PMC:4330249 / 14983-23438 JSONTXT

{"project":"2_test","denotations":[{"id":"25705153-8939849-44841375","span":{"begin":313,"end":315},"obj":"8939849"},{"id":"25705153-17163581-44841376","span":{"begin":506,"end":508},"obj":"17163581"},{"id":"25705153-19458912-44841377","span":{"begin":510,"end":512},"obj":"19458912"},{"id":"25705153-16858664-44841378","span":{"begin":514,"end":516},"obj":"16858664"},{"id":"25705153-18719855-44841379","span":{"begin":518,"end":520},"obj":"18719855"},{"id":"25705153-20829362-44841380","span":{"begin":728,"end":730},"obj":"20829362"},{"id":"25705153-18719855-44841381","span":{"begin":732,"end":734},"obj":"18719855"},{"id":"25705153-20429769-44841382","span":{"begin":736,"end":738},"obj":"20429769"},{"id":"25705153-16858664-44841383","span":{"begin":1304,"end":1306},"obj":"16858664"},{"id":"25705153-17163581-44841384","span":{"begin":1656,"end":1658},"obj":"17163581"},{"id":"25705153-19458912-44841385","span":{"begin":1660,"end":1662},"obj":"19458912"},{"id":"25705153-20429769-44841386","span":{"begin":1664,"end":1666},"obj":"20429769"},{"id":"25705153-20429769-44841387","span":{"begin":1963,"end":1965},"obj":"20429769"},{"id":"25705153-18023328-44841388","span":{"begin":2515,"end":2517},"obj":"18023328"},{"id":"25705153-15208674-44841389","span":{"begin":2629,"end":2631},"obj":"15208674"},{"id":"25705153-15208674-44841390","span":{"begin":2742,"end":2744},"obj":"15208674"},{"id":"25705153-9106657-44841391","span":{"begin":3057,"end":3059},"obj":"9106657"},{"id":"25705153-17512402-44841392","span":{"begin":3241,"end":3243},"obj":"17512402"},{"id":"25705153-24888707-44841393","span":{"begin":3508,"end":3510},"obj":"24888707"},{"id":"25705153-24170547-44841394","span":{"begin":3674,"end":3676},"obj":"24170547"},{"id":"25705153-19458912-44841395","span":{"begin":3997,"end":3999},"obj":"19458912"},{"id":"25705153-14744432-44841396","span":{"begin":4311,"end":4313},"obj":"14744432"},{"id":"25705153-16467120-44841397","span":{"begin":4487,"end":4489},"obj":"16467120"},{"id":"25705153-16239906-44841398","span":{"begin":4568,"end":4570},"obj":"16239906"},{"id":"25705153-18523647-44841399","span":{"begin":4883,"end":4885},"obj":"18523647"},{"id":"25705153-17377525-44841400","span":{"begin":5126,"end":5128},"obj":"17377525"},{"id":"25705153-11832206-44841401","span":{"begin":5388,"end":5390},"obj":"11832206"},{"id":"25705153-10200555-44841402","span":{"begin":5500,"end":5502},"obj":"10200555"},{"id":"25705153-23608376-44841403","span":{"begin":5648,"end":5650},"obj":"23608376"},{"id":"25705153-19458912-44841404","span":{"begin":5674,"end":5676},"obj":"19458912"},{"id":"25705153-18719855-44841405","span":{"begin":6122,"end":6124},"obj":"18719855"},{"id":"25705153-21078664-44841406","span":{"begin":6926,"end":6928},"obj":"21078664"},{"id":"25705153-22327045-44841407","span":{"begin":7254,"end":7256},"obj":"22327045"},{"id":"25705153-23963693-44841408","span":{"begin":7489,"end":7491},"obj":"23963693"},{"id":"25705153-23089555-44841409","span":{"begin":8184,"end":8186},"obj":"23089555"},{"id":"25705153-21078664-44841410","span":{"begin":8357,"end":8359},"obj":"21078664"},{"id":"25705153-23089555-44841411","span":{"begin":8361,"end":8363},"obj":"23089555"}],"text":"Inhibition of Cell Cycle and Induction of Apoptosis by Nimbolide\nThe loss of the ability to regulate the cell-cycle is characteristic of cancer cells and results in uncontrollable proliferation. Processing cells through the first gap (G) phase of the cell cycle is a step that is frequently disordered in cancer [52]. Nimbolide has been investigated in different studies for its ability to mediate cell cycle arrest. In many in vitro and in vivo studies, nimbolide has shown cell cycle-regulatory effects [18, 25, 53, 54]. It has been reported that nimbolide inhibits cell proliferation by interfering with cell cycle kinetics by inducing G0/G1 and S phase arrest, primarily caused through the repression of cyclin A/cyclin D1 [16, 54, 55].