Sapintoxin D is a weak tumour promoter in Sencar mouse skin

Antiviral Activity of Diterpene Esters on Chikungunya Virus and HIV Replication

Recently, new daphnane, tigliane, and jatrophane diterpenoids have been isolated from various Euphorbiaceae species, of which some have been shown to be potent inhibitors of chikungunya virus (CHIKV) replication. To further explore this type of compound, the antiviral activity of a series of 29 commercially available natural diterpenoids was evaluated. Phorbol-12,13-didecanoate (11) proved to be the most potent inhibitor, with an EC50 value of 6.0 ± 0.9 nM and a selectivity index (SI) of 686, which is in line with the previously reported anti-CHIKV potency for the structurally related 12-O-tetradecanoylphorbol-13-acetate (13). Most of the other compounds exhibited low to moderate activity, including an ingenane-type diterpene ester, compound 28, with an EC50 value of 1.2 ± 0.1 μM and SI = 6.4. Diterpene compounds are known also to inhibit HIV replication, so the antiviral activities of compounds 1-29 were evaluated also against HIV-1 and HIV-2. Tigliane- (4β-hydroxyphorbol analogues 10, 11, 13, 15, 16, and 18) and ingenane-type (27 and 28) diterpene esters were shown to inhibit HIV replication in vitro at the nanomolar level. A Pearson analysis performed with the anti-CHIKV and anti-HIV data sets demonstrated a linear relationship, which supported the hypothesis made that PKC may be an important target in CHIKV replication.

Some phorbol esters might partially resemble bryostatin 1 in their actions on LNCaP prostate cancer cells and U937 leukemia cells

Phorbol 12-myristate 13-acetate (PMA) and bryostatin 1 are both potent protein kinase C (PKC) activators. In LNCaP human prostate cancer cells, PMA induces tumor necrosis factor alpha (TNFα) secretion and inhibits proliferation; bryostatin 1 does not, and indeed blocks the response to PMA. This difference has been attributed to bryostatin 1 not localizing PKCδ to the plasma membrane. Since phorbol ester lipophilicity influences PKCδ localization, we have examined in LNCaP cells a series of phorbol esters and related derivatives spanning some eight logs in lipophilicity (logP) to see if any behave like bryostatin 1. The compounds showed marked differences in their effects on proliferation and TNFα secretion. For example, maximal responses for TNFα secretion relative to PMA ranged from 97 % for octyl-indolactam V to 24 % for phorbol 12,13-dibenzoate. Dose-response curves ranged from monophasic for indolactam V to markedly biphasic for sapintoxin D. The divergent patterns of response, however, correlated neither to lipophilicity, to plasma membrane translocation of PKCδ, nor to the ability to interact with model membranes. In U937 human leukemia cells, a second system in which PMA and bryostatin 1 have divergent effects, viz. PMA but not bryostatin 1 inhibits proliferation and induces attachment, all the compounds acted like PMA for proliferation, but several induced a reduced level or a biphasic dose-response curve for attachment. We conclude that active phorbol esters are not all equivalent. Depending on the system, some might partially resemble bryostatin 1 in their behavior; this encourages the concept that bryostatin-like behavior may be obtained from other structural templates.

Pharmacological evaluation of ricinine, a central nervous system stimulant isolated from Ricinus communis

The extract of the pericarp of castor bean (Ricinus communis) showed some typical central nervous system stimulant effects when administered to mice. The animals became exophthalmic, presented tremors and clonic seizures and died a few minutes after receiving larger doses of the extract. At lower doses the extract improved memory consolidation and showed some neuroleptic-like properties, such as a decrease in exploratory behavior and catalepsy. The memory-improving effect and the seizure-eliciting properties of the extract were also observed with the administration of ricinine, a neutral alkaloid isolated from the extract. However, the neuroleptic-like properties of the extract were not observed with ricinine. As the therapeutic index of ricinine is of the order of 200, the compound may be considered as a promising cognition-enhancing drug that may be used for the treatment of human amnesias.