What Can We Learn from the Evolution of Protein-Ligand Interactions to Aid the Design of New Therapeutics?

Efforts to increase affinity in the design of new therapeutic molecules have tended to lead to greater lipophilicity, a factor that is generally agreed to be contributing to the low success rate of new drug candidates. Our aim is to provide a structural perspective to the study of lipophilic efficiency and to compare molecular interactions created over evolutionary time with those designed by humans. We show that natural complexes typically engage in more polar contacts than synthetic molecules bound to proteins. The synthetic molecules also have a higher proportion of unmatched heteroatoms at the interface than the natural sets. These observations suggest that there are lessons to be learnt from Nature, which could help us to improve the characteristics of man-made molecules. In particular, it is possible to increase the density of polar contacts without increasing lipophilicity and this is best achieved early in discovery while molecules remain relatively small.     

Growth of human embryonic fibroblasts at clonal density: concordance with results from mass cultures.

In the past, it has been difficult to grow human diploid fibroblast cells at clonal densities. Newly devised cell culture media and rigorously controlled environmental conditions have greatly increased the ease with which such cells can be cloned. The present work was undertaken to determine whether, under appropriate conditions, diploid fibroblast cells from human embryonic lung, grow as well at clonal densities as in mass culture. The parameters studied were: (1) population doubling time, (2) in vitro proliferative capacity, (3) attachment, (4) percentage of non-dividing cells. In all cases essentially the same results were obtained for cultures at clonal densities and mass cultures. These results indicate that the behavior of these types of cells in clonal culture can be used to infer the behavior of individual cells and clones within a mass culture.     

Turnover of arachidonic acid in the major diacyl and ether phospholipids of human platelets

In this work, the uptake and release of [3H]arachidonic acid by the diacyl and ether species of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) in human platelets were studied. Uptake of [3H]arachidonic acid into 1,2-diacyl-PC and 1,2-diacyl-PE was much greater than into the ether phospholipids of the same class. In [3H]arachidonoyl-labeled platelets stimulated by thrombin, there was a decrease in total [3H] arachidonoyl-PC. This was accounted for mostly by a decrease in 1-acyl-2-[3H]arachidonoyl-PC while the level of 1-O-alkyl-2-[3H]arachidonoyl-PC (a precursor for platelet-activating factor) increased slightly. However, in ionophore A23187-stimulated platelets, the reduction of total [3H]arachidonoyl-PC was due to a decrease in both 1-acyl-2-[3H]arachidonoyl-PC and 1-O-alkyl-2-[3H] arachidonoyl-PC, suggesting that ionophore should yield more platelet-activating factor than thrombin. In both thrombin- and ionophore-stimulated platelets, there was a net increase in total [3H]arachidonoyl-PE. This consisted of a decrease in 1,2-diacyl-PE, which was essentially complete by 1 min, followed by an increase in 1-O-alk-1'-enyl-2-[3H]arachidonoyl-PE, which was slower and not apparent until 3-5 min after thrombin. During reincubation of labeled platelets with saline, the 1-O-alkyl-2-[3H]arachidonoyl-PC increased by a factor of 2, between 0 and 4 h, with no significant change in the radioactivity of any other phospholipid. Thus, upon stimulation of human platelets, arachidonic is released from both 1,2-diacyl-PC and 1,2-diacyl-PE for metabolism by platelet cyclooxygenase and lipoxygenase, while certain ether pools of PC and PE also collect arachidonic acid.