdenia tenacissima

Eighteen previously unreported pregnane glycosides, namely marsdenosides S1–S18, along with 15 known analogues, have been isolated from the stems of Marsdenia tenacissima. The structures of the undescribed compounds were elucidated by spectroscopic means, and their absolute configurations were established on the basis of time-dependent density functional theory (TD-DFT) based electronic circular dichroism (ECD) calculation, X-ray crystallography and acid hydrolysis. All the isolates were evaluated for their chemo-reversal ability against P-glycoprotein (P-gp)-mediated multidrug resistance (MDR) in MCF-7/ADR cell line, and nine ones displayed moderate MDR reversal activity with reversal folds in the range of 2.45–9.01. The most active 12-O-acetyl-20-O-benzoyl-(14,17,18-orthoacetate)-dihydrosarcostin-3-O-β-d-thevetopyranosyl-(1 → 4)-O-β-d-oleandropyranosyl-(1 → 4)-O-β-d-cymaropyranoside increased the sensitivity of MCF-7/ADR cell to adriamycin comparably to the reference drug verapamil (RF = 8.93).

Pregnane steroids and steroid glycosides with multidrug resistance reversal activity from Marsdenia tenacissima

Twenty compounds comprising four pregnane steroids (2-4 & 20) and 16 pregnane glycosides (1 & 5-19) have been obtained from the ethanol extract of the roots of a Dai ethnological herb, Marsdenia tenacissima. Their structures were characterized on the basis of comprehensive spectroscopic analyses with 17 ones (1-17) being reported for the first time, including the rare cases (2 & 3) of free C21 steroids with 17α-acetyl substitution, compounds 4-7 bearing an unusual 14α-OH, and the first examples with simultaneous 14α-OH/17α-acetyl substitution (7) and glycosylation at C-12 position (10 & 11). An empirical rule for the identification of C-17 configuration, in C21 steroids incorporating the marsdenin constitution structure, was also proposed. All the isolates, along with an array of previously reported analogues in our compound library, were screened for their chemo-reversal ability against P-glycoprotein (P-gp)-mediated multidrug resistance (MDR) in MCF-7/ADR cell line, and six compounds exhibited moderate MDR reversal activity with reversal folds ranging from 1.92 to 4.44.

CDK6-PI3K signaling axis is an efficient target for attenuating ABCB1/P-gp mediated multi-drug resistance (MDR) in cancer cells

BackgroundMultidrug resistance (MDR) mediated by ATP binding cassette subfamily B member 1 (ABCB1/P-gp) is a major cause of cancer chemotherapy failure, but the regulation mechanisms are largely unknown.MethodsBased on single gene knockout, we studied the regulation of CDK6-PI3K axis on ABCB1-mediated MDR in human cancer cells. CRISPR/Cas9 technique was performed in KB-C2 cells to knockout cdk6 or cdk4 gene. Western blot, RT-PCR and transcriptome analysis were performed to investigate target gene deletion and expression of critical signaling factors. The effect of cdk4 or cdk6 deficiency on cell apoptosis and the cell cycle was analyzed using flow cytometry. In vivo studies were performed to study the sensitivity of KB-C2 tumors to doxorubicin, tumor growth and metastasis.ResultsDeficiency of cdk6 led to remarkable downregulation of ABCB1 expression and reversal of ABCB1-mediated MDR. Transcriptomic analysis revealed that CDK6 knockout regulated a series of signaling factors, among them, PI3K 110α and 110β, KRAS and MAPK10 were downregulated, and FOS-promoting cell autophagy and CXCL1-regulating multiple factors were upregulated. Notably, PI3K 110α/110β deficiency in-return downregulated CDK6 and the CDK6-PI3K axis synergizes in regulating ABCB1 expression, which strengthened the regulation of ABCB1 over single regulation by either CDK6 or PI3K 110α/110β. High frequency of alternative splicing (AS) of premature ABCB1 mRNA induced by CDK6, CDK4 or PI3K 110α/110β level change was confirmed to alter the ABCB1 level, among them 10 common skipped exon (SE) events were found. In vivo experiments demonstrated that loss of cdk6 remarkably increased the sensitivity of KB-C2 tumors to doxorubicin by increasing drug accumulation of the tumors, resulting in remarkable inhibition of tumor growth and metastasis, as well as KB-C2 survival in the nude mice.ConclusionsCDK6-PI3K as a new target signaling axis to reverse ABCB1-mediated MDR is reported for the first time in cancers. Pathways leading to inhibition of cancer cell proliferation were revealed to be accompanied by CDK6 deficiency.

