Disulfide bond disrupting agents activate the unfolded protein response in EGFR- and HER2-positive breast tumor cells

Abstract

Many breast cancer deaths result from tumors acquiring resistance to available therapies. Thus, new therapeutic agents are needed for targeting drug-resistant breast cancers. Drug-refractory breast cancers include HER2+ tumors that have acquired resistance to HER2-targeted antibodies and kinase inhibitors, and “Triple-Negative” Breast Cancers (TNBCs) that lack the therapeutic targets Estrogen Receptor, Progesterone Receptor, and HER2. A significant fraction of TNBCs overexpress the HER2 family member Epidermal Growth Factor Receptor (EGFR). Thus agents that selectively kill EGFR+ and HER2+ tumors would provide new options for breast cancer therapy. We previously identified a class of compounds we termed Disulfide bond Disrupting Agents (DDAs) that selectively kill EGFR+ and HER2+ breast cancer cells in vitro and blocked the growth of HER2+ breast tumors in an animal model. DDA-dependent cytotoxicity was found to correlate with downregulation of HER1-3 and Akt dephosphorylation. Here we demonstrate that DDAs activate the Unfolded Protein Response (UPR) and that this plays a role in their ability to kill EGFR+ and HER2+ cancer cells. The use of breast cancer cell lines ectopically expressing EGFR or HER2 and pharmacological probes of UPR revealed all three DDA responses: HER1-3 downregulation, Akt dephosphorylation, and UPR activation, contribute to DDA-mediated cytotoxicity. Significantly, EGFR overexpression potentiates each of these responses. Combination studies with DDAs suggest that they may be complementary with EGFR/HER2-specific receptor tyrosine kinase inhibitors and mTORC1 inhibitors to overcome drug resistance.

Mechanistic Elucidation of the Antitumor Properties of a Novel Death Receptor 5 Activator

“…An unexpected and striking finding is the apparent selectivity of DDAs against cancer cells over normal cells in vitro and in vivo (herein (Fig. 6C) and elsewhere (Ferreira et al, 2015, Ferreira et al, 2017). Multiple mechanisms explain the oncotoxicity of DDAs.…”

“…Previous studies revealed that breast cancer cells that overexpress EGFR or HER2 are particularly sensitive to DDAs (Ferreira et al, 2015, Ferreira et al, 2017, Wang, Ferreira et al, 2019. This work employed MDA-MB-468 TNBC cells and BT474 luminal B cells as models of EGFR and HER2 overexpressing breast cancer, respectively.…”

“…1C, left panel), suggesting that DDAs activate the extrinsic apoptotic pathway in cancer cells. T47D cells were used as a model for low EGFR/HER2 luminal A cancers as employed previously (Ferreira et al, 2015, Ferreira et al, 2017, Wang et al, 2019. These studies showed that T47D cells engineered to overexpress EGFR or HER2 are highly sensitive to DDAs.…”

“…Previous reports (Ferreira, Law et al, 2015, Ferreira, Wang et al, 2017, Law, Ferreira et al, 2016 describe a novel chemical class of anticancer agents termed Disulfide bond Disrupting Agents (DDAs). DDAs selectively kill cancer cells that overexpress EGFR or HER2 (Ferreira et al, 2015), and DDA treatment is associated with decreased expression of EGFR, HER2, and HER3 and reduced phosphorylation of the prosurvival serine/threonine kinase Akt.…”

“…DDAs selectively kill cancer cells that overexpress EGFR or HER2 (Ferreira et al, 2015), and DDA treatment is associated with decreased expression of EGFR, HER2, and HER3 and reduced phosphorylation of the prosurvival serine/threonine kinase Akt. DDA-mediated cancer cell death is also associated with activation of the Unfolded Protein Response (UPR) (Ferreira et al, 2017). The Endoplasmic Reticulum (ER) stress that triggers the UPR can activate multiple cell death pathways (reviewed in (Wang, Law et al, 2018)).…”