The intracellular distribution and transportation process are essential for maintaining PD-L1 (programmed death-ligand 1) expression, and intervening in this cellular process may provide promising therapeutic strategies. Here, through a cell-based high content screening, it is found that the ABCB1 (ATP binding cassette subfamily B member 1) modulator zosuquidar dramatically suppresses PD-L1 expression by triggering its autophagic degradation. Mechanistically, ABCB1 interacts with PD-L1 and impairs COP II-mediated PD-L1 transport from ER (endoplasmic reticulum) to Golgi apparatus. The treatment of zosuquidar enhances ABCB1-PD-L1 interaction and leads the ER retention of PD-L1, which is subsequently degraded in the SQSTM1-dependent selective autophagy pathway. In CT26 mouse model and a humanized xenograft mouse model, zosuquidar significantly suppresses tumor growth and accompanies by increased infiltration of cytotoxic T cells. In summary, this study indicates that ABCB1 serves as a negative regulator of PD-L1, and zosuquidar may act as a potential immunotherapy agent by triggering PD-L1 degradation in the early secretory pathway.

UNASSIGNED: In lung transplant patients, direct oral anticoagulants are often taken in combination with immunosuppressive drugs such as tacrolimus. Since tacrolimus is a substrate and inhibitor of the efflux protein ABCB1, also transporting direct oral anticoagulants, a possible drug-drug interaction mediated by competition for this transporter needs to be investigated.
UNASSIGNED: To determine the in vitro effect of tacrolimus on ABCB1-mediated rivaroxaban transport in order to support clinician practice.
UNASSIGNED: Recombinant cell line models, based on human embryonic kidney 293 cells, were generated by a stable transfection process to overexpress ABCB1 or not (control cells). The impact of tacrolimus on ABCB1-mediated rivaroxaban transport was assessed by accumulation experiments.
UNASSIGNED: ABCB1 expression decreased the cellular accumulation of rivaroxaban and tacrolimus at their respective clinically relevant concentrations when compared with control cells. This confirms the involvement of ABCB1 in the active transport of tacrolimus and rivaroxaban. However, tacrolimus had no significant influence on rivaroxaban disposition at those clinically relevant concentrations.
UNASSIGNED: Our study does not provide evidence for a possible interaction between tacrolimus and rivaroxaban when used together in practice.

Gefitinib is a selective inhibitor of the epidermal growth factor receptor that is used to treat advanced and metastatic non-small cell lung cancer (NSCLC). Dermatological adverse reactions are most commonly associated with gefitinib treatment. The cause of adverse reactions in individuals is multifactorial. Pharmacogenetics is an effective tool to detect such adverse reactions. This case report describes a female patient with NSCLC who was administered gefitinib at a dose of 250 mg/day. However, due to severe adverse dermatological reactions, the treatment was interrupted for 15 d and antibiotic therapy was administered to manage the skin rashes, maculopapular rashes, and hyperpigmentation. Treatment adherence was adequate, and no drug interactions were detected. A pharmacogenetic analysis revealed homozygosity in the ATP-binding cassette (ABC)-B1 rs1128503 (c.1236A>G), heterozygosity in ABCG2 rs2231142 (c.421G>T) and rs2622604 (c.-20+614T>C), and a non-functional variant of the cytochrome P450 family 3, subfamily A, member 5 (CYP3A5). The relationship between altered genetic variants and the presence of adverse reactions induced by gefitinib is still controversial. Overall, this case report highlights the importance of continuing to study pharmacogenetics as predictors of adverse drug reactions.

Human P-glycoprotein (P-gp) utilizes energy from ATP hydrolysis for the efflux of chemically dissimilar amphipathic small molecules and plays an important role in the development of resistance to chemotherapeutic agents in most cancers. Efforts to overcome drug resistance have focused on inhibiting P-gp-mediated drug efflux. Understanding the features distinguishing P-gp inhibitors from substrates is critical. Cryo-electron microscopy has revealed distinct binding patterns, emphasizing the role of the L-site or access tunnel in inhibition. We substituted 5-9 residues of the L-site with alanine to investigate whether the binding of a second inhibitor molecule to the L-site is required for inhibiting drug efflux. We reveal, for the first time, that mutations in the L-site affect the drug efflux activity of P-gp, despite their distance from the substrate-binding pocket (SBP). Surprisingly, after the mutations were introduced, inhibitors such as tariquidar and zosuquidar still inhibited drug efflux by mutant P-gps. Communication between the transmembrane helices (TMHs) and nucleotide-binding domains (NBDs) was evaluated using the ATPase assay, revealing distinct modulation patterns by inhibitors for the mutants, with zosuquidar exhibiting substrate-like stimulation of ATPase. Furthermore, L-site mutations abolished ATP-dependent thermal stabilization. In silico molecular docking studies corroborated the altered inhibitor binding due to mutations in the L-site residues, shedding light on their critical role in substrate transport and inhibitor interactions with P-gp. These findings suggest that inhibitors bind either to the SBP alone, and/or to alternate site(s) when the L-site is disabled by mutagenesis.