Curcumin reverses doxorubicin resistance in colon cancer cells at the metabolic level

Doxorubicin (Dox) is commonly used for the treatment of malignant tumors, including colon cancer. However, the development of P-glycoprotein (P-gp)-mediated multidrug resistance (MDR) in tumor chemotherapy has seriously reduced the therapeutic efficacy of Dox. Natural product curcumin (Cur) was demonstrated to have a variety of pharmacological effects, such as anti-tumor, anti-oxidation and anti-aging activities. Here, we examined the MDR reversal capability of Cur in drug sensitive-(SW620) and resistant-(SW620/Ad300) colon cancer cells, and elucidated the underlying molecular mechanisms at the metabolic level. It was found that Cur reversed P-gp-mediated resistance in SW620/Ad300 cells by enhancing the Dox-induced cytotoxicity and apoptosis. Further mechanistic studies indicated that Cur inhibited the ATP-dependent transport activity of P-gp, thereby increasing the intra-celluar accumulation of Dox in drug-resistant cells. Metabolomics analysis based on UPLC-MS/MS showed that the MDR phenomenon in SW620/Ad300 cells was closely correlated with the upregulation of spermine and spermidine synthesis and D-glutamine metabolism. Cur significantly inhibited the biosynthesis of spermine and spermidine by decreasing the expression of ornithine decarboxylase (ODC) and suppressed D-glutamine metabolism, which in turn decreased the anti-oxidative stress ability and P-gp transport activity of SW620/Ad300 cells, eventually reversed MDR. These findings indicated the MDR reversal activity and the related mechanism of action of Cur, suggesting that Cur could be a promising MDR reversal agent for cancer treatment.

Design, Synthesis and Biological Evaluation of Dimethyl Cardamonin (DMC) Derivatives as P-glycoprotein-mediated Multidrug Resistance Reversal Agents

Background: P-glycoprotein (P-gp) has been regarded as an important factor in the multidrug resistance (MDR) of tumor cells within the last decade, which can be solved by inhibiting Pgp to reverse MDR. Thus, it is an effective strategy to develop inhibitor of P-gp. Objective: In this study, the synthesis of a series of derivatives had been carried out by bioisosterism design on the basis of Dimethyl Cardamonin (DMC). Subsequently, we evaluated their reversal activities as potential P-glycoprotein (P-gp)-mediated Multidrug Resistance (MDR) agents. Methods: Dimethyl cardamonin derivatives were synthesized from acetophenones and the corresponding benzaldehydes in the presence of 40% KOH by Claisen-Schmidt reaction. Their cytotoxicity and reversal activities in vitro were assessed with MTT. Moreover, the compound B4 was evaluated by Doxorubicin (DOX) accumulation, Western blot and wound-healing assays deeply. Results and Conclusion: The results showed that compounds B2, B4 and B6 had the potency of MDR reversers with little intrinsic cytotoxicity. Meanwhile, these compounds also demonstrated the capability to inhibit MCF-7 and MCF-7/DOX cells migration. Besides, the most compound B4 was selected for further study, which promoted the accumulation of DOX in MCF-7/DOX cells and inhibited the expressionof P-gp at protein levels. Conclusion: The above findings may provide new insights for the research and development of Pgp- mediated MDR reversal agents.

Quercetin overcomes colon cancer cells resistance to chemotherapy by inhibiting solute carrier family 1, member 5 transporter

P-glycoprotein (P-gp)-mediated multidrug resistance (MDR) remains a significant impediment to the success of cancer chemotherapy. The natural flavonoid Quercetin (Que) has been reported to be able to inhibit P-gp-mediated MDR in various cancer cells. However, the MDR reversal effect of Que on human colon cancer cells and its mechanism at the metabolic level requires further clarification. This study was designed to provide a better understanding of the MDR reversal effect of Que. Our present results showed that 33 μM of Que significantly improved the cytotoxicity of doxorubicin (Dox) to P-gp-overexpressed SW620/Ad300 cells by proliferation and apoptpsis assay. Further mechanism studies demonstrated that Que inhibited the ATP-driven transport activity of P-gp, which in turn increased the intracellular accumulation of Dox. The metabolomics studies based on UPLC-MS/MS analysis revealed that Que could reverse the MDR by significantly blocking D-glutamine and D-glutamate metabolism, and the underlying mechanism is that Que down-regulated the expression of the glutamine transporter solute sarrier family 1, member 5 (SLC1A5) in SW620/Ad300 cells. This is the first time to report that Que was a SLC1A5 inhibitor, which could be served as a template compound to potentially develop novel P-gp-mediated MDR reversal modulators in cancer chemotherapy.

