Copper(II) complexes (1–4) of tri‐ or tetradentate bis(2‐methylbenzimidazolyl)amine ligands (L1–L4) have been prepared and characterized by spectroscopic methods in solution, as well as in the solid state by X‐ray crystallography. The ligands act as tridentate donors towards the cupric ions through one central amine and two benzimidazole N atoms in the solid state; a water ligand and a bridging perchlorate group define the distorted octahedral environments of 2 and 3. Complex 4 has square‐pyramidal coordination geometry, with an additional thioether donor attached to the central N atom in the axial position. Electrospray mass spectrometry characterized the complexes as monomeric in acetonitrile solution. Cyclic voltammetry studies established that amine N benzyl‐containing 3 has the highest half‐wave redox potential of all of these complexes at –0.08 V (vs. Fc+/Fc) for the Cu2+/Cu+ couple. The complexes display dose‐dependent cytotoxicity against one human and four murine cancer cell lines. Complexes 3 and 4 have good antiproliferative activity against the human chronic leukemia cell line K562. Moreover, for 3 the proliferation of all malignant cell lines decreases at concentrations lower than the IC50 for healthy bone marrow cells.

In the search for novel chemotherapeutic agents for cancer treatment, capsaicin has been shown to inhibit proliferation and induce apoptosis in various types of cancer cell line, including leukaemia cell lines. The capsaicin analogues, rinvanil and phenylacetylrinvanil (PhAR), share a binding affinity for vanilloid receptors and may have biological activities similar to capsaicin; however, their anticancer potential has not yet been reported. This study analyses the antineoplastic activities of rinvanil and PhAR in leukaemia versus normal cells. P388, J774 and WEHI-3 leukaemia cell lines, as well as mouse bone marrow mononuclear cells, were cultured with varying concentrations of rinvanil and PhAR. Following this, proliferation and apoptosis were determined by the sulforhodamine B (SRB) assay and DNA ladder. Cultured leukaemia cell lines and mouse bone marrow mononuclear cells demonstrated a dose-dependent inhibition of proliferation, while non-diseased cells were less sensitive to the cytotoxic effect of capsaicin, rinvanil and PhAR. Rinvanil and PhAR also induced apoptosis in leukaemia cell lines but not in bone marrow. Given the lower IC50 values for apoptosis induction in leukaemia cells compared with that of normal cells, PhAR is a promising selective anticancer agent.

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