Modulating the function of ATP-binding cassette subfamily G member 2 (ABCG2) with inhibitor cabozantinib

c-MET tyrosine kinase inhibitors reverse drug resistance mediated by the ATP-binding cassette transporter B1 (ABCB1) in cancer cells

This study investigated the potential of MET kinase inhibitors, cabozantinib, crizotinib, and PHA665752, in reversing multidrug resistance (MDR) mediated by ABCB1 in cancer cells. The accumulation of the fluorescent probe, Rhodamine 123, was assessed using flow cytometry and fluorescence microscopy in MDR MES-SA/DX5 and parental cells. The growth inhibitory activity of MET inhibitors as monotherapies and in combination with chemotherapeutic drugs was evaluated by MTT assay. CalcuSyn software was used to analyze the combination index (CI) as an index of drug-drug interaction in combination treatments. Results showed that at concentrations of 5, and 25 μM, c-MET inhibitors significantly increased Rhodamine 123 accumulation in MDR cells, with ratios up to 17.8 compared to control cells, while exhibiting no effect in parental cells. Additionally, the combination of c-MET inhibitors with the chemotherapeutic agent doxorubicin synergistically enhanced cytotoxicity in MDR cells, as evidenced by combination index (CI) values of 0.54 ± 0.08, 0.69 ± 0.1, and 0.85 ± 0.07 for cabozantinib, crizotinib, and PHA665752, respectively. While all three c-MET inhibitors stimulated ABCB1 ATPase activity in different manners at certain concentrations, PHA-665752 suppressed it at high concentration. In silico analysis also suggested that the transmembrane domains (TMD) of ABCB1 transporters could be considered potential target for these agents. Our results suggest that c-MET inhibitors can serve as promising MDR reversal agents in ABCB1-medicated drug-resistant cancer cells.

Sensitizing cholangiocarcinoma to chemotherapy by inhibition of the drug-export pump MRP3

AIMS

Drug export through ABC proteins hinders cancer response to chemotherapy. Here, we have evaluated the relevance of MRP3 (ABCC3) in cholangiocarcinoma (CCA) as a potential target to overcome drug resistance.

METHODS

Gene expression was analyzed in silico using the TCGA-CHOL database and experimentally (mRNA and protein) in resected CCA tumors. The effect of manipulating MRP3 function/expression was evaluated in vitro and in vivo.

RESULTS

High MRP3 expression at the plasma membrane of human CCA cells was found. MRP3 overexpression in HEK293T cells selectively impaired the cytotoxic effect of etoposide, cisplatin, SN-38, and mitoxantrone. Reduced MRP3 activity with shRNAs or pan-MRP blockers enhanced the sensitivity to these drugs. MRP3 interaction with natural and semisynthetic compounds (≈40,000) was evaluated by virtual drug screening and molecular docking. Two identified potential MRP3 inhibitors (EM-114, EM-188), and sorafenib impaired MRP3 transport activity and enhanced sensitivity of CCA cells to etoposide and cisplatin. The antitumor effect of cisplatin in the mouse xenograft model was enhanced by co-treatment with sorafenib, which was accompanied by a higher intratumor accumulation of cisplatin.

CONCLUSIONS

Genetic and pharmacological MRP3 inhibition enhances the anti-CCA effect of several drugs, which constitutes a promising strategy to improve the response to chemotherapy in CCA patients.

Strategies to enhance the response of liver cancer to pharmacological treatments

In contrast to other types of cancers, there is no available efficient pharmacological treatment to improve the outcomes of patients suffering from major primary liver cancers, i.e., hepatocellular carcinoma and cholangiocarcinoma. This dismal situation is partly due to the existence in these tumors of many different and synergistic mechanisms of resistance, accounting for the lack of response of these patients, not only to classical chemotherapy but also to more modern pharmacological agents based on the inhibition of tyrosine kinase receptors (TKIs) and the stimulation of the immune response against the tumor using immune checkpoint inhibitors (ICIs). This review summarizes the efforts to develop strategies to overcome this severe limitation, including searching for novel drugs derived from synthetic, semisynthetic, or natural products with vectorial properties against therapeutic targets to increase drug uptake or reduce drug export from cancer cells. Besides, immunotherapy is a promising line of research that is already starting to be implemented in clinical practice. Although less successful than in other cancers, the foreseen future for this strategy in treating liver cancers is considerable. Similarly, the pharmacological inhibition of epigenetic targets is highly promising. Many novel "epidrugs," able to act on "writer," "reader," and "eraser" epigenetic players, are currently being evaluated in preclinical and clinical studies. Finally, gene therapy is a broad field of research in the fight against liver cancer chemoresistance, based on the impressive advances recently achieved in gene manipulation. In sum, although the present is still dismal, there is reason for hope in the non-too-distant future.

