3D model (JSmol)
|Molar mass||456.71 g·mol−1|
|Melting point||316 to 318 °C (601 to 604 °F; 589 to 591 K)|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|what is ?)(|
Betulinic acid is a naturally occurring pentacyclic triterpenoid which has antiretroviral, antimalarial, and anti-inflammatory properties, as well as a more recently discovered potential as an anticancer agent, by inhibition of topoisomerase. It is found in the bark of several species of plants, principally the white birch (Betula pubescens) from which it gets its name, but also the ber tree (Ziziphus mauritiana), selfheal (Prunella vulgaris), the tropical carnivorous plants Triphyophyllum peltatum and Ancistrocladus heyneanus, Diospyros leucomelas, a member of the persimmon family, Tetracera boiviniana, the jambul (Syzygium formosanum), flowering quince (Pseudocydonia sinensis, former Chaenomeles sinensis KOEHNE), rosemary, and Pulsatilla chinensis.
In 1995, betulinic acid was reported as a selective inhibitor of human melanoma. Then it was demonstrated to induce apoptosis in human neuroblastoma in vitro and in vivo in model systems. At one time, it was undergoing drug development with assistance from the Rapid Access to Intervention Development program of the National Cancer Institute. Also, betulinic acid was found active in vitro against neuroectodermal (neuroblastoma, medulloblastoma, Ewing's sarcoma) and malignant brain tumors, ovarian carcinoma, in human leukemia HL-60 cells, and malignant head and neck squamous cell carcinoma SCC25 and SCC9 cell lines. In contrast, epithelial tumors, such as breast, colon, small cell lung and renal cell carcinomas, as well as T-cell leukemia cells, were completely unresponsive to treatment with betulinic acid.
Mode of action
Regarding the mode of action of betulinic acid, little is known about its antiproliferative and apoptosis-inducing mechanisms. In neuroectodermal tumor cells, betulinic acid–induced apoptosis is accompanied by caspase activation, mitochondrial membrane alterations and DNA fragmentation. Caspases are produced as inactive proenzymes, which are proteolytically processed to their active forms. These proteases can cooperate in proteolytic cascades, in which caspases activate themselves and each other. The initiation of the caspases cascade may lead to the activation of endonucleases such as caspase-activated DNAase (CAD). After activation, CAD contributes to DNA degradation. Betulinic acid induces apoptosis by direct effects on mitochondria, leading to cytochrome-C release, which in turn regulates the "downstream" caspase activation. Betulinic acid bypasses resistance to CD95 and doxorubicin-mediated apoptosis, due to different molecular mechanism of betulinic acid-induced apoptosis.
The role of p53 in betulinic acid-induced apoptosis is controversial. Fulda suggested a p53-independent mechanism of the apoptosis, based on no accumulation of wild-type p53 detected upon treatment with the betulinic acid, whereas wild-type p53 protein strongly increased after treatment with doxorubicin. The suggestion is supported by study of Raisova. Alternatively,Rieber suggested betulinic acid exerts its inhibitory effect on human metastatic melanoma partly by increasing p53.
The study also demonstrated preferential apoptotic effect of betulinic acid on C8161 metastatic melanoma cells, with greater DNA fragmentation and growth arrest and earlier loss of viability than their nonmetastatic C8161/neo 6.3 counterpart. Comparing betulinic acid with other treatment modes, Zuco demonstrated it was less than 10% as potent as doxorubicin and showed an in vitro antiproliferative activity against melanoma and nonmelanoma cell lines, including those resistant to doxorubicin. On the human normal dermatoblast cell line, betulinic acid was one-half to one-fifth as toxic as doxorubicin. The ability of betulinic acid to induce two different effects (cytotoxic and cytostatic) on two clones derived from the same human melanoma metastasis suggests the development of clones resistant to this agent will be more unlikely, than that to conventional cytotoxic drugs. Moreover, in spite of the lower potency compared with doxorubicin, betulinic acid seems to be selective for tumor cells with minimal toxicity against normal cells. The effect of betulinic acid on melanoma cell lines is stronger than its growth-inhibitory effect on primary melanocytes. A study of a combination of betulinic acid with γ-irradiation showed clearly additive effects, and indicated they differ in their modes of action.
C-3 esterification of betulinic acid led to the discovery of bevirimat, an HIV-1 maturation inhibitor patented by Rhone-Poulenc (now Sanofi-Aventis). The clinical development, however, was stopped due to poor pharmacodynamic properties.
