Activation of lysosomal mediated cell death in the course of autophagy by mTORC1 inhibitor

Lysosomal biogenesis plays a vital role in cell fate. Under certain conditions, excessive lysosomal biogenesis leads to susceptibility for lysosomal membrane permeabilization resulting in various pathological conditions including cell death. In cancer cells apoptosis machinery becomes dysregulated during the course of treatment, thus allows cancer cells to escape apoptosis. So it is therefore imperative to identify cytotoxic agents that exploit non-apoptotic mechanisms of cell death. Our study showed that pancreatic cancer cells treated with SDS-203 triggered an incomplete autophagic response and a nuclear translocation of transcriptional factor TFEB. This resulted in abundant biosynthesis and accumulation of autophagosomes and lysosomes into the cells leading to their death. It was observed that the silencing of autophagy genes didn’t alter the cell fate, whereas siRNA-mediated silencing of TFEB subdued SDS-203 mediated lysosomal biogenesis and associated cell death. Further mouse tumors treated with SDS-203 showed a significant reduction in tumor burden and increased expression of lysosomal markers. Taken together this study demonstrates that SDS-203 treatment triggers non-apoptotic cell death in pancreatic cancer cells through a mechanism of lysosome over accumulation.

Total Synthesis and Conformational Analysis of Naturally Occurring Lipovelutibols along with Lead Optimization of Lipovelutibol D

Four lipopeptaibols, namely, lipovelutibols A-D, were recently isolated from psychrotrophic fungus Trichoderma velutinum and reported to have significant cytotoxic activity against HL-60, MDA-MD-231, A549, and LS180 cancer cell lines. In the present study, these peptides were synthesized in a solution using a segment condensation approach. The conformational analysis of these peptides carried out using CD spectrophotometry revealed the formation of 310-helix, and the NMR-VT experiments showed intramolecular hydrogen bonding for NH-5, NH-6, and NH-7. Lipovelutibol D showed potent cytotoxic activity and was chosen for lead optimization. It involved N- and C-terminal truncation, N- and C-terminal modification, random deletion, l/d configuration replacement, and other synthetic analogues. These were tested against various breast cancer cell lines. The C-terminal aldehyde analogue resulting from lead optimization of lipovelutibol D was found to have almost twofold enhanced cytotoxicity against MDA-MB-231 breast cancer cell lines.

14-Residue peptaibol velutibol A from Trichoderma velutinum: its structural and cytotoxic evaluation

Velutibol A (1), a new 14-residue peptaibol was isolated from the Himalayan cold habitat fungus Trichoderma velutinum. The structural characterization was carried out by 1D and 2D NMR studies, and tandem mass studies, and Marfey's method aided in determining the stereochemistry of the amino acids. The CD analysis revealed folding of the peptide in a 3₁₀-helical conformation. The intramolecular H-bonding was determined by an NMR-VT experiment. Cytotoxic evaluation was carried out against a panel of cancer cell lines. The cell cycle assay was carried out on human myeloid leukaemia (HL-60) cells and revealed the formation of apoptotic bodies and DNA damage in a dose-dependent manner. Three other peptaibols namely velutibol B (2), velutibol C (3), and velutibol D (4) were also isolated in trace amounts from the psychotropic fungus and characterized through tandem mass spectroscopy and Marfey's analysis.

Velutibol A (1), a new 14-residue peptaibol isolated from the Himalayan cold habitat fungus Trichoderma velutinum.

PID1 increases chemotherapy-induced apoptosis in medulloblastoma and glioblastoma cells in a manner that involves NFκB

