Nimbolide sensitizes human colon cancer cells to TRAIL through reactive oxygen species- and ERK-dependent up-regulation of death receptors, p53, and Bax

A review on the impact of TRAIL on cancer signaling and targeting via phytochemicals for possible cancer therapy

Anticancer therapies have been the continual pursuit of this age. Cancer has been ravaging all across the globe breathing not just threats but demonstrating them. Remedies for cancer have been frantically sought after. Few have worked out, yet till date, the available cancer therapies have not delivered a holistic solution. In a world where the search for therapies is levitating towards natural remedies, solutions based on phytochemicals are highly prospective attractions. A lot has been achieved with inputs from plant resources, providing numerous natural remedies. In the current review, we intensely survey the progress achieved in the treatment of cancer through phytochemicals-based programmed cell death of cancer cells. More specifically, we have further reviewed and discussed the role of phytochemicals in activating apoptosis via Tumor Necrosis Factor-Alpha-Related Apoptosis-Inducing Ligand (TRAIL), which is a cell protein that can attach to certain molecules in cancer cells, killing cancer cells. The objective of this review is to enlist the various phytochemicals that are available for specifically contributing towards triggering the TRAIL cell protein-mediated cancer therapy and to point out the research gaps that require future research motivation. This is the first review of this kind in this research direction.

Molecular dissection of anti-colon cancer activity of NARI-29: special focus on H2O2 modulated NF-κB and death receptor signaling

Accumulating evidence attributes the role of aldose reductase (AR) in modulating ROS and inflammation which are the main factor responsible for cancer progression and drug resistance. Epalrestat is the only AR inhibitor being used in Asian countries. It did not make it to the markets of the USA and Europe due to marginal efficacy as an antioxidant and anti-inflammatory agent owing to difficulty reaching intracellular targets. In our previous studies, we attempted to synthesize the epalrestat analogs and reported that the compound 4-((Z)-5-((Z)-2-Cyano-3-phenylallylidene)-4-oxo-2-thioxothiazolidin-3-yl) benzoic acid named as NARI-29 has potent AR inhibition compared to epalrestat. In the current study, we aimed to find the effect of NARI-29 on ROS-induced cancer progression and TRAIL resistance in colon cancer in vitro models. In the first part of the study, we demonstrated that the NARI-29 has specific AKR1B1 inhibition and superior drug-like properties than epalrestat using bioinformatics tools. In the second part of the study, it was proven that NARI-29 has induced the hydrogen peroxide-triggered TRAIL-induced apoptosis in the colon cancer cells via modulating the AKR1B1/4HNE/FOXO3a/DR axis. The selective cytotoxicity of NARI-29 (10-fold) compared to epalrestat (4-fold) toward cancer cells is due to its differential ROS regulation and anti-inflammatory activities. Altogether, these data show that NARI-29 may be a potential candidate for AR inhibitors, which will be used to prevent colon cancer progression and as adjuvant therapy for preventing TRAIL resistance.

Oxymatrine hydrazone (OMTH) synthesis and its protective effect for rheumatoid arthritis through downregulation of MEK/NF-κB pathway

Rheumatoid arthritis (RA) is one of the inflammatory diseases detected in more than 1% of the world population. In the present study, oxymatrine hydrazone (OMTH) was synthesized and investigated for treatment of RA in vitro in TNF-α induced fibroblast-like synoviocyte cell model. Cell viability and apoptosis were detected using MTT and flow cytometry assays, respectively. ELISA was used for determination of inflammatory cytokines and western blotting for evaluation of protein expression. Pretreatment of HFLS-RA cells with 0.5, 1.0, 1.5, 2.0, and 2.5 μM doses of OMTH suppressed TNF-α induced promotion of proliferative potential in dose-based manner. The OMTH pretreatment of TNF-α exposed HFLS-RA cells significantly increased apoptotic cell proportion. In TNF-α exposed HFLS-RA cells OMTH pretreatment elevated Bax and suppressed Bcl-2 expression. Treatment of HFLS-RA cells with OMTH prevented TNF-α mediated elevation of IL-1β, IL-6 and IL-8. Moreover, OMTH treatment of HFLS-RA cells effectively suppressed TNF-α mediated elevated levels of MMP-1 and MMP-13. Pretreatment of HFLS-RA cells with OMTH reversed TNF-α mediated promotion of iNOS and COX-2 levels. The MEK/1/2 and p65 phosphorylation in TNF-α exposed HFLS-RA cells was reduced by OMTH pre-treatment in dose-based manner. Thus, OMTH successfully inhibited TNF-α-mediated increased viability of RA synovial cells and activated apoptosis. Pretreatment of TNF-α exposed synovial cells with OMTH targeted phosphorylation of MEK/NF-κB. Therefore, OMTH may act as potential therapeutic agent for RA treatment.

Vanillin oxime inhibits lung cancer cell proliferation and activates apoptosis through JNK/ERK-CHOP pathway

Lung cancer despite advancement in the medical field continues to be a major threat to human lives and accounts for a high proportion of fatalities caused by cancers globally. The current study investigated vanillin oxime, a derivative of vanillin, against lung cancer cells for development of treatment and explored the mechanism. Cell viability changes by vanillin oxime were measured using MTT assay. Vanillin oxime-mediated apoptosis was detected in A549 and NCI-H2170 cells at 48 h of exposure by flow cytometry. The CEBP homologous protein (CHOP) and death receptor 5 (DR5) levels were analysed by RT-PCR and protein levels by Western blotting. Vanillin oxime in concentration-dependent way suppressed A549 and NCI-H2170 cell viabilities. On exposure to 12.5 and 15 μM concentrations of vanillin oxime elevated Bax, caspase-3, and -9 levels in A549 and NCI-H2170 cells were observed. Vanillin oxime exposure suppressed levels of Bcl-2, survivin, Bcl-xL, cFLIP, and IAPs proteins in A549 and NCI-H2170 cells. It stimulated significant elevation in DR4 and DR5 levels in A549 and NCI-H2170 cells. In A549 and NCI-H2170 cells vanillin oxime exposure caused significant (p < 0.05) enhancement in CHOP and DR5 mRNA expression. Vanillin oxime exposure of A549 and NCI-H2170 cells led to significant (p < 0.05) enhancement in levels of phosphorylated extracellular-signal-regulated kinase and c-Jun N-terminal kinase. Thus, vanillin oxime inhibits pulmonary cell proliferation via induction of apoptosis through tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) mediated pathway. Therefore, vanillin oxime may be studied further to develop a treatment for lung cancer.

Alternol Sensitizes Renal Carcinoma Cells to TRAIL-Induced Apoptosis

Purpose: Tumor necrosis factor–related apoptosis-inducing ligand (TRAIL), a member of the TNF family, can selectively induce cancer cell death while sparing normal cells. However, the application of TRAIL-based antitumor therapies has been hindered due to drug resistance. Alternol is a new compound isolated from microbial fermentation that possesses antitumor activity in different tumors. In our research, we discovered that alternol can sensitize TRAIL-induced apoptosis in renal carcinoma cells (RCCs).

