P‐glycoprotein and cytochrome P450 3A act together in restricting the oral bioavailability of paclitaxel

Paclitaxel is avidly transported by P‐glycoprotein (P‐gp/MDR1/ABCB1). This results in low oral bioavailability, which can be boosted by coadministration of P‐gp inhibitors. Unlike paclitaxel, docetaxel is extensively metabolized by CYP3A4 and its oral bioavailability can be enhanced in mice and humans by coadministration of the potent CYP3A inhibitor ritonavir. Unexpectedly, ritonavir also enhances the oral bioavailability of paclitaxel in humans. We aimed to resolve the mechanism underlying this enhancement. Using mice lacking Cyp3a and/or P‐gp, we investigated the combined and separate restricting roles of Cyp3a and P‐gp in the oral bioavailability of paclitaxel, and the boosting effect of ritonavir. CYP3A4‐humanized mice were used for translation to the human situation. P‐gp had a dominant effect (11.6‐fold, p < 0.001) over Cyp3a (<1.5‐fold, n.s.) in limiting plasma concentrations of oral paclitaxel. However, in the absence of P‐gp, Cyp3a decreased paclitaxel plasma concentrations twofold (p < 0.001). Coadministered ritonavir inhibited Cyp3a‐mediated metabolism, but not P‐gp‐mediated transport of paclitaxel. Owing to the dominant effect of P‐gp, ritonavir enhanced only paclitaxel plasma concentrations in P‐gp‐deficient mice. Mouse liver microsomes metabolized paclitaxel far less efficiently than human or CYP3A4‐transgenic liver microsomes, revealing much lower efficiency of paclitaxel metabolism by mouse than by human CYP3As. Accordingly, ritonavir could enhance the oral bioavailability of paclitaxel in CYP3A4‐humanized mice, despite the fact that these mice are P‐gp‐proficient. Our results show that CYP3A4 inhibition most likely underlies the boosting effect of ritonavir on oral paclitaxel bioavailability in humans. Furthermore, CYP3A4‐humanized mice allow improved understanding of CYP3A4‐mediated paclitaxel metabolism in humans.     

Individual and combined roles of CYP3A, P-glycoprotein (MDR1/ABCB1) and MRP2 (ABCC2) in the pharmacokinetics of docetaxel

Docetaxel is one of the most widely used anticancer drugs. A major problem with docetaxel treatment, however, is the considerable interpatient variability in docetaxel exposure. Another disadvantage of the drug is that it has a very low oral bioavailability and can, therefore, only be administered intravenously. The drug-metabolizing enzyme CYP3A and the drug transporter MDR1 (P-glycoprotein) are major determinants of docetaxel pharmacokinetics. In vitro studies have indicated that docetaxel is also a substrate for the drug transporter MRP2, but the in vivo importance of MRP2 for docetaxel is currently unknown. We, therefore, investigated the role of MRP2 in the pharmacokinetics of docetaxel by utilizing Mrp2(-/-) mice. We also generated and characterized Cyp3a/Mdr1a/b/Mrp2(-/-) combination knockout mice to get more insight into how these drug-handling systems work together in determining docetaxel pharmacokinetics. The systemic exposure in Mrp2(-/-) mice was not significantly different from wild-type, after either oral or intravenous administration. Strikingly, however, in Cyp3a/Mdr1a/b/Mrp2(-/-) mice, systemic docetaxel exposure was increased 166-fold after oral administration when compared with wild-type mice, and 2.3-fold when compared with Cyp3a/Mdr1a/b(-/-) mice. Interestingly, this 166-fold increase was disproportionate compared with that for the separate Cyp3a (12-fold) or Mdr1a/b/Mrp2 (4-fold) knockouts. The oral bioavailability was increased to 73% in the Cyp3a/Mdr1a/b/Mrp2(-/-) strain, versus only 10% in wild-type mice. Our data thus indicate that in the absence of CYP3A and Mdr1a/b activity, Mrp2 has a marked impact on docetaxel pharmacokinetics. These findings could have important implications for improving the oral bioavailability and reducing the variability in docetaxel exposure.     