Dual P-Glycoprotein and CA XII Inhibitors: A New Strategy to Reverse the P-gp Mediated Multidrug Resistance (MDR) in Cancer Cells.

A new series of N,N-bis(alkanol)amine aryl diesters was synthesized and studied as dual P-glycoprotein (P-gp) and carbonic anhydrase XII inhibitors (CA XII). These hybrids should be able to synergistically overcome P-gp mediated multidrug resistance (MDR) in cancer cells. It was reported that the efflux activity of P-gp could be modulated by CA XII, as the pH reduction caused by CA XII inhibition produces a significant decrease in P-gp ATPase activity. The new compounds reported here feature both P-gp and CA XII binding moieties. These hybrids contain a N,N-bis(alkanol)amine diester scaffold found in P-glycoprotein ligands and a coumarin or benzene sulfonamide moiety to target CA XII. Many compounds displayed a dual activity against P-gp and CA XII being active in the Rhd 123 uptake test on K562/DOX cells and in the hCA XII inhibition test. On LoVo/DOX cells, that overexpress both P-gp and CA XII, some coumarin derivatives showed a high MDR reversal effect in Rhd 123 uptake and doxorubicin cytotoxicity enhancement tests. In particular, compounds 7 and 8 showed higher activity than verapamil and were more potent on LoVo/DOX than on K562/DOX cells overexpressing only P-gp. They can be considered as valuable candidates for selective P-gp/CA XII inhibition in MDR cancer cells.

Novel virosecurinine bivalent mimetics as potent reversal agents against P-glycoprotein-mediated multidrug resistance

Multidrug resistance (MDR) is a main cause of chemotherapy failure and patient death. This situation usually involves a glycoprotein (P-gp) mediated drug efflux, resulting in a low cellular drug concentration and insensitivity. Here we report the design, synthesis and evaluation of novel (+/−)-securinine bivalents as P-gp inhibitors in vitro and in vivo. MTT assays reflected that bivalent mimetics of securinine particularly the virosecurinine bivalent mimetic 8C showed promissing MDR reversal potential in both P-gp highly expressed cell line HepG2/DOX and MCF-7/ADM. At a 10 μM concentration, 8C can entirely reverse the resistance of HepG2/DOX to doxorubicin (DOX), and is more effective than the positive control verapamil (VRP). Fluorescence, flow cytometry, and DOX efflux assays demonstrated that 8C can facilitate the accumulation and diminish the efflux of intracellular DOX. Molecular docking analysis and western blot assays indicated that 8C accomplished this by competitively inhibiting the activity of P-gp rather than by affecting its expression. Compound 8C was also observed to reverse drug resistance effectively in xenograft models when combined with DOX. This study lays a foundation for the discovery of (+/−)-securinine ramifications as P-gp inhibitors and provides a promising lead compound 8C as a P-gp mediated MDR reversal agent.

Interactions between artemisinin derivatives and P-glycoprotein

BackgroundArtemisinin was isolated and identified in 1972, which was the starting point for a new era in antimalarial drug therapy. Furthermore, numerous studies have demonstrated that artemisinin and its derivatives exhibit considerable anticancer activity both in vitro, in vivo, and even in clinical Phase I/II trials. P-glycoprotein (P-gp) mediated multi-drug resistance (MDR) is one of the most serious causes of chemotherapy failure in cancer treatment. Interestingly, many artemisinin derivatives exhibit excellent ability to overcome P-gp mediated MDR and even show collateral sensitivity against MDR cancer cells. Furthermore, some artemisinin derivatives show P-gp-mediated MDR reversal activity. Therefore, the interaction between P-gp and artemisinin derivatives is important to develop novel combination treatment protocols with artemisinin derivatives and established anticancer drugs that are P-gp substrates. PurposeThis systematic review provides an updated overview on the interaction between artemisinin derivatives and P-gp and the effect of artemisinin derivatives on the P-gp expression level. ResultsArtemisinin derivatives exhibit multi-specific interactions with P-gp. The currently used artemisinin derivatives are not transported by P-gp. However, some of novel synthetized artemisinin derivatives exhibit P-gp substrate properties. Furthermore, many artemisinin derivatives act as P-gp inhibitors, which exhibit the potential to reverse MDR towards clinically used anticancer drugs. ConclusionTherefore, studies on the interaction between artemisinin derivatives and P-gp provide important information for the development of novel anti-cancer artemisinin derivatives to reverse P-gp mediated MDR and for the design of rational artemisinin-based combination therapies against cancer.

