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Acute ischemic stroke treatment faces an unresolved obstacle as capillary reperfusion remains insufficient after thrombolysis and thrombectomy causing neuronal damage and poor prognosis. Hypoxia-induced capillary constriction is mediated by actomyosin contraction in precapillary smooth muscle cells (SMCs) therefore smooth muscle myosin-2 could be an ideal target with potentially high impact on reperfusion of capillaries. Methods: The myosin-2 inhibitor para-aminoblebbistatin (AmBleb) was tested on isolated human and rat arterioles to assess the effect of AmBleb on vasodilatation. Transient middle cerebral artery occlusion (MCAO) was performed on 38 male Wistar rats followed by local administration of AmBleb into the ischemic brain area. Development of brain edema and changes in cerebrovascular blood flow were assessed using MRI and SPECT. We also tested the neurological deficit scores and locomotor asymmetry of the animals for 3 weeks after the MCAO operation. Results: Our results demonstrate that AmBleb could achieve full relaxation of isolated cerebral arterioles. In living animals AmBleb recovered cerebral blood flow in 32 out of the 65 affected functional brain areas in MCAO operated rats, whereas only 8 out of the 67 affected areas were recovered in the control animals. Animals treated with AmBleb also showed significantly improved general and focal deficit scores in neurological functional tests and showed significantly ameliorated locomotor asymmetry. Conclusion: Direct inhibition of smooth muscle myosin by AmBleb in pre-capillary SMCs significantly contribute to the improvement of cerebral blood reperfusion and brain functions suggesting that smooth muscle myosin inhibition may have promising potential in stroke therapies as a follow-up treatment of physical or chemical removal of the occluding thrombus. Published version

Inefficient cerebral reperfusion is a major unresolved problem in ischemic stroke treatment because hypoxia-induced constriction of capillaries remains persistent even after recanalization by thrombolysis or thrombectomy. Capillary constriction is mediated by actomyosin contraction in precapillary smooth muscle cells (SMCs). We have developed and tested a formulation and administration technique to target the ischemic brain region and developed a promising small-molecule myosin-2 inhibitor (para-aminoblebbistatin (AmBleb) that mainly exerts its effect through direct inhibition of smooth muscle myosin-2 (SMM) in SMCs. The efficacy of SMM inhibition was tested in a rodent transient Middle Cerebral Artery Occlusion (tMCAO) stroke model. SMM was targeted by the direct administration of AmBleb into the ischemic region. AmBleb significantly accelerated the improvement of neurological deficits. Regional cerebral blood flow (rCBF) in the most important cortical and subcortical regions (e.g. motor- and somatosensory cortices, optic pathways, striatum, corpus callosum) showed drastic improvement in the AmBleb treated animals in line with the significant reduction of neurological deficits. We further optimized AmBleb and developed our lead compound MPH-222, which possesses significantly improved pharmacological properties than those of AmBleb. As observed with AmBleb, MPH-222 also fully relaxed isolated human and rat cerebral arterioles, and improved neurological functions of tMCAO operated rats characterized by significantly improved neurological deficits as well as enhanced locomotor symmetry. Moreover, as opposed to AmBleb, markedly lower MPH-222 dose was enough to achieve efficient concentrations in the ischemic region when catheter-based direct intra-arterial administration was applied. This result suggests that direct myosin inhibitor administration may be an optimal add-on therapy to thrombectomy. Funded by the Hungarian National Research, Development and Innovation Office (NVKP 16-1-2016-0051 and PIACI-KFI-2019-00488).

Post-stroke muscle spasticity affects 37% of stroke survivors and disables self-supporting life management. There is a high unmet medical need for an efficient antispastic drug because current muscle relaxants are often of limited efficacy and cause severe neurological and cardiovascular side effects due to targeting the central or peripheral nervous system. We developed a new-generation anti-spastic oral drug, MPH-220, which efficiently relaxes spastic skeletal muscles and lacks cardiovascular and neurological adverse effects because it selectively targets skeletal myosin, the contractile protein of muscles. MPH-220 is an efficient skeletal muscle specific actomyosin relaxant demonstrated on human muscle samples. Orally administered MPH-220 reduces muscle force of living rats without cardiovascular side effects. Brain-damage induced spastic animals showed drastic improvement in gait disorders upon oral MPH-220 treatment resulting in significantly straightened body posture, reduced number of spontaneous falling and cramping, and more ordered limb positions. Due to selective accumulation of MPH-220 in skeletal muscle tissues, antispastic effect was maintained for more than 10 hours. Due to its mechanism of action MPH-220 does not cause complete loss of muscle tone even at high doses. Furthermore, MPH-220 has excellent ADMET properties for oral administration: it is highly absorptive, non-mutagenic and has no effects on hERG channels, kinases, nuclear hormone receptors and GPCRs. Considering these results, MPH-220 is a promising anti-spastic oral drug candidate, which provides potential nervous system-independent therapies for spasticity and muscle stiffness without cardiovascular and neuronal side effects. Phase I clinical trials are scheduled for the beginning of 2021. Funded by the Hungarian National Research, Development and Innovation Office (NVKP 16-1-2016-0051 and PIACI-KFI-2019-00488).