P‐glycoprotein (MDR1/ABCB1) restricts brain accumulation and cytochrome P450‐3A (CYP3A) limits oral availability of the novel ALK/ROS1 inhibitor lorlatinib

Lorlatinib (PF‐06463922) is a promising oral anaplastic lymphoma kinase (ALK) and ROS1 inhibitor currently in Phase III clinical trials for treatment of non‐small‐cell lung cancer (NSCLC) containing an ALK rearrangement. With therapy‐resistant brain metastases a major concern in NSCLC, lorlatinib was designed to have high membrane and blood–brain barrier permeability. We investigated the roles of the multidrug efflux transporters ABCB1 and ABCG2, and the multispecific drug‐metabolizing enzyme CYP3A in plasma pharmacokinetics and tissue distribution of lorlatinib using genetically modified mouse strains. In vitro, human ABCB1 and mouse Abcg2 modestly transported lorlatinib. Following oral lorlatinib administration (at 10 mg/kg), brain accumulation of lorlatinib, while relatively high in wild‐type mice, was still fourfold increased in Abcb1a/1b^?/? and Abcb1a/1b;Abcg2^?/? mice, but not in single Abcg2^?/? mice. Lorlatinib plasma levels were not altered. Oral coadministration of the ABCB1/ABCG2 inhibitor elacridar increased the brain accumulation of lorlatinib in wild‐type mice fourfold, that is, to the same level as in Abcb1a/1b;Abcg2^?/? mice, without altering plasma exposure. Similar results were obtained for lorlatinib testis accumulation. In Cyp3a^?/? mice, the plasma exposure of lorlatinib was increased 1.3‐fold, but was then twofold reduced upon transgenic overexpression of human CYP3A4 in liver and intestine, whereas relative tissue distribution of lorlatinib remained unaltered. Our data indicate that lorlatinib brain accumulation is substantially limited by P‐glycoprotein/ABCB1 in the blood–brain barrier, but this can be effectively reversed by elacridar coadministration. Moreover, oral availability of lorlatinib is markedly restricted by CYP3A4 activity. These insights may be used in optimizing the therapeutic application of lorlatinib.     

Expression levels and activation of a PXR variant are directly related to drug resistance in osteosarcoma cell lines

BACKGROUND: Approximately 30% to 40% of all patients with osteosarcomas ultimately experience recurrence. The study investigated the hypothesis that the resistance of osteosarcoma to chemotherapy may be related to the expression of a pregnane xenobiotic receptor (PXR) variant protein and its role as the major inducer of P450 3A4 in these tumors. METHODS: Polymerase chain reaction (PCR) and Western blot analysis were used to determine PXR mRNA and protein expression, respectively. Real-time PCR and CYP3A catalytic activity using 7-benzyl-trifluoromethyl coumarin (BFC) as the probe substrate were used to measure the induction of P450 3A4 or MDR1. siRNA transfections were performed for PXR and cytotoxicity determined by a colorimetric based assay or Annexin v-Fitc staining. RESULTS: Differences were observed in the molecular size of the PXR protein expressed in sarcoma cell lines when compared with the wildtype PXR expressed in normal liver, kidney, or small intestine. A polyclonal PXR antibody raised against the N-terminus of the wildtype PXR did not detect PXR expressed in these sarcoma cell lines. In the osteosarcoma cell lines, etoposide and doxorubicin were better inducers of P450 3A4 and MDR1 than rifampin. siRNA against PXR down-regulated P450 3A4 expression only in the osteosarcoma cell line. Cytotoxicity assays showed that the resistance of the osteosarcoma cell lines to etoposide correlated with PXR protein expression levels and activation of P450 3A4 and could be prevented by ketoconazole. CONCLUSION: The results suggest that PXR plays a critical role in the regulation of P450 3A4 expression in osteosarcoma and that its expression and activation in these tumors may influence the effect of chemotherapeutic agents on the induction of target genes implicated in drug resistance.     

P-glycoprotein (MDR1/ABCB1) controls brain accumulation and intestinal disposition of the novel TGF-β signaling pathway inhibitor galunisertib

