Antibiotic inhibition of the Plasmodium apicoplast decreases haemoglobin degradation and antagonises dihydroartemisinin action

Abstract

The World Health Organisation (WHO) recommends artemisinin (ART) combinations for treatment of uncomplicated Plasmodium falciparum malaria. Understanding the interaction between co-administered drugs within combination therapies is clinically important to prevent unintended consequences. The WHO guidelines recommend second line treatments that combine artesunate with tetracycline, doxycycline, or clindamycin—antibiotics that target the Plasmodium relict plastid, the apicoplast. In addition, antibiotics can be used simultaneously against other infectious diseases, leading to their inadvertent combination with ARTs. One consequence of apicoplast inhibition is a perturbation to haemoglobin uptake and trafficking—a pathway required for activation of ART derivatives. Here, we show that apicoplast-targeting antibiotics reduce the abundance of the catalyst of ART activation (free haem) in P. falciparum, likely through diminished haemoglobin digestion. We demonstrate antagonism between ART and these antibiotics, suggesting that apicoplast inhibitors reduce ART activation. These data have potential clinical implications due to the reliance on—and widespread use of—both ARTs and these antibiotics in malaria endemic regions.

Antagonistic antimalarial properties of a methoxyamino chalcone derivative and 3-hydroxypyridinones in combination with dihydroartemisinin againstPlasmodium falciparum

“…Our finding that C3 antagonizes ART is in line with a recent report that other apicoplast−targeting antimalarials also antagonize ART [31]. These findings caution against the use of ART partner drugs that inhibit the Fd−FNR interaction and other apicoplast targets, which may reduce ART efficacy in malaria chemotherapy.…”

“…The interactions between DHA and the test compounds were assessed as the fractional inhibition concentration (□FIC) index, and the mean □FICs of the combinations were compared between fd wild-type (fd WT ) and fd -mutated (fd MT ) parasites using Welch’s T-test (Figure 3). An antagonistic effect was indicated when □FIC >1.1, an additive effect was indicated when 0.9 < □FIC < 1.1, and synergism was indicated when □FIC< 0.9, using the criteria established by previous studies of antimalarial interactions [31,32]. For the DHA and C3 combinations, the mean □FICs were moderately antagonistic.…”

“…The FICs of the combinations from at least three individual experiments were used to calculate the mean values of □FIC. Interactions were assigned as synergistic (□FIC <0.9), additive (0.9 < □FIC < 1.1), or antagonistic (□FIC >1.1), with 1.1 < □FIC < 1.2 representing slight antagonism, 1.2 < □FIC < 1.45 representing moderate antagonism, 1.45 < □FIC < 3.3 representing antagonism, 3.3 < □FIC < 10 representing strong antagonism, and □FIC >10 representing very strong antagonism [31,32].…”

“…An antagonistic effect was indicated when FIC >1.1, an additive effect was indicated when 0.9 < FIC < 1.1, and synergism was indicated when FIC< 0.9, using the criteria established by previous studies of antimalarial interactions [31,32]. For the DHA and C3 combinations, the mean FICs were moderately antagonistic.…”

Roles of the apicoplast across the life cycles of rodent and human malaria parasites

“…For instance, the key antimalarial artemisinin is potentiated by parasite haem digestion (Pandey et al, 1999 ), but Kennedy et al showed that haem digestion is perturbed by common apicoplast inhibitors (Kennedy et al, 2019 ), which begs the question of whether apicoplast inhibitors might be antagonistic to artemisinin, and indeed any derivatives of artemisinin requiring activation by haem digestion. Early indications are that doxycycline—a widely used, apicoplast targeting antimalarial (Dahl et al, 2006 ; Goodman et al, 2007 )—is indeed antagonistic to artemisinin because it impedes haem digestion and thereby blunts the impact of artemisinin (Crisafulli et al, 2021 ).…”