A first-in-class β-glucuronidase responsive conjugate for selective dual targeted and photodynamic therapy of bladder cancer

In this report, we present a novel prodrug strategy that can significantly improve the efficiency and selectivity of combined therapy for bladder cancer. Our approach involved the synthesis of a conjugate based on a chlorin-e6 photosensitizer and a derivative of the tyrosine kinase inhibitor cabozantinib, linked by a β-glucuronidase-responsive linker. Upon activation by β-glucuronidase, which is overproduced in various tumors and localized in lysosomes, this conjugate released both therapeutic modules within targeted cells. This activation was accompanied by the recovery of its fluorescence and the generation of reactive oxygen species. Investigation of photodynamic and dark toxicity in vitro revealed that the novel conjugate had an excellent safety profile and was able to inhibit tumor cells proliferation at submicromolar concentrations. Additionally, combined therapy effects were also observed in 3D models of tumor growth, demonstrating synergistic suppression through the activation of both photodynamic and targeted therapy.

Overexpression of ABCC1 and ABCG2 confers resistance to talazoparib, a poly (ADP-Ribose) polymerase inhibitor

AIMS

The overexpression of ABC transporters on cancer cell membranes is one of the most common causes of multidrug resistance (MDR). This study investigates the impact of ABCC1 and ABCG2 on the resistance to talazoparib (BMN-673), a potent poly (ADP-ribose) polymerase (PARP) inhibitor, in ovarian cancer treatment.

METHODS

The cell viability test was used to indicate the effect of talazoparib in different cell lines. Computational molecular docking analysis was conducted to simulate the interaction between talazoparib and ABCC1 or ABCG2. The mechanism of talazoparib resistance was investigated by constructing talazoparib-resistant subline A2780/T4 from A2780 through drug selection with gradually increasing talazoparib concentration.

RESULTS

Talazoparib cytotoxicity decreased in drug-selected or gene-transfected cell lines overexpressing ABCC1 or ABCG2 but can be restored by ABCC1 or ABCG2 inhibitors. Talazoparib competitively inhibited substrate drug efflux activity of ABCC1 or ABCG2. Upregulated ABCC1 and ABCG2 protein expression on the plasma membrane of A2780/T4 cells enhances resistance to other substrate drugs, which could be overcome by the knockout of either gene. In vivo experiments confirmed the retention of drug-resistant characteristics in tumor xenograft mouse models.

CONCLUSIONS

The therapeutic efficacy of talazoparib in cancer may be compromised by its susceptibility to MDR, which is attributed to its interactions with the ABCC1 or ABCG2 transporters. The overexpression of these transporters can potentially diminish the therapeutic impact of talazoparib in cancer treatment.

Foretinib, a c-MET receptor tyrosine kinase inhibitor, tackles multidrug resistance in cancer cells by inhibiting ABCB1 and ABCG2 transporters

BACKGROUND

ABC transporter-mediated multidrug resistance (MDR) remains a major obstacle for cancer pharmacological treatment. Some tyrosine kinase inhibitors (TKIs) have been shown to reverse MDR. The present study was designed to evaluate for the first time whether foretinib, a multitargeted TKI, can circumvent ABCB1 and ABCG2-mediated MDR in treatment-resistant cancer models.

METHODS

Accumulation of fluorescent substrates of ABCB1 and ABCG2 in ABCB1-overexpressing MES-SA/DX5 and ABCG2-overexpressing MCF-7/MX and their parenteral cells was evaluated by flow cytometry. The growth inhibitory activity of single and combination therapy of foretinib and chemotherapeutic drugs on MDR cells was examined by MTT assay. Analysis of combined interaction effects was performed using CalcuSyn software.

RESULTS

It was firstly proved that foretinib increased the intracellular accumulation of rhodamine 123 and mitoxantrone in MES-SA/DX5 and MCF-7/MX cancer cells, with accumulation ratios of 12 and 2.2 at 25 μM concentration, respectively. However, it did not affect the accumulation of fluorescent substrates in the parental cells. Moreover, foretinib synergistically improved the cytotoxic effects of doxorubicin and mitoxantrone. The means of combination index (CI) values at fraction affected (Fa) values of 0.5, 0.75, and 0.9 were 0.64 ± 0.08 and 0.47 ± 0.09, in MES-SA/DX5 and MCF-7/MX cancer cells, respectively. In silico analysis also suggested that the drug-binding domain of ABCB1 and ABCG2 transporters could be considered as potential target for foretinib.

CONCLUSION

Overall, our results suggest that foretinib can target MDR-linked ABCB1 and ABCG2 transporters in clinical cancer therapy.

Amelioration of pain and anxiety in sleep-deprived rats by intra-amygdala injection of cinnamaldehyde

Background

Sleep disorders are accompanied by increased anxiety and somatic pain. In addition, it has been observed that anxiety and pain have a boosting effect on each other, resulting in continued sleep disturbances. Amygdala's (CeA) central nucleus plays a crucial role in these processes. Cinnamaldehyde (Cinn) is an aromatic compound with anti-anxiety, antioxidant, and sleep-promoting properties. The present study uses sleep-deprived rats to examine the effects of an intra-CeA injection of Cinn on pain and anxiety.