Galunisertib (LY2157299), a promising small-molecule inhibitor of the transforming growth factor-beta (TGF-β) receptor, is currently in mono- and combination therapy trials for various cancers including glioblastoma, hepatocellular carcinoma and breast cancer. Using genetically modified mouse models, we investigated the roles of the multidrug efflux transporters ABCB1 and ABCG2, the OATP1A/1B uptake transporters and the drug-metabolizing CYP3A complex in galunisertib pharmacokinetics. In vitro, galunisertib was vigorously transported by human ABCB1, and moderately by mouse Abcg2. Orally administered galunisertib (20 mg/kg) was very rapidly absorbed. Galunisertib brain-to-plasma ratios were increased by ~24-fold in Abcb1a/1b^−/− and Abcb1a/1b;Abcg2^−/− mice compared to wild-type mice, but not in single Abcg2^−/− mice, whereas galunisertib oral availability was not markedly affected. However, recovery of galunisertib in the small intestinal lumen was strongly reduced in Abcb1a/1b^−/− and Abcb1a/1b;Abcg2^−/− mice. Oral coadministration of the ABCB1/ABCG2 inhibitor elacridar boosted galunisertib brain accumulation in wild-type mice to equal the levels seen in Abcb1a/1b;Abcg2^−/− mice. Oatp1a/1b deficiency did not alter oral galunisertib pharmacokinetics or liver distribution. Cyp3a^−/− mice showed a 1.9-fold higher plasma AUC_{0–1 hr} than wild-type mice, but this difference disappeared over 8 hr. Also, transgenic human CYP3A4 overexpression did not significantly alter oral galunisertib pharmacokinetics. Abcb1 thus markedly restricts galunisertib brain penetration and affects its intestinal disposition, possibly through biliary excretion. Elacridar coadministration could fully inhibit both processes, without causing acute toxicity. Moreover, mouse Cyp3a, but not human CYP3A4, may eliminate galunisertib at high plasma concentrations. These insights may help to guide the further clinical development and application of galunisertib.     

Bone marrow niche chemoprotection of metastatic solid tumors mediated by CYP3A4

Background

The bone/bone marrow is one of the most common sites for metastatic solid tumors. Moreover, the tumor microenvironment is an essential part of cancer homeostasis. Previously, it was shown that cytochrome P450 enzymes (CYPs) are present in the bone marrow (BM) microenvironment, particularly in the mesenchymal stroma cells, at levels comparable to those of hepatocytes. It was found that the CYPs play important roles in nurturing and maintaining normal hematopoietic stem cells as well as multiple myeloma and leukemia cells, including protecting them from toxic insults. It was hypothesized that the CYPs in the BM microenvironment might play a similar role in solid tumors metastatic to bone.

Methods

The interaction between the BM microenvironment and malignant cells that routinely metastasize to the bone (lung, breast, and prostate cancer) was modeled. Via genetic engineering and pharmacological approaches, the role of stromal cytochrome P450 3A4 (CYP3A4) in drug resistance promoted by the BM microenvironment in niche–cancer models in vitro and in vivo was interrogated.

Results

BM stroma protected prostate, breast, and lung cancer cells from cytotoxic chemotherapy. Stromal CYP3A4 was at least partially responsible for this protection in vitro and in vivo. Moreover, inhibiting CYP3A4 with clarithromycin overcame the stroma-mediated chemoresistance toward prostate, breast, and lung cancer cells.

Conclusions

These results suggest that, similar to observations from hematologic malignancies, the BM microenvironment, through expression of CYPs, creates a sanctuary site from chemotherapy for metastatic solid tumors. Targeting these sanctuaries holds promise for eradicating bone metastasis in solid tumors.     

Risk of non-small cell lung cancer and the cytochrome P4501A1 Ile462Val polymorphism

Objective The Ile462Val substitution in the cytochrome P450 1A1 gene (CYP1A1) results in increased enzymatic activity. Preliminary data suggesting a link between this polymorphism and lung cancer risk in Caucasians are inconsistent, reflecting small sample sizes and the relatively low frequency of the variant.Methods The data set consisted of 1050 primary non-small cell lung cancer cases and 581 controls, a large homogenous population designed specifically to address previous inconsistencies. Patients were genotyped using a PCR-RFLP technique.Results Carriers of the valine allele, CYP1A1*2C, (Ile/Val or Val/Val genotypes) were significantly over-represented in non-small cell lung cancer compared to controls (OR=1.9; 95% CI=1.2–2.9; p=0.005) when adjusted for confounders, particularly in women (OR=4.6; 95% CI=1.7–12.4; p=0.003). The valine variant was statistically significantly over-represented in cases of lung cancer younger than the median age (64 years) (OR=2.5; 95% CI=1.3–4.8; p=0.005) and cases with less than the median cumulative tobacco-smoke exposure (46 pack-years) (OR=2.4; 95% CI=1.3–4.7; p=0.007).Conclusions These new data establish an association between the CYP1A1 Ile462Val polymorphism and the risk of developing non-small cell lung cancer, especially among women.     

