Anti-Cancer Agents in Medicinal Chemistry (Formerly Current Medicinal Chemistry - Anti-Cancer Agents) - Volume 13, Issue 10, 2013

The concept of Ayurvedic expert guided drug discovery and development is defined and put to test systematically for the first time in literature. Western Science has explored only ~5% of the approximately 25,000 species of higher plants for drug leads. The ancient medical science of Ayurveda has however employed a much larger spectrum of plants for clinical treatment. Clerodendrum viscosum (CV), a commonly growing weed in the Indian subcontinent has been employed by S. Nirmalananda (Ayurvedic expert) for the treatment of cervical cancer. Here we isolate and characterize a water extract fraction (Cv-AP) from the root of CV and evaluate its anticervical cancer cell bioactivity. Our results indicate that Cv-AP possesses pro-apoptotic, anti-proliferative, and anti-migratory activity in a dose-dependent fashion against cervical cancer cell lines. In contrast, primary fibroblasts (control healthy cells), when exposed to similar concentrations of this extract, fail to undergo apoptosis and remain relatively unaffected. These findings suggest that Clerodendrum viscosum (CV) is a readily available source of components with potent anti-cancer activity and selective bioactivity against cervical cancer cells. The major component in CV-AP was identified as a glycoprotein via SDS Page and Concanavalin-A binding studies. This study serves to illustrate that systematic collaboration with Ayurveda is a practical and powerful strategy in drug discovery and development.

Herein we describe a brief account of betulin and betulinic acid: two natural products isolated from birch bark, their chemical modifications and further biological/medicinal applications.

In continuation of our studies with chemoprevention potential of plant-derived naphthoquinone derivatives, leaf powder of the medicinal plant Lawsonia inermis L, commonly known as ‘henna’, was evaluated by its inhibition of the Epstein-Barr virus early antigen (EBV-EA) activation induced by the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) in Raji cells. Lawsone (2-hydroxy- 1,4-naphthoquinone), the reddish orange pigment artifact formed during the extraction or preparation of the dye from henna leaves and believed to be the active component, was also assessed in this in vitro assay. Both showed a profound inhibition (>88%) of EBV-EA activation. In the in vivo two-stage mouse skin carcinogenesis study using UV-B radiation for initiation and TPA for tumor promotion, oral feeding of henna (0.0025%) in drinking water ad libitum decreased tumor incidence by 66% and multiplicity by 40% when compared to the positive control at 10 weeks of treatment. Similarly, in the above mouse model, orally fed lawsone (0.0025%) decreased tumor incidence by 72% and multiplicity by 50%. The tumor inhibitory trend continued throughout the 20-week test period. Similar antitumor activities were observed when henna (0.5 mg/ml) was applied topically on the back skin in the UV-B initiated, TPA promoted and peroxynitrite initiated, TPA promoted mouse skin carcinogenesis models. Topically applied lawsone (0.015 mg/ml) also exhibited similar protection against tumor formation in the 7,12-dimtehylbenz(a)anthracene induced and TPA promoted skin cancer in mice. Also, there was a delay of 1 to 2 weeks in tumor appearance in both henna and lawsone treated groups compared to control in all three test models. This study ascertains the skin cancer chemopreventive activity of henna leaf powder and lawsone when administered by either oral (through drinking water) or topical (by application on the back skin) routes. Further, it emphasizes the need for the evaluation of these henna-derived green chemopreventive candidates in combination with currently used sunscreen agents for complementary anticancer potential against UV-induced skin carcinogenesis.

Curcumin, an important component of the culinary spice turmeric, has been shown to harbor anticancer properties against a wide range of cancer cells with minimal toxicity toward normal cells. Two general tyrosine kinase inhibitors (TKIs) sunitinib and sorafenib are currently used in treating renal cancer. Though the use of these TKIs has significantly improved survival, both elicit distressing side effects, limiting their long-term use. We tested the activity of sunitinib and sorafenib to eliminate 786-O renal cancer cells and the efficacy of curcumin to enhance this process. A four-fold decrease in the IC50 of sunitinib, from 4.5 µM to 1.2 µM, was observed in the presence of 20-µM curcumin. However, curcumin did not potentiate the activity of sorafenib. The sunitinib-curcumin (SunC) combination sharply inhibited hyperphosphorylation of the tumor suppressor protein Rb within 8 hours of SunC treatment. Although the levels of cyclin D1 did not change in 8 hours, its expression was dramatically inhibited after 24 hours of SunC exposure. Since curcumin is known to inhibit the cyclin D1-dependent G1/S-phase kinase CDK4 and the cyclin B-dependent G2/M-phase kinase CDK1 that catalyze phosphorylation-mediated inactivation of Rb, our results indicate that SunC containing a lower dose of sunitinib would be effective in restoring the tumor suppressor activity of Rb, thereby truncating cell cycle and triggering cell death. Our results submit the possibility of using SunC as an effective antitumor formulation to reduce the dose and risk of adverse effects of sunitinib.