Methods

Sleep deprivation (SD) was induced using the platform technique. 35 male Wistar rats were divided into five groups. Anxiety state and nociception were evaluated among groups using formalin test (F.T.), open field test (OFT), and elevated plus maze (EPM). Anxiety tests (OFT and EPM) were conducted in all groups. The first group was undergone FT without induction of SD (SD-FT+). The second group received SD without FT(SD+FT-). The third group received both SD and FT(SD+FT+). The treatment and vehicle groups have undergone both SD and FT in addition to the respectively intra-CeA injection of Cinn (SD+FT+ Cinn) and Cinn vehicle (SD+FT+ VC). The recorded behaviors were analyzed between groups using IBM SPSS 24th version.

Results

SD did not lead to any significant difference in nociceptive behaviors in FT between groups SD-FT+ and SD+FT+ (P ≥ 0.05). At the same time, there was a considerable discrepancy in rearing behaviors (P < 0.006) and the number of fecal boli (P < 0.004) recorded in OFM between these groups. Treatment with Cinn led to decreased nociception (P < 0.038), decreased rearing behaviors (P < 0.01), and reduced defecation (P < 0.004) in group SD + FT+ Cinn in comparison to the group SD+FT+. There were no differences in anxiety test results between the first and second groups (P ≥ 0.05).

Conclusion

SD can lead to elevated anxiety, while intra-CeA injection of Cinn ameliorated both perceptions of acute pain and anxiety. Besides, the conduction of FT before the anxiety test led to no disturbance in the results of anxiety tests.

Perspectives on drug repurposing to overcome cancer multidrug resistance mediated by ABCB1 and ABCG2

The overexpression of the human ATP-binding cassette (ABC) transporters in cancer cells is a common mechanism involved in developing multidrug resistance (MDR). Unfortunately, there are currently no approved drugs specifically designed to treat multidrug-resistant cancers, making MDR a significant obstacle to successful chemotherapy. Despite over two decades of research, developing transporter-specific inhibitors for clinical use has proven to be a challenging endeavor. As an alternative approach, drug repurposing has gained traction as a more practical method to discover clinically effective modulators of drug transporters. This involves exploring new indications for already-approved drugs, bypassing the lengthy process of developing novel synthetic inhibitors. In this context, we will discuss the mechanisms of ABC drug transporters ABCB1 and ABCG2, their roles in cancer MDR, and the inhibitors that have been evaluated for their potential to reverse MDR mediated by these drug transporters. Our focus will be on providing an up-to-date report on approved drugs tested for their inhibitory activities against these drug efflux pumps. Lastly, we will explore the challenges and prospects of repurposing already approved medications for clinical use to overcome chemoresistance in patients with high tumor expression of ABCB1 and/or ABCG2.

Primary and acquired resistance to first-line therapy for clear cell renal cell carcinoma

The introduction of first-line combinations had improved the outcomes for metastatic renal cell carcinoma (mRCC) compared to sunitinib. However, some patients either have inherent resistance or develop resistance as a result of the treatment. Depending on the kind of therapy employed, many factors underlie resistance to systemic therapy. Angiogenesis and the tumor immune microenvironment (TIME), nevertheless, are inextricably linked. Although angiogenesis and the manipulation of the tumor microenvironment are linked to hypoxia, which emerges as a hallmark of renal cell carcinoma (RCC) pathogenesis, it is only one of the potential elements involved in the distinctive intra- and inter-tumor heterogeneity of RCC that is still dynamic. We may be able to more correctly predict therapy response and comprehend the mechanisms underlying primary or acquired resistance by integrating tumor genetic and immunological markers. In order to provide tools for patient selection and to generate hypotheses for the development of new strategies to overcome resistance, we reviewed the most recent research on the mechanisms of primary and acquired resistance to immune checkpoint inhibitors (ICIs) and tyrosine kinase inhibitors (TKIs) that target the vascular endothelial growth factor receptor (VEGFR).We can choose patients' treatments and cancer preventive strategies using an evolutionary approach thanks to the few evolutionary trajectories that characterize ccRCC.