Human OATP1B1, OATP1B3 and OATP1A2 can mediate the in vivo uptake and clearance of docetaxel

Organic anion transporting polypeptides (human: OATPs and mouse: Oatps) are uptake transporters with important roles in drug pharmacokinetics and toxicity. We aimed to study the in vivo impact of mouse and human OATP1A/1B transporters on docetaxel plasma clearance and liver and intestinal uptake. Docetaxel was administered to Oatp1a/1b knockout and liver‐specific humanized OATP1B1, OATP1B3 and OATP1A2 transgenic mice. Experiments were conducted with a low polysorbate 80 (2.8%) formulation, as 8% polysorbate somewhat inhibited docetaxel plasma clearance after intravenous administration. After intravenous administration (10 mg/kg), Oatp1a/1b knockout mice had an approximately threefold higher plasma area under the curve (AUC). Impaired liver uptake was evident from the significantly reduced (approximately threefold) liver‐to‐plasma AUC ratios. Absence of mouse Oatp1a/1b transporters did not affect the intestinal absorption of orally administered docetaxel (10 mg/kg), while the systemic exposure of docetaxel was again substantially increased owing to impaired liver uptake. Most importantly, liver‐specific expression of each of the human OATP1B1, OATP1B3 and OATP1A2 transporters provided a nearly complete rescue of the increased plasma levels of docetaxel in Oatp1a/1b‐null mice after intravenous administration. Our data show that one or more of the mouse Oatp1a/1b transporters and each of the human OATP1A/1B transporters can mediate docetaxel uptake in vivo. This might be clinically relevant for OATP1A/1B‐mediated tumor uptake of docetaxel and for docetaxel clearance in patients in whom the transport activity of OATP1A/1B transporters is reduced owing to genetic variation or pharmacological inhibition, leading to potentially altered toxicity and therapeutic efficacy of this drug.     

CYP1A1和GSTM1基因多态性及其对个体肺癌易感性的联合效应:meta分析

背景与目的谷胱甘肽转移酶M1(glutathione S-transferase M1,GSTM1)和细胞色素P4501A1(cyto-chrome P450A1,CYP1A1)均存在基因多态性,并且对肺癌发病风险有一定的影响,两者联合作用对肺癌发病风险的影响尚无确切定论。本研究旨在探讨CYP1A1和GSTM1基因多态性及其联合效应与肺癌危险性的关系。方法在PubMed数据库、EMBASE数据库、中国生物医学文献数据库(china biology medicine,CBM)和中国知识基础设施工程数据库(china national knowledge infrastructure,CNKI)中查询文献,时间范围从各数据库建库至2011年3月。使用STATA10软件进行meta分析统计,对于每篇入选的文献均计算肺癌发生危险性调整混杂因素后优势比(odd ratio,OR)及其95%置信区间(confidence interval,CI)。结果 15篇文献最终被纳入本次研究。Meta分析显示GSTM1基因缺失时CYP1A1基因IIe/Val位点为纯合突变型时肺癌发病风险明显高于杂合型与纯合突变型联合,总体OR分别...     

Multiplex PCR with Confronting Two-pair Primers for CYP1A1 Ile462Val,GSTM1, GSTT1, and NQO1 C609T

Polymerase chain reaction with confronting two-pair primers (PCR-CTPP) is an effective genotyping method ‍for single nucleotide polymorphisms (SNPs) in aspects of reducing time and costs for analysis. So far we have ‍established PCR-CTPP conditions for tens of SNPs, including a triplex genotyping (Kawase et al., 2003). In the ‍present study we report a quadruplex PCR-CTPP to genotype simultaneously four functional polymorphisms of ‍carcinogen-metabolizing enzymes, CYP1A1 Ile462Val, GSTM1 null, GSTT1 null and NQO1 C609T, which were ‍reported that they have significant associations with smoking-related cancers. We applied this method for 475 health ‍check-up examinees to demonstrate the performance. Among the subjects, the genotype frequency of CYP1A1 ‍Ile462Val was 56.8% for Ile/Ile, 38.1% for Ile/Val and 5.1% for Val/Val. The null type frequencies of GSTM1 and ‍GSTT1 were 52.8% and 49.9%, respectively. And the genotype frequency of NQO1 C609T was 41.9% for C/C, ‍41.3% for C/T and 16.8% for T/T. Their distributions were similar to those reported for Japanese by other studies. ‍To the best of our awareness, this is the first paper that reports the success in quadruplex PCR-CTPP. The applied ‍polymorphisms are useful ones, which would be adopted not only for research purposes, but also for risk assessment ‍of individuals exposed to carcinogenic substances. This convenient genotyping would be applied for cancer prevention ‍especially in Asian Pacific regions, where expensive genotyping methods are hardly available.     

