Abstract A10: Gallbladder cancer disparities in New Mexico: Examining the role of environmental heavy metal exposures as a driver of gallbladder epithelial signaling dysfunction
Authors: Gullapalli Rama R. , Caldwell Trevar S. , Rivera Megan N. , Sharma Priyanka 
Published: June 2022

Introduction: Gallbladder carcinoma (GBC) is a rare, yet deadly, malignancy of the human gut (5-year survival &lt;8%). NM is a global hotspot for GBC. Native Americans (NA) living in New Mexico (NM) have a 5- to 8-fold higher incidence of GBC compared to Caucasians in NM. The risk factors driving GBC incidence disparities in NM are unknown. We hypothesize that heavy metal exposures such as cadmium (Cd) and uranium (U) may play a key role in gallbladder carcinogenesis in NM due to the abundance of these metals in the local New Mexican environment.

Methods and Procedures: We established a retrospective clinical cohort of 24 GBC patients in NM stratified by ethnicity. Archived FFPE samples were sequenced using DNA-seq approaches to identify key mutational patterns of GBC in NM. Key changes were validated via Immunohistochemistry and FISH approaches. Next, we used primary human GB cell lines to measure effects of Cd exposures on GB cell signaling activation. In particular, we focused on effects on Akt, MAPK, and COX-2 signaling. A combination of cell viability, quantitative reactive oxygen species (ROS), and Western blot-based molecular biology assays was used to understand Cd exposure effects on cell signaling dysregulation in a gallbladder epithelial cell model.

Results: DNA-seq analysis results show the mutational spectrum of GBC samples in NM for the first time. We observed an elevated incidence of mutations in the Akt and MAPK gene pathways similar to results from earlier studies in GBC patients in China. TP53 was the commonest mutation seen in the NM GBC cohort (36%). Of importance, we observed that approximately 25% of NM GBC patients have a targetable HER2 amplification (n=6/24). In our GB epithelial cell studies, we observed a dose-dependent reduction of cell viability of gallbladder epithelial cells due to Cd exposures. The measured EC50 values of gallbladder primary cells range from 11-18 μM. Importantly, we observed activation of the Akt and MAPK signaling pathways via increased phosphorylation. The ROS activity in GB epithelial cells is elevated due to Cd exposures, which are responsible for activation of Akt and MAPK pathways. We also observed that Cd exposures led to elevation of the COX-2 expression, supporting its role in chronic GB inflammation that is characteristic of gallbladder carcinogenesis.

Conclusions: While there is epidemiologic evidence for a role for heavy metal exposures in GBC, the basic research evidence supporting this hypothesis is lacking thus far. Our study shows, for the first time, a definitive role for cadmium exposures in GB cell signaling activation via the Akt and MAPK signaling pathways. Additionally, Cd exposure may also lead to COX-2 activation, which is a second key feature that explains the chronic inflammatory origins of GBC. Thus, our initial studies demonstrate a role for environmental heavy metal exposures (Cd) in gallbladder carcinogenesis for the first time. Future research will seek to strengthen the role of Cd and U in particular in GB carcinogenesis in NM.

Citation Format: Rama R. Gullapalli, Trevar S. Caldwell, Megan N. Rivera, Priyanka Sharma. Gallbladder cancer disparities in New Mexico: Examining the role of environmental heavy metal exposures as a driver of gallbladder epithelial signaling dysfunction [abstract]. In: Proceedings of the AACR Special Conference on Environmental Carcinogenesis: Potential Pathway to Cancer Prevention; 2019 Jun 22-24; Charlotte, NC. Philadelphia (PA): AACR; Can Prev Res 2020;13(7 Suppl): Abstract nr A10.