Materials and Methods: Cytotoxic activity was measured by MTT assay. Apoptosis was probed using the PI/annexin V method. Real-time PCR and western blot were used to test the levels of mRNA and protein, respectively. Luciferase assay was used to investigate whether CHOP regulated the expression of death receptor (DR) 5 through transcription. A xenogeneic tumor transplantation model was used to evaluate the anticancer effects of alternol/TRAIL in vivo.

Results: When the mechanisms were investigated, we discovered that alternol increased DR5 expression. DR5 knockdown by siRNA eliminated the enhanced effect of alternol on TRAIL-mediated apoptosis. Alternol reduced the expression of antiapoptotic proteins and increased the levels of proapoptotic proteins. Moreover, alternol increased the level of CHOP, which is necessary for the enhancing effect of alternol on TRAIL-induced apoptosis, given that downregulation of CHOP abrogated the synergistic effect. DR5 upregulation induced by alternol required the production of reactive oxygen species (ROS). Removing ROS inhibited the induction of DR5 and blocked the antiapoptotic proteins induced by alternol.

Conclusion: Taken together, our research suggested that alternol increased TRAIL-mediated apoptosis via inhibiting antiapoptotic proteins and upregulating DR5 levels via ROS generation and the CHOP pathway.

Azadirachtin A inhibits the growth and development of Bactrocera dorsalis larvae by releasing cathepsin in the midgut

Azadirachtin, a botanical insecticide with high potential, has been widely used in pest control. Azadirachtin has shown strong biological activity against Bactrocera dorsalis in toxicological reports, but its mechanism remains unclear. This study finds that azadirachtin A inhibits the growth and development of Bactrocera dorsalis larvae. The larval weights and body sizes of the azadirachtin-treated group were significantly less than those of the control group in a concentration-dependent manner. Further, pathological sections revealed that azadirachtin destroyed the midgut cell structure and intestinal walls, while TUNEL staining showed that azadirachtin could induce apoptosis of midgut cells, and Western blot analysis indicated that Bcl-XL expression was inhibited and cytochrome c (CytC) released into the cytoplasm. The results also imply azadirachtin-induced structural alterations in the Bactrocera dorsalis larvae midgut by activation of apoptosis. RNA-seq analysis of midgut cells found that 482 and 708 unique genes were upregulated and downregulated, respectively. These differentially expressed genes (DEGs) were enriched in apoptotic and lysosomal signaling pathways and included 26 genes of the cathepsin family. qRT-PCR verified the expression patterns of some DEGs, indicating that Cathepsin F was upregulated by 278.47-fold and that Cathepsin L and Cathepsin D were upregulated by 28.06- and 8.97-fold, respectively. Finally, association analysis between DEGs and DEMs (differentially expressed metabolites) revealed that azadirachtin significantly reduced the digestion and absorption of carbohydrates, proteins, fats, vitamins and minerals in the midgut. In conclusion, azadirachtin induces the release of cathepsin from lysosomes, causing apoptosis in the midgut. Ultimately, this leads to reduced digestion and absorption of nutrient metabolites in the midgut and inhibition of the growth and development of Bactrocera dorsalis larvae.

Nimbolide ameliorates unilateral ureteral obstruction-induced renal fibrosis by inhibition of TGF-β and EMT/Slug signalling

Chronic kidney disease (CKD) involves interstitial fibrosis as an underlying pathological process associated with compromised renal function irrespective of etiological cause of the injury. The transforming growth factor-β (TGF-β) plays a pivotal role in progression of renal fibrosis. TGF-β transduces its downstream signalling by phosphorylation of smad2/3 and also regulates epithelial-mesenchymal-transition (EMT), a program centrally involved in activation of fibroblasts. Renal fibrosis was induced in Swiss albino mice by unilateral ureteral obstruction of animals. Kidney tissues were evaluated for fibrotic protein expression by western blot and immunohistochemistry. The administration of nimbolide (NB) to UUO animals reduced the oxidative stress, expression of ECM proteins, TGF-β, p-smad and EMT program. Further, NB administration also improved histoarchitecture of obstructed kidney and reduced the collagen deposition in kidney. Our results provided compelling evidence to support antifibrotic activity of NB by reduction in oxidative stress, TGF-β, and EMT program in fibrotic kidney. The administration of NB in animals blunted the UUO-induced renal injury, inflammation and reduced fibrogenesis in obstructed kidney.

DnaJ homolog subfamily A member1 (DnaJ1) is a newly discovered anti-apoptotic protein regulated by azadirachtin in Sf9 cells

Background

Azadirachtin, one of the most promising botanical insecticides, has been widely used for pest control. Azadirachtin induces apoptosis in insect cell lines, including Sf9, SL-1 and BTI-Tn-5B1–4. Mitochondrial and lysosomal pathways are likely involved in the azadirachtin-induced apoptosis, however, detailed molecular mechanisms remain largely undefined.

Results

Azadirachtin-induced apoptosis in Sf9 cells was verified by morphological observation, Hoechst 33258 staining, and a Caspase-3-based analysis. Comparative two-dimensional gel electrophoresis (2-DE) coupled with a linear ion trap quadrupole (LTQ)-MS/MS analysis identified 12 prominent, differentially expressed proteins following azadirachtin treatment. These differentially expressed genes are involved in regulating cytoskeleton development, signal transduction, gene transcription, and cellular metabolism. Knockdown gene expression of a gene encoding a DnaJ homolog enhanced apoptosis induced by azadirachtin in Sf9 cells.

Conclusion

Azadirachtin treatment induces apoptosis in Sf9 cells and affects expression of multiple genes with functions in cytoskeleton development, signal transduction, gene regulation, and cellular metabolisms. Azadirachtin induces apoptosis at least partially by down-regulation of Sf-DnaJ in Sf9 cells.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4801-z) contains supplementary material, which is available to authorized users.

Overcoming chemotherapy drug resistance by targeting inhibitors of apoptosis proteins (IAPs)

Inhibitors of apoptosis (IAPs) are a family of proteins that play a significant role in the control of programmed cell death (PCD). PCD is essential to maintain healthy cell turnover within tissue but also to fight disease or infection. Uninhibited, IAPs can suppress apoptosis and promote cell cycle progression. Therefore, it is unsurprising that cancer cells demonstrate significantly elevated expression levels of IAPs, resulting in improved cell survival, enhanced tumor growth and subsequent metastasis. Therapies to target IAPs in cancer has garnered substantial scientific interest and as resistance to anti-cancer agents becomes more prevalent, targeting IAPs has become an increasingly attractive strategy to re-sensitize cancer cells to chemotherapies, antibody based-therapies and TRAIL therapy. Antagonism strategies to modulate the actions of XIAP, cIAP1/2 and survivin are the central focus of current research and this review highlights advances within this field with particular emphasis upon the development and specificity of second mitochondria-derived activator of caspase (SMAC) mimetics (synthetic analogs of endogenously expressed inhibitors of IAPs SMAC/DIABLO). While we highlight the potential of SMAC mimetics as effective single agent or combinatory therapies to treat cancer we also discuss the likely clinical implications of resistance to SMAC mimetic therapy, occasionally observed in cancer cell lines.