The drug efflux transporter P-glycoprotein, encoded by the ABCB1 gene, promotes acquired chemoresistance. We explored the presence and clinical relevance of circulating cell-free ABCB1 transcripts (cfABCB1tx) in ovarian cancer patients (173 longitudinal serum samples from 79 cancer patients) using digital droplet PCR. cfABCB1tx were readily detectable at primary diagnosis (median 354 mRNA copies/20 µl serum), paralleled FIGO-stage and predicted surgical outcome (p = 0.023, p=0.022, respectively). Increased cfABCB1tx levels at primary diagnosis indicated poor PFS (HR = 2.329, 95%CI:1.374-3.947, p = 0.0017) and OS (HR = 2.074, 95%CI:1.194-3.601, p = 0.0096). cfABCB1tx induction under platinum-based chemotherapy was an independent predictor for poor OS (HR = 2.597, 95%CI: 1.218-5.538, p = 0.013) and paralelled a micrometastatic phenotype, shaped by the presence of disseminated tumor cells in the bone marrow. A strong correlation was observed between cfABCB1tx and circulating transcripts of the metastasis-inducer MACC1, which is the transcriptional activator of ABCB1. Combined assessment of cfABCB1tx and circulating cell-free MACC1 transcripts (cfMACC1tx) resulted in an improved prognostic prediction, with  the cfABCB1tx-high/cfMACC1tx-high phenotype bearing the highest risk for relapse and death. Conclusively, we provide proof of principle, that ABCB1 transcripts are readily traceable in the liquid-biopsy of ovarian cancer patients, advancing a new dimension for systemic monitoring of ABCB1/P-glycoprotein expression dynamics.

Drug transporters play a pivotal role in modulating drug disposition and are subject to alterations under inflammatory conditions. This study aimed to elucidate the intricate expression patterns of drug transporters during both acute and chronic inflammation, which are closely linked to malignant transformation. To investigate acute inflammation, we employed an in vitro model by subjecting Caco-2 cells to various inflammatory stimuli (IL-1β, TNF-α, or LPS) individually or in combination. The successful induction of inflammation was confirmed by robust increases in IL-6 and NO production. Notably, inflamed Caco-2 cells exhibited significantly diminished levels of ABCB1 and ABCG2, while the expression of ABCC2 was upregulated. For chronic inflammation induction in vivo, we employed the well-established AOM/DSS mouse model known for its association with colitis-driven tumorigenesis. Persistent inflammation was effectively monitored throughout the experiment via elevated IL-6 and NO levels. The sequential stages of tumorigenesis were confirmed through Ki-67 immunohistochemistry. Intriguingly, we observed gradual alterations in the expression patterns of the studied drug transporters during stepwise induction, with ABCB1, ABCG2, and ABCC1 showing downregulation and ABCC2 exhibiting upregulation. Immunohistochemistry further revealed dynamic changes in the expression of ABCB1 and ABCC2 during the induction cycles, closely paralleling the gradual increase in Ki-67 expression observed during the development of precancerous lesions. Collectively, our findings underscore the significant impact of inflammation on drug transporter expression, potentially influencing the process of malignant transformation of the colon.

The P-glycoprotein (ABCB1)-mediated multidrug resistance (MDR) has emerged as a significant impediment to the efficacy of cancer chemotherapy in clinical therapy, which could promote the development of effective agents for MDR reversal. In this work, we reported the exploration of novel pyrazolo [1,5-a]pyrimidine derivatives as potent reversal agents capable of enhancing the sensitivity of ABCB1-mediated MDR MCF-7/ADR cells to paclitaxel (PTX). Among them, compound 16q remarkably increased the sensitivity of MCF-7/ADR cells to PTX at 5 μM (IC50 = 27.00 nM, RF = 247.40) and 10 μM (IC50 = 10.07 nM, RF = 663.44). Compound 16q could effectively bind and stabilize ABCB1, and does not affect the expression and subcellular localization of ABCB1 in MCF-7/ADR cells. Compound 16q inhibited the function of ABCB1, thereby increasing PTX accumulation, and interrupting the accumulation and efflux of the ABCB1-mediated Rh123, thus resulting in exhibiting good reversal effects. In addition, due to the potent reversal effects of compound 16q, the abilities of PTX to inhibit tubulin depolymerization, and induce cell cycle arrest and apoptosis in MCF-7/ADR cells under low-dose conditions were restored. These results indicate that compound 16q might be a promising potent reversal agent capable of revising ABCB1-mediated MDR, and pyrazolo [1,5-a]pyrimidine might represent a novel scaffold for the discovery of new ABCB1-mediated MDR reversal agents.

