Rational design of ligands targeting triplet repeating transcripts that cause RNA dominant disease: application to myotonic muscular dystrophy type 1 and spinocerebellar ataxia type 3

Herein, we describe the design of high affinity ligands that bind expanded rCUG and rCAG repeat RNAs expressed in myotonic dystrophy type 1 (DM1) and spinocerebellar ataxia type 3. These ligands also inhibit, with nanomolar IC(50) values, the formation of RNA-protein complexes that are implicated in both disorders. The expanded rCUG and rCAG repeats form stable RNA hairpins with regularly repeating internal loops in the stem and have deleterious effects on cell function. The ligands that bind the repeats display a derivative of the bisbenzimidazole Hoechst 33258, which was identified by searching known RNA-ligand interactions for ligands that bind the internal loop displayed in these hairpins. A series of 13 modularly assembled ligands with defined valencies and distances between ligand modules was synthesized to target multiple motifs in these RNAs simultaneously. The most avid binder, a pentamer, binds the rCUG repeat hairpin with a K(d) of 13 nM. When compared to a series of related RNAs, the pentamer binds to rCUG repeats with 4.4- to >200-fold specificity. Furthermore, the affinity of binding to rCUG repeats shows incremental gains with increasing valency, while the background binding to genomic DNA is correspondingly reduced. Then, it was determined whether the modularly assembled ligands inhibit the recognition of RNA repeats by Muscleblind-like 1 (MBNL1) protein, the expanded-rCUG binding protein whose sequestration leads to splicing defects in DM1. Among several compounds with nanomolar IC(50) values, the most potent inhibitor is the pentamer, which also inhibits the formation of rCAG repeat-MBNL1 complexes. Comparison of the binding data for the designed synthetic ligands and MBNL1 to repeating RNAs shows that the synthetic ligand is 23-fold higher affinity and more specific to DM1 RNAs than MBNL1. Further studies show that the designed ligands are cell permeable to mouse myoblasts. Thus, cell permeable ligands that bind repetitive RNAs have been designed that exhibit higher affinity and specificity for binding RNA than natural proteins. These studies suggest a general approach to targeting RNA, including those that cause RNA dominant disease.

Activity of Hoechst 33258 against Pneumocystis carinii f. sp. muris, Candida albicans, and Candida dubliniensis

Hoechst 33258 is a compound that binds nucleic acids. We report that Hoechst 33258 exhibits antimicrobial activity against Pneumocystis carinii f. sp. muris in a mouse model for P. carinii pneumonia and against Candida albicans and Candida dubliniensis in vitro. Relative to saline treatment, a 14-day, daily treatment of mice with 37.5 mg of Hoechst 33258/kg of body weight after inoculation with P. carinii reduced by about 100-fold the number of P. carinii organisms detected by either PCR or by microscopy after silver staining. For comparison, treatment based on a dose of 15 to 20 mg of the trimethoprim component in trimethoprim-sulfamethoxazole/kg reduced the number of P. carinii by about fourfold. In vitro inhibition of P. carinii group I intron splicing was observed with a 50% inhibitory concentration (IC50) of 30 microM in 2 or 4 mM Mg2+, suggesting RNA as a possible target. However, Hoechst 33258 inhibits growth of Candida strains with and without group I introns. IC50s ranged from 1 to 9 microM for strains with group I introns and were 12 and 32 microM for two strains without group I introns. These studies demonstrate that compounds that bind fungal nucleic acids have the potential to be developed as new therapeutics for Pneumocystis and possibly other fungi, especially if they could be directed to structures that are not present in mammalian cells, such as self-splicing introns.

Radioprotective effects of DNA ligands Hoechst-33342 and 33258 in whole body irradiated mice

