Expression Level and Biomarker Potential of Hemoxygenase-1 in Pancreatic Cancer

Abstract

<h3>Purpose/Objective(s)</h3> In pancreatic ductal adenocarcinoma (PDAC), hypoxia is key mediator of resistance to chemo-radiotherapy and a prominent feature of PDAC tumor microenvironment (TME). Heme oxygenase-1 (HMOX-1) is an Nrf2-regulated gene that plays a critical role in modulation of oxidative stress and ROS production. Previous research suggested that HMOX-1 is expressed in the hypoxic PDAC TME and is induced upon exposure to chemotherapy. Utilizing a tumor microarray (TMA) of PDAC patients treated at our institution, we sought to determine baseline expression of HMOX-1 in the tumor and the TME and whether it could be a biomarker of resistance to neoadjuvant treatment (NAT). <h3>Materials/Methods</h3> Four TMAs containing 80 cores (of normal and cancerous pancreatic tissue) on each slide were stained with HMOX-1 antibody. Slides were manually evaluated and computer-assisted morphometric analysis of digital images was performed using the Aperio Image Analysis software™. Immunohistochemistry (IHC) staining was manually scored as follows: Tumor cells staining, Normal and hyperplasia cell staining, TME staining, Intensity of IHC stain (negative = 0, borderline = +/-, minimal = 1, moderate = 2, or severe = 3); Localization of stain and its distribution (homogenous, heterogeneous, focal, multifocal, and/or variable). The Positive Pixel Count algorithm was used to quantify the amount of stain present in a scanned slide image and derive the H-score which represents a combination of number weak positives, moderate positives, and strong positives/Number of Total positive/ pixels on each core. <h3>Results</h3> Through the Oncology Research Information Exchange Network (ORIEN) program, we developed 6 TMAs of PDAC patients that were treated at our institution between 2013-2020. Four out of 6 available PDAC TMAs were evaluated for expression of HMOX-1 equaling to 320 cores representing 101 patients. 35% of those patients received NAT. Seven out of 14 patients who received RT as part of their NAT were treated with SBRT. A total of 175 eligible cores were included in the final analysis. Overall, there was minimal cytoplasmic cell staining in pancreatic cancer cells. Only 5 out of 175 eligible cores were considered true positives. The 5 positive cores represented 5 different patients. None of these patients received NAT. One true positive underwent whole genome sequencing and was found to have a BRIP1 (BRCA-1 interacting protein) germline mutation. There was no staining in the TME and mild inflammatory cell staining (macrophages and subset of lymphocytes). <h3>Conclusion</h3> We showed that HMOX-1 is not overexpressed at baseline in pancreatic cancer tissue, limiting its use as a predictive marker for resistance to NAT. However, given its inducible nature, it could be primarily expressed upon exposure to these therapies. Future research is needed to investigate mechanism of HMOX-1 induction after treatment. Our future goal is to utilize this clinically rich resource to investigate other relevant proteins that may predict response to therapy.