Effect of methotrexate treatment on expression levels of multidrug resistance protein 2, breast cancer resistance protein and organic anion transporters Oat1, Oat2 and Oat3 in rats.

The ATP binding cassette (ABC) transporters, multidrug resistance protein 2 (Mrp2; Abcc2) and breast cancer resistance protein (Bcrp; Abcg2), and organic anion transporters (Oats) mediate excretion of methotrexate (MTX) and many other drugs. However, it is not known whether MTX treatment leads to any changes in the expression of these transporters. We examined the effect of MTX treatment on expression of Mrp2, Bcrp and Oats in rats. MTX was single injected intraperitoneally at doses of 10, 50 and 150 mg/kg, and then Western blot analysis was performed. The levels of Mrp2, Oat1 and Oat2 on day 1 after the treatment showed no significant change. Four days after injection of 150 mg/kg MTX, the Mrp2 levels in the liver and ileum, but not in the kidney, were markedly down-regulated to 20 +/- 3.6% and 8.9 +/- 3.8% (mean +/- SEM) of controls, respectively. Renal Oat1 and Oat3 were also down-regulated to 56.4 +/- 4.3% (Oat1) and 54.3 +/- 5.5% (Oat3) of controls. These effects of MTX were almost recovered by leucovorin which rescues normal cells from MTX toxicity. MTX treatment also decreased mRNA levels of constitutive androstane receptor (CAR) and pregnane X receptor (PXR) to 65.5 +/- 17.9% and 59.6 +/- 14.5% of controls in the liver, respectively. MTX treatment has no apparent effect on expression levels of Bcrp, cytochrome P450 2B6 and 3A1. In conclusion, these data indicate that MTX treatment down-regulates expression levels of Mrp2, Oat1 and Oat3, and its effects are recovered by leucovorin.

Chronopharmacology of melatonin in mice to maximize the antitumor effect and minimize the rhythm disturbance effect.

The influence of dosing time on the antitumor effect and the rhythm disturbance effect of melatonin (MLT) was investigated in ICR male mice under a light/dark (12:12) cycle. In tumor-bearing mice, the antitumor effect of MLT (1 mg/kg intraperitoneal) was most effective in the dark phase; and the rhythm disturbance effect of MLT on the locomotor activity was more serious in the light phase than in the dark phase. The antitumor effect and the rhythm disturbance effect of MLT increased when the specific binding of MLT receptor in target tissues, tumor or suprachiasmatic nucleus, increased and they decreased when the level decreased. Furthermore, because luzindole, an MT1 and MT2 blocker, caused the antitumor effect or rhythm disturbance effect of MLT to decrease, it is suggested that the time-dependent change of the pharmacological effects of MLT were influenced by that of MLT receptor(s) function. On the other hand, there was no significant dosing time-dependent change of MLT concentration in tumor or brain after injection. Thus, the pharmacokinetic factor does not seem to contribute to the dosing time-dependent effect of MLT. These results suggest that by choosing the most suitable dosing time for MLT, the efficacy of the drug can be increased, and the toxicity of the drug can be decreased in certain experimental and clinical situations.

Cell kinetics-dependent antitumor effect of irinotecan hydrochloride induced by the synchronizing effect of hydroxyurea: cell kinetics and dosing time.

Influence of hydroxyurea (HU) on the antitumor effect of irinotecan hydrochloride (CPT-11) was investigated in ICR male mice transplanted with sarcoma 180 cells (S-180). A single dose of CPT-11 (100 mg/kg) was injected at various times after a single dose of HU (300 mg/kg). The relative tumor weight varied significantly depending on the timing of CPT-11 injection after HU injection (P < 0.01). The higher antitumor effect of CPT-11 was observed when DNA synthesis of S-180 cells increased (20 hr), and the lower effect was observed when the DNA synthesis decreased (0 hr). The loss of body weight also varied significantly depending on the timing of CPT-11 injection after HU injection (P < 0.01). The toxicity of CPT-11 was higher when the inhibitory effect of HU on DNA synthesis of bone marrow cells was stronger (15 hr), and the lower toxicity was observed when the inhibitory effect was not observed (0 hr). The plasma SN-38 concentration at 2 hr after CPT-11 injection was higher at 20 hr after HU injection than at 0 hr after HU injection. The difference in plasma esterase activity between 0 hr and 20 hr after HU injection was regarded as the mechanism underlying the dosing time-dependent difference of the SN-38 concentration. These experiments suggest that HU can produce a different phase of cell cycle between tumor cells and normal cells. This leads to increase the antitumor effect of CPT-11 without increasing the adverse effect of the drug. It is essential to consider the dosing time in the two-drug combination therapy.