Gene-by-Environment Interaction of Bcrp-/- and Methionine- and Choline-Deficient Diet-Induced Nonalcoholic Steatohepatitis Alters SN-38 Disposition

Representative Rodent Models for Renal Transporter Alterations in Human Nonalcoholic Steatohepatitis

Alterations in renal elimination processes of glomerular filtration and active tubular secretion by renal transporters can result in adverse drug reactions. Nonalcoholic steatohepatitis (NASH) alters hepatic transporter expression and xenobiotic elimination, but until recently, renal transporter alterations in NASH were unknown. This study investigates renal transporter changes in rodent models of NASH to identify a model that recapitulates human alterations. Quantitative protein expression by surrogate peptide liquid chromatography-coupled mass spectrometry (LC-MS/MS) on renal biopsies from NASH patients was used for concordance analysis with rodent models, including methionine/choline deficient (MCD), atherogenic (Athero), or control rats and Leprdb/db MCD (db/db), C57BL/6J fast-food thioacetamide (FFDTH), American lifestyle-induced obesity syndrome (ALIOS), or control mice. Demonstrating clinical similarity to NASH patients, db/db, FFDTH, and ALIOS showed decreases in glomerular filtration rate (GFR) by 76%, 28%, and 24%. Organic anion transporter 3 (OAT3) showed an upward trend in all models except the FFDTH (from 3.20 to 2.39 pmol/mg protein), making the latter the only model to represent human OAT3 changes. OAT5, a functional ortholog of human OAT4, significantly decreased in db/db, FFDTH, and ALIOS (from 4.59 to 0.45, 1.59, and 2.83 pmol/mg protein, respectively) but significantly increased for MCD (1.67 to 4.17 pmol/mg protein), suggesting that the mouse models are comparable to human for these specific transport processes. These data suggest that variations in rodent renal transporter expression are elicited by NASH, and the concordance analysis enables appropriate model selection for future pharmacokinetic studies based on transporter specificity. These models provide a valuable resource to extrapolate the consequences of human variability in renal drug elimination. SIGNIFICANCE STATEMENT: Rodent models of nonalcoholic steatohepatitis that recapitulate human renal transporter alterations are identified for future transporter-specific pharmacokinetic studies to facilitate the prevention of adverse drug reactions due to human variability.

Transporter and metabolic enzyme-mediated intra-enteric circulation of SN-38, an active metabolite of irinotecan: A new concept

SN-38, an active metabolite of irinotecan (CPT-11), is thought to circulate enterohepatically via organic anion-transporting polypeptides (OATPs), UDP-glucuronyl transferases (UGTs), multidrug resistance-related protein 2 (MRP2), and breast cancer resistance protein (BCRP). These transporters and enzymes are expressed in not only hepatocytes but also enterocytes. Therefore, we hypothesized that SN-38 circulates between the intestinal lumen and the enterocytes via these transporters and metabolic enzymes. To test this hypothesis, metabolic and transport studies of SN-38 and its glucuronide (SN-38G) were conducted in Caco-2 cells. The mRNA levels of UGTs, MRP2, BCRP, and OATP2B1 were confirmed in Caco-2 cells. SN-38 was converted to SN-38G in Caco-2 cells. The efflux of intracellularly generated SN-38G across the apical (digestive tract) membranes was significantly higher than the efflux across the basolateral (blood, portal vein) membranes of Caco-2 cells cultured on polycarbonate membranes. SN-38G efflux to the apical side was significantly reduced in the presence of MRP2 and BCRP inhibitors, suggesting that SN-38G is transported across the apical membrane by MRP2 and BCRP. Treatment of Caco-2 cells with OATP2B1 siRNA increased the SN-38 residue on the apical side, confirming that OATP2B1 is involved in the uptake of SN-38 into enterocytes. No SN-38 was detected on the basolateral side with or without siRNA treatment, suggesting that the enterohepatic circulation of SN-38 is limited, contrary to previous reports. These results suggest that SN-38 is absorbed into the enterocytes via OATP2B1, glucuronidated by UGTs to SN-38G, and excreted into the digestive tract lumen by MRP2 and BCRP. SN-38G can be deconjugated by β-glucuronidase from intestinal bacteria in the digestive tract lumen to regenerate SN-38. We named this new concept of local drug circulation "intra-enteric circulation." This mechanism may allow SN-38 to circulate in the intestine and cause the development of delayed diarrhea, a serious side effect of CPT-11.

Downregulation of breast cancer resistance protein by long-term fractionated radiotherapy sensitizes lung adenocarcinoma to SN-38

Chemotherapy is usually the subsequent treatment for non-small cell lung cancer patients with acquired radioresistance after long-term fractionated radiotherapy. However, few studies have focused on the selection of chemotherapeutic drugs to treat lung adenocarcinoma patients with radioresistance. Our study compared the sensitivity changes of lung adenocarcinoma cells to conventional chemotherapeutic drugs under radioresistant circumstances by using three lung adenocarcinoma cell models, which were irradiated with fractionated X-rays at a total dose of 60 Gy. The results showed that the toxicities of paclitaxel, docetaxel and SN-38 were increased in radioresistant cells. The IC₅₀ values of docetaxel and SN-38 decreased 0 ~ 3 times and 3 ~ 36 times in radioresistant cells, respectively. Notably, the A549 radioresistant cells were approximately 36 times more sensitive to SN-38 than the parental cells. Further results revealed that the downregulation of the efflux transporter BCRP by long-term fractionated irradiation was an important factor contributing to the increased cytotoxicity of SN-38. In addition, the reported miRNAs and transcriptional factors that regulate BCRP did not participate in the downregulation. In conclusion, these results presented important data on the sensitivity changes of lung adenocarcinoma cells to chemotherapeutic drugs after acquiring radioresistance and suggested that irinotecan (the prodrug of SN-38) might be a promising drug candidate for lung adenocarcinoma patients with acquired radioresistance.

