Betulinic acid, a natural compound with potent anticancer effects. Anticancer Drugs. 2010;21:215-227. [PMID: 20075711 DOI: 10.1097/cad.0b013e3283357c62]

Betulinic acid inhibits autophagic flux and induces apoptosis in human multiple myeloma cells in vitro

AIM

To investigate the effects of betulinic acid (BA) on apoptosis and autophagic flux in multiple myeloma cells and the relationship between the two processes.

METHODS

The proliferation of human multiple myeloma KM3 cells was measured with MTT assay. FITC/PI double-labeled flow cytometry (FCM) and Hoechst 33258 staining were used to analyze the cell apoptosis. Caspase 3, PARP, Beclin1, LC3-II, and P62 were detected using Western blotting.

RESULTS

Treatment of KM3 cells with BA (5-25 μg/mL) suppressed the cell proliferation in time- and dose-dependent manners. The IC(50) values at 12, 24, and 36 h were 22.29, 17.36, and 13.06 μg/mL, respectively. BA treatment dose-dependently induced apoptosis of KM3 cells, which was associated with the activation of caspase 3. However, Z-DEVD-FMK, a specific inhibitor of caspase 3, did not decrease, but rather sensitized the cells to BA-induced apoptosis, suggesting an alternative mechanism involved. On other hand, BA treatment dose-dependently increased the accumulation of LC3-II and P62 in KM3 cells, representing the inhibition of autophagic flux. Furthermore, BA treatment dose-dependently downregulated the expression of Beclin 1, an important inducer of autophagy, in KM3 cells. In the presence of BA, Z-DEVD-FMK induced autophagy and increased the amount of LC3-II in KM3 cells, which may occur via attenuating BA-induced decrease in the level of Beclin 1. Similarly, rapamycin, an autophagy inducer, increased the amount of LC3-II in KM3 cells. In the presence of BA, rapamycin caused further increase in the amount of LC3-II. Furthermore, rapamycin sensitized BA-treated KM3 cells to apoptosis.

CONCLUSION

The results demonstrate that BA induces apoptosis and blocks autophagic flux in KM3 cells. Furthermore, in addition to activation of caspase 3, the inhibition of autophagic flux also contributes to the BA-mediated apoptosis of KM3 cells.

Lanostanoids from fungi: a group of potential anticancer compounds

Lanostanes are a group of tetracyclic triterpenoids derived from lanosterol. They have relevant biological and pharmacological properties, such as their cytotoxic effects via induction of apoptosis. This review compiles the most relevant lanostanoids studied from 2000 to 2011, principally those isolated from Ganoderma lucidum and other related fungi, such as Poria cocos, Laetiporus sulphureus, Inonotus obliquus, Antrodia camphorata, Daedalea dickinsii, and Elfvingia applanata, which have great potential as anticancer agents because of their cytotoxic or apoptotic effects. The compounds were selected on the basis of their proapoptotic mechanisms, through their ability to modify transcriptional activities via nuclear factors or genes and the activation or inhibition of pro- or antiapoptotic proteins; studies based only on their cytotoxicity were excluded from this review in the absence of complementary studies on their mechanisms of action. A total of 81 compounds from Ganoderma lucidum and other species from this genus are included, as well as 96 compounds isolated from other fungi, principally Poria cocos. Some of these compounds were found to arrest the cell cycle in the G1 phase, increase levels of p53 and Bax, or inhibit the phosphorylation of Erk1/2 or the activation of NF-κB and AP-1. Other lanostanes have inhibitory effects on the growth of androgen prostate carcinoma through increasing the expression of p21, which activates the tumor suppressor protein p53, while other compounds have been shown to selectively inhibit topo II activity without affecting topo I. General considerations concerning the chemical structure-biological activities of these compounds are also discussed.