New Therapeutic Strategy for Overcoming Multidrug Resistance in Cancer Cells with Pyrazolo[3,4-d]pyrimidine Tyrosine Kinase Inhibitors

Simple Summary

P-glycoprotein (P-gp) is an ATP-binding cassette transporter whose overexpression in cancer cells is one of the main causes of multidrug resistance (MDR). Tyrosine kinase inhibitors (TKIs) have been reported to interact with ABC transporters and in some cases, increase the susceptibility of cancer cells to chemotherapy. We investigated the potential of novel TKI pyrazolo[3,4-d] pyrimidines and their prodrugs to inhibit P-gp in two MDR cancer cell lines with P-gp overexpression. The tested compounds were able to suppress P-gp by inhibiting its ATPase activity. Interestingly, prodrugs displayed a stronger potential to modulate P-gp and showed higher interaction energies in the docking simulations compared to their parent drugs. Furthermore, prodrugs showed significant potential to inhibit P-gp activity even in prolonged treatment and therefore to enhance the efficacy of doxorubicin and paclitaxel in MDR cancer cells. All of these characteristics imply that the new TKIs could be considered a valuable strategy for combating resistant cancers, especially in combination with other chemotherapeutics.

Abstract

Tyrosine kinase inhibitors (TKIs) often interact with the multidrug resistant (MDR) phenotype of cancer cells. In some cases, TKIs increase the susceptibility of MDR cancer cells to chemotherapy. As the overexpression of membrane transporter P-glycoprotein (P-gp) is the most common alteration in MDR cancer cells, we investigated the effects of TKI pyrazolo[3,4-d]pyrimidines on P-gp inhibition in two cellular models comprising sensitive and corresponding MDR cancer cells (human non-small cell lung carcinoma and colorectal adenocarcinoma). Tested TKIs showed collateral sensitivity by inducing stronger inhibition of MDR cancer cell line viability. Moreover, TKIs directly interacted with P-gp and inhibited its ATPase activity. Their potential P-gp binding site was proposed by molecular docking simulations. TKIs reversed resistance to doxorubicin and paclitaxel in a concentration-dependent manner. The expression studies excluded the indirect effect of TKIs on P-gp through regulation of its expression. A kinetics study showed that TKIs decreased P-gp activity and this effect was sustained for seven days in both MDR models. Therefore, pyrazolo[3,4-d]pyrimidines with potential for reversing P-gp-mediated MDR even in prolonged treatments can be considered a new therapeutic strategy for overcoming cancer MDR.

Cabozantinib Reverses Topotecan Resistance in Human Non-Small Cell Lung Cancer NCI-H460/TPT10 Cell Line and Tumor Xenograft Model

Cabozantinib (CBZ) is a small molecule tyrosine kinase receptor inhibitor, which could also inhibit the ABCG2 transporter function. Therefore, CBZ could re-sensitize cancer cells that are resistant to ABCG2 substrate drugs including topotecan (TPT). However, its reversal effect against TPT resistance has not been tested in a TPT-induced resistant cancer model. In this study, a new TPT selected human non-small cell lung cancer (NSCLC)-resistant cell model NCI-H460/TPT10 with ABCG2 overexpression and its parental NCI-H460 cells were utilized to investigate the role of CBZ in drug resistance. The in vitro study showed that CBZ, at a non-toxic concentration, could re-sensitize NCI-H460/TPT10 cells to TPT by restoring intracellular TPT accumulation via inhibiting ABCG2 function. In addition, the increased cytotoxicity by co-administration of CBZ and TPT may be contributed by the synergistic effect on downregulating ABCG2 expression in NCI-H460/TPT10 cells. To further verify the applicability of the NCI-H460/TPT10 cell line to test multidrug resistance (MDR) reversal agents in vivo and to evaluate the in vivo efficacy of CBZ on reversing TPT resistance, a tumor xenograft mouse model was established by implanting NCI-H460 and NCI-H460/TPT10 into nude mice. The NCI-H460/TPT10 xenograft tumors treated with the combination of TPT and CBZ dramatically reduced in size compared to tumors treated with TPT or CBZ alone. The TPT-resistant phenotype of NCI-H460/TPT10 cell line and the reversal capability of CBZ in NCI-H460/TPT10 cells could be extended from in vitro cell model to in vivo xenograft model. Collectively, CBZ is considered to be a potential approach in overcoming ABCG2-mediated MDR in NSCLC. The established NCI-H460/TPT10 xenograft model could be a sound clinically relevant resource for future drug screening to eradicate ABCG2-mediated MDR in NSCLC.

Combination of HGF/MET-targeting agents and other therapeutic strategies in cancer

MET receptor has emerged as a druggable target across several human cancers. Agents targeting MET and its ligand hepatocyte growth factor (HGF) including small molecules such as crizotinib, tivantinib and cabozantinib or antibodies including rilotumumab and onartuzumab have proven their values in different tumors. Recently, capmatinib was approved for treatment of metastatic lung cancer with MET exon 14 skipping. In this review, we critically examine the current evidence on how HGF/MET combination therapies may take advantage of synergistic effects, overcome primary or acquired drug resistance, target tumor microenvironment, modulate drug metabolism or tackle pharmacokinetic issues. Preclinical and clinical studies on the combination of HGF/MET-targeted agents with conventional chemotherapeutics or molecularly targeted treatments (including EGFR, VEGFR, HER2, RAF/MEK, and PI3K/Akt targeting agents) and also the value of biomarkers are examined. Our deeper understanding of molecular mechanisms underlying successful pharmacological combinations is crucial to find the best personalized treatment regimens for cancer patients.

