Advances in cancer therapy have all come from understanding the biology and or genetic make-up of a particular cancer. When these factors are identified, treatments can then be 'personalized'with tumor specificity by targeting of cancer-related receptors, and less toxicity from off-site injury. Unlike other solid tumors, G-protein coupled receptors (GPCRs) have been shown to play a critical role in mediation of growth of gastrointestinal cancers. We have identified a receptor on pancreatic cancer, the CCK-B receptor, which is over-expressed in cancer compared to normal tissues and responsible for growth stimulation. Our research team has shown that gastrin stimulates growth of pancreatic cancer by mediating its effects in an autocrine fashion through this GPCR. We have shown that if gastrin's interaction at the receptor can be blocked, pancreatic cancer is inhibited. One problem has been in developing an agent to selectively block this receptor that can potentially be used therapeutically. Our lab and others have attempted to raise a monoclonal antibody to the gastrin binding site of the CCK-B receptor but have been unsuccessful due to the similar homology between human and mouse sequences. Therefore, we have undertaken a different strategy using DNA aptamers to target the CCK- B receptor in pancreatic cancer. DNA aptamers - highly structured oligonucleotides that bind selectively to receptor targets with affinities comparable to or better than antibodies, are more stable in the peripheral blood than monoclonal antibodies, and they are not immunogenic. We synthesized two peptides corresponding to the gastrin binding site on the extracellular, N-terminus of the CCK-B receptor. Using a technique called Systematic Evolution of Ligands by Exponential Enrichment (SELEX) we identified specific DNA aptamers that bind to the external gastrin binding site of the CCK-B receptor. We hypothesize that selective DNA aptamers to the CCK-B receptor can specifically target pancreatic cancer and inhibit growth by blocking the actions of gastrin. In order to test this hypothesis we propose the following aims: 1) Characterize the binding affinities (Kd) and IC50 of a panel of aptamers we have identified using pancreatic cancer cells in vitro to select aptamers with the greatest affinities for growth studies. 2) Study the efficacy of aptamers to inhibit growth of pancreatic cancer in culture and in mice bearing an orthotopic pancreatic cancer. The role of CCK-B targeted aptamers on apoptosis will also be investigated. The long term goal of our research is to improve treatment and survival of patients with pancreatic cancer.
Gastrin stimulates growth of pancreatic cancer by its interaction with a G-protein coupled receptor called the CCK-B receptor which is over expressed in pancreatic cancer cells. Due to similar homology of the receptor binding site in animals, attempts to raise antibodies to block the receptor have been unsuccessful;therefore, we have designed CCK-B receptor selective DNA aptamers to target and block gastrin's interaction at this receptor. This project involves testing a panel of DNA aptamers with high selectivity and specificity to inhibit growth of human pancreatic cancer in vitro and in vivo.
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