Dimethylaminopyridine derivatives of lupane triterpenoids cause mitochondrial disruption and induce the permeability transition

Triterpenoids are a large class of naturally occurring compounds, and some potentially interesting as anticancer agents have been found to target mitochondria. The objective of the present work was to investigate the mechanisms of mitochondrial toxicity induced by novel dimethylaminopyridine (DMAP) derivatives of pentacyclic triterpenes, which were previously shown to inhibit the growth of melanoma cells in vitro. MCF-7, Hs 578T and BJ cell lines, as well as isolated hepatic mitochondria, were used to investigate direct mitochondrial effects. On isolated mitochondrial hepatic fractions, respiratory parameters, mitochondrial transmembrane electric potential, induction of the mitochondrial permeability transition (MPT) pore and ion transport-dependent osmotic swelling were measured. Our results indicate that the DMAP triterpenoid derivatives lead to fragmentation and depolarization of the mitochondrial network in situ, and to inhibition of uncoupled respiration, induction of the permeability transition pore and depolarization of isolated hepatic mitochondria. The results show that mitochondrial toxicity is an important component of the biological interaction of DMAP derivatives, which can explain the effects observed in cancer cells.     

Oxidation at C-16 enhances butyrylcholinesterase inhibition in lupane triterpenoids

A set of triterpenoids with different grades of oxidation in the lupane skeleton were prepared and evaluated as cholinesterase inhibitors. Allylic oxidation with selenium oxide and Jones’s oxidation were employed to obtain mono-, di- and tri-oxolupanes, starting from calenduladiol (1) and lupeol (3). All the derivatives showed a selective inhibition of butyrylcholinesterase over acetylcholinesterase (BChE vs. AChE). A kinetic study proved that compounds 2 and 9, the more potent inhibitors of the series, act as competitive inhibitors. Molecular modeling was used to understand their interaction with BChE, the role of carbonyl at C-16 and the selectivity towards this enzyme over AChE. These results indicate that oxidation at C-16 of the lupane skeleton is a key transformation in order to improve the cholinesterase inhibition of these compounds.     

New derivatives of lupane triterpenoids disturb breast cancer mitochondria and induce cell death

Novel cationic dimethylaminopyridine derivatives of pentacyclic triterpenes were previously described to promote mitochondrial depolarization and cell death in breast and melanoma cell lines. The objective of this work was to further investigate in detail the mechanism of mitochondrial perturbations, correlating those effects with breast cancer cell responses to those same agents. Initially, a panel of tumor and non-tumor cell lines was grown in high-glucose or glucose-free glutamine-containing media, the later forcing cells to synthesize ATP by oxidative phosphorylation only. Cell proliferation, cell cycle, cell death and mitochondrial membrane polarization were evaluated. Inhibition of cell proliferation was observed, accompanied by an arrest in the G1-cell cycle phase, and importantly, by loss of mitochondrial membrane potential. On a later time-point, caspase-9 and 3 activation were observed, resulting in cell death. For the majority of test compounds, we determined that cell toxicity was augmented in the galactose media. To investigate direct evidences on mitochondria isolated rat liver mitochondria were used. The results showed that the compounds were strong inducers of the permeability transition pore. Confirming our previous results, this work shows that the novel DMAP derivatives strongly interact with mitochondria, resulting in pro-apoptotic signaling and cell death.     

Study of skin anti-ageing and anti-inflammatory effects of dihydroquercetin, natural triterpenoinds, and their synthetic derivatives

Accessible triterpenoids of ursane and lupane series, the flavonoid dihydroquercetin and their synthetic derivatives with polar substituents were tested in vitro for inhibition of collagenase 1 (MMP-1) in UVB irradiation assay. Ursolic acid and uvaol disuccinate were the most active inhibitors in the ursane series. In the lupane series, the best inhibition was manifested by carboxymethyl ester of betulonic acid and betulin succinates. Down- regulation of MMP-1 by dihydroquercetin and its synthetic derivatives surpassed the activity of a standard (retinoic acid).     

