Figure 2. ES_I treatment protects HeLa cells from SLTx, but not from ricin.

A. ES_I treatment reduces cellular protein synthesis levels. Cells were treated with ES_I or its inactive derivative ES_R35 for 2, 3 or 5 h, and remaining protein synthesis ability was determined, shown relative to control cells treated with the vehicle DMSO. N = 3, bars +/− 1 S.D. B. ES_I treatment has no effect on ricin intoxication. Cells treated with DMSO (open symbols), ES_I (filled symbols, left-hand panel) or ES_R35 (filled symbols, right hand panel) were challenged for 1 (circles), 2 (squares) or 4 h (triangles) with graded doses of ricin and remaining protein synthesis levels were determined. Typical single assays are shown. C, D. ES_I treatment protects cells from SLTx challenge. Cells treated with DMSO, ES_I or ES_R35 were challenged with graded doses of SLTx for 1 (upper), 2 (middle) or 4 h (lower) and remaining levels of protein synthesis ability were determined. Typical single assays are shown in C, from which the IC₅₀ (concentration of SLTx that reduced protein synthesis to half that of control non-toxin treated cells treated in parallel) values were determined, and means of 3 or 4 independent experiments (+/− 1 S.D.) are shown in D, expressed as fold protection (IC₅₀ drug treated cells: IC₅₀ DMSO treated cells). Protective effects from ES_I and ES_R35 treated cells were compared using an unpaired t-test (1 h, p = 0.0048, t = 4.358, n = 4; 2 h, p<.0001, t = 12.28, n = 4; 4 h, p = 0.0377, t = 3.060, n = 3; *, significant: **, very significant: ***, extremely significant).