Establishment and Characterization of a Topotecan Resistant Non-small Cell Lung Cancer NCI-H460/TPT10 Cell Line

While topotecan (TPT) is a first- and second-line chemotherapeutic drug in treating lung cancer, the development of drug resistance in tumors still reserves as a major obstacle to chemotherapeutic success. Therefore, a better understanding of the mechanisms of topotecan resistance is critical. In this study, the first topotecan-resistant human non-small cell lung cancer (NSCLC) cell line, termed NCI-H460/TPT10, was established from the parental NCI-H460 cell line. NCI-H460/TPT10 cells exhibited a 394.7-fold resistance to TPT, and cross-resistance to SN-38, mitoxantrone, and doxorubicin, compared to parental NCI-H460 cells. Overexpression of ABCG2 localized on the cell membrane, but not ABCB1 or ABCC1, was found in NCI-H460/TPT10 cells, indicating that ABCG2 was likely to be involved in topotecan-resistance. This was confirmed by the abolishment of drug resistance in NCI-H460/TPT10 cells after ABCG2 knockout. Moreover, the involvement of functional ABCG2 as a drug efflux pump conferring multidrug resistance (MDR) was indicated by low intracellular accumulation of TPT in NCI-H460/TPT10 cells, and the reversal effects by ABCG2 inhibitor Ko143. The NCI-H460/TPT10 cell line and its parental cell line can be useful for drug screening and developing targeted strategies to overcome ABCG2-mediated MDR in NSCLC.

Superior Pyrimidine Derivatives as Selective ABCG2 Inhibitors and Broad-Spectrum ABCB1, ABCC1, and ABCG2 Antagonists

In the search for highly effective modulators addressing ABCG2-mediated MDR, 23 pyrimidines were synthesized and biologically assessed. Seven derivatives with (a) nitrogen- and/or halogen-containing residue(s) had extraordinary potencies against ABCG2 (IC₅₀ < 150 nM). The compounds competitively inhibited ABCG2-mediated Hoechst 33342 transport but were not substrates of ABCG2. The most potent MDR reverser, compound 19, concentration-dependently increased SN-38-mediated cancer cell death at 11 nM (EC₅₀), time-dependently doubled SN-38 toxicity in a period of 7 days at 10 nM, and half-maximally accelerated cell death combined with SN-38 at 17 nM. No induction of ABCG2 was observed. Furthermore, 11 pyrimidines were revealed as triple ABCB1/ABCC1/ABCG2 inhibitors. Five possessed IC₅₀ values below 10 μM against each transporter, classifying them as some of the 50 most potent multitarget ABC transporter inhibitors. The most promising representative, compound 37, reversed ABCB1-, ABCC1-, and ABCG2-mediated MDR, making it one of the three most potent ABC transporter inhibitors and reversers of ABC transporters-mediated MDR.

NVP-CGM097, an HDM2 Inhibitor, Antagonizes ATP-Binding Cassette Subfamily B Member 1-Mediated Drug Resistance

Multidrug resistance (MDR) is a major challenge in the treatment of tumors. It refers to cancer cells become resistant to not only the therapeutic drug, but also cross-resistant to multiple drugs with distinct structures and mechanisms of action when they are exposed to a drug for a period of time. An essential mechanism of MDR is the aberrant expression and function of ATP-binding cassette (ABC) transporters. Therefore, blocking the function of ABC transporters has the therapeutic potential in reversing MDR. The hdm2 oncogene product, HDM2 (also known as MDM2), is an important negative regulator of the p53 tumor suppressor. NVP-CGM097 is an HDM2 inhibitor that can inhibit the proliferation of tumor cells and is currently under clinical trials. In this study, we evaluate whether NVP-CGM097 could reverse ABCB1-mediated MDR. The results of reversal experiment showed that NVP-CGM097 remarkably reversed ABCB1-mediated MDR but not ABCG2-mediated MDR. The results of Western blot and immunofluorescence suggested that the level of expression and subcellular localization of ABCB1 protein were not significantly altered by NVP-CGM097. Mechanism studies indicated that NVP-CGM097 could reverse ABCB1-mediated MDR by directly blocking the ABCB1-mediated drug efflux and raising the accumulation of chemotherapeutic drugs in cancer cells. ATPase analysis showed that low concentration NVP-CGM097 activates ABCB1 ATPase activity while high concentration NVP-CGM097 inhibited ABCB1-associated ATPase. Docking study indicated that NVP-CGM097 tended to bind to the inhibitory site, which led to slight but critical conformational changes in the transporter and reduced the ATPase activity. Overall, our study demonstrates that NVP-CGM097 can be used in conjunction with chemotherapeutic drugs to counteract MDR and improve the antitumor responses.