Discovery of aromatic amides with triazole-core as potent reversal agents against P-glycoprotein-mediated multidrug resistance

P-glycoprotein (P-gp)-mediated multidrug resistance (MDR) is a major impediment for clinical cancer therapy. 19 novel aromatic amides with triazole-core as MDR reversal agents were designed and synthesized via click chemistry to reverse MDR. Among them, compound 42 was identified as the most promising candidate with high potency (EC50 = 78.1 ± 5.4 nM), low cytotoxity (SI > 1282) and persistent duration in reversing doxorubicin (DOX) resistance in K562/A02 cells. 42 also enhanced the potency of other P-gp associated cytotoxic agents with different structures. In further study, remarkably increased intracellular accumulation of Rh123 and DOX in K562/A02 cells was achieved by compound 42, while CYP3A4 activity had no change by compound 42. These results indicate that compound 42 as a relatively safe modulator of P-gp-mediated MDR has good potential for further development.

Mesoporous polydopamine nanoparticles with co-delivery function for overcoming multidrug resistance via synergistic chemo-photothermal therapy.

Theranostic agents for combined chemo-photothermal therapy have attracted intensive interest in the treatment of multi-drug resistance (MDR) in cancer therapy. However, the development of simple theranostic agents as dual hosts for both heat and a high payload of chemotherapeutic agents remains a big challenge. Herein, mesoporous polydopamine nanoparticles (MPDA) were successfully developed with properties of a high payload of DOX (up to 2000 μg mg-1) and the drug efflux inhibitor TPGS (d-α-tocopheryl polyethylene glycol 1000 succinate), as well as strong near-infrared absorption. Particularly, DOX and TPGS were sequentially loaded in the pore space and on the external particle surface of MPDA via π-π stacking and hydrophobic interactions, resulting in a MPDA-DOX@TPGS complex. The DOX release observably relies on the pH value and glutathione (GSH). Furthermore, it is possible to accelerate the rate of drug release by NIR irradiation. Importantly, the MPDA-DOX@TPGS complex was found to escape from endosomes after cellular uptake and release the loaded drugs into the cytosol. By TPGS mediated MDR reversal, the delivered DOX induced significant cytotoxicity to MCF-7/ADR cells. Besides, MPDA can absorb the NIR light and convert it into fatal heat to kill the cancer cells. As a consequence, the combined therapy in our system yields a synergistic effect with high therapeutic efficacy.

Osthole shows the potential to overcome P-glycoprotein‑mediated multidrug resistance in human myelogenous leukemia K562/ADM cells by inhibiting the PI3K/Akt signaling pathway.

P-glycoprotein (P-gp)-mediated multidrug resistance (MDR) has been reported to play a pivotal role in tumorchemotherapy failure. Study after study has illustrated that the phosphoinositide 3-kinase (PI3K)/Akt signaling cascade is involved in the MDR phenotype and is correlated with P-gp expression in many human malignancies. In the present study, osthole, an O-methylated coumarin, exhibited potent reversal capability of MDR in myelogenous leukemia K562/ADM cells. Simultaneously, the uptake and efflux of Rhodamine-123 (Rh-123) and the accumulation of doxorubicin assays combined with flow cytometric analysis suggested that osthole could increase intracellular drug accumulation. Furthermore, osthole decreased the expression of multidrug resistance gene1 (MDR1) at both the mRNA and protein levels. Further experiments elucidated that osthole could suppress P-gp expression by inhibiting the PI3K/Akt signaling pathway which might be the main mechanism accounting for the reversal potential of osthole in the MDR in K562/ADM cells. In conclusion, osthole combats MDR and could be a promising candidate for the development of novel MDR reversal modulators.

