RESUMO
Paclitaxel, a chemotherapeutic agent used in the treatment of breast cancer and other solid tumor types, including ovarian and lung, causes a dosedependent neuropathic pain, which limits its use. Chemically modified tetracycline3 (COL3) has anticancer properties and was previously reported to inhibit neuroinflammation and protect against paclitaxelinduced neuropathic pain (PINP) in mice models. However, it is not known whether it affects the anticancer activities of paclitaxel. Thus, the aim of the present study was to evaluate the effect of COL3 on the anticancer activity of paclitaxel on the breast cancer cell lines MCF7 (estrogen receptorpositive), pII [estrogen receptornegative (ERve)] and MDAMB231 (ERve). Cell proliferation, apoptosis and cell cycle stage were determined using an MTT assay, Annexin V/7aminoactinomycin D and flow cytometry. The expression of various signaling molecules was determined with ELISAbased proteome profiling and western blotting. Additionally, the degree of cell invasion was determined with a Matrigel assay and caspase3 activity was determined with a colorimetric assay. Treatment with paclitaxel or COL3 alone inhibited cell proliferation in a concentrationdependent manner in all cell lines. The antiproliferative effects of paclitaxel and COL3 in combination varied from synergism against MDAMB231 and pII cells to notably additive and slight antagonism against MCF7 cells. In the highly proliferative and invasive pII cells, the observed synergistic antiproliferative effect was partially through the induction of apoptosis via modulation of caspase3 levels and activity, and P70S6K phosphorylation, but not cell cycle arrest. COL3 inhibited the invasion of pII cells in a concentrationdependent manner partially through inhibiting total matrix metalloproteinase activity. The combination regimen significantly inhibited the expression of two proteases, ADAM metallopeptidase with thrombospondin type 1 motif 1 and proteinase 3. In conclusion, the combination of paclitaxel and COL3 indicated additive to synergistic antiproliferative effects on breast cancer cells mediated partially via the induction of apoptosis. The combination regimen could further inhibit invasion and metastasis. Thus, COL3 could be a beneficial adjunct to a paclitaxelbased anticancer regimen to improve therapeutic outcome and reduce the adverse effects of paclitaxel, primarily PINP.