Repurposing Tyrosine Kinase Inhibitors to Overcome Multidrug Resistance in Cancer: A Focus on Transporters and Lysosomal Sequestration

Tyrosine kinase inhibitors (TKIs) are being increasingly used to treat various malignancies. Although they were designed to target aberrant tyrosine kinases, they are also intimately linked with the mechanisms of multidrug resistance (MDR) in cancer cells. MDR-related solute carrier (SLC) and ATB-binding cassette (ABC) transporters are responsible for TKI uptake and efflux, respectively. However, the role of TKIs appears to be dual because they can act as substrates and/or inhibitors of these transporters. In addition, several TKIs have been identified to be sequestered into lysosomes either due to their physiochemical properties or via ABC transporters expressed on the lysosomal membrane. Since the development of MDR represents a great concern in anticancer treatment, it is important to elucidate the interactions of TKIs with MDR-related transporters as well as to improve the properties that would prevent TKIs from diffusing into lysosomes. These findings not only help to avoid MDR, but also help to define the possible impact of combining TKIs with other anticancer drugs, leading to more efficient therapy and fewer adverse effects in patients.

CM082 Enhances the Efficacy of Chemotherapeutic Drugs by Inhibiting the Drug Efflux Function of ABCG2

The overexpression of ATP-binding cassette (ABC) transporters is one of the important mechanisms of multidrug resistance (MDR). Some tyrosine kinase inhibitors (TKIs) such as CM082 might be a potential ABC transporter inhibitor, thus potentially reversing MDR. We used a 3-(4,5-dimethylthiazol-2-yl)-2,5-dimethyltetrazolium bromide (MTT) assay to determine the cytotoxicity and reversal effect of CM082. A xenograft model was established to evaluate the reversal MDR efficacy in vivo. The intracellular accumulation and efflux of ABCG2 substrates were measured by flow cytometry. We investigated the binding sites of ABCG2 via photolabeling ABCG2 with [125I]-iodoarylazidoprazosin (IAAP). Quantitative real-time PCR and western blot were utilized to analyze mRNA and protein expression. We found that CM082 could enhance the efficacy of substrate in ABCG2-overexpressing cells both in vitro and in vivo. Furthermore, CM082 significantly increased intracellular accumulation of ABCG2 substrates by inhibiting the efflux activity. CM082 stimulated ABCG2 ATPase activity and competed with [125I]-IAAP photolabeling of ABCG2 in a concentration-dependent manner. However, CM082 did not alter ABCG2 expression at protein and mRNA levels or inhibit vascular endothelial growth factor (VEGF) downstream signaling of AKT and extracellular signal-regulated kinase (ERK). Further research is encouraged to confirm whether CM082 concomitant with anticancer drugs of ABCG2 substrates could improve the clinical outcomes of cancer treatment in cancer patients with ABCG2 overexpression.

Elevated system exposures of baicalin after combinatory oral administration of rhein and baicalin: Mainly related to breast cancer resistance protein (ABCG2), not UDP-glucuronosyltransferases

ETHNOPHARMACOLOGICAL RELEVANCE

A traditional Chinese medicine (TCM) prescription follows the principle of compatibility (peiwu) to achieve the fundamental purpose: to increase efficacy and reduce toxicity. Rhei rhizoma, commonly known as Chinese rhubarb, is the most frequently used herb with Radix Scutellariaee. This classic fixed compatibility is considered for heat-clearing, qi regulation and detoxifying to gain better efficacy and reduce cytotoxicity with respect to unilateral medicine. With this in mind, we propose it is highly promising to find ingredients in rhubarb to increase the bioavailability of baicalin.

AIM OF STUDY

In the present study, effect of rhien on pharmacokinetic profile of baicalin in rat plasma was investigated, and the underlying mechanisms were partly dissected through intestinal absorption, metabolism and biliary excretion with in vivo, in vitro and in situ assays.

MATERIALS AND METHODS

Pharmacokinetic analysis in rats was first performed to provide a general overview of the in vivo exposure of baicalin and rhein after co-administration, while the biliary excretion study provided insight to the effect of rhein on the transport of baicalin from hepatocytes to bile. In vitro incubation and inhibition studies in human/rat liver microsome and human/rat intestinal S9 fraction were conducted to elucidate the role of uridine diphosphate-glucuronosyltransferases (UGTs) on the hepatic and intestinal metabolism of baicalein (the aglycone of baicalin), and to determine whether rhein can affect the UGT-mediated glucuronidation of baicalein. In situ intestinal perfusion study was designed to investigate the effect of rhein on intestinal absorption of baicalin, and breast cancer resistance protein (BCRP) inhibitor was co-perfused as positive control to demonstrate the role of the efflux transporter, while BCRP-MDCK II cell(Madin-Daby canine kidney cell) model was used as an in vitro approach to further confirm the conclusion.

