Numerous studies have suggested that iron (Fe) chelators such as desferrioxamine (DFO) may be useful antitumor agents (Blatt and Stitely, Cancer Res 47:1749, 1987; Becton and Bryles, Cancer Res 48:7189, 1988). Recent work with several analogues of the lipophilic Fe chelator, pyridoxal isonicotinoyl hydrazone (PIH), indicate that some of these ligands are considerably more efficient than DFO both in terms of their Fe chelation efficacy and at preventing 3H-thymidine incorporation by neuroblastoma (NB) cells (Richardson and Ponka, J Lab Clin Med 124:660, 1994). Considering this fact, the present study was designed to test the antiproliferative effect of a wide range of PIH analogues to identify the most active compounds. A total of 36 ligands have been examined that were synthesized by condensation of three types of aromatic aldehydes (pyridoxal, salicylaldehyde, and 2-hydroxy-1- naphthyladehyde) with a range of acid hydrazides. The effects of these chelators were assessed using the human NB cell line, SK-N-MC. Although PIH was far more effective than DFO at preventing Fe uptake from transferrin, it was less effective than DFO at preventing cellular proliferation (DFO ID50 = 22 mumol/L; PIH ID50 = 75 mumol/L). In contrast, 14 PIH analogues were far more efficient than DFO at preventing proliferation (ID50 = 1 to 7 mumol/L) and may have potential as antitumor agents. The most effective compounds were those hydrazones derived from 2-hydroxy-1-naphthylaldehyde. Most of the PIH analogues were considerably more effective than DFO at both preventing 59Fe uptake from 59Fe-transferrin and in mobilizing 59Fe from prelabeled NB cells. In addition, a linear relationship between Fe chelation efficacy and antiproliferative activity was found only for hydrazones derived from salicylaldehyde. Apart from gallium (Ga) nitrate having an antiproliferative effect by itself, this metal potentiated the antiproliferative effect of PIH but not that of DFO. Spectrophotometric studies showed that PIH could chelate Ga, and it can be suggested that, like the PIH-Fe complex that donates Fe to reticulocytes (Ponka et al, Biochim Biophys Acta 718:151, 1982), the PIH-Ga complex may efficiently bestow Ga to NB cells. The results suggest that analogues of PIH deserve further vigorous investigation because they may be useful therapeutic agents for the treatment of cancer.

The biosynthesis of coenzyme A (CoA) from pantothenate and the utilization of CoA in essential biochemical pathways represent promising antimalarial drug targets. Pantothenamides, amide derivatives of pantothenate, have potential as antimalarials, but a serum enzyme called pantetheinase degrades pantothenamides, rendering them inactive in vivo. In this study, we characterize a series of 19 compounds that mimic pantothenamides with a stable triazole group instead of the labile amide. Two of these pantothenamides are active against the intraerythrocytic stage parasite with 50% inhibitory concentrations (IC 50 s) of ϳ50 nM, and three others have submicromolar IC 50 s. We show that the compounds target CoA biosynthesis and/or utilization. We investigated one of the compounds for its ability to interact with the Plasmodium falciparum pantothenate kinase, the first enzyme involved in the conversion of pantothenate to CoA, and show that the compound inhibits the phosphorylation of [ 14 C]pantothenate by the P. falciparum pantothenate kinase, but the inhibition does not correlate with antiplasmodial activity. Furthermore, the compounds are not toxic to human cells and, importantly, are not degraded by pantetheinase. Due to drug resistance by Plasmodium falciparum, the parasite responsible for malaria, it is vital to identify new chemotherapeutics targeting novel parasite pathways. P. falciparum does not survive its asexual red blood cell (RBC) stage without access to exogenous pantothenate (vitamin B 5 ) (1-3). Pantothenate is metabolized by five enzymes into coenzyme A (CoA), a cofactor estimated to be required by 9% of all enzymes (4). The first enzyme in the CoA biosynthetic pathway is pantothenate kinase (PanK), which catalyzes the phosphorylation of pantothenate into phosphopantothenate. Several pantothenate analogues have been shown to inhibit the growth of P. falciparum in vitro, including pantothenol (5), 801 (6), and various other analogues (7,8). Pantothenol (Fig. 1) has also been shown to possess antiplasmodial activity in vivo in a mouse model of malaria (5). Recently, pantothenamides, amides of pantothenate initially investigated for antibacterial activity (9-11), have been shown to possess potent antiplasmodial activity (12). Unfortunately, the effectiveness of pantothenamides as antiplasmodials is attenuated by pantetheinase (12), an enzyme found in human serum (13). The endogenous substrate of pantetheinase is pantetheine, which is broken down by pantetheinase into pantothenate and cysteamine (14). Pantetheinase also breaks down pantothenamides (12), including the prototypical pantothenamide, N-pentylpantothenamide (N5-Pan [ Fig. 1]). The breakdown of pantothenamides is an obstacle that needs to be overcome if these compounds are to be of any use as antimicrobial agents.There are two obvious ways by which the breakdown of pantothenamides by pantetheinase can be prevented: (i) development of a pantetheinase inhibitor that can be coadministered with the pantothenamide, a strategy recently demonstrated to b...

Pantothenamides are N-substituted pantothenate derivatives which are known to exert antimicrobial activity through interference with coenzyme A (CoA) biosynthesis or downstream CoA-utilizing proteins. A previous report has shown that replacement of the ProR methyl group of the benchmark N-pentylpantothenamide with an allyl group (R-anti configuration) yielded one of the most potent antibacterial pantothenamides reported so far (MIC of 3.2 μM for both sensitive and resistant Staphylococcus aureus). We describe herein a synthetic route for accessing the corresponding R-syn diastereomer using a key diastereoselective reduction with Baker's yeast, and report on the scope of this reaction for modified systems. Interestingly, whilst the R-anti diastereomer is the only one to show antibacterial activity, the R-syn isomer proved to be significantly more potent against the malaria parasite (IC 50 of 2.4 ± 0.2 μM). Our research underlines the striking influence that stereochemistry has on the biological activity of pantothenamides, and may find utility in the study of various CoA-utilizing systems. Keywordspantothenamides; antibacterial; antiplasmodial; baker's yeast; coenzyme A Infectious diseases remain a major contributing factor to worldwide mortality. Moreover, the development of antimicrobial resistance is raising significant concerns about the increasingly limited efficacy of currently available treatments. 1 There have been considerable efforts towards discovering and characterising novel therapeutic targets for antimicrobial drugs. One such target which has emerged as a promising point-of-attack is