Potentiation of the anti-tumour effect of docetaxel by conjugated linoleic acids (CLAs) in breast cancer cells in vitro

Response rates of tumours to docetaxel (DOCT) are 45-60% in advanced breast cancer but problems associated with side effects, drug resistance and high costs occur. Conjugated linoleic acids (CLAs) also have anti-tumorigenic activity that elicits similar changes in oncogene expression to DOCT and could augment DOCT efficacy. CLA isomers appear to differ in cytotoxicity toward cancer cells. Effects of two CLA isomers on cytotoxicity of DOCT in breast cancer cells (MCF-7; MDA-MB-231) in vitro were assessed. Cells were incubated up to 72 h with 40 microM each of LA or CLA isomers (cis-9, trans-10 CLA, or trans-10, cis-12 CLA) or a 50:50 isomer mix, alone or with DOCT (0-64 microM); a pilot study determined IC(50) and IC(70) concentrations. Treatments were concurrent (CLA and DOCT together) or sequential (CLA then DOCT). MTT assay determined cell viability. Trans-10, cis-12 CLA was the most effective fatty acid (P<0.001) and increased with treatment time. IC(50) and IC(70) concentrations of DOCT were determined, concurrently or sequentially, with and without fatty acids, in the two cell types. Concurrent treatment with trans-10, cis-12 CLA and DOCT augmented inhibition of cell growth in one or both cell lines (decreased IC(50) and IC(70) in MCF-7; P<0.05 but only IC(50) in MDA-MB-231; P<0.05). CLA mix reduced IC(50) and IC(70) in MDA-MB-231 (P<0.001) but not in MCF-7. Cis-9, trans-11 CLA and LA had no effect. Sequential treatment with CLAs then DOCT reduced IC(50) and IC(70) in MCF-7 but not in MDA-MB-231. The latter had increased IC(50) and IC(70) with LA treatment (P<0.05) and increased IC(70) with cis-9, trans-11 CLA (P<0.05) with sequential but not concurrent treatment. Longer pre-incubation times with trans-10, cis-12 CLA (24-72 h) elicited greater reductions in IC(50) and IC(70) in MCF-7 cells. Results show that CLA isomers augment anti-tumour effects of docetaxel in breast cancer cells and suggest possible dual treatment regimens.