Inhibition of 14-kDa PLA2 by 2-acylamino-alkylphospholipids: the influence of amide acidity.

2-Acylamino-alkyl phospholipids are potent competitive inhibitors of 14-kDa phospholipases A2 (e.g., human nonpancreatic secretory PLA2). As concluded from X-ray studies the amide hydrogen of these inhibitors forms a hydrogen bond to His-48 in the active site of the enzyme. We investigated the quantitative contribution of this hydrogen bond to inhibition using especially designed inhibitors that bear different acyl chains with and without electron withdrawing or donating substituents, thus differing in amide acidity. Relative free enthalpies DeltaDeltaG of enzyme-inhibitor complex formations were calculated from Xi(50) values determined by pH-stat titration using a mixed micelles assay and PLA2 from Naja mocambique mocambique. A quantitative relationship between amide acidity and DeltaDeltaG values is presented. Comparison of isoacidic and isosteric inhibitors reveals that (i) the hydrogen bond of the amide proton to His-48 is crucial for strong PLA2 inhibition, (ii) regardless of the headgroup unsubstituted N-acyl groups result in optimal amide acidity for PLA2 inhibition and (iii) the exceptionally strong inhibition by acetamides and the isosteric fluoroacetamides is due to an additional steric effect.

Targeting of endothelial KDR receptors with 3G2 immunoliposomes in vitro.

Immunoliposomes (IL) containing anti-angiogenic drugs directed selectively to the easily accessible kinase insert domain containing receptor (KDR) vascular endothelial growth factor (VEGF), which is predominantly expressed on tumour vessels are a promising tool to inhibit tumour angiogenesis. To explore this strategy, we have prepared fluorescent-labelled IL presenting antibodies against the KDR receptor (3G2) on their surface. 3G2-IL were composed of egg phosphatidylcholine and cholesterol (6:4), containing 2 mol% of the new thiol reactive linker lipid O-(3-cholesteryloxycarbonyl)propionyl-O'-m-maleimido-benzoyl tetraethylene glycol. Specific binding of 3G2-IL to immobilised recombinant KDR was used to show the maintenance of sufficient immunoreactivity of 3G2 antibodies upon the coupling procedure. 3G2-IL bound to Chinese hamster ovarian (CHO) cells stably transfected to overexpress KDR to a five times higher amount as compared to mock-transfected CHO cells. Subsequently, specific binding of 3G2-IL to KDR could also be demonstrated on KDR expressing cells, human umbilical vein endothelial cells and human microvascular endothelial cells, whereas only low binding of 3G2-IL to NIH-3T3 mouse fibroblast cells, which do not express KDR, was found. The binding of 3G2-IL to KDR receptors could not be blocked by VEGF, suggesting that the binding site for VEGF is not identical with the epitope recognised by 3G2. We could demonstrate that 3G2-IL is able to bind in vitro even in the presence of high levels of VEGF.

A simple approach to DOTAP and its analogs bearing different fatty acids.

A simple synthesis of N-[1-(2,3-dioleoyloxy)propyl]-N,N,N-trimethylammonium methyl sulfate (DOTAP) and its analogs differing in the fatty acids is presented. The synthesis is designed as quasi-one-pot reaction and the precipitating products are purified by simple recrystallization.

Synthesis and PLA2-inhibitory properties of 2(R)-acetamido-alkylphosphomethanols with a variable aggregate anchor.

Acylamino inhibitors of 14 kDa-PLA2 were synthesized which differ in the moiety that is not bound into the enzyme's active site but immersed in the lipid aggregate when a ternary inhibitory complex is formed. Our results indicate that this part of the inhibitors does not significantly influence inhibitory properties as long the amphiphilic character is retained. So, inhibitory and biophysical properties should be variable independently.