An alternative dogma on reduced artemisinin susceptibility: A new shadow from east to west

In PNAS, Demas et al. (1) show, by long-term in vitro selection using culture-adapted Plasmodium falciparum isolates from Senegal, that the gene encoding the actin-binding protein P. falciparum coronin (pfcoronin) and its genetic variants (G50E, R100K, and E107V) can reduce the susceptibility of the parasite to the active metabolite of the fast-acting antimalarial drug artemisinin, dihydroartemisinin (DHA). Resistance to artemisinins is a global threat in malaria control and elimination efforts (2).

Artemisinin resistance, first reported in Southeast Asia and still extremely rare, was associated with the P. falciparum PfKelch13-propeller domain (kelch13 mutations: Y493H, R539T, I543T, and C580Y) (3). PfCoronin, which is structurally similar to Kelch13, is believed to interact with F-actin via its N-terminal propeller domain and to mediate actin organization and motility in merozoites and sporozoites (4, 5). The worldwide map of the occurrence of kelch13, however, indicates absence of the Asian artemisinin-resistance alleles in Africa (6–8). So far, it is not clear whether the pfcoronin variants G50E, R100K, and E107V occur in natural P. falciparum populations—in particular, in clinical isolates from Africa.

We looked at a total of 353 P. falciparum patient isolates that were earlier characterized for the absence of kelch13 gene mutations (7–10) from 4 African countries to verify whether these isolates carry the pfcoronin mutations G50E, R100K, and E107V, which were described by Demas et al. (1) to be associated with reduced susceptibility to DHA. A total of 297 samples were successfully genotyped by direct Sanger sequencing. Details of the study groups from Gabon (n = 102), Congo (n = 48), Ghana (n = 57), and Kenya (n = 90) are described elsewhere (7–10). The pfcoronin mutations G50E, R100K, and E107V were not observed at all among the isolates. However, 14 distinct mutations, including several nonsynonymous substitutions, were identified in the pfcoronin exon-3 (Table 1). None of the isolates carried the Asian kelch13 resistance alleles M476I, Y493H, R539T, I543T, and C580Y. The mutation P76S (DNA position C562T) was observed to be most frequent (>10%) among isolates from central and west Africa. There was no indication of artemisinin or artemisinin-based combination therapy resistance in these patients. The functional role of the observed pfcoronin P76S needs to be elucidated among central and west African P. falciparum isolates.

Table 1.

pfcoronin mutations observed in 4 African countries

Amino acid change	SNP position	Gabon, n (%) (n = 102)	Ghana, n (%) (n = 57)	Kenya, n (%) (n = 90)	Congo, n (%) (n = 48)	Total, n (%) (N = 297)
I53I	C495T	0	1 (2)	0	0	1 (0.3)
V62M	G520A	1 (1)	1 (2)	0	0	2 (0.7)
K69K/I/R	A542A/T/G	0	3 (5)	0	11 (23)	14 (5)
P76S	C562T	11 (11)	9 (16)	4 (4)	8 (17)	32 (11)
N110N/Y/D	A664A/T/G	0	1 (2)	0	5 (10)	6 (2)
N112N/Y/D	A670A/T/G	0	0	0	1 (2)	1 (0.3)
K115K/stop/E	A679A/T/G	0	0	0	1 (2)	1 (0.3)
L121L/F/L	A699A/T/G	0	0	0	1 (2)	1 (0.3)
K127K/stop/E	A715A/T/G	0	0	0	1 (2)	1 (0.3)
K127K/I/R	A716A/T/G	0	0	0	5 (10)	5 (2)
V128V	A720A/T/G	0	0	0	1 (2)	1 (0.3)
N134N/Y/D	A736A/T/G	0	0	0	4 (8)	4 (1)
N137N/Y/D	A745A/T/G	0	0	0	10	10 (3)
N137N/I/S	A746A/T/G	0	0	0	2 (4)	2 (0.7)

SNP, single nucleotide polymorphism.

Much effort has been made in recent years to determine the genetic basis of artemisinin resistance, which still remains unclear to a large extent. There is an obvious difference in occurrence of pfkelch13 and pfcoronin alleles between Asia and Africa, which may also cause differences in parasite clearance rates during treatment with artemisinin-containing antimalarial combinations. However, we should bear in mind that parasite clearance rate or failure of an artemisinin-containing antimalarial is also, and even most often, determined by the activity of the partner drug, such as lumefantrine, amodiaquine, piperaquine, and pyronaridine.