The novel pyrrolidine nor-lobelane analog UKCP-110 [cis-2,5-di-(2-phenethyl)-pyrrolidine hydrochloride] inhibits VMAT2 function, methamphetamine-evoked dopamine release, and methamphetamine self-administration in rats

Abstract

Both lobeline and lobelane attenuate methamphetamine self-administration in rats by decreasing methamphetamine-induced dopamine release via interaction with vesicular monoamine transporter-2 (VMAT2). A novel derivative of nor-lobelane, cis-2,5-di-(2-phenethyl)-pyrrolidine hydrochloride (UKCP-110), and its trans-isomers, (2R,5R)-trans-di-(2-phenethyl)-pyrrolidine hydrochloride (UKCP-111) and (2S,5S)-trans-di-(2-phenethyl)-pyrrolidine hydrochloride (UKCP-112), were evaluated for inhibition of [(3)H]dihydrotetrabenazine binding and [(3)H]dopamine uptake by using a rat synaptic vesicle preparation to assess VMAT2 interaction. Compounds were evaluated for inhibition of [(3)H]nicotine and [(3)H]methyllycaconitine binding to assess interaction with the major nicotinic receptor subtypes. In addition, compounds were evaluated for inhibition of methamphetamine-evoked endogenous dopamine release by using striatal slices. The most promising compound, UKCP-110, was evaluated for its ability to decrease methamphetamine self-administration and methamphetamine discriminative stimulus cues and for its effect on food-maintained operant responding. UKCP-110, UKCP-111, and UKCP-112 inhibited [(3)H]dihydrotetrabenazine binding (K(i) = 2.66 ± 0.37, 1.05 ± 0.10, and 3.80 ± 0.31 μM, respectively) and had high potency inhibiting [(3)H]dopamine uptake (K(i) = 0.028 ± 0.001, 0.046 ± 0.008, 0.043 ± 0.004 μM, respectively), but lacked affinity at nicotinic receptors. Although the trans-isomers did not alter methamphetamine-evoked dopamine release, UKCP-110 inhibited (IC(50) = 1.8 ± 0.2 μM; I(max) = 67.18 ± 6.11 μM) methamphetamine-evoked dopamine release. At high concentrations, UKCP-110 also increased extracellular dihydroxyphenylacetic acid. It is noteworthy that UKCP-110 decreased the number of methamphetamine self-infusions, while having no effect on food-reinforced behavior or the methamphetamine stimulus cue. Thus, UKCP-110 represents a new lead in the development of novel pharmacotherapies for the treatment of methamphetamine abuse.

Fig. 1.

Structures of lobeline, lobelane, nor-lobelane, UKCP-110, UKCP-111, and UKCP-112.

Fig. 2.

Effect of UKCP-110 and its trans-isomers (UKCP-111 and UKCP-112) on [³H]DTBZ binding (top) and [³H]DA uptake (bottom) into synaptic vesicles. Concentration-dependent increases in inhibition of [³H]DTBZ binding and inhibition of vesicular [³H]DA uptake by UKCP-110 and its trans-isomers are shown. For the binding assays, control represents specific [³H]DTBZ binding in the absence of compound. Data are mean (± S.E.M.) specific [³H]DTBZ binding presented as a percentage of the respective control (1100 ± 96.2 fmol/mg control, n = 22 rats; n = 3–5 rats/compound). For the uptake assays, control represents [³H]DA uptake in the absence of compound. Data are mean (± S.E.M.) specific [³H]DA uptake as a percentage of the respective control (35.8 ± 5.33 pmol/min/mg, control, n = 24 rats; n = 4 rats/compound). Previous results for [³H]DTBZ binding (Zheng et al., 2008) and [³H]DA uptake (Nickell et al., 2010) for lobeline and lobelane are illustrated.

Fig. 3.

Analogs do not inhibit [³H]nicotine (top) or [³H]MLA (bottom) binding. Analog concentration response curves for inhibition of [³H]nicotine (NIC) and [³H]MLA binding to rat whole brain membranes are shown. Nonspecific binding was determined in the presence of 10 μM cytisine or 10 μM NIC for the [³H]NIC and [³H]MLA assays, respectively. Control represents [³H]NIC or [³H]MLA binding in the absence of analog (46.4 ± 4.20 and 49.1 ± 2.31 fmol/mg protein, respectively). Data are mean ± S.E.M. (n = 3–4 rats/compound).

Fig. 4.

Effect of exposure to UKCP-111 alone and in combination with methamphetamine on DA (top) and DOPAC (bottom) fractional release. DA and DOPAC fractional release represents the amount of DA and DOPAC in each 5-min sample. The arrows indicate the point in time at which analog was added to the superfusion buffer and analog remained in the buffer until the end of the experiment. Methamphetamine (METH) was added to the buffer for 15 min as indicated by the brackets. Data are mean ± S.E.M pg/ml/mg slice weight (n = 3).

Fig. 5.

Effect of exposure to UKCP-112 alone and in combination with methamphetamine on DA (top) and DOPAC (bottom) fractional release. The arrows indicate the point in time at which analog was added to the superfusion buffer and analog remained in the buffer until the end of the experiment. METH was added to the buffer for 15 min as indicated by the brackets. Data are mean ± S.E.M pg/ml/mg slice weight (n = 3).

Fig. 6.

Effect of UKCP-110 alone and in combination with methamphetamine on DA (top left) and DOPAC (top right) fractional release and total methamphetamine-evoked DA overflow (bottom). The arrows indicate the point in time at which analog was added to the superfusion buffer and analog remained in the buffer until the end of the experiment. METH was added to the buffer for 15 min as indicated by the brackets. Data are mean ± S.E.M pg/ml/mg slice weight (n = 6).

Fig. 7.

Effect of UKCP-110 on the number of methamphetamine infusions (top) and time course of methamphetamine self-administration (bottom). UKCP-110 dose-dependently decreased the number of METH infusions (0.03 mg/kg/infusion) over the 60-min session. Total and cumulative METH infusions earned in 5-min blocks are presented as mean ± S.E.M. *, different from saline (n = 6).

Fig. 8.

Effect of UKCP-110 on food maintained responding (top) and time course of responding (bottom). Total and cumulative number of pellets earned in 5-min blocks across a 15-min session are presented as mean ± S.E.M. (n = 12).

Fig. 9.

No tolerance to repeated treatment with UKCP-110 on methamphetamine self-administration. Repeated administration of UKCP-110 decreased METH self-administration over the course of seven sessions. Data are presented as mean ± S.E.M. number of METH infusions (0.03 mg/kg/infusion) earned over seven consecutive 60-min sessions. *, different from saline (n = 7/group).