We recently identified
ASP5736, (N-(diaminomethylene)-1-(3,5-difluoropyridin-4-yl)-4-fluoroisoquinoline-7-carboxamide (2E)-but-2-enedioate), a novel antagonist of
5-HT5A receptor, and here describe the in vitro and in vivo characterization of this compound.
ASP5736 exhibited a high affinity for the human
5-HT5A receptor (Ki = 3.6 ± 0.66 nM) and antagonized
5-carboxamidotryptamine (5-CT)-induced Ca(2+) influx in human cells stably expressing the
5-HT5A receptor with approximately 200-fold selectivity over other receptors, including other
5-HT receptor subtypes,
enzymes, and channels except human
5-HT2c receptor (Ki = 286.8 nM) and
5-HT7 receptor (Ki = 122.9 nM). Further,
ASP5736 dose-dependently antagonized the 5-CT-induced decrease in cAMP levels in HEK293 cells stably expressing the
5-HT5A receptor. We then evaluated the effects of
ASP5736 on
cognitive impairments in several animal models of
schizophrenia. Working memory deficit in MK-801-treated mice and visual learning deficit in neonatally
phencyclidine (PCP)-treated mice were both ameliorated by
ASP5736. In addition,
ASP5736 also attenuated MK-801- and
methamphetamine (MAP)-induced hyperactivity in mice without causing sedation,
catalepsy, or plasma
prolactin increase. The addition of
olanzapine did not affect ASP5736-induced cognitive enhancement, and neither the
sedative nor cataleptogenic effects of
olanzapine were worsened by
ASP5736. These results collectively suggest that
ASP5736 is a novel and potent
5-HT5A receptor antagonist that not only ameliorates positive-like symptoms but also
cognitive impairments in animal models of
schizophrenia, without adverse effects. Present studies also indicate that
ASP5736 holds potential to satisfy currently unmet medical needs for the treatment of
schizophrenia by either mono-
therapy or co-administered with commercially available
antipsychotics.