In vitro and in vivo characterization of the antimalarial lead compound SSJ-183 in Plasmodium models

Figures & data

Figure 1 Molecular structure of SSJ-183.

Figure 2 Stage-dependent effects of SSJ-183 on [³H]hypoxanthine incorporation in synchronous cultures of Plasmodium falciparum strain NF54.

Notes: Cultures were exposed to seven different concentrations of the compound for 6 or 24 hours. After removal of SSJ-183, parasites were incubated for another 24 hours in the presence of [³H]hypoxanthine. Compound effects are expressed as the percentage of growth of the respective development stage relative to an untreated control. The open bar is the ring stage, the filled bar is the trophozoite stage and the hatched bar is the schizont stage. Each bar represents the mean ± SD of n=3–4 independent experiments. Significant (*P<0.05) differences between ring- and schizont-stages or trophozoites- and schizont-stages were determined by a one-way ANOVA with Tukey’s Honestly Significant Difference (HSD) test.
Abbreviations: SD, standard deviation; n, number; h, hours.

Table 1 In vitro interaction of drug combinations against two Plasmodium falciparum strains

Drug combination	ΣFICa						Mean ΣFIC		Interaction
	K1			NF54			K1	NF54
	1:3	1:1	3:1	1:3	1:1	3:1
Atovaquone + proguanil	0.28 ± 0.02	0.22 ± 0.02	0.20 ± 0.02	0.37 ± 0.08	0.29 ± 0.06	0.26 ± 0.31	0.23 ± 0.02	0.31 ± 0.07	Synergism
SSJ-183 + artemisinin	0.67 ± 0.06	0.73 ± 0.15	0.97 ± 0.31	0.60 ± 0.10	0.67 ± 0.15	0.80 ± 0.17	0.79 ± 0.16	0.69 ± 0.10	Synergism
SSJ-183 + mefloquine	1.2 ± 0.5	1.2 ± 0.4	1.2 ± 0.6	1.1 ± 0.1	1.1 ± 0.1	1.0 ± 0.2	1.2 ± 0.0	1.1 ± 0.0	Additive action
SSJ-183 + piperaquine	1.5 ± 0.3	1.5 ± 0.2	1.3 ± 0.2	1.3 ± 0.2	1.3 ± 0.1	1.2 ± 0.1	1.4 ± 0.1	1.3 ± 0.1	Additive action
SSJ-183 + amodiaquine	1.7 ± 0.2	1.5 ± 0.2	1.4 ± 0.3	1.6 ± 0.3	1.7 ± 0.3	1.0 ± 0.3	1.5 ± 0.2	1.4 ± 0.4	Antagonism
SSJ-183 + pyronaridine	1.6 ± 0.6	1.8 ± 0.5	1.5 ± 0.3	1.7 ± 0.2	1.8 ± 0.6	1.4 ± 0.4	1.7 ± 0.1	1.7 ± 0.2	Antagonism

Notes:

a Values are the means and standard deviations from three or more experiments.

Abbreviations: ΣFIC, sum of fractional inhibitory concentration; ND, not determined.

Table 2 In vitro cross-resistance experiments with various sensitive and resistant Plasmodium falciparum strains (IC₅₀ values are the mean of 2 to 3 independent experiments)

Isolate	Origin	Resistance	IC50 (ng/mL) SSJ-183*	IC50 (ng/mL) chloroquinea	IC50 (ng/mL) pyrimethaminea	IC50 (ng/mL) artesunate
NF54	Airport, NL	–	21	5.7	4.5	3.5
K1	Thailand	CQ, PYR	23	157	2,521	2.6
W2	Indochina	CQ, PYR	24	169	3,463	2.9
7G8	Brazil	PYR	17	71	2,607	2.1
TM90C2A	Thailand	CQ, PYR, MQ	50	90	4,787	4.1
D6	Sierra Leone	–	39	8.3	1.3	5.0
V1/S	Vietnam	CQ, PYR	21	237	5,456	3.1
Maximum IC50			50	237	5,456	5.0
Minimum IC50			17	5.7	1.3	2.1
Maximum/minimum			2.9-fold	42-fold	4200-fold	2.4-fold

Notes:

* In this experiment, SSJ-183 stock solution (10 mg/mL) was directly diluted in the hypoxanthine-free medium, resulting, for example, in an IC₅₀ against nF54 parasites that is ~7× higher compared with the value obtained when the SSJ-183 stock solution was first diluted 1/50 in DDDT (3.2 ng/mL).

a Adapted with permission from Brunner R, Aissaoui H, Boss C, et al. Identification of a new chemical class of antimalarials. J Infect Dis. 2012;206(5):735–743.¹⁷

Abbreviations: IC₅₀, Half-maximal inhibitory concentration; DDDT, dimethyl sulfoxide; NL, The Netherlands.

Figure 3 In vivo efficacy in Plasmodium berghei-infected mice: onset of action and recrudescence for control (•), artesunate (○) and SSJ-183 (□) following a single oral dose of 100 mg/kg on day 3 postinfection (n=5 mice for each).

Abbreviation: n, number.

Table 3 Pharmacokinetic parameters for SSJ-183, N-deethyl SSJ-183 and bis-N,N-deethyl SSJ-183 after oral administration (20 mg/kg) of SSJ-183 to noninfected and Plasmodium berghei-infected NMRI mice

Parameter	SSJ-183	N-deethyl SSJ-183	Bis-N,N-deethyl SSJ-183
Noninfected mice
T1/2 (h)	10.3	9.0	15.2
cmax (ng/mL)	1,297.8	139.6	21.1
Tmax (h)	1	4	4
AUC0-inf (h · ng/mL)	13,893	2,569	556
P. berghei-infected mice
T1/2 (h)	10.1	8.8	14.3
Cmax (ng/mL)	1,108.1	147.1	31.1
Tmax (h)	1	4	8
AUC0-inf (h · ng/mL)	13,847	2,715	715

Abbreviations: T_1/2, half-time; C_max’ maximum concentration; T_max’ maximum time; AUC_0-inf’ area under the curve from time 0 to infinity; h, hours; P. berghei, Plasmodium berghei.

Figure 4 Plasma concentration versus time profiles for (A) SSJ-183, (B) N-deethyl SSJ-183, and (C) bis-N,N-deethyl SSJ-183 following oral administration of SSJ-183 (20 mg/kg) to noninfected (filled circles) and Plasmodium berghei-infected (open triangles) NMRI mice.

Brunner R Aissaoui H Boss C Identification of a new chemical class of antimalarials J Infect Dis 2012 206 5 735 743 22732921

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