AMPA receptor; PAM/positive allosteric modulator

CX 516 is a benzylpiperidine AMPAkine, an AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) modulator, that enhances the function of glutamate when it binds allosterically to the AMPA receptor channel complex. CX 516 slows receptor deactivation with a longer open time, slower excitatory postsynaptic potential (EPSP) decay and improvement of hippocampal long term potentiation (LTP).

Subcutaneous injection of CX516 (10 and 20 mg/kg) markedly reduces certain extradimensional deficits caused by early postpartum or subchronic phencyclidine therapy [1].

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Results: The specific extradimensional deficits produced by sub-chronic or early postnatal PCP treatment were significantly attenuated by sertindole and dose-dependently by CX516.
Conclusion: Findings here further establish PCP treatment as model of executive functioning deficits related to schizophrenia and provide evidence that direct glutamatergic interventions could improve these, when assessed in the ID-ED attentional set-shifting task.
With respect to the effect of acute pharmacological challenges, sertindole (1.25 mg/kg, p.o.) was effective in reversing the ED shift performance deficit induced by the sub-chronic PCP (p < 0.001) and the early postnatal PCP (p < 0.001), both compared to acute saline challenge. Similarly, two doses of CX516 (10 and 20 mg/kg, s.c.) were highly significant (p ≤ 0.001) in improving the ED shift deficit induced by either treatment regimes. Interestingly, CX516 administered at 5 and 40 mg/kg, s.c., was ineffective at reversing the ED impairment induced by the sub-chronic PCP treatment regime. In direct contrast, the CX516 dose of 5 mg/kg was able to reverse the ED deficit induced by early postnatal PCP (p < 0.05). Among treatments effective in reversing ED shift deficits (sertindole and CX516, 5 (only early postnatal PCP), 10, and 20 mg/kg in both models), neither of these groups differed significantly from the vehicle-treated control groups, with respect to their ED discrimination score [1].

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In a clinical setting, a preliminary study showed a positive clinical effect of CX516 when given as an add-on therapy to clozapine (Goff et al. 2001). Unfortunately, these findings could not be replicated in a recent follow-up study (Goff et al. 2008), despite good statistical power and a low attrition. It is well known that CX516 is a low potency agent (for review see Arai and Kessler 2007; Black 2005); hence, a sub-optimal exposure might underlie the lack of effect in clinical studies. And although few clinical studies have reported plasma concentration levels, a commonly applied clinical dose of 900 mg converts to ~13 mg/kg (p.o.) in a person of average weight and corresponds to a plasma concentration of about 8 µM (Lynch et al. 1997; Ingvar et al. 1997). Even though the clearance is lower in humans, this comparably low plasma level might explain the negative clinical findings. This is supported, in part, by data in the current study, where a dose of 5 mg/kg CX516 did not improve rat ID–ED test performance in the sub-chronic PCP treatment regimen and showed only minimal significance in the early postnatal PCP treatment regimen. Even though the no effect limit, was not found with reversal of attentional set-shifting deficits by CX516 in the early postnatal PCP treatment regimen, it appears that a “U-shape” dose–response relationship exists in both animal models of schizophrenia. An absent or diminished effect at the lower dose (5 mg/kg) could be explained simply by the lower plasma concentration, and thus lower brain exposure, as could be the case for the sub-chronically PCP-treated animals. For animals treated with early postnatal PCP, however, the effect of the 5-mg/kg dose might suggest a higher sensitivity towards CX516 exposure in this animal model.

In another clinical study, CX516 was administered as a single agent, but was ineffective in improving psychosis and cognition measures in schizophrenia patients; however, this preliminary study was both underpowered and suffered from patient dropout, especially at the higher doses of CX516 (Marenco et al. 2002). In the present study, a “wash-out” of the CX516 reversal effect at the 40-mg/kg dose was seen in both animal disease models. Altered behavior at higher doses was observed in another animal study, where a suppression of exploratory behavior was observed (Granger et al. 1993). In the current study, no apparent adverse effects were observed for CX516 at doses from 5 to 40 mg/kg; however, in a pilot study testing a dose of 80 mg/kg, we observed that the rats lost interest in digging for food rewards. Instead they showed an overt licking behavior, licking silicone connections in the test box. Although speculative, we suggest that this could be due to the excitotoxic action of CX516 caused by stimulation of the glutamatergic system.

