In vivo characterisation of the small-conductance KCa (SK) channel activator 1-ethyl-2-benzimidazolinone (1-EBIO) as a potential anticonvulsant.

Owing to their activation by increased intracellular Ca(2+) levels following burst firing, and the resultant hyperpolarisation and dampening of neuronal excitability, the small-conductance Ca(2+)-activated K(+) (SK(Ca)) channels have been proposed as a potential target for novel antiepileptic drugs. Indeed, the channel activator 1-ethyl-2-benzimidazolinone (1-EBIO) has been shown to reduce epileptiform activity in vitro. Accordingly, this study has investigated the therapeutic potential of 1-EBIO using a range of in vivo seizure models, and assessed the adverse effect liability with the rotarod and locomotor activity paradigms. To aid benchmarking of 1-EBIO's therapeutic and adverse effect potential, it was tested alongside two currently marketed antiepileptic drugs, phenytoin and levetiracetam. 1-EBIO was found to be effective at reducing seizure incidence in mice following maximal electroshock (ED(50) 36.0 mg/kg) as well as increasing the threshold to electrically- and pentylenetetrazole-induced seizures (TID(10)s 7.3 and 21.5 mg/kg, respectively). However, results from the mouse rotarod test revealed a strong adverse effect potential within the therapeutic dose range (ID(50) 35.6 mg/kg), implying a significantly inferior therapeutic index with respect to the comparator compounds. These results, therefore, support the in vitro data detailing 1-EBIO's reduction of epileptiform activity. However, the use of in vivo models has revealed a significant adverse effect potential within the therapeutic dose range. Nevertheless, given the multiplicity of SK(Ca) channel subunits and that 1-EBIO has been shown to enhance additional, non-SK(Ca) carried currents, these findings do not preclude the possibility that more selective enhancers of SK(Ca) function could prove to be effective as antiepileptic medications.

Evidence that the novel imidazoline compound FT005 is an alpha(2)-adrenoceptor agonist.

1: The aim of this study was to determine whether the hyperglycaemic action of the novel imidazoline compound FT005 could be mediated by activation of alpha(2)-adrenoceptors, using a variety of in vivo and in vitro methods including radioligand binding. 2: FT005 produced a dose-dependent increase in blood glucose levels of CBA/Ca mice (0.125-25 mg kg(-1), i.p.). The time course of this hyperglycaemic effect matched that of adrenaline (1 mg kg(-1)) more closely than glucagon (1 mg kg(-1)) or the K(ATP) channel opener diazoxide (25 mg kg(-1)). The hyperglycaemic effect of FT005 (1 mg kg(-1)) was significantly reduced by the alpha(2)-adrenoceptor antagonist rauwolscine (0.5 mg kg(-1)). 3: FT005 produced a significant reduction in plasma insulin levels of mice 30 min after administration. The hyperglycaemic effect of FT005 (25 mg kg(-1)), although still present, was significantly less in fasted mice in which insulin levels are lower, suggesting that a reduction of insulin secretion contributes to the action of FT005. 4: When studied in the mouse isolated vas deferens preparation, FT005 produced a complete inhibition of neurogenic contractions, which was blocked by rauwolscine. This is consistent with activation of pre-synaptic alpha(2)-adrenoceptors. 5: In radioligand binding studies FT005 completely displaced the alpha(2)-adrenoceptor antagonist [(3)H]-RX821002 from mouse whole brain homogenates. The displacement was best described by a two-site model of interaction comprising high and low affinity components. 6: The results indicate that FT005 is an agonist at alpha(2)-adrenoceptors. A reduction in insulin secretion contributes to the hyperglycaemic action of FT005, although an additional mechanism can not be excluded.

Phase I studies of CBP501, a G2 checkpoint abrogator, as monotherapy and in combination with cisplatin in patients with advanced solid tumors.