Alkylation of α-amino acid derived iminoesters with Baylis-Hillman (BH) reaction template based allyl bromides/allyl acetates followed by acidic hydrolysis furnished α-methylene-β-substituted-pyroglutamates and α-alkylidene pyroglutamates respectively. Application of these methodologies has been demonstrated in the synthesis of fused [3.2.0]-γ-lactam-β-lactones. Further, substrate controlled stereoselective alkylation of L-threonine derived oxazoles with BH reaction based allyl bromides and acetates yielded optically pure α-methylene-β-substituted pyroglutamates, and α-alkylidene pyroglutamates. These methodologies have been applied in the preparation of chiral [3.2.0] heterobicyclic pyroglutamates containing hydroxyethyl side chain. All the synthesized pyroglutamates have been evaluated for their anti-cancer and enzyme proteasome inhibition activity.

Curcumin, which is derived from the plant Curcuma longa, has received considerable attention as a possible anti-cancer agent. In cell culture, curcumin is capable of inducing apoptosis in cancer cells at concentrations that do not affect normal cells. One draw-back holding curcumin back from being an effective anti-cancer agent in humans is that it is almost completely insoluble in water and therefore has poor absorption and subsequently poor bioavailability. Here we have generated a number of curcumin derivatives (tetrahydro-curcumin, curcumin mono-carboxylic acid, curcumin mono-galactose, curcumin mono-alkyne and dendrimer-curcumin conjugate) to test whether any of them display both cytotoxicity and water solubility. Of those tested only dendrimer-curcumin conjugate exhibited both water solubility and cytotoxicity against SKBr3 and BT549 breast cancer cells. When compared to curcumin dissolved in DMSO, dendrimer-curcumin conjugate dissolved in water was significantly more effective in inducing cytotoxicity, as measured by the MTT assay and effectively induced cellular apoptosis measured by caspase-3 activation. Since dendrimer-curcumin conjugate is water soluble and capable of inducing potent cytotoxic effects on breast cancer cell lines, it may prove to be an effective anti-cancer therapy to be used in humans.

Previous studies indicate that extracts and purified components from Garcinia species inhibit the growth of human colon cancer cells. Garcinia benzophenones activate the expression of genes in the endoplasmic reticulum and cellular energy stress (mTOR) pathways. This study examines the growth inhibitory and synergistic effects of Garcinia benzophenones, alone or combined with chemopreventive agents, on human colon cancer cells. To find optimal combination treatments, HT29 colon cancer cells were treated with benzophenones alone, or combined with chemopreventive agents, and cell growth measured using the MTT assay. To reveal effects on signaling pathways, we assessed effects of the MEK inhibitor U0126 and the ER IP3 receptor antagonist heparin, as well as effects on the phosphorylation of 4E-BP-1 (mTOR pathway), using Western blot analysis. New and known benzophenones from Garcinia intermedia inhibited the growth of human colon cancer cells; an alcohol extract of Garcinia xanthochymus, as well as purified guttiferones (guttiferone E and xanthochymol), preferentially inhibited the growth of colon cancer versus nonmalignant intestinal epithelial cells. Guttiferone E exhibited synergy with the NSAID sulindac sulfide and xanthochymol, with the spice turmeric. Guttiferone A did not alter phosphorylation of 4E-BP-1, indicating that the mTORC1 pathway is not involved in its action. The effects of xanthochymol were enhanced by U0126, at low doses, and were blocked by heparin, indicating that the MEK pathway is involved, while the ER IP3 receptor is critical for its action. These studies indicate the potential of benzophenones, alone or combined with sulindac sulfide or turmeric, to prevent and treat colon cancer.

Cancer is a diverse class of diseases which differ widely in their cause and biology. The aberrant behavior of cancer reflects up regulation of certain oncogenic signaling pathways that promote proliferation, inhibit apoptosis, and enable the cancer to spread and evoke angiogenesis. Phosphoinositide-3-kinase(PI3K)/Akt/mammalian target of rapamycin (mTOR) pathway controls various biological processes that are important for normal functioning of the cell via cell cycle progression, survival, migration, transcription, translation and metabolism. However, PI3K signaling pathway is dysregulated almost in all cancers which is due to the amplification and genetic mutation of PI3K gene, encoding catalytic and regulatory subunit of PI3K isoforms. The current review focuses on the structural features of various PI3K isoforms including Akt and mTOR and their inhibition using specific small molecule inhibitors in an attempt to achieve an attractive target for cancer prevention and chemotherapy.