Rapid access to new bioconjugates of betulonic acid via click chemistry

Plant-derived pentacyclic triterpenoids of lupane and oleanane families provide a versatile structural platform for the discovery of new biologically active compounds. A number of semisynthetic derivatives of these molecules, possess high medical efficiency including antiviral (HIV-1), anticancer and immunomodulating activity. Even small structural changes in these triterpenoid derivatives were reported to lead to significant changes in their activity, making a convincing case for a systematic study of structure-activity relationships in this class of compounds.Our earlier work opened synthetic access to alkynes derived from the betulonic scaffold and enabled the development of a new family of biohybrids using Click Chemistry (CC). The computer-aided prediction of several types of biological activity were performed with program PASS (Prediction Activity Spectra of Substances. Experimental studies based on mouse models verified the SAR predictions obtained by the PASS program. The observed correlation between the anti-inflammatory and antioxidant activity indicates substantial contribution of the latter in the mechanism of anti-inflammatory effect of the triazole derivatives of betulonic acid.     

Biological activity and pharmacological prospects of lupane terpenoids: II. Semisynthetic lupane derivatives

The discussion of lupane triterpenoids as prospective medicinal preparations is continued, and semisynthetic triterpenoids are being discussed. Acyl derivatives that mainly exhibit high anti-HIV, antitumor, and organoprotective activities are described.     

Triterpenoids from Salvia deserta

From the aerial parts of Salvia deserta a new oleanane and two new lupane triterpenoids have been isolated, together with five already known ursane, oleanane and lupane derivatives. The structures of the new substances were established by spectroscopic means.     

Anti-HIV activity of natural triterpenoids and hemisynthetic derivatives 2004–2009

The continued advance of HIV-AIDS makes the development of relatively inexpensive, freely accessible, and mechanistically more diverse antiviral therapies an urgent need. Natural products are, directly or indirectly, an important potential source of compounds meeting these conditions. A review of the recent literature indicates that some hemisynthetic triterpenoid derivatives, particularly belonging to the lupane, oleanane and ursane series, may be nearing a stage where they can be used to complement existing therapeutic approaches. On the other hand, although some natural derivatives of tetracyclic terpenoid families have revealed many novel structures and some promise as anti-HIV substances, their chemical modification to improve their potency and selectivity remains practically untouched. While ongoing work with the more ‘classical’ pentacyclic triterpenoids will continue to be a fertile field for HIV-AIDS drug discovery, the other structural groups offer unprecedented opportunities for the development of additional substances with useful properties and for the discovery of novel targets for antiviral therapy.     

Biological activity and pharmacological prospects of lupane terpenoids: II. Semisynthetic lupane derivatives

The discussion of lupane triterpenoids as prospective medicinal preparations is continued, and semisynthetic triterpenoids are being discussed. Acyl derivatives that mainly exhibit high anti-HIV, antitumor, and organo-protective activities are described. The English version of the paper: Russian Journal of Bioorganic Chemistry, 2006, vol. 32, no. 3; see also http://www.maik.ru.     

Inhibition of rat renal 11 beta-hydroxysteroid dehydrogenase by steroidal compounds and triterpenoids; structure/function relationship

Various compounds with steroidal structure were tested for inhibitory effects on enzymatic activity of 11 beta-hydroxysteroid dehydrogenase (11 beta-HSD) from rat renal microsomes. Most substances exerting inhibitory potency on both the oxidative as well as the reductive activity can be classified into two main groups: pentacyclic triterpenoids of the oleane type and steroidal detergents of the CHAPS-series. Inhibition is competitive, as was shown for one compound of each group. The IC50 values of the various inhibitors range over five orders of magnitude. In all cases, oxidative activity was inhibited more effectively than reductive activity. An attempt has been made to correlate structural properties and inhibitory potency. In brief, inhibition seems to be enhanced by a C11-oxygen function, which is present in all endogenous glucocorticosteroids and a C7-OH function. Inhibition is reduced by a large and polar substituent at C3 in the A-ring. A large D-ring substituent, such as a bisgluconamidopropyl side chain or even an additional E-ring, does not prevent binding to the enzyme, although inhibition seems to be influenced by its steric conformation. The cardiac glycosides and steroidal antibiotics tested exert no inhibitory effect on 11 beta-HSD. Cholesterol and pentacyclic triterpenoids of the lupane type exhibit a very poor inhibition, probably caused by the localization of planar structures in the ring systems, which differs from that of the effective oleane type inhibitors.     

