Chlorbipram: A novel PDE4 inhibitor with improved safety as a potential antidepressant and cognitive enhancer

Major depressive disorder is a common, but serious, psychiatric dysfunction that affects 21% of the population worldwide. Rolipram, a first-generation phosphodiesterase-4 (PDE4) inhibitor, has been shown to have significant antidepressant and cognitive enhancement effects; however, it was unsuccessful in clinic trials because of PDE4-dependent side effects such as nausea and emesis. In this study, we investigated the neuropharmacology of the novel PDE4 inhibitor chlorbipram and the classical PDE4 inhibitor rolipram. Using antidepressant-sensitive behavioral tests, we demonstrated that the acute single administration of chlorbipram (0.075-0.6 mg/kg) produced antidepressant-like effects, as evidenced by decreases in the duration of immobility in Kunming mice in the forced swim and tail suspension tests, and no significant changes in locomotor activity. Scopolamine-induced cognitive dysfunction was also significantly attenuated in the Morris water maze test after the treatment of Sprague Dawley rats with different doses of chlorbipram (0.5-1.5 mg/kg). Furthermore, we evaluated the emetic potential of chlorbipram in beagle dogs. After oral administration, 0.5 mg/kg rolipram showed emetic profiles in all dogs within 20 minutes, whereas chlorbipram did not induce any emesis during the 120-min observation period, even at the 1.0 mg/kg dose. Together, our data suggest that chlorbipram is a novel antidepressant and cognitive enhancer with little or no emetic potency.