Alnylam Pharmaceuticals presents new pre-clinical data of ALN-AT3 at ISTH meeting

Published on July 2, 2013 at 8:53 AM · No Comments

Alnylam Pharmaceuticals, Inc. (Nasdaq: ALNY), a leading RNAi therapeutics company, announced today that it has presented new pre-clinical data from its RNAi therapeutic program for the treatment of hemophilia and rare bleeding disorders. The data were presented at the XXIV Congress of the International Society on Thrombosis and Haemostasis (ISTH) being held June 29 - July 4, 2013 in Amsterdam. The new pre-clinical data demonstrate that ALN-AT3, a subcutaneously administered RNAi therapeutic targeting antithrombin (AT), can normalize thrombin generation and improve hemostasis in hemophilia mice and fully correct thrombin generation in a non-human primate (NHP) hemophilia "inhibitor" model. ALN-AT3 is a key program in the company's "Alnylam 5x15" product strategy, which is aimed at advancing five RNAi therapeutic programs directed toward genetically validated disease targets into clinical development - including programs in advanced stages - by the end of 2015. ALN-AT3 utilizes the company's proprietary GalNAc conjugate delivery platform which enables subcutaneous dose administration.

“An RNAi Therapeutic Targeting Antithrombin Increases Thrombin Generation and Improves Hemostasis”

"Hemophilia and other rare bleeding disorders are characterized by deficiencies in clotting factors that ultimately lead to inadequate thrombin generation and a bleeding phenotype. ALN-AT3 is aimed at correcting these defects by knockdown of AT - an endogenous anticoagulant - thus, increasing thrombin generation and improving hemostasis. This innovative approach is strongly supported in human genetics by findings in hemophilia patients who have co-inherited prothrombotic traits, including AT deficiency, and are characterized with a mild bleeding phenotype," said Akshay Vaishnaw, M.D., Ph.D., Executive Vice President and Chief Medical Officer of Alnylam. "We are very excited by these new data with ALN-AT3 which demonstrate normalization of thrombin generation and improvement of hemostasis in hemophilia models. Most importantly, we have demonstrated that ALN-AT3 can fully correct thrombin generation in a non-human primate hemophilia 'inhibitor' model, providing key proof of concept for our program. Finally, by administering highly exaggerated doses of ALN-AT3 to wild type and hemophilia animals, we've demonstrated that our RNAi therapeutic has a very wide therapeutic index in the hemophilia setting. We remain on track to file an investigational new drug application for ALN-AT3 in mid-2013 and to initiate our Phase I study in late 2013."

"The unmet need for new therapeutic options to treat hemophilia patients remains very high, particularly in those patients that develop inhibitory antibodies to their replacement factor. Indeed, availability of a safe and effective subcutaneously administered therapeutic with a long duration of action would represent a marked improvement over currently available approaches for prophylaxis," said Claude Negrier, M.D., head of the Hematology Department and director of the Haemophilia Comprehensive Care Centre at Edouard Herriot University Hospital in Lyon. "I am very encouraged by Alnylam's pre-clinical progress to date with ALN-AT3, especially the results in a non-human primate hemophilia 'inhibitor' model showing full correction of impaired thrombin generation. These results are particularly important since clinical studies have demonstrated that thrombin generation correlates strongly with bleeding phenotype; severe hemophilia patients have low thrombin generation as compared to moderate and mild patients who have significantly higher levels. I very much look forward to the advancement of this important program in the clinical setting in the months to come."

In a presentation titled "An RNAi Therapeutic Targeting Antithrombin Increases Thrombin Generation and Improves Hemostasis," Alnylam scientists and collaborators presented data demonstrating efficacy of ALN-AT3 in models of hemophilia. First, a series of studies were performed in murine models of hemophilia. A single subcutaneous dose of ALN-AT3 that resulted in plasma AT reduction of 90% led to normalization of thrombin generation in hemophilia B (HB) mice. In addition, in a microvessel laser injury model, both hemophilia A (HA) and HB mice treated with a single subcutaneous dose of ALN-AT3 demonstrated marked improvements in hemostatic plug formation compared to untreated HA or HB mice. Additional studies were performed in NHP models. In wild type NHPs, repeat dosing with ALN-AT3 resulted in potent, titratable, and reversible silencing of plasma AT3. Weekly subcutaneous doses of 0.50 mg/kg resulted in 90% AT knockdown, while an ED50 knockdown was achieved at a dose as low as 0.125 mg/kg. Dosing was continued for over five months with consistent pharmacologic effects, including no evidence of tachyphylaxis or any neutralizing immune response associated with prolonged exposure to ALN-AT3. Studies were then performed in an NHP hemophilia "inhibitor" model, in which a HA phenotype was induced via administration of a polyclonal anti-factor VIII antibody. The anti-factor VIII antibody treatment resulted in a sharp decrease in plasma factor VIII activity levels to less than 1% of normal, similar to a severe hemophilia state in the presence of anti-factor VIII inhibitors. Animals received six weekly doses of saline or ALN-AT3 at 0.25 or 0.50 mg/kg. ALN-AT3 treated animals showed the expected level of AT knockdown but also showed a statistically significant (p<0.01 by ANOVA) dose-dependent increase in thrombin generation, fully restoring this hemostatic parameter back to normal levels. These results demonstrate that ALN-AT3 can normalize thrombin generation in the absence of functional levels of factor VIII and/or in the presence of anti-factor VIII antibodies in a large animal model, providing key proof of concept for the program.

In addition, Alnylam presented results of tolerability studies that demonstrate a wide therapeutic index for ALN-AT3 in the hemophilia setting. Highly exaggerated doses of ALN-AT3 resulting in essentially complete ablation of AT were evaluated in wild-type and hemophilia mice. Specifically, weekly doses of ALN-AT3 at 10 or 30 mg/kg in wild-type mice were associated with mortality, consistent with the genetics of homozygous AT deficiency which is known to be embryonic lethal. In sharp contrast, seven weekly doses of greater than 100 mg/kg were very well tolerated in HA mice; 100% of animals survived, and there were no toxicologically significant findings in clinical or anatomic pathology exams. Furthermore, single doses as high as 500 mg/kg were very well tolerated in both HA and HB mice. Since ALN-AT3 efficacy toward improved hemostasis is achieved at weekly doses less than 1 mg/kg, these results support a greater than 100-fold therapeutic index for ALN-AT3 in the hemophilia setting.

Alnylam plans to file an investigational new drug (IND) application for ALN-AT3 in mid-2013. The company then plans to initiate a Phase I clinical trial in late 2013, with initial clinical data for ALN-AT3 in hemophilia patients expected to be reported in 2014.

Source:

Alnylam Pharmaceuticals, Inc.

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