The interaction between prothidium dibromide and DNA at the molecular level

Trypanosoma Congolense Resistant to Trypanocidal Drugs Homidium and Diminazene and their Molecular Characterization in Lambwe, Kenya

PURPOSE

African animal trypanosomiasis (AAT) is a disease affecting livestock in sub-Saharan Africa. The use of trypanocidal agents is common practice to control AAT. This study aimed to identify drug-resistant Trypanosoma congolense in Lambwe, Kenya, and assess if molecular test backed with mice tests is reliable in detecting drug sensitivity.

METHODS

Blood samples were collected from cattle, in Lambwe, subjected to buffy coat extraction and Trypanosoma spp. detected under a microscope. Field and archived isolates were subjected to molecular characterization. Species-specific T. congolense and TcoAde2 genes were amplified using PCR to detect polymorphisms. Phylogenetic analysis were performed. Four T. congolense isolates were evaluated individually in 24 test mice per isolate. Test mice were then grouped (n=6) per treatement with diminazene, homidium, isometamidium, and controls. Mice were subsequently assessed for packed cell volume (PCV) and relapses using microscopy.

RESULTS

Of 454 samples, microscopy detected 11 T. congolense spp, eight had TcoAde2 gene, six showed polymorphisms in molecular assay. Phylogenetic analysis grouped isolates into five. Two archived isolates were homidium resistant, one was also diminazene resistant in mice. Two additional isolates were sensitive to all the drugs. Interestingly, one sensitive isolate lacked polymorphisms, while the second lacked TcoAde2, indicating the gene is not involved in drug sensitivity. Decline in PCV was pronounced in relapsed isolates.

CONCLUSION

T. congolense associated with homidium and diminazene resistance exist in Lambwe. The impact can be their spread and AAT increase. Polymorphisms are present in Lambwe strains. TcoAde2 is unlikely involved in drug sensitivity. Molecular combined with mice tests is reliable drug sensitivity test and can be applied to other genes. Decline in PCV in infected-treated host could suggest drug resistance.

An Update on African Trypanocide Pharmaceutics and Resistance

African trypanosomiasis is associated with Trypanosoma evansi, T. vivax, T. congolense, and T. brucei pathogens in African animal trypanosomiasis (AAT) while T. b gambiense and T. b rhodesiense are responsible for chronic and acute human African trypanosomiasis (HAT), respectively. Suramin sodium suppresses ATP generation during the glycolytic pathway and is ineffective against T. vivax and T. congolense infections. Resistance to suramin is associated with pathogen altered transport proteins. Melarsoprol binds irreversibly with pyruvate kinase protein sulfhydryl groups and neutralizes enzymes which interrupts the trypanosome ATP generation. Melarsoprol resistance is associated with the adenine-adenosine transporter, P2, due to point mutations within this transporter. Eflornithine is used in combination with nifurtimox. Resistance to eflornithine is caused by the deletion or mutation of TbAAT6 gene which encodes the transmembrane amino acid transporter that delivers eflornithine into the cell, thus loss of transporter protein results in eflornithine resistance. Nifurtimox alone is regarded as a poor trypanocide, however, it is effective in melarsoprol-resistant gHAT patients. Resistance is associated with loss of a single copy of the genes encoding for nitroreductase enzymes. Fexinidazole is recommended for first-stage and non-severe second-stage illnesses in gHAT and resistance is associated with trypanosome bacterial nitroreductases which reduce fexinidazole. In AAT, quinapyramine sulfate interferes with DNA synthesis and suppression of cytoplasmic ribosomal activity in the mitochondria. Quinapyramine sulfate resistance is due to variations in the potential of the parasite's mitochondrial membrane. Pentamidines create cross-links between two adenines at 4–5 pairs apart in adenine-thymine-rich portions of Trypanosoma DNA. It also suppresses type II topoisomerase in the mitochondria of Trypanosoma parasites. Pentamidine resistance is due to loss of mitochondria transport proteins P2 and HAPT1. Diamidines are most effective against Trypanosome brucei group and act via the P2/TbAT1 transporters. Diminazene aceturate resistance is due to mutations that alter the activity of P2, TeDR40 (T. b. evansi). Isometamidium chloride is primarily employed in the early stages of trypanosomiasis and resistance is associated with diminazene resistance. Phenanthridine (homidium bromide, also known as ethidium bromide) acts by a breakdown of the kinetoplast network and homidium resistance is comparable to isometamidium. In humans, the development of resistance and adverse side effects against monotherapies has led to the adoption of nifurtimox-eflornithine combination therapy. Current efforts to develop new prodrug combinations of nifurtimox and eflornithine and nitroimidazole fexinidazole as well as benzoxaborole SCYX-7158 (AN5568) for HAT are in progress while little comparable progress has been done for the development of novel therapies to address trypanocide resistance in AAT.

