For comprehensive functional recovery after spinal cord injury, one must minimize the death of affected neurons and myelinating oligodendrocytes. We have previously reported that a neurotrophin receptor, p75, plays a role in apoptosis of oligodendrocytes after spinal cord injury [7]. As for the ligand that binds and activates the apoptotic cascade of p75 in vivo, we have identified proNGF [8], a novel form of the ligand, which binds p75 selectively [9], and whose expression is upregulated consequent to the injury. Here, our goal is to minimize the loss of oligodendrocytes after injury by blocking p75 activation from the outset, where we disrupt the ability of proNGF to initiate p75-mediated death. As a translational application, an applied goal is to develop an effective and minimally invasive therapeutic strategy with a high likelihood of success in human clinical trials. In this endeavor, we have developed a non-peptide, small molecule, LM11A-31 (C31), that not only blocks proNGF-mediated oligodendrocyte apoptosis in vitro, but also crosses the blood brain barrier when delivered by IV/PO routes or IP injection, providing enormous therapeutic potential. C31 is especially well suited for CNS therapeutics, since the ratio of the compound detected in the brain vs. plasma is greater than 5.0. We thus propose to determine whether C31 is effective at improving functional recovery after spinal cord injury, and determine the optimal dose concentration in terms of maximal improvement without obvious cytotoxicity. Our preliminary data suggest that p75 is one of the receptors involved in cytochrome C release after spinal cord injury. Cytochrome C release into the cytosol represents dysregulation of mitochondrial homeostasis, a hallmark of many pathological conditions. We found that C31 inhibits cytochrome C release that is induced by contusion injury in mice, suggesting that C31 indeed targets p75 in vivo when delivered by IP injection. Our preliminary data also suggest that C31 is not toxic when administered for an extended period of time at 100 mg/kg/day for 4 months and at single dosages of up to 2000 mg/kg in normal adult mice. Even in mice that have undergone contusion injury, C31 is not toxic at 10, 25, and 100 mg/kg, when delivered by IP for 28-42 days, twice daily. We therefore propose to test the efficacy of C31 in a full-scale trial as a way to promote functional recovery of injured mice. Under this goal, we propose to determine the optimal dosage of C31 that promotes motor behavior and coordination without any toxicity for an extended period or significant benefit in pain sensation. Once the optimum dose is determined, we will assess whether oligodendrocyte survival has increased at that concentration.
The proposed study will assess the potential efficacy of inhibiting death receptor signaling in the overall effort of improving locomotor function and reducing pain sensation after spinal cord injury. The compound is specifically developed based on our extensive biochemical analyses to counteract the initiating event that leads to killing the myelinating glia. This mechanism-based targeted approach suggests that severe side effect is highly unlikely because we know the target. More importantly, the compound is small and without any charge, allowing it to cross blood-brain-barrier with high efficiency. This feature is important since the compound can be delivered to the spinal cord in a non-invasive way, such as daily injections or oral intake. In addition, since myelinating glia continue to die off long after the injury, it allows us to administer therapy long after injury has taken place and potentially achieve a beneficial effect. We anticipate that a trial in primate models will be feasible in 4-5 years.
| Tep, Chhavy; Lim, Tae Hee; Ko, Pyung On et al. (2013) Oral administration of a small molecule targeted to block proNGF binding to p75 promotes myelin sparing and functional recovery after spinal cord injury. J Neurosci 33:397-410 |
