Recent results show that a-tocopheryl succinate (a-TOS) is a proapoptotic agent with antineoplastic activity. As modifications of the vitamin E (VE) molecule may affect its apoptogenic activity, we tested a number of newly synthesised VE analogues using malignant cell lines. Analogues of a-TOS with lower number of methyl substitutions on the aromatic ring were less active than a-TOS. Replacement of the succinyl group with a maleyl group greatly enhanced the activity, while it was lower for the glutaryl esters. Methylation of the free succinyl carboxyl group on a-TOS and d-TOS completely prevented the apoptogenic activity of the parent compounds. Both Trolox and its succinylated derivative were inactive. a-tocotrienol (a-T3 H) failed to induce apoptosis, while g-T3 H was apoptogenic, and more so when succinylated. Shortening the aliphatic side chain of g-T3 by one isoprenyl unit increased its activity. Neither phytyl nor oleyl succinate caused apoptosis. These findings show that modifications of different functional moieties of the VE molecule can enhance apoptogenic activity. It is hoped that these observations will lead to the synthesis of analogues with even higher apoptogenic and, consequently, antineoplastic efficacy.

Vitamin E (VE) analogues, epitomized by a-tocopheryl succinate (a-TOS), are proapoptotic agents with selective antineoplastic activity. The molecule of a-TOS comprises several structurally and functionally distinct moieties that can be modified in order to yield analogues with higher activity. In order to find analogues with higher apoptogenic efficacy, we prepared novel compounds where the ester bond was replaced by an amide bond. All of these analogues were significantly more proapoptotic than their ester counterparts, with a-tocopheryl maleyl amide being the most effective. Importantly, methylation of the free carboxylic group completely obliterated apoptogenic activity of the compounds. Similarly as shown for the ester analogues, the amides induced apoptosis by mitochondrial destabilization. Superiority of amides over the ester analogues may be due to their higher partitioning into the lipid phase, as suggested by the log p-values that were lower for the amides than the corresponding esters. In conclusion, we present evidence that modification of the ester bond of agents such as a-TOS can be used as a basis for generating novel analogues with higher efficacy of killing malignant cells, an activity that suggests anticancer effect of the agents. ' 2005 Wiley-Liss, Inc.

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