Cinnamaldehyde (CIN) has been shown to exert chemopreventive activity against several types of human cancer cells. We previously reported that CIN induced apoptosis of human hepatoma PLC/PRF/5 cells and this effect was associated with activation of the pro-apoptotic Bcl-2 family of proteins and the MAPK cascade. To further clarify the underlying mechanism of CIN-induced apoptosis, we examined in this study its relationship with the mitochondrial death pathway using the mitochondrial permeability transition (MPT) inhibitor, cyclosporin A (CsA), and the general caspase inhibitor, z-VAD-fmk. Results indicated that CIN-induced apoptosis involved enhanced ROS generation, disruption of mitochondrial potential, and the mitochondrial release of cytochrome c and Smac/DIABLO into the cytosol, which in turn promoted caspase-3 to its active form and the subsequent cleavage of PARP. Treatment with CIN also downregulated protein levels of the anti-apoptotic factors XIAP and Bcl-2 with concomitant accumulation of the pro-apoptotic Bax in a timedependent manner. These mitochondria-related apoptotic effects induced by CIN were however blocked by CsA and z-VAD-fmk pretreatments, which prevented cells from undergoing programmed cell death triggered by CIN. Furthermore, the increase of Bax and decrease of Bcl-2 and XIAP protein expression due to CIN treatment were also reversely modulated by the two inhibitors. Taken together, these results suggested that CIN is an apoptotic inducer that acts on the mitochondrial death pathway in PLC/PRF/5 cells and its effect could be blocked by CsA and z-VAD-fmk.

The present investigation was undertaken to gain insight into the molecular mechanism by which myricetin induces apoptosis in human hepatocarcinoma HepG2 cells. Myricetin caused the disruption of mitochondrial membrane potential in a dose-dependent manner. Moreover, myricetin triggered translocation of the pro-apoptotic protein Bax to the mitochondria, downregulation of anti-apoptotic Bcl-2 expression and upregulated the expression of pro-apoptotic protein Bad in the mitochondria. The present study also showed that myricetin promoted the release of cytochrome C from mitochondria into the cytosol followed by an increase in the proteolytic activation of caspase-3 and the concomitant degradation of PARP protein. Additionally, western blot analysis showed that the Akt/p70s6k1 pathway was inhibited in myricetin-treated HepG2 cells, accordingly the phosphorylation of Bad at Ser136 was downregulated. Collectively, these findings indicate that myricetin induced apoptosis in HepG2 cell through mitochondria apoptotic pathway and Akt/p70s6k1/Bad signaling. Present results provide new information on the possible mechanisms for the anti-cancer activity of myricetin.

Twenty six compounds (coumarins, flavonoids and alkaloids) were evaluated for their ability to inhibit the growth of three human tumor cell lines: breast adenocarcinoma (MCF-7), non-small cell lung cancer (NCI-H460) and melanoma (A375-C5). Three of them [3-hydroxyflavone (6), 2’-hydroxy-3,4,4’,5,6’-pentamethoxychalcone (11), Siderin (20)] were very potent in inhibiting all human tumor cell lines tested. The structure / activity relationship is discussed.

A series of new diaryl ether linked pyrrolobenzodiazepine (PBD) conjugates (4a-i, 5a-i and 6a-f) was synthesized and evaluated for their anticancer activity against a panel of 11 human cancer cell lines. These conjugates exhibited significant anticancer activity with GI50 values in the range of 0.1-3.88 μM. Some of the potent conjugates (4b, 4h, 5h, 6b, 6c and 6e) were further investigated on cell cycle distribution. FACS analysis showed the accumulation of cells in G0 phase indicating the apoptosis inducing nature of these conjugates. Moreover, compound 6b caused a decrease in the mitochondrial membrane potential, which indicates the apoptotic nature of the compound through mitochondrial mediated pathway. Further conjugates 4b, 4h and 6b induce the activation of caspase and PARP proteins, followed by apoptotic cell death in MCF7 cell line.