Immunomodulatory triterpenoids from the oleogum resin of Boswellia carterii Birdwood

The immunomodulatory bioassay-guided fractionation of the oleogum resin of frankincense (Boswellia carterii Birdwood) resulted in the isolation and identification of 9 compounds; palmitic acid and eight triterpenoids belonging to lupane, ursane, oleanane, and tirucallane skeleta were isolated form the resin. These triterpenoids are lupeol, beta-boswellic acid, 11-keto-beta-boswellic acid, acetyl beta-boswellic acid, acetyl 11-keto-beta-boswellic acid, acetyl-alpha-boswellic acid, 3-oxo-tirucallic acid, and 3-hydroxy-tirucallic acid. The structures of the isolated compounds were deduced based on spectroscopic evidences. The lymphocyte transformation assay of the isolated compounds proved that the total extract retained more activity than that of any of the purified compounds.     

Oleanane triterpenoids in the prevention and therapy of breast cancer: current evidence and future perspectives

Breast cancer is one of the most frequently diagnosed cancers and major cause of death in women in the world. Emerging evidence underscores the value of dietary and non-dietary phytochemicals, including triterpenoids, in the prevention and treatment of breast cancer. Oleanolic acid, an oleanane-type pentacyclic triterpenoid, is present in a large number of dietary and medicinal plants. Oleanolic acid and its derivatives exhibit several promising pharmacological activities, including antioxidant, anti-inflammatory, hepatoprotective, cardioprotective, antipruritic, spasmolytic, antiallergic, antimicrobial and antiviral effects. Numerous studies indicate that oleanolic acid and other oleanane triterpenoids modulate multiple intracellular signaling pathways and exert chemopreventive and antitumor activities in various in vitro and in vivo model systems. A series of novel synthetic oleanane triterpenoids have been prepared by chemical modifications of oleanolic acid and some of these compounds are considered to be the most potent anti-inflammatory and anticarcinogenic triterpenoids. Accumulating studies provide extensive evidence that synthetic oleanane derivatives inhibit proliferation and induce apoptosis of various cancer cells in vitro and demonstrate cancer preventive or antitumor efficacy in animal models of blood, breast, colon, connective tissue, liver, lung, pancreas, prostate and skin cancer. This review critically examines the potential role of oleanolic acid, oleanane triterpenoids and related synthetic compounds in the chemoprevention and treatment of mammary neoplasia. Both in vitro and in vivo studies on these agents and related molecular mechanisms are presented. Several challenges and future directions of research to translate already available impressive preclinical knowledge to clinical practice of breast cancer prevention and therapy are also presented.     

Biological activity and pharmacological prospects of lupane terpenoids: I. natural lupane derivatives

The biological activity of natural and semisynthetic lupane triterpenoids is discussed in a two-part review. The first part is devoted to the pharmacological properties of natural lupane triterpenoids. Betulinic acid has proven to be the most effective antitumor agent among more than fifty natural lupanes.     

Biological activity and pharmacological prospects of lupane terpenoids: I. Natural lupane derivatives

The biological activity of natural and semisynthetic lupane triterpenoids is discussed in a two-part review. The first part is devoted to the pharmacological properties of natural lupane triterpenoids. Betulinic acid has proven to be the most effective antitumor agent among more than fifty natural lupanes.     

Synthesis and Pharmacological Activity of Betulin Dinicotinate

The assignment of NMR resonances of lupane triterpenoids was refined by the example of 3O,28O-dinicotinoylbetulin, obtained by acylation of betulin. Hepatoprotective, antiulcer, antiinflammatory, reparative, and anti-HIV activities were found for the compound. In addition, it was demonstrated to have immunomodulatory activity, for the first time detected among lupane triterpenoids.     

