Inhibition of Hedgehog signaling sensitizes NSCLC cells to standard therapies through modulation of EMT-regulating miRNAs.

BACKGROUND: Epidermal growth factor receptor- tyrosine kinase inhibitors (EGFR-TKIs) benefit Non-small cell lung cancer (NSCLC) patients, and an EGFR-TKIi erlotinib, is approved for patients with recurrent NSCLC. However, resistance to erlotinib is a major clinical problem. Earlier we have demonstrated the role of Hedgehog (Hh) signaling in Epithelial-to-Mesenchymal transition (EMT) of NSCLC cells, leading to increased proliferation and invasion. Here, we investigated the role of Hh signaling in erlotinib resistance of TGF-ß1-induced NSCLC cells that are reminiscent of EMT cells. METHODS: Hh signaling was inhibited by specific siRNA and by GDC-0449, a small molecule antagonist of G protein coupled receptor smoothened in the Hh pathway. Not all NSCLC patients are likely to benefit from EGFR-TKIs and, therefore, cisplatin was used to further demonstrate a role of inhibition of Hh signaling in sensitization of resistant EMT cells. Specific pre- and anti-miRNA preparations were used to study the mechanistic involvement of miRNAs in drug resistance mechanism. RESULTS: siRNA-mediated inhibition as well as pharmacological inhibition of Hh signaling abrogated resistance of NSCLC cells to erlotinib and cisplatin. It also resulted in re-sensitization of TGF-ß1-induced A549 (A549M) cells as well the mesenchymal phenotypic H1299 cells to erlotinib and cisplatin treatment with concomitant up-regulation of cancer stem cell (CSC) markers (Sox2, Nanog and EpCAM) and down-regulation of miR-200 and let-7 family miRNAs. Ectopic up-regulation of miRNAs, especially miR-200b and let-7c, significantly diminished the erlotinib resistance of A549M cells. Inhibition of Hh signaling by GDC-0449 in EMT cells resulted in the attenuation of CSC markers and up-regulation of miR-200b and let-7c, leading to sensitization of EMT cells to drug treatment, thus, confirming a connection between Hh signaling, miRNAs and drug resistance. CONCLUSIONS: We demonstrate that Hh pathway, through EMT-induction, leads to reduced sensitivity to EGFR-TKIs in NSCLCs. Therefore, targeting Hh pathway may lead to the reversal of EMT phenotype and improve the therapeutic efficacy of EGFR-TKIs in NSCLC patients.

Targeting the Hedgehog signaling pathway for cancer therapy.

INTRODUCTION: Hedgehog (Hh) signaling pathway plays key roles in embryonic development, formation and maintenance of cancer stem cells (CSCs) and acquisition of epithelial-to-mesenchymal transition (EMT). Since CSCs and EMT are important biological factors responsible for cancer cell invasion, metastasis, drug resistance and tumor recurrence, the Hh signaling pathway is believed to be an important target for cancer therapy. AREAS COVERED: In recent years, small-molecule inhibitors of Hh signaling have been synthesized for cancer treatment. Clinical trials using these inhibitors are being conducted to determine their toxicity profiles and efficacies. In addition, nutraceuticals (such as isoflavones, curcumin, vitamin D, etc) have been shown to inhibit cancer growth through downregulation of Hh signaling. EXPERT OPINION: Inhibition of Hh signaling is important for suppression of cancer growth, invasion, metastasis and recurrence in cancer therapy. However, targeting only one molecule in Hh signaling may not be sufficient to kill cancer cells because cancers show deregulation of multiple signals. Therefore, utilizing new technologies to determine alterations in Hh and other signals for individuals and designing combination strategies with small-molecule Hh inhibitors, nutraceuticals and other chemotherapeutics in targeted personalized therapy could have a significant effect on improving the overall survival of patients with cancers.

Garcinol-induced apoptosis in prostate and pancreatic cancer cells is mediated by NF- kappaB signaling.

Garcinol, obtained from Garcinia indica, is a potent antioxidant. Its anticancer activity has been investigated; however, there is no published report on its action against prostate and pancreatic cancer cells. We have earlier reported its activity against breast cancer cells, and here we tested our hypothesis that garcinol could inhibit cell proliferation and induce apoptosis in prostate as well as pancreatic cancer cells. Using multiple techniques such as MTT, Histone-DNA ELISA, activated caspase assays