Cabozantinib reverses multidrug resistance of human hepatoma HepG2/adr cells by modulating the function of P‐glycoprotein

Cabozantinib, a small-molecule multitargeted tyrosine kinase inhibitor, has entered into a phase III clinical trial for the treatment of hepatocellular carcinoma (HCC). This study assessed the mechanistic effect of cabozantinib on the reversal of P-glycoprotein (P-gp)-mediated multidrug resistance (MDR). CCK-8 assays and tumour xenografts were used to investigate the reversal of MDR in vitro and in vivo respectively. Substrate retention assays were evaluated by fluorescence microscope and flow cytometry. Western blotting was used to detect protein expression levels. mRNA expression was determined by qPCR. The ATPase activity of P-gp was investigated using Pgp-Glo(™) assay systems. The binding mechanism of cabozantinib to P-gp at the molecular level was evaluated using docking analysis. Cabozantinib enhanced the cytotoxicity of P-gp substrate drugs in HepG2/adr and HEK293-MDR1 cells but had no effect on non-P-gp substrates. In addition, cabozantinib increased the accumulation of P-gp substrates in HepG2/adr cells but had no effect in HepG2 cells. Furthermore, cabozantinib did not alter the expression of P-gp mRNA or protein but did stimulate the activity of P-gp ATPase. The docking study indicated that cabozantinib and verapamil may partially share a binding site on P-gp. The reversal concentrations of cabozantinib did not affect the expression of MET, AKT and ERK1/2. Significantly, cabozantinib increased the inhibitory efficacy of doxorubicin in P-gp-overexpressing HepG2/adr cell xenografts in nude mice. Cabozantinib reverses P-gp-mediated MDR by directly inhibiting the efflux function of P-gp, indicating that cabozantinib may help to reverse P-gp-mediated MDR in HCC and other cancer chemotherapy.

Synthesis and evaluation of substituted dibenzo[c,e]azepine-5-ones as P-glycoprotein-mediated multidrug resistance reversal agents

A series of substituted dibenzo[c,e]azepine-5-ones (7a–h) were synthesized and evaluated as P-glycoprotein (P-gp)-mediated multidrug resistance (MDR) reversal agents. The most potent compound 7h could significantly and selectively enhance the chemo-sensitivity of drug-resistant K562/A02 cells to the cytotoxic effect of adriamycin (ADR) in a dose-dependent manner. Further studies indicated that 7h could markedly increase intracellular accumulation of both rhodamine 123 and ADR in K562/A02 cells and inhibit their efflux from the cells. And 7h had little effect on the levels of P-gp mRNA and protein in K562/A02 cells. These results suggest that the anti-MDR effect of 7h might be attributed to the inhibition of drug efflux function of P-gp, leading to the increased drug accumulation in K562/A02 cells, and thus the compound could be served as a lead for developing P-gp-mediated MDR reversal agents.

Perifosine downregulates MDR1 gene expression and reverses multidrug-resistant phenotype by inhibiting PI3K/Akt/NF-κB signaling pathway in a human breast cancer cell line

P-glycoprotein (P-gp)-mediated multidrug resistance (MDR) is the major clinical impediment to chemotherapy of breast cancers. Down-regulation of PI3K/Akt pathway has been described as related to reversal of MDR in cancer cells. Here, we investigated the reversal effect on MDR phenotype of perifosine, a new Akt inhibitor, in breast cancer cell lines. In this study, MCF-7/ADM cells and MCF-7 cells were treated with different concentrations of perifosine. Our results suggested that perifosine reversed MDR partially by downregulation of P-gp expression and inhibition of PI3K/Akt/NF-κB pathway in the MCF-7/ADM cell line. The novel Akt inhibitor perifosine may be a promising new drug due to its ability to reverse MDR in human breast cancer cells.