RESULTS

The AUC and C_max of baicalin were increased to 189.93% and 305.73%, respectively, and the clearance of baicalin was significantly decreased from 4.17 ± 2.40 to 1.65 ± 0.79 L/h/kg following oral co-administration of rhein. The AUC of baicalin was markedly increased and the biliary clearance was significantly decreased when baicalin and rhein were co-administered intravenously. The effect of rhein on the glucuronidation of baicalein in various subcellular fractions was examined, and it was found that rhein did not affect the UGT-mediated glucuronidation of baicalein. Results of in situ intestinal perfusion revealed that co-perfusion with Ko143 (a potent BCRP inhibitor) or rhein significantly reduced the cumulative excretion amount of baicalin, from 9.27 ± 2.79 to 2.80 ± 0.97 or 4.84 ± 0.60 nM, respectively. Additionally, the efflux ratio P_app(BL-AP)/P_app(AP-BL) of baicalin in BCRP-MDCK II was decreased significantly in the presence of rhein or Ko143, which meant rhein could inhibit the BCRP-mediated efflux transport of baicalin.

CONCLUSIONS

These results indicated that rhein can increase the bioavailability of baicalin by inhibiting BCRP-mediated efflux transport of baicalin in enterocytes and hepatocytes rather than by affecting the activity of UGT enzyme.

Biological evaluation of non-basic chalcone CYB-2 as a dual ABCG2/ABCB1 inhibitor

The enhancement of drug efflux caused by ATP-binding cassette (ABC) transporters (including ABCG2 and ABCB1) overexpression is an important factor for multidrug resistance (MDR) in cancers. After testing the reversal activities of 19 chalcone and bis-chalcone derivatives on MDR cancer cell lines, we found that non-basic chalcone CYB-2 exhibited the most potent reversal activities against both ABCG2- and ABCB1-mediated MDR. The mechanistic studies show that this compound can increase the accumulation of anticancer drugs in both ABCG2- and ABCB1-overexpressing cancer cell lines, resulting from the blocked efflux function of the MDR cancer cell lines. This inhibition is due to the barred ABCG2 and ABCB1 ATPase activities rather than altering the expression or localization of ABCG2 or ABCB1 transporters. The previous studies showed that non-basic chalcones were ABCG2-specific inhibitors; however, we found that non-basic chalcone CYB-2 can be developed as an ABCG2/ABCB1 dual inhibitor to overcome MDR in cancers that co-express both ABCG2 and ABCB1. Moreover, non-basic chalcone CYB-2 has synthetic tractability compared to other chalcone-based derivatives.

M3814, a DNA-PK Inhibitor, Modulates ABCG2-Mediated Multidrug Resistance in Lung Cancer Cells

M3814, also known as nedisertib, is a potent and selective DNA-dependent protein kinase (DNA-PK) inhibitor under phase 2 clinical trials. ABCG2 is a member of the ATP-binding cassette (ABC) transporter family that is closely related to multidrug resistance (MDR) in cancer treatment. In this study, we demonstrated that M3814 can modulate the function of ABCG2 and overcome ABCG2-mediated MDR. Mechanistic studies showed that M3814 can attenuate the efflux activity of ABCG2 transporter, leading to increased ABCG2 substrate drugs accumulation. Furthermore, M3814 can stimulate the ABCG2 ATPase activity in a concentration-dependent manner without affecting the ABCG2 protein expression or cell surface localization of ABCG2. Moreover, the molecular docking analysis indicated a high affinity between M3814 and ABCG2 transporter at the drug-binding cavity. Taken together, our work reveals M3814 as an ABCG2 modulator and provides a potential combination of co-administering M3814 with ABCG2 substrate-drugs to overcome MDR.

Quinacrine and curcumin synergistically increased the breast cancer stem cells death by inhibiting ABCG2 and modulating DNA damage repair pathway

Cancer stem cell like cells (CSCs) present a challenge in the management of cancers due to their involvement in the development of resistance against various chemotherapeutic agents. Over expression of ABCG2 transporter gene is one of the factors responsible for drug resistance in CSCs, which causes efflux of therapeutic drugs from these cells. The development of inhibitors against CSCs has not achieved any significant success, till date. In this work, we have evaluated the anti-proliferative activity of curcumin (Cur) and quinacrine (QC) against CSCs using in vitro model system. Cur and QC synergistically inhibited the proliferation, migration and invasion of CSCs enriched side population (SP) cells of cigarette smoke condensate induced breast epithelial transformed (MCF-10A-Tr) generated metastatic cells. Cur + QC combination increased the DNA damage and inhibited the DNA repair pathways in SP cells. Uptake of QC increased in Cur pre-treated SP cells and this combination inhibited the ABCG2 activity by the reduction of ATP hydrolysis in cells. In vitro DNA binding reconstitution system suggests that QC specifically binds to DNA and caused DNA damage inside the cell. Decreased level of ABCG2, representative cell survival and DNA repair proteins were noted after Cur + QC treatment in SP cells. The molecular docking studies were performed to examine the binding behaviour of these drugs with ABCG2, which showed that QC (-53.99 kcal/mol) and Cur (-45.90 kcal/mol) occupy a highly overlapping interaction domain. This suggested that in Cur pre-treated cells, the Cur occupied the ligand-binding site in ABCG2, thus making the ligand binding site unavailable for the QC. This causes an increase in the intracellular concentration of QC. The results indicate that Cur + QC combination causes CSCs death by increasing the concentration of QC in the cells and thus causing the DNA damage and inhibiting the DNA repair pathways through modulating the ABCG2 activity.