Background: Mortality rates for leukemia are high despite considerable improvements in treatment. Since polyphenols exert pro-apoptotic effects in solid tumors, our study investigated the effects of polyphenols in haematological malignancies. The effect of eight polyphenols (quercetin, chrysin, apigenin, emodin, aloe-emodin, rhein, cis-stilbene and trans-stilbene) were studied on cell proliferation, cell cycle and apoptosis in four lymphoid and four myeloid leukemic cells lines, together with normal haematopoietic control cells. Methods: Cellular proliferation was measured by CellTiter-Glo® luminescent assay; and cell cycle arrest was assessed using flow cytometry of propidium iodide stained cells. Apoptosis was investigated by caspase-3 activity assay using flow cytometry and apoptotic morphology was confirmed by Hoescht 33342 staining. Results: Emodin, quercetin, and cis-stilbene were the most effective polyphenols at decreasing cell viability (IC50 values of 5-22 µM, 8-33 µM, and 25-85 µM respectively) and inducing apoptosis (AP50 values (the concentration which 50% of cells undergo apoptosis) of 2-27 µM, 19-50 µM, and 8-50 µM respectively). Generally, lymphoid cell lines were more sensitive to polyphenol treatment compared to myeloid cell lines, however the most resistant myeloid (KG-1a and K562) cell lines were still found to respond to emodin and quercetin treatment at low micromolar levels. Non-tumor cells were less sensitive to all polyphenols compared to the leukemia cells. Conclusions: These findings suggest that polyphenols have anti-tumor activity against leukemia cells with differential effects. Importantly, the differential sensitivity of emodin, quercetin, and cis-stilbene between leukemia and normal cells suggests that polyphenols are potential therapeutic agents for leukemia.

We have synthesized a large variety of CA-4 analogues having a non-isomerizable C-linker between the A- and B-aromatic rings. Most of them displayed a nanomolar level of cytotoxicity against a panel of human cancer cell lines and inhibited tubulin polymerization at a micromolar level. Among all these compounds, the most interesting compounds were undoubtedly isoCA-4 and structural analogues 18-20 as well as benzil derivatives 11 which displayed a comparable level of activity than that of CA-4. Moreover, it has been demonstrated that these drugs arrested cancer cells in the G2/M phase of cellular cycle and induced apoptosis at very low concentrations. In vitro antivascular effects and the binding mode of the most active compounds was also investigated.

P-glycoprotein (P-gp) is responsible for the multidrug resistance (MDR) and involved in the expulsion of xenobiotics out of cell. In this paper, homology modeling, docking and molecular dynamics simulation (MDS) was performed for the human P-gp desmosdumotin inhibitor. Docking study was carried out in the P-gp nucleotide binding domain 2 (NBD2). The desmosdumotin binding region occupied the ATP binding region (flavonoid binding region) with hydrophobic and hydrophilic interactions. Analysis of root mean square deviations (RMSDs) of active site residues indicated the binding site residues were stable throughout the simulation period. As shown in previous results with structurally similar flavonoid compounds, van der Waals and electrostatic interactions were found to be important factors for the desmosdumotin-NBD2 inhibition. Docking results suggest that desmosdumotin interacts with the NBD2 through both hydrogen bonds (Lys1076, Ser1077 and Thr1078) and hydrophobic interactions (Tyr1044, Val1052, Gly1073 and Cys1074). In addition, the involvement of other amino-acids was identified via MDS (Lys1076 and Ser1077 for hydrogen bonds and Tyr1044, Val1052, Gly1073, Cys1074 and Gly1075 for hydrophobic interactions). Thus, current preliminary model of interactions between desmosdumotin-NBD2 could be helpful to understand the in-depth inhibition mechanism of P-gp at NBD2 level and to design more potent inhibitors which could effectively overcome MDR of anticancer agents.

Cancer is the second leading cause of death, preceded only by cardiovascular diseases, and there is epidemiological evidence that demonstrate this tendency is emerging worldwide. Brazil has an extensive vegetal biodiversity with more than 55,000 species listed. Such biodiversity collaborates with the finding of compounds which could be the basis for the design of new anti-tumor drugs, with fewer side effects than the conventional chemotherapy used currently. Cedrelone is a limonoid isolated from Trichilia catigua (Meliaceae) which is a native Brazilian plant. This study demonstrates that cedrelone inhibits proliferation, adhesion, migration and invasion of breast tumor cells from the line MDA-MB-231. The effects of cell migration and invasion on MDA-MB-231 cell may be explained, at least in part, by the ability of cedrelone to inhibit MMP activity. We also demonstrate that cedrelone is able to induce apoptosis in MDA-MB-231 cells. There are only a few works investigating the effect of limonoids in cellular processes closely related to tumor progression such as adhesion, migration and invasion. To the best of our knowledge, this is the first work describing the effects of a limonoid on tumor and non-tumor cell adhesion process.