MRP2 (ABCC2) transports taxanes and confers paclitaxel resistance and both processes are stimulated by probenecid

Knockout Transporter Cell Lines to Assess Substrate Potential Towards Efflux Transporters

P-glycoprotein (P-gp), breast cancer resistance protein (BCRP) and multidrug resistance transporter 2 (MRP2) are efflux transporters involved in the absorption, excretion, and distribution of drugs. Bidirectional cell assays are recognized models for evaluating the potential of new drugs as substrates or inhibitors of efflux transporters. However, the assays are complicated by a lack of selective substrates and/or inhibitors, as well simultaneous expression of several efflux transporters in cell lines used in efflux models. This project aims to evaluate an in vitro efflux cell assay employing model substrates and inhibitors of P-gp, BCRP and MRP2 with knockout (KO) cell lines. The efflux ratios (ER) of P-gp (digoxin, paclitaxel), BCRP (prazosin, rosuvastatin), MRP2 (etoposide, olmesartan) and mixed (methotrexate, mitoxantrone) substrates were determined in wild-type C2BBe1 and KO cells. For digoxin and paclitaxel, the ER decreased to less than 2 in the cell lines lacking P-gp expression. The ER decreased to less than 3 for prazosin and less than 2 for rosuvastatin in the cell lines lacking BCRP expression. For etoposide and olmesartan, the ER decreased to less than 2 in the cell lines lacking MRP2 expression. The ER of methotrexate and mitoxantrone decreased in single- and double-KO cells without BCRP and MRP2 expression. These results show that KO cell lines have the potential to better interpret complex drug-transporter interactions without depending upon multi-targeted inhibitors or overlapping substrates. For drugs that are substrates of multiple transporters, the single- and double-KO cells may be used to assess their affinities for the different transporters.

Structural basis for the modulation of MRP2 activity by phosphorylation and drugs

Multidrug resistance-associated protein 2 (MRP2/ABCC2) is a polyspecific efflux transporter of organic anions expressed in hepatocyte canalicular membranes. MRP2 dysfunction, in Dubin-Johnson syndrome or by off-target inhibition, for example by the uricosuric drug probenecid, elevates circulating bilirubin glucuronide and is a cause of jaundice. Here, we determine the cryo-EM structure of rat Mrp2 (rMrp2) in an autoinhibited state and in complex with probenecid. The autoinhibited state exhibits an unusual conformation for this class of transporter in which the regulatory domain is folded within the transmembrane domain cavity. In vitro phosphorylation, mass spectrometry and transport assays show that phosphorylation of the regulatory domain relieves this autoinhibition and enhances rMrp2 transport activity. The in vitro data is confirmed in human hepatocyte-like cells, in which inhibition of endogenous kinases also reduces human MRP2 transport activity. The drug-bound state reveals two probenecid binding sites that suggest a dynamic interplay with autoinhibition. Mapping of the Dubin-Johnson mutations onto the rodent structure indicates that many may interfere with the transition between conformational states.

FTY720 increases paclitaxel efficacy in cisplatin-resistant oral squamous cell carcinoma

BACKGROUND

Oral squamous cell carcinoma has high recurrence and cisplatin resistance. As cancer stem cells, autophagy, and sphingolipids have been appointed as associated with chemotherapy resistance, we tested combined treatments targeting autophagy and/or sphingolipid metabolism with paclitaxel using cisplatin-resistant oral squamous cell carcinoma cells.

METHODS

Cisplatin-resistant oral squamous cell carcinoma cells were maintained under exposition to FTY720 and chloroquine combined with paclitaxel and submitted to viability, clonogenicity, and spheres formation assays. The xenograft tumor model using cisplatin-resistant CAL27 cells was adopted to examine the drug combinations' potential antitumoral efficacy. Using an animal model, sphingolipids profiles from plasma and tissue samples were obtained by liquid chromatography coupled to mass spectrometry to identify potential lipids associated with drug response.

RESULTS AND DISCUSSION

Our results showed higher autophagic flux in cisplatin-resistant Ooral squamous cell carcinoma (CAL27 and SCC9) cells than in parental cells. The combinations of an autophagy inhibitor (chloroquine) or an autophagy inducer/sphingosine kinase 1 antagonist (FTY720) with paclitaxel (PTX) had a synergistic antitumor effect. Treated CisR cells lost clonogenicity and tumor sphere abilities and reduced proteins associated with proliferation, survival, and cancer stem cells. FTY720 plus PTX had higher antitumor efficacy than PTX against CAL27 CisR xenograft tumor formation. Additionally, increases in glucosylceramide, dehydroglucosylceramide, and sphingomyelin were presented in responsive tumors.

CONCLUSION

FTY720 sensitizes cisplatin-resistant oral squamous cell carcinoma cells for paclitaxel.

Predicting disruptions to drug pharmacokinetics and the risk of adverse drug reactions in non-alcoholic steatohepatitis patients

The liver plays a central role in the pharmacokinetics of drugs through drug metabolizing enzymes and transporters. Non-alcoholic steatohepatitis (NASH) causes disease-specific alterations to the absorption, distribution, metabolism, and excretion (ADME) processes, including a decrease in protein expression of basolateral uptake transporters, an increase in efflux transporters, and modifications to enzyme activity. This can result in increased drug exposure and adverse drug reactions (ADRs). Our goal was to predict drugs that pose increased risks for ADRs in NASH patients. Bibliographic research identified 71 drugs with reported ADRs in patients with liver disease, mainly non-alcoholic fatty liver disease (NAFLD), 54 of which are known substrates of transporters and/or metabolizing enzymes. Since NASH is the progressive form of NAFLD but is most frequently undiagnosed, we identified other drugs at risk based on NASH-specific alterations to ADME processes. Here, we present another list of 71 drugs at risk of pharmacokinetic disruption in NASH, based on their transport and/or metabolism processes. It encompasses drugs from various pharmacological classes for which ADRs may occur when used in NASH patients, especially when eliminated through multiple pathways altered by the disease. Therefore, these results may inform clinicians regarding the selection of drugs for use in NASH patients.

Combination of Antimalarial and CNS Drugs with Antineoplastic Agents in MCF-7 Breast and HT-29 Colon Cancer Cells: Biosafety Evaluation and Mechanism of Action

Drug combination and drug repurposing are two strategies that allow to find novel oncological therapies, in a faster and more economical process. In our previous studies, we developed a novel model of drug combination using antineoplastic and different repurposed drugs. We demonstrated the combinations of doxorubicin (DOX) + artesunate, DOX + chloroquine, paclitaxel (PTX) + fluoxetine, PTX + fluphenazine, and PTX + benztropine induce significant cytotoxicity in Michigan Cancer Foundation-7 (MCF-7) breast cancer cells. Furthermore, it was found that 5-FU + thioridazine and 5-fluorouracil (5-FU) + sertraline can synergistically induce a reduction in the viability of human colorectal adenocarcinoma cell line (HT-29). In this study, we aim to (1) evaluate the biosafety profile of these drug combinations for non-tumoral cells and (2) determine their mechanism of action in cancer cells. To do so, human fetal lung fibroblast cells (MRC-5) fibroblast cells were incubated for 48 h with all drugs, alone and in combination in concentrations of 0.25, 0.5, 1, 2, and 4 times their half-maximal inhibitory concentration (IC₅₀). Cell morphology and viability were evaluated. Next, we designed and constructed a cell microarray to perform immunohistochemistry studies for the evaluation of palmitoyl-protein thioesterase 1 (PPT1), Ki67, cleaved-poly (ADP-ribose) polymerase (cleaved-PARP), multidrug resistance-associated protein 2 (MRP2), P-glycoprotein (P-gp), and nuclear factor-kappa-B (NF-kB) p65 expression. We demonstrate that these combinations are cytotoxic for cancer cells and safe for non-tumoral cells at lower concentrations. Furthermore, it is also demonstrated that PPT1 may have an important role in the mechanism of action of these combinations, as demonstrated by their ability to decrease PPT1 expression. These results support the use of antimalarial and central nervous system (CNS) drugs in combination regimens with chemotherapeutic agents; nevertheless, additional studies are recommended to further explore their complete mechanisms of action.