\nIn another interesting molecular study, a Japanese group has proved that nimbolide, a triterpenoid present in certain edible parts of A. indica, arrested HT-29 cells in the G2/M and G0/G1 stages apparently through upregulation of p21, which is a well-known downstream effector of the p53. p53 is a very important anticancer protein that regulates a large number of genes that are involved in cancer progression. Nimbolide has also been shown to upregulate cyclin D2 and CDK2 and to suppress the expression of cyclin A, cyclin E, CDK2, and Rad17 at the same time [53]. Flow cytometric analysis of U937 cells showed that nimbolide treatment (1-2.5 µM) resulted in cell cycle disruption by decreasing the number of cells in G0/G1 phase, with initial increases in S and G2/M phases. It is shown that nimbolide can affect cell cycle progression and induce apoptosis in colon cancer, oral carcinoma, and cervical cancer [18, 25, 55]. Nimbolide significantly suppressed the viability of HeLa cells in a dose-dependent manner by inducing cell cycle arrest at G0/G1 phase, accompanied by p21 accumulation and down-regulation of the cell cycle regulatory proteins cyclin B, cyclin D1, and proliferating cell nuclear antigen (PCNA) [55].\nNimbolide treatment results in the accumulation of cells in G0/G1 phase and decreased in S-phase by up regulating p21 and downregulating the cell cycle-regulatory proteins cyclins and PCNA. Cyclin D1 is known as a proto-oncogene whose gene amplification and protein overexpression of which are frequently observed in tumor cells. The activated cyclin D1/CDK4 and cyclin D1/CDK6 complex phosphorylates the retinoblastoma protein to induce the expression of target genes essential for S phase entry, facilitating the progression from G1 to S phase [56]. Cyclin B1 is a G2/mitotic-specific protein that plays a role in the initiation of mitosis and tumorigenesis [57]. It was reported that cyclin B1 depletion inhibits proliferation and induces apoptosis in human tumor cells [57]. Nimbolide treatment decreases cyclin (A1, B1, C, D1, and E1) expression in breast cancer cells. p21Waf1/Cip1, originally identified as an inhibitor of the cyclin/CDK complexes, has also been shown to have a role as an adaptor protein that assembles and promotes the kinase activity of cyclin D/CDK4 complexes [58]. The level of p21 was significantly increased in nimbolide-treated breast cancer cell lines. PCNA, a cofactor for DNA polymerase δ, plays a central role in cell cycle progression [59]. PCNA is involved in a wide range of cellular functions, including DNA replication, repair, and epigenetic maintenance, and is often used as a diagnostic and prognostic marker. The protein expression of PCNA is decreased in nimbolide-treated breast cancer cells [19]. Nimbolide directly inhibited CDK4/CDK6 kinase activity, leading to hypophosphorylation of the retinoblastoma protein, cell cycle arrest at G1-S, and cell death [42]. In animal tumor models, nimbolide (100 µg/kg) has been shown to exhibit chemopreventive activity against 7,12-dimethylbenzanthracene (DMBA) 3-induced hamster buccal pouch carcinogenesis by downregulating proteins involved in cell cycle progression and transduce apoptosis by both the intrinsic and extrinsic pathways [25].