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Effects of 6-aminonicotinamide on cell growth, poly(ADP-ribose) synthesis and nucleotide metabolism
Abstract:
The purpose of this study was to determine if the cytotoxic effects of 6-aminonicotinamide are solely the result of an inhibition of poly(ADP-ribose) synthesis. The effects of 6-aminonicotinamide on cell growth, poly(ADP-ribose) synthesis and nucleotide concentrations were compared with the effect of 3-aminobenzamide, a more potent inhibitor of poly(ADP-ribose) synthesis. The growth of L1210 cells was not inhibited by 1 mM 3-aminobenzamide and was only slightly inhibited by 5 mM 3-aminobenzamide even though poly(ADP-ribose) synthesis, as measured by the N-methyl N-nitrosourea induced depletion of NAD+, was inhibited substantially. In contrast, 6-aminonicotinamide was found to be a potent inhibitor of L1210 and CHO cell growth. A 5 mM concentration of 3-aminobenzamide had no effect on purine and pyrimidine ribonucleotide concentrations or on the ATP to ADP ratio, but it did cause a slight elevation of NAD+. 6-Aminonicotinamide at 0.01 mM caused a depletion of purine and pyrimidine nucleotides and NAD+ as well as a reduction in the ATP to ADP ratio. 6-Aminonicotinamide at 1 mM caused a substantial inhibition of purine nucleotide synthesis from [14C] glycine but did not stimulate ATP breakdown. We conclude that inhibition of poly(ADP-ribose) synthesis caused little growth inhibition in itself and that the effects of 6-amininicotinamide on nucleotide metabolism were sufficient to produce an inhibition of both cell growth and DNA repair.
Insights
6-aminonicotinamide inhibits cell growth by disrupting nucleotide metabolism, not solely by blocking poly(ADP-ribose) synthesis. This finding clarifies its cytotoxic mechanism in cancer research.
Area of Science:
- Biochemistry
- Cell Biology
- Pharmacology
Background:
- Poly(ADP-ribose) synthesis is a crucial cellular process involved in DNA repair and cell survival.
- 6-aminonicotinamide (6-AN) is known to inhibit poly(ADP-ribose) synthesis, but its precise cytotoxic mechanisms are not fully understood.
- 3-aminobenzamide (3-AB) is a well-established inhibitor of poly(ADP-ribose) synthesis used for comparison.
Purpose of the Study:
- To investigate whether the cytotoxic effects of 6-aminonicotinamide are exclusively due to the inhibition of poly(ADP-ribose) synthesis.
- To compare the effects of 6-AN and 3-AB on cell growth, poly(ADP-ribose) synthesis, and nucleotide concentrations in L1210 and CHO cells.
Main Methods:
- Comparative analysis of cell growth inhibition by 6-AN and 3-AB.
- Measurement of poly(ADP-ribose) synthesis using NAD+ depletion assay induced by N-methyl N-nitrosourea.
- Quantification of purine and pyrimidine ribonucleotide concentrations, NAD+, and ATP/ADP ratio.
Main Results:
- 3-AB, a potent inhibitor of poly(ADP-ribose) synthesis, showed minimal inhibition of L1210 cell growth.
- 6-AN significantly inhibited the growth of L1210 and CHO cells at low concentrations.
- 6-AN caused a pronounced depletion of nucleotides and NAD+, and reduced the ATP/ADP ratio, indicating widespread metabolic disruption.
Conclusions:
- Inhibition of poly(ADP-ribose) synthesis alone contributes minimally to growth inhibition.
- The cytotoxic effects of 6-AN are primarily mediated by its profound impact on nucleotide metabolism.
- Disruption of nucleotide metabolism by 6-AN is sufficient to inhibit both cell growth and DNA repair processes.