Design, synthesis and biological evaluation of novel betulinic acid derivatives

BACKGROUND

Tumor, is one of the major reason for human death, due to its widespread occurrence. Betulinic acid derivatives have attracted considerable attention as cancer chemopreventive agents and also as cancer therapeutics. Many of its derivatives inhibit the growth of human cancer cell lines by triggering apoptosis. With this background, we planned to synthesize a series of betulinic acid derivatives to assess their antiproliferation efficacy on human cancer cell lines.

RESULTS

A series of novel betulinic acid derivatives were designed and synthesized as highlighted by the preliminary antitumor evaluation against MGC-803, PC3, A375, Bcap-37 and A431 human cancer cell lines in vitro. The pharmacological results showed that some of the compounds displayed moderate to high levels of antitumor activities with most of new exhibiting higher inhibitory activities compared to BA. The IC50 values of compound 3c on the five cancer cell lines were 2.3, 4.6, 3.3, 3.6, and 4.3 μM, respectively. Subsequent fluorescence staining and flow cytometry analysis (FCM) indicated that compound 3c could induce apoptosis in MGC-803 and PC3 cell lines, and the apoptosis ratios reached the peak (37.38% and 33.74%) after 36 h of treatment at 10 μM.

CONCLUSIONS

This study suggests that most of betulinic acid derivatives could inhibit the growth of human cancer cell lines. Furthermore, compound 3c could induce apoptosis of cancer cells.

Influence of betulinic acid on lymphocyte subsets and humoral immune response in mice

Betulinic acid is a pentacyclic triterpene found in many plant species, among others, in the bark of white birch Betula alba. Betulinic acid was reported to display a wide range of biological effects, including antiviral, antiparasitic, antibacterial, anticancer and anti-inflammatory activities. The effects of betulinic acid (50, 5, 0.5 mg/kg) administered orally five times at 24 hours intervals to non-immunized and red blood cells (SRBC)-immunized mice were determined. The present study examined the total number of lymphocytes in the thymus, spleen and mesenteric lymph nodes, and the percentage of subsets of T cells (CD4+CD8+, CD4CD8, CD4+, CD8+) in thymus,T (CD3+, CD4+, CD8+) and B (CD19+) lymphocytes in the spleen and mesenteric lymph nodes, as well as white blood cell (WBC) and differential leukocyte counts in non-immunized mice, and humoral immune response in SRBC-immunized mice. SRBC was injected 24 hours after administration of the last dose of betulinic acid. It was found that betulinic acid administered orally five times at the dose of 0.5 mg/kg increased the total number of thymocytes, splenocytes, lymphocytes of mesenteric lymph node cells, and the weight ratio of the spleen and mesenteric lymph nodes in non-immunized mice. Betulinic acid also changed the percentage of T cell subsets in the thymus and T and B lymphocytes in peripheral lymphatic organs. The effects of betulinic acid on T and B cell subpopulations depended on the dose applied. The strongest stimulating effect of betulinic acid was observed when the drug was administered at the dose of 0.5 mg/kg. Five exposures to betulinic acid (0.5 mg/kg) decreased the percentage of immature CD4+CD8+ thymic cells with corresponding increases in the percentage and absolute count of mature, single-positive CD4+ thymocytes and decreased the percentage and total count of CD3+ splenocytes and mesenteric lymph node cells with corresponding decreases in the percentage and absolute count of CD4+ and CD8+ cells. Multiple administration of betulinic acid at the investigated doses augmented the percentage and absolute count of CD19+ cells in the peripheral lymphatic organs. Moreover, betulinic acid at the dose of 5 mg/kg administered prior to SRBC immunization increased the number of plaque forming cells (PFC) but decreased the production of anti-SRBC antibodies on day 4 after priming. Thus, betulinic acid is a potential biological response modifier and may strengthen the immune response of its host.