Genetic variations in the ATP-binding cassette transporter ABCC10 are associated with neutropenia in Japanese patients with lung cancer treated with nanoparticle albumin-bound paclitaxel

ABCC10/MRP7, an ATP-binding cassette (ABC) transporter, has been implicated in the extracellular transport of taxanes. Our group reported that the ABCC10 single nucleotide polymorphism (SNPs), rs2125739, influences docetaxel cytotoxicity in lung cancer cell lines as well as its side effects in clinical practice. In this study, we investigated whether the rs2125739 variant could affect paclitaxel (PTX) cytotoxicity in lung cancer cell lines. We also investigated the effect of rs2125739 on the efficacy and safety of nanoparticle albumin-bound PTX (nab-PTX) in clinical practice. The association between rs2125739 genotypes and the 50% inhibitory concentration (IC₅₀) of PTX was investigated in 18 non-small cell lung cancer (NSCLC) cell lines, HeLa cells, and genome-edited HeLa cells. Next, blood samples from 77 patients with NSCLC treated with carboplatin plus nab-PTX were collected and analyzed for six SNPs, including rs2125739. The clinical outcomes among the different genotype groups were evaluated. In NSCLC cell lines, HeLa cells, and genome-edited HeLa cells, the IC₅₀ was significantly higher in the ABCC10 rs2125739 T/T group than in the T/C and C/C groups. In 77 patients with NSCLC, there were no significant differences in clinical outcomes between the T/T and T/C groups. However, the rs2125739 T/T genotype was associated with a higher frequency of Grades 3/4 neutropenia. In contrast, there was no association between other SNPs and clinical efficacy or neutropenia. Our results indicate that the ABCC10 rs2125739 variant is associated with neutropenia in response to nab-PTX treatment.

An ester derivative of tenacigenin B from Marsdenia tenacissima (Roxb.) Wight et Arn reversed paclitaxel-induced MDR in vitro and in vivo by inhibiting both P-gp and MRP2

ETHNOPHARMACOLOGICAL RELEVANCE

Marsdenia tenacissima is a medicinal plant, used as a raw material for cancer treatment in China. In our previous studies, 11α-O-2-methylbutanoyl-12β-O-tigloyl-tenacigenin B (MT2), the main steroid aglycone isolated from M. tenacissima, was found to significantly enhance the antitumor activity of paclitaxel (PTX) in vivo. However, it is unclear whether MT2 reverses multidrug resistance (MDR) in tumors.

AIM OF THE STUDY

To determine the role and mechanism of MT2 in reversing tumor MDR.

MATERIALS AND METHODS

MDR cell line HeLa/Tax was established from the human cervical carcinoma cell line HeLa by long-term exposure to subtoxic concentrations of PTX and was used to evaluate the ability of MT2 to restore chemosensitivity of cells both in vitro and in a nude mouse model. The expression of P-glycoprotein (P-gp) and multidrug resistance-associated protein 2 (MRP2) was determined using western blotting and immunohistochemistry. The substrate transport function was assessed using an MDR function assay kit. The binding modes of MT2 and P-gp were determined using the conformation-sensitive anti-P-gp antibodies. The permeability and transport properties of MT2 were analyzed in Caco-2 cell monolayers.

RESULTS

Compared to parental cells, HeLa/Tax cells overexpress P-gp and MRP2 and are approximately 100-360 fold more resistant to the anticancer drugs PTX, docetaxel, and vinblastine. MT2 at 5 or 10 μmol/L significantly increased the sensitivity of HeLa/Tax to these three anticancer drugs (18-56-fold decrease in IC₅₀ value) and suppressed the expression of P-gp and MRP2. Knockdown of P-gp with small interfering RNA partially reversed MT2-induced sensitivity to PTX in HeLa/Tax cells. Moreover, MT2 directly inhibited P-gp-mediated substrate transport while interacting with membrane P-gp in non-substrate ways. MT2 was highly permeable and could not be transported in the Caco-2 cell monolayers. In nude mice bearing HeLa/Tax xenografts, the combination treatment with MT2 and PTX exerted a synergistic inhibitory effect on the growth of tumors and the expression of P-gp and MRP2 without increasing toxicity.

CONCLUSION

MT2 is a potential agent for reversing MDR. It impedes membrane drug efflux pumps by suppressing P-gp and MRP2 expression, and directly inhibiting the transport function of P-gp.

Bacteria-Mediated Intracellular Click Reaction for Drug Enrichment and Selective Apoptosis of Drug-Resistant Tumor Cells

Functionalized biocarriers that can perform bio-orthogonal reactions in tumor cells may provide solutions to overcome the efflux of the chemotherapeutic agent from drug-resistant tumor cells. Herein, we report the enrichment of therapeutic drugs in tumor cells through intracellular click reaction with functionalized bacteria. Specifically, an intracellular bioactive drug enrichment template (OPV@Escherichia coli) is constructed by combining positively charged oligo(phenylene-vinylene)-alkyne (OPV-C≡CH) with E. coli via electrostatic interaction. After the cell uptake of OPV@E. coli and Cu(II)-based complex, Cu(I) generated in situ can catalyze the bio-orthogonal click reaction to covalently anchor the azide-bearing molecules of cyanine 5 (Cy5-N₃) and paclitaxel (PTX-N₃) on OPV@E. coli. These molecules and their functions were retained and enriched inside the drug-resistant tumor cells A549T, which can label cells with fluorescent probes and selectively induce the apoptosis of drug-resistant tumor cells.

Pacific Blue-Taxoids as Fluorescent Molecular Probes of Microtubules

Taxoids such as paclitaxel (Taxol) are an important class of anticancer drugs that bind β-tubulin and stabilize cellular microtubules. To provide new chemical tools for studies of microtubules, we synthesized derivatives of paclitaxel modified at the 7-position with the small coumarin-derived fluorophore Pacific Blue (PB). Three of these Pacific Blue-Taxoids termed PB-Gly-Taxol, PB-β-Ala-Taxol, and PB-GABA-Taxol bind purified crosslinked microtubules with affinities of 34-265 nM, where the affinity can be tuned based on the length of an amino acid linker. When added to living cells in the presence of verapamil or probenecid as inhibitors of efflux, these compounds allow visualization of the microtubule network by confocal microscopy. We describe methods for the synthesis of these probes, determination of their affinities for crosslinked tubulin, and imaging of microtubules in living HeLa cells. We further describe their uptake by Caco-2 cells and two transporter-deficient Caco-2 knockout cell lines in the absence and presence of efflux inhibitors by flow cytometry. These studies revealed that p-glycoprotein (MDR1) and multidrug-resistance protein 2 (MRP2) are major mediators of efflux of these molecular probes. These compounds provide useful tools for studies of microtubules and cellular efflux transporters in living cells.

Circadian Influences on Chemotherapy Efficacy in a Mouse Model of Brain Metastases of Breast Cancer

Chemotherapy is more effective in the treatment of peripheral tumors than brain metastases, likely reflecting the reduced ability of chemotherapy to cross the blood-brain barrier (BBB) and blood-tumor barrier at efficacious concentrations. Recent studies demonstrate circadian regulation of the BBB. Thus, we predicted that optimally timed chemotherapy would increase anti-tumor efficacy in a model of brain metastases of breast cancer (BMBC). First, we characterized novel daily alterations in BBB permeability to a commonly used chemotherapeutic, 14C-paclitaxel, within BMBC following injections given at four time points across the day. Peak and trough 14C-paclitaxel concentrations within BMBC occurred during the mid-dark phase and at the beginning of the light phase, respectively. Notably, chemotherapy injections during the dark phase increased cell death within BMBC and delayed onset of neurological symptoms relative to injections during the light phase. These data provide strong evidence for the beneficial effects of chrono-chemotherapy for the treatment of BMBC.

Tissue Type Differences in ABCB1 Expression and Paclitaxel Tissue Pharmacokinetics in Patients With Esophageal Cancer

Background: Data from previous work suggests that there is no correlation between systemic (plasma) paclitaxel exposure and efficacy in patients treated for esophageal cancer. In this trial, we investigated ATP-binding cassette efflux transporter expression and intratumoral pharmacokinetics of paclitaxel to identify changes which could be a first sign of chemoresistance.

