Background & Aims
Neuropathic pain is a common condition of following spinal cord injury (SCI). For over a decade, we have shown that Rac1-PAK1 regulated dendritic spine remodeling contributes to SCI- induced hyperexcitability underlying neuropathic pain. There is a large body of evidence that demonstrates PAK1—a downstream Rac1 effector and regulator of actin cytoskeletal dynamics—is a promising target for neurological disease. Previously, we have shown that administration of with the PAK1 inhibitor romidepsin normalized dendritic spine dysgenesis and reduced pain in a model of burn injury. The purpose of the current study is to determine if intrathecal (IT) administration of romidepsin attenuates SCI related dendritic spine dysgenesis and neuropathic pain. The results of the study support the repurposing of romidepsin, in a new indication to manage neuropathic pain after SCI.
Methods
Surgical procedures: Male and female Thy1-YFP mice underwent a spinal contusion SCI model. Following a laminectomy, a mild SCI (50 kDyn) was performed using the infinite horizons impactor device at segmental level T10. For sham surgery, animals underwent laminectomy, but did not receive the injury. Over the course of a 4-week period we assessed the efficacy of continuous IT delivery using osmotic mini pumps of vehicle or romidepsin delivery following SCI..The Basso Mouse Scale (BMS) of locomotion was used weekly to evaluate gross motor functioning. To assess neuropathic pain, we administered Von Frey (i.e., a mechanical sensitivity assay) as well as two thermal sensitivity assays, Hargreaves, and Thermal Gradient. Histology was done at experimental endpoint to determine effects on (1) bioavailability of romidepsin treatment in the spinal cord, and (2) effects of romidepsin treatment on SCI-induced dendritic spine dysgenesis.
Results
At the end of the four-week treatment period, SCI decreased withdrawal latency on the Hargreaves compared to baseline. As predicted, IT romidepsin increased the withdrawal latency compared to vehicle treatment and was comparable to baseline. For the Thermal Gradient assay, IT romidepsin treatment in SCI subjects resulted in a greater preference for neutral temperature zones (89.6% of 1-hour) compared to the vehicle treated subjects (63.4% of 1-hour). IT administration of Romidepsin did not impair gross motor function and both groups recovered equally. Following 4 weeks of romidepsin treatment, histological analysis detected an elevated expression of acetyl histone 3 (H3) within the spinal cord dorsal horn, which is a biomarker of romidepsin activity and evidence of the release of drug into the spinal cord. As expected, along the reduction in neuropathic pain, romidepsin treatment attenuated SCI-induced dendritic spine dysgenesis, evidenced by reduction of spine number and size.
Conclusions
This study demonstrated that IT administration of romidepsin effectively alleviates thermal hyperalgesia caused by SCI in mice. Importantly, this effect was achieved without adversely affecting gross motor functioning, as assessed by BMS. Romidepsin is a histone deacetylase (HDAC) inhibitor that reduces PAK1 activity without affecting PAK1 expression. Thus, the elevated H3 observed in romidepsin treated SCI subjects is evidence of the drug’s activity. Dendritic spine dysgenesis is an established correlate of pain following SCI. Thus, the attenuation of thermal hyperalgesia by romidepsin can be attributed to the inhibition of PAK1 cytoskeletal remodeling, which in turn prevented dendritic spine dysgenesis. Overall, the findings support the hypothesis that IT romidepsin administration holds therapeutic promise in ameliorating thermal hyperalgesia associated with SCI.
References
Guo, Y. et al.”Therapeutic potential of Pak1 inhibition for pain associated with cutaneous burn injury.” Molecular Pain 14 (2018).
Piekarz RL, et al. “Phase 2 trial of romidepsin in patients with peripheral T-cell lymphoma.” Blood 117.22: 5827-34 (2010).
Tan, A.M. et al. “Neuropathic pain memory is maintained by Rac1-regulated dendritic spine remodeling after spinal cord injury.” J Neurosci 28:13173-13183 (2008).
Tan, A.M., Waxman, S.G. “Dendritic spine dysgenesis in neuropathic pain.” Neurosci Lett 601:54-60 (2015).
Walter, J. S. et al. “A database of self- reported secondary medical problems among VA spinal cord injury patients: Its role in clinical care and.” Journal of Rehabilitation Research & Development 39.1-4: 53-61 (2002).
Presenting Author
Sierra Kauer
Poster Authors
Topics
- Specific Pain Conditions/Pain in Specific Populations: Neuropathic Pain - Central