Hideyuki Saito

Constitutive Overexpression of P-glycoprotein, Rather than Breast Cancer Resistance Protein or Organic Cation Transporter 1, Contributes to Acquisition of Imatinib-Resistance in K562 Cells

PurposeThe purpose of this study was to investigate the contribution of drug transporters in acquired imatinib-resistance. Specifically, we focused on the efflux transporters, P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP), and an influx transporter, organic cation transporter 1 (OCT1).Materials and methodsWe established imatinib-resistant K562 cells (K562/IM). Real-time PCR or Western blot analyses were performed to examine the mRNA or protein levels. Alamar blue method was used in the cytotoxicity assay. The transport activities and intracellular imatinib levels were measured by flow cytometry and HPLC, respectively.ResultsK562/IM displayed a 47-fold increase in resistance to imatinib over the parent K562 cells. Both P-gp and BCRP were overexpressed in K562/IM relative to K562. Furthermore, the intracellular imatinib level was markedly reduced in K562/IM. Interestingly, cyclosporin A, a P-gp inhibitor, but not fumitremorgin C, a BCRP inhibitor, restored both imatinib-sensitivity and the intracellular imatinib level. By contrast, no significant difference in the expression and function of OCT1 was observed between K562/IM and K562.ConclusionsP-gp, rather than BCRP or OCT1, is partially responsible for the development of imatinib-resistance due to constitutive and functional overexpression, leading to reduced intracellular accumulation of imatinib in K562/IM.

Regulation of renal organic ion transporters in cisplatin-induced acute kidney injury and uremia in rats

PurposeThe purpose of this study was to examine the regulation of renal organic ion transporters in cisplatin-induced acute kidney injury (AKI) and its relation with indoxyl sulfate (IS), a uremic toxin.MethodsThe IS concentrations in the serum and kidney were monitored by high-performance liquid chromatography. Uptake of p-aminohippuric acid, estrone-3-sulfate and tetraethylammonium were examined using renal slices. Real-time PCR and immunoblotting were performed to examine the mRNA and protein expression of rOATs, rOCTs and rMATE1 in the kidney, respectively.ResultsThe serum and renal IS levels were markedly elevated in cisplatin-treated rats. However, this effect was largely reversed by administration of AST-120, an oral charcoal adsorbent. The functions of renal basolateral organic anion and cation transporters were reduced in cisplatin-treated rats. The levels of mRNA and protein corresponding to rOAT1, rOAT3, rOCT2 and rMATE1, but not rOCT1, were depressed in the kidney of cisplatin-treated rats. Administration of AST-120 to cisplatin-treated rats partially restored the function and expression level of these transporters.ConclusionsCisplatin-induced AKI causes down-regulation of renal organic ion transporters accompanied by accumulation of serum and renal IS. IS could be involved in the mechanism of down-regulation of rOAT1, rOAT3 and rMATE1 under cisplatin-induced AKI.

Phase I and pharmacokinetic study of amrubicin, a synthetic 9-aminoanthracycline, in patients with refractory or relapsed lung cancer

Amrubicin is a novel synthetic 9-aminoanthracycline derivative and is converted enzymatically to its C-13 hydroxy metabolite, amrubicinol, whose cytotoxic activity is 10–100 times that of amrubicin. We aimed to determine the maximum tolerated dose (MTD) of amrubicin and to characterize the pharmacokinetics of amrubicin and amrubicinol in previously treated patients with refractory or relapsed lung cancer. The 15 patients were treated with amrubicin intravenously at doses of 30, 35, or 40xa0mg/m2 on three consecutive days every 3xa0weeks for a total of 43 courses. Neutropenia was the major toxicity (grade 4, 67%). The MTD was 40xa0mg/m2, with the specific dose-limiting toxicities being grade 4 neutropenia persisting for >4xa0days, febrile neutropenia, or grade 3 arrhythmia in the three patients treated at this dose. A patient with non-small-cell lung cancer showed a partial response, and ten individuals experienced a stable disease. The area under the plasma concentration versus time curve (AUC) for amrubicin and that for amrubicinol increased with amrubicin dose. The amrubicin AUC was significantly correlated with the amrubicinol AUC. The recommended phase II dose of amrubicin for patients with lung cancer refractory to standard chemotherapy is thus 35xa0mg/m2 once a day for three consecutive days every 3xa0weeks.

Involvement of Indoxyl Sulfate in Renal and Central Nervous System Toxicities During Cisplatin-induced Acute Renal Failure

PurposeThe purpose of the present study was to explore the involvement of indoxyl sulfate (IS) in nephrotoxicity and central nervous system (CNS) toxicity in cisplatin (CDDP)-treated rats.Materials and MethodsRenal function was evaluated by serum creatinine and BUN levels. The IS levels in the serum, brain and kidney was monitored by high-performance liquid chromatography method. Body weight and rectal temperature were monitored. Real-time PCR analysis was performed to examine rPer2 mRNA expression.ResultsRenal function deteriorated in a time-dependent manner after administration of CDDP. The concentration of IS in the serum, brain and kidney markedly increased 24–84xa0h after commencement of CDDP treatment. The observed increase in the levels of serum creatinine, BUN and IS was suppressed by concomitant administration of AST-120. Rectal temperature was significantly lowered 72–92xa0xa0h after CDDP-treatment, which was partially restored by coadministration of AST-120. Moreover, the amplitude of rectal temperature rhythms was disrupted by treatment with CDDP. Circadian rhythm of rPer2 mRNA expression, a clock gene, in suprachiasmatic nucleus (SCN) and kidney was disturbed in CDDP-treated rats.ConclusionsAn increase in the IS level and the associated disturbance to the circadian rhythm are involved in the renal and CNS toxicities in CDDP-treatment.