Pinus Roxburghii essential oil anticancer activity and chemical composition evaluation

The present study was conducted to appraise the anticancer activity of Pinus roxburghii essential oil along with chemical composition evaluation. MTT assay revealed cytotoxicity induction in colon, leukemia, multiple myeloma, pancreatic, head and neck and lung cancer cells exposed to essential oil. Cancer cell death was also observed through live/dead cell viability assay and FACS analysis. Apoptosis induced by essential oil was confirmed by cleavage of PARP and caspase-3 that suppressed the colony-forming ability of tumor cells and 50 % inhibition occurred at a dose of 25 μg/mL. Moreover, essential oil inhibited the activation of inflammatory transcription factor NF-κB and inhibited expression of NF-κB regulated gene products linked to cell survival (survivin, c-FLIP, Bcl-2, Bcl-xL, c-Myc, c-IAP2), proliferation (Cyclin D1) and metastasis (MMP-9). P. roxburghii essential oil has considerable anticancer activity and could be used as anticancer agent, which needs further investigation to identify and purify the bioactive compounds followed by in vivo studies.

ShDcR3 sensitizes TRAIL-resistant HCC cells by inducing caspase-dependent apoptosis while suppressing NF-κB dependent cFLIPL expression

Evidence has shown that most hepatocellular carcinoma (HCC) cells are resistant to tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL)-mediated apoptosis. However, the molecular mechanisms underlying TRAIL-mediated apoptosis resistance are not well understood. In this study, we reported that downregulation of Decoy receptor 3 (DcR3) expression by lentiviral vectors carrying shRNA against DcR3 (LV-ShDcR3, shDcR3) in Huh7 both greatly enhanced TRAIL-mediated apoptosis and reduced cell proliferation capability. In addition, silencing DcR3 resulted in upregulation of the cell apoptotic regulators including Bid, caspase-3, and caspase-8. Caspase inhibitors inhibited shDcR3-mediated cell death, which indicated that downregulation of DcR3 expression in Huh7 cells increased TRAIL-induced caspase-dependent apoptotic cell death. Furthermore, although the knockdown of DcR3 altered the expression of some Bcl-2- and IAP-family proteins, this change was inhibited by pretreatment with a pancaspase inhibitor, which indicated the cytotoxic effect of shDcR3 was not due to the expression of these proteins. In contrast, shDcR3 significantly inhibited TRAIL-induced transcription factor nuclear κB (NF-κB) activation through the IκB kinase (IKK) pathway, as well as inhibited TRAIL-induced increases in FLICE-inhibitory protein long form (cFLIP_L) expression at the transcriptional level. Silencing cFLIP_L expression mimicked the cytotoxic effect of shDcR3 on TRAIL-mediated cell apoptosis. Moreover, overexpression of cFLIP_L effectively prevented the increase in cell apoptosis in Huh7 cells co-treated with TRAIL and shDcR3. Taken together, our findings indicated that silencing DcR3 sensitizes TRAIL-mediated apoptosis in HCC cells by inhibiting NF-κB.

Synergistic Anti-tumour Effects of Quercetin and Oncolytic Adenovirus expressing TRAIL in Human Hepatocellular Carcinoma

The combination of oncolytic adenoviruses and specific chemotherapy agents is fast emerging as a novel therapeutic approach for resistan the patocellular carcinoma (HCC) cells. A detailed analysis of the network between adenovirus and chemotherapeutic agents can help design an effective strategy to combat HCC. We sought to investigate whether a combined treatment of ZD55-TRAIL and quercetin can have an enhanced cell-killing effect on HCC cells. In-vitro experiments showed that quercetin can enhance ZD55-TRAIL mediated growth inhibition and apoptosis in HCC cells. In addition, we showed that quercetin reduced ZD55-TRAIL mediated NF-κB activation and down-regulated its downstream targets, which in turn promoted the pro-apoptotic action of ZD55-TRAIL. Furthermore, in-vivo experiments in mice injected with HuH-7 cells resulted in significantly greater reduction in tumour growth and volume following combined ZD55-TRAIL and quercetin treatment. In conclusion, we demonstrated that quercetin could sensitize human HCC cells to apoptosis via ZD55-TRAIL in-vitro and in-vivo and presented ZD55-TRAIL and quercetin combination as a suitable anti-HCC therapy.

Nimbolide induces apoptosis in human nasopharyngeal cancer cells

Nasopharyngeal carcinoma (NPC), a tumor arising from epithelial cells that cover the surface and line the nasopharynx, is a rare malignancy worldwide but is prevalent in certain geographical areas, such as Southern Asia (Taiwan, Hong Kong, Singapore, Malaysia, and Southern China) and North Africa. Despite advances in diagnostic techniques and improvements in treatment modalities, the prognosis of NPC remains poor. Therefore, an effective chemotherapy regimen that enhances tumor sensitivity to chemotherapeutics is urgently required. Nimbolide, derived from Azadirachta indica, has a wide range of beneficial effects, including anti-inflammatory and anticancer properties. The present study evaluated the antitumor activity of nimbolide in NPC cells and its underlying mechanisms. Our results revealed that the treatment of HONE-1 cells with nimbolide potently inhibited cell viability. Moreover, nimbolide led to cell cycle arrest, which subsequently activated caspase-3, -8, and -9 and poly (ADP-ribose) polymerase to induce cell apoptosis. Moreover, nimbolide induced Bik, Bax, and t-Bid expression in HONE-1 cells. The results indicated that nimbolide induces apoptosis through the modulation of extracellular signal-regulated kinases 1 and 2 (ERK1/2) pathways. Nimbolide induces apoptosis in human NPC cells and is a potential chemopreventive agent against NPC proliferation. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 2085-2092, 2017.

