Structural and energetic insight into the interactions between the benzolactam inhibitors and tumor marker HSP90α.

The heat shock protein 90α (HSP90α) provides a promising molecular target for cancer therapy. A series of novel benzolactam inhibitors exhibited distinct inhibitory activity for HSP90α. However, the structural basis for the impact of distinct R1 substituent groups of nine benzolactam inhibitors on HSP90α binding affinities remains unknown. In this study, we carried out molecular docking, molecular dynamics (MD) simulations, and molecular mechanics and generalized Born/surface area (MM-GBSA) binding free energy calculations to address the differences. Molecular docking studies indicated that all nine compounds presented one conformation in the ATP-binding site of HSP90α N-terminal domain. MD simulations and subsequent MM-GBSA calculations revealed that the hydrophobic interactions between all compounds and HSP90α contributed the most to the binding affinity and a good linear correlation was obtained between the calculated and the experimental binding free energies (R=0.88). The per residue decomposition revealed that the most remarkable differences of residue contributions were found in the residues Ala55, Ile96, and Leu107 defining a hydrophobic pocket for the R1 group, consistent with the analysis of binding modes. This study may be helpful for the future design of novel HSP90α inhibitors.

Noncovalent DNA binding drives DNA alkylation by leinamycin: evidence that the Z,E-5-(thiazol-4-yl)-penta-2,4-dienone moiety of the natural product serves as an atypical DNA intercalator.

Molecular recognition and chemical modification of DNA are important in medicinal chemistry, toxicology, and biotechnology. Historically, natural products have revealed many interesting and unexpected mechanisms for noncovalent DNA binding and covalent DNA modification. The studies reported here characterize the molecular mechanisms underlying the efficient alkylation of duplex DNA by the Streptomyces-derived natural product leinamycin. Previous studies suggested that alkylation of duplex DNA by activated leinamycin (2) is driven by noncovalent association of the natural product with the double helix. This is striking because leinamycin does not contain a classical noncovalent DNA-binding motif, such as an intercalating unit, a groove binder, or a polycation. The experiments described here provide evidence that leinamycin is an atypical DNA-intercalating agent. A competition binding assay involving daunomycin-mediated inhibition of DNA alkylation by leinamycin provided evidence that activated leinamycin binds to duplex DNA with an apparent binding constant of approximately 4.3 ± 0.4 × 10(3) M(-1). Activated leinamycin caused duplex unwinding and hydrodynamic changes in DNA-containing solutions that are indicative of DNA intercalation. Characterization of the reaction of activated leinamycin with palindromic duplexes containing 5'-CG and 5'-GC target sites, bulge-containing duplexes, and 5-methylcytosine-containing duplexes provided evidence regarding the orientation of leinamycin with respect to target guanine residues. The data allow construction of a model for the leinamycin-DNA complex suggesting how a modest DNA-binding constant combines with proper positioning of the natural product to drive efficient alkylation of guanine residues in the major groove of duplex DNA.

Effects of 7-nitroindazole on long-term potentiation induced by l-clausenamide and high-frequency stimulation in rat hippocampus in vivo.

AIM: To study the antagonistic effect of selective neuronal nitric-oxide synthase (nNOS) inhibitor 7-nitroindazole on the long-term potentiation (LTP) induced by l-clausenamide (Cla) in rat hippocampus in vivo. METHODS: Population spike (PS) of evoked potentials was determined by extracellular recording technique in the hippocampal dentate gyrus (DG) of anesthetized rats. RESULTS: 7-Nitroindazole 2 nmol icv blocked the induction of LTP elicited by high-frequency (100 Hz) stimulation or Cla 5 nmol icv (P < 0.01), and L-arginine 225 mg.kg-1 i.p. prevented the action of 7-nitroindazole (P < 0.01). CONCLUSION: Nitric oxide produced by nNOS plays a role in the induction of Cla-induced LTP in hippocampus.

The role of protein kinase C in laminin-mediated neurite outgrowth.

Laminin is a potent stimulator of neurite outgrowth in rat pheochromocytoma (PC12) cells. Here, we investigated the role of protein kinase C (PKC) in the mechanism of laminin-mediated neurite outgrowth in PC12 cells. Phorbol ester activators of PKC have been shown to have divergent effects on laminin-mediated neurite outgrowth. Therefore, we tested the effect of the non-phorbol PKC activator, indolactam V. At 1.0 microM indolactam V inhibited laminin-mediated neurite outgrowth by 85%. Further, the PKC inhibitor H7 blocked the inhibitory effect of indolactam V on laminin-mediated neurite outgrowth. Direct measurement of protein kinase C activity in the soluble (cytosolic) and particulate (membrane) fractions of PC12 cells showed that laminin failed to alter protein kinase C activity. These data demonstrate that PKC activation inhibits laminin-mediated neurite outgrowth and that laminin does not activate PKC in PC12 cells.