PfPK7 is an "orphan" kinase displaying regions of homology to multiple protein kinase families. PfPK7 functions in regulating parasite proliferation/development as evident from the phenotype analysis of knockout parasites. Despite this regulatory role, the functions of PfPK7 in signaling pathways are not known. To better understand PfPK7-regulated phosphorylation events, we performed isobaric tag-based quantitative comparative phosphoproteomics of the schizont and segmenter stages from wild-type and pfpk7 parasite lines. This analysis identified 3,875 phosphorylation sites on 1,047 proteins. Among these phosphorylation events, 146 proteins with 239 phosphorylation sites displayed reduction in phosphorylation in the absence of PfPK7. Further analysis of the phosphopeptides revealed three motifs whose phosphorylation was down regulated in the pfpk7 cell line in both schizonts and segmenters. Decreased phosphorylation following loss of PfPK7 indicates that these proteins may function as direct substrates of PfPK7. We demonstrated that PfPK7 is active toward three of these potential novel substrates; however, PfPK7 did not phosphorylate many of the other proteins, suggesting that decreased phosphorylation in these proteins is an indirect effect. Our phosphoproteomics analysis is the first study to identify direct substrates of PfPK7 and reveals potential downstream or compensatory signaling pathways.

Drugs against malaria are losing their effectiveness because of emerging drug resistance. This underscores the need for novel therapeutic options for malaria with mechanism of actions distinct from current antimalarials. To identify novel pharmacophores against malaria we have screened compounds containing structural features of natural products that are pharmacologically relevant. This screening has identified a 4-nitro styrylquinoline (SQ) compound with submicromolar antiplasmodial activity and excellent selectivity. SQ exhibits a cellular action distinct from current antimalarials, acting early on malaria parasite's intraerythrocytic life cycle including merozoite invasion. The compound is a fast-acting parasitocidal agent and also exhibits curative property in the rodent malaria model when administered orally. In this report, we describe the synthesis, preliminary structure-function analysis, and the parasite developmental stage specific action of the SQ scaffold.

A library of enriched marine natural product fractions was screened for their antiplasmodial activity using a SYBR green I fluorescence-based assay. Fractions derived from a sponge of the genus Spongosorites exhibited potent inhibition of Plasmodium falciparum growth. This genus of sponge has been reported to contain the nortopsentin and topsentin class of bis-indole imidazole alkaloids. This is the first report of nortopsentin A inhibiting parasite growth at the trophozoite stage at submicromolar 50% inhibitory concentrations (IC 50 ). Over 300 million clinical cases of malaria occur annually, resulting in more than 1 million deaths (1). Unfortunately, because of the prevalence of drug-resistant malaria parasite strains, existing drugs are increasingly losing their efficacy. Therefore, there is an urgent need to identify new drug leads to reduce the global malaria burden. Marine biological diversity provides an excellent opportunity to identify novel drug leads from secondary metabolites of marine organisms. Although research aiming to discover novel marine-derived antiplasmodial agents is relatively recent, over 60 active compounds have been reported to date (2). One of the more important leads is manzamine A, a structurally complex ␤-carboline alkaloid isolated from a Haliclona sp. Manzamine A cleared 90% of the parasite burden in P. berghei-infected mice with a single intraperitoneal dose (3, 4). Unfortunately, toxicity issues have limited the clinical development of the compound.A library of enriched chemical fractions derived from marine organisms collected at depths greater than 50 m was prepared at Harbor Branch Oceanographic Institute using medium-pressure liquid chromatography on an ISCO Combiflash purification system. These materials were screened for their ability to inhibit the chloroquine-sensitive P. falciparum strain 3D7 and the chloroquine-resistant strain Dd2. The enriched fractions were solubilized in ethanol and, when necessary, further diluted in culture medium for assay. The inhibitory properties of the library were evaluated at 5 g/ml using a SYBR green I assay (5, 6) with the chloroquine-sensitive P. falciparum strain 3D7 (1% parasitemia)

A deep-water sponge of the genus Spongosorites has yielded a bis-indole alkaloid which we have named dragmacidin G. Dragmacidin G was first reported by us in the patent literature and has recently been reported by Hitora et al. from a sponge of the genus Lipastrotheya. Dragmacidin G is the first in this series of compounds to have a pyrazine ring linking the two indole rings. It also has a rare N-(2-mercaptoethyl)-guanidine side chain. Dragmacidin G shows a broad spectrum of biological activity including inhibition of methicillin-resistant Staphylococcus aureus, Mycobacterium tuberculosis, Plasmodium falciparum, and a panel of pancreatic cancer cell lines.

We screened a collection of synthetic compounds consisting of natural-product-like substructural motifs to identify a spirocyclic chromane as a novel antiplasmodial pharmacophore using an unbiased cell-based assay. The most active spirocyclic compound UCF 201 exhibits a 50% effective concentration (EC50) of 350 nM against the chloroquine-resistant Dd2 strain and a selectivity over 50 using human liver HepG2 cells. Our analyses of physicochemical properties of UCF 201 showed that it is in compliance with Lipinski's parameters and has an acceptable physicochemical profile. We have performed a limited structure-activity-relationship study with commercially available chromanes preserving the spirocyclic motif. Our evaluation of stage specificities of UCF 201 indicated that the compound is early-acting in blocking parasite development at ring, trophozoite and schizont stages of development as well as merozoite invasion. SPC is an attractive lead candidate scaffold because of its ability to act on all stages of parasite's aexual life cycle unlike current antimalarials.