Systemic, but not local, treatment with Epothilone D improves motor skills and axonal regrowth after focal stroke in adult male mice
A stroke or cerebrovascular accident is one of the leading causes of death worldwide. Ischemic stroke, the most common form, is caused by a blockage in blood supply to the brain. It triggers a cascade of pathological events including inflammation, excitotoxicity and release of free radicals that lead to cell death. To date, drug therapies have attempted to target the loss of nerve cells. These therapies are collectively known as neuroprotectants. However, these therapies have failed to translate into the clinic. The only FDA-approved treatments for acute stroke are either thrombolytic agents such as alteplase and tenecteplase that have a therapeutic window of 4.5-6 h, or endovascular stent clot retrieval devices that can be used within 24 h. While these work well, they are only useful in approximately 15% of all stroke cases, which is why there is a compelling need to find new stroke treatments. Recently, tumour suppression drugs have proven their ability in promoting microtubule (MT) equilibrium and growth cone development. In preclinical studies, the cancer treatment medications taxol and epothilones showed a capacity to stabilise microtubules (MTs). Epothilones have more advantages than taxol, such as the ability to cross the blood-brain barrier and induce less tissue toxicity. Epothilones represent a potential pharmacological treatment to modulate functional recovery outcomes after a stroke. Although the pharmacokinetics and pharmacodynamics of epothilone and taxol are available, more data needs to be collected to clarify their therapeutic potential. It is important to accurately test whether isotypes of these drug families can reduce drug-related side-effects, and to find the most appropriate pharmaceutical preparation for axonal growth and synaptic rewiring for functional recovery. To date, there has not been any trial to use a MT stabilizing agent in an animal stroke model. This project’s general aim is to test the effect of systemic and local administration of epothilone D on functional recovery and axonal growth in a mouse stroke model. The D isotype was investigated because it is a more potent microtubule stabilizer than other epothilone isotypes. In this project adult male mice were randomly distributed among 6 groups (n=7 per group). Stroke was induced by photothrombosis in the treatment groups, while sham animals received the same procedure without a photothrombosis reaction. Epothilone D or vehicle was administered either as weekly 1.5 mg/kg intraperitoneal injections for 3 weeks or locally into the stroke cavity in the form of a hyaluronan/ heparin gel (5 nM). Animals were tested on grid walking and cylinder tasks for 7 weeks before euthanasia. Brains were collected for histological assessment. It was evident that epothilone D administered systemically significantly reduced the number of forelimb foot faults contralateral to the stroke injury side from 6 weeks post-stroke in a gridwalking task compared to mice receiving vehicle instead of epothilone D (P<0.05). Furthermore, axonal sprouting in the motor and premotor cortexes (assessed using neuroanatomical labelling following injection of the tract tracing dye biotinylated dextran amine, BDA) was improved in systemic epothilone D-treated stroke-affected mice in comparison to vehicle-treated stroke-affected animals (P=0.001). However, animals which received local infusion of epothilone D in the stroke cavity failed to show signs of improved behavioural outcomes or a significant change at the level of axonal sprouting. These results are promising regarding the potential use of epothilone D and other MT stabilizing drugs in stroke recovery, and they warrant further optimization to refine the delivery method and improve the outcomes.
Advisor: Oorschot, Dorothy; Anderson, Gerg
Degree Name: Master of Health Sciences
Degree Discipline: Anatomy
Publisher: University of Otago
Keywords: Stroke; microtubules; microtubule stabilization agent; Functional recovery; Epothilone D
Research Type: Thesis