Drugs that show protective effects from ricin toxicity in in vitro protein synthesis assays

Abstract

We used an in-vitro, inhibition of protein synthesis assay (PSI) to test a wide variety of drugs for possible therapeutic use against ricin, a toxic glycoprotein that causes death in animals by inhibiting protein synthesis. Selection of test drugs was based on possible interference with ricin activity at different stages of the toxic process. Most of the drugs tested had no effect on ricin-induced PSI, were toxic when tested alone, or enhanced the toxicity of ricin. The only ones showing protection were galactose, lactose, and several derivatives of these sugars, Brefeldin A (BFA), 3'-azido-3'-deoxythymidine (AZT), and a purine derivative (BM33203). THe sugar derivatives provided 50% protection against a PSI ED99 of ricin (0.1 micrograms/ml). Concentrations of BFA greater than 0.5 micro M caused about 50% PSI by itself, but blocked any further inhibitory effects of ricin. AZT, at optimum concentrations, reached a maximum protection level of about 40% in the presence of an ED99 dose of ricin, while the nucleoside derivative, BM33203 and AZT appeared to have an additive effect, showing up to 80% protection from an ED99 dose of ricin. Drugs showing protection in the PSI cell assay showed no protection from ricin in a cell-free translation assay used to determine if they would block ricin at the protein synthesis site.

Inhibitors of Intravesicular Acidification Protect Against Shiga Toxin in a pH‐Independent Manner

“…As shown in Figure C,D, bafilomycin A1 treatment sensitized HEp‐2 cells to ricin. This is in agreement with earlier observations that bafilomycin, nigericin and chloroquine sensitize CHO and Vero cells to ricin ( ), suggesting that the inhibitors do not block retrograde transport in general.…”

Medical Countermeasures against Ricin Intoxication

“…The ilimaquinone blocks the cytotoxicity of ricin in Vero cells in a dose-dependent manner by disruption of the Golgi apparatus and its fragmentation into small vesicular structures [ 108 , 109 ]. Similarly, brefeldin A (BFA), an isoprenoid fungal metabolite, inhibits ricin toxicity in vitro by dismantling the structure and function of the Golgi apparatus [ 110 , 111 ]. However, BFA irreversibly impairs intracellular protein transport and secretion and sensitizes some cell lines to ricin (MDCK and PtK2 kidney epithelial cell lines) [ 112 ].…”

Ricin Toxin

“…In recent years, a wide variety of chemotheraputic agents has systematically been screened in an in vitro Vero cell inhibition of protein synthesis assay for efficacy against ricin toxicity. 55 More than 150 agents, including cellular membrane effectors, calcium channel-blocking agents, sodium-calcium exchangers, reducing agents, antioxidants, effectors of endocytosis, nucleoside derivatives, antibacterials, ricin analogs, effectors of cellular metabolism, and competitors for binding have been tested. Of these, only five agents showed promise in vitro and were screened in mouse-protection assays:…”