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Alnylam and Collaborators Publish In Vivo Research on Validation of a Mammalian Host Gene

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Alnylam Pharmaceuticals, Inc. has announced the publication of a new study in Cell Host & Microbe on the role of a host gene, heme oxygenase-1 (HO-1), in the cause and pathway of malaria parasitic infection.

The collaboration was led by scientists at Unidade de Malaria in Portugal, and included scientists at Massachusetts Institute of Technology, Roche Kulmbach GmbH (formerly Alnylam Europe AG), and Alnylam.

In the new research, in vivo studies demonstrated that HO-1 is a critical host factor involved in the liver stage of malaria infection in a mouse model. Results from the studies showed that RNAi therapeutics that silence HO-1 can significantly inhibit the initial liver stage of malaria infection and completely block the resulting transmission of disease to red blood cells.

“Our new research findings highlight the critical role of certain host-pathogen interactions occurring during malaria infection, in this case the role of HO-1,” said Maria M. Mota, Ph.D., Associate Professor, Instituto de Medicina Molecular. “Our studies also point to the powerful approach of RNAi technology for in vivo validation of key disease-associated genes.”

In the current study, HO-1 was validated as a host gene required for the liver stage of malaria (Plasmodium berghei and Plasmodium yoelii) infection. Liver HO-1 gene expression was significantly increased upon infection of mice with malaria sporozoites, the cells that infect new hosts.

Mice lacking the HO-1 gene were found to be resistant to liver infection by malaria. Further, increased expression of HO-1 in transgenic mice was associated with an increased extent of malarial liver infection. RNAi technology using in vivo delivery of siRNAs, the molecules that mediate RNAi, provided validation of the HO-1 genetic data. RNAi treatment resulted in a greater than 60% silencing of HO-1 messenger RNA (mRNA) in the liver of treated mice.

Mice treated with a HO-1 specific siRNA showed markedly reduced liver infection and complete attenuation of any detectable red blood cell stage infection, whereas animals treated with a control siRNA developed a normal course of infection. These data point to the potential therapeutic applications of RNAi for the treatment of a major parasitic infection such as malaria and to broader RNAi therapeutic strategies in infectious diseases through the targeting of host factors.

“We are thrilled to publish these new data for this serious global health problem, as RNAi technology and, potentially RNAi therapeutics, could lead to new treatment options,” said Victor Kotelianski, M.D., Ph.D., Vice President of Research at Alnylam.

“The World Health Organization estimates that each year 300 to 500 million cases of malaria occur and that more than 1 million people die of malaria, especially in developing countries. While the specific implications of RNAi therapeutics as a possible treatment for malaria remain to be fully understood, these new data certainly highlight the potential of RNAi in addressing major unmet medical needs.”