Peptidomimetic and Organometallic Derivatives of Primaquine Active against Leishmania infantum

Abstract

The current treatment of visceral leishmaniasis is made difficult by the low efficacy, elevated costs, low bioavailability, and high toxicity of many of the available drugs. Primaquine, an antimalarial 8-aminoquinoline, displays activity against Leishmania spp., and several of its derivatives have been developed as potential antileishmanial drugs. However, primaquine exhibits low oral bioavailability due to oxidative deamination of its aliphatic chain. We previously developed peptidomimetic and organometallic derivatives of primaquine, with higher resistance to proteolytic degradation and oxidative deamination, which presented significant activity against primaquine-sensitive pathogens such as Plasmodium or Pneumocystis. In light of these relevant findings, we decided to evaluate these compounds against both the promastigote and intramacrophagic amastigote forms of Leishmania infantum, the agent of Mediterranean visceral leishmaniasis. We found that several of these compounds had significant activity against L. infantum. One of the peptidomimetic (3c) and one of the organometallic (7a) derivatives of primaquine were active against the clinically relevant intramacrophagic amastigote form of the parasite, causing >96% reductions in the number of amastigotes per 100 macrophages at 60 and 40 M, respectively, while being less cytotoxic for host cells than the reference drugs sitamaquine and miltefosine. Hence, compounds 3c and 7a represent new entries toward the development of new antileishmanial leads.

Primaquine derivatives: Modifications of the terminal amino group

“…The replacement of primaquine aliphatic chain by hexylferrocene led to a~45-foldhigher activity against liver stage parasitaemia in comparison to primaquine. Several primacenes displayed significant activity against Leishmania infantum with one of them being active against the clinically relevant intramacrophagic amastigote form of the parasite [129].…”

N -Cinnamoylated Aminoquinolines as Promising Antileishmanial Agents

“…To respond to those needs, we have tested the activity of cinnamic acid conjugates of the 8-aminoquinoline primaquine (PQ) and the 4-aminoquinoline chloroquine (CQ) against L. infantum. The rationale for these tests was that (i) these conjugates have been recently reported as interesting antimalarial leads (8)(9)(10) and (ii) PQ (compound 1) and CQ (compound 3) have proven activity against several protozoans, including visceralizing Leishmania (11)(12)(13)(14)(15).…”

“…We also evaluated the cytotoxicity of the most interesting compounds, by the resazurin methodology (13). Macrophages (8 ϫ 10 4 /well) were treated with CQ and compounds 5a and 5c to 5g for 72 h at 37°C, in a concentration range of 0.63 to 100 M. The concentrations that caused a 50% loss of host cell viability (CC 50 [in M]) (Table 2) were determined with GraphPad software from plots of percentages of viability in relation to the control concentration relative to the inhibitor concentration.…”

“…For that purpose, differentiated macrophages (4 ϫ 10 5 /well), derived from the bone marrow of BALB/c mice, were infected with stationary promastigotes of L. infantum (4 ϫ 10 6 /well), as previously described (13). Compounds were added after 24 h of infection at concentrations between 2.5 and 40 M. Cells were fixed and stained with Hemacolor (Merck, Germany) 72 h later.…”

“…Their antileishmanial activity was initially evaluated on the promastigote stage of L. infantum (MHOM/MA/67/ ITMAP-263, zymodeme MON-1; laboratory reference strain [16]). Briefly, promastigotes (1 ϫ 10 6 /well) were cultured at 25°C in complete RPMI medium (Gibco, Life Technologies) (13) supplemented with the different compounds at concentrations between 0.63 and 80 M. The antileishmanial activity was assessed at 72 h of culture by the resazurin methodology, as previously reported (13). All the 50% inhibitory concentration (IC 50 ) (M) values reported herein were determined with GraphPad Prism 5.0 software (GraphPad Software Inc.) from plots of percentages of parasite growth in relation to control versus inhibitor concentrations.…”