Substituted tetrahydroisoquinoline compound B3 inhibited P-glycoprotein-mediated multidrug resistance in-vitro and in-vivo

P-glycoprotein (P-gp) mediated multidrug resistance (MDR) is one of the main obstacles in tumour chemotherapy. A promising approach to reverse MDR is the combined use of nontoxic and potent P-gp inhibitor with conventional anticancer drugs. We have examined the potential of a newly synthesized tetrahydroisoquinoline derivative B3 as a MDR-reversing agent. The MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay was used to examine the effect of B3 on the cytotoxicity in K562/A02 and MCF-7/ADM cells caused by doxorubicin (adriamycin). Accumulation and efflux of P-gp substrate rhodamine123 in K562/A02 and primary cultured rat brain microvessel endothelial cells (RBMECs) were measured to evaluate the inhibitory effect of B3 on P-gp. The K562/A02 xenograft model in nude mice was established to examine MDR-reversing efficacy of B3 in-vivo. The results indicated that co-administration of B3 resulted in an increase on chemosensitivity of K562/A02 and MCF-7/ADM cells to doxorubicin in a dose-dependent manner. Rhodamine123 accumulation in K562/A02 cells and RBMECs were significantly enhanced after the incubation with various concentrations of B3. Furthermore, B3 inhibited the efflux of rhodamine123 from RBMECs. Co-administration of B3 with doxorubicin significantly decreased weight and volume of tumour in nude mice. In conclusion, B3 is a novel and potent MDR reversal agent with the potential to be an adjunctive agent for tumour chemotherapy.

Aporphine alkaloids and their reversal activity of multidrug resistance (MDR) from the stems and rhizomes ofSinomenium acutum

Chromatographic separation of the MeOH extract from the stems and rhizomes of Sinomemium acutum led to the isolation of nine alkaloids and a lignan. Their structures were determined to be dauriporphine (1), bianfugecine (2), dauriporphinoline (3), menisporphine (4), (-)-syringaresinol (5), N-feruloyltyramine (6), acutumine (7), dauricumine (8), sinomenine (9), and magnoflorine (10) by spectroscopic means. These compounds were examined for their P-gp mediated MDR reversal activity in human cancer cells. Compound 1 showed the most potent P-gp MDR inhibition activity with an ED50 value 0.03 microg/mL and 0.00010 microg/mL in the MES-SA/DX5 and HCT15 cells, respectively.

Correlation of calculated molecular orbital energies of some phenothiazine compounds with MDR reversal properties

Molecular orbital energies of energetically minimized series of extended aromatic and aminoalkyl side chain substituted phenothiazine compounds have been considered with respect to charge transfer (CT) binding properties to P-glycoprotein (P-gp) amino acids of the first P-gp loop. A dependency of decreasing energies of lowest unoccupied orbitals ( E lumo) with reduced CT binding properties to an increasing P-gp mediated multidrug resistance (MDR) has been found for the extended aromatic compounds.

Reversal of MRP-mediated vincristine resistance in KB cells by buthionine sulfoximine in combination with PAK-104P

The mechanism of multidrug resistance protein (MRP)-mediated multidrug resistance (MDR) is still unclear. MRP reportedly transports some GSH conjugates. Recently, we demonstrated that a pyridine analog, 2-[4-(diphenylmethyl)-1-piperazinyl]ethyl 5-(trans-4,6-dimethyl-1,3,2-dioxaphosphorinan-2-yl)-2,6-dimethyl-4-(3-nitrophenyl)-3-pyridinecarboxylate P-oxide (PAK-104P), that reversed P-glycoprotein (P-gp)-mediated MDR directly interacted with MRP and completely reversed the vincristine (VCR) resistance in MRP-mediated MDR C-A120 cells. We investigated the reversing effect of PAK-104P in C-A120 cells in combination with buthionine sulfoximine (BSO), another MDR-reversing agent with a different reversing mechanism. In immunoblots, MRP was overexpressed in C-A120 cells. The level of ATP-dependent [ 3H]VCR uptake was high in membrane vesicles from KB-C2 cells, but low in those from C-A120 and parental KB-3-1 cells. The sensitivity to VCR of C-A120 cells, but not of KB-C2 cells, was considerably increased by 100 μM BSO. VCR accumulation in C-A120 cells, but not in KB-C2 cells, was also enhanced by BSO. BSO did not inhibit ATP-dependent [ 3H]LTC 4 uptake in C-A120 vesicles. The combination of BSO with PAK-104P at their low concentrations resulted in complete reversal of VCR resistance in C-A120 cells. These findings suggested that BSO might not directly interact with MRP and reversed resistance in MRP-mediated MDR cells by reducing the intracellular glutathione (GSH) level that was needed for the transport of drugs by MRP and suggested a role for the combination of drug resistance-modulating agents with different reversing mechanisms in the reversal of MRP-mediated MDR.