ADR-001

Cardiotoxicity is the main complication of adriamycin (ADR), which is a widely used chemotherapeutic agent.

To examine the potential cardioprotective effect of melatonin (MEL) on acute ADR cardiotoxicity in a rat model.

Cardioprotection was assessed on the basis of myocardial lipid peroxidation and ultrastructure. Rats were given MEL at a daily dose of 5 mg/kg and ADR 15 mg/kg, intraperitoneally. The MEL-1 group rats received one dose and the MEL-7 group rats six daily doses of MEL and were sacrificed at the end of one and seven days, respectively. Rats in the ADR-1 and ADR-7 groups were each given a single dose of ADR, and were then sacrificed 24 h and seven days later, respectively. The MEL+ADR-1 group rats received one dose each of ADR and MEL simultaneously and were sacrificed 24 h later. The MEL+ADR-7 group received a single dose of ADR plus a daily MEL dose for six consecutive days, and were sacrificed seven days after the ADR injection.

Lipid peroxidation products were elevated in both ADR-1 and ADR-7 groups, and this elevation was significantly inhibited by MEL treatment. Electron microscopy confirmed that ADR was positively cardiotoxic after one and seven days of exposure. The extent of ADR-induced myocardial damage was markedly reduced when MEL was combined with ADR (MEL+ADR-1 and MEL+ADR-7).

The results suggest that MEL is highly efficacious at reducing the acute cardiotoxic effects of high dose ADR, and that it acts by preventing lipid peroxidation.

Anthracenyl-amino acid conjugates (AAC) represent a novel class of topoisomerase (topo) inhibitor. The relationship between mechanism of enzyme inhibition and in vitro cytotoxicity has been investigated in a panel of 5 Chinese hamster ovary (CHO) and 2 human ovarian cancer cell lines (A2780) shown to possess different drug resistance phenotypes associated with altered expression of topo I and topo II. From a total of 13 compounds, 4 displayed broad-spectrum activity (IC50 ranging from 3.5-29.7 microM). NU/ICRF 500 (topo II catalytic inhibitor) was 1.4-fold more active against CHO ADR-1, which overexpresses topo II and was essentially noncross-resistant in CHO ADR-r (13.9-fold resistant to doxorubicin (DOX)) and 2780AD (1,460-fold resistant to DOX). NU/ICRF 505, which stabilises topo I cleavable complexes, was noncross-resistant in CHO ADR-3 (3,4-fold resistant to camptothecin) and only 1.8-fold cross-resistant in 2780AD. Hypersensitivity was recorded in ADR-r that overexpresses topo I. The most active compound was NU/ICRF 506, a dual catalytic inhibitor of topo I and II. Hypersensitivity was observed in ADR-r (1.4-fold) but not ADR-1, indicating that topo I is the likely nuclear target, and a low level of resistance was seen in the CHO ADR-6 drug transport mutant and 2780AD. The topo II catalytic inhibitor NU/ICRF 513 only produced hypersensitivity in ADR-r. These data suggest that NU/ICRF 500, 505, and 506 induce cell death, at least partly, through topo inhibition. NU/ICRF 513 appears to be cytotoxic via a nontopo mechanism of action. In addition, NU/ICRF 505 significantly inhibited the growth of two human xenografts (HT-29 colon cancer and NX002 nonsmall-cell lung cancer) in nude mice after i.p. administration at a dose of 25 mg/kg. The important properties of noncross-resistance and in vivo antitumour activity merit further development of AAC as potential new anticancer drugs.