Increased Sensitivity to Long‐term 5‐Fluorouracil Exposure of Human Colon Cancer HT‐29 Cells Resistant to Short‐term Exposure

Abstract

Key words: HT-29 human colon cancer -5-Fluorouracil-resistance -Dual actions of 5-FUExposure time 5-FU is a unique anticancer agent with two major pharmaco-biochemical actions: of its active metabolites, FUTP is fraudulently incorporated into RNA and impairs the multiple functions of RNA, while FdUMP blocks the catalytic activity of TS by forming a ternary covalent complex with its co-substrate, 5, 10-CH 2 -FH 4 , which inhibits DNA synthesis. Thus 5-FU potentially exerts both RNAand DNA-directed actions against target cells.One of the factors determining which action 5-FU preferentially exerts on the target cells seems to be their innate biochemical characteristics of 5-FU metabolism. If the resultant intracellular concentration of FUTP or FdUMP is lower than the effective level, 5-FU may exert only one of its dual actions. However, it seems to exert dual actions against the majority of cancer cells, although the efficacy of such actions varies. Another determinant is the length of the exposure time to 5-FU. We have previously developed a method for the kinetic analysis of the cell-killing action of anticancer agents which can classify them into cell cycle phase-nonspecific (type I) drugs and cell cycle phase-specific (type II) drugs. 1,2) According to this analysis, FUrd and FdUrd showed typical kinetic profiles for type I and II drugs, respectively. 5-FU had a FUrd-like kinetic profile for cell killing action when cells were exposed for a short time and a FdUrd-like profile when they were continuously exposed for a long time. 3, 4)These results suggested that 5-FU exerts RNA-directed action under short exposure conditions and DNA-directed action under long, continuous exposure conditions. The former requires a high 5-FU concentration, while for the latter, a low concentration is sufficient.In view of the dual actions of 5-FU, which depend on the exposure time, it might be possible to develop a subline which acquires resistance to short/long exposure to 5-FU, but does not show cross-resistance to long/short exposure. Based on this idea, we have established some 5-FU-resistant sublines of human gastro-intestinal cancer cell lines by repeated long-term exposure to 5-FU. However, we failed to obtain a subline of the type we had expected. In the present study, we tried repeated 1-h exposure of human colon cancer HT-29 cells to 5-FU, and established a subline named HT-29/5-FU/S. This subline is resistant to short-term exposure to 5-FU, exhibited no cross-resistance to long-term exposure to 5-FU, and had rather higher sensitivity than its parent cells.

Circumvention of 5‐Fluorouracil Resistance in Human Stomach Cancer Cells by Uracil Phosphoribosyltransferase Gene Transduction

“…20) In the case of resistance to 5-FU, poor activity of several enzymes involved in the anabolism of 5-FU has also been demonstrated. [5][6][7][8][9] Clinically, the relationship between response to 5-FU-based chemotherapy and content or activity of TS in tumor tissue has been extensively investigated. Most tumors with a relatively high content of TS are less responsive to 5-FU, though tumors with low TS content are not necessarily responsive.…”

“…5,6) We also established 5-FU-resistant sublines of three different human colon and stomach cancer cell lines, and found that poor conversion of 5-FU into its active metabolites due to reduced activity levels of enzymes involved in pyrimidine nucleotide synthesis is a major mechanism of resistance. [7][8][9] Reversal of drug resistance is an intriguing subject, and several successful approaches, at least experimentally, have been reported in the field of P-glycoprotein-associated multidrug resistance. However, few approaches to overcoming resistance to 5-FU have been reported, probably due to difficulty in modulating 5-FU-activating enzyme activity.…”

Prediction of 5-Fluorouracil and Cisplatin Synergism for Advanced Gastrointestinal Cancers Using a Collagen Gel Droplet Embedded Culture

“…Low concentrations of 5-FU exert a DNA-directed action with long exposure time, while high concentrations of 5-FU exert RNA-directed influence under short-term exposure conditions. 27 We speculate that CDDP may modulate the DNA-directed action of 5-FU by increasing the intracellular pool of 5,10-CH 2 -FH 4 . Therefore, the exposure time setting for 5-FU was fixed at 7 days in this experiment according to our clinical experience.…”

A microfluidic-based platform for tumour spheroid culture, monitoring and drug screening

“…Intrinsic or acquired resistance of colon cancer cells to 5-fluorouracil is a phenomenon widely reported in the literature. 30,[35][36][37][38][39] Moreover, there have been reports on drug resistance of HT-29 cells enhanced by higher drug concentrations. 36 However, none of these effects has been satisfyingly explained.…”