\nApoptosis, or programmed cell death, is essential for the maintenance of development and homeostasis of multi-cellular organisms by eliminating superfluous or unwanted cells. Any alteration or change in the normal process of apoptosis may increase cell survival and support tumor development and progression [60]. The extrinsic and intrinsic pathways represent the two major well-studied apoptotic processes. Inefficient apoptosis is considered one of the hallmarks of tumorigenicity [61]. Moreover, induction of apoptosis is an important target for cancer therapy [62]. The extrinsic pathway is initiated by cell surface-expressed death receptors of the tumor necrosis factor superfamily. One of the central pathways of apoptosis is initiated by cytokines, such as tumor necrosis factor-α, Fas ligand (FasL), and tumor necrosis factor-α-related apoptosis-inducing ligand (TRAIL) [63]. The intrinsic pathway is initiated by anticancer drugs, growth factor withdrawal, or hypoxia or via induction of oncogenes. These stimuli induce permeabilization of the outer mitochondrial membrane and activate the mitochondrial pathway [64].\nCaspases are a family of evolutionarily conserved cysteine proteases that play a essential role in the majority of apoptotic pathways. Death signals activate the proteolytic cascade of caspases through two main pathways: an extrinsic and intrinsic pathway [65]. Both pathways converge to the activation of caspase-3, the closer homolog of Caenorhabditis elegans CED-3 [66]. Caspase-3 activates downstream enzymes of the caspase family and contributes with them to generate the typical apoptotic cell death phenotype [67]. Harish Kumar et al. [25] reported that nimbolide transduces apoptosis by both the intrinsic and extrinsic pathways in DMBA-induced hamster buccal pouch carcinogenesis. Working on the choriocarcinoma (BeWo) cells, have shown that nimbolide, induces apoptosis through engagement of the mitochondrial pathway. The involvement of this pathway is based on the observation that nimbolide mediates the upregulation of Apaf1 and a caspase-3 and decrease in the Bcl2/Bax ratio [54].\nNimbolide sensitizes human colon cancer cell lines (HCT-116 and HT-29) to TRAIL through reactive oxygen species- and Erk-dependent up-regulation of death receptors, p53, and Bax. A normal breast cell line (MCF-10A) and breast cancer cell lines (MCF-7) were treated with nimbolide (1-5 µM) for 6 h, followed by TRAIL for 24 h. The results indicated that whereas nimbolide and TRAIL alone were minimally effective in inducing apoptosis in MCF-7 cells, the combination of both enhanced the number of apoptotic cells to 42%. Conversely, the combination of nimbolide and TRAIL was unable to evoke apoptosis in the normal breast cell line. The results showed a lack of DR5 and DR4 induction in MCF-10A cells by nimbolide, whereas a dose-dependent induction of these receptors was observed in MCF-7 cells [68]. The decreased expression of Bcl-2 and increased expression of bax, cytochrome c, Smac, and caspases, together with changes in nuclear morphology and mitochondrial transmembrane potential, seen in nimbolide treatment and inhibition of NF-κB activation by nimbolide, stimulate the intrinsic apoptotic pathway in HepG2 cells [17]. In another study, nimbolide repressed cell proliferation by inhibiting the IGF1/IGF-IR-PI3K/Akt pathway and induced apoptosis through the activation of both the extrinsic and intrinsic apoptotic pathways in prostate cancer cells [43].\nNimbolide also induced apoptosis in breast cancer cells by upregulating pro-apoptotic protein (Bad, Bax, FasL, FADD, TRAIL, and cytochrome c) expression and down-regulating anti-apoptotic proteins (Bcl-2, Bcl-xL, Mcl-1, and XIAP-1). Nimbolide activates caspase-3, -8, and -9, which favors the cleavage of poly(ADP) ribose polymerase into 115- and 85-kDa peptides, thus inducing apoptosis in breast cancer cell lines. Further, the nimbolide-induced apoptotic cells were detected using DAPI and AO/EtBr dual staining. After treatment with nimbolide, the cells exhibited the typical morphological changes associated with apoptosis: cell shrinkage, nuclear condensation, and membrane blebbing [30]. Activation of caspase-3, -8, and -9, suggests that nimbolide potentiated both the extrinsic and intrinsic pathways of apoptosis in human breast and colon cancer cells [68, 30]. The overview of all of the signaling molecules modulated by nimbolide is shown in Fig. 4."}