Radioprotective effects of bisbenzimidole derived DNA ligands Hoechst-33342 (H-342) and Hoechst-33258 (H-258) have been investigated in whole body irradiated stain-A and Balb/c mice (Co-60 Gamma-ray, absorbed doses of 2.5 to 10 Gy delivered at dose rates of 0.01 to 0.50 Gy/min). Biodistribution of Hoechst dyes (2 or 5 mg/kg, body wt., i.v.) and their effects on cell cycle kinetics in bone marrow were studied by flow cytometry. Protection against radiation-induced chromosomal aberrations, micronuclei formation, alterations in DNA content dispersion, inhibition of erythropoiesis and animal lethality were investigated. Significant amount of DNA bound Hoechst could be observed in liver, intestine, kidney and brain for more than 14 days after its administration, while in the bone marrow cells, a reduction in the bound Hoechst was noticed after 7 days. H-342 significantly reduced the radiation-induced chromosome aberrations mainly due to a decrease in the frequency of acentrics (nearly 30%), while a marginal decrease (10%) in the dicentrics was observed at all the dose rates studied. Both H-342 and H-258 reduced the radiation-induced micronuclei formation in a dose dependent manner (2-10 mg/kg body wt.) and this protective effect was observed up to 6 days after the administration. Neither of the two compounds induced any cytogenetic damage in the bone marrow cells of unirradiated animals nor induced tumours at the doses used here (< 5 mg/kg, body wt. i.v.). Reduction in cytogenetic damage of bone marrow cells led to a faster recovery of erythropoesis as observed by increased PCE/NCE ratio in the peripheral blood erythrocytes of the animals which received Hoechst before irradiation. H-258 (5 mg/kg body wt.) given 18 hr before irradiation reduced radiation-induced animal death (5-9 Gy), while no significant effect was observed at higher doses (10 Gy). However, H-342, which has a higher cell permeability, even at a lower dose (2 mg/kg body wt.) showed significant protection at 10 Gy. The protective effects could be enhanced further, by combining these DNA binding agents with the glucose analogue, 2-deoxy-D-glucose (2-DG) which has been shown earlier to protect bone marrow cells against radiation damage.

Phase I-II study of pibenzimol hydrochloride (NSC 322921) in advanced pancreatic carcinoma

Pibenzimol is a fluorescent molecule known to bind to double stranded DNA. It also induces prolongation of the G2 phase of the cell cycle, inhibition of DNA replication and cessation of the growth of some cells in late S phase after DNA content has been doubled. It has been shown to increase the life span of mice bearing intraperitoneally implanted L1210 and P388 leukemia. These factors coupled with the affinity of pibenzimol for pancreatic tissue led us to conduct a phase I-II trial of pibenzimol hydrochloride in patients with advanced pancreatic cancer. Twenty-six patients were treated with a five day continuous infusion of pibenzimol at a dose ranging from 6-28 mg/m2/d. There were no treatment related deaths. Major toxicity was hyperglycemia which was self-limited. No objective responses were noted.

Phase II study of pibenzimol in pancreatic cancer. A Southwest Oncology Group study

Twenty-three patients with advanced pancreatic adenocarcinoma were treated with Pibenzimol utilizing a daily intravenous schedule for five days. There were no objective responses seen. The major toxicity was pancreatic with grade 3 hyperglycemia in eleven patients. Pibenzimol is inactive in patients with advanced pancreatic adenocarcinoma.

The effects of some drugs--pentamidine, stibocaptate, Hoechst 33258, F 151, compound 'E' and Nifurtimox--on Onchocerca volvulus in chimpanzees

Several drugs were investigated for action against Onchocerca volvulus in chimpanzees. Pentamidine at 4 mg/kg daily for 16 days had no filaricidal action; nor did stibocaptate at 10 mg/kg monthly for 8 months. Hoechst 33258, a substituted bis-benzamidazole, showed micro- and macrofilaricidal activity; F151 (an arsenical compound) showed a purely macrofilaricidal action; and Compound E (a reaction product of Hoechst 33258 and F151) was micro- and macrofilaricidal. The toxicity of the three last-mentioned compounds was high, and further trials were not made. Nifurtimox, at doses of up to 40 mg/kg for 10 days, was shown not be microfilaricidal, but there was a suggestion that this drug may have some macrofilaricidal action.

Studies on Brugia pahangi. 13. The anthelmintic effect of compounds F151 (Friedheim), HOE 33258 (Hoechst) and their reaction product

F151 was a potent filaricide against adult Brugia pahangi in cats and jirds. HOE 33258 did not kill adult worms in cats but had a marginal effect on adult worms in the peritoneal cavity of jirds. It was not immediately microfilaricidal in cats but the microfilarial counts of treated cats fell within a few weeks of treatment. The reaction product, or mixture, of these two compounds (V5851 = E) was strongly macrofilaricidal in cats and jirds.