Methods: Patients with esophageal cancer treated with paclitaxel and carboplatin (± concomitant radiotherapy) were included. During the first and last cycle of weekly paclitaxel, blood samples and biopsies of esophageal mucosa and tumor tissue were taken. Changes in paclitaxel exposure and expression of ABCB1 (P-glycoprotein) over time were studied in both tumor tissue and normal appearing esophageal mucosa.

Results: ABCB1 was significantly higher expressed in tumor tissue compared to esophageal tissue, during both the first and last cycle of paclitaxel (cycle 1: p < 0.01; cycle 5/6: p = 0.01). Interestingly, ABCB1 expression was significantly higher in adenocarcinoma than in squamous cell carcinoma (p < 0.01). During the first cycle, a trend towards a higher intratumoral paclitaxel concentration was observed compared to the esophageal mucosa concentration (RD:43%; 95%CI: −3% to 111% p = 0.07). Intratumoral and plasma paclitaxel concentrations were significantly correlated during the first cycle (AUC_0–48 h: r = 0.72; p < 0.01).

Conclusion: Higher ABCB1 expression in tumor tissue, and differences between histological tumor types might partly explain why tumors respond differently to systemic treatment. Resistance by altered intratumoral paclitaxel concentrations could not be demonstrated because the majority of the biopsies taken at the last cycle of paclitaxel did contain a low amount of tumor cells or no tumor.

Role of multidrug resistance-associated proteins in cancer therapeutics: past, present, and future perspectives

Cancer, a major public health problem, is one of the world's top leading causes of death. Common treatments for cancer include cytotoxic chemotherapy, surgery, targeted drugs, endocrine therapy, and immunotherapy. However, despite the outstanding achievements in cancer therapies during the last years, resistance to conventional chemotherapeutic agents and new targeted drugs is still the major challenge. In the present review, we explain the different mechanisms involved in cancer therapy and the detailed outlines of cancer drug resistance regarding multidrug resistance-associated proteins (MRPs) and their role in treatment failures by common chemotherapeutic agents. Further, different modulators of MRPs are presented. Finally, we outlined the models used to analyze MRP transporters and proposed a future impact that may set up a base or pave the way for many researchers to investigate the cancer MRP further.

Androgen/Androgen Receptor Signaling in Ovarian Cancer: Molecular Regulation and Therapeutic Potentials

Ovarian cancer (OVCA) arises from three cellular origins, namely surface epithelial cells, germ cells, and stromal cells. More than 85% of OVCAs are EOCs (epithelial ovarian carcinomas), which are the most lethal gynecological malignancies. Cancer stem/progenitor cells (CSPCs) are considered to be cancer promoters due to their capacity for unlimited self-renewal and drug resistance. Androgen receptor (AR) belongs to the nuclear receptor superfamily and can be activated through binding to its ligand androgens. Studies have reported an association between AR expression and EOC carcinogenesis, and AR is suggested to be involved in proliferation, migration/invasion, and stemness. In addition, alternative AR activating signals, including both ligand-dependent and ligand-independent, are involved in OVCA progression. Although some clinical trials have previously been conducted to evaluate the effects of anti-androgens in EOC, no significant results have been reported. In contrast, experimental studies evaluating the effects of anti-androgen or anti-AR reagents in AR-expressing EOC models have demonstrated positive results for suppressing disease progression. Since AR is involved in complex signaling pathways and may be expressed at various levels in OVCA, the aim of this article was to provide an overview of current studies and perspectives regarding the relevance of androgen/AR roles in OVCA.

Genetic dissection of maize seedling traits in an IBM Syn10 DH population under the combined stress of lead and cadmium

The heavy metals lead and cadmium have become important pollutants in the environment, which exert negative effects on plant morphology, growth and photosynthesis. It is particularly significant to uncover the genetic loci and the causal genes for lead and cadmium tolerance in plants. This study used an IBM Syn10 DH population to identify the quantitative trait loci (QTL) controlling maize seedling tolerance to lead and cadmium by linkage mapping. The broad-sense heritability of these seedling traits ranged from 65.8-97.3% and 32.0-98.8% under control (CK) and treatment (T) conditions, respectively. A total of 53 and 64 QTL were detected under CK and T conditions, respectively. Moreover, 42 QTL were identified using lead and cadmium tolerance coefficient (LCTC). Among these QTL, five and two major QTL that explained > 10% of phenotypic variation were identified under T condition and using LCTC, respectively. Furthermore, eight QTL were simultaneously identified by T and LCTC, explaining 5.23% to 9.21% of the phenotypic variations. Within these major and common QTL responsible for the combined heavy metal tolerance, four candidate genes (Zm00001d048759, Zm00001d004689, Zm00001d004843, Zm00001d033527) were previously reported to correlate with heavy metal transport and tolerance. These findings will contribute to functional gene identification and molecular marker-assisted breeding for improving heavy metal tolerance in maize.

Taxanes in cancer treatment: Activity, chemoresistance and its overcoming

Since 1984, when paclitaxel was approved by the FDA for the treatment of advanced ovarian carcinoma, taxanes have been widely used as microtubule-targeting antitumor agents. However, their historic classification as antimitotics does not describe all their functions. Indeed, taxanes act in a complex manner, altering multiple cellular oncogenic processes including mitosis, angiogenesis, apoptosis, inflammatory response, and ROS production. On the one hand, identification of the diverse effects of taxanes on oncogenic signaling pathways provides opportunities to apply these cytotoxic drugs in a more rational manner. On the other hand, this may facilitate the development of novel treatment modalities to surmount anticancer drug resistance. In the latter respect, chemoresistance remains a major impediment which limits the efficacy of antitumor chemotherapy. Taxanes have shown impact on key molecular mechanisms including disruption of mitotic spindle, mitosis slippage and inhibition of angiogenesis. Furthermore, there is an emerging contribution of cellular processes including autophagy, oxidative stress, epigenetic alterations and microRNAs deregulation to the acquisition of taxane resistance. Hence, these two lines of findings are currently promoting a more rational and efficacious taxane application as well as development of novel molecular strategies to enhance the efficacy of taxane-based cancer treatment while overcoming drug resistance. This review provides a general and comprehensive picture on the use of taxanes in cancer treatment. In particular, we describe the history of application of taxanes in anticancer therapeutics, the synthesis of the different drugs belonging to this class of cytotoxic compounds, their features and the differences between them. We further dissect the molecular mechanisms of action of taxanes and the molecular basis underlying the onset of taxane resistance. We further delineate the possible modalities to overcome chemoresistance to taxanes, such as increasing drug solubility, delivery and pharmacokinetics, overcoming microtubule alterations or mitotic slippage, inhibiting drug efflux pumps or drug metabolism, targeting redox metabolism, immune response, and other cellular functions.

Exploring pharmacogenetics of paclitaxel- and docetaxel-induced peripheral neuropathy by evaluating the direct pharmacogenetic-pharmacokinetic and pharmacokinetic-neuropathy relationships

Introduction: Peripheral neuropathy (PN) is an adverse effect of several classes of chemotherapy including the taxanes. Predictive PN biomarkers could inform individualized taxane treatment to reduce PN and enhance therapeutic outcomes. Pharmacogenetics studies of taxane-induced PN have focused on genes involved in pharmacokinetics, including enzymes and transporters. Contradictory findings from these studies prevent translation of genetic biomarkers into clinical practice. Areas covered: This review discusses the progress toward identifying pharmacogenetic predictors of PN by assessing the evidence for two independent associations; the effect of pharmacogenetics on taxane pharmacokinetics and the evidence that taxane pharmacokinetics affects PN. Assessing these direct relationships allows the reader to understand the progress toward individualized taxane treatment and future research opportunities. Expert opinion: Paclitaxel pharmacokinetics is a major determinant of PN. Additional clinical trials are needed to confirm the clinical benefit of individualized dosing to achieve target paclitaxel exposure. Genetics does not meaningfully contribute to paclitaxel pharmacokinetics and may not be useful to inform dosing. However, genetics may contribute to PN sensitivity and could be useful for estimating patients' optimal paclitaxel exposure. For docetaxel, genetics has not been demonstrated to have a meaningful effect on pharmacokinetics and there is no evidence that pharmacokinetics determines PN.