Pharmacokinetics of amrubicin and its active metabolite amrubicinol in lung cancer patients

Amrubicin, a synthetic 9-aminoanthracycline agent, was recently approved in Japan for treatment of small-cell lung cancer and non-small-cell lung cancer. Amrubicin is converted enzymatically to the C-13 hydroxy metabolite amrubicinol, which is active and possesses a cytotoxicity 10 to 100 times that of the parent drug. The purpose of this study was to characterize the pharmacokinetics of amrubicin and its active metabolite amrubicinol. Amrubicin was administered on days 1-3 in 16 patients with advanced lung cancer. The pharmacokinetics analysis of amrubicin and amrubicinol was performed by high-performance liquid chromatography. When 45 mg/m2 amrubicin was administered in a bolus injection once every 24 hours for 3 consecutive days, the areas under the curves (0 to 72 hours) for amrubicin and amrubicinol were 13,490 and 2585 ngu2009·u2009h/mL, respectively. The apparent total clearance (CLapp) of amrubicin was 15.4 L/h. The area-under-the-curve ratio of amrubicinol to amrubicin was 15.1 ± 4.6% (mean ± SD) at doses ranging from 30 to 45 mg/m2. Interindividual variability in the enzymatic conversion of amrubicin to amrubicinol was small. In contrast, a large interindividual variability in the CLapp of amrubicin was observed (CV = 49.8%). The areas under the curves of amrubicin and amrubicinol seemed to be associated with the severity of hematologic toxicities. There is a possibility that monitoring of the plasma concentrations of amrubicin and amrubicinol may provide an efficient tool for establishing the optimal dosage of amrubicin in each patient.

Pharmacokinetic changes of irinotecan by intestinal alkalinization in an advanced colorectal cancer patient

The prevention of irinotecan (CPT-11)-induced diarrhea, a well-known adverse reaction to the drug, by treatment with intestinal alkalinization has been carried out in patients with colorectal cancer in Japan. Under acidic conditions, CPT-11 and its active metabolite, SN-38, exists preferably as the lactone form, whereas both exist as the carboxylate form under basic conditions. It has been suggested that the lactone forms of both CPT-11 and SN-38 are diffused passively across the intestinal mucosal membranes, whereas the carboxylate forms are actively transported. The intestinal uptake rate of both forms appears to be pH sensitive under physiological conditions, but it remains unclear whether intestinal alkalinization treatment affects the pharmacokinetics of CPT-11 and SN-38. This study was designed to evaluate the pharmacokinetics of CPT-11 and SN-38 in a colorectal cancer patient with or without alkalinization treatment. We found that intestinal alkalinization significantly decreased the plasma levels of CPT-11 and SN-38. In particular, the AUC of SN-38 was markedly decreased to 56 from 107 ng·h/mL. Intestinal alkalinization was effective in preventing CPT-11-induced diarrhea, but this treatment changed the pharmacokinetics of CPT-11 and SN-38 in the body.

Effect of S‐1 on pharmacokinetics of irinotecan in a patient with colorectal cancer

Effect of S-1 on pharmacokinetics of irinotecan in a patient with colorectal cancer To the Editor: Pharmacokinetic modulation of irinotecan (CPT-11) with cyclosporine (INN, ciclosporin) and phenobarbital has been reported in the Journal. CPT-11 is widely used in the treatment of several types of solid tumors. The active metabolite, SN-38, is enzymatically formed from CPT-11 by carboxylesterases. SN-38 is subsequently conjugated by uridine diphosphate–glucuronosyltransferase 1A, forming the inactive metabolite SN-38 glucuronide (SN-38G). Furthermore, CPT-11 is oxidized to inactive metabolite (APC) by cytochrome P450 (CYP) 3A. CPT-11 and its metabolites possess a labile -hydroxy-3-lactone, which can undergo reversible hydrolysis in a pH-dependent manner. Recently, the possible efficacy of combination therapy with CPT-11 and S-1 for colorectal cancer has been suggested. S-1 is an oral anticancer agent composed of tegafur, a prodrug of 5-fluorouracil; 5-chloro-2,4-dihydroxypyridine; and potassium oxonate. A previous clinical study reported that 5-fluorouracil inhibits the conversion of CPT-11 to SN-38. The potential for pharmacokinetic drug interactions should be determined when combination chemotherapy is conducted. In this study we exam-

Effects of oral administration of S-1 on the pharmacokinetics of SN-38, irinotecan active metabolite, in patients with advanced colorectal cancer.

Previous studies have assessed the efficacy and safety of combined treatment with irinotecan (7-ethyl-10-[4-[1-piperidino]-1-piperidino]carbonyloxycamptothecin, CPT-11) and S-1, containing tegafur, a prodrug of 5-fluorouracil, in the treatment of colorectal and gastric cancer. The objective of this study was to describe the interaction between CPT-11 and S-1 in 4 patients with colorectal cancer. Coadministration of S-1 changed the pharmacokinetic behavior of CPT-11 and its metabolites. In particular, maximum plasma concentration (Cmax) and area under the plasma concentration curve (AUC) of 7-ethyl-10-hydroxycampothecin (SN-38) was markedly decreased by coadministration of S-1. For SN-38, the median ratio of Cmax and AUC with S-1 to those without S-1 was median 0.34 (range 0.24-0.78) and 0.56 (range 0.23-0.68), respectively. A markedly difference in drug interaction among individual patients was observed. We conclude that the plasma concentration of SN-38 was decreased by oral administration of S-1 in patients with colorectal cancer. This observation might be important for clinical decisions regarding combination therapy.