Abstract 6148: Disulfide isomerases AGR2, ERp44, and PDIA1 maintain death receptor 5 in an auto-inhibited, monomeric form

Previous studies indicated that compounds termed Disulfide bond Disrupting Agents (DDAs) exhibit anti-cancer activity that is associated with downregulation of EGFR/HER1, HER2, and HER3, and activation of Death Receptors 4 and 5 (DR4/5). DDA-induced HER1-3 downregulation is preceded by disulfide-mediated oligomerization. In contrast, DDA-mediated DR4/5 oligomerization results in DR5 upregulation, and activation of DR4/5 pro-apoptotic signaling through Caspases 8 and 3. However, the precise mechanisms by which altered disulfide bonding stabilizes and activates DR5 are unknown. A recent report indicated that the extracellular domain of DR5 acts in an auto-inhibitory manner to prevent DR5 oligomerization and pro-apoptotic signaling in the absence of its ligand, TRAIL. A subsequent paper showed that the DR5 auto-inhibitory domain is a positive patch consisting of three basic residues. Importantly, the structure of the auto-inhibitory loop is formed by two disulfide bonds. We hypothesize that DDAs disrupt the disulfide bonds that make up the auto-inhibitory loop, resulting in DR5 oligomerization, and activation of Caspase 8/3-driven apoptosis in a TRAIL-independent manner. Due to their novel mechanisms of action, DDAs may overcome the pharmacological liabilities that have limited the efficacy of TRAIL analogs and DR5 agonist antibodies. Another unanswered question is how precisely DDAs alter DR5 and EGFR disulfide bonding. The direct targets of DDA action were revealed through affinity purification studies with biotinylated-DDA analogs. These studies identified the protein disulfide isomerases AGR2, ERp44, and PDIA1 as DDA target proteins, explaining how DDAs alter DR5 and EGFR disulfide bonding patterns. Consistent with this interpretation, knockdown of AGR2 or ERp44, or expression of catalytically null AGR2 or ERp44 mutants, mimicked DDAs in inducing disulfide-mediated DR5 oligomerization and Caspase 8 activation. Together, these results demonstrate a fundamentally novel, ligand-independent mechanism for activation of DR5 through DDA-mediated inhibition of the PDIs AGR2, ERp44, and PDIA1. Significantly, DDAs are the first identified active site inhibitors of AGR2 and ERp44.

Citation Format: Brian K. Law, Mary E. Law, Elham Yaaghubi, Amanda Ghilardi, Brad J. Davis, Renan Ferreira, Samantha Eggleston, Jade Nguyen, Grace Alexandrow, Jin Koh, Sixue Chen, Chi-Wu Chiang, Coy Heldermon, Peter Norgaard, Ronald K. Castallano, Zaafir M. Dulloo. Disulfide isomerases AGR2, ERp44, and PDIA1 maintain death receptor 5 in an auto-inhibited, monomeric form. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6148.

Inhibitors of ERp44, PDIA1, and AGR2 induce disulfide-mediated oligomerization of Death Receptors 4 and 5 and cancer cell death

Breast cancer mortality remains unacceptably high, indicating a need for safer and more effective therapeutic agents. Disulfide bond Disrupting Agents (DDAs) were previously identified as a novel class of anticancer compounds that selectively kill cancers that overexpress the Epidermal Growth Factor Receptor (EGFR) or its family member HER2. DDAs kill EGFR+ and HER2+ cancer cells via the parallel downregulation of EGFR, HER2, and HER3 and activation/oligomerization of Death Receptors 4 and 5 (DR4/5). However, the mechanisms by which DDAs mediate these effects are unknown. Affinity purification analyses employing biotinylated-DDAs reveal that the Protein Disulfide Isomerase (PDI) family members AGR2, PDIA1, and ERp44 are DDA target proteins. Further analyses demonstrate that shRNA-mediated knockdown of AGR2 and ERp44, or expression of ERp44 mutants, enhance basal DR5 oligomerization. DDA treatment of breast cancer cells disrupts PDIA1 and ERp44 mixed disulfide bonds with their client proteins. Together, the results herein reveal DDAs as the first small molecule, active site inhibitors of AGR2 and ERp44, and demonstrate roles for AGR2 and ERp44 in regulating the activity, stability, and localization of DR4 and DR5, and activation of Caspase 8.

