Potent, Gut-Restricted Inhibitors of Divalent Metal Transporter 1: Preclinical Efficacy against Iron Overload and Safety Evaluation

Divalent metal transporter 1 (DMT1) cotransports ferrous iron and protons and is the primary mechanism for uptake of nonheme iron by enterocytes. Inhibitors are potentially useful as therapeutic agents to treat iron overload disorders such as hereditary hemochromatosis or β-thalassemia intermedia, provided that inhibition can be restricted to the duodenum. We used a calcein quench assay to identify human DMT1 inhibitors. Dimeric compounds were made to generate more potent compounds with low systemic exposure. Direct block of DMT1 was confirmed by voltage clamp measurements. The lead compound, XEN602, strongly inhibits dietary nonheme iron uptake in both rats and pigs yet has negligible systemic exposure. Efficacy is maintained for >2 weeks in a rat subchronic dosing assay. Doses that lowered iron content in the spleen and liver by >50% had no effect on the tissue content of other divalent cations except for cobalt. XEN602 represents a powerful pharmacological tool for understanding the physiologic function of DMT1 in the gut. SIGNIFICANCE STATEMENT: This report introduces methodology to develop potent, gut-restricted inhibitors of divalent metal transporter 1 (DMT1) and identifies XEN602 as a suitable compound for in vivo studies. We also report novel animal models to quantify the inhibition of dietary uptake of iron in both rodents and pigs. This research shows that inhibition of DMT1 is a promising means to treat iron overload disorders.

Characterization of peroxisome-deficient mutants of Hansenula polymorpha

In the methylotrophic yeast Hansenula polymorpha, approximately 25% of all methanol-utilization-defective (Mut-) mutants are affected in genes required for peroxisome biogenesis (PER genes). Previously, we reported that one group of per mutants, termed Pim-, are characterized by the presence of a few small peroxisomes with the bulk of peroxisomal enzymes located in the cytosol. Here, we describe a second major group of per mutants that were observed to be devoid of any peroxisome-like structure (Per-). In each Per- mutant, the peroxisomal methanol-pathway enzymes alcohol oxidase, catalase and dihydroxyacetone synthase were present and active but located in the cytosol. Together, the Pim- and Per- mutant collections involved mutations in 14 different PER genes. Two of the genes, PER5 and PER7, were represented by both dominant-negative and recessive alleles. Diploids resulting from crosses of dominant per strains and wild-type H. polymorpha were Mut- and harbored peroxisomes with abnormal morphology. This is the first report of dominant-negative mutations affecting peroxisome biogenesis.

Discrimination among thermophilic Campylobacter species by polymerase chain reaction amplification of 23S rRNA gene fragments

By comparing nucleic acid sequences determined for one of the most variable areas of 23S rRNA genes of 23 Campylobacter strains, we were able to identify regions specific for thermophilic Campylobacter strains. Oligonucleotide primers corresponding to these unique regions were synthesized and used in the polymerase chain reaction. One primer pair selectively detected all thermophilic Campylobacter species, while four other primer pairs allowed discrimination among the thermophilic species Campylobacter coli, Campylobacter jejuni subsp. jejuni, Campylobacter lari, and Campylobacter upsaliensis. All primer sets were tested successfully on a large number of clinical isolates.

Construction and characterisation of a yeast artificial chromosome library containing two haploid Beta vulgaris L. genome equivalents

We have constructed a yeast artificial chromosome (YAC) library using high-molecular-weight DNA prepared from agarose-embedded protoplasts of a sugar beet (Beta vulgaris L.) cell suspension line, Ar+. This library contains 15,000 clones with an average insert size of 140 kb. Based on a sugar beet haploid genome size of 1.1 x 10(3) Mb it should represent approximately two haploid genome equivalents. The library is organised as an ordered array in duplicate microtitre plates. High-density filters, each containing 864 YAC clones, have been screened in colony hybridisation experiments. In this way, sugar beet YAC clones have been identified containing chloroplast DNA, mitochondrial DNA and two satellite DNAs. Ten pools of DNA from 1500 individual YAC clones have also been prepared for rapid PCR screening of the library. Using this approach, in combination with colony hybridisation, we have been able to isolate sugar beet YAC clones containing a transcribed low-copy-number gene.

Identification and mapping of loci involved in motility, adsorption to wheat roots, colony morphology, and growth in minimal medium on the Azospirillum brasilense Sp7 90-MDa plasmid

We have constructed a cosmid library of the Azospirillum brasilense Sp7 90-MDa plasmid (p90) and established the EcoRI restriction map of this plasmid. The central regions of cloned p90 DNA fragments from several recombinant cosmids were deleted by restriction endonuclease digestion and replaced by a DNA cassette encoding kanamycin resistance. Using these in vitro constructed deletions for marker exchange in Sp7, we made six different p90 deletion derivatives spanning all together 50% of the total length of p90. Comparison of the deletion derivatives with Sp7 for several properties revealed p90 loci involved in colony morphology, growth on minimal medium, motility, and adsorption to wheat roots. In analogy with the rhizobial symbiotic plasmids (pSym), we propose to denote the p90 plasmid as a rhizocoenotic plasmid (pRhico), carrying several genes involved in the A. brasilense-plant root interaction.