Impact of variants in ATP-binding cassette transporters on breast cancer treatment

There has been substantial interest in the impact of ATP-binding cassette (ABC) transporter variability on breast cancer drug resistance. Here, we provide a systematic review of ABC variants in breast cancer therapy. Notably, most studies used small heterogeneous cohorts and their identified associations lack statistical stringency, replication and mechanistic support. We conclude that commonly studied ABC polymorphisms are not suitable to accurately predict therapy response or toxicity in breast cancer patients and cannot guide treatment decisions. However, recent research shows that ABC transporters harbor a plethora of rare variants with individually small effect sizes, and we argue that a shift in strategy from target variant interrogation to comprehensive profiling might hold promise to drastically improve the predictive power of outcome models.

Role for Drug Transporters in Chemotherapy-Induced Peripheral Neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN) is a common and dose-limiting toxicity to widely used chemotherapeutics. Although the exact molecular mechanism of chemotherapy-induced peripheral neuropathy remains elusive, there is consensus that it is caused by damage to the peripheral nervous system leading to sensory symptoms. Recently developed methodologies have provided evidence of expression of drug transporters in the peripheral nervous system. In this literature review, we explore the role for drug transporters in CIPN. First, we assessed the transport of chemotherapeutics that cause CIPN (taxanes, platins, vincristine, bortezomib, epothilones, and thalidomide). Second, we cross-referenced the transporters implicated in genetic or functional studies with CIPN with their expression in the peripheral nervous system. Several drug transporters are involved in the transport of chemotherapeutics that cause peripheral neuropathy and particularly efflux transporters, such as ABCB1 and ABCC1, are expressed in the peripheral nervous system. Previous literature has linked genetic variants in efflux transporters to higher risk of peripheral neuropathy with the taxanes paclitaxel and docetaxel and the vinca alkaloid vincristine. We propose that this might be due to accumulation of the chemotherapeutics in the peripheral nervous system due to reduced neuronal efflux capacity. Thus, concomitant administration of efflux transporter inhibitors may lead to higher risk of adverse events of drugs that cause CIPN. This might prove valuable in drug development where screening new drugs for neurotoxicity might also require drug transporter consideration. There are ongoing efforts targeting drug transporters in the peripheral nervous system to reduce intraneuronal concentrations of chemotherapeutics that cause CIPN, which might ultimately protect against this dose-limiting adverse event.

P-Glycoprotein Inhibition Exacerbates Paclitaxel Neurotoxicity in Neurons and Patients With Cancer

Paclitaxel-induced peripheral neuropathy (PIPN) is a common and dose-limiting adverse event. The role of P-glycoprotein (P-gp) in the neuronal efflux of paclitaxel was assessed using a translational approach. SH-SY5Y cells were differentiated to neurons and paclitaxel toxicity in the absence and presence of a P-gp inhibitor was determined. Paclitaxel caused marked dose-dependent toxicity in SH-SY5Y-derived neurons. Paclitaxel neurotoxicity was exacerbated with concomitant P-gp inhibition by valspodar and verapamil, consistent with increased intracellular accumulation of paclitaxel. Patients with cancer treated with paclitaxel and P-gp inhibitors had a 2.4-fold (95% confidence interval (CI) 1.3-4.3) increased risk of peripheral neuropathy-induced dose modification while a 4.7-fold (95% CI 1.9-11.9) increased risk for patients treated with strong P-gp inhibitors was observed, and a 7.0-fold (95% CI 2.3-21.5) increased risk in patients treated with atorvastatin. Atorvastatin also increased neurotoxicity by paclitaxel in SH-SY5Y-derived neurons. Clinicians should be aware that comedication with P-gp inhibitors may lead to increased risk of PIPN.

Effects of Chrysin and Its Major Conjugated Metabolites Chrysin-7-Sulfate and Chrysin-7-Glucuronide on Cytochrome P450 Enzymes and on OATP, P-gp, BCRP, and MRP2 Transporters

Chrysin is an abundant flavonoid in nature, and it is also contained by several dietary supplements. Chrysin is highly biotransformed in the body, during which conjugated metabolites chrysin-7-sulfate and chrysin-7-glucuronide are formed. These conjugates appear at considerably higher concentrations in the circulation than the parent compound. Based on previous studies, chrysin can interact with biotransformation enzymes and transporters; however, the interactions of its metabolites have been barely examined. In this in vitro study, the effects of chrysin, chrysin-7-sulfate, and chrysin-7-glucuronide on cytochrome P450 enzymes (2C9, 2C19, 3A4, and 2D6) as well as on organic anion-transporting polypeptides (OATPs; 1A2, 1B1, 1B3, and 2B1) and ATP binding cassette [P-glycoprotein, multidrug resistance-associated protein 2, and breast cancer resistance protein (BCRP)] transporters were investigated. Our observations revealed that chrysin conjugates are strong inhibitors of certain biotransformation enzymes (e.g., CYP2C9) and transporters (e.g., OATP1B1, OATP1B3, OATP2B1, and BCRP) examined. Therefore, the simultaneous administration of chrysin-containing dietary supplements with medications needs to be carefully considered due to the possible development of pharmacokinetic interactions. SIGNIFICANCE STATEMENT: Chrysin-7-sulfate and chrysin-7-glucuronide are the major metabolites of flavonoid chrysin. In this study, we examined the effects of chrysin and its conjugates on cytochrome P450 enzymes and on organic anion-transporting polypeptides and ATP binding cassette transporters (P-glycoprotein, breast cancer resistance protein, and multidrug resistance-associated protein 2). Our results demonstrate that chrysin and/or its conjugates can significantly inhibit some of these proteins. Since chrysin is also contained by dietary supplements, high intake of chrysin may interrupt the transport and/or the biotransformation of drugs.

Genetic associations of docetaxel-based chemotherapy-induced myelosuppression in Chinese Han population

WHAT IS KNOWN AND OBJECTIVE

Myelosuppression, an adverse drug reaction (ADR), often causes medical treatment termination in cancer patients. It has been known that genetic components, such as single-nucleotide polymorphisms (SNPs), influence the risk of myelosuppression at the individual-patient level. However, due to ethnic variation in frequency of genetic polymorphisms, results reported in Caucasian patients may not be generalizable to the Chinese Han population. Until now, few researches on myelosuppression included Chinese Han patients. In this study, we conducted a systematic study of potential biomarkers for docetaxel-induced myelosuppression in Han Chinese patients.

METHODS

We examined 61 SNPs in 36 genes that code for drug transporters, metabolism enzymes, nuclear receptors and DNA repair pathway in 110 Chinese Han patients receiving docetaxel-based chemotherapy. Genotyping was conducted using the Sequenom MassARRAY system. Significant SNPs were identified by logistic regression, and gene-gene interactions were investigated by generalized multifactor dimensionality reduction (GMDR) analysis.

RESULTS AND DISCUSSION

Our results revealed that 11 SNPs in nine genes (SLC15A1, SLCO1A2, CYP2D6, FMO3, UGT1A1, NAT2, SULT2A1, PXR and HNF4α) were associated with docetaxel-induced myelosuppression. GMDR analyses suggested that a 3-locus model: SLC15A1 rs2297322-PXR rs3732359-FMO3 rs2266782 was an appropriate predictive model of docetaxel-induced myelosuppression (P = .017, Testing Bal.Acc = 0.653, CV Consistency = 10/10).

WHAT IS NEW AND CONCLUSION

Our findings suggest multiple novel predictive biomarkers of docetaxel-induced myelosuppression: SLC15A1 rs2297322, PXR rs3732359 and FMO3 rs2266782. These discoveries should help in advancing future personalized therapy of docetaxel-based chemotherapy specific to Chinese Han patients.

Bioavailability Enhancement of Poorly Soluble Drugs: The Holy Grail in Pharma Industry

Background:

Bioavailability, one of the prime pharmacokinetic properties of a drug, is defined as the fraction of an administered dose of unchanged drug that reaches the systemic circulation and is used to describe the systemic availability of a drug. Bioavailability assessment is imperative in order to demonstrate whether the drug attains the desirable systemic exposure for effective therapy. In recent years, bioavailability has become the subject of importance in drug discovery and development studies.

