Indiana University (IU) School of Medicine scientists have identified a previously unrecognized connection between two proteins that help pancreatic tumor cells survive against oxidative stress. Exploiting this connection could offer a new treatment approach not only for pancreatic cancer, but also other tumors that rely on the redox pathway.
Pancreatic ductal adenocarcinoma (PDAC) is an aggressive cancer that is highly resistant to therapy, surviving despite hypoxia, oxidative stress, and nutrient deprivation, explain Mark Kelley, PhD, Betty and Earl Herr Professor of Pediatric Oncology Research at the IU School of Medicine, and study co-authors in Redox Biology.
They say that the redox effector factor-1 (Ref-1) protein plays a key role in overcoming oxidative stress in pancreatic tumors. It is crucial for base excision DNA repair and acts as a redox regulator of transcription factors that promote PDAC progression and therapy resistance, including HIF-1α, NF-κB, STAT3, AP-1, and p53.
Given this critical role, small-molecule inhibitors, such as APX3330, APX2009, and APX2014, have emerged as promising therapeutic agents that selectively block Ref-1. APX3330 is currently in clinical trials and has demonstrated oral bioavailability and a good safety profile in human Phase I/II studies, while APX2014 represents a second-generation analog with increased potency and redox-targeting specificity.
Yet, so far, inhibiting Ref-1 alone has not consistently produced strong results in PDAC, indicating that upstream redox regulators may affect Ref-1 activity and drug response.
Kelley and colleagues hypothesized that one such regulator could be peroxiredoxin 1 (PRDX1), which is abundant in mammalian cells, often overexpressed in cancers like PDAC, and has been linked to cellular proliferation, inflammation, and survival.
They therefore carried out a series of in vitro and in vivo experiments to investigate whether targeting both Ref-1 and PRDX1 could produce synergistic therapeutic effects in PDAC.
First, they showed that blocking PRDX1 through small interfering RNA or CRISPR/Cas9 knockout sensitized PDAC cell lines to APX2014 both in vitro and in vivo without affecting Ref-1’s endonuclease function, suggesting that the observed effects are driven by impairment of redox signaling rather than DNA repair.
Furthermore, blocking PRDX1, but not other members of the PRDX family, significantly increased cell death in pancreatic cancer cells after treatment with APX3330, APX2009, and APX2014.
The researchers then confirmed the translational potential of the dual blockade treatment in a mouse PDAC xenograft model. They found that PRDX1-knockout tumors treated with APX2014 were smaller and had lower Ref-1 and Ki-67 levels, indicating reduced tumor cell proliferation, than untreated mice. In addition, the mice given PRDX1 survived for longer than those in the control group.
Together these results “support that PRDX1 loss enhances the anti-tumor effects of Ref-1 inhibition in PDAC,” Kelley et al remark.
To further translate the findings to a clinical setting, the investigators carried out a tissue microarray analysis, which showed that both Ref-1 and PRDX1 are significantly overexpressed in tumor tissue taken from people with PDAC compared with adjacent normal tissues.
This indicates that “both proteins demonstrate strong biomarker potential,” Kelley told Inside Precision Medicine, adding that “patients with progressive disease in the APX3330 trial had notably higher serum Ref-1 levels than those with stable disease.”
He suggests that “patients with more than a two-fold increase in PRDX1 and/or Ref-1 staining intensity could be prioritized for APX-based therapy,” but cautions that additional validation will be needed to refine thresholds and establish biomarker-driven inclusion criteria for treatment.
Study co-author Melissa Fishel, PhD, associate professor of pediatrics and pharmacology and toxicology, and the Myles Brand Scholar in Cancer Research at the IU School of Medicine, said that the findings have the potential to impact precision medicine for patients with PDAC.
“They facilitate a test-and-treat workflow: screen for Ref-1/PRDX1, treat patients with high biomarker levels using Ref-1 inhibition, verify on-target suppression (e.g., CA9, Survivin, NF-κB pathways), and escalate to rational combinations for those showing a pharmacodynamic response,” she told Inside Precision Medicine.
“Additionally, through the IU Simon Comprehensive Cancer Center tissue bank, we are collecting patient tissue for the generation of organoids. Using this screening paradigm, perhaps we can more quickly determine which patients will respond to the combination therapy.”
The researchers conclude that their findings “strongly support dual targeting of Ref-1 and PRDX1 as a promising new therapeutic strategy for PDAC and potentially other redox-dependent cancers.” According to Kelley, these could include esophageal cancers, colorectal cancers, and certain sarcomas. “The APX3330 trial showed responses in multiple cancers, including a 357-day partial response in colorectal cancer,” he said.