Phosphotyrosine Interaction Domain containing 1 (PID1; NYGGF4) inhibits growth of medulloblastoma, glioblastoma and atypical teratoid rhabdoid tumor cell lines. PID1 tumor mRNA levels are highly correlated with longer survival in medulloblastoma and glioma patients, suggesting their tumors may have been more sensitive to therapy. We hypothesized that PID1 sensitizes brain tumors to therapy. We found that PID1 increased the apoptosis induced by cisplatin and etoposide in medulloblastoma and glioblastoma cell lines. PID1 siRNA diminished cisplatin-induced apoptosis, suggesting that PID1 is required for cisplatin-induced apoptosis. Etoposide and cisplatin increased NFκB promoter reporter activity and etoposide induced nuclear translocation of NFκB. Etoposide also increased PID1 promoter reporter activity, PID1 mRNA, and PID1 protein, which were diminished by NFκB inhibitors JSH-23 and Bay117082. However, while cisplatin increased PID1 mRNA, it decreased PID1 protein. This decrease in PID1 protein was mitigated by the proteasome inhibitor, bortezomib, suggesting that cisplatin induced proteasome dependent degradation of PID1. These data demonstrate for the first time that etoposide- and cisplatin-induced apoptosis in medulloblastoma and glioblastoma cell lines is mediated in part by PID1, involves NFκB, and may be regulated by proteasomal degradation. This suggests that PID1 may contribute to responsiveness to chemotherapy.

Palladium-catalyzed arylation of 2H-chromene: a new entry to pyrano[2,3-c]carbazoles

Various pyrano[2,3-c]carbazoles are synthesized in high yields over five steps from commercially available resorcinol. Palladium-catalyzed arylation remains a key step in this novel strategy. The versatility of this protocol has been demonstrated by the first total synthesis of naturally occurring carbazole clauraila C.

3-(2,6-Dichloro-benzyloxy)-11-oxo-olean-12-ene-29-oic acid, a semisynthetic derivative of glycyrrhetic acid: synthesis, antiproliferative, apoptotic and anti-angiogenesis activity

The synthesis and biological evaluation of the semisynthetic analogs of glycyrrhetic acid are described.

Autophagy triggered by magnolol derivative negatively regulates angiogenesis

Angiogenesis has a key role in the tumor progression and metastasis; targeting endothelial cell proliferation has emerged as a promising therapeutic strategy for the prevention of cancer. Previous studies have revealed a complex association between the process of angiogenesis and autophagy and its outcome on tumorigenesis. Autophagy, also known as type-II cell death, has been identified as an alternative way of cell killing in apoptotic-resistant cancer cells. However, its involvement in chemoresistance and tumor promotion is also well known. In this study, we used a derivate of natural product magnolol (Ery5), a potent autophagy inducer, to study the association between the autophagy and angiogenesis in both in vitro and in vivo model system. We found that the robust autophagy triggered by Ery5, inhibited angiogenesis and caused cell death independent of the apoptosis in human umbilical cord vein endothelial cells and PC-3 cells. Ery5 induced autophagy effectively inhibited cell proliferation, migration, invasion and tube formation. We further demonstrated that Ery5-mediated autophagy and subsequent inhibition of angiogenesis was reversed when autophagy was inhibited through 3-methyl adenine and knocking down of key autophagy proteins ATG7 and microtubule-associated protein light chain 3. While evaluating the negative regulation of autophagy on angiogenesis, it was interesting to find that angiogenic environment produced by the treatment of VEGF and CoCl2 remarkably downregulated the autophagy and autophagic cell death induced by Ery5. These studies, while disclosing the vital role of autophagy in the regulation of angiogenesis, also suggest that the potent modulators of autophagy can lead to the development of effective therapeutics in apoptosis-resistant cancer.

Disruption of the PI3K/AKT/mTOR signaling cascade and induction of apoptosis in HL-60 cells by an essential oil from Monarda citriodora

We have isolated an essential oil from Monarda citriodora (MC) and characterized its 22 chemical constituents with thymol (82%), carvacrol (4.82%), β-myrcene (3.45%), terpinen-4-ol (2.78%) and p-cymene (1.53%) representing the major constituents. We have reported for the first time the chemotherapeutic potential of MC in human promyelocytic leukemia HL-60 cells by means of apoptosis and disruption of the PI3K/AKT/mTOR signaling cascade. MC and its major constituent, thymol, inhibit the cell proliferation in different types of cancer cell lines like HL-60, MCF-7, PC-3, A-549 and MDAMB-231. MC was found to be more cytotoxic than thymol in HL-60 cells with an IC50 value of 22 μg/ml versus 45 μg/ml for thymol. Both MC and thymol induce apoptosis in HL-60 cells, which is evident by Hoechst staining, cell cycle analysis and immuno-expression of Bcl-xL, caspase-3,-8,-9 and PARP-1 cleavage. Both induce apoptosis by extrinsic and intrinsic apoptotic pathways that were confirmed by enhanced expression of death receptors (TNF-R1, Fas), caspase-9, loss of mitochondrial membrane potential and regression of Bcl-2/Bax ratio. Interestingly, both MC and thymol inhibit the downstream and upstream signaling of PI3K/AKT/mTOR pathway. The degree of apoptosis induction and disruption of the PI3K signaling cascade by MC was significantly higher when compared to thymol.