A major inconvenience for the future clinical development of betulinic acid and analogues resides in their poor solubility in aqueous media such as blood serum and polar solvents used for bioassays. To circumvent this problem of hydrosolubility and to enhance pharmacological properties, many derivatives were synthesized and evaluated for cytotoxic activity. One study showed C-20 modifications involve the loss of cytotoxicity. Another study demonstrated the importance of the presence of the -COOH group, since compounds substituted at this position, such as lupeol and methyl betulinate, were less active on human melanoma than betulinic acid. Moreover, some C-28 amino acids and C-3 phthalates derivatives exhibited higher cytotoxic activity against cancer cell lines with improved selective toxicity and water solubility. Chatterjee et al. obtained the 28-O-β-D-glucopyranoside of betulinic acid by microbial transformation with Cunninghamella species, while Baglin et al. obtained it by organic synthesis. This glucoside did not exhibit any significant in vitro activity on human melanoma (MEL-2) and human colorectal adenocarcinoma (HT-29) cell lines, which confirms the importance of the carboxylic acid function to preserve the cytotoxicity. Recently, Gauthier et al. synthesized a series of 3-O-glycosides of betulinic acid which exhibited a strongly potent in vitro anticancer activity against human cancer cell lines.
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- Tan Y, Yu R, Pezzuto JM (July 2003). "Betulinic acid-induced programmed cell death in human melanoma cells involves mitogen-activated protein kinase activation". Clinical Cancer Research. 9 (7): 2866–75. PMID 12855667.
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- Wick W, Grimmel C, Wagenknecht B, Dichgans J, Weller M (June 1999). "Betulinic acid-induced apoptosis in glioma cells: A sequential requirement for new protein synthesis, formation of reactive oxygen species, and caspase processing". The Journal of Pharmacology and Experimental Therapeutics. 289 (3): 1306–12. PMID 10336521.
- Thurnher D, Turhani D, Pelzmann M, Wannemacher B, Knerer B, Formanek M, Wacheck V, Selzer E (September 2003). "Betulinic acid: a new cytotoxic compound against malignant head and neck cancer cells". Head & Neck. 25 (9): 732–40. doi:10.1002/hed.10231. PMID 12953308.
- Liu X, Jutooru I, Lei P, Kim K, Lee SO, Brents LK, Prather PL, Safe S (July 2012). "Betulinic acid targets YY1 and ErbB2 through cannabinoid receptor-dependent disruption of microRNA-27a:ZBTB10 in breast cancer". Molecular Cancer Therapeutics. 11 (7): 1421–31. doi:10.1158/1535-7163.MCT-12-0026. PMC 4924623. PMID 22553354.
- Raisova M, Hossini AM, Eberle J, Riebeling C, Wieder T, Sturm I, Daniel PT, Orfanos CE, Geilen CC (August 2001). "The Bax/Bcl-2 ratio determines the susceptibility of human melanoma cells to CD95/Fas-mediated apoptosis". The Journal of Investigative Dermatology. 117 (2): 333–40. doi:10.1046/j.0022-202x.2001.01409.x. PMID 11511312.
- Rieber M, Strasberg Rieber M (May 1998). "Induction of p53 without increase in p21WAF1 in betulinic acid-mediated cell death is preferential for human metastatic melanoma". DNA and Cell Biology. 17 (5): 399–406. doi:10.1089/dna.1998.17.399. PMID 9628583.
- Selzer E, Pimentel E, Wacheck V, Schlegel W, Pehamberger H, Jansen B, Kodym R (May 2000). "Effects of betulinic acid alone and in combination with irradiation in human melanoma cells". The Journal of Investigative Dermatology. 114 (5): 935–40. doi:10.1046/j.1523-1747.2000.00972.x. PMID 10771474.
- Novel 3,28-Disubstituted Betulinic Acid Derivatives as Potent Anti-HIV Agents Aims/Hypothesis Out-licensing. iptechex pharmalicensing, IP Technology Exchange (2013)
- Gauthier C, Legault J, Lebrun M, Dufour P, Pichette A (October 2006). "Glycosidation of lupane-type triterpenoids as potent in vitro cytotoxic agents". Bioorganic & Medicinal Chemistry. 14 (19): 6713–25. doi:10.1016/j.bmc.2006.05.075. PMID 16787747.