Pre-clinical safety studies of erythrocyte encapsulated thymidine phosphorylase

MNGIE (Mitochondrial neurogastrointestinal encephalomyopathy) is a life-threatening inherited metabolic disorder caused by a defect in the gene coding for the enzyme thymidine phosphorylase, resulting in affected individuals producing little or no active enzyme. Thymidine phosphorylase is essential for the normal metabolism of DNA metabolites, and in its absence, these metabolites accumulate in the body producing toxic effects on the nervous system and skeletal muscle, causing gastrointestinal dysmotility (e.g. vomiting and anorexia), neuropathy (nerve damage leading to, for example, loss of sensation and abnormal eye movements) and severe muscle weakness. MNGIE is relentlessly progressive with patients dying at an average reported age of 38 years. No specific treatment is currently available. The research team at St. George?s University of London are world leaders in developing the red blood cell as a vehicle for carrying therapeutic proteins in the blood. In the current study they are investigating the effectiveness of using patient?s own red blood cells to carry the missing thymidine phosphorylase in the circulation. The red blood cells provide a protected environment in which the enzyme can function. The encapsulated enzyme reduces the levels of toxic metabolites in the blood, thus relieving the nervous system and muscle of their toxic effects. The aim of this proposal is to conduct pre-clinical safety studies in two animal species and to establish a manufacturing process for the production of clinical grade thymidine phosphorylase; the data obtained will support their application to the UK and USA regulatory bodies to extend this work into a phase II/III clinical trials programme. Results from these studies will be made available to patient support groups and charities specialising in rare inherited metabolic disorders.

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is a fatal inherited metabolic disorder caused by a deficiency of thymidine phosphorylase, leading to a pathological accumulation of thymidine and deoxyuridine. MNGIE is relentlessly progressive with patients dying at an average age of 37.6 years. There is no recognised treatment. The encapsulation of therapeutic enzymes within autologous erythrocytes is an approach for enzyme replacement therapy which is employed clinically by our group. Encapsulation within the erythrocyte has the advantage of maintaining enzyme activity within the circulation for the life span of the erythrocyte and preventing the formation of inactivating antibodies against the enzyme. This approach is applicable to disorders where pathologically elevated plasma metabolites are able to permeate the erythrocyte membrane. Preliminary data from our clinical pilot studies of erythrocyte encapsulated thymidine phosphorylase show a reduction in plasma thymidine. The aim of this proposal is to obtain regulatory pre-clinical toxicity data from two animal species, and to establish a GMP-compliant manufacturing pathway for recombinant thymidine phosphorylase for clinical use. Both will make a significant contribution to our clinical trial applications to the regulatory bodies, the MHRA and the FDA, from which approval will be sought to develop this investigational therapy into a clinical trials programme.