COL‑3 enhances the anti‑proliferative and pro‑apoptotic effects of paclitaxel in breast cancer cells

Paclitaxel, a chemotherapeutic agent used in the treatment of breast cancer and other solid tumor types, including ovarian and lung, causes a dose‑dependent neuropathic pain, which limits its use. Chemically modified tetracycline‑3 (COL‑3) has anticancer properties and was previously reported to inhibit neuroinflammation and protect against paclitaxel‑induced 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 COL‑3 on the anticancer activity of paclitaxel on the breast cancer cell lines MCF‑7 (estrogen receptor‑positive), pII [estrogen receptor‑negative (ER‑ve)] and MDA‑MB‑231 (ER‑ve). Cell proliferation, apoptosis and cell cycle stage were determined using an MTT assay, Annexin V/7‑aminoactinomycin D and flow cytometry. The expression of various signaling molecules was determined with ELISA‑based proteome profiling and western blotting. Additionally, the degree of cell invasion was determined with a Matrigel assay and caspase‑3 activity was determined with a colorimetric assay. Treatment with paclitaxel or COL‑3 alone inhibited cell proliferation in a concentration‑dependent manner in all cell lines. The anti‑proliferative effects of paclitaxel and COL‑3 in combination varied from synergism against MDA‑MB‑231 and pII cells to notably additive and slight antagonism against MCF‑7 cells. In the highly proliferative and invasive pII cells, the observed synergistic anti‑proliferative effect was partially through the induction of apoptosis via modulation of caspase‑3 levels and activity, and P70S6K phosphorylation, but not cell cycle arrest. COL‑3 inhibited the invasion of pII cells in a concentration‑dependent 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 COL‑3 indicated additive to synergistic anti‑proliferative effects on breast cancer cells mediated partially via the induction of apoptosis. The combination regimen could further inhibit invasion and metastasis. Thus, COL‑3 could be a beneficial adjunct to a paclitaxel‑based anticancer regimen to improve therapeutic outcome and reduce the adverse effects of paclitaxel, primarily PINP.