Sulforaphane metabolites reduce resistance to paclitaxel via microtubule disruption

Long treatment with paclitaxel (PTX) might increase resistance and side-effects causing a failure in cancer chemotherapy. Here we uncovered that either sulforaphane-cysteine (SFN-Cys) or sulforaphane-N-acetyl-cysteine (SFN-NAC) induced apoptosis via phosphorylated ERK1/2-mediated upregulation of 26 S proteasome and Hsp70, and downregulation of βIII-tubulin, XIAP, Tau, Stathmin1 and α-tubulin causing microtubule disruption in human PTX-resistant non-small cell lung cancer (NSCLC) cells. Knockdown of either βIII-tubulin or α-tubulin via siRNA increased cell sensitivity to PTX, indicating that these two proteins help cells increase the resistance. Tissue microarray analysis showed that overexpression of βIII-tubulin correlated to NSCLC malignant grading. Immunofluorescence staining also showed that SFN metabolites induced a nest-like microtubule protein distribution with aggregation and disruption. Co-immunoprecipitation showed that SFN metabolites reduced the interaction between βIII-tubulin and Tau, and that between α-tubulin and XIAP. The combination of PTX with SFN metabolites decreased the resistance to PTX, and doses of both PTX and SFN metabolites, and enhanced apoptosis resulting from activated Caspase-3-caused microtubule degradation. Importantly, the effective dose of SFN metabolites combined with 20 nM PTX will be low to 4 μM. Thus, we might combine SFN metabolites with PTX for preclinical trial. Normally, more than 20 μM SFN metabolites only leading to apoptosis for SFN metabolites hindered their applications. These findings will help us develop a low-resistance and high-efficiency chemotherapy via PTX/SFN metabolites combination.