Development of resistance of novikoff hepatoma TO 5-fluoro-2'-deoxyuridine

✍ Scribed by William H. Wolberg

• Publisher: John Wiley and Sons
• Year: 1970
• Tongue: French
• Weight: 626 KB
• Volume: 6
• Category: Article
• ISSN: 0020-7136
• DOI: 10.1002/ijc.2910060213

✦ Synopsis

Abstract

Three strains of Novikoff hepatoma were studied in tissue culture; the N1‐S1 or FUDR‐sensitive strain, N1‐S1/FUDR which is grown in and is resistant to 1 × 10^−5^M FUDR, and the cells which emerged as FUDR‐resistant after 10 generations when N1‐S1 was exposed to 1 × 10^−7^M FUDR. Inhibition of growth of N1‐S1 cells by FUDR was related to the concentration of the drug in the medium. The uptake of formate and serine into DNA‐thymine of these cells was inhibited by FUDR and the degree of inhibition was likewise proportional to the concentration of drug in the medium. The cells derived from N1‐S1 which were resistant to FUDR resembled the stable resistant strain, N1‐S1/FUDR, in that they lacked the ability to incorporate thymidine into DNA at 4.0 × 10^−8^M. Such cells apparently had less thymidine kinase activity and consequently also had a decreased ability to convert FUDR to the active monophosphate. Because of the decrease in thymidine kinase activity, the resistant strain, N1‐S1/FUDR, utilized thymidine as a source for DNA‐thymidine to a lesser extent than did the sensitive strain N1‐S1. However, both strains used serine and formate as the source of the 5‐methyl carbon of DNA‐thymidine to a similar extent.

Growth studies in shaker flasks with a mixture consisting of 75% N1‐S1 and 25% N1‐S1/FUDR cells treated with FUDR demonstrated that rapid overgrowth by the 25% resistant cells obscured the significant killing of sensitive cells by the drug. Clonal studies revealed that a small portion of cells resistant to FUDR were present in the sensitive N1‐S1 strain of cells. The number of colonies which survived depended upon the concentration of the drug, but approximately 0.6% of the N1‐S1 cells grew in the presence of 1 × 10^−5^M FUDR. These studies led to the conclusion that the development of drug resistance in this system was actually a process of selection by which FUDR killed a certain percentage of cells determined by its concentration. Biochemically resistant cells which were present as a small proportion of the original “sensitive” tumor continued to proliferate and ultimately emerged as the dominant population.