The 70 kDa heat shock protein (HSP70) isoforms play distinct roles in cancer, but their structural similarity limits isoform-specific inhibition. Here, we modified nonselective HSP70 inhibitor S1g-10 via a subcellular anchoring strategy to generate compounds 5 and 8, which selectively target mitochondrial-localized GRP75 and ER-localized GRP78, respectively. Both compounds modulated their intended targets in vivo. Additionally, GRP75, but not GRP78, was identified as a key regulator of mitochondrial membrane stability in breast cancer cells and maintains the stemness of breast cancer stem cells (BCSCs). Compared with normal cells, compound 5 exhibited selective toxicity against breast cancer cells and effectively suppressed the properties of BCSCs. This study provides novel chemical probes for studying specific isoforms of HSP70 and introduces a strategy to develop GRP75-targeted therapeutics for breast cancer.
Jiang et al. (Fri,) studied this question.