Cytotoxic heterocyclic triterpenoids derived from betulin and betulinic acid

The aim of this work was to synthesize a set of heterocyclic derivatives of lupane, lup-20(29)-ene, and 18α-oleanane, and to investigate their cytotoxic activities. Some of those heterocycles were previously known in the oleanane (allobetulin) group; however, to our knowledge the syntheses and biological activities of lupane heterocycles have not been reported before. Starting from betulin (1) and betulinic acid (2), we prepared 3-oxo compounds and 2-bromo-3-oxo compounds 3-10, 2-hydroxymethylene-3-oxo compounds 11-13 and β-oxo esters 14-16. Condensation of these intermediates with hydrazine, phenylhydrazine, hydroxylamine, or thiourea yielded the pyrazole and phenylpyrazole derivatives 17-22, pyrazolones 23-25, isoxazoles 26 and 27, and thiazoles 28-31. Fifteen compounds (14-16, 18-25, and 29-32) have not been reported before. The cytotoxicity was measured using panel of seven cancer cell lines with/without MDR phenotype and non tumor MRC-5 and BJ fibroblasts. The preferential cytotoxicity to cancer cell lines, particularly to hematological tumors was observed, the bromo acids 5, 6 showed highest activity and selectivity against tumor cells.     

Synthesis and cytotoxicity of lupane-type triterpenoid glyceryl esters

A new series of betulinic acid and betulin derivatives were synthesized by introducing a D-glycerol moiety at the C-3 and/or C-28 positions of the lupane skeleton. The resulting glyceryl esters were evaluated in vitro for their cytotoxic activity against A549, DLD-1 and WS1 human cell lines. The structure-activity relationships study revealed that the incorporation of a glycerol unit at the C-3 or C-28 position of the lupane core resulted in compounds exhibiting potent cytotoxic activity together with decreased liposolubility.     

4-Quinolones cause a selective loss of mitochondrial DNA from mouse L1210 leukemia cells

The 4-quinolone antibiotics nalidixic acid and ciprofloxacin and potent inhibitors of the bacterial type II topoisomerase DNA gyrase. Treatment of mouse L1210 leukemia cells with these drugs resulted in a delayed inhibition of cell proliferation. Prior to inhibition of cell proliferation, there was a time-dependent decrease in the cellular content of mitochondrial DNA (mtDNA). The decrease in mtDNA was associated with a decrease in the rate of mitochondrial respiration and an increase in the concentration of lactate in the growth medium. Inhibition of cell proliferation by 4-quinolones was reversible upon drug washout. However, there was a 2- to 4-day lag before the growth rate returned to normal levels. This was preceeded by an increase in mtDNA content and mitochondrial respiration. These studies suggest that inhibition of mammalian cell proliferation by 4-quinolone drugs is related to the selective depletion of mtDNA. © 1993 Wiley-Liss, Inc.     

Synthesis and pharmacological activity of betulin dinicotinate

The assignment of NMR resonances of lupane triterpenoids was refined by the example of 3,28-dinicotinoylbetulin, obtained by acylation of betulin. Hepatoprotective, untiulcer, antiinflammatory, reparative, and anti-HIV activities were found for the compound. In addition, it was demonstrated to have immunomodulatory activity, for the first time detected among lupane triterpenoids. The English version of the paper: Russian Journal of Bioorganic Chemistry, 2002, vol. 28, no. 6; see also http://www.maik.ru.     

Active derivatives of oligonucleotides with a zwitterionic terminal phosphate group for design of affinity reagents and probes

Method of synthesis and isolation of oligonucleotide derivatives with a zwitterionic terminal phosphate group, containing N-methylimidazole (MeIm), 4-dimethylaminopyridine (DMAP) or 4-dimethylaminopyridine 1-oxide (DMAPO) residues has been developed. Mononucleotide derivatives were used to study the reactivity of these compounds to various nucleophiles and the dependence of hydrolysis rate on pH of solution. These compounds interact rapidly and quantitatively with aliphatic amines and much slower with water, aniline and methanol. MeIm derivatives are most active to nucleophiles, whereas the reactivity of DMAP derivatives is ca. 5 times lower and that of DMAPO derivatives is lower by 2 order of magnitude. This method of activating terminal phosphate group is promising for synthesis of various oligonucleotide phosphoramidates.