A novel one-step microbial transformation of betulin to betulinic acid catalysed by Cunninghamella blakesleeana

Betulinic acid and its derivatives are potential bioactive compounds present in nature. This study investigated the biotransformation of betulin to betulinic acid by Cunninghamella blakesleeana cells. LC-MS analysis demonstrated that betulin could be transformed into at least five products from cultured C. blakesleeana cells, among which betulinic acid was the most important. The presented method provides an attractive alternative approach to chemical synthesis, because is less time-consuming and more environmentally friendly. C. blakesleeana can transform betulin into potent derivatives with high pharmacological activities.

Natural compounds as anticancer agents: Experimental evidence

Cancer prevention research has drawn much attention worldwide. It is believed that some types of cancer can be prevented by following a healthy life style. Cancer chemoprevention by either natural or synthetic agents is a promising route towards lowering cancer incidence. In recent years, the concept of cancer chemoprevention has evolved greatly. Experimental studies in animal models demonstrate that the reversal or suppression of premalignant lesions by chemopreventive agents is achievable. Natural occurring agents such as dietary phytochemicals, tea polyphenols and resveratrol show chemopreventive activity in animal models. Moreover, clinical trials for testing the safety and efficacy of a variety of natural agents in preventing or treating human malignancy have been ongoing. Here, we summarize experimental data on the chemopreventive or tumor suppressive effects of several natural compounds including curcumin, (-)-epigallocatechin-3-gallate, resveratrol, indole-3-carbinol, and vitamin D.

Triterpenoids

This review covers the isolation and structure determination of triterpenoids, including squalene derivatives, protostanes, lanostanes, holostanes, cycloartanes, dammaranes, euphanes, tirucallanes, tetranortriterpenoids, quassinoids, lupanes, oleananes, friedelanes, ursanes, hopanes, serratanes and saponins; 305 references are cited.

Alkylidene branched lupane derivatives: synthesis and antitumor activity

Several novel alkylidene branched lupane derivatives have been prepared. Many of these compounds showed a significant cytotoxicity. The most active compound, 2-methylene-betulonic acid, showed IC(50) values between 0.2 and 0.6 μM for 15 different human cancer cell lines. Cytotoxicity can be improved by encapsulation in liposomes. These compounds act by triggering apoptotic cell death as shown by DNA-laddering experiments and acridine orange/ethidium bromide staining.

Therapeutic effect of enhancing endothelial nitric oxide synthase (eNOS) expression and preventing eNOS uncoupling

Nitric oxide (NO) produced by the endothelium is an important protective molecule in the vasculature. It is generated by the enzyme endothelial NO synthase (eNOS). Similar to all NOS isoforms, functional eNOS transfers electrons from nicotinamide adenine dinucleotide phosphate (NADPH), via the flavins flavin adenine dinucleotide and flavin mononucleotide in the carboxy-terminal reductase domain, to the heme in the amino-terminal oxygenase domain. Here, the substrate L-arginine is oxidized to L-citrulline and NO. Cardiovascular risk factors such as diabetes mellitus, hypertension, hypercholesterolaemia or cigarette smoking reduce bioactive NO. These risk factors lead to an enhanced production of reactive oxygen species (ROS) in the vessel wall. NADPH oxidases represent major sources of this ROS and have been found upregulated in the presence of cardiovascular risk factors. NADPH-oxidase-derived superoxide avidly reacts with eNOS-derived NO to form peroxynitrite (ONOO(-)). The essential NOS cofactor (6R-)5,6,7,8-tetrahydrobiopterin (BH(4) ) is highly sensitive to oxidation by this ONOO(-). In BH(4) deficiency, oxygen reduction uncouples from NO synthesis, thereby converting NOS to a superoxide-producing enzyme. Among conventional drugs, compounds interfering with the renin-angiotensin-aldosterone system and statins can reduce vascular oxidative stress and increase bioactive NO. In recent years, we have identified a number of small molecules that have the potential to prevent eNOS uncoupling and, at the same time, enhance eNOS expression. These include the protein kinase C inhibitor midostaurin, the pentacyclic triterpenoids ursolic acid and betulinic acid, the eNOS enhancing compounds AVE9488 and AVE3085, and the polyphenolic phytoalexin trans-resveratrol. Such compounds enhance NO production from eNOS also under pathophysiological conditions and may thus have therapeutic potential.