牛蒡子苷元调控Notch/Hes-1信号通路对口腔鳞状细胞癌HSC-3细胞增殖、凋亡和侵袭的影响

目的：探究牛蒡子苷元（ARC）通过调控Notch/Hes-1信号通路对口腔鳞状细胞癌（OSCC）HSC-3细胞增殖、凋亡和侵袭的影响及其机制。方法：使用不同质量浓度的ARC处理人HSC-3细胞,CCK-8法检测ARC对细胞增殖活力的影响,以选择适宜的药物浓度。将HSC-3细胞分为对照组、ARC-L组（10 mg/L ARC）、ARC-M组（20 mg/L ARC）、ARC-H组（40 mg/L ARC）和ARC-H+Jagged1/FC组（40 mg/L ARC+1.2μg/mL Jagged1/FC）。采用EdU法检测细胞增殖能力,划痕愈合实验、Transwell实验和流式细胞术分别检测细胞的迁移、侵袭能力及细胞周期和细胞凋亡率,WB法检测增殖（c-Myc、cyclin D1）、凋亡（BAX、Bcl-2、survivin）、EMT(E-cadherin、vimentin、Snail)及Notch/Hes-1通路（Notch 1、Hes-1、NICD）相关蛋白的表达水平。结果：与0 mg/L相比,10～80 mg/L的ARC均能显著降低HSC-3细胞增殖活力（均P<0.05）。与...     

Resveratrol and chemoprevention

Resveratrol is a phytoalexin, highly abundant in skins of red grapes and moderately abundant in peanuts and blueberries. Originally a constituent of oriental medicines, it has lately been rediscovered for a plethora of beneficial properties such as anti-cancer, anti-aging, antiviral, cardiovascular and neuroprotective effects, thereby making it one of the most sought after phytochemicals for supplementing human diet. Studies done in various laboratories have shown its modulatory effects on multitudes of cell signaling and gene expression pathways. Although most of its effects have been observed in cultured cells, quite a few have also been validated in whole animals as well. It is thus necessary to have a comprehensive look at all those effects of resveratrol in an organismal context. The following review summarizes the effects of resveratrol in the context of chemoprevention.     

Activated pregnane X receptor inhibits cervical cancer cell proliferation and tumorigenicity by inducing G2/M cell-cycle arrest

Pregnane X receptor (PXR) regulates cell proliferation and carcinogenesis in female reproductive tissue. We showed that PXR was expressed in cervical cells and tissue samples. PXR were lower or greatly diminished in cancer tissues compared to normal control. Functionally, activation of human PXR by rifampicin or ectopic expression of constitutively-activated human VP-PXR inhibited cervical cell proliferation. Constitutively-activated VP-PXR attenuated CaSki and HeLa xenograft tumor growth in nude mice compared with control. The cellular proliferation inhibition of PXR by causing G2/M cell-cycle arrest is involved up-regulation of Cullin1-3, MAD2L1, and down-regulation of ANAPC2 and CDKN1A. Our data suggests that PXR signaling inhibits tumor cell proliferation in vitro and cervical carcinoma growth in vivo.     

The role of nuclear receptors in pharmacokinetic drug-drug interactions in oncology

Drug-drug interactions can have a major impact on treatment outcome in cancer patients. These patients are at high risk of such interactions, because they are treated with combinations of multiple cytotoxic anticancer drugs or hormonal agents often co-administered with prophylactic antiemetics and analgesics to provide palliation. Interactions between drugs can affect the pharmacokinetics of concomitantly administered chemotherapeutic agents. Especially, due to the specific properties of anticancer drugs, such as a narrow therapeutic index and steep dose-toxicity curve, small pharmacokinetic changes can have significant clinical consequences like decreased therapeutic efficacy or increased toxicity. An important mechanism that underlies these interactions is the induction of enzymes or efflux transporters involved in the biotransformation and clearance of anticancer drugs. Several nuclear receptors, like the pregnane X receptor (PXR), constitutively androstane receptor (CAR), have been shown to regulate induction. Activation of these receptors will lead to induction of important enzymes like cytochrome P450 3A4 (CYP3A4), which is involved in the biotransformation of more than 50% of all clinically used drugs. Therefore, concomitant administration of agents that activate PXR will affect the pharmacokinetics of drugs that are substrate for PXRs target genes, which include CYP3A4 and MDR-1. Understanding of the molecular mechanisms that underlie enzyme induction and the identification of (new) drugs involved in pharmacokinetic drug-drug interactions may contribute to the predictability of drug-drug interactions and eventually help to develop safer anticancer regimens.