Full manuscript title: Ultrasound-guided intraparenchymal injection of slow release Chondroitinase ABC-37 in the chronic phase of spinal cord injury improves long-term recovery

It is well-established that early treatment with chondroitinase ABC (ChABC) improves functional recovery in preclinical models of spinal cord injury (SCI). To increase the potential for clinical translation, research is now focused on optimizing treatment conditions and enhancing the enzymatic stability of ChABC formulations. The current study tested the in vivo efficacy of a novel formulation of ChABC, Src homology-3 (SH3)-ChABC-37, that has 37 mutations and is delivered by affinity release from a crosslinked methylcellulose (xMC) modified with SH3-binding peptides (bp). The study also tested a gap in knowledge, comparing the effects of the route of administration on the efficacy of SH3-ChABC-37/xMC-bp. Male Sprague Dawley rats were given a single subarachnoid injection or a novel ultrasound guided intraparenchymal injection of SH3-ChABC-37/xMC-bp or vehicle (xMC-bp only), 28 days after a moderate, lower thoracic contusion injury. Recovery of locomotor and sensory function was assessed for 27 days post SCI, and prior to SH3-ChABC-37/xMC-bp treatment, and then following treatment until 112 days post SCI. We found that the single intraparenchymal injection of SH3-ChABC-37/xMC-bp produced a significant 1.5-point increase in BBB scores after day 28. There was no effect of subarachnoid administered SH3-ChABC-37/xMC-bp. Importantly, irrespective of the administration route, SH3-ChABC-37/xMC-bp did not produce pain. While pain symptoms worsened after day 28 in rats treated with xMC-bp only, SH3-ChABC-37/xMC-bp blocked further development of pain symptoms. These data confirm the in vivo efficacy of SH3-ChABC-37/xMC-bp and indicate that intraparenchymal administration may further improve treatment efficacy, even when applied in the chronic phase of SCI.