The animal trypanosomiases and their chemotherapy: a review

Pathogenic animal trypanosomes affecting livestock have represented a major constraint to agricultural development in Africa for centuries, and their negative economic impact is increasing in South America and Asia. Chemotherapy and chemoprophylaxis represent the main means of control. However, research into new trypanocides has remained inadequate for decades, leading to a situation where the few compounds available are losing efficacy due to the emergence of drug-resistant parasites. In this review, we provide a comprehensive overview of the current options available for the treatment and prophylaxis of the animal trypanosomiases, with a special focus on the problem of resistance. The key issues surrounding the main economically important animal trypanosome species and the diseases they cause are also presented. As new investment becomes available to develop improved tools to control the animal trypanosomiases, we stress that efforts should be directed towards a better understanding of the biology of the relevant parasite species and strains, to identify new drug targets and interrogate resistance mechanisms.

Binding of 2-azaanthraquinone derivatives to DNA and their interference with the activity of DNA topoisomerases in vitro

We have investigated the binding ability to DNA of compounds belonging to the 2-azaanthraquinone-type structure and have examined the effect on the activity of DNA gyrase as well as on mammalian topoisomerases in vitro. Using different biophysical techniques it was found that one of these ligands, 9-((2-dimethylamino)ethyl)amino)-6-hydroxy-7-methoxy-5, 10-dihydroxybenzo[g]isoquinoline-5,10-dione (TPL-I), is an intercalating DNA binding agent, whereas the parent compound tolypocladin (TPL) and a derivative (TPL-II) showed almost no similar affinity to DNA. CD measurements demonstrated a significant and selective binding tendency of TPL-I to alternating purine/pyrimidine sequences with some preference for poly(dA-dT). poly(dA-dT). Tm values were increased of the ligand complex with the alternating AT-containing duplex polymer. The binding to various DNAs was characterized by CD and visible absorption spectral changes. From the latter, different binding constants of 6.2 x 10(5) and 1.5 x 10(5) M-1 were obtained for poly(dA-dT).poly(dA-dT) and poly(dA). poly(dT), respectively. Sedimentation measurements with supercoiled pBR322 plasmid DNA clearly indicated an intercalative binding mechanism associated with an unwinding angle of about 18 degrees. These results suggest that the intercalative binding of TPL-I is promoted by the 2-(dimethylamino)ethylamino group substituted on carbon 9 of the anthraquinone system. The cytotoxic compound TPL-I, but not TPL or TPL-II, effectively inhibited the DNA supercoiling reaction of DNA gyrase and the activity of mammalian topoisomerases I and II as measured by the relaxation assay. TPL-I affects the cleavage reaction of topoisomerases on a single site located in alternating purine-pyrimidine sequence regions. The inhibitory potency of TPL-I can be ascribed to a blocking of cleavage sites on the DNA substrate, which correlates with the sequence preference of the ligand.

The unwinding of circular DNA by intercalating agents as determined by gel electrophoresis

The conventional counting of electrophoretically resolvable topoisomers is an attractive technique for determining the number of superhelical turns in a closed circular DNA molecule. The method can be extended in order to determine the unwinding produced by a drug, if its binding constants are known under similar environmental conditions. Ethidium bromide was found to unwind a DNA molecule derived from the plasmid pBR322 by 26.0 degrees in a magnesium-containing buffer. The method is convenient for investigating the possible effects of different environmental changes (such as ionic strength, ionic species, or temperature) on the unwinding angle produced by a particular drug. It can also give an early indication of multiple modes of binding.

A Gaussian disorientation model for interpreting linear dichroism measurements of DNA-drug fibres and films

The optical linear dichroism of DNA-drug fibres and films can provide valuable information on the geometry of the binding and its extent, especially when used in conjunction with X-ray diffraction data from the same specimens. We have considered the macroscopic orientation of the helices within a fibre or film to be characterized by a Gaussian distribution of the helix axes about the fibre (or film) axis. Using this model we have obtained analytical expressions for the dichroic ratio without resorting to computer simulation techniques or numerical integration methods, and used them to interpret the results of experiments using DNA-phenanthridine fibres. As the humidity is increased, ethidium and dimidium bromide show an increased fraction of binding perpendicular to the helix axis, consistent with intercalation. Prothidium shows little preferred orientation in its binding, and the occurrence of a significant proportion of intercalation can be excluded.

A comparison of the base-pair specificities of three phenanthridine drugs using solution spectroscopy

1. The absorption spectrum of three phenanthridine drugs (ethidium, dimidium and prothidium bromide) bound to natural DNAs of differing G-C content were obtained using a novel mixing scheme and analysed according to the excluded site binding model. 2. Ethidium bromide shows a strong G-C specificity at low binding ratios. especially at low ionic concentration. 3. Dimidium bromide shows a less strong G-C specificity. 4. For both drugs, the binding site size reflects a situation close to nearest-neighbour exclusion. 5. Prothidium shows no specificity in its binding. The binding modes are different than for the other two phenanthridines, and it is suggested that the primary mode is "sideways" intercalation.