Chemotherapy sensitizes therapy-resistant cells to mild hyperthermia by suppressing heat shock protein 27 expression in triple-negative breast cancer

Purpose: Triple-negative breast cancer (TNBC) is a clinically aggressive disease with poor prognosis. Conventional che-motherapeutics are generally able to shrink the tumor mass, but often fail to completely eradicate cancer stem-like cells (CSCs) that are responsible for high risk of relapse and frequent metastases. In this study, we examined thermal sensibility of CSCs, developed an approach that enabled concurrent elimination of both the bulk of cancer cells and CSCs, and investigated the underlying mechanism. Experimental Design: We designed a platform consisting of gold nanoparticle-coated porous silicon microparticle (AuPSM) that was also loaded with docetaxel micelles (mDTXs) to enable concurrent killing of the bulk of cancer cells by released mDTX and CSCs by mild hyperthermia upon stimulation of AuPSM with near infrared. In addition, we examined the role of heat shock proteins in sensitizing CSC killing. Finally, we applied mDTX-loaded AuPSM to treat mice with SUM159 and 4T1 orthotopic tumors and evaluated tumor growth and tumor metastasis. Results: MDA-MB-231 and SUM159 TNBC cells treated with mDTX-loaded AuPSM and mild hyperthermia displayed significantly reduced efficiencies in mammosphere formation than those treated with mDTX alone or mild hyperthermia alone. Combination treatment also completely inhibited SUM159 orthotopic tumor growth and 4T1 tumor metastasis. Mechanistically, DTX treatment suppressed expression of heat shock protein 27 in cancer cells including the CSCs, rendering cells sensitive to mild hyperthermia. Conclusions: Our results indicate that chemotherapy sensitizes CSC to mild hyperthermia. We have developed an effective therapeutic approach to eliminate therapy-resistant cells in TNBC.