CCD-3693: An Orally Bioavailable Analog of the Endogenous Neuroactive Steroid, Pregnanolone, Demonstrates Potent Sedative Hypnotic Actions in the Rat DALE M. EDGAR, WESLEY F. SEIDEL, KELVIN W. GEE, NANCY C. LAN, GEORGE FIELD, HAIJI XIA, JON E. HAWKINSON, SCOTT WIELAND, RICHARD B. CARTER, and PAUL L. WOOD Sleep Research Center, Department of Psychiatry and Behavioral Sciences, Stanford University School of Medicine, Stanford (D.M.E., W.F.S.); Department of Pharmacology, College of Medicine, University of California, Irvine (K.W.G.); and CoCensys Inc., Irvine, California (N.C.L., G.F., H.X., J.E.H., S.W., R.B.C., P.L.W.) Accepted for publication March 5, 1997 ABSTRACT An endogenous neuroactive steroid, pregnanolone, and an orally available synthetic analog, CCD-3693, were administered to rats at the middle of their circadian activity phase (6 hr after lights off). Electroencephalogram-defined sleep-wake states, locomotor activity and body temperature were concurrently measured 30 hr before and after treatment. Identical proce- dures were used to test triazolam and zolpidem. Triazolam (0.1–1.6 mg/kg), zolpidem (2.5–10 mg/kg) and the neuroactive steroids (10 –30 mg/kg) produced dose-dependent increases in non-rapid eye movement (NREM) sleep. At this dose and time of day (in which the rats were predominantly awake during the 6 hr before treatment) the neuroactive steroids appeared more intrinsically efficacious in promoting NREM sleep than the ben- zodiazepine ligands. The neurosteroids did not, however, sig- nificantly interfere with rapid eye movement sleep and were more selective in reducing (EEG) wakefulness, with relatively less locomotor activity impairment during waking than triazo- lam and zolpidem. In addition, the benzodiazepine receptor ligands showed distinct “rebound” wakefulness after the NREM sleep-promoting effect subsided, although the neuroactive ste- roids did not. In addition, in vitro binding studies and in vivo pharmacological data confirmed that CCD-3693 was orally ac- tive in standard tests of anxiety, anticonvulsant, loss-of-righting and passive avoidance. The clinical efficacy of benzodiazepines as sedative/hypnot- ics in unquestioned. These compounds are limited, however, by negative effects on psychomotor performance, by interac- tions with alcohol and by dependence liability (Shader and Greenblatt, 1993). A recent advance in the hypnotic area has been the clinical introduction of zolpidem, a nonbenzodiaz- epine with an approximately 20-fold greater affinity for ben- zodiazepine receptors on GRCs containing 1 subunits than those containing 2 or 3 subunits and a 800-fold greater affinity for 1 over 5 containing GRCs (Pritchett and See- burg, 1990). This increase in benzodiazepine receptor sub- type specificity appears to result in an improved hypnotic profile over classical benzodiazepines; however, the 20-fold separation in receptor subtype affinities defines the narrow dosing range needed not to disrupt normal sleep architecture and maintain a superior clinical profile. Dosing above this range can result in disruptions of normal sleep architecture (Hoehns and Perry, 1993) and rebound insomnia on the next night’s sleep (Roehrs et al., 1986). Barbiturates, which are also allosteric modulators of the GRC, also have been used extensively as hypnotics, with their clinical use limited by their abuse potential and low therapeutic indices (Mellinger et al., 1985). Neuroactive ste- roids are the first class of endogenous compounds (Hu et al., 1987) known to act as positive allosteric modulators of the GRC (Cottrell et al., 1987; Gee et al., 1988; Lan et al., 1990, 1991; Puia et al., 1990; Shingai et al., 1991; McNeil et al., 1992; Paul and Purdy, 1992; Woodward et al., 1992). Consis- tent with their site of action, they have also been shown to possess hypnotic and anesthetic actions (Atkinson et al., 1965; Gyermek, 1967; Mendelson et al., 1987; Mok and Krieger, 1990; Steiger et al., 1993). Although significant syn- thetic efforts have been applied to the design of neuroactives- teroids with i.v. anesthetic activity (Phillipps, 1975), the de- Received for publication August 20, 1996. ABBREVIATIONS: ANOVA, analysis of variance; CT, circadian time; CNS, central nervous system; EEG, electroencephalogram; EMG, electro- myogram; GABA, -aminobutyric acid; GC-MS, gas chromatography-mass spectometry; GRC, GABA A receptor complex; HPCD, 2-hydroxypro- pyl--cyclodextrin; LMA, locomotor activity; LRR, loss-of-righting reflex; ML, medial-lateral; NREM, non-rapid eye movement sleep; PTZ, pentyleneteterazol; REM, rapid eye movement sleep (paradoxical sleep); T b , body temperature; TBPS, t-butylbicyclophosphorothionate; preg- nanolone, 3-hydroxy-5-pregnan-20-one; CCD-3693, 19-nor-3-trifluromethyl-3-hydroxy-5-pregnan-20-one. 0022-3565/97/2821-0420$03.00/0 THE JOURNAL OF PHARMACOLOGY AND EXPERIMENTAL THERAPEUTICS Vol. 282, No. 1 Copyright © 1997 by The American Society for Pharmacology and Experimental Therapeutics Printed in U.S.A. JPET 282:420 –429, 1997 420 at ASPET Journals on December 27, 2016 jpet.aspetjournals.org Downloaded from