Downregulation of DcR3 sensitizes hepatocellular carcinoma cells to TRAIL-induced apoptosis

Decoy receptor 3 (DcR3) has been recently described as an antiapoptosis and prometastasis factor since it can competitively bind to FasL, TL1A, and LIGHT, and it is highly expressed in many malignant tumors. Downregulation of DcR3 can promote tumor cell apoptosis and inhibit metastasis. A previous study demonstrated that reduction of DcR3 could induce tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-mediated apoptosis in pancreatic cancer cells. However, whether such an effect is seen in hepatocellular carcinoma (HCC) remains to be explored. This study was designed to investigate the sensitivity of HCC cells to TRAIL after silencing DcR3, and this was done by evaluating the expression of DcR3 in HCC cells and the effect on TRAIL-mediated apoptosis after downregulation of DcR3. Our data showed that DcR3 was highly expressed in HepG2, BEL-7402, Hep3B, Huh-7, MHCC97H, and SMCC7721 cell lines compared with normal liver cell line LO-2. Both HepG2 and BEL-7402 were tolerant to TRAIL-mediated apoptosis, and the tolerance was negatively correlated to the expression of DcR3. Silencing of DcR3 with shRNA and treatment with TRAIL induced obvious apoptosis in HepG2 and BEL-7402, with more cancer cells found in the G1 phase. SiDcR3 combined with TRAIL could induce activation of caspases-3, -8, and -9, raise the expression of the apoptotic protein Bax, and reduce the expression of antiapoptotic proteins (Bcl-2, Mcl-1, Bcl-XL, IAP-2, and survivin). Caspase-8 inhibitor Ac-IETD-CHO significantly decreased the activation of caspase cascade, indicating that the extrinsic pathway may have a vital role in the apoptotic events induced by SiDcR3/TRAIL. Furthermore, our results showed that the TRAIL death receptor 5 (DR5) was upregulated and that DR5 neutralizing antibody abrogated the effect of SiDcR3. Our results demonstrated that downregulation of DcR3 could enhance TRAIL-mediated apoptosis in HCC through the death receptor pathway. In the future, this might be useful as a clinical treatment method of liver cancer.

Anti-cancer effect of bee venom on colon cancer cell growth by activation of death receptors and inhibition of nuclear factor kappa B

Bee venom (BV) has been used as a traditional medicine to treat arthritis, rheumatism, back pain, cancerous tumors, and skin diseases. However, the effects of BV on the colon cancer and their action mechanisms have not been reported yet. We used cell viability assay and soft agar colony formation assay for testing cell viability, electro mobility shift assay for detecting DNA binding activity of nuclear factor kappa B (NF-κB) and Western blotting assay for detection of apoptosis regulatory proteins. We found that BV inhibited growth of colon cancer cells through induction of apoptosis. We also found that the expression of death receptor (DR) 4, DR5, p53, p21, Bax, cleaved caspase-3, cleaved caspase-8, and cleaved caspase-9 was increased by BV treatment in a dose dependent manner (0–5 μg/ml). Consistent with cancer cell growth inhibition, the DNA binding activity of nuclear factor kappa B (NF-κB) was also inhibited by BV treatment. Besides, we found that BV blocked NF-κB activation by directly binding to NF-κB p50 subunit. Moreover, combination treatment with BV and p50 siRNA or NF-κB inhibitor augmented BV-induced cell growth inhibition. However, p50 mutant plasmid (C62S) transfection partially abolished BV-induced cell growth inhibiton. In addition, BV significantly suppressed tumor growth in vivo. Therefore, these results suggested that BV could inhibit colon cancer cell growth, and these anti-proliferative effects may be related to the induction of apoptosis by activation of DR4 and DR5 and inhibition of NF-κB.

The Limonoids TS3 and Rubescin E Induce Apoptosis in Human Hepatoma Cell Lines and Interfere with NF-κB Signaling

Hepatocellular carcinoma (HCC) is extremely resistant towards pharmacological therapy. To date, the multi-kinase inhibitor Sorafenib is the only available therapeutic agent with the potential to prolong patient survival. Using the human hepatoma cell lines HepG2 and Huh7, we analyzed anti-cancer activities of 6 purified havanensin type limonoids isolated from the traditional African medicinal plant Trichilia rubescens Oliv. Our results show that two of the compounds, TR4 (TS3) and TR9 (Rubescin E) reduced hepatoma cell viability, but not primary hepatocyte viability, at TC50s of 5 to 10 μM. These were significantly lower than the TC50s for Sorafenib, the histone deacetylase inhibitor SAHA or 5-Fluoruracil. In comparison, TR3 (Rubescin D), a limonoid isolated in parallel and structurally highly similar to TR4 and TR9, did not interfere with hepatoma cell viability. Both, TR4 and TR9, but not TR3, induced apoptosis in hepatoma cells and interfered with NF-κB activation. TR4 as well as TR9 significantly supported anti-cancer activities of Sorafenib. In summary, the limonoids TR4 and TR9 exhibit anti-cancer activities and support Sorafenib effects in vitro, having the potential to support future HCC therapy.

Ginsenoside compound K sensitizes human colon cancer cells to TRAIL-induced apoptosis via autophagy-dependent and -independent DR5 upregulation

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is a potent cancer cell-specific apoptosis-inducing cytokine with little toxicity to most normal cells. However, acquired resistance of cancer cells to TRAIL is a roadblock. Agents that can either potentiate the effect of TRAIL or overcome resistance to TRAIL are urgently needed. This article reports that ginsenoside compound K (CK) potentiates TRAIL-induced apoptosis in HCT116 colon cancer cells and sensitizes TRAIL-resistant colon cancer HT-29 cells to TRAIL. On a cellular mechanistic level, CK downregulated cell survival proteins including Mcl-1, Bcl-2, surviving, X-linked inhibitor of apoptosis protein and Fas-associated death domain-like IL-1-converting enzyme-inhibitory protein, upregulated cell pro-apoptotic proteins including Bax, tBid and cytochrome c, and induced the cell surface expression of TRAIL death receptor DR5. Reduction of DR5 levels by siRNAs significantly decreases CK- and TRAIL-mediated apoptosis. Importantly, our results indicate, for the first time, that DR5 upregulation is mediated by autophagy, as blockade of CK-induced autophagy by 3-MA, LY294002 or Atg7 siRNAs substantially decreases DR5 upregulation and reduces the synergistic effect. Furthermore, CK-stimulated autophagy is mediated by the reactive oxygen species–c-Jun NH2-terminal kinase pathway. Moreover, we found that p53 and the C/EBP homologous (CHOP) protein is also required for DR5 upregulation but not related with autophagy. Our findings contribute significantly to the understanding of the mechanism accounted for the synergistic anticancer activity of CK and TRAIL, and showed a novel mechanism related with DR5 upregulation.

Anticancer properties of nimbolide and pharmacokinetic considerations to accelerate its development

Nimbolide is one of the main components in the leaf extract of Azadirachta indica (A. indica). Accumulating evidence from various in vitro and in vivo studies indicates that nimbolide possesses potent anticancer activity against several types of cancer and also shows potential chemopreventive activity in animal models. The main mechanisms of action of nimbolide include anti-proliferation, induction of apoptosis, inhibition of metastasis and angiogenesis, and modulation of carcinogen-metabolizing enzymes. Although multiple pharmacodynamic (PD) studies have been carried out, nimbolide is still at the infant stage in the drug development pipeline due to the lack of systematic pharmacokinetic (PK) studies and long-term toxicological studies. Preclinical PK and toxicological studies are vital in determining the dosage range to support the safety of nimbolide for first-in-human clinical trials. In this review, we will provide a comprehensive summary for the current status of nimbolide as an anticancer and chemopreventive lead compound, and highlight the importance of systematic preclinical PK and toxicological studies in accelerating the process of application of nimbolide as a therapeutic agent against various malignancies.

