Liver organotropism and biotransformation of a novel platinum-ursodeoxycholate derivative, Bamet-UD2, with enhanced antitumour activity

BACKGROUND/AIMS

Several members of a novel family of bile acid derivatives with cytostatic and virostatic activity have been synthesized and characterized. The aim of this work was to investigate the liver organotropism and biotransformation of two novel compounds with enhanced DNA-reactivity: Bamet-D3, in which a glycine-polyamine tandem was used as a spacer to separate the glycocholic acid moiety from the platinum(II) atom, and Bamet-UD2, in which cisplatin was directly bound to the carboxylate group of two ursodeoxycholic acid moieties.

METHODS

Drug uptake and "in vitro" toxicity were investigated using rat hepatocytes in primary culture. Following i.v. administration of 0.5 mumol cisplatin, Bamet-D3 or Bamet-UD2, bile output, urinary and fecal excretion, organ distribution and pharmacokinetic parameters were determined in short-term (3 h) and long-term (14 days) experiments carried out on anaesthetized and conscious rats, respectively. Liver biotransformation was investigated by HPLC analysis of bile samples. Total platinum was measured by flameless atomic absorption spectroscopy. Using Nude mice, antitumour activity was investigated in subcutaneously implanted Hepa 1-6 mouse hepatoma cells.

RESULTS

Uptake by rat hepatocytes was Bamet-UD2 (11.3 nmol/mg protein) > Bamet-D3 (5.6 nmol/mg protein) > cisplatin (2.1 pmol/mg protein). Bamet-UD2 induced "in vitro" cell toxicity, which was not observed for Bamet-D3 or cisplatin. On the contrary, no toxicity "in vivo" for Bamet-UD2 was found which was observed for cisplatin and Bamet-D3. This may be related with the fact that bile output of Bamet-UD2, which occurs with no major biotransformation, was > 10 fold higher than that of cisplatin and 3-fold higher than that of Bamet-D3, which was previously transformed into at least three different metabolites. Fecal excretion was Bamet-UD2 > Bamet-D3 > cisplatin, whereas urinary output was Bamet-D3 > cisplatin > Bamet-UD2. Accordingly, a marked liver- and a reduced kidney-vectoriality for Bamet-UD2, but not for Bamet-D3, was observed. Bamet-UD2 and cisplatin, but not Bamet-D3, were efficient in inhibiting tumour growth whereas, only Bamet-UD2 significantly prolonged survival time.

CONCLUSIONS

There results indicate that Bamet-UD2 is a cisplatin-ursodeoxycholate derivative with strong antitumour activity, marked hepatobiliary organotropism, and reduced toxic side-effects as compared to the parent drug cisplatin.

Relationship between DNA-reactivity and cytostatic effect of two novel bile acid-platinum derivatives, Bamet-UD2 and Bamet-D3

BACKGROUND AND AIMS

Several platinum(II)-bile acid derivatives, named Bamets, have been previously synthesized. Their ability to interact with DNA, their cytostatic activity and their liver organotropic properties have been characterized. Two new compounds of this family, with particular structural properties, have been developed. Bamet-UD2 was formed by two ursodeoxycholic acid moieties bound by the carboxylate groups to cisplatin. In contrast, in Bamet-D3, glycine and a polyamine were used as tandem spacer elements to separate a cholic acid moiety from the platinum(II) atom. The aim of this work was to evaluate how these changes affect the ability of these compounds to interact with DNA and reduce tumour cell growth.

MATERIALS AND METHODS

Drug reactivity with DNA was determined by changes in the electrophoretic mobility of the pUC18 plasmid test and by the ethidium bromide (EthBr) displacement assay. Cytostatic activity was measured against two mouse-derived cell lines from lymphocytic leukemia (L1210) and sarcoma (S-180-II).