Breast Cancer Resistance Protein and Multidrug Resistance Protein 2 Mediate the Disposition of Leonurine-10-O-β-glucuronide

Background:

Leonurine (Leo), a promising antilipemic agent that has been approved for clinical trials, is extensively metabolized into bioactive Leonurine-10-O-β-glucuronide (L-10-G) vivo.

Objective:

To explore the effects of breast cancer resistance protein (Bcrp) and multidrug resistance protein 2 (Mrp2) on the disposition of L-10-G.

Methods:

The pharmacokinetics, tissue distribution and intestinal perfusion of Leo were studied by using efflux transporter gene knockout mouse models. The enzyme kinetics via liver and intestinal microsomes were also examined.

Results:

After intravenous injection with Leo, the AUC0-∞ values of L-10-G in Bcrp1-/- and Mrp2-/- mice were 1.55-fold and 16.80-fold higher, respectively, than those in wild-type FVB mice (P < 0.05). After oral administration, the AUC0-∞ value of L-10-G showed a 2.82-fold increase in Mrp2-/- mice compared with wild-type FVB mice (P < 0.05). After gavage with Leo for 10 and 25 min, the bile accumulation of L-10-G in Mrp2-/- mice was 3-fold and 22-fold lower, respectively, than that in wild-type FVB mice (P < 0.05). Besides, the intestinal excreted amount of L-10-G showed 2.22-fold and 2.68-fold decrease in Bcrp1-/- and Mrp2-/- mice, respectively, compared with that in wild-type FVB mice (P < 0.05). The clearance of L-10-G decreased in liver microsomes and increased in intestinal microsomes of Bcrp1-/- and Mrp2-/- mice compared to the wild-type FVB mice (P < 0.05).

Conclusion:

Both Bcrp and Mrp2 are involved in the disposition of L-10-G, and Mrp2 exhibits a superior influence.

Multi-factorial pharmacokinetic interactions: unraveling complexities in precision drug therapy

Introduction: Precision drug therapy requires accounting for pertinent factors in pharmacokinetic (PK) inter-individual variability (i.e., pharmacogenetics, diseases, polypharmacy, and natural product use) that can cause sub-therapeutic or adverse effects. Although each of these individual factors can alter victim drug PK, multi-factorial interactions can cause additive, synergistic, or opposing effects. Determining the magnitude and direction of these complex multi-factorial effects requires understanding the rate-limiting redundant and/or sequential PK processes for each drug.Areas covered: Perturbations in drug-metabolizing enzymes and/or transporters are integral to single- and multi-factorial PK interactions. Examples of single factor PK interactions presented include gene-drug (pharmacogenetic), disease-drug, drug-drug, and natural product-drug interactions. Examples of multi-factorial PK interactions presented include drug-gene-drug, natural product-gene-drug, gene-gene-drug, disease-natural product-drug, and disease-gene-drug interactions. Clear interpretation of multi-factorial interactions can be complicated by study design, complexity in victim drug PK, and incomplete mechanistic understanding of victim drug PK.Expert opinion: Incorporation of complex multi-factorial PK interactions into precision drug therapy requires advances in clinical decision tools, intentional PK study designs, drug-metabolizing enzyme and transporter fractional contribution determinations, systems and computational approaches (e.g., physiologically-based pharmacokinetic modeling), and PK phenotyping of progressive diseases.

A Pharmacokinetic Natural Product-Disease-Drug Interaction: A Double Hit of Silymarin and Nonalcoholic Steatohepatitis on Hepatic Transporters in a Rat Model

Patients with nonalcoholic steatohepatitis (NASH) exhibit altered hepatic protein expression of metabolizing enzymes and transporters and altered xenobiotic pharmacokinetics. The botanical natural product silymarin, which has been investigated as a treatment of NASH, contains flavonolignans that inhibit organic anion-transporting polypeptide (OATP) transporter function. The purpose of this study was to assess the individual and combined effects of NASH and silymarin on the disposition of the model OATP substrate pitavastatin. Male Sprague Dawley rats were fed a control or a methionine- and choline-deficient diet (NASH model) for 8 weeks. Silymarin (10 mg/kg) or vehicle followed by pitavastatin (0.5 mg/kg) were administered intravenously, and the pharmacokinetics were determined. NASH increased mean total flavonolignan area under the plasma concentration-time curve (AUC_{0-120 min}) 1.7-fold. Silymarin increased pitavastatin AUC_{0-120 min} in both control and NASH animals approx. 2-fold. NASH increased pitavastatin plasma concentrations from 2 to 40 minutes, but AUC_{0-120 min} was unchanged. The combination of silymarin and NASH had the greatest effect on pitavastatin AUC_{0-120 min}, which increased 2.9-fold compared with control vehicle-treated animals. NASH increased the total amount of pitavastatin excreted into the bile 2.7-fold compared with control animals, whereas silymarin decreased pitavastatin biliary clearance approx. 3-fold in both control and NASH animals. This double hit of NASH and silymarin on hepatic uptake transporters is another example of a multifactorial pharmacokinetic interaction that may have a greater impact on drug disposition than each hit alone. SIGNIFICANCE STATEMENT: Multifactorial effects on xenobiotic pharmacokinetics are within the next frontier for precision medicine research and clinical application. The combination of silymarin and NASH is a probable clinical scenario that can affect drug uptake, liver concentrations, biliary elimination, and ultimately, efficacy and toxicity.