Nimbolide Inhibits Nuclear Factor-КB Pathway in Intestinal Epithelial Cells and Macrophages and Alleviates Experimental Colitis in Mice

Nimbolide is a limonoid extracted from neem tree (Azadirachta indica) that has antiinflammatory properties. The effect of nimbolide on the nuclear factor-kappa B (NF-κB) pathway in intestinal epithelial cells (IECs), macrophages and in murine colitis models was investigated. The IEC COLO 205, the murine macrophage cell line RAW 264.7, and peritoneal macrophages from interleukin-10-deficient (IL-10^-/- ) mice were preconditioned with nimbolide and then stimulated with tumor necrosis factor-α (TNF-α) or lipopolysaccharide. Dextran sulfate sodium-induced acute colitis model and chronic colitis model in IL-10^-/- mice were used for in vivo experiments. Nimbolide significantly suppressed the expression of inflammatory cytokines (IL-6, IL-8, IL-12, and TNF-α) and inhibited the phosphorylation of IκBα and the DNA-binding affinity of NF-κB in IECs and macrophages. Nimbolide ameliorated weight loss, colon shortening, disease activity index score, and histologic scores in dextran sulfate sodium colitis. It also improved histopathologic scores in the chronic colitis of IL-10^-/- mice. Staining for phosphorylated IκBα was significantly decreased in the colon tissue after treatment with nimbolide in both models. Nimbolide inhibits NF-κB signaling in IECs and macrophages and ameliorates experimental colitis in mice. These results suggest nimbolide could be a potentially new treatment for inflammatory bowel disease. Copyright © 2016 John Wiley & Sons, Ltd.

Therapeutics Role of Azadirachta indica (Neem) and Their Active Constituents in Diseases Prevention and Treatment

Neem (Azadirachta indica) is a member of the Meliaceae family and its role as health-promoting effect is attributed because it is rich source of antioxidant. It has been widely used in Chinese, Ayurvedic, and Unani medicines worldwide especially in Indian Subcontinent in the treatment and prevention of various diseases. Earlier finding confirmed that neem and its constituents play role in the scavenging of free radical generation and prevention of disease pathogenesis. The studies based on animal model established that neem and its chief constituents play pivotal role in anticancer management through the modulation of various molecular pathways including p53, pTEN, NF-κB, PI3K/Akt, Bcl-2, and VEGF. It is considered as safe medicinal plants and modulates the numerous biological processes without any adverse effect. In this review, I summarize the role of Azadirachta indica in the prevention and treatment of diseases via the regulation of various biological and physiological pathways.

Marine Drugs Regulating Apoptosis Induced by Tumor Necrosis Factor-Related Apoptosis-Inducing Ligand (TRAIL)

Marine biomass diversity is a tremendous source of potential anticancer compounds. Several natural marine products have been described to restore tumor cell sensitivity to TNF-related apoptosis inducing ligand (TRAIL)-induced cell death. TRAIL is involved during tumor immune surveillance. Its selectivity for cancer cells has attracted much attention in oncology. This review aims at discussing the main mechanisms by which TRAIL signaling is regulated and presenting how marine bioactive compounds have been found, so far, to overcome TRAIL resistance in tumor cells.

Nimbolide Induces ROS-Regulated Apoptosis and Inhibits Cell Migration in Osteosarcoma

Osteosarcoma (OS) is a primary malignant tumor of bone and is most prevalent in children and adolescents. OS is frequently associated with pulmonary metastasis, which is the main cause of OS-related mortality. OS has a poor prognosis and is often unresponsive to conventional chemotherapy. In this study, we determined that Nimbolide, a novel anti-cancer therapy, acts by modulating multiple mechanisms in osteosarcoma cells. Nimbolide induces apoptosis by increasing endoplasmic reticulum (ER) stress, mitochondrial dysfunction, accumulation of reactive oxygen species (ROS), and finally, caspase activation. We also determined that Nimbolide inhibits cell migration, which is crucial for metastasis, by reducing the expression of integrin αvβ5. In addition, our results demonstrate that integrin αvβ5 expression is modulated by the PI3K/Akt and NF-κB signaling cascade. Nimbolide has potential as an anti-tumor drug given its multifunctional effects in OS. Collectively, these results help us to understand the mechanisms of action of Nimbolide and will aid in the development of effective therapies for OS.

Embelin sensitizes acute myeloid leukemia cells to TRAIL through XIAP inhibition and NF-κB inactivation

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) shows promising result in cancer therapy and induces apoptosis in a wide variety of tumor cells, without causing toxicity to normal cells. However, many tumor cells including acute myeloid leukemia (AML) showed certain degrees of resistance to TRAIL and the mechanism remains largely unknown. Embelin is a potent XIAP inhibitor which has been shown to inhibit the proliferation of tumor cells and cause cell apoptosis. In this study, we investigated the effects of Embelin on the TRAIL-induced apoptosis and the underlying mechanism. Here, we chose an adenovirus vector as the expression vector for TRAIL, which was named Ad-TRAIL. The results in vitro showed that the co-treatment of Embelin and Ad-TRAIL has synergistically suppressed the proliferation of AML cells. Embelin has the ability to enhance TRAIL-induced apoptosis and activate caspase pathway. More interestingly, we found that the underlying mechanism for these talent skills of Embelin is through reducing the TRAIL-mediated activation of NF-κB and decreasing its transcriptional activity. Furthermore, our results in vivo suggest that combined therapy of Embelin and Ad-TRAIL caused significant growth inhibition of HL-60 xenograft tumors. Our results suggested that Embelin could sensitize AML cell to TRAIL through the repression of NF-κB signal pathway in vitro and in vivo, and combined therapy of Ad-TRAIL and Embelin may be the attractive candidate for clinical application in treatment of AML.

Anticancer activity of NOB1-targeted shRNA combination with TRAIL in epithelial ovarian cancer cells

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) based strategy is a promising targeted therapeutic approach for the treatment of ovarian cancer. However, the effectiveness of the treatment remains limited due to the inherent or acquired resistance of tumor cells to TRAIL. Our previously study demonstrated that downregulation of NOB1 (NIN1/RPN12 binding protein 1 homolog) expression by a lentiviral short hairpin RNA (shRNA) delivery system (Lv/sh-NOB1) suppressed ovarian cancer growth. Here, Lv/sh-NOB1 and TRAIL were combined and tested the effects of this combination on ovarian cancer cells to identify more effective therapeutics against ovarian cancer by several in vitro experiments. Tumor growth ability in SKVO3 xenograft nude mice was also determined to define this combination treatment effect in tumorigenesis in vivo. In vitro assay showed that Lv/sh-NOB1 in combination with TRAIL treatment in ovarian cancer cell synergistically suppressed the proliferation and colony formation, as well as induced cell apoptosis and increased the activity of caspase-3, -8 and -9. In vivo assay showed that Lv/sh-NOB1 combination with TRAIL synergistically suppressed tumor growth of nude mice model. Importantly, we found that downregulation of NOB1 could upregulate DR5 expression and active MAPK pathway, which might contribute to increase sensitivity TRAIL to ovarian cancer cells. These findings suggested that Lv/sh-NOB1 combination with TRAIL treatment may be a potential treatment approach for ovarian cancer.

