"Hereditary non-polyposis colorectal cancer (HNPCC) is an inherited disorder where individuals have an increased risk of developing colorectal cancer before age 50. Current HNPCC treatments involve colectomy, which has debilitating aftereffects. HNPCC is caused by genetic mutations of MLH1 and MSH2, which are both involved in DNA mismatch repair. Dysfunctional
DNA repair causes cancer by preventing DNA damage from being fixed or marked for repair.
Seventy percent of HNPCC patients have mutations in MLH1 and MSH2. MLH1 is involved in DNA mismatch repair by binding to PMS2 to form a complex around damaged DNA to direct other proteins to fix the damage. MSH2 is a tumor suppressor gene that heterodimerizes with MSH6 and MSH3 to form the MutSα and MutSβ complexes, respectively. This review will
describe current treatments for HNPCC and a theoretical approach to treating it using a CRISPR-Cas9n-based genetic therapy. First, CRISPR-Cas9n and gRNA will be added into an integrase-deficient lentiviral vector as plasmids with replicative abilities silenced. The IDLV vector will be injected into the brachial artery. Upon entry into the colon, the Cas9n will initiate single-strand breaks in MSH2 and MLH1 genes of progenitor and paneth cells, stem cells in the colonic villi, to cut out the mutated copy and put in a new copy. Once this occurs, the likelihood of aggressive HNPCC will reduce because the normal functions of MLH1 and MSH2 will be restored. Therefore, using CRISPR-Cas9n can treat HNPCC with reduced aftereffects for patients with mutations in MLH1 and MSH2 genes."