Towards a therapy for phosphomannomutase 2 deficiency: the prodrug approach for the delivery of alpha-glucose-1,6-bisphosphate

Phosphomannomutase2 deficit, or PMM2-CDG, is the most common congenital disorder of glycosylation affecting over 1,000 patients globally and it is still without a cure. The majority of the mutations causing the disease destabilize PMM2, which, under physiological conditions, catalyses the conversion of mannose-6-phosphate into mannose- 1-phosphate. Mannose-1-phosphate is in turn converted into guanosine diphosphate-mannose, a fundamental precursor for N-glycosylation process of proteins. All PMM2-CDG patients have some residual PMM2 enzymatic activity since complete absence of this activity is incompatible with life. A promising strategy to cure PMM2-CDG is based on the use of pharmacological chaperones (PCs), which are low molecular weight compounds able to stabilize the mutated enzyme and increase its intracellular concentration. In-vitro tests have demonstrated that alpha-glucose- 1,6-bisphosphate binds, stabilizes and increases the activity of PMM2 (both wild type and mutants). Regrettably, it cannot be directly administered to cell cultures for its inability to cross cell membranes. In this framework, prodrug strategy plays a central role in drug development allowing the improvement of a specific parent drug. Consistently, we designed and synthesized a promising prodrug of alpha-glucose-1,6-bisphosphate, 2,3,4-tri-O-acetylglucose-1,6- bis(diphenylphosphate) (LipoG-1,6P). LipoG-1,6P has shown great chemical stability at physiological pH while its half-life in human serum was 10.5 hours. Moreover, its cytotoxicity in HEK293 cells was evaluated by MTT test. The next step will be evaluating the capability of LipoG-1,6P to cross the cell membrane, to release PC (alpha-glucose-1,6- bisphosphate) and consequently enhance PMM2 enzymatic activity.