Dopaminergic properties and experimental anti-parkinsonian effects of IPX750 in rodent models of Parkinson disease

With a view toward improving the neural bioavailability of administered dopaminergic compounds, including dopamine, synthetic efforts have been directed toward enhancing the brain bioavailability of these compounds by accessing cellular sugar transport systems with stereoselective dopaminergic drugs. While synthesis and chemistry of the resultant class of compounds has recently been described in US Patent No. 6,548,484, the associated biologic properties have not previously been reported. One member of this new class, IPX-750, is a pro-drug dopamine-gluconamine designed to retain stereospecificity of binding at: glucose transporters (GLUT 1/ GLUT 3 and intestinal Na+/glucose co-transporters SGLT1), dopamine transporter (DAT); and, dopaminergic receptors of the D1/D2 families. Designed to be cleavable by tissue amidases, results reported here show that intact IPX-750 pro-drug retains dopaminergic agonist-binding and biologic activities both in vitro and in vivo. IPX-750, like dopamine, exhibited predominant D5/D1 binding specificity with lower binding activity at D2. As expected, binding was highly stereospecific, ie, IPX-760, a benzamide differing in just a hydrogen atom and keto oxygen from IPX-750, bound with 6-fold lower activity at D5. In cell culture, activation resulted from binding of IPX-750 at D I or D5 in transfected cells was measured by increased intracellular cAMP. Interestingly, considering prior reported in vitro toxicity of dopamine oxidized and metabolic product dopamine, no evidence of in vitro toxicity was observed at up to 72 hrs in cell cultures at the EC50 of IPX-750 for increasing intracellular cAMP. IPX-750 was evaluated in the Parkinson's disease animal models, including MPTP mouse model, the 6-hydroxydopamine (6-OHDA) rat model and the Nurr1(+/-) knockout mouse model. In MPTP-lesioned and Nurr1+/- knockout mice, IPX-750 significantly increased Rota-rod time. In 6-OHDA-lesioned rats, IPX-750 significantly decreased apomorphine (APO)-induced rotation. Worthy of note, after cessation of IPX-750 treatments the anti-parkinsonian activity in MPTP-lesioned and Nurr1+/- mice required about 2 weeks to washout, suggesting a possible biologic reservoir of drug. In addition, after eight weeks of twice daily administration of 20 mg/kg IPX-750, mice did not show statistical difference in the total number of TH-positive neurons in substantia nigra (SN). These combined results suggest (i) that stereospecific glycoconjugation may be an effective method to improve penetrability of drugs through the blood brain barrier; (ii) treatment with bioavailable IPX-750 in vitro did not show evidence for neurotoxicity; and, (iii) IPX-750 possesses dopaminergic properties and exerts anti-parkinsonian effects in three different PD rodent models, suggesting therapeutic potential for this new class of drugs in treating dopamine deficiency diseases.