Dual Inhibitors as a New Challenge for Cancer Multidrug Resistance Treatment

BACKGROUND

Dual-targeting in cancer treatment by a single drug is an unconventional approach in relation to drug combinations. The rationale for the development of dualtargeting agents is to overcome incomplete efficacy and drug resistance frequently present when applying individual targeting agents. Consequently, -a more favorable outcome of cancer treatment is expected with dual-targeting strategies.

METHODS

We reviewed the literature, concentrating on the association between clinically relevant and/or novel dual inhibitors with the potential to modulate multidrug resistant phenotype of cancer cells, particularly the activity of P-glycoprotein. A balanced analysis of content was performed to emphasize the most important findings and optimize the structure of this review.

RESULTS

Two-hundred and forty-five papers were included in the review. The introductory part was interpreted by 9 papers. Tyrosine kinase inhibitors' role in the inhibition of Pglycoprotein and chemosensitization was illustrated by 87 papers. The contribution of naturalbased compounds in overcoming multidrug resistance was reviewed using 92 papers, while specific dual inhibitors acting against microtubule assembling and/or topoisomerases were described with 55 papers. Eleven papers gave an insight into a novel and less explored approach with hybrid drugs. Their influence on P-glycoprotein and multidrug resistance was also evaluated.

CONCLUSION

These findings bring into focus rational anticancer strategies with dual-targeting agents. Most evaluated synthetic and natural drugs showed a great potential in chemosensitization. Further steps in this direction are needed for the optimization of anticancer treatment.

A temperature-sensitive phase-change hydrogel of topotecan achieves a long-term sustained antitumor effect on retinoblastoma cells

Background

Retinoblastoma (Rb) is one of the most common malignancies among children. Following early diagnosis and prompt treatment, the clinical outcome or prognosis of Rb is promising. However, the prognosis or survival rates of patients with late-stage Rb remain poor. Current therapeutic strategies for advanced Rb mainly involve the use of advanced chemotherapeutic options. However, the efficacy of these strategies is not satisfactory. Therefore, the development of novel strategies to achieve a more effective antitumor effect on late-stage Rb is of crucial importance.

Methods and materials

Topotecan was dissolved in phosphate-buffered saline and prepared into a temperature-sensitive phase-change hydrogel (termed Topo-Gel). Moreover, Topo-Gel was injected into tumor tissues formed by Y79 cells (an Rb cell line) in nude mice to examine the long-term release and long-acting antitumor effect of Topo-Gel on Rb tumors.

Results

Topo-Gel transforms from liquid to a hydrogel at near body temperatures (phase-change temperature [T_1/2] was 37.23±0.473 °C), and maintains the slow release of topotecan in Rb tumor tissues. Following the subcutaneous injection of Topo-Gel, the treatment induced long-acting inhibition of tumor growth and relieved the adverse effects associated with topotecan. Topo-Gel, a temperature-sensitive phase-change hydrogel, is a slow-release system that prolongs the presence of topotecan in Rb tissues, and preserves the efficacy of topotecan in the long term.

Conclusion

Preparation of topotecan into a temperature-sensitive phase-change hydrogel achieves a long-term sustained antitumor effect on Rb cells, and may be a useful strategy for the treatment of intraocular Rb.

Tyrosine kinase inhibitors enhanced the efficacy of conventional chemotherapeutic agent in multidrug resistant cancer cells

Multidrug resistance (MDR) triggered by ATP binding cassette (ABC) transporter such as ABCB1, ABCC1, ABCG2 limited successful cancer chemotherapy. Unfortunately, no commercial available MDR modulator approved by FDA was used in clinic. Tyrosine kinase inhibitors (TKIs) have been administrated to fight against cancer for decades. Almost TKI was used alone in clinic. However, drug combinations acting synergistically to kill cancer cells have become increasingly important in cancer chemotherapy as an approach for the recurrent resistant disease. Here, we summarize the effect of TKIs on enhancing the efficacy of conventional chemotherapeutic drug in ABC transporter-mediated MDR cancer cells, which encourage to further discuss and study in clinic.