Exploration of Benzothiazole Rhodacyanines as Allosteric Inhibitors of Protein–Protein Interactions with Heat Shock Protein 70 (Hsp70)

Cancer
cells rely on the chaperone heat shock protein 70 (Hsp70)
for survival and proliferation. Recently, benzothiazole rhodacyanines
have been shown to bind an allosteric site on Hsp70, interrupting
its binding to nucleotide-exchange factors (NEFs) and promoting cell
death in breast cancer cell lines. However, proof-of-concept molecules,
such as JG-98, have relatively modest potency (EC50 ≈
0.7–0.4 μM) and are rapidly metabolized in animals. Here,
we explored this chemical series through structure- and property-based
design of ∼300 analogs, showing that the most potent had >10-fold
improved EC50 values (∼0.05 to 0.03 μM) against
two breast cancer cells. Biomarkers and whole genome CRISPRi screens
confirmed members of the Hsp70 family as cellular targets. On the
basis of these results, JG-231 was found to reduce tumor burden in
an MDA-MB-231 xenograft model (4 mg/kg, ip). Together, these studies
support the hypothesis that Hsp70 may be a promising target for anticancer
therapeutics.