Limonoids from Azadirachta indica var. siamensis extracts and their cytotoxic and melanogenesis-inhibitory activities

Six new limonoids, 7-benzoyl-17-epinimbocinol (5), 3-acetyl-7-tigloylnimbidinin (8), 1-isovaleroyl-1-detigloylsalanninolide (15), 2,3-dihydro-3α-methoxynimbolide (16), deacetyl-20,21-epoxy-20,22-dihydro-21-deoxyisonimbinolide (26), and deacetyl-20,21,22,23-tetrahydro-20,22-dihydroxy-21,23-dimethoxynimbin (27), along with 28 known limonoids, 1-4, 6, 7, 9-14, 17-25, and 28-34, and two known flavonoids, 35 and 36, have been isolated from the extracts of bark, leaves, roots, and seeds of Azadirachta indica A. Juss. var. siamensis Valeton (Siamese neem tree; Meliaceae). The structures of the new compounds were elucidated on the basis of extensive spectroscopic analysis and comparison with literature data. All of these compounds were evaluated for their cytotoxic activities against leukemia (HL60), lung (A549), stomach (AZ521), and breast (SK-BR-3) cancer cell lines. Eleven compounds, 1, 2, 4-7, 13, 16, 17, 29, and 30, exhibited potent cytotoxicities against one or more cell lines with IC50 values in the range of 0.1-9.3 μM. Compound 16 induced apoptotic cell death in AZ521 cells upon evaluation of the apoptosis-inducing activity by flow cytometric analysis. Western blot analysis on AZ521 cells revealed that compound 16 activated caspases-3, -8, and -9, while increasing the ratio of Bax/Bcl-2. This suggested that 16 induced apoptosis via both mitochondrial and death receptor pathways in AZ521. In addition, upon evaluation of all compounds against the melanogenesis in B16 melanoma cells induced with α-melanocyte-stimulating hormone (α-MSH), 20 limonoids, i.e., 1-3, 6, 9-11, 18, 19, 21-29, 32, and 34, and two flavonoids, 35 and 36, exhibited melanogenesis-inhibitory activities, with no, or almost no, toxicities to the cells at lower and/or higher concentrations, which were more potent than the reference arbutin, a known melanogenesis inhibitor. Western blot analysis showed that nimbin (18) reduced the protein levels of microphtalmia-associated transcription factor (MITF), tyrosinase, tyrosine-related protein 1 (TRP-1), and TRP-2 mostly in a concentration-dependent manner, indicating that 18 inhibits melanogenesis on a α-MSH-stimulated B16 melanoma cells by, at least in part, inhibiting the expression of MITF, followed by decreasing the expression of tyrosinase, TRP-1, and TRP-2.

Induction of cell cycle arrest, DNA damage, and apoptosis by nimbolide in human renal cell carcinoma cells

Nimbolide is a tetranortriterpenoid isolated from the leaves and flowers of Azadirachta indica which has been shown to exhibit anticancer, antioxidant, anti-inflammatory, and anti-invasive properties in a variety of cancer cells. However, the anti-tumor effect on human renal cell carcinoma (RCC) cells is unknown. In this study, we found that nimbolide treatment had a cytotoxic effect on 786-O and A-498 RCC cells in a dose-dependent manner. According to flow cytometric analysis, nimbolide treatment resulted in G2/M arrest in 786-O and A-498 cells accompanied with an increase in the phosphorylation status of p53, cdc2, cdc25c, and decreased expressions of cyclin A, cyclin B, cdc2, and cdc25c. Nimbolide also caused DNA damage in a dose-dependent manner as determined by comet assay and measurement of γ-H2AX. In addition, apoptotic cells were observed in an Annexin V-FITC/propidium iodide double-stained assay. The activities of caspase-3, -9, and poly ADP-ribose polymerase (PARP) were increased, and the expression of pro-caspase-8 was decreased in nimbolide-treated 786-O and A-498 cells. Western blot analysis revealed that the levels of intrinsic-related apoptotic proteins Bax and extrinsic-related proteins (DR5, CHOP) were significantly increased in nimbolide-treated 786-O and A-498 cells. In addition, the expressions of Bcl-2 and Mcl-1 were decreased in 786-O and A-498 cells after nimbolide treatment. We conclude that nimbolide can inhibit the growth of human RCC cells by inducing G2/M phase arrest by modulating cell cycle-related proteins and cell apoptosis by regulating intrinsic and extrinsic caspase signaling pathways. Nimbolide may be a promising therapeutic strategy for the treatment of RCC.

Targeting TNF-related apoptosis-inducing ligand (TRAIL) receptor by natural products as a potential therapeutic approach for cancer therapy

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has been shown to selectively induce apoptotic cell death in various tumor cells by engaging its death-inducing receptors (TRAIL-R1 and TRAIL-R2). This property has led to the development of a number of TRAIL-receptor agonists such as the soluble recombinant TRAIL and agonistic antibodies, which have shown promising anticancer activity in preclinical studies. However, besides activating caspase-dependent apoptosis in several cancer cells, TRAIL may also activate nonapoptotic signal transduction pathways such as nuclear factor-kappa B, mitogen-activated protein kinases, AKT, and signal transducers and activators of transcription 3, which may contribute to TRAIL resistance that is being now frequently encountered in various cancers. TRAIL resistance can be overcome by the application of efficient TRAIL-sensitizing pharmacological agents. Natural compounds have shown a great potential in sensitizing cells to TRAIL treatment through suppression of distinct survival pathways. In this review, we have summarized both apoptotic and nonapoptotic pathways activated by TRAIL, as well as recent advances in developing TRAIL-receptor agonists for cancer therapy. We also briefly discuss combination therapies that have shown great potential in overcoming TRAIL resistance in various tumors.

Nimbolide from Azadirachta indica and its derivatives plus first-generation cephalosporin antibiotics: a novel drug combination for wound-infecting pathogens

We evaluate the in vitro efficacy of nimbolide, desacetylnimbin, and the amide derivatives of nimbolide in combination with first-generation cephalosporin antibiotics against major wound-associated bacterial pathogens.

Review on molecular and chemopreventive potential of nimbolide in cancer

Cancer is the most dreaded disease in human and also major health problem worldwide. Despite its high occurrence, the exact molecular mechanisms of the development and progression are not fully understood. The existing cancer therapy based on allopathic medicine is expensive, exhibits side effects; and may also alter the normal functioning of genes. Thus, a non-toxic and effective mode of treatment is needed to control cancer development and progression. Some medicinal plants offer a safe, effective and affordable remedy to control the cancer progression. Nimbolide, a limnoid derived from the neem (Azadirachta indica) leaves and flowers of neem, is widely used in traditional medical practices for treating various human diseases. Nimbolide exhibits several pharmacological effects among which its anticancer activity is the most promising. The previous studies carried out over the decades have shown that nimbolide inhibits cell proliferation and metastasis of cancer cells. This review highlights the current knowledge on the molecular targets that contribute to the observed anticancer activity of nimbolide related to induction of apoptosis and cell cycle arrest; and inhibition of signaling pathways related to cancer progression.