Repurposing Tranexamic Acid as an Anticancer Agent

Tranexamic Acid (TA) is a clinically used antifibrinolytic agent that acts as a Lys mimetic to block binding of Plasminogen with Plasminogen activators, preventing conversion of Plasminogen to its proteolytically activated form, Plasmin. Previous studies suggested that TA may exhibit anticancer activity by blockade of extracellular Plasmin formation. Plasmin-mediated cleavage of the CDCP1 protein may increase its oncogenic functions through several downstream pathways. Results presented herein demonstrate that TA blocks Plasmin-mediated excision of the extracellular domain of the oncoprotein CDCP1. In vitro studies indicate that TA reduces the viability of a broad array of human and murine cancer cell lines, and breast tumor growth studies demonstrate that TA reduces cancer growth in vivo. Based on the ability of TA to mimic Lys and Arg, we hypothesized that TA may perturb multiple processes that involve Lys/Arg-rich protein sequences, and that TA may alter intracellular signaling pathways in addition to blocking extracellular Plasmin production. Indeed, TA-mediated suppression of tumor cell viability is associated with multiple biochemical actions, including inhibition of protein synthesis, reduced activating phosphorylation of STAT3 and S6K1, decreased expression of the MYC oncoprotein, and suppression of Lys acetylation. Further, TA inhibited uptake of Lys and Arg by cancer cells. These findings suggest that TA or TA analogs may serve as lead compounds and inspire the production of new classes of anticancer agents that function by mimicking Lys and Arg.

A novel proteotoxic combination therapy for EGFR+ and HER2+ cancers

While HER2 and EGFR are overexpressed in breast cancers and multiple other types of tumors, the use of EGFR and/or HER2 inhibitors have failed to cure many cancer patients, largely because cancers acquire resistance to HER2/EGFR-specific drugs. Cancers that overexpress the HER-family proteins EGFR, HER2, and HER3 are uniquely sensitive to agents that disrupt HER2 and EGFR protein folding. We previously showed that disruption of disulfide bond formation by Disulfide Disrupting Agents (DDAs) kills HER2/EGFR overexpressing cells through multiple mechanisms. Herein, we show that interference with proline isomerization in HER2/EGFR overexpressing cells also induces cancer cell death. The peptidyl-prolyl isomerase inhibitor Cyclosporine A (CsA) selectively kills EGFR+ or HER2+ breast cancer cells in vitro by activating caspase-dependent apoptotic pathways. Further, CsA synergizes with the DDA tcyDTDO to kill HER2/EGFR overexpressing cells in vitro and the two agents cooperate to kill HER2+ tumors in vivo. There is a critical need for novel strategies to target HER2+ and EGFR+ cancers that are resistant to currently available mechanism-based agents. Drugs that target HER2/EGFR protein folding, including DDAs and CsA, have the potential to kill cancers that overexpress EGFR or HER2 through the induction of proteostatic synthetic lethality.

Abstract 447: A novel proteotoxic combination therapy for EGFR+ and HER2+ cancers

EGFR and/or HER2 are frequently overexpressed oncoproteins in HER2+ breast cancer, Triple Negative Breast Cancer (TNBC), and Inflammatory Breast Cancer (IBC). However, EGFR and/or HER2 targeting agents have failed to make major advances in improving survival for these cancer patients, largely because these cancers frequently develop resistance to these drugs. The identification of novel treatment strategies is critically needed. Overexpression of EGFR and/or HER2 presents a severe burden to the secretary pathway, as HER-family proteins EGFR, HER2, HER3 share conserved extracellular cysteine-rich and proline-rich repeats that form numerous disulfide bonds and control cis-trans isomerization in the protein folding processes. We demonstrated that the disulfide bond disrupting Agents (DDAs) selectively killed EGFR+ and/or HER2+ breast cancer cells in vitro and decreased tumor growth of HER2+ cancer in a xenograft mouse model. DDA-dependent anti-cancer actions resulted from downregulation of EGFR/HER2/HER3, induction of AKT dephosphorylation, and activation of Endoplasmic Reticulum (ER) stress. We also investigated a novel proteotoxic combination therapy employing DDAs and Proline Isomerase Inhibitors (PIIs) in treating breast cancers. PIIs potentiated the efficacy of DDAs in downregulating EGFR/HER2/HER3 levels and initiating ER stress, and the combination was highly synergistic in reducing EGFR+ and/or HER2+ breast cancer cell viability. Importantly, the combination of DDAs and PIIs overcame single drug resistance, significantly decreased tumor volumes and increased the survival of xenograft mice. Evidence that the drug combination was effective against metastatic breast cancer cells is also provided.

Citation Format: Mengxiong Wang, Renan Ferreira, Mary Law, Elham Yaaghubi, Coy Heldermon, Ronald Castellano, Brian Law. A novel proteotoxic combination therapy for EGFR+ and HER2+ cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 447.

One-pot synthesis, FT-IR, NMR and density functional method (B3LYP) studies on 2-(cyclohexylamino)-2-oxo-1-(pyridin-2-yl)ethyl benzoate

2-(Cyclohexylamino)-2-oxo-1-(pyridin-2-yl)ethyl benzoate has been synthesized and characterized by elemental analysis, FT-IR, (1)H NMR and (13)C NMR. Geometrical structures, vibrational frequencies, (1)H and (13)C chemical shift values, molecular electrostatic potential maps and several thermodynamic parameters of title compound in the ground state have been calculated by using the density functional method with 6-31G(d) basis set. The IR spectrum of title compound was interpreted in terms of potential energy distribution (PED) analysis and NMR chemical shifts were also simulated using the GaussView program. Comparison of the theoretical vibrational spectra, (1)H and (13)C NMR chemical shifts of title compound showed a good agreement with the experimental data.