Mechanisms and implications of selective cell-surface Grp94 inhibition in breast cancer cells

Abstract

Several intracellular chaperones have been shown to be secreted by distinct cellular types, including vascular, immune and tumor cells. Protein disulfide isomerase (PDI), as well as 70 and 90kDa heat shock protein (Hsp70 and Hsp90) families play extracellular roles in pathological conditions such as thrombosis, vascular remodeling and cancer survival and metastasis generation. Inhibition of intracellular cytosolic Hsp90 with PU-H71 constitutes a promising emerging therapy in cancer, now undergoing clinical trial. Recently, the novel cell-permeable compounds PU-H54 and PU-WS13, which target the endoplasmic reticulum-located Hsp90 paralog Grp94 were shown to promote apoptosis in breast cancer cells with high expression Human Epidermal Receptor 2-HER2. CsGrp94 interacts and stabilizes HER2 at the plasma membrane, and apoptosis correlates with decreased cell-surface (cs)HER2 levels. A feature of most tumors is hypoxic conditions, which could increase Grp94 expression. Here we propose to design a cell-impermeable analog of PU-WS13 for selective csGrp94 targetting. We will investigate whethert hypoxic conditions promote enhanced csGrp94 in breast cancer cells even with low HER2 cell-surface levels and that selective csGrp94 inhibition may enhance efficacy of tumor cell apoptosis also in these cells. In addition, this investigation aims to uncover novel csGrp94 oncogenic clients besides HER2, using proteomics analyses of pull down csGrp94 assays. Such developments may lead to a better mechanistic understanding of chaperone inhibition as a therapeutic tool in cancer and may improve its efficacy.