Correlation of antimalarial activity with plDNA cleavable complex formation. (A) Asynchronous parasites were treated with solvent (lane 3), 5.6 μM ciprofloxacin (lane 4), gatifloxacin (lane 5), levofloxacin (lane 6), fleroxacin (lane 7), or nalidixic acid (lane 8) for 30 min, and processed for plDNA analysis (107 parasitized erythrocytes/lane). (B) Parasites were treated with solvent or 12 μM drug as in (A); 2 × 107 parasitized erythrocytes/lane. (C) Antimalarial activity versus plDNA cleavable complex formation for ciprofloxacin (□), gatifloxacin (●), levofloxacin (▲), and fleroxacin (○). Depicted potencies are the negative log of the cognate EC50s (in molar). EC50 of antimalarial activity is from Table 1. EC50 of cleavable complex formation was obtained from seven experiments, including those in Panels A and B; EC50 and R2 values for plDNA linearization were: gatifloxacin (7.9 μM, 0.80), ciprofloxacin (71 μM, 0.98), levofloxacin (22 μM, 0.92), fleroxacin (260 μM, 0.97). Markers are EcoR I-digested plDNA linears (lanes 1) and UV-nicked plDNA (lanes 2). N, nicked circular plDNA; IV, form Four; L, linearized circles; CC, covalently closed circular plDNA. Arrow indicates well.