Semi-synthesis and antiproliferative evaluation of PEGylated pentacyclic triterpenes.

Several PEGylated derivatives of oleanolic and maslinic acids have been semi-synthesized, attaching one acid-PEG reagent to the hydroxyl group/s at C-2 or C-2/C-3 of the A rings of these natural triterpenes, and also to their corresponding C-28 benzyl derivatives. Several monomeric and dimeric PEGylated compounds have also been produced by linking one diamine-PEG reagent to the carboxyl group at C-28 of the same natural triterpenes and also to their corresponding C-2 or C-2/C-3 acetylated derivatives. The cytotoxic effects of 12 triterpenic PEGylated derivatives in three cancer-cell lines (B16F10, HT29, and Hep G2) have been assayed. The best results have been achieved by the PEGylated-amine derivative of oleanolic acid, with IC50 concentrations between 0.22 and 3.78 µM, being between 28- and 963-fold more effective than its natural precursor. The percentages of apoptosis induction have also been determined for the five PEGylated derivatives with the lowest cytotoxicity data. All five compounds showed apoptotic effects on the treated cells, with a total apoptosis rate of 99% in the B16F10 cells, 80% in the Hep G2 cells, and 51% in the HT29 cells. We have also studied the changes in the mitochondrial membrane potential (MMP) to elucidate the possible mechanism involved in the apoptotic responses (intrinsic or extrinsic). Finally, to verify the results found in the cytometry assays, we have used fluorescence microscopy techniques to determine changes in the cell morphology. These PEGylated derivatives of natural triterpenoids, which can induce apoptosis at very low concentrations in different tumour lines, may represent new effective therapeutic drugs against these diseases.

Solid-phase library synthesis of bi-functional derivatives of oleanolic and maslinic acids and their cytotoxicity on three cancer cell lines.

A wide set of 264 compounds has been semisynthesized with high yields and purities. These compounds have been obtained through easy synthetic processes based on a solid-phase combinatorial methodology. All the members of this library have one central core of a natural pentacyclic triterpene (oleanolic or maslinic acid) and differ by 6 amino acids, coupled with the carboxyl group at C-28 of the triterpenoid skeleton, and by 10 different acyl groups attached to the hydroxyl groups of the A-ring of these molecules. According to the literature on the outstanding and promising pharmacological activities of other similar terpene derivatives, some of these compounds have been tested for their cytotoxic effects on the proliferation of three cancer cell lines: B16-F10, HT29, and Hep G2. In general, we have found that around 70% of the compounds tested show cytotoxicity in all three of the cell lines selected; around 60% of the cytotoxic compounds are more effective than their corresponding precursors, that is, oleanolic (OA) or maslinic (MA) acids; and nearly 50% of the cytotoxic derivatives have IC50 values between 2- to 320-fold lower than their corresponding precursor (OA or MA).

Semi-synthesis of acylated triterpenes from olive-oil industry wastes for the development of anticancer and anti-HIV agents.

A broad set of potential bioactive conjugate compounds has been semi-synthesized through solution- and solid-phase organic procedures, coupling two natural pentacyclic triterpene acids, oleanolic (OA) and maslinic acids (MA), at the hydroxyl groups of the A-ring of the triterpene skeleton, with 10 different acyl groups. These acyl OA and MA derivatives have been tested for their anti-proliferative (against the b16f10 murine melanoma cancer cells) and antiviral (as inhibitors of the HIV-1-protease) effects. Several derivatives have shown high levels of early and total apoptosis (up to 90%). Most of the compounds that exhibited anti-proliferative effects also generated ROS, probably involving the activation of an intrinsic apoptotic route. The only four compounds that did not cause the release of ROS could be related to the participation of a probable extrinsic activation of the apoptosis mechanism. A great number of these acyl OA and MA derivatives have proved to be potent inhibitors of the HIV-1-protease, the most active inhibitors having IC50 values between 0.31 and 15.6 µM, these values being between 4 and 186 times lower than their non-acylated precursors. The potent activities exhibited in the apoptosis-activation processes and in the inhibition of the HIV-1-protease by some OA and MA acylated derivatives imply that these compounds could be used as new, safe, and effective anticancer and/or antiviral drugs.

Maslinic acid derivatives induce significant apoptosis in b16f10 murine melanoma cells.

Maslinic acid (2α,3ß-dihydroxyolean-12-en-28-oic acid), a natural dihydroxylated pentacyclic triterpene acid isolated from olive-pressing residues, has been investigated together with some of its derivatives regarding the induction of apoptosis in B16F10 melanoma cells. Some of the compounds tested are described in this work, but others come from previous studies. Ten of these derivatives induce over 80% of apoptosis, clearly promoting cell death in B16F10 melanoma. By contrast, the induction cell death through necrosis was very slightly significant with these compounds. These results indicate that maslinic acid derivatives are promising chemopreventive and chemotherapeutic agents.