R-1 Methanandamide Phosphate,a water soluble prodrug analog of AEA, exhibited similar activity to that of AEA in the growth inhibition of C6 glioma cells[1].

Arachidonoyl ethanolamide (AEA) was the first endogenous cannabinoid (CB). AEA has been isolated and characterized as an agonist acting on the receptors CB1 and CB2 [2,3]. Since then, several related endocannabinoids have been isolated, most notably was 2-arachidonoyl glycerol (2-AG). The phosphate ester of R-1 methanandamide, R-1MAP, has been tested as a water soluble prodrug analog of AEA [4]. The activity of R-1MAP was essentially equivalent to that of AEA in inhibiting the growth of C6 glioma cells. However, when tested for the inhibitory effects of AEA binding to the isolated rat brain CB1 receptors, arachidonoyl ethanolamide phosphate (AEA-P) has shown about 5-fold less potent as an agonist with a Ki value of about 200 nM [5]. In normotensive Dutch Belted rabbits of either gender, the phosphate ester of R-methanandamide reduced intraocular pressure (IOP) [1].

References:
1.  Juntunen J, Huuskonen J, Laine K, et al. Anandamide prodrugs: 1. Water-soluble phosphate esters of arachidonylethanolamide and R-methanandamide[J]. European journal of pharmaceutical sciences, 2003, 19(1): 37-43.
2.  W. A. Devane, L. Hanus, A. Breuer, et al. Isolation and structure of a brain constituent that binds to the cannabinoid receptor. Science 258, 1946-1949(1992).
3.  C. C. Felder, E. M. Briley, J. Axelrod, et al. Anandamide, an endogenous cannabimimetic eicosanoid, binds to the cloned human cannabinoid receptor and stimulates receptor-mediated signal transduction. Proceedings of the National Academy of Sciences of the United States of America 90, 7656-7660 (1993).
4.  C. J. Fowler, K. O. Jonsson, A. Andersson, et al. Inhibition of C6glioma cell proliferation by anandamide, 1-arachidonoylglycerol, and by a water soluble phosphate ester of anandamide: Variability in response and involement of arachidonic acid. Biochemical Pharmacology 66, 757-767 (2003).
5.  T. Sheskin, L. Hanus, J. Slager, et al. Structural requirements for binding of anandamide-type compounds to the brain cannabinoid receptor. Journal of Medicinal Chemistry 40, 659-667 (1997).