Enhanced liver blood concentrations of adenine arabinoside accomplished by lactosaminated poly-L-lysine coupling: implications for regional chemotherapy of hepatic micrometastases

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Doxorubicin coupled to lactosaminated human albumin remains confined within mouse liver cells after the intracellular release from the carrier

BACKGROUND

The hepatocyte receptor for asialoglycoproteins, which binds and internalises galactosyl terminating peptides, was found to be expressed also on the cells of the majority of hepatocarcinomas.

AIMS

To verify whether doxorubicin coupling to lactosaminated albumin, a galactosyl terminating neoglycoprotein, produces selective drug accumulation in hepatocytes with reduced concentrations in extra-hepatic tissues, thus facilitating the use of the drug in hepatocarcinoma treatment.

METHODS

Doxorubicin concentrations were measured in organs of mice injected with the free or coupled drug.

RESULTS

In mice injected with the coupled drug, the ratios between doxorubicin concentrations in liver and those in heart, intestine, spleen and kidney were 8-14 times higher than in animals that received the same dose of the free drug.

CONCLUSIONS

Due to the very efficient liver targeting of doxorubicin, the lactosaminated human albumin-doxorubicin conjugate appears to have the potential of improving the chemotherapy of hepatocellular carcinomas through the asialoglycoprotein receptor.

Floxuridine coupling with lactosaminated human albumin to increase drug efficacy on liver micrometastases

BACKGROUND

Conjugates of nucleoside analogues with galactosyl terminating peptides selectively enter hepatocytes through the asialoglycoprotein receptor. After intracellular release from the carrier, the drugs partly exit from hepatic cells into hepatic blood.

AIMS

To establish whether administration of a conjugate of floxuridine with lactosaminated human albumin selectively enhances drug concentrations in hepatic blood. Floxuridine is a fluoropyrimidine active on human colorectal cancer, a tumour which metastasises first to the liver.

METHODS

In rats injected with free or conjugated floxuridine, plasma levels of the drug were determined in hepatic veins and in inferior vena cava, in order to measure drug concentrations in hepatic blood and in the systemic circulation, respectively.

RESULTS

Ratios between floxuridine levels in hepatic veins and those in systemic circulation were found to be seven times higher in rats injected with the conjugate (p=0.000).

CONCLUSIONS

The present results suggest that coupling to lactosaminated albumin might improve the effect of floxuridine in adjuvant chemotherapy of colorectal cancer by exposing the cells of liver micrometastases (nourished by hepatic sinusoids) to enhanced drug concentrations.

Conjugates of nucleoside analogs with lactosaminated human albumin to selectively increase the drug levels in liver blood: requirements for a regional chemotherapy

Nucleoside analogs (NAs) conjugated with galactosyl terminating peptides selectively enter hepatocytes via the asialoglycoprotein receptor and, after intracellular release from the carrier, partly exit from these cells into the bloodstream, resulting in higher concentrations in liver blood than in systemic circulation. Therefore, conjugates of anticancer NAs can be exploited to accomplish a loco-regional noninvasive treatment of liver micrometastases. In the present experiments we studied whether the enhancement of drug levels in liver blood achieved when NAs are given in the coupled form depends on the rate of drug elimination from the bloodstream. Three NAs, adenine arabinoside (ara-A), 5-fluoro-2'-deoxyuridine (FUdR), and 2',2'-difluorodeoxycytidine, were coupled with lactosaminated human albumin, a galactosyl terminating carrier. In rats that received an intravenous bolus injection of these conjugates, we compared the drug concentrations in liver blood to those in the systemic circulation. We found that enhanced levels of NAs in liver blood were only achieved by administering the conjugates of the drugs (ara-A and FUdR), which are rapidly cleared from the bloodstream. Increased drug levels also were obtained when ara-A and FUdR conjugates were slowly infused (a way of administration often used for anticancer drugs). The experiments also showed that galactosyl terminating conjugates of NAs might have the potential to produce a therapeutic effect only when the coupled drugs are active at low blood concentrations, since the amounts of drugs introduced into hepatocytes and released by these cells in the bloodstream cannot be increased when the receptor for the hepatic uptake of galactosyl terminating peptides is saturated.

Efficacy of lactosaminated and intact N-succinylchitosan-mitomycin C conjugates against M5076 liver metastatic cancer

In this study,lactosaminated N-succinyl-chitosan (Lac-Suc) was investigated for its liver targeting ability in the early metastatic stage of liver cancer, and subsequently Lac-Suc-mitomycin C conjugate (Lac-Suc-MMC) and highly-succinylated N-succinyl-chitosan (Suc(II))-MMC conjugate (Suc(II)-MMC) were examined for efficacy against the liver metastasis. Mice into which M5076 cells were inoculated intravenously were used as liver metastatic models. Fluorescently labelled Lac-Suc (Lac-Suc-FTC) was intravenously administered at a daily dose of 0.2 mg/mouse for 4 days or at a single dose of 0.8 mg/mouse at 3 days post-inoculation. At a dose of 0.2 mg/mouse for 4 days, liver accumulation of Lac-Suc-FTC was increased after all except the fourth injection, indicating that the capacity of accumulation might be limited to around 110 microg per mouse with repeated daily administration at 0.2 mg/mouse. As to the efficacy of intravenous administration at 7 days post-inoculation, Lac-Suc-MMC was less effective at a dose of 1 mg kg(-1) for 4 days than a single dose of 4 mg kg(-1). This result was not in accordance with that expected from the biodistribution study. On the other hand, with intravenous administration at 3 days post-inoculation, Suc(II)-MMC was more effective on repeated administration, and it showed higher efficacy than Lac-Suc-MMC at both 1 mg kg(-1) for 4 days and 4 mg kg(-1) as a single dose. Further, with intravenous administration at 3 days post-inoculation, Suc(II)-MMC exhibited a much higher survival effect at a dose of 4 mg kg(-1) for 4 days.

Coupling of 5-fluoro 2'-deoxyuridine to lactosaminated poly-l-lysine: an approach to a regional, non-invasive chemotherapy of liver micrometastases

Nucleoside analogs conjugated with galactosyl-terminating peptides selectively enter liver cells and after intracellular release from the carrier partly exit into bloodstream, resulting in higher concentrations in liver blood than in systemic circulation. The aim of the present experiments was to ascertain whether, in mice injected with non-toxic doses of a 5-fluoro 2'-deoxyuridine (FUdR) conjugate with lactosaminated poly-L-lysine (L-poly(LYS)), the drug was released by hepatic cells in high enough amounts to be pharmacologically active on neoplastic cells infiltrating the liver. We observed that L-poly(LYS)-FUdR inhibited the growth of hepatic metastases induced by intrasplenic administration of murine colon carcinoma C-26 cells. L-poly(LYS)-FUdR was not toxic for C-26 cells in vitro, was selectively taken up by mouse liver, and was stable in mouse blood, indicating that the effect on the metastases was due to FUdR (and/or its active metabolites) released in liver blood after the conjugate was taken up by the hepatic cells. These results suggest that L-poly(LYS)-FUdR might be useful in adjuvant chemotherapy of tumors giving liver metastases. The drug released from hepatic cells into liver blood following conjugate administration via the peripheral venous route might accomplish a locoregional, non-invasive treatment of micrometastases nourished by liver sinusoids.