Phosphodiesterase 7 inhibitors for the treatment of Multiple Sclerosis

Abstract

Multiple Sclerosis (MS) is an autoimmune chronic inflammatory and neurodegenerative disease of the central nervous system. Until recently, first line therapies were long-term injectable immunosuppressants, with a limited efficacy. Although the first oral drug has been approved, treatments with new mechanisms of action to improve the disease progression are still needed. For the development of new low molecular weight compounds for the oral treatment of MS, a drug discovery program was initiated targeting phosphodiesterase 7 (PDE7). This PDE is responsible for the hydrolysis of intracellular cyclic adenosine monophosphate (cAMP), with a crucial role on immunomodulatory and neuroprotective processes. In order to design novel PDE7 inhibitors, virtual modeling approaches based on structural information of PDE enzymes were followed. The synthesis of a large number of compounds belonging to different chemical families led to the selection of two PDE7 inhibitors for further characterization. These compounds were active in the nanomolar range against PDE7, and did not show significant effects over other PDEs, as measured by in vitro enzymatic assays. Incubation of different MS relevant cell types with these compounds resulted in an increase of intracellular cAMP levels. Both molecules also showed neuroprotective effects, being able to decrease nitrite production after lipopolysaccharide induced cellular damage. Additionally, immunocytochemistry studies revealed neurogenic properties of the compounds, as they induced the differentiation of neurospheres. In vivo efficacy of these molecules was studied in two MS animal models (female mice): the experimental autoimmune encephalomyelitis and the Theiler’s virus model. When treated at the peak of the disease, clinical scores of the animals were significantly improved, and anti-inflammatory and neuroprotective properties of the compounds were observed by immunohistochemical analyses of spinal cords (decreased microglia reactivity, cellular infiltrates and pro-inflammatory cytokines, maintenance of myelin organization and protection from axonal damage). Pharmacokinetic results after single oral administration showed that selected molecules were present in plasma and brain, at levels supporting their biological activity. The compounds also showed good preliminary ADME-tox and security profiles. The control of cAMP levels by PDE7 specific inhibitors represents a new approach for the treatment of neuroinflammatory diseases, such as MS, showing anti-inflammatory, neuroprotective and neurogenic properties