5-FU Chemotherapy Failure in Some Colorectal Cancer Patients with Microsatellite Instability

Abstract

Human colorectal cancer (CRC) is the third most commonly diagnosed cancer as well as the second leading cause of cancer mortality in the United States. The hypothesis to be tested in this study is that the loss of TGFβ signaling causes overexpression of the uridine phosphorylase (UP) gene in human CRC when treated with 5-fluorouracil (5-FU), a common chemotherapeutic reagent. As a result, 5-FU may be metabolized via the RNA pathway, causing an increase in host-toxicity. Conversely, a mutation in the KRAS gene may drive the reaction towards the antitumor, DNA metabolic pathway. This mechanism would explain the ineffective nature of 5-FU-based treatments on tumors, some of which are TFGβ signaling-deficient, that are usually characterized as microsatellite instability high (MSI-H). If so, situational inhibition of UP may increase the intended anti-tumor activity of the 5-FU treatment while decreasing host-toxicity in this subcategory of MSI-H tumors, thus allowing only patients whose tumors have a 5-FU-susceptible genetic profile to be treated successfully with 5-FU based therapy. Cancerous cell lines containing different combinations of TGFBR2 and KRASᴳ¹³ᴰ mutations will be cultured and photographed. The cell lines Hke3 and Hkh2 contain a TGFBR2 mutation and have a morphological pattern that closely resembles the colonic mucosa while the HCT116 cell line contains both TGFBR2 and KRASᴳ¹³ᴰ mutations and has less structured morphology. Following culturing, UP and TP mRNA expression levels in all cell lines will be determined through reverse transcriptase (RT)-PCR and normalized to β-actin. If the hypothesis is supported, and then verified in patients, personalized therapy can be used to determine whether 5-FU should be administered in colorectal cancer cases in which KRASᴳ¹³ᴰ and TGFBR2 mutations are present or absent.