Methods:

A systematic literature review in the field of bioavailability and the approaches towards its enhancement have been comprehensively done, purely focusing upon recent papers. The data mining was performed using databases like PubMed, Science Direct and general Google searches and the collected data was exhaustively studied and summarized in a generalized manner.

Results:

The main prospect of this review was to generate a comprehensive one-stop summary of the numerous available approaches and their pharmaceutical applications in improving the stability concerns, physicochemical and mechanical properties of the poorly water-soluble drugs which directly or indirectly augment their bioavailability.

Conclusion:

The use of novel methods, including but not limited to, nano-based formulations, bio-enhancers, solid dispersions, lipid-and polymer-based formulations which provide a wide range of applications not only increases the solubility and permeability of the poorly bioavailable drugs but also improves their stability, and targeting efficacy. Although, these methods have drastically changed the pharmaceutical industry demand for the newer potential methods with better outcomes in the field of pharmaceutical science to formulate various dosage forms with adequate systemic availability and improved patient compliance, further research is required.

MRP2-mediated transport of etoposide in MDCKII MRP2 cells is unaffected by commonly used non-ionic surfactants

The aim of the present study was to investigate the ability of non-ionic surfactants to inhibit MRP2-mediated transport in vitro in MDCKII MRP2 cells. Transport studies across MDCKII MRP2 cell monolayers were performed using ³H-etoposide and ³H-digoxin. 19 different non-ionic surfactants, including several polysorbates (PS), cremophor EL, vitamin E-TPGS, and n-nonyl β-D-glucopyranoside (NG), were investigated. Barrier function of the cells was investigated measuring TEER and transport of ¹⁴C-glycine. The amount of isotope was quantified using liquid scintillation counting. In MDCKII MRP2 cells a polarized transport of etoposide and digoxin in the secretory (basolateral to apical) direction with efflux ratios of 5.5 ± 0.7 and 18.5 ± 4.2, respectively, was measured. P-gp inhibitors such as valspodar and zosuquidar did not affect etoposide transport, and furthermore PS20 decreased secretory transport of digoxin, but not of etoposide. Transport of etoposide was therefore mainly MRP2-mediated and used as a probe to investigate pharmaceutical excipients. Non-ionic surfactants did not modulate etoposide transport across intact cell monolayers of MRP2 overexpressing MDCKII cells, although preliminary studies suggest that most were able to alter MRP2-mediated efflux of the fluorescent 5-chloromethylfluorescein (CMF). In conclusion, etoposide transport across MDCKII MRP2 cells was modulated by cyclosporin A, an inhibitor of MRP2 and P-gp, but not by specific P-gp inhibitors (valspodar and zosuquidar), which suggests that etoposide transport is primarily influenced by MRP2. In addition, commonly used non-ionic surfactants did not decrease MRP2-mediated etoposide transport in MDCKII MRP2 cells. These results suggest that etoposide transport in MDCKII MRP2 cells is a model system to investigate MRP2 interactions, and that surfactants may not have a large potential for increasing oral bioavailability of drugs through inhibition of MRP2 transport activity.

Multi-drug resistance protein 2 (MRP2) expression, adjuvant tamoxifen therapy, and risk of breast cancer recurrence: a Danish population-based nested case-control study

BACKGROUND

Adjuvant tamoxifen therapy approximately halves the risk of recurrence in estrogen receptor-positive (ER+) breast cancer patients, but many women respond insufficiently to therapy. Expression of multi-drug resistance protein 2 (MRP2) in breast cancer may potentiate tamoxifen resistance. Thus, we investigated the expression of MRP2 in breast cancer as a predictor of tamoxifen therapy effectiveness.

MATERIAL AND METHODS

We conducted a case-control study nested in the Danish Breast Cancer Group clinical database. The study included women aged 35-69 years diagnosed with stage l-lll breast cancer during 1985-2001, in Jutland, Denmark. We identified 541 recurrent breast cancers (cases) among women with estrogen receptor positive (ER+) disease treated with tamoxifen for at least 1 year (ER+/TAM+) and 300 cases among women with estrogen receptor-negative (ER-) disease, never treated with tamoxifen (ER-/TAM-). We matched one recurrence-free control to each recurrent case. We retrieved paraffin-embedded primary tumor tissue for all patients, and all available recurrent tumor tissue from pathology archives. MRP2 expression was evaluated using immunohistochemistry. We computed odds ratios (ORs) and 95% confidence intervals (95% CIs) associating MRP2 expression (positive vs. none) with breast cancer recurrence in conditional logistic regression models. We compared MRP2 expression in paired primary- and recurrent tumors.

RESULTS

MRP2 expression was more prevalent in the ER+/TAM + group, than in the ER-/TAM - group. No predictive utility of MRP2 for breast cancer recurrence was found in the ER+/TAM + group (OR_adj = 0.96, 95% CI 0.70, 1.33). Further, no prognostic utility was found in the ER-/TAM - group (OR_adj = 0.81, 95% CI 0.53, 1.23). MRP2 expression was not increased in recurrent versus primary tumors.

CONCLUSIONS

MRP2 expression is neither a predictive marker of tamoxifen effectiveness nor a prognostic marker in breast cancer.

The Syk inhibitor R406 is a modulator of P-glycoprotein (ABCB1)-mediated multidrug resistance

In a previously published study, higher levels of spleen tyrosine kinase (Syk) were observed in recurrent post-chemotherapy ovarian cancers compared to primary tumors. Syk inhibition was found to stabilize microtubules and potentiate paclitaxel activity in cellular models of taxane-resistant ovarian cancers. We further studied the effects of Syk inhibition on paclitaxel activity in Syk(+) ovarian cancer cell models and in variants selected for taxane resistance. Syk inhibition was accomplished using RNAi and by exposure to the small molecule competitive inhibitor R406, the active metabolite of fostamatinib. Exposure to R406 or to a SYK-specific pool of siRNAs did not alter taxane activity in the OVCAR-3 cell line, which has the most Syk content in our panel of nine human ovarian cancer cell lines. However, treatment with R406 sensitised the multidrug resistant (MDR) variants MES-SA/Dx5 and SK-OV-3/TR to paclitaxel in a dose-dependent manner resulting from the inhibition of the ABCB1/P-glycoprotein (P-gp) drug transporter. These observations are Syk-independent since both MDR cell models are Syk negative. R406 modulated resistance to other known P-gp substrates, and we observed orthovanadate-sensitive ATPase stimulation resulting from treatment with R406. These data indicate that the chemo-sensitizing effect of R406 in taxane-resistant cells previously reported was not associated with Syk but resulted from the modulation of P-gp-mediated MDR.

Transient receptor potential vanilloid-type 2 targeting on stemness in liver cancer

The malignant phenotype of the cells resulting from human liver cancer is driven by liver cancer stem-like cells (LCSLCs). Transient Receptor Potential Vanilloid-type 2 channel (TRPV2) contributes to the progression of different tumor types, including liver cancer. In the current study, the TRPV2 expression levels give rise to the effect on stemness in liver cancer cell lines. TRPV2 knockdown in HepG2 cells enhanced spheroid and colony formation, and expression levels of CD133, CD44 and ALDH1 whereas the opposite effects were observed in TRPV2 enforced expression in SMMC-7721 cells. Furthermore, TRPV2 overexpression restored inhibition of spheroid and colony formation, and stem cell markers expression in HepG2 cells with TRPV2 silencing. The addition of the TRPV2 agonist probenecid and the TRPV2 antagonist tranilast suppressed and/or increased in vitro spheroid and colony formation, and stem cell marker expression of LCSLCs and/or liver cancer cell lines, respectively. Notably, probenecid and tranilast significantly inhibited or promoted tumor growth of HepG2 xenografts in the severe combined immunodeficiency (SCID) mouse model, respectively. TRPV2 expression at protein levels revealed converse correlation with those of CD133 and CD44 in human hepatocellular carcinoma (HCC) tissue. Collectively, the data demonstrate that TRPV2 exert effects on stemness of liver cancer and is a potential target in the treatment of human liver cancer patients.