PURPOSE: Two phase I dose-escalation studies were conducted to determine the maximum tolerated dose (MTD) and safety profile of the G(2) checkpoint abrogator CBP501, as a single agent and in combination with cisplatin. EXPERIMENTAL DESIGN: Patients with advanced solid tumors were treated with CBP501 alone (D1/D8/D15, q4w, from 0.9 mg/m(2)), or with cisplatin (both on D1, q3w, from 3.6 mg/m(2) CBP501, 50 mg/m(2) cisplatin). Dose escalation proceeded if dose-limiting toxicity (DLT) was observed in 1 or less of 3 to 6 patients; CBP501 dose increments were implemented according to the incidence of toxicity. MTD was determined from DLTs occurring during the first two cycles. RESULTS: In the combination study, the DLT was a histamine-release syndrome (HRS) occurring 10 to 60 minutes after initiating infusion that was attenuated by prophylaxis comprising dexamethasone, diphenhydramine, ranitidine, and loratadine. The MTD was 25 mg/m(2) CBP501 and 75 mg/m(2) cisplatin, with two patients at the highest dose (36.4 mg/m(2) CBP501, 75 mg/m(2) cisplatin) experiencing grade 3 HRS. The only DLT with monotherapy was transient G(3) rise of troponin in one patient. Grade 3 to 4 treatment-related events were rare. Promising activity was observed with CBP501/cisplatin, mainly in ovarian and mesothelioma patients who had previously progressed on platinum-containing regimens. Among ovarian cancer patients, low expression of DNA repair proteins was associated with partial response or stable disease. CONCLUSIONS: CBP501 is well tolerated in patients as monotherapy and with cisplatin. At the recommended phase II dose (RP2D), the combination is feasible and HRS manageable with prophylaxis. Evidence of antitumor activity was observed in platinum-resistant patients.

First demonstration of a functional role for central nervous system betaine/{gamma}-aminobutyric acid transporter (mGAT2) based on synergistic anticonvulsant action among inhibitors of mGAT1 and mGAT2.

In a recent study, EF1502 [N-[4,4-bis(3-methyl-2-thienyl)-3-butenyl]-3-hydroxy-4-(methylamino)-4,5,6,7-tetrahydrobenzo [d]isoxazol-3-ol], which is an N-substituted analog of the GAT1-selective GABA uptake inhibitor exo-THPO (4-amino-4,5,6,7-tetrahydrobenzo[d]isoxazol-3-ol), was found to inhibit GABA transport mediated by both GAT1 and GAT2 in human embryonic kidney (HEK) cells expressing the mouse GABA transporters GAT1 to 4 (mGAT1-4). In the present study, EF1502 was found to possess a broad-spectrum anticonvulsant profile in animal models of generalized and partial epilepsy. When EF1502 was tested in combination with the clinically effective GAT1-selective inhibitor tiagabine [(R)-N-[4,4-bis(3-methyl-2-thienyl)-3-butenyl]nipecotic acid] or LU-32-176B [N-[4,4-bis(4-fluorophenyl)-butyl]-3-hydroxy-4-amino-4,5,6,7-tetrahydrobenzo[d]isoxazol-3-ol], another GAT1-selective N-substituted analog of exo-THPO, a synergistic rather than additive anticonvulsant interaction was observed in the Frings audiogenic seizure-susceptible mouse and the pentylenetetrazol seizure threshold test. In contrast, combination of the two mGAT1-selective inhibitors, tiagabine and LU-32-176B, resulted in only an additive anticonvulsant effect. Importantly, the combination of EF1502 and tiagabine did not result in a greater than additive effect in the rotarod behavioral impairment test. In subsequent in vitro studies conducted in HEK-293 cells expressing the cloned mouse GAT transporters mGAT1 and mGAT2, EF1502 was found to noncompetitively inhibit both mGAT1 and the betaine/GABA transporter mGAT2 (K(i) of 4 and 5 muM, respectively). Furthermore, in a GABA release study conducted in neocortical neurons, EF1502 did not act as a substrate for the GABA carrier. Collectively, these findings support a functional role for mGAT2 in the control of neuronal excitability and suggest a possible utility for mGAT2-selective inhibitors in the treatment of epilepsy.