1. Drug disposition of incadronate in the nude rat with bone metastases induced by A375 human melanoma cells was studied after intravenous administration.2. The pharmacokinetics of incadronate (plasma concentration, urinary excretion and bone uptake) in rat with bone metastases was not markedly different from that in the control rat. This compound, however, was selectively taken up in the bone region around metastatic tumour nests.3. Drug concentrations in the bone region around tumour nests were 3-10 mu g/g, these levels being higher than the IC50 (0.35 mu g/ml) for the inhibitory effect of this drug on osteoclasts in vitro.4. In contrast, concentrations in the tumour nest itself was < 0.7 mu g/g, being markedly lower than the IC50 (35 mu g/ml) for the inhibitory effect on the proliferation of tumour cells in vitro.5. These results strongly suggest that pharmacological action of incadronate in mouse with bone metastases (inhibitory effect on the growth of metastatic tumour in bone) is caused not by the direct action on the tumour cells but by the distribution of the drug in the perifocal bone region followed by inhibition of the activity of osteoclasts, resulting in inhibition of the osteolytic process, which is necessary for the progress of metastatic tumour.

We investigated the effects of dose, sex and age on the uptake and elimination of incadronate, a new biosphosphonate, in rat bone after intravenous administration. Following administration of 0.03-3 mg/kg to young male rats (age 7 weeks),intact drug concentration in humerus at 24 hr after administration (C24 hr) increased in a dose-dependent manner, indicating the linear uptake of the drug into bone. The estimated bone uptake clearance of 0.13 ml/min./g bone is comparable to the estimated plasma flow rate in bone, suggesting that uptake into bone is plasma flow-limited. Concentration from 24 hr after administration had declined bi-exponentially. Although t1/2 beta (350-444 days) was little altered among doses, t1/2 alpha was prolonged with increasing dose from 13.4 to 16.2 days. This effect seemed to be due to inhibition of bone resorption at higher doses resulting in the suppression of drug release from bone. No sex difference was seen on C24 hr in young rats, while the value in senescent (age 12 months) rats was 24% greater in females than in males. When comparing between ages it is seen that C24 hr values in senescent rats decreased to 50-66% of those in young rats. As for elimination from bone, t1/2 beta values in senescent rats were shortened to 76-79% of those in young rats. In contrast, little difference in t1/2 alpha was observed between ages or in either t1/2 alpha and t1/2 beta between sexes.

A high-performance liquid chromatographic method for the sensitive determination of 1-hydroxy-2-(imidazo[1,2-a]pyridin-3-yl)ethane-1,1-bisphosphonic acid monohydrate (YM529) in plasma, urine and bone is described. Plasma obtained in high-dose animal studies is treated by method A, a simple method using 1 ml of plasma, which is based on deproteinization of plasma followed by coprecipitation of the drug with calcium phosphate and dissolution of the precipitate in EDTA. Plasma obtained in low-dose clinical studies is treated by method B, a more sensitive method using 4 ml of plasma, which is based on direct precipitation of the drug prior to the deproteinization in method A. Urine and bone samples are prepared by solid-phase extraction using a Sep-Pak C18 cartridge coupled with method A. The drug is separated with a reversed-phase column using a mobile phase at pH 7, and detected with a fluorescence detector following postcolumn alkalization of the mobile phase to enhance fluorescence intensity. The limit of determination is 0.2 ng/ml for method A and 0.05 ng/ml for method B in plasma, 0.05 ng/ml in urine, and 5 ng/g in bone.

1. We have investigated the disposition and metabolism of YM17E after intravenous and oral administration in the rat and dog. 2. Bioavailability of YM17E was 5-9% at oral doses of 3-30 mg/kg in rat, and 9 and 13% at oral doses of 10 and 30 mg/kg in dog. 3. Five N-demethylated metabolites, which have significant pharmacological activity, were found in rat and dog plasma after oral administration. Plasma concentrations of each of these metabolites were comparable with that of unchanged drug. 4. When 14C-YM17E was administered to rat, AUC of unchanged drug was 7% of that of radioactivity. However, AUC of the combined concentration of unchanged drug and five active metabolites was about 50% of that of radioactivity, indicating that the pharmacological activity of the agent was maintained in spite of its biotransformation. 5. After oral administration of 14C-YM17E at a dose of 10 mg/kg to rat, radioactivity was distributed widely to almost all tissues except the brain. The concentration of radioactivity in the liver, one of the target organs, was 65 times higher than that in plasma at 1 h after administration. 6. A significant amount of radioactivity in the liver was located in the microsomal subfraction, which contains much acyl CoA:cholesterol acyl transferase activity. More than 50% of this microsomal radioactivity was derived from unchanged YM17E and five active metabolites. 7. From excretion data in the bile duct-cannulated rat, the absorption ratio of YM17E from the gastrointestinal tract in this species was estimated to be at least 40%, suggesting that the low bioavailability of the drug is due to extensive first-pass metabolism. 8. Some 95% of the administered radioactivity was excreted in the faeces of rat following iv or po doses of 14C-YM17E.

We describe a reversed-phase high-performance liquid chromatographic method for the determination in plasma of YM17E (I), an inhibitor of acyl CoA:cholesterol acyltransferase, and its five metabolites using electrochemical detection. This method enables simultaneous quantification of 1 and five active metabolites. The plasma sample is extracted by a one-step solid-phase extraction using a SepPak C18 cartridge, with high recovery and reproducibility of the analytes. The method is sensitive and the limits of determination are 0.5 ng/ml for I and 1 ng/ml for metabolites M1, M2-a, M2-b, M3 and M4. This method is applicable to rat, dog and human plasma, and is useful for pharmacokinetic studies.