An oral quinoline derivative, MPT0B392, causes leukemic cells mitotic arrest and overcomes drug resistant cancer cells

Despite great advances in the treatment of acute leukemia, a renaissance of current chemotherapy needs to be improved. The present study elucidates the underlying mechanism of a new synthetic quinoline derivative, MPT0B392 (B392) against acute leukemia and its potential anticancer effect in drug resistant cells. B392 caused mitotic arrest and ultimately led to apoptosis. It was further demonstrated to be a novel microtubule-depolymerizing agent. The effects of oral administration of B392 showed relative potent anti-leukemia activity in an in vivo xenograft model. Further investigation revealed that B392 triggered induction of the mitotic arrest, followed by mitochondrial membrane potential loss and caspases cleavage by activation of c-Jun N-terminal kinase (JNK). In addition, B392 enhanced the cytotoxicity of sirolimus in sirolimus-resistant acute leukemic cells through inhibition of Akt/mTOR pathway and Mcl-1 protein expression, and also was active in the p-glycoprotein (p-gp)-overexpressing National Cancer Institute/Adriamycin-Resistant cells with little susceptibility to p-gp. Taken together, B392 has potential as an oral mitotic drug and adjunct treatment for drug resistant cancer cells.

Cross-Linking of Thiolated Paclitaxel-Oligo(p-phenylene vinylene) Conjugates Aggregates inside Tumor Cells Leads to "Chemical Locks" That Increase Drug Efficacy

How to reduce the resistance of certain tumor cells to paclitaxel (PTX) and related taxoid anticancer drugs is a major challenge for improving cure rates. An oligo(p-phenylenevinylene) unit with thiol groups and a PTX unit (OPV-S-PTX), which enhances drug efficacy and reverses resistance is thus designed. The mechanism involves diffusion of OPV-S-PTX into the cell, where π-π interactions lead to aggregation. Cross-linking of the aggregates via oxidation of thiol groups is favored in tumor cells because of the higher reactive oxygen species (ROS) concentration. Cross-linked aggregates "chemically lock" the multichromophore particle for a more persistent effect. The IC₅₀ of OPV-S-PTX for tumor cell line A549 is reduced down to 0.33 × 10^-9 m from that observed for PTX itself (41 × 10^-9 m). Enhanced efficacy by OPV-S-PTX is proposed to proceed via acceleration of microtubule bundle formation. A549/T-inoculated xenograft mice experiments reveal suppression of tumor growth upon OPV-S-PTX treatment. Altogether, these results show that the internal cross-linking of OPV-S-PTX through ROS provides a means to discriminate between tumor and healthy cells and the formation of the chemically locked particles enhances drug efficacy and helps in reducing resistance.

Renal Drug Transporters and Drug Interactions

Transporters in proximal renal tubules contribute to the disposition of numerous drugs. Furthermore, the molecular mechanisms of tubular secretion have been progressively elucidated during the past decades. Organic anions tend to be secreted by the transport proteins OAT1, OAT3 and OATP4C1 on the basolateral side of tubular cells, and multidrug resistance protein (MRP) 2, MRP4, OATP1A2 and breast cancer resistance protein (BCRP) on the apical side. Organic cations are secreted by organic cation transporter (OCT) 2 on the basolateral side, and multidrug and toxic compound extrusion (MATE) proteins MATE1, MATE2/2-K, P-glycoprotein, organic cation and carnitine transporter (OCTN) 1 and OCTN2 on the apical side. Significant drug-drug interactions (DDIs) may affect any of these transporters, altering the clearance and, consequently, the efficacy and/or toxicity of substrate drugs. Interactions at the level of basolateral transporters typically decrease the clearance of the victim drug, causing higher systemic exposure. Interactions at the apical level can also lower drug clearance, but may be associated with higher renal toxicity, due to intracellular accumulation. Whereas the importance of glomerular filtration in drug disposition is largely appreciated among clinicians, DDIs involving renal transporters are less well recognized. This review summarizes current knowledge on the roles, quantitative importance and clinical relevance of these transporters in drug therapy. It proposes an approach based on substrate-inhibitor associations for predicting potential tubular-based DDIs and preventing their adverse consequences. We provide a comprehensive list of known drug interactions with renally-expressed transporters. While many of these interactions have limited clinical consequences, some involving high-risk drugs (e.g. methotrexate) definitely deserve the attention of prescribers.

The role of membrane transporters in ovarian cancer chemoresistance and prognosis

INTRODUCTION

Ovarian cancer has the highest mortality rate of all cancers in women. There is currently no effective method for early diagnosis, limiting the precision of clinical expectations. Predictions of therapeutic efficacy are currently not available either. Specifically, the development of chemoresistance against conventional chemotherapy poses a fundamental complication. Some membrane transporters have been reported to influence chemoresistance, which is often associated with a poor prognosis. Areas covered: The aim of this article is to review the existing information about membrane transporters and their role in both ovarian cancer chemoresistance and its outcomes. We then highlight limitations of current methodologies and suggest alternatives providing avenues for future research. Expert opinion: Membrane transporters play an important role in development of chemoresistance and affect prognosis of ovarian cancer patients; however, due to variations in methodology and in patient populations, their specific roles have yet to be clarified. For further evaluation of the clinical utility of membrane transporters, it is essential to validate results and improve methods for marker assessment across laboratories. A promising area for future research is to identify the genetic variability in potential markers in peripheral blood. These markers would then stratify patients into defined groups for optimal intervention.

High-content screening of clinically tested anticancer drugs identifies novel inhibitors of human MRP1 (ABCC1)

Multidrug resistance protein 1 (MRP1/ABCC1), an integral transmembrane efflux transporter, belongs to the ATP-binding cassette (ABC) protein superfamily. MRP1 governs the absorption and disposition of a wide variety of endogenous and xenobiotic substrates including various drugs across organs and physiological barriers. Additionally, its overexpression has been implicated in multidrug resistance in chemotherapy of multiple cancers. Here, we describe the development of a high content imaging-based screening assay for MRP1 activity. This live cell-based automated microscopy assay is very robust and allows simultaneous detection of cell permeable, non-toxic and potent inhibitors. The validity of the assay was demonstrated by profiling a library of 386 anti-cancer compounds, which are under clinical trials, for interactions with MRP1. The assay identified 12 potent inhibitors including two known MRP1 inhibitors, cyclosporine A and rapamycin. On the other hand, MRP1-inhibitory activity of tipifarnib, AZD1208, deforolimus, everolimus, temsirolimus, HS-173, YM201636, ESI-09, TAK-733, and CX-6258 has not been previously reported. Inhibition of MRP1 activity was further validated using flow cytometry and confocal microscopy for the respective detection of calcein and doxorubicin in MRP1-overexpressing cells. Among the identified compounds, tipifarnib, AZD1208, rapamycin, deforolimus, everolimus, TAK-733, and temsirolimus resensitized MRP1-overexpressing H69AR cells towards vincristine, a cytotoxic chemotherapeutic agent, by 2-6-fold. Using purified HEK293 membrane vesicles overexpressing MRP1, MRP2, MRP3, and MRP4, we also demonstrated that the identified compounds exert differential and selective response on the uptake of estradiol glucuronide, an endogenous MRP substrate. In summary, we demonstrated the effectiveness of the high content imaging-based high-throughput assay for profiling compound interaction with MRP1.

Paclitaxel in Breast Cancer

Paclitaxel, a chemotherapeutic drug isolated from the Pacific yew, was approved for the treatment of metastatic breast cancer in 1994 and remains one of the most important agents in the treatment of patients with this disease. It is currently approved for the adjuvant treatment of node-positive breast cancer, administered sequentially after a standard doxorubicin-containing regimen, and for metastatic disease after failure of combination chemotherapy or relapse within 6 months of adjuvant chemotherapy. In this article, data on the pharmacology, clinical efficacy and safety of paclitaxel for the treatment of breast cancer will be reviewed.