Nimbolide targets BCL2 and induces apoptosis in preclinical models of Waldenströms macroglobulinemia

Neem leaf extract (NLE) has medicinal properties, which have been attributed to its limonoid content. We identified the NLE tetranorterpenoid, nimbolide, as being the key limonoid responsible for the cytotoxicity of NLE in various preclinical models of human B-lymphocyte cancer. Of the models tested, Waldenströms macroglobulinemia (WM) cells were most sensitive to nimbolide, undergoing significant mitochondrial mediated apoptosis. Notably, nimbolide toxicity was also observed in drug-resistant (bortezomib or ibrutinib) WM cells. To identify putative targets of nimbolide, relevant in WM, we used chemoinformatics-based approaches comprised of virtual in silico screening, molecular modeling and target–ligand reverse docking. In silico analysis revealed the antiapoptotic protein BCL2 was the preferential binding partner of nimbolide. The significance of this finding was further tested in vitro in RS4;11 (BCL2-dependent) tumor cells, in which nimbolide induced significantly more apoptosis compared with BCL2 mutated (Jurkat BCL2^Ser70-Ala) cells. Lastly, intraperitoneal administration of nimbolide in WM tumor xenografted mice, significantly reduced tumor growth and IgM secretion in vivo, while modulating the expression of several proteins as seen on immunohistochemistry. Overall, our data demonstrate that nimbolide is highly active in WM cells, as well as other B-cell cancers, and engages BCL2 to exert its cytotoxic activity.

Targeting death receptors for TRAIL by agents designed by Mother Nature

Selective killing of cancer cells is one of the major goals of cancer therapy. Although chemotherapeutic agents are being used for cancer treatment, they lack selectivity toward tumor cells. Among the six different death receptors (DRs) identified to date, DR4 and DR5 are selectively expressed on cancer cells. Therefore, unlike chemotherapeutic agents, these receptors can potentially mediate selective killing of tumor cells. In this review we outline various nutraceuticals derived from 'Mother Nature' that can upregulate DRs and thus potentiate apoptosis. These nutraceuticals increase tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL)-induced apoptosis of cancer cells through different mechanisms. First, nutraceuticals have been found to induce DRs through the upregulation of various signaling molecules. Second, nutraceuticals can downregulate tumor cell-survival pathways. Third, nutraceuticals alone have been found to activate cell-death pathways. Although both TRAIL and agonistic antibodies against DR4 and DR5 are in clinical trials, combination with nutraceuticals is likely to boost their anticancer potential.

Phloroglucinol induces apoptosis via apoptotic signaling pathways in HT-29 colon cancer cells

Phloroglucinol is a polyphenolic compound that is used to treat and prevent several human diseases, as it exerts beneficial biological activities, including anti-oxidant, anti-inflammatory and anticancer properties. The aim of the present study was to investigate the effects of phloroglucinol on apoptotic signaling pathways in HT-29 colon cancer cells. The results indicated that phloroglucinol suppressed cell viability and induced apoptosis in HT-29 cells in a concentration-dependent manner. Phloroglucinol treatment of HT-29 cells resulted in characteristic apoptosis-related changes: altered Bcl-2 family proteins, cytochrome c release, and activation of caspase-3 and caspase-8. This study also showed that proteins involved in apoptosis were stimulated by treatment with phloroglucinol. These findings demonstrated that phloroglucinol exerts anticancer activity in HT-29 colon cancer cells through induction of apoptosis.

Neem components as potential agents for cancer prevention and treatment

Azadirachta indica, also known as neem, is commonly found in many semi-tropical and tropical countries including India, Pakistan, and Bangladesh. The components extracted from neem plant have been used in traditional medicine for the cure of multiple diseases including cancer for centuries. The extracts of seeds, leaves, flowers, and fruits of neem have consistently shown chemopreventive and antitumor effects in different types of cancer. Azadirachtin and nimbolide are among the few bioactive components in neem that have been studied extensively, but research on a great number of additional bioactive components is warranted. The key anticancer effects of neem components on malignant cells include inhibition of cell proliferation, induction of cell death, suppression of cancer angiogenesis, restoration of cellular reduction/oxidation (redox) balance, and enhancement of the host immune responses against tumor cells. While the underlying mechanisms of these effects are mostly unclear, the suppression of NF-κB signaling pathway is, at least partially, involved in the anticancer functions of neem components. Importantly, the anti-proliferative and apoptosis-inducing effects of neem components are tumor selective as the effects on normal cells are significantly weaker. In addition, neem extracts sensitize cancer cells to immunotherapy and radiotherapy, and enhance the efficacy of certain cancer chemotherapeutic agents. This review summarizes the current updates on the anticancer effects of neem components and their possible impact on managing cancer incidence and treatment.

YM155 sensitizes triple-negative breast cancer to membrane-bound TRAIL through p38 MAPK- and CHOP-mediated DR5 upregulation

Because available treatments have limited efficacy in triple-negative breast cancer (TNBC), the identification of new therapeutic strategies to improve patients' outcome is urgently needed. In our study, we investigated the effects of the administration of the small molecule selective survivin suppressant YM155, alone or in association with CD34+ cells transduced with a replication-deficient adenovirus encoding the human tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) gene (CD34-TRAIL+ cells), in three TNBC cell models. YM155 exposure significantly impaired TNBC cell growth and selectively modulated survivin expression at both mRNA and protein level. In addition, co-culturing YM155-treated TNBC cells with CD34-TRAIL+ cells resulted in markedly increased cytotoxic effect and apoptotic response in comparison with single treatments. Such a chemosensitizing effect was observed only in TNBC cells inherently expressing DR5 and relied on the ability of YM155 to upregulate DR5 expression through a p38 MAPK- and CHOP-dependent mechanism. YM155/CD34-TRAIL+ combination also showed a significant inhibitory effect on the growth of DR5-expressing TNBC cells following xenotransplantation into NOD/SCID mice, in the absence of toxicity. Overall, our data (i) provide, for the first time, evidence that YM155 sensitizes TNBC cells to CD34-TRAIL+ cells-induced apoptosis by a mechanism involving the downregulation of survivin and the simultaneous p38 MAPK- and CHOP-mediated upregulation of DR5, and (ii) suggest the combination of YM155 with TRAIL-armed CD34+ progenitor cells as a promising therapeutic option for patients with TNBC expressing DR5.

