Clarification of the Binding Mode of Teleocidin and Benzolactams to the Cys2 Domain of Protein Kinase Cδ by Synthesis of Hydrophobically Modified, Teleocidin-Mimicking Benzolactams and Computational Docking Simulation

Abstract

Phorbol esters (12-O-tetradecanoylphorbol 13-acetate; TPA) and teleocidins are known to be potent tumor promoters and to activate protein kinase C (PKC) by binding competitively to the enzyme. The relationship between the chemical structures and the activities of these compounds has attracted much attention because of the marked structural dissimilarities. The benzolactam 5, with an eight-membered lactam ring and benzene ring instead of the nine-membered lactam ring and indole ring of teleocidins, reproduces the active ring conformation and biological activities of teleocidins. Herein we describe the synthesis of benzolactams with hydrophobic substituents at various positions. Structure-activity data indicate that the existence of a hydrophobic region between C-2 and C-9 and the steric factor at C-8 play critical roles in the appearance of biological activities. We also computationally simulated the docking of teleocidin and the modified benzolactam molecules to the Cys2 domain structure observed in the crystalline complex of PKCdelta with phorbol 13-acetate. Teleocidin and benzolactams fitted well into the same cavity as phorbol 13-acetate. Of the three functional groups hydrogen-bonding to the protein, two hydrogen-bonded with protein atoms in common with phorbol 13-acetate, but the third one hydrogen-bonded with a different protein atom from that in the case of phorbol 13-acetate. The model explains well the remarkable difference in activity between 5 and its analogue having a bulky substituent at C-8.

Current Status and Future Prospects of C1 Domain Ligands as Drug Candidates

“…In addition, the lower Ki value of ILV (34) compared to compound 38 (80 and 1700 nM, respectively) was explained by CH/π interactions between the indole ring in ILV and Pro241 in PKCδ [135,140].…”

“…The structurally simplest member of the family is (-)-indolactam V (ILV, 34), which can be produced in large quantities in Actinomycetes and has therefore been used as a starting point for the synthesis of new derivatives [58]. Several groups -the Irie, the Kozikowski, and the Endo groups -have carried out research into these compounds, revealed important structure-activity relationships and developed novel indolactam and benzolactam derivatives with improved selectivity profiles (see, for example, [133][134][135]). …”

“…ILV and several benzolactam derivatives have been reported to inhibit the proliferation of HL-60 leukemia cells [135,147,148]. The benzolactam 39 inhibits the proliferation of two breast carcinoma cell lines [152].…”

Challenges to the development of bryostatin‐type anticancer drugs based on the activation mechanism of protein kinase Cδ

“…5). Although 12-epi-PDBu, 85 ingenol 3-benzoate, 86 (À)-indolactam-V (ILV), 87,88 5-prenyl-ILV, 89 (3R)-indolinelactam-V (ILLV), 90 8 or 9-decylbenzolactam-V8 (BLV8), [91][92][93] bound selectively to the C1B domain of PKCd [ratio: K i (C1A)/ K i (C1B)450], 9-decyl-benzolactone-V8 (BLnV8), 94 thio-ILV, 95 and aplysiatoxin (ATX) 96,97 showed less preference for the C1B domain comparable to bryo-1 (ratio: 8.8). Especially, ATX and its artificial derivative 3-O-Me-ATX displayed an unexpected binding preference (ratio: 29 and 19, respectively), with the potent binding affinity at the nanomolar level.…”

C1 domain-targeted isophthalates as protein kinase C modulators: structure-based design, structure–activity relationships and biological activities

“…In addition, one of the carbonyl groups of the template forms a hydrogen bond with a backbone amide proton as the C3 carbonyl of phorbol-13-O-acetate. phorbol esters, DAGs and benzolactams and derivatives of them are thought to interact with either the hydrophobic amino acids surrounding the ligand binding cleft or with the hydrophobic moiety in the lipid bilayer [17,22,23]. Also hydrophobic interactions of ligands are important for high-affinity binding to the protein.…”