11alpha-13-dihydrohelenalin and Carcinoma--Ehrlich-Tumor

This study deals with the cytotoxicity of helenanolide-type (10 alpha-methylpseudoguaianolide) sesquiterpene lactones. We determined the influence of substitution patterns on the toxicity of 21 helenanolides to a cloned Ehrlich ascites tumor cell line, EN2. Within a series of helenalin esters, the acetate (2) and isobutyrate (3) were more toxic than helenalin itself (1). Esters with larger acyl groups (tiglate 4 and isovalerate 5) exhibited a decreased toxicity compared with the parent alcohol (1). Similar relationships were observed between the 6,8-diastereomer of helenalin, mexicanin I (6) and its acetate (7) and isovalerate (8). In contrast, cytotoxicity within a series of 11 alpha, 13-dihydrohelenalin esters (9-12) was shown to be directly related to the size and lipophilicity of the ester side chain, dihydrohelenalin (9) being the least toxic compound in this group. Investigation of several 2,3-dihydrohelenalin derivatives (13-21) with 2 alpha-hydroxy-4-oxo- and 2 alpha,4 alpha-dihydroxy- or -O-acyl-substituted cyclopentane rings (arnifolins and chamissonolides, respectively), for which no pharmacological data have been reported so far, revealed further interesting influences of the substitution pattern on cytotoxicity. The results may be interpreted in terms of lipophilicity and steric effects on the accessibility of the reactive sites considered responsible for biological activity.

Topics: Animals; Antineoplastic Agents, Phytogenic; Carcinoma, Ehrlich Tumor; Chromatography, High Pressure Liquid; Computer Simulation; Drug Screening Assays, Antitumor; Lactones; Mice; Models, Structural; Molecular Conformation; Sesquiterpenes; Structure-Activity Relationship; Tetrazolium Salts; Thiazoles; Tumor Cells, Cultured

Evidence is presented that sesquiterpene lactones or ketones containing the O=CC=CH2 moiety, e.g., tenulin and helenalin, alkylate the thiol group of reduced glutathione and L-cysteine in vitro. A proposal is offered that this mechanism of action is responsible for the observed potent in vivo antitumor activity of these agents in the Ehrlich ascites and Walker 256 carcinosarcoma and to a lesser extent in the P388 leukemic screen. Inhibition of tumor growth is thought to occur due to the O=CC=CH2 system alkylating by rapid Michael addition the SH biological nucleophiles of key regulatory enzymes of nucleic acid and chromatin metabolism. This proposition is in accord with the ability of these agents to inhibit DNA synthesis and gene activity of Ehrlich ascites cells.

Topics: Animals; Antineoplastic Agents, Phytogenic; Ascitic Fluid; Carcinoma 256, Walker; Carcinoma, Ehrlich Tumor; Chromatin; Cyclopentanes; Cysteine; DNA, Neoplasm; Glutathione; Histidine; Lactones; Leukemia, Experimental; Leukemia, Lymphoid; Male; Mice; Mice, Inbred DBA; Neoplasm Proteins; Rats; Sesquiterpenes; Sesquiterpenes, Guaiane; Spectrophotometry, Ultraviolet; Time Factors