In a preprint, TMP-316 improved weight bearing on the injured forelimb in rats after spinal cord injury
In a preprint, TMP-316 improved weight bearing on the injured forelimb in rats after spinal cord injury
The bioRxiv preprint, published on September 4, describes TMP-316, a compound that simultaneously inhibits four related branches of the AGC kinase family. A single dose administered to male rats into the space containing cerebrospinal fluid immediately before a cervical spinal cord injury improved gait measures.
In adult mammals, axons, the neuronal projections that transmit signals, regrow poorly after spinal cord injury. The authors tested the hypothesis that several overlapping signaling pathways jointly restrict this growth. In cultured neurons, compounds that inhibited S6K1 and ROCK2 increased the growth of neurites, which are early neuronal projections. Adding inhibition of PKCγ or PKX increased growth further. The four proteins, S6K1, ROCK2, PKCγ, and PKX, belong to related branches of the AGC kinase family, a group of enzymes that regulate other proteins.
The original compound, RO48, had already improved recovery after spinal cord injury in mouse models, but it also acted on hERG, a cardiac potassium channel, and remained in the cerebrospinal fluid for only a short time. The authors generated 371 RO48 analogues and selected them according to neurite growth while also testing their effects on S6K1 and ROCK2. This process produced TMP-316, which stimulated projection growth in rat neurons and in human neurons derived from reprogrammed cells.
All four branches have a similar region that binds ATP, the molecule that supplies energy to cells. Computational modeling predicted that TMP-316 could bind to this region in all four proteins. The authors propose that the shared structure of this region makes it possible to develop a single compound that acts on several targets.
In the experiment, male rats were randomly assigned to three groups of 12 to 13 animals: vehicle, approximately 0.3 mg/kg TMP-316, or approximately 1 mg/kg TMP-316. The compound was administered into the lumbar space containing cerebrospinal fluid immediately before injury at C5–C6. The specialists who assessed movement did not know which animals had received the compound. At approximately 1 mg/kg, the composite gait score began to differ from the control on day 14, with the largest differences observed from days 28 through 42. Analysis of movement showed that the injured forelimb supported more weight and that support by both forelimbs reappeared during stance.