KVA-D-88, a Novel Preferable Phosphodiesterase 4B Inhibitor, Decreases Cocaine-Mediated Reward Properties in Vivo

Abstract

Cocaine addiction remains a major public concern throughout the world especially in developed countries. In the last three decades, significant achievements have led to a greater understanding of the signaling pathways involved in the development of cocaine addiction; however, there are no FDA-approved treatments available to reverse or block this brain disease due to either the unsatisfactory therapeutic efficacy or severe side effects. Previous studies have demonstrated that chronic exposure to cocaine elevates levels of cyclic AMP (cAMP) as a neuroadaptative response in reward-related brain regions. Phosphodiesterase 4 (PDE4) inhibitors, which elevate cAMP levels, have been shown to block cocaine-mediated behavioral changes related to psychoactive and reinforcing properties. Unfortunately, previously studied PDE4 inhibitors induce severe side-effects, which limit their clinical usage. In this study, we identified a novel PDE4B inhibitor, KVA-D-88, with an improved selectivity profile compared to previous compounds (e.g., rolipram). Pharmacokinetic studies have shown that this compound is brain penetrant and preferably acts on PDE4B compared to PDE4D in vitro, alluding to less unwanted side effects with KVA-D-88 in vivo. Interestingly, pretreatment with KVA-D-88 significantly inhibited cocaine-induced hyperlocomotor activity. In cocaine self-administering mice with differential schedules, KVA-D-88 strikingly decreased the number of active nose-pokes and cocaine infusions and reduced the break point. Taken together, our findings demonstrate that this novel PDE4 inhibitor, KVA-D-88, could inhibit cocaine-mediated rewarding effects implying its potential clinical usage for cocaine addiction.

Keywords: PDE4 inhibitors; cAMP; cocaine; drug addiction; locomotor activity; self-administration.

Fig. 1:. Pharmacokinetic studies of KVA-D-88 in vivo.

KVA-D-88 was synthesized and administered into mice by either i.v. (1 mg/kg) or oral approach (10 mg/kg). The blood was then collected for determining its pharmacokinetic parameters. (A) Representative molecular structure of KVA-D-88. (B) PK parameters of KVA-D88 in mice with either i.v. injections or oral approach. (C) The concentration-time curve of KVA-D-88 in vivo after either i.v. injections or oral approach.

Fig. 2:. Characterization of PDE4 in vivo and in vitro.

KVA-D-88 was administered into mice (n = 4) by either i.p. injection (10 mg/kg) or p.o. approach (10 mg/kg) and 30 min or 24 hours later, mice were sacrificed for the removal blood and brain. The concentrations of KVA-D-88 were determined in these two tissues to calculate the concentration ratio of brain vs. plasma. (A) Brain and plasma KVA-D-88 concentration 30 min after i.p. injection (n = 4). (B) The IC₅₀ of KVA-D-88 on PDE4B and PDE4D in vitro. HEK293 cells were cultured and transfected with PDE4B1 expression vector, CRE luciferase reporter and a control renilla luciferase vector. The cells were dosed with KVA-D-88 and incubated overnight. Forskolin was added and incubated for 5 – 6 h. A dual luciferase assay was performed for measuring firefly luminescence. The intensity of renilla luminescence was served as internal control. Cell based assays were performed in triplicate at each concentration. The EC₅₀ value was determined by the concentration causing a half-maximal percent activity. (C) The non-linear dose-response curve of KVA-D-88 on PDE4. (D) The non-linear dose-response curve of apremilast on PDE4. (E) The table of EC₅₀ of KVA-D-88 and apremilast on PDE4 in vitro.

Fig. 3:. The effects of KVA-D-88 on cocaine-mediated locomotor activity.

WT mice (both genders, 3 month old) were employed for these experiments. Mice were divided into four groups with various treatments (± KVA-D-88 ± cocaine). Mice were pre-injected with KVA-D-88 (i.p.) 30 min later followed with cocaine injection (20 mg/kg, i.p.). Mice were then immediately put into open field to record their locomotor activity for 45 min. (A) The effects of KVA-D88 (10 mg/kg) on acute locomotion responses in male WT mice (* P < 0.05, cocaine vs. control; # P < 0.05, cocaine + KVA-D-88 vs. cocaine; n = 6 – 8). (B) The effects of KVA-D88 (5 mg/kg) on acute locomotion responses in male WT mice (* P < 0.05, cocaine vs. control; # P < 0.05, cocaine + KVA-D-88 vs. cocaine; n = 6 – 8). (C) The effects of KVA-D88 (10 mg/kg) on acute locomotion responses in female WT mice (* P < 0.05, cocaine vs. control; # P < 0.05, cocaine + KVA-D-88 vs. cocaine; n = 6 – 8). (D) The effects of KVA-D88 (5 mg/kg) on acute locomotion responses in female WT mice (* P < 0.05, cocaine vs. control; # P < 0.05, cocaine + KVA-D-88 vs. cocaine; n = 6 – 8). (E) The effects of KVA-D-88 on cocaine-mediated sensitization on locomotor activity (* P < 0.05; cocaine vs. control, # P < 0.05, cocaine + KVA-D-88 vs. cocaine; n = 6 – 8).

Fig. 4:. The effects of KVA-D-88 on active nose-poking and cocaine infusions in self-administered mice under FR1 schedule.

(A) The effect of KVA-D-88 (5 mg/kg) on the numbers of cocaine intake in the self-administered mice under FR1 schedule (P < 0.05, n = 6). (B) The effect of KVA-D-88 (5 mg/kg) on the numbers of active nose-poking in the self-administered mice under FR1 schedule (P < 0.05, n = 6). (C) The effect of KVA-D-88 (2.5 mg/kg) on the numbers of cocaine intake in the self-administered mice under FR1 schedule (P < 0.05, n = 6). (D) The effect of KVA-D-88 (2.5 mg/kg) on the numbers of active nose-poking in the self-administered mice under FR1 schedule (P < 0.05, n = 6). (E) The effect of KVA-D-88 (5.0 mg/kg) on the ratio of cocaine self-administration in the self-administered mice under FR1 schedule (P < 0.05, n = 6).

Fig. 5:. The effects of KVA-D-88 on active nose-poking and cocaine infusions in self-administered mice under FR3 or PR schedule.

WT mice (3 month old) were trained to develop stable cocaine self-administration on FR1 schedule. Then mice were switched to an FR3 schedule with or without KVA-D-88 pre-injection and the numbers of active nose-poke and cocaine infusions were recorded. Another batch of mice were switched to a PR schedule with or without KVA-D-88 pre-injection and the numbers of active nose-poke and cocaine infusions were recorded. (A) The effect of KVA-D-88 (5 mg/kg) on the numbers of cocaine intake in the self-administered mice under FR3 (P < 0.05, n = 6). (B) The effect of KVA-D-88 (5 mg/kg) on the numbers of active nose-poke in the self-administered mice under FR3 (P < 0.05, n = 6). (C) The effect of KVA-D-88 (5 mg/kg) on breaking point in the self-administered mice under PR (P < 0.05, n = 6).