Introduction: Over 6 million people in the US suffer from Alzheimer’s disease (AD). There are no drugs that prevent the death of nerve cells in AD, nor has any drug been identified that can stimulate their replacement. Even if nerve cells could be replaced, the toxic environment of the brain will kill them unless they are protected by a drug. Therefore, drugs that stimulate the generation of new neurons (neurogenesis) alone will not be effective; a drug with both neurogenic and neuroprotective properties is required. With the ability to use cells derived from human embryonic stem cells (hESCs) as a screen to identify neurogenic compounds, we have shown that it is now be possible to identify and tailor drugs for therapeutic use in AD. This was the overall goal of this application, and to date we have made outstanding progress, making a drug that is both neurogenic for human cells and has therapeutic efficacy in a rigorous mouse model of AD.
Using a novel drug discovery paradigm based upon human stem-cell derived nerve-precursor cells, we have made a very potent drug called CAD-31. CAD-31 potently stimulates neurogenesis in human cells in culture and in mice, and prevents nerve cell death in cell culture models of toxicities associated with old age and AD. Very few, if any, drugs or drug candidates are both neuroprotective and neurogenic, particularly in animals. We harnessed the power of hESCs and medicinal chemistry to develop CAD-31. We completed extensive pharmacokinetic and safety studies on the six best of over 200 compounds that were synthesized. Of those six, one compound, CAD-31, was the best in terms of medicinal chemical, pharmacokinetic, neuroprotective and neurogenic properties. This compound underwent extensive testing for safety and passed with flying colors. It was then put into an AD mouse model where it stimulated neurogenesis, prevented behavioral deficits and some of the disease pathology. Finally, it was determined that CAD-31 is able to reverse AD symptoms in old AD mice that already have the disease. This is the most clinically relevant model of AD since therapies can only be initiated once the disease is identified.
In summary, this work has produced a novel AD drug candidate that is developed based upon a set of assays never before used by pharmaceutical companies. It presents a unique opportunity to expand the use of hESCs for the development of a therapeutic for a disease for which there is no cure. This work could lead to a paradigm shift in drug discovery for the treatment of neurodegenerative disease.