Synthesis of GTP-derived Ras ligands.

A practical and convenient method for the synthesis of acid- and base-sensitive GTP analogues carrying a further substituent at the terminal phosphate has been developed. Key to the successful synthesis of these potential ligands of the Ras protein is the use of Pd0-sensitive allyl protecting groups in a one-pot synthesis that avoids evaporation steps. Initial biochemical analysis of a representative compound revealed that such GTP analogues can bind to Ras and might open up the possibility of developing small molecules that can act as deactivators of oncogenic Ras.

Development of natural product-derived receptor tyrosine kinase inhibitors based on conservation of protein domain fold.

Receptor tyrosine kinases (RTKs) such as Tie-2, IGF1R, Her-2/Neu, EGFR, and VEGFR1-3 play crucial roles in the control of cell growth and differentiation. Inhibition of such RTKs has become a major focus of current anticancer drug development, and therefore the discovery of new classes of inhibitors for these signal-transducing proteins is of prime importance. We have recently proposed a novel concept for improving the hit-finding process by employing natural products as biologically validated starting points in structural space for compound library development. In this concept, natural products are regarded as evolutionary chosen ligands for protein domains which are structurally conserved yet genetically mobile. Here we report on the discovery of novel and highly selective VEGFR-2 and -3, Tie-2, and IGF1R inhibitors derived from the naturally occurring Her-2/Neu kinase inhibitor nakijiquinone C and developed on the basis of this concept. Based on the structure of the natural product, a small library (74 members) was synthesized and investigated for inhibition of kinases with highly similar ATP-binding domains. The library yielded inhibitors with IC(50)s in the low micromolar range with high frequency (7 out of 74). In particular, four inhibitors of Tie-2 were found, a kinase critically involved in the formation of new blood vessels from preexisting ones (angiogenesis) and believed to be a new promising target in antitumor therapy. These results support the "domain concept". To advance the development of improved inhibitors, extensive molecular modeling studies were undertaken, including the construction of new homology models for VEGFR-2 and Tie-2. These studies revealed residues in the kinase structure which are crucial to the development of tailor-made receptor tyrosine kinase inhibitors.

Identification of mono- and bisubstrate inhibitors of protein farnesyltransferase and inducers of apoptosis from a pepticinnamin E library.

A library of 51 analogues of the naturally occurring protein farnesyltransferase inhibitor pepticinnamin E was investigated biologically. Several compounds with pronounced inhibitory activity were discovered with the lowest IC(50) value reaching 1 microM. The library contains inhibitors which are competitive to either farnesylpyrophosphate or the peptide substrate and a bisubstrate inhibitor. This activity is supported and rationalized by molecular modelling experiments and different binding modes of the inhibitors deduced from them. Several compounds induced apoptosis in a Ras-transformed tumour cell line, and in one case this correlated with farnesyltransferase-inhibiting activity.