Know your ABCs: Characterization and gene expression dynamics of ABC transporters in the polyphagous herbivore Helicoverpa armigera

Polyphagous insect herbivores are adapted to many different secondary metabolites of their host plants. However, little is known about the role of ATP-binding cassette (ABC) transporters, a multigene family involved in detoxification processes. To study the larval response of the generalist Helicoverpa armigera (Lepidoptera) and the putative role of ABC transporters, we performed developmental assays on artificial diet supplemented with secondary metabolites from host plants (atropine-scopolamine, nicotine and tomatine) and non-host plants (taxol) in combination with a replicated RNAseq experiment. A maximum likelihood phylogeny identified the subfamily affiliations of the ABC transporter sequences. Larval performance was equal on the atropine-scopolamine diet and the tomatine diet. For the latter we could identify a treatment-specific upregulation of five ABC transporters in the gut. No significant developmental difference was detected between larvae fed on nicotine or taxol. This was also mirrored in the upregulation of five ABC transporters when fed on either of the two diets. The highest number of differentially expressed genes was recorded in the gut samples in response to feeding on secondary metabolites. Our results are consistent with the expectation of a general detoxification response in a polyphagous herbivore. This is the first study to characterize the multigene family of ABC transporters and identify gene expression changes across different developmental stages and tissues, as well as the impact of secondary metabolites in the agricultural pest H. armigera.

Pharmacokinetic effects of curcumin on docetaxel mediated by OATP1B1, OATP1B3 and CYP450s

Curcumin can synergistically enhance docetaxel's in vitro and in vivo antitumor activity and has been co-administrated with docetaxel in clinical trials. The aim of our study is to investigate the effect of curcumin on the pharmacokinetics of docetaxel and explore its mechanism on OATP1B1, OATP1B3 and human liver microsomes (HLMs). In rats, curcumin increased the docetaxel area under the plasma concentration-time curve (AUC0-8h) and the terminal half-life (t1/2) to 1.86- and 1.55-fold, respectively. Moreover, curcumin decreased the clearance (CL) of docetaxel to 52.1%. Human embryonic kidney 293 (HEK293) cells stably expressing OATP1B1 and OATP1B3 were used to observe the effects of curcumin on OATP1B1 and OATP1B3-mediated uptake of docetaxel. Curcumin exhibited potent inhibition on OATP1B1 and OATP1B3-mediated docetaxel uptake with IC50 values of 3.81 ± 1.19 μM and 33.70 ± 1.22 μM, respectively. The inhibition of curcumin on docetaxel metabolism in HLMs indicated that curcumin can modestly inhibit the metabolism of docetaxel with the IC50 value of 22.70 ± 1.13 μM and Ki value of 24.72 ± 4.24 μM. The preclinical and clinical improved docetaxel's therapeutic efficacy when co-administrated with curcumin may be due to the inhibition of curcumin on OATP1B1, OATP1B3 and HLMs activities. Close attention should be paid when combined treatment with docetaxel and curcumin carried out clinically.

Significant effect of age on docetaxel pharmacokinetics in Japanese female breast cancer patients by using the population modeling approach

PURPOSE

Docetaxel is frequently used in the treatment of a wide variety of solid tumors, including breast cancer. The aim of this study is to obtain the population pharmacokinetic parameters of docetaxel in Japanese female patients with breast cancer.

METHODS

Blood samples from 24 patients were collected sequentially before and after docetaxel infusion. Genomic DNA was isolated from the peripheral blood and genotyped for the selected polymorphisms in the candidate genes of drug transporters and metabolizing enzymes. The influence of patient characteristics on the pharmacokinetics of docetaxel was evaluated using the nonlinear-mixed-effect modeling program, NONMEM. As a basis for comparison, the pharmacokinetics of another taxane paclitaxel in 41 separate female patients with breast cancer was calculated.

RESULTS

A two-compartment model adequately described the pharmacokinetic profiles of docetaxel. The population mean estimates of the total body clearance for patients aged 58 years or less and the central volume of distribution for docetaxel were 32.6 L/h and 5.77 L, respectively. In patients over 58 years, the clearance was 24 % higher than that in the younger patients. No influences of the genotypes examined were noted on the clearance of docetaxel. The clearance of paclitaxel was not affected by patient age.

CONCLUSIONS

Patients over the age of 58 years showed significantly higher clearance of docetaxel than that in patients aged 58 years or less. Since the clearance of paclitaxel was not affected by the age, it is possible that the pharmacokinetic mechanisms of docetaxel might be specifically affected by age in females.

Elevated alpha1-acid glycoprotein in gastric cancer patients inhibits the anticancer effects of paclitaxel, effects restored by co-administration of erythromycin

Paclitaxel (PTX) which easily elutes into ascites is widely used to treat gastric cancer patients with peritoneal carcinomatosis (PC), but clinical outcomes are suboptimal. Increased concentrations of α1-acid glycoprotein (AGP), an important drug-binding protein, have been reported in the plasma and ascites of cancer patients. This study sought to clarify whether AGP binds to PTX and alters its anticancer effects. AGP concentrations were measured in the serum and ascites of gastric cancer patients with PC and in the serum of healthy volunteers. The in vitro effects of AGP and AGP plus erythromycin (EM) on PTX were evaluated by MTT assays in the gastric cancer cell lines. We also measured AGP concentrations in the ascites of PC model mice and examined the effects of EM plus PTX on PC. The mean AGP concentrations in the serum and ascites of gastric cancer patients with PC were 1524 and 834 μg/mL, respectively, higher than the mean AGP concentration of 650 μg/mL observed in the sera of healthy volunteers. AGP > 400 μg/mL significantly suppressed the cell growth inhibitory effect of PTX in vitro, but the co-administration of EM restored it. Elevated AGP concentrations were observed in the ascites of PC model mice. Administration of PTX alone did not markedly diminish PC, whereas co-administration of PTX and EM significantly reduced PC (p = 0.011). AGP is an important regulatory factor modulating the anticancer activity of intraperitoneal PTX. The co-administration of PTX and EM may be effective in treating gastric cancer patients with PC.

Predicting paclitaxel-induced neutropenia using the DMET platform

AIM

The use of paclitaxel in cancer treatment is limited by paclitaxel-induced neutropenia. We investigated the ability of genetic variation in drug-metabolizing enzymes and transporters to predict hematological toxicity.

PATIENTS & METHODS

Using a discovery and validation approach, we identified a pharmacogenetic predictive model for neutropenia. For this, a drug-metabolizing enzymes and transporters plus DNA chip was used, which contains 1936 SNPs in 225 metabolic enzyme and drug-transporter genes.

RESULTS

Our 10-SNP model in 279 paclitaxel-dosed patients reached 43% sensitivity in the validation cohort. Analysis in 3-weekly treated patients only resulted in improved sensitivity of 79%, with a specificity of 33%. None of our models reached statistical significance.

CONCLUSION

Our drug-metabolizing enzymes and transporters-based SNP-models are currently of limited value for predicting paclitaxel-induced neutropenia in clinical practice. Original submitted 9 March 2015; Revision submitted 20 May 2015.

Are pharmacogenomic biomarkers an effective tool to predict taxane toxicity and outcome in breast cancer patients? Literature review

PURPOSE

Breast cancer is a heterogeneous disease, characterized by various molecular phenotypes that correlate with different prognosis and response to treatments. Taxanes are some of the most active chemotherapeutic agents for breast cancer; however, their utilization is limited, due to hematologic and cumulative neurotoxicity on treated patients. To understand why only some patients experience severe adverse effects and why patients respond and develop resistance with different rates to taxane therapy, the metabolic pathways of these drugs should be completely unraveled. The variant forms of several genes, related to taxane pharmacokinetics, can be indicative markers of clinical parameters, such as toxicity or outcome.

METHODS

The search of the data has been conducted through PubMed database, presenting clinical data, clinical trials and basic research restricted to English language until June 2015.

RESULTS

We studied the literature in order to find any possible association between the major pharmacogenomic variants and specific taxane-related toxicity and patient outcome. We found that the data of these studies are sometimes discordant, due to both the small number of enrolled patients and the heterogeneity of the examined population.

CONCLUSIONS

Among all analyzed genes, only CYP1B1 and ABCB1 resulted the strongest candidates to become biomarkers of clinical response to taxane therapy in breast cancer, although their utilization still remains an experimental procedure. In the future, greater studies on genetic polymorphisms should be performed in order to identify differentiating signatures for patients with higher toxicity and with resistant or responsive outcome, before the administration of taxanes.

