Coupling the cell-penetrating peptides transportan and transportan 10 to primaquine enhances its activity against liver-stage malaria parasites

Abstract

Novel primaquine-cell penetrating peptide conjugates were synthesised and tested in vitro against liver stage Plasmodium berghei parasites. Generally, the conjugates were more active than the parent peptides and, in some cases, than the parent drug. These are unprecedented findings that may open a new route towards antimalarial drug rescuing.

Scheme 1. Synthetic route towards PQ-C4-CPP conjugates: (i) 20% piperidine in N,N-dimethylformamide (DMF), r.t., 20 min; (ii) 5 molar equivalents (eq.), respective to resin reactive groups, of O-(benzotriazol-1-yl)-N,N,N′,N′-tetramethyluronium hexafluorophosphate (HBTU) and of Fmoc-protected amino acid (Fmoc-AA-OH), 10 eq. of N-ethyl-N,N-diisopropylamine (DIEA) in DMF, r.t., 60 min; (iii) trifluoroacetic acid (TFA)/water/triisopropylsilane cocktail in 95 : 2.5 : 2.5 volumetric proportion (1 mL/100 mg of resin), r.t., 120 min; (iv) 20 eq. of succinic anhydride and of DIEA in DMF, r.t., 60 min; (v) 5 eq. of PQ and of HBTU, 10 eq. DIEA in DMF, r.t., 60 min. Grey sphere stands for the polymer support used for peptide chain assembly, which was a Rink-amide resin in this case.

Scheme 2. Synthesis of TP10-S2-PQ: TP10-Cys, pre-assembled by SPPS, was reacted with PQ-Cys(Npys), previously prepared by coupling PQ to Boc-Cys(NPys)-OH.

Fig. 1. In vitro screening of the activity of the selected CPP and their respective PQ-C4-CPP conjugates against liver-stage P. berghei parasites, according to a previously reported method: infection burden (bars) and host cell confluency (dots) are expressed as % of control. The compounds were assayed at 1, 5 and 10 μM, and PQ was included as the reference parent drug, for comparison. The graph shows representative data from 3 independent experiments, each of which employing 3 replicates for each experimental condition.