Effects of side chain length of 10-methyl-aplog-1, a simplified analog of debromoaplysiatoxin, on PKC binding, anti-proliferative, and pro-inflammatory activities

Effect of phenolic-hydroxy-group incorporation on the biological activity of a simplified aplysiatoxin analog with an (R)-(-)-carvone-based core

We synthesized a phenolic hydroxy group-bearing version (1) of a simplified analog of aplysiatoxin comprising a carvone-based conformation-controlling unit. Thereafter, we evaluated its antiproliferative activity against human cancer cell lines and its binding affinity to protein kinase C (PKC) isozymes. The antiproliferative activity and PKC-binding ability increased with the introduction of the phenolic hydroxy group. The results of molecular dynamics simulations and subsequent relative binding free-energy calculations conducted using an alchemical transformation procedure showed that the phenolic hydroxy group in 1 could form a hydrogen bond with a phospholipid and the PKC. The former hydrogen bonding formation facilitated the partitioning of the compound from water to the phospholipid membrane and the latter compensated for the loss of hydrogen bond with the phospholipid upon binding to the PKC. This information may facilitate the development of rational design methods for PKC ligands with additional hydrogen bonding groups.

Biological evaluation of a phosphate ester prodrug of 10-methyl-aplog-1, a simplified analog of aplysiatoxin, as a possible latency-reversing agent for HIV reactivation

10-Methyl-aplog-1 (10MA-1), a simplified analog of aplysiatoxin, exhibits a high binding affinity for protein kinase C (PKC) isozymes with minimal tumor-promoting and pro-inflammatory activities. A recent study suggests that 10MA-1 could reactivate latent human immunodeficiency virus (HIV) in vitro for HIV eradication strategy. However, further in vivo studies were abandoned by a dose limit caused by the minimal water solubility of 10MA-1. To overcome this problem, we synthesized a phosphate ester of 10MA-1, 18-O-phospho-10-methyl-aplog-1 (phos-10MA-1), to improve water solubility for in vivo studies. The solubility, PKC binding affinity, and biological activity of phos-10MA-1 were examined in vitro, and the biological activity was comparable with 10MA-1. The pharmacokinetic studies in vivo were also examined, which suggest that further optimization for improving metabolic stability is required in the future.

Invivo anti-cancer activity of 10-methyl-aplog-1, a simplified analog of aplysiatoxin, and its possible signaling pathway associated with G1 arrest

Naturally occurring protein kinase C (PKC) activators such as phorbol esters, teleocidins, and aplysiatoxins, have the potential to become anti-cancer agents, since they are anti-proliferative against specific cancer cell lines in vitro. However, their potent tumor-promoting and proinflammatory activities have hampered their clinical uses. Recently, we developed 10-methyl-aplog-1 (1), a simplified analog of tumor-promoting debromoaplysiatoxin (DAT), which retained anti-proliferative activity comparable to DAT, but induced neither tumorigenesis nor inflammation on mouse skin. Our previous study suggested that PKCα and δ were involved in the cell line-selective anti-proliferative activity of 1, but the downstream signaling of PKC isozymes remained unknown. In this study, we confirmed that 1 inhibited the growth of three aplog-sensitive cancer cell lines (NCI-H460, HCC-2998, and HBC-4) without severe side effects in mice xenograft models. In addition, in vitro analysis using A549, one of the aplog-sensitive cell lines in vitro, revealed that PKCα induced PP2A-mediated attenuation of the Akt/S6 signaling axis. Since S6 inhibition in A549 was reported to result in G1 arrest, this pathway could be involved in the PKCα-dependent anti-proliferative activity of 1.

AI and computational chemistry-accelerated development of an alotaketal analogue with conventional PKC selectivity

The protein kinase C (PKC) family consists of ten isozymes and is a potential target for treating cancer, Alzheimer’s disease, and HIV infection. Since known natural PKC agonists have little...

Synthesis and biological activities of simplified aplysiatoxin analogs focused on the CH/π interaction

Debromoaplysiatoxin (DAT) is a potent protein kinase C (PKC) activator with tumor-promoting and pro-inflammatory activities. Irie and colleagues have found that 10-methyl-aplog-1 (1), a simplified analog of DAT, has strong anti-proliferative activity against several cancer cell lines with few adverse effects. Therefore, 1 is a potential lead compound for cancer therapy. We synthesized a new derivative 2 which has a naphthalene ring at the side chain terminal position instead of a benzene ring, to increase CH/π interactions with Pro-241 of the PKCδ-C1B domain. Based on the synthetic route of 1, 2 was convergently synthesized in 26 linear steps from 6-hydroxy-1-naphthoic acid with an overall yield of 0.18%. Although the anti-proliferative activity of 2 was more potent than that of 1, the binding potency of 2 to the PKCδ-C1B domain did not exceed that of 1. Molecular dynamics simulation indicated the capability of 2 to simultaneously form hydrogen bonds and CH/π interactions with the PKCδ-C1B domain. Focusing on the hydrogen bonds, their geometry in the binding modes involving the CH/π interactions seemed to be sub-optimal, which may explain the slightly lower affinity of 2 compared to 1. This study could be of help in optimizing such interactions and synthesizing a promising lead cancer compound.