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Fig. 7 | BMC Biology

Fig. 7

From: Macrolides rapidly inhibit red blood cell invasion by the human malaria parasite, Plasmodium falciparum

Fig. 7

Macrolide modification lowers invasion inhibitory IC50, but not apicoplast-targeting ‘delayed death’ inhibition. (a) Addition of an L-megosamine sugar [41] to form Meg-erythromycin (6-O-megosaminyl erythromycin A, IC50 13 μM) or an oxime group (150 μM) lowered the invasion inhibitory IC50 activity compared to the parent drug erythromycin A (IC50 420 μM). (b) Screening of an azithromycin analogue panel identified three compounds (12e, 15 μM; 1j, 7 μM; 11c, 28 μM) with up to 5-fold lower invasion inhibitory IC50 compared to the parent azithromycin (in DMSO, 38 μM). (c) Treatment of parasites during in cycle (40 hours, rings to schizonts), 1 cycle (90 hours, 1 cycle of replication) and 2 cycle (120 hours, 2 cycles of replication) assays with azithromycin (in DMSO) and analogues (12e, 1j), indicated that the IC50 of 1 cycle (40 hour and 90 hour, high drug concentration) inhibition was greatly reduced for the analogues compared to azithromycin. In contrast, the IC50 of the delayed death phenotype was almost identical for azithromycin and its analogues. d) Video microscopy of merozoite invasion was performed in the presence of a no drug control (0 μM), 122 μM of analogue 12e (2 × IC80) and azithromycin (AZR; both in DMSO). Merozoites that contacted the erythrocyte and i) invaded (cont–invade), ii) deformed but did not invade (cont–deform), or iii) released without deforming or invading (cont–detach) were tallied and analyzed as per Fig. 4. (e) Removal of the cladinosyl sugar (azithromycin descladinosyl, 50 μM) from azithromycin increased the invasion inhibitory IC50 compared to azithromycin (10 μM). The additional removal of the desosaminyl sugar (azithromycin desglycan, IC50 >1,600 μM) resulted in loss of invasion inhibitory activity compared to azithromycin. Data represent the mean and SEM of three or more experiments (**P ≤0.01, ***P ≤0.001)

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