The effects of a series of 102 bisphosphonates on the inhibition of growth of Entamoeba histolytica and Plasmodium falciparum in vitro have been determined, and selected compounds were further investigated for their in vivo activity. Forty-seven compounds tested were active (IC 50 < 200 µM) versus E. histolytica growth in vitro. The most active compounds (IC 50 ∼ 4-9 µM) were nitrogen-containing bisphosphonates with relatively large aromatic side chains. Simple n-alkyl-1-hydroxy-1,1-bisphosphonates, known inhibitors of the enzyme farnesylpyrophosphate (FPP) synthase, were also active, with optimal activity being found with C9-C10 side chains. However, numerous other nitrogen-containing bisphosphonates known to be potent FPP synthase inhibitors, such as risedronate or pamidronate, had little or no activity. Several pyridine-derived bisphosphonates were quite active (IC 50 ∼ 10-20 µM), and this activity was shown to correlate with the basicity of the aromatic group, with activity decreasing with increasing pK a values. The activities of all compounds were tested versus a human nasopharyngeal carcinoma (KB) cell line to enable an estimate of the therapeutic index (TI). Five bisphosphonates were selected and then screened for their ability to delay the development of amebic liver abscess formation in an E. histolytica infected hamster model. Two compounds were found to decrease liver abscess formation at 10 mg/kg ip with little or no effect on normal liver mass. With P. falciparum, 35 compounds had IC 50 values <200 µM in an in vitro assay. The most active compounds were also simple n-alkyl-1-hydroxy-1,1-bisphosphonates, having IC 50 values around 1 µM. Five compounds were again selected for in vivo investigation in a Plasmodium berghei ANKA BALB/c mouse suppressive test. The most active compound, a C9 n-alkyl side chain containing bisphosphonate, caused an 80% reduction in parasitemia with no overt toxicity. Taken together, these results show that bisphosphonates appear to be useful lead compounds for the development of novel antiamebic and antimalarial drugs.

Microneedle patches contain micron-scale needles coated with bioactive agents for minimally invasive drug delivery to the skin. In this study, we introduce layer-by-layer approaches to the fabrication of ultrathin DNA- and protein-containing polyelectrolyte films (or ‘polyelectrolyte multilayers’, PEMs) on the surfaces of stainless steel microneedles. DNA-containing PEMs were fabricated on microneedles by the alternating deposition of plasmid DNA and a hydrolytically degradable poly(β-amino ester). Protein-containing PEMs were fabricated using sodium poly(styrene sulfonate) (SPS) and bovine pancreatic ribonuclease A (RNase A) conjugated to a synthetic protein transduction domain. Layer-by-layer assembly resulted in ultrathin, uniform, and defect-free coatings on the surfaces of the microneedles, as characterized by fluorescence microscopy. These films eroded and thereby released DNA or protein when incubated in saline or when inserted into porcine cadaver skin, and deposited DNA or protein along the edges of microneedle tracks to depths of ~500 to 600μm. We conclude that PEM-coated microneedles offer a novel and useful approach to the transdermal delivery of DNA- and protein-based therapeutics and could also prove useful in other applications.