Vascular anatomy influences experimental stroke treatment effectiveness

A preclinical study from Duke University researchers suggests that the effectiveness of an experimental approach to limiting stroke-related brain injury may depend not only on the drug itself, but also on the brain's collateral circulation: the network of small "backup" blood vessels that can help sustain tissue when a major artery is blocked.

In mouse models of ischemic stroke, the researchers found that AZD1390, a brain-penetrant inhibitor of the ATM kinase, reduced acute infarct volume in strains with dense collateral vessel networks. The treatment did not reduce infarct volume in mice with fewer collateral connections. When the drug was applied directly to the brain surface soon after stroke in those low-collateral models, however, infarct volume was also reduced.

The findings were published in Ferroptosis and Oxidative Stress.

The findings suggest that vascular access to threatened brain tissue may be an important determinant of therapeutic response. Variation in collateral blood vessels could therefore be an important consideration when evaluating treatments intended to reach ischemic tissue.

Ischemic stroke occurs when blood flow to part of the brain is interrupted. The resulting shortage of oxygen and glucose can trigger several forms of cellular injury. The Duke team investigated whether inhibiting ATM, a protein best known for its role in the DNA-damage response, could lessen lipid oxidative injury associated with ferroptosis, an iron-dependent form of regulated cell death.

The researchers first tested several ATM inhibitors in cell and organotypic brain-slice models. In slices exposed to oxygen and glucose deprivation, an experimental model of ischemic injury, the inhibitors protected neurons from cell death. AZD1390 also reduced lipid-peroxidation-associated measurements and the induction of ferroptosis-associated transcripts.

The team then tested AZD1390 in mice after permanent middle cerebral artery occlusion, a model of ischemic stroke. Given orally two hours after vessel occlusion, the drug reduced infarct volume measured 72 hours later by 55.6% in B6/J mice and 37.1% in B6/NJ mice, compared with vehicle-treated controls. No significant reduction was observed in BALB mice.

The difference was associated with collateral vascular anatomy. B6/J and B6/NJ mice have relatively dense connections between major cerebral arterial territories, whereas BALB mice have fewer such connections. The finding was reinforced in genetically modified mice lackingRabep2, a gene associated with reduced collateral vessel density: oral AZD1390 reduced infarct volume in wild-type and heterozygous mice, but not in Rabep2 knockout mice.

To examine whether restricted vascular access might contribute to the lack of response, the researchers applied AZD1390 directly to the exposed cortical surface 15 minutes after stroke induction. Under those conditions, infarct volume was reduced by 28.8% in BALB mice and by 35.2% in Rabep2 knockout mice.

The experiments do not establish that collateral circulation alone explains the treatment response. The topical and oral treatment experiments used different delivery routes and different treatment times, so earlier application may also have contributed to the apparent benefit of topical treatment. In addition, the study assessed infarct volume at 72 hours and did not measure neurological function, behavioral recovery, long-term outcomes, or safety.

The molecular findings also require further testing. Although the results are consistent with reduced ferroptosis-associated lipid oxidative injury, the measurements used are not specific enough to prove that ATM-dependent ferroptosis is the sole mechanism involved. Direct ATM target-engagement studies, genetic experiments, ferroptosis-specific rescue studies, and analyses of oxidized phospholipids will be needed.

AZD1390 is an investigational, orally available ATM inhibitor that has been studied for its ability to reach the brain in other clinical contexts. The present findings were obtained in cells, brain slices, and mice; they do not demonstrate safety or effectiveness for people with stroke.

The study adds to efforts to understand why stroke treatments can produce different responses across biological settings. It also highlights collateral vascular anatomy as a potential consideration for future preclinical and translational studies of therapies intended to reach ischemic brain tissue.