Inducing apoptosis in chemotherapy-resistant B-lineage acute lymphoblastic leukaemia cells by targeting HSPA5, a master regulator of the anti-apoptotic unfolded protein response signalling network.

We present previously unknown evidence that the immunoglobulin heavy chain binding protein BIP/HSPA5, also known as glucose regulated protein (GRP)78, serving as a pivotal component of the pro-survival axis of the unfolded protein response (UPR) signalling network, is abundantly expressed in relapsed B-lineage acute lymphoblastic leukaemia (ALL) and contributes to chemotherapy resistance of leukaemic B-cell precursors. The resistance of B-lineage ALL cells to the standard anti-leukaemic drug vincristine was overcome by the HSPA5 inhibitor epigallocatechin gallate, which inhibits the anti-apoptotic function of HSPA5 by targeting its ATP-binding domain. Notably, chemotherapy-resistant B-lineage ALL cells underwent apoptosis within 48 h of exposure to a doxorubicin-conjugated cell-penetrating cyclic anti-HSPA5 peptide targeting surface-expressed HSPA5 molecules on leukaemia cells. The identification of the HSPA5 as a chemoresistance biomarker and molecular target for B-lineage ALL may lead to new anti-leukaemic treatment strategies that are much needed.