The proposed comprehensive studies will validate a treatment strategy for behavioral and learning disabilities associated with neurofibromatosis. It is well known that people with neurofibromatosis suffer from a variety of behavioral changes and learning problems. The biologic basis for these changes and disabilities is difficult to study in humans. Animal models have therefore been employed to conduct this research. Both mice and fruit flies with mutations in a neurofibromatosis gene have memory and learning problems that can be studied. In mice, the research has suggested that the Neurofibromin protein is required in a specific brain structure called the hippocampus that is important for learning and memory, including spatial learning and memory, and for behavioral performance, including anxiety and depressive behaviors. Learning and memory functions in fruit flies are also impaired by mutations in the same neurofibromatosis gene. In fruit flies, it has been possible to show that a drug developed to treat cancer can effectively treat the learning and memory problems associated with neurofibromatosis. This drug inhibits a molecule that can cause cancer when it is unregulated. It also inhibits the normal molecule. We have studied the function of the normal molecule in learning and memory in mice. Similar to fruit flies, we have found that inhibition of this molecule can enhance retention of spatial memory in mice. We therefore proposed as part of a Department of Defense-funded pilot project to test the applicability of this strategy to treat mice engineered to have neurofibromatosis. In our pharmacological studies, we used the lowest effective dose of an Alk inhibitor (1.8 mg/kg) with activity against central nervous system tumors. This dose was more than 10-fold lower than the maximal effective dose of (20 mg/kg). We treated 2- to 3-month-old mice daily for 3.5 weeks. The drug or vehicle was made up in jellies to allow easy daily administration without the risk of injury due to repeated oral gavage and as voluntary oral administration would be the most relevant administration route for human patients. When we trained mice to locate a novel platform location hidden beneath opaque water, NF1 mice showed impairments in locating it. This means that NF1 mice are impaired in spatial memory. Strikingly, these impairments were not seen when the Alk inhibitor was used.

We are excited to find this low dose efficacious, as these studies have the ultimate objective of motivating treatment of humans with neurofibromatosis. To this end, minimization of drug toxicity is paramount. We are encouraged that this low dose is sufficient to rescue completely the memory impairment in NF1 mice. However, in our pilot project, the length of treatment was limited to 3.5 weeks. In addition, in our pilot study we did not assess potential effects of the Alk inhibitor on behavioral performance, including circadian (sleep/wake) activity of the mice. Alk in flies has very recently been implicated in the regulation of sleep. Therefore, the results described above are preliminary and subject both to refinement and confirmation in more comprehensive studies. We propose here more definitive and detailed studies to justify clinical trials in humans of Alk inhibition to treat NF1.

Ultimately this research will lead to an effective treatment for behavioral changes and learning disabilities associated with neurofibromatosis. The drug that has been applied in fruit flies can be easily orally administered to mice using an administration route relevant for humans. The patients who are likely to benefit are those with mutations in NF1, 90% of neurofibromatosis patients, who suffer from behavioral changes and learning disabilities. The benefits will be to enable them to be more active during the day time and learn and to function intellectually at higher levels. The time frame for achieving these patient-related outcomes could be very short. A similar drug is already Food and Drug Administration (FDA)-approved for treating cancer. We are not using this drug because it does not get into the brain. If the alternative drug we are testing works, it would need to obtain FDA approval. The issues of human tolerability and the process required for FDA approval would determine the time frame for achievement of a patient-related benefit.

The field of neurofibromatosis research will be greatly advanced by clarification of the mechanism underlying learning disabilities associated with NF1 mutation. We have studied the molecule that is targeted by the drug. Its function is not well understood in the mammalian brain. The connection of this molecule to Neurofibromin will provide new insights into Neurofibromin function in behavioral performance and learning and memory. It will also provide new therapeutic targets for treatment of neurofibromatosis.