This thesis investigates the characteristics of an Hv1 (voltage-gated proton) channel inhibitor, a peptide fraction from a spider venom discovered in our laboratory. Since Hv1 is expressed in breast cancer cells (based on the literature and our preliminary experiments in the JIMT-1 breast cancer cell line), our peptide discovery has future therapeutic potential. Breast cancer, being the most prevalent cancer among women worldwide, presents significant challenges due to its complex risk factors, including genetic predispositions like BRCA1 and BRCA2 mutations, and environmental influences. Our research examines the pharmacology of GsAF-II using the patch clamp technique on transiently expressed Hv1 ion channels. A unique aspect of our study is the introduction of GsAF-II, as a new inhibitor of Hv1. The results demonstrate significant inhibitory effects of GsAF-II on Hv1 channels, suggesting its potential therapeutic applications in disrupting cancer cells pH regulation. These findings propose a new path for cancer treatment through ion channel inhibition, with particular emphasis on the innovative use of peptide compounds from spider venom. Further studies are recommended to refine the selectivity and effectiveness of GsAF-II, establishing a foundation for innovative cancer treatment strategies. This research contributes to the broader fight against breast cancer, offering insights into novel therapeutic targets and potential treatments.