BACKGROUND: Pharmacotherapy for brain diseases is severely compromised by the blood-brain barrier (BBB). ABCB1 and ABCG2 are drug transporters that restrict drug entry into the brain and their inhibition can be used as a strategy to boost drug delivery and pharmacotherapy for brain diseases.
METHODS: We employed elacridar and tariquidar in mice to explore the conditions for effective inhibition at the BBB. Abcg2;Abcb1a/b knockout (KO), Abcb1a/b KO, Abcg2 KO and wild-type (WT) mice received a 3 h i.p. infusion of a cocktail of 8 typical substrate drugs in combination with elacridar or tariquidar at a range of doses. Abcg2;Abcb1a/b KO mice were used as the reference for complete inhibition, while single KO mice were used to assess the potency to inhibit the remaining transporter. Brain and plasma drug levels were measured by LC-MS/MS.
RESULTS: Complete inhibition of ABCB1 at the BBB is achieved when the elacridar plasma level reaches 1200 nM, whereas tariquidar requires at least 4000 nM. Inhibition of ABCG2 is more difficult. Elacridar inhibits ABCG2-mediated efflux of weak but not strong ABCG2 substrates. Strikingly, tariquidar does not enhance the brain uptake of any ABCG2-subtrate drug. Similarly, elacridar, but not tariquidar, was able to inhibit its own brain efflux in ABCG2-proficient mice. The plasma protein binding of elacridar and tariquidar was very high but similar in mouse and human plasma, facilitating the translation of mouse data to humans.
CONCLUSIONS: This work shows that elacridar is an effective pharmacokinetic-enhancer for the brain delivery of ABCB1 and weaker ABCG2 substrate drugs when a plasma concentration of 1200 nM is exceeded.

UNASSIGNED: Allelic variants of genes encoding enzymes of the esterase system (CES1) and P-glycoprotein (ABCB1) can change the metabolism and pharmacokinetics of dabigatran. Therefore, they act as determining factors in the development of side effects, especially bleeding. We analyzed the genotype-phenotype relationship of ABCB1 (rs1045642, rs4148738, rs2032582, and rs1128503) and CES1 (rs8192935, rs71647871, and rs2244613) polymorphisms in patients with atrial fibrillation who had been treated with dabigatran.
UNASSIGNED: A total of 150 patients were recruited for this study. TaqMan technology was used for SNP genotyping.
UNASSIGNED: Patients with the rs2244613 GG genotype had a lower concentration (55.27 ± 34.22 ng/ml) compared to those with the TT genotype (63.33 ± 52.25 ng/ml) (additive model, P = 0.000). Individuals with the rs8192935 AA genotype had a lower concentration (52.72 ± 30.45 ng/ml) compared to those with the GG genotype (79.78 ± 57 ng/ml) (additive model, P = 0.001). The APTT values among the different genotypes of the ABCB1 SNPs, rs4148738 and rs1045642, were significantly different (P = 0.035 and P = 0.024, respectively).
UNASSIGNED: Our research demonstrates that the CES1 polymorphisms, rs8192935 and rs2244613, are associated with the pharmacodynamics and pharmacokinetics of dabigatran in the Kazakh subpopulation.

Paclitaxel is commonly used to treat breast, ovarian, lung, esophageal, gastric, pancreatic cancer, and neck cancer cells. Cancer recurrence is observed in patients treated with paclitaxel due to paclitaxel resistance emergence. Resistant mechanisms are observed in cancer cells treated with paclitaxel, docetaxel, and cabazitaxel including changes in the target molecule β-tubulin of mitosis, molecular mechanisms that activate efflux drug out of the cells, and alterations in regulatory proteins of apoptosis. This review discusses new molecular mechanisms of taxane resistance, such as overexpression of genes like the multidrug resistance genes and EDIL3, ABCB1, MRP1, and TRAG-3/CSAG2 genes. Moreover, significant lncRNAs are detected in paclitaxel resistance, such as lncRNA H19 and cross-resistance between taxanes. This review contributed to discovering new treatment strategies for taxane resistance and increasing the responsiveness of cancer cells toward chemotherapeutic drugs.