TARGETED DRUG-DELIVERY TO THE BRAIN VIA PHOSPHONATE DERIVATIVES - I -DESIGN, SYNTHESIS AND EVALUATION OF AN ANIONIC CHEMICAL DELIVERY SYSTEM FOR TESTOSTERONE
G. Somogyi et al., TARGETED DRUG-DELIVERY TO THE BRAIN VIA PHOSPHONATE DERIVATIVES - I -DESIGN, SYNTHESIS AND EVALUATION OF AN ANIONIC CHEMICAL DELIVERY SYSTEM FOR TESTOSTERONE, International journal of pharmaceutics, 166(1), 1998, pp. 15-26
An anionic chemical delivery system (aCDS) was designed and evaluated
for brain-targeted delivery of testosterone (T). In this system, targe
ting is achieved through the use of a specific, (acyloxy)alkyl-phospho
nate-type, targetor moiety. The systemically administered T-aCDS can e
nter the brain by passive transport due to its increased lipophilicity
. Hydrolytic cleavage by esterases releases, via a chemically unstable
, short-lived intermediate, a negatively charged, hydrophilic phosphon
ate compound (TP-). This is locked in the brain and should provide sus
tained, site-specific release of the active drug following a phosphoro
lytic attack by alkaline phosphatase or by phosphodiesterase. In vivo
evaluations found maximum T-aCDS brain levels 5-10 min after administr
ation; they fell under the detection-limit (<0.1 mu g/g) after 60 min.
With the employed (pivaloyloxy)methyl phosphonate ester, cleavage by
esterases, the first metabolic step in the decomposition process, was
not very fast. Maximum concentration of the decomposition product (TP-
) was obtained at 30 min after administration; it did not decrease sig
nificantly during the study proving that this negatively charged inter
mediate is 'locked in' the brain. However, the phosphonate derivative
of the secondary, hindered hydroxyl group in this product was fairly r
esistant to phosphorolytic attack, the second metabolic step. The rele
ased drug could not be detected indicating that testosterone release,
if any, is slower than metabolism and/or elimination. (C) 1998 Elsevie
r Science B.V. All rights reserved.