The anticancer potential of flavonoids isolated from the stem bark of Erythrina suberosa through induction of apoptosis and inhibition of STAT signaling pathway in human leukemia HL-60 cells

Erythrina suberosa is an ornamental tall tree found in India, Pakistan, Nepal, Bhutan, Burma, Thailand and Vietnam. We have isolated four known distinct metabolites designated as α-Hydroxyerysotrine, 4'-Methoxy licoflavanone (MLF), Alpinumisoflavone (AIF) and Wighteone. Among the four isolated metabolites the two flavonoids, MLF and AIF were found to be the most potent cytotoxic agent with IC50 of ∼20μM in human leukemia HL-60 cells. We are reporting first time the anticancer and apoptotic potential of MLF and AIF in HL-60 cells. Both MLF and AIF inhibited HL-60 cell proliferation and induce apoptosis as measured by several biological endpoints. MLF and AIF induce apoptosis bodies formation, enhanced annexinV-FITC binding of the cells, increased sub-G0 cell fraction, loss of mitochondrial membrane potential (Δψm), release of cytochrome c, Bax, activation of caspase-9, caspase-3 and PARP (poly ADP Ribose polymers) cleavage in HL-60 cells. MLF and AIF also increase the expression of apical death receptor, Fas, with inhibition of anti-apoptotic protein Bid. All the above parameters revealed that these two flavonoids induce apoptosis through both extrinsic and intrinsic apoptotic pathways in HL-60 cells. In spite of apoptosis, these two flavonoids significantly inhibit nuclear transcription factor NF-κB and STAT (Signal Transducer and Activator of Transcription) signaling pathway, which are highly expressed in leukemia. The present study provide an insight of molecular mechanism of cell death induced by MLF and AIF in HL-60 cells which may be useful in managing and treating leukemia.

Tiron and trolox potentiate the autophagic cell death induced by magnolol analog Ery5 by activation of Bax in HL-60 cells

This study describes the mechanism of trolox and tiron induced potentiation of cytotoxicity caused by Ery5, an analog of magnolol, in human myeloid leukemia HL-60 cells. Ery5 induced cytotoxicity in HL-60 cells by involving activation of bax and cleavage of caspase 3, which contributed towards activation of both apoptotic and autophagic pathways. Trolox and tiron, even at non-toxic concentrations, contributed to the cytotoxicity of Ery5 by activation of autophagic proteins like ATG7, ATG12 and LC3-II. Z-VAD-fmk mediated reduction in the cytotoxicity and expression of autophagic proteins, further suggested that autophagy induced by Ery5 is largely dependent upon caspases. Interestingly, Ery5 induced autophagy was accompanied by the downregulation of PI3K/AKT pathway whereas, trolox and tiron strongly enhanced this effect. In addition to that treatment of cells with Ery5, trolox and tiron individually, displayed a marked upregulation of Bax. The involvement of Bax in trolox and tiron induced enhancement of the cytotoxicity of Ery5 was confirmed, when siRNA induced silencing of Bax led to increased viability of the cells and exerted a strong inhibitory effect on LC3-II accumulation and p62 degradation in case of cells treated by the combination of Ery5 with trolox or tiron. Additionally, an important role of PARP in Ery5 mediated cell death has been suggested by PARP silencing experiments, however, potentiation of autophagic cytotoxicity by trolox and tiron did not seem to be dependent on PARP-1. Therefore, Bax seems to play a vital role in trolox and tiron mediated potentiation of autophagic cell death by Ery5 in HL-60 cells.