Currently, the only Food and Drug Administration-approved treatment of
acute stroke is recombinant
tissue plasminogen activator, which must be administered within 6 hours after
stroke onset. The pan-selective σ-receptor agonist N,N'-di-o-tolyl-
guanidine (o-DTG) has been shown to reduce
infarct volume in rats after
middle cerebral artery occlusion, even when administered 24 hours after
stroke. DTG derivatives were synthesized to develop novel compounds with greater potency than o-DTG. Fluorometric Ca(2+) imaging was used in cultured cortical neurons to screen compounds for their capacity to reduce
ischemia- and
acidosis-evoked cytosolic Ca(2+) overload, which has been linked to
stroke-induced neurodegeneration. In both assays, migration of the methyl moiety produced no significant differences, but removal of the group increased potency of the compound for inhibiting
acidosis-induced [Ca(2+)](i) elevations. Chloro and bromo substitution of the methyl moiety in the meta and para positions increased potency by ≤160%, but fluoro substitutions had no effect. The most potent DTG derivative tested was N,N'-di-p-bromo-phenyl-
guanidine (p-BrDPhG), which had an IC(50) of 2.2 µM in the
ischemia assay, compared with 74.7 μM for o-DTG. Microglial migration assays also showed that p-BrDPhG is more potent than o-DTG in this marker for microglial activation, which is also linked to neuronal injury after
stroke. Radioligand binding studies showed that p-BrDPhG is a pan-selective σ
ligand. Experiments using the σ-1 receptor-selective antagonist 1-[2-(3,4-dichlorophenyl)ethyl]-4-methylpiperazine dihydrochloride (BD-1063) demonstrated that p-BrDPhG blocks Ca(2+) overload via σ-1 receptor activation. The study identified four compounds that may be more effective than o-DTG for the treatment of
ischemic stroke at delayed time points.