Identification of bioactive constituents of Ziziphus jujube fruit extracts exerting antiproliferative and apoptotic effects in human breast cancer cells

ETHNOPHARMACOLOGICAL RELEVANCE

Ziziphus extracts have been used in Traditional Chinese Medicine for the treatment of cancer.

AIM OF THE STUDY

In the present study we have investigated the effects of Ziziphus jujube extracts (ZEs) on breast cancer.

MATERIALS AND METHODS

We evaluated the effects of increasing concentrations of ZEs on ERα positive MCF-7 and ERα negative SKBR3 breast cancer cell proliferation using MTT assays. Apoptosis was analyzed by evaluating the involvement of some pro-apoptotic proteins, including Bax, Bad, Bid and PARP cleavage by immunoblotting analysis. Moreover, the effects of ZEs treatment on apoptosis were tested by both DNA fragmentation and terminal deoxynucleotidyl transferase dUTP nick end-labeling (TUNEL) staining. By using chromatographic techniques, we identified the constituents of the effective extracts.

RESULTS

ZE1, ZE2, and ZE4 exerted significant antiproliferative effects on estrogen receptor alpha (ERα) positive MCF-7 (IC(50) values of 14.42, 7.64, 1.69μg/mL) and ERα negative SKBR3 (IC(50) values of 14.06, 6.21, 3.70μg/mL) human breast cancer cells. Remarkably, ZEs did not affect cell viability of both normal human fibroblasts BJ1-hTERT and nonmalignant breast epithelial MCF-10A cells. Treatment with ZEs induced cell death by apoptosis in both malignant breast cells. We found that the most effective extracts ZE2 and ZE4 shared a number of triterpenic acids, already known for their anticancer activities.

CONCLUSIONS

Our data provide a rational base for the use of Ziziphus extracts in the treatment of breast cancer in Traditional Chinese Medicine.

New ionic derivatives of betulinic acid as highly potent anti-cancer agents

Betulinic acid is a natural compound with high in vitro cytotoxicity toward many cancer cells. However, the poor water solubility of this compound hampers an effective in vivo cancer study. We prepared new ionic derivatives of betulinic acid with higher water solubilities, without losing the structural integrity and functionality of this compound. As a result, these new ionic derivatives have shown much higher inhibitory effects against different cancer cell lines such as melanoma A375, neuroblastoma SH-SY5Y and breast adenocarcinoma MCF7. For A375 cell lines, the derivative 5 exhibited a low IC(50) value of 36 μM (vs 154 μM for betulinic acid); for MCF7 cell lines, the derivative 5 also exhibited a low IC(50) value of 25 μM (vs 112 μM for betulinic acid). The high cytotoxicity of these new derivatives can be linked to their greatly improved water solubility. Our assay method used little DMSO in aiding the dissolution of these derivatives to demonstrate the advantage of improved water solubility and to mimic the in vivo study conditions. The cell viability studies based on both MTT and LDH assay methods have confirmed the high inhibitory effect of our ionic derivatives of betulinic acid (particularly 4 and 5) against different cancer cells.

A novel triterpene extract from mistletoe induces rapid apoptosis in murine B16.F10 melanoma cells