The literature contains numerous studies describing CX516 function in brain slices and animal models (for review see Arai and Kessler 2007; Black 2005). In general, the effect of CX516 arises from the ability to augment AMPA receptor transmission and promote long-term potentiation (LTP) formation, when investigated in hippocampal slices (Granger et al. 1993; Staubli et al. 1994; Arai et al. 1994). Since the results from in vivo studies also demonstrated a promotion of LTP by CX516, it was subsequently investigated for its positive effect in a number of animal models of memory. CX516 administration has been proven to promote long-term reference memory, as well as short-term and working memory (for review see Black 2005). Interestingly, in two later studies looking at AMPA function, it was first shown that CX516 did not produce an enhancement in LTP in hippocampal slices (only a lowering of stimulations threshold), whereas it did in slices from the PFC (Black et al. 2000). Furthermore, CX516 was shown to enhance AMPA response in the PFC, both in vitro and in vivo (Baumbarger et al. 2001). Although the discrepancy between these data sets is unclear, the latter setting together with the present data would, in theory, make CX516 ideal for the treatment of the PFC-mediated executive functioning deficits seen in schizophrenia [1].

Animal/Disease Models: Male Lister Hooded rat (56-63 days after birth) [1]
Doses: 5, 10, 20 and 40 mg/kg
Route of Administration: subcutaneous injection
Experimental Results: Two doses (10 and 20 mg/kg) The improvement in extradimensional transformation defects caused by either treatment regimen is very significant. Two doses (5 and 40 mg/kg) were ineffective in reversing extradimensional damage induced by subchronic postpartum phencyclidine regimen.

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For comparative evaluation of the effect on deficits in executive functioning, sertindole was dosed 120 min prior to presentation of the first discrimination problem (1.25 mg/kg, perorally (p.o.)), and this dose was adapted from Goetghebeur and Dias (2009) and Rodefer et al. (2008). Based on exposure data (see Table 1), it was determined to dose CX516 (5, 10, 20, and 40 mg/kg, s.c.) at two time points, first 30 min prior to presentation of the first discrimination and second approximately 60 min later (before starting the intradimensional shift 2 reversal discrimination), meaning that all animals were dosed at the same stage of the ID–ED task. Control animals (acute vehicle injections) were counterbalanced for s.c. and p.o. administrations, and the different vehicles were applied.[1]

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CX516 was dissolved in isotonic water (D-glucose) and pH adjusted to 7 using methansulfonic acid.
Exposure: Exposure data of CX516 were collected in two separate experiments. Firstly, the pharmacokinetic profile of CX516 was assessed for a dose of 40 mg/kg (s.c), with collections at 30, 60, and 90 min (n = 4), in both the sub-chronic and early postnatal animal disease models. Secondly, in order to investigate the relationship between CX516 plasma and brain concentrations and the effect on reversal of the PCP-induced ED shift performance deficit (pharmacodynamics), CX516 was dosed (5, 10, 20, or 40 mg/kg) twice, first at 30 min prior to the presentation of the first discrimination and again approximately 60 min later. Samples were collected at 90 min (n = 4) [1].

[1]. Reversal of cognitive deficits by an ampakine (CX516) and sertindole in two animal models of schizophrenia--sub-chronic and early postnatal PCP treatment in attentional set-shifting. Psychopharmacology (Berl). 2009 Nov;206(4):631-40.

CX-516 is a N-acylpiperidine.

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Drug Indication
Investigated for use/treatment in alzheimer's disease, memory loss, autism, neurologic disorders, dementia, schizophrenia and schizoaffective disorders, attention deficit/hyperactivity disorder (ADHD), and sleep disorders.

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Mechanism of Action
CX 516 is a benzylpiperidine AMPAkine, an AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) modulator, that enhances the function of glutamate when it binds allosterically to the AMPA receptor channel complex. CX516 slows receptor deactivation with a longer open time, slower excitatory postsynaptic potential (EPSP) decay and improvement of hippocampal long term potentiation (LTP).