Diaminothiazoles evade multidrug resistance in cancer cells and xenograft tumour models and develop transient specific resistance: understanding the basis of broad-spectrum versus specific resistance

Acquired drug resistance poses a challenge in cancer therapy. Drug efflux is the most common mechanism of resistance displayed by hydrophobic drugs beyond a certain size. However, target specific changes and imbalance between the pro- and anti-apoptotic proteins are also found quite often in many tumours. A number of small antimitotic agents show high potential for multidrug resistant tumours, mainly because they are able to evade the efflux pumps. However, these compounds are also likely to suffer from resistance upon prolonged treatment. Thus, it is important to find out agents that are sensitive to resistant tumours and to know the resistance mechanisms against small molecules so that proper combinations can be planned. In this report, we have studied the efficiency of diaminothiazoles, a novel class of tubulin targeting potential anticancer compounds of small size, in multidrug resistant cancer. Studies in model cell lines raised against taxol and the lead diaminothiazole, DAT1 [4-amino-5-benzoyl-2-(4-methoxy phenyl amino) thiazole], and the xenograft tumours derived from them, show that diaminothiazoles are highly promising against multidrug resistant cancers. They were able to overcome the expression of efflux protein MDR1 and certain tubulin isotypes, could sensitize improper apoptotic machinery and ablated checkpoint proteins Bub1 and Mad2. Further, we have found that the resistance against microtubule binding compounds with higher size is broad-spectrum and emerges due to multiple factors including overexpression of transmembrane pumps. However, resistance against small molecules is transient, specific and is contributed by target specific changes and variations in apoptotic factors.

Inter-patient variability in docetaxel pharmacokinetics: A review

Docetaxel is a frequently used chemotherapeutic agent in the treatment of solid cancers. Because of the large inter-individual variability (IIV) in the pharmacokinetics (PK) of docetaxel, it is challenging to determine the optimal dose in individual patients in order to achieve optimal efficacy and acceptable toxicity. Despite the established correlation between systemic docetaxel exposure and efficacy, the precise factors influencing docetaxel PK are not yet completely understood. This review article highlights currently known factors that influence docetaxel PK, and focusses on those that are clinically relevant. For example, liver impairment should be taken into account when calculating docetaxel dosages as this may decrease docetaxel clearance. In addition, drug-drug interactions may be of distinct clinical importance when using docetaxel. Particularly, drugs strongly inhibiting CYP3A4 such as ketoconazole should not be concurrently administered without dose modification, as they may decrease the clearance of docetaxel. Gender, castration status, and menopausal status might be of importance as potential factors influencing docetaxel PK. The role of pharmacogenetics in predicting docetaxel PK is still limited, since no polymorphisms of clinical importance have yet been established.

Multidrug Resistance Proteins (MRPs) and Cancer Therapy

The ATP-binding cassette (ABC) transporters are members of a protein superfamily that are known to translocate various substrates across membranes, including metabolic products, lipids and sterols, and xenobiotic drugs. Multidrug resistance proteins (MRPs) belong to the subfamily C in the ABC transporter superfamily. MRPs have been implicated in mediating multidrug resistance by actively extruding chemotherapeutic substrates. Moreover, some MRPs are known to be essential in physiological excretory or regulatory pathways. The importance of MRPs in cancer therapy is also implied by their clinical insights. Modulating the function of MRPs to re-sensitize chemotherapeutic agents in cancer therapy shows great promise in cancer therapy; thus, multiple MRP inhibitors have been developed recently. This review article summarizes the structure, distribution, and physiological as well as pharmacological function of MRP1-MRP9 in cancer chemotherapy. Several novel modulators targeting MRPs in cancer therapy are also discussed.

Genetic variability in drug transport, metabolism or DNA repair affecting toxicity of chemotherapy in ovarian cancer

Background

This study aimed to determine whether single nucleotide polymorphisms (SNPs) in genes involved in DNA repair or metabolism of taxanes or platinum could predict toxicity or response to first-line chemotherapy in ovarian cancer.

Methods

Twenty-six selected SNPs in 18 genes were genotyped in 322 patients treated with first-line paclitaxel-carboplatin or carboplatin mono-therapy. Genotypes were correlated with toxicity events (anemia, neutropenia, thrombocytopenia, febrile neutropenia, neurotoxicity), use of growth factors and survival.

Results

The risk of anemia was increased for variant alleles of rs1128503 (ABCB1, C > T; p = 0.023, OR = 1.71, 95% CI = 1.07-2.71), rs363717 (ABCA1, A > G; p = 0.002, OR = 2.08, 95% CI = 1.32-3.27) and rs11615 (ERCC1, T > C; p = 0.031, OR = 1.61, 95% CI = 1.04-2.50), while it was decreased for variant alleles of rs12762549 (ABCC2, C > G; p = 0.004, OR = 0.51, 95% CI = 0.33-0.81). Likewise, increased risk of thrombocytopenia was associated with rs4986910 (CYP3A4, T > C; p = 0.025, OR = 4.99, 95% CI = 1.22-20.31). No significant correlations were found for neurotoxicity. Variant alleles of rs2073337 (ABCC2, A > G; p = 0.039, OR = 0.60, 95% CI = 0.37-0.98), rs1695 (ABCC1, A > G; p = 0.017, OR = 0.55, 95% CI 0.33-0.90) and rs1799793 (ERCC2, G > A; p = 0.042, OR = 0.63, 95% CI 0.41-0.98) associated with the use of colony stimulating factors (CSF), while rs2074087 (ABCC1, G > C; p = 0.011, OR = 2.09, 95% CI 1.18-3.68) correlated with use of erythropoiesis stimulating agents (ESAs). Homozygous carriers of the rs1799793 (ERCC2, G > A) G-allele had a prolonged platinum-free interval (p = 0.016).

Conclusions

Our data reveal significant correlations between genetic variants of transport, hepatic metabolism, platinum related detoxification or DNA damage repair and toxicity or outcome in ovarian cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/s40360-015-0001-5) contains supplementary material, which is available to authorized users.

Apical ABC transporters and cancer chemotherapeutic drug disposition

ATP-binding cassette (ABC) transporters are transmembrane efflux transporters that mediate cellular extrusion of a broad range of substrates ranging from amino acids, lipids, and ions to xenobiotics including many anticancer drugs. ABCB1 (P-GP) and ABCG2 (BCRP) are the most extensively studied apical ABC drug efflux transporters. They are highly expressed in apical membranes of many pharmacokinetically relevant tissues such as epithelial cells of the small intestine and endothelial cells of the blood capillaries in brain and testis, and in the placental maternal-fetal barrier. In these tissues, they have a protective function as they efflux their substrates back to the intestinal lumen or blood and thus restrict the intestinal uptake and tissue disposition of many compounds. This presents a major challenge for the use of many (anticancer) drugs, as most currently used anticancer drugs are substrates of these transporters. Herein, we review the latest findings on the role of apical ABC transporters in the disposition of anticancer drugs. We discuss that many new, rationally designed anticancer drugs are substrates of these transporters and that their oral availability and/or brain disposition are affected by this interaction. We also summarize studies that investigate the improvement of oral availability and brain disposition of many cytotoxic (e.g., taxanes) and rationally designed (e.g., tyrosine kinase inhibitor) anticancer drugs, using chemical inhibitors of these transporters. These findings provide a better understanding of the importance of apical ABC transporters in chemotherapy and may therefore advance translation of promising preclinical insights and approaches to clinical studies.

Modulators of the human ABCC2: hope from natural sources?

Human ABCC2 is an ATP-binding cassette transporter involved in the export of endobiotics and xenobiotics. It is involved in cisplatin resistance in cancer cells, particularly in ovarian cancer. The few known ABCC2 modulators are poorly efficient, so it is necessary to explore new ways to select and optimize efficient compounds ABCC2. Natural products offer an original scaffold for such a strategy and brings hope for this aim. This review covers basic knowledge about ABCC2, from distribution and topology aspects to physiological and pathological functions. It summarizes the effect of natural products as ABCC2 modulators. Certain plant metabolites act on different ABCC2 regulation levels and therefore are promising candidates to block the multidrug resistance mediated by ABCC2 in cancer cells.