Effective treatments for central nervous system (CNS) injuries, diseases, and disorders remain a serious challenge for preclinical research scientists and clinicians This newsletter discusses some compounds that are in clinical trials or proteins/pathways that warrant consideration as therapeutic targets (Fig. 1).
Rho Family GTPase Modulation
Rho family GTPases control a myriad of neuronal processes, including neurite (axonal and dendritic) growth and differentiation, axonal guidance and pathfinding, and the development, growth, and maintenance of dendritic spines. In this context, the most studied and characterized Rho family GTPases are RhoA, Rac1, and Cdc42. Thus, these GTPases have also received the most attention in the arena of therapeutic intervention in various CNS injuries, diseases, and disorders1,2.
Rho activity is involved in the neuronal response to CNS trauma such as spinal cord injury. The drug VX-210 (formerly known as Cethrin or BA-210; licensed to Vertex Pharmaceuticals), is a direct-acting, cell-permeable Rho inhibitor derived from C3 transferase, designed to offer both a regenerative and neuroprotective effect after acute spinal cord injury3,4. Blocking the Rho pathway allows growth cones to form and extend, processes critical to axon regeneration. As of February 2016, VX-210 is in Phase II/III clinical trials for treatment of acute spinal cord injuries4-6. Another Rho-directed drug is BA-1049 which inhibits Rho-associated protein kinase 2 (ROCK2). BA-1049 is being evaluated as a treatment for glaucoma and cerebral vascular disorders (e.g., cerebral cavernous malformations)3.
Rac1 inhibitors have been evaluated for treatment of Alzheimer’s disease (AD) and neurodevelopmental disorders (e.g., Fragile X syndrome [FXS])2,7. EHT1864, a Rac1 inhibitor, blocks production of Aß peptides (Aß 40 and Aß 42 ) that form the plaques that characterize AD. EHT1864 indirectly inhibits γ-secretase activity which reduces the processing of the amyloid precursor protein7. The authors replicated these findings with the Rac1 inhibitor NSC237667. NSC23766 also inhibits the exaggerated long-term depression activity in hippocampal neurons of an animal model of FXS (Fmr 1 knockout mice)2.
Cdc42 inhibition has been studied with ZCL278, a selective, cell permeable, small molecule inhibitor, discovered by high-throughput in silico screening that binds directly in the surface groove of Cdc42, a region essential for GEF binding. Because Cdc42 has a crucial role in establishing neuronal polarity, the effect of Cdc42 inhibition with ZCL278 on neuronal development was evaluated. ZCL278 inhibits Cdc42-mediated neuronal branching in primary neonatal cortical neurons. In addition, the extension of filopodia and microspikes from migrating growth cones were inhibited in the presence of ZCL2788. With an inhibitor such as ZCL278, it will be much easier to dissect the exact role that Cdc42 has in mediating pathways responsible for neuron growth and development.
The studies discussed here represent just the tip of the iceberg for potential treatments for a variety of CNS injuries, diseases, and disorders. Both targets and therapeutics can only be expected to grow exponentially in the coming years as more is learned about how Rho-family (and other members of the Ras superfamily) GTPases regulate CNS functions in normal and pathological conditions and rational drug design advances continue.
Cytoskeleton, Inc. has been a reliable source of compound screening services in the areas of pre-clinical drug development programs and early compound screening in primary HTS projects, as well as secondary screening and compound target validation. We also have extensive experience in gene design and expression with an eye for producing highly purified biological active proteins. Our expertise in protein purification is the basis for the complementary skill of assay design. We have produced many functional assays for kinesins (e.g., Eg5, CenPE, MKLP2), dynein [cytoplasmic]), myosins (e.g., cardiac, smooth, skeletal, and non-muscle isoforms), small G-proteins (e.g., Rho, Arf, Ral families), tubulins (e.g., tumor, plant, and fungal origins), and actin binding proteins; many of them are multi-protein assays that might have protein complexes of 3 or more subunits, e.g., a soluble sarcomere format and the Arp2/3 complex based assay. Our experiences in antibody and ELISA technology complements the cytoskeletal and signal transduction focus. We support all of our services with a dedicated technical services department and years of laboratory experience in the fields of cell biology, cancer biology, and neuroscience.
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