Nimbolide inhibits IGF-I-mediated PI3K/Akt and MAPK signalling in human breast cancer cell lines (MCF-7 and MDA-MB-231)

The insulin-like growth factor I (IGF-I) signalling pathway contributes a major role on various cancer cell proliferation, survival and cell cycle. The present study was aimed to investigate the effect of nimbolide on IGF signalling and cell cycle arrest in MCF-7 and MDA-MB-231 breast cancer cell lines. The protein expression of IGF signalling molecules and cell cycle protein levels was assessed by western blot analysis. In order to study the interaction of nimbolide on IGF-1 signalling pathway, IGF-I and phosphoinositide 3-kinase (PI3K) inhibitor (LY294002) were used to treat MCF-7 and MDA-MB-231 cells. Further, the cell cycle arrest was analysed by flow cytometry. The protein expression of IGF signalling molecules was significantly decreased in nimbolide-treated breast cancer cells. PI3K inhibitor and IGF-I with nimbolide treatment notably inhibited phosphorylated Akt. The cell cycle arrest was observed at the G0/G1 phase, and accumulation of apoptotic cells was observed in nimbolide-treated breast cancer cell lines. Nimbolide also increased the protein expression of p21 and decreased the cyclins in both the cell lines. Nimbolide decreases the proliferation of breast cancer cells by modulating the IGF signalling molecules, which could be very useful for the breast cancer treatment.

Chemopreventive and therapeutic effects of nimbolide in cancer: the underlying mechanisms

Cancer chemoprevention is a strategy taken to block, reverse or retard the multistep process of carcinogenesis, including the blockage of its vital morphogenetic milestones viz. normal-preneoplasia-neoplasia-metastasis. Naturally occurring phytochemicals are becoming increasingly popular over synthetic drugs for several reasons, including safety, efficacy and easy availability. Nimbolide, a triterpene derived from the leaves and flowers of neem, is widely used in traditional medical practices for treating various human ailments. The neem limonoid exhibits multiple pharmacological effects among which its anticancer activity is the most promising. The preclinical and mechanistic studies carried over the decades have shown that nimbolide inhibits tumorigenesis and metastasis without any toxicity and unwanted side effects. Nimbolide exhibits anticancer activity through selective modulation of multiple cell signaling pathways linked to inflammation, survival, growth, invasion, angiogenesis and metastasis. The present review highlights the current knowledge on molecular targets that contribute to the observed anticancer activity of nimbolide related to (i) inhibition of carcinogenic activation and induction of antioxidant and carcinogen detoxification enzymes, (ii) induction of growth arrest and apoptosis; and (iii) suppression of proinflammatory signaling pathways related to cancer progression.

Neem Limonoids as Anticancer Agents: Modulation of Cancer Hallmarks and Oncogenic Signaling

Neem (Azadirachta indica A. Juss) is one of the most versatile medicinal plants, widely distributed in the Indian subcontinent. Neem is a rich source of limonoids that are endowed with potent medicinal properties predominantly antioxidant, anti-inflammatory, and anticancer activities. Azadirachtin, gedunin, and nimbolide are more extensively investigated relative to other neem limonoids. Accumulating evidence indicates that the anticancer effects of neem limonoids are mediated through the inhibition of hallmark capabilities of cancer such as cell proliferation, apoptosis evasion, inflammation, invasion, and angiogenesis. The neem limonoids have been demonstrated to target oncogenic signaling kinases and transcription factors chiefly, NF-κB, Wnt/β-catenin, PI3K/Akt, MAPK, and JAK/STAT signaling pathways. Neem limonoids that target multiple pathways that are aberrant in cancer are ideal candidates for cancer chemoprevention and therapy.

The plant alkaloid and anti-leukemia drug homoharringtonine sensitizes resistant human colorectal carcinoma cells to TRAIL-induced apoptosis via multiple mechanisms

TNF-related apoptosis-inducing ligand (TRAIL) is a pro-apoptotic ligand from the TNF-alpha family that is under consideration, along with agonistic anti-TRAIL receptor antibodies, as a potential anti-tumor agent. However, most primary human tumors are resistant to monotherapy with TRAIL apoptogens, and thus the potential applicability of TRAIL in anti-tumor therapy ultimately depends on its rational combination with drugs targeting these resistances. In our high-throughput screening for novel agents/drugs that could sensitize TRAIL-resistant colorectal cancer cells to TRAIL-induced apoptosis, we found homoharringtonine (HHT), a cephalotaxus alkaloid and tested anti-leukemia drug, to be a very effective, low nanomolar enhancer of TRAIL-mediated apoptosis/growth suppression of these resistant cells. Co-treatment of TRAIL-resistant RKO or HT-29 cells with HHT and TRAIL led to the effective induction of apoptosis and the complete elimination of the treated cells. HHT suppressed the expression of the anti-apoptotic proteins Mcl-1 and cFLIP and enhanced the TRAIL-triggered activation of JNK and p38 kinases. The shRNA-mediated down-regulation of cFLIP or Mcl-1 in HT-29 or RKO cells variably enhanced their TRAIL-induced apoptosis but it did not markedly sensitize them to TRAIL-mediated growth suppression. However, with the notable exception of RKO/sh cFLIP cells, the downregulation of cFLIP or Mcl-1 significantly lowered the effective concentration of HHT in HHT + TRAIL co-treatment. Combined HHT + TRAIL therapy also led to the strong suppression of HT-29 tumors implanted into immunodeficient mice. Thus, HHT represents a very efficient enhancer of TRAIL-induced apoptosis with potential application in TRAIL-based, anti-cancer combination therapy.

Aldose reductase inhibition enhances TRAIL-induced human colon cancer cell apoptosis through AKT/FOXO3a-dependent upregulation of death receptors

One of the major problems associated with the chemotherapy of tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) that selectively kills tumor cells is decreased drug resistance. This warranted the development of safe novel pharmacological agents that could sensitize the tumor cells to TRAIL. Herein, we examined the role of aldose reductase (AR) in sensitizing cancer cells to TRAIL and potentiating TRAIL-induced apoptosis of human colon cancer cells. We demonstrate that AR inhibition potentiates TRAIL-induced cytotoxicity in cancer cells by upregulation of both death receptor (DR)-5 and DR4. Knockdown of DR5 and DR4 significantly (>85%) reduced the sensitizing effect of the AR inhibitor fidarestat on TRAIL-induced apoptosis. Further, AR inhibition also downregulates cell survival proteins (Bcl-xL, Bcl-2, survivin, XIAP, and FLIP) and upregulates the expression of proapoptotic proteins such as Bax and alters mitochondrial membrane potential, leading to cytochrome c release, caspases-3 activation, and PARP cleavage. We found that AR inhibition regulates AKT/PI3K-dependent activation of forkhead transcription factor FOXO3a. Knockdown of FOXO3a significantly (>80%) abolished AR inhibition-induced upregulation of DR5 and DR4 and apoptosis in colon cancer cells. Overall, our results show that fidarestat potentiates TRAIL-induced apoptosis through downregulation of cell survival proteins and upregulation of death receptors via activation of the AKT/FOXO3a pathway.