Inhibitors of the protein disulfide isomerase family for the treatment of multiple myeloma

Abstract

Multiple Myeloma (MM) is highly sensitive to disruptions in cellular protein homeostasis. Proteasome inhibitors (PIs) are initially effective in the treatment of MM, although cures are not achievable and the emergence of resistance limits the durability of responses. New therapies are needed for refractory patients, and those that combat resistance to standard of care agents would be particularly valuable. Screening of multiple chemical libraries for PI re-sensitizing compounds identified E61 as a potent enhancer of multiple PIs and MM specific activity. Using a tandem approach of click chemistry and peptide mass fingerprinting, we identified multiple protein disulfide isomerase (PDI) family members as the primary molecular targets of E61. PDIs mediate oxidative protein folding, and E61 treatment induced robust ER and oxidative stress responses as well as the accumulation of ubiquitinylated proteins. A chemical optimization program led to a new structural class of indene (exemplified by lead E64FC26), which are highly potent pan-style inhibitors of PDIs. In mice with MM, E64FC26 improved survival and enhanced the activity of bortezomib without any adverse effects. This work demonstrates the potential of E64FC26 as an

Endoplasmic Reticulum Protein Disulfide Isomerase Shapes T Cell Efficacy for Adoptive Cellular Therapy of Tumors

“…Targeting PDI is a fruitful strategy to reduce tumor cell viability and control tumor growth [7,23]. The pan-PDI inhibitor E64FC26 was recently identified as an early drug candidate with anti-myeloma activity in vitro and in vivo, with the ability to synergistically enhance the activity of FDA-approved proteasome inhibitors [8]. Targeting redox-dependent proteins is a strategy to enhance T cell tumor control, and compounds that simultaneously boost T cell anti-tumor potential while restricting tumor growth are exciting candidates for cancer immunotherapy.…”

“…E64FC26 increased CD8 T cell viability, evidenced by the percentage of live T cells (Supplemental Figure S1, Figure 1A) and reduced Annexin/propidium iodide (PI) positive T cells relative to vehicle controls ( Figure 1B). We conducted the study with 0.5 µM E64FC26 given the enhanced T cell viability and previous reports of impaired malignant cell survival at this dose [8].…”

“…Leveraging the UPR-mediated cell death pathway led to the development of a new class of therapeutics that target protein disulfide isomerase (PDI), a redox-dependent protein folding enzyme with isomerase and chaperone activity. In multiple myeloma cells, inhibition of PDI led to an accumulation of unfolded/misfolded proteins demonstrated by increased ubiquitination, rapid cell death through activation of the UPR, and enhanced efficacy of FDA-approved proteasome inhibitors [7,8]. PDI is an emerging drug target in oncology, and, while the anti-tumor effects of PDI inhibition have been well documented, the consequence of PDI modulation on healthy immune cells has not been assessed.…”

“…Here we assessed the effect of pan-PDI inhibitor E64FC26 [8] on healthy Pmel TCR-transgenic CD8 T cells specific for gp100 melanoma antigen in vitro and in vivo. We demonstrate the surprising finding that PDI inhibition attenuates the UPR and promotes viability of healthy T cells, whereas it activates the UPR and restricts survival in oncogenic T cells.…”

A metabolic switch in proteasome inhibitor-resistant multiple myeloma ensures higher mitochondrial metabolism, protein folding and sphingomyelin synthesis

“…Targeting protein disulfide isomerase in MM in vitro and in vivo has been suggested as a promising therapeutic strategy in combination with bortezomib. 15 Mitochondria serve as a major source of ATP through oxidative phosphorylation (OXPHOS). Increased ATP levels in PI-resistant cells are consistent with increased activity of the tricarboxylic acid cycle and the metabolic shift towards OXPHOS observed previously in these cells.…”