Figure 3.

Comparison of the mutagenic potencies of AZT, ddI, and AZT + ddI, at the HPRT (A) and TK (B) loci in TK6 cells. Cultures (n = 5 per group) were exposed to 0, 33, 100, or 300 μM AZT or ddI, alone or in equimolar combinations for 3 days. A cell cloning assay was used to measure the HPRT or TK mutant frequency. Induced mutant frequencies were obtained by subtracting the mutant frequencies in control groups from those in exposed samples. Average mutant frequencies in control samples ranged from 5.3 ± 1.2 (average ± SD) to 9.0 ± 2.4 × 10⁻⁶ for HPRT, and 6.8 ± 0.5 to 15.1 ± 2.4 × 10⁻⁶ for TK. AZT, empty bar; ddI, gray bar; AZT + ddI, black bar.