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Rationale: Therapies treating cognitive impairments in schizophrenia especially deficits in executive functioning are not available at present. Objective: The current study evaluated the effect of ampakineCX516 in reversing deficits in executive functioning as represented in two animal models of schizophrenia and assessed by a rodent analog of the intradimensional-extradimensional (ID-ED) attentional set-shifting task. The second generation antipsychotic, sertindole, provided further validation of the schizophrenia-like disease models. Methods: Animals were subjected to (a) sub-chronic or (b) early postnatal phencyclidine (PCP) treatment regimes: (a) Administration of either saline or PCP (5 mg/kg, intraperitonally b.i.d. for 7 days) followed by a 7-day washout period and testing on day 8. (b) On postnatal days (PNDs) 7, 9, and 11, rats were subjected to administration of either saline or PCP (20 mg/kg, subcutaneously (s.c.)) and tested on PNDs 56-95, after reaching adulthood. The single test session required rats to dig for food rewards in a series of discriminations following acute administration of either vehicle, or CX516 (5-40 mg/kg, s.c.), or sertindole (1.25 mg/kg, perorally). [1]

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In summary, schizophrenia-related cognitive impairments are poorly treated by existing therapies, possibly due to an exclusive focus on dopamine D2 receptor antagonism, as being the main predictor of drug efficiency (Weinberger 2007). The current study represents a different approach building on the glutamate hypothesis of schizophrenia, suggesting disturbances in the glutamate homeostasis as an underlying cause of the executive functioning deficits seen in schizophrenia (Owen et al. 1991). The two animal models of schizophrenia (i.e., sub-chronic and early postnatal PCP models) tested here represents different ways to model the schizophrenia disease pattern. And although similar in their detection of effects in the ID–ED task when treated with CX516 and sertindole, there are important differences, like the time required to prepare animals and consistency of the induced deficit. Indeed, the early postnatal model takes longer to prepare, but then offers a larger window for applying chronic antipsychotic drug treatment to mimic the clinical situation more closely. This study emphasizes the important role of glutamate homeostasis in the brain and increases our insight into possible novel treatment regimens for cognitive disturbances affecting schizophrenia patients. Interestingly, attempts to reverse the PCP-induced deficits in attentional set-shifting by the use of the ampakine CX516 and the second generation antipsychotic sertindole were similar in these theoretically different animal models of schizophrenia. These data add further to support the potential of both approaches in relieving the cognitive deficits associated with schizophrenia, thereby improving the translational aspect of the ID–ED test paradigm. [1]

C14H15N3O

241.294

241.121

C, 69.69; H, 6.27; N, 17.41; O, 6.63

154235-83-3

CX516-d10;1286653-21-1

148184

White to light yellow solid powder

1.2±0.1 g/cm3

433.1±25.0 °C at 760 mmHg

88-90ºC

215.8±23.2 °C

0.0±1.0 mmHg at 25°C

1.640

0.57

0

3

1

18

301

0

C1CCN(CC1)C(=O)C2=CC3=NC=CN=C3C=C2

ANDGGVOPIJEHOF-UHFFFAOYSA-N

InChI=1S/C14H15N3O/c18-14(17-8-2-1-3-9-17)11-4-5-12-13(10-11)16-7-6-15-12/h4-7,10H,1-3,8-9H2

piperidin-1-yl(quinoxalin-6-yl)methanone

BDP 12; BDP-12; CX-516; BDP12; Ampalex; 154235-83-3; BDP 12; 1-(quinoxalin-6-ylcarbonyl)piperidine; 1-(6-Quinoxalinylcarbonyl)piperidine; SPD-420; CX 516; CX516; SPD420; brand name: Ampalex;

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

H2O : ~100 mg/mL (~414.44 mM)
DMSO : ≥ 41 mg/mL (~169.92 mM)

Solubility in Formulation 1: ≥ 2.75 mg/mL (11.40 mM) (saturation unknown) in 10% DMSO + 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 27.5 mg/mL clear DMSO stock solution to 400 μL PEG300 and mix evenly; then add 50 μL Tween-80 to the above solution and mix evenly; then add 450 μL normal saline to adjust the volume to 1 mL.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

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Solubility in Formulation 2: ≥ 2.75 mg/mL (11.40 mM) (saturation unknown) in 10% DMSO + 90% (20% SBE-β-CD in Saline) (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 27.5 mg/mL clear DMSO stock solution to 900 μL of 20% SBE-β-CD physiological saline solution and mix evenly.
Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.

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Solubility in Formulation 3: ≥ 2.75 mg/mL (11.40 mM) (saturation unknown) in 10% DMSO + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 27.5 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.

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 (Please use freshly prepared in vivo formulations for optimal results.)