The European mistletoe Viscum album L. is a plant used for remedies in cancer treatment. The benefit of commonly used aqueous extracts is controversial but the plant contains water insoluble triterpene acids providing interesting anticancer properties. Triterpene extracts (TE) from plants and single triterpenoids such as oleanolic acid (OA) or betulinic acid (BA) are known for their cytotoxic effects on cancer cell lines in vitro. We report here cytotoxic effects of a novel OA-rich triterpene extract from mistletoe (V. album L., Santalaceae) solubilized by 2-hydroxypropyl-β-cyclodextrin (2-HP-β-CD) on B16.F10 mouse melanoma cells. The 2-HP-β-CD solubilized triterpene extract (STE) was highly cytotoxic by causing DNA fragmentation, followed by loss of membrane integrity and intracellular adenosine-5'-triphosphate (ATP). Blocking the caspase machinery by inhibitors aborted DNA fragmentation and delayed the cytotoxic effects but did not prevent cell death. The solubilization by 2-HP-β-CD allows a solvent-free application of triterpene extracts in the in vitro setting. These findings suggest the use of STE from mistletoe as a solvent-free anticancer drug for preclinical animal experiments and clinical trials.

Chemoprevention of melanoma

Despite advances in drug discovery programs and molecular approaches for identifying drug targets, incidence and mortality rates due to melanoma continue to rise at an alarming rate. Existing preventive strategies generally involve mole screening followed by surgical removal of the benign nevi and abnormal moles. However, due to lack of effective programs for screening and disease recurrence after surgical resection, there is a need for better chemopreventive agents. Although sunscreens have been used extensively for protecting from UV-induced melanomas, results of correlative population-based studies are controversial, with certain studies suggest increased skin cancer risk in sunscreen users. Therefore, these studies require further authentication to conclusively confirm the chemoprotective efficacy of sunscreens. This chapter reviews the current understanding regarding melanoma chemoprevention and the various strategies used to accomplish this objective.

Terpenoids as potential chemopreventive and therapeutic agents in liver cancer

Despite significant advances in medicine, liver cancer, predominantly hepatocellular carcinoma remains a major cause of death in the United States as well as the rest of the world. As limited treatment options are currently available to patients with liver cancer, novel preventive control and effective therapeutic approaches are considered to be reasonable and decisive measures to combat this disease. Several naturally occurring dietary and non-dietary phytochemicals have shown enormous potential in the prevention and treatment of several cancers, especially those of the gastrointestinal tract. Terpenoids, the largest group of phytochemicals, traditionally used for medicinal purposes in India and China, are currently being explored as anticancer agents in clinical trials. Terpenoids (also called "isoprenoids") are secondary metabolites occurring in most organisms, particularly plants. More than 40 000 individual terpenoids are known to exist in nature with new compounds being discovered every year. A large number of terpenoids exhibit cytotoxicity against a variety of tumor cells and cancer preventive as well as anticancer efficacy in preclinical animal models. This review critically examines the potential role of naturally occurring terpenoids, from diverse origins, in the chemoprevention and treatment of liver tumors. Both in vitro and in vivo effects of these agents and related cellular and molecular mechanisms are highlighted. Potential challenges and future directions involved in the advancement of these promising natural compounds in the chemoprevention and therapy of human liver cancer are also discussed.

Suppression of STAT3 and HIF-1 alpha mediates anti-angiogenic activity of betulinic acid in hypoxic PC-3 prostate cancer cells

BACKGROUND

Signal transducer and activator of transcription 3 (STAT3) is a transcription factor that regulates various cellular processes such as cell survival, angiogenesis and proliferation. In the present study, we examined that betulinic acid (BA), a triterpene from the bark of white birch, had the inhibitory effects on hypoxia-mediated activation of STAT3 in androgen independent human prostate cancer PC-3 cells.

METHODOLOGY/PRINCIPAL FINDINGS

BA inhibited the protein expression and the transcriptional activities of hypoxia-inducible factor-1α (HIF-1α) under hypoxic condition. Consistently, BA blocked hypoxia-induced phosphorylation, DNA binding activity and nuclear accumulation of STAT3. In addition, BA significantly reduced cellular and secreted levels of vascular endothelial growth factor (VEGF), a critical angiogenic factor and a target gene of STAT3 induced under hypoxia. Furthermore, BA prevented in vitro capillary tube formation in human umbilical vein endothelial cells (HUVECs) maintained in conditioned medium of hypoxic PC-3 cells, implying anti-angiogenic activity of BA under hypoxic condition. Of note, chromatin immunoprecipitation (ChiP) assay revealed that BA inhibited binding of HIF-1α and STAT3 to VEGF promoter. Furthermore, silencing STAT3 using siRNA transfection effectively enhanced the reduced VEGF production induced by BA treatment under hypoxia.

