Effects of VSN16R: Evidence for a non-CB1, non-CB2 target

Carolyn Tanner1, David Baker2, David L. Selwood3, Roger Pertwee1, Ruth A. Ross1. 1Institute of Medical Sciences, University of Aberdeen, Aberdeen, United Kingdom, 2Neuroscience Centre, Institute of Cell and Molecular Science, Barts and the London School of Medicine and Dentistry, Queen Mary University of London, London, United Kingdom, 3Department of Chemistry, The Wolfson Institute for Biomedical Research, University College London, London, United Kingdom.

VSN16R is a novel, water-soluble compound that produces vasorelaxation through a non-CB1, non-CB2 cannabinoid receptor (Hoi et al., 2007). The aim of this study was to characterise further the effects of VSN16R.

VSN16R was investigated in the [35S]GTPγS binding assay performed with mouse brainstem, cerebellar and forebrain membranes. Peripheral effects of VSN16R were investigated in human neutrophils and mouse isolated vasa deferentia from wild type,

CB1-/- and CB2-/- C57BL/6 mice. Data have been expressed as mean values together with SEM values or 95% confidence limits.

VSN16R did not stimulate [35S]GTPγS binding in any brain region tested (Emax <10%). VSN16R significantly inhibited fMLP-induced human neutrophil migration at 10nM (74.81%±9.81), 100nM (51.46%±7.62) and 1μM (51.41%±6.43) (P<0.05, P<0.0001, P<0.0001 respectively, one sample t-test, n = 12 from 3 different donors).

VSN16R also inhibited electrically-evoked contractions of mouse isolated vasa deferentia (Emax 56.25%, 48.22 – 63.77, pEC50 7.98±0.18, n = 8). There was no significant difference in either the efficacy or potency of the compound in vasa deferentia taken from CB1-/- (Emax 55.96%, 47.86 – 64.07, pEC50 7.90±0.19, n = 4) or CB2-/- (Emax 51.98%, 45.05 – 58.92, pEC50 7.85±0.19, n = 12) mice compared to wild type mice (P>0.05). Putative GPR55 ligands, CBD (10μM, Emax 44.61%, 35.19 – 54.02, pEC50 7.23±0.25, n = 7) and N-arachidonoyl-L-serine (1μM, Emax 52.77%, 40.86 – 64.67, pEC50 6.94±0.25, n = 8) significantly reduced the potency but not efficacy of VSN16R in wild type mouse isolated vasa deferentia (P<0.05, P<0.01 respectively) (Student’s unpaired t-test).

Taken together these data support previous reports suggesting VSN16R acts through a non-CB1, non-CB2 receptor (Hoi et al., 2007). GPR55, or a related orphan receptor, is hypothesised to modulate human neutrophil migration (McHugh et al., 2008); further experiments are ongoing to establish if this receptor does indeed mediate the observed effects of VSN16R.

Hoi, et al. (2007) Br J Pharmacol 152: 751-764.
McHugh, et al. (2008) Mol Pharmacol 73: 441-450.