Optimization of Aryl Amides that Extend Survival in Prion-Infected Mice

Abstract

Developing therapeutics for neurodegenerative diseases (NDs) prevalent in the aging population remains a daunting challenge. With the growing understanding that many NDs progress by conformational self-templating of specific proteins, the prototypical prion diseases offer a platform for ND drug discovery. We evaluated high-throughput screening hits with the aryl amide scaffold and explored the structure-activity relationships around three series differing in their N-aryl core: benzoxazole, benzothiazole, and cyano. Potent anti-prion compounds were advanced to pharmacokinetic studies, and the resulting brainpenetrant leads from each series, together with a related N-aryl piperazine lead, were escalated to long-term dosing and efficacy studies. Compounds from each of the four series doubled the survival of mice infected with a mouse-passaged prion strain. Treatment with aryl amides altered prion strain properties, as evidenced by the distinct patterns of neuropathological deposition of prion protein and associated astrocytic gliosis in the brain; however, none of the aryl amide compounds resulted in drug-resistant prion strains, in contrast to previous studies on compounds with the 2-aminothiazole (2-AMT) scaffold. As seen with 2-AMTs and other effective anti-prion compounds reported to date, the novel aryl amides reported here were ineffective in prolonging the survival of transgenic mice infected with human prions. Most encouraging is our discovery that aryl amides show that the development of drug resistance is not an inevitable consequence of efficacious anti-prion therapeutics.

Developing Therapeutics for PrP Prion Diseases

“…In addition to the N-aryl piperazine and N-aryl oxazoles, we also explored SAR for the N-aryl heterocycles and N-linked cyano benzyl series (Giles et al 2016). Based on N-aryl benzothiazole and N-aryl benzoxazole hits, we first tested a range of commercially available analogs.…”

“…Based on N-aryl benzothiazole and N-aryl benzoxazole hits, we first tested a range of commercially available analogs. In the N-aryl benzothiazole series, a 6-methyl substituent on the benzothiazole ring in combination with a furyl amide was determined to be important for potency (Giles et al 2016). Single-dose pharmacokinetics by oral gavage showed that IND114431 (Fig.…”

“…Various carbonyl linked aryl substituents that were tested on an N-(4-cyanophenyl) backbone had sub-100 μM potency, and a derivatized 3-phenylpyridine, IND126256 (Fig. 5), was identified to have the best brain exposure of the series (Giles et al 2016). …”

“…However, dosing at 25 mg/kg per day resulted in a survival index of 181 (Table 4) (Giles et al 2016). Surprisingly, each of the other three lead compounds led to similar extension in survival despite differing potency in the cell assay and pharmacokinetics: IND114431, IND116135, and IND126256 had survival indices of 220, 233, and 227, respectively, in Tg(MoPrP) mice (Table 4) (Giles et al 2016). As with the 2-AMT treatments, each compound appeared to produce a unique neuropathological signature.…”

“…However, in contrast to IND24 and IND81, treatment with any of the four aryl amide compounds did not significantly change the glycoform ratio. Moreover, when CAD5 cells were infected with brains of mice treated with aryl amides, they propagated strains susceptible to the respective aryl amide, suggesting that drug-resistance is not an inevitable outcome of effective anti-prion therapeutics (Giles et al 2016). …”