CONCLUSIONS/SIGNIFICANCE

Taken together, our results suggest that BA has anti-angiogenic activity by disturbing the binding of HIF-1α and STAT3 to the VEGF promoter in hypoxic PC-3 cells.

Betulinic acid protects against cerebral ischemia-reperfusion injury in mice by reducing oxidative and nitrosative stress

Increased production of reactive oxygen and nitrogen species following cerebral ischemia-reperfusion is a major cause for neuronal injury. In hypercholesterolemic apolipoprotein E knockout (ApoE-KO) mice, 2h of middle cerebral artery (MCA) occlusion followed by 22h of reperfusion led to an enhanced expression of NADPH oxidase subunits (NOX2, NOX4 and p22phox) and isoforms of nitric oxide synthase (neuronal nNOS and inducible iNOS) in the ischemic hemisphere compared with the non-ischemic contralateral hemisphere. This was associated with elevated levels of 3-nitrotyrosine, an indicator of peroxynitrite-mediated oxidative protein modification. Pre-treatment with betulinic acid (50mg/kg/day for 7days via gavage) prior MCA occlusion prevented the ischemia reperfusion-induced upregulation of NOX2, nNOS and iNOS. In parallel, betulinic acid reduced the levels of 3-nitrotyrosine. In addition, treatment with betulinic acid enhanced the expression of endothelial eNOS in the non-ischemic hemispheres. Finally, betulinic acid reduced infarct volume and ameliorated the neurological deficit in this mouse stroke model. In conclusion, betulinic acid protects against cerebral ischemia-reperfusion injury in mice. This is likely to result from a reduction of oxidative stress (by downregulation of NOX2) and nitrosative stress (by reduction of nNOS and iNOS), and an enhancement of blood flow (by upregulation of eNOS).

Triterpenoids as potential agents for the chemoprevention and therapy of breast cancer

Breast cancer remains a major cause of death in the United States as well as the rest of the world. In view of the limited treatment options for patients with advanced breast cancer, preventive and novel therapeutic approaches play an important role in combating this disease. The plant-derived triterpenoids, commonly used for medicinal purposes in many Asian countries, posses various pharmacological properties. A large number of triterpenoids are known to exhibit cytotoxicity against a variety of tumor cells as well as anticancer efficacy in preclinical animal models. Numerous triterpenoids have been synthesized by structural modification of natural compounds. Some of these analogs are considered to be the most potent antiinflammatory and anticarcinogenic triterpenoids known. This review examines the potential role of natural triterpenoids and their derivatives in the chemoprevention and treatment of mammary tumors. Both in vitro and in vivo effects of these agents and related molecular mechanisms are presented. Potential challenges and future directions involved in the advancement of these promising compounds in the prevention and therapy of human breast cancer are also identified.

Conjugates of betulin derivatives with AZT as potent anti-HIV agents

Fourteen novel conjugates of 3,28-di-O-acylbetulins with AZT were prepared as anti-HIV agents, based on our previously reported potent anti-HIV triterpene leads, including 3-O-acyl and 3,28-di-O-acylbetulins. Nine of the conjugates (49-53, 55, 56, 59, and 60) exhibited potent anti-HIV activity at the submicromolar level, with EC(50) values ranging from 0.040 to 0.098muM in HIV-1(NL4-3) infected MT-4 cells. These compounds were equipotent or more potent than 3-O-(3',3'-dimethylsuccinyl)betulinic acid (2), which is currently in Phase IIb anti-AIDS clinical trial.