RESULTS

Bamet-UD2, and more markedly Bamet-D3, induced changes in the electrophoretic mobility of pUC18, suggesting the formation of DNA-drug interactions. Bamet-UD2 displaced EthBr from its binding to DNA. This effect was stronger in the case of Bamet-D3. Scatchard plots revealed that pre-incubation with both Bamet-UD2 and Bamet-D3 decreased the number of DNA sites available and their ability to bind EthBr. In spite of the enhanced DNA-reactivity of Bamet-D3, its ability to reduce tumour cell growth was much weaker than that of Bamet-UD2, which was seen to exert a very strong cytostatic effect.

CONCLUSION

Although the distance between the platinum atom and the bile acid moiety affects the in vitro Bamet reactivity with DNA, other factors determine the overall cytostatic activity of these compounds.

Effect of maternal cholestasis on bile acid transfer across the rat placenta-maternal liver tandem

Cholestasis of pregnancy induces alterations in bile acid transport by human trophoblast plasma membrane (TPM) vesicles. We investigated whether maternal cholestasis affects the overall ability of the rat placenta to carry out vectorial bile acid transfer from the fetus to the mother. Complete obstructive cholestasis (OCP) was maintained during the last week of pregnancy and released at term (day 21), before experiments were performed. In situ single-pass perfusion of one placenta per rat with 250 nmol [(14)C]glycocholic acid (GC) revealed an impaired uptake in OCP rats (2.28 vs. 5.53 nmol in control rats). Approximately 100% of GC taken up by control placentas was secreted in maternal bile over 120 minutes (5.38 nmol), whereas this was only 61% (1.40 nmol) of the GC taken up by OCP placentas. When 5 nmol GC was administered through the jugular vein no significant difference between both groups in total GC bile output was found. The efficiency (V(max)/K(M)) of adenosine triphosphate (ATP)-dependent GC transport by vesicles from the maternal side of TPM was decreased (-41%) in OCP. Moreover, histological examination of the placentas suggested a reduction in the amount of functional trophoblast in the OCP group. This was consistent with a lower antipyrine diffusion across the placenta in these animals. In sum, our results indicate that maternal cholestasis affects the ability of the placenta to efficiently carry out bile acid transfer from fetal to maternal blood. Changes in both the structure and the functionality of the chorionic tissue may account for this impairment.

Beneficial effect of ursodeoxycholic acid on alterations induced by cholestasis of pregnancy in bile acid transport across the human placenta

BACKGROUND/AIMS

The existence of impairment in bile acid transport across the placenta during intrahepatic cholestasis of pregnancy and the effect of ursodeoxycholic acid treatment (1 g/day) were investigated.

METHODS

Kinetic parameters were calculated from experiments carried out on membrane vesicles obtained from basal (TPMb, fetal-facing) and apical (TPMa, maternal-facing) trophoblast plasma membranes. Bile acid uptake was measured using varying concentrations of [14C]-glycocholate and a rapid filtration technique.

RESULTS

The maximal velocity of transport (Vmax), the apparent affinity constant (Kt) and the efficiency (Ef) of transport (Vmax/Kt) of the anion:bile acid exchanger located at the TPMb were reduced in intrahepatic cholestasis of pregnancy. Ursodeoxycholic acid induced a reversal of Vmax, Kt and Ef to normal values. Owing to the 3-fold increase in Vmax, with no change in Kt, intrahepatic cholestasis of pregnancy induced an enhancement in Ef of ATP-independent bile acid transport across TPMa. Both Vmax and Ef were restored to normal values by ursodeoxycholic acid. Finally, in ATP-dependent bile acid transport across TPMa, a reduction in the Ef due to an increase in Vmax together with a more pronounced increase in Kt was found. This impairment was also reversed by ursodeoxycholic acid.

CONCLUSIONS

These results suggest that placenta bile acid transport systems are impaired in intrahepatic cholestasis of pregnancy. Moreover, together with the confirmed beneficial effect for intrahepatic cholestasis of pregnancy patients, such as the relief of pruritus and the improvement in biochemical markers of cholestasis, ursodeoxycholic acid treatment restores the ability of the placenta to carry out vectorial bile acid transfer.