Antitumour activity of 3-chlorodeoxylapachol, a naphthoquinone from Avicennia germinans collected from an experimental plot in southern Florida

As part of an ongoing collaborative effort to discover new anticancer agents from plants, an extract obtained from the leaves and twigs of Avicennia germinans, collected in a coastal area of southern Florida, was identified as possessing cytotoxic activity in a panel of human cancer cell lines. Fractionation of the petroleum ether partition, using cytotoxicity to guide the fractionation, led to the isolation of 3-chlorodeoxylapachol. The antitumour potential of 3-chlorodeoxylapachol was demonstrated with the in-vivo hollow fibre assay, a model of antitumour activity using human cancer cell-filled fibres implanted into mice. The possibility that this compound is an artefact of the isolation procedure was ruled out by liquid chromatography-mass spectrometry analysis of extracts prepared without the use of chlorinated solvent. In conclusion, 3-chlordeoxylapachol, a secondary metabolite obtained from the chloroform-soluble extract of a mangrove tree, was cytotoxic in a panel of human cancer cells, and active against KB human cancer cells in the murine hollow fibre antitumour model, with selectivity in KB cells for the intravenous site at lower doses, indicating possible metabolic activation.