Preclinical Data on New Protease HCV Inhibitor ITMN 191

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Preclinical Data on New Protease HCV Inhibitor ITMN 191

By Liz Highleyman

There were four presentations at DDW on ITMN 191, a novel oral HCV

NS3/4A protease inhibitor being developed by InterMune. One

presentation revealed for the first time the molecular structure of

ITMN 191, which was discovered using rational drug design. The aim

was to construct an agent with potent and selective activity against

the HCV NS3/4A protease enzyme, and one that worked across multiple

genotypes.

In a second study, researchers performed biochemical assays to

measure the potency of ITMN against different HCV genotypes. Among

their findings:

Using parts of the NS3/4A protease complex derived from HCV genotypes

1b, 1a, 2, and 3, the EC50 (50% effective concentration) of ITMN 191

was 300 pM (picomoles), 400 pM, 400 pM, and 12.4 nM (nanomoles),

respectively.

The EC50 value against full-length genotype 1b protease was 900 pM.

ITMN 191 retained potency against NS3/4A mutations at positions A156

and D168, which confer resistance to other experimental NS3/4A

inhibitors.

ITMN 191 is 97.9% bound by human serum protein.

ITMN 191 to be metabolized by multiple isoforms of the cytochrome

P450 (CYP) enzyme system. ITMN 191 did not inhibit isoforms 1A2,

2C19, 2C9, or 2D6, but did reduce activity of isofom 3A4 by about one-

third; this has implications for drug interactions.

After 120 minutes of incubation of ITMN 191 with rat, dog, human, or

monkey hepatocytes, 81%, 73%, 35%, and 19% of the compound remained

intact.

After administering a human-equivalent dose of 290 mg oral ITMN 191

twice daily for seven days, trough levels in the livers of rats and

cynomolgus monkeys were 390-fold and 52-fold the EC90 (90% effective

concentration) after the last dose.

The authors concluded that ITMN 191 is a " highly potent, orally

absorbed inhibitor of the NS3/4A protease found in the liver of rats

and cynomolgus monkeys at levels predictive of human efficacy. "

Concentrations in the Liver

A third study further analyzed ITMN 191 concentrations in the liver

of animals. Studies of similar drugs suggest that a high liver

concentration is associated with increased potency. Multidose

pharmacokinetic studies were done in rats, beagle dogs, and monkeys.

Following a single oral dose of 30 mg/kg in rats, ITMN 191 provided

an average Cmax (maximum concentration) in the liver that was 3098

times the replicon EC90 value; levels were much lower in plasma and

in the heart.

Following a 7-day twice daily regimen of 30 mg/kg oral ITMN 191 in

rats, average concentrations in the liver at apparent Cmax and trough

(minimum concentration) levels were 1646-fold and 152-fold the EC90

value, respectively; Cmax concentrations were more than twice as high

in the liver compared with plasma (liver-to-plasma ratio of 2.4:1).

Following a 7-day twice daily regimen of 15 mg/kg oral ITMN 19 in

beagles, the corresponding concentrations were 3048-fold and 58-fold

the EC90; the liver-to-plasma ratio was 51:1.

Following the same 7-day 15 mg/kg regimen in cynomolgus monkeys,

corresponding average Cmax and trough concentrations were 238-fold

and 52-fold the EC90; the liver-to-plasma ratio was 70:1.

Resistance

The final study assessed resistance to ITMN 191 using HCV replicon

models, adding increasing concentrations ranging from 20 nM to 320

nM.

In a genotype 1b replicon, ITMN 191 had an EC50 of 2.1 nM and an EC90

of 5.6 nM.

The potency of ITMN 191 was reduced by 149-fold against replicons

that remained viable in the presence of the highest (320 nM) dose of

the drug.

Sequence analysis showed that all such replicons carried the D168A

mutation; the majority also carried both the V116M and E30A

mutations.

The authors concluded that HCV replicons with reduced sensitivity to

ITMN 191 harbor the D168A mutation; the V116M and E30A mutations may

reduce replication fitness through an indirect mechanism. The D168V

mutation, which confers resistance to the discontinued experimental

HCV protease inhibitor BILN-2061, was not observed in this study. No

mutations were detected that conferred reduced sensitivity to both

BILN-2061 and VX-950.

In summary, ITMN-191 demonstrated promising activity and oral

bioavailability in preclinical studies. It retained activity against

HCV mutations with resistance to other experimental protease

inhibitors, suggesting a favorable cross-resistance profile. Based on

these data, ITMN 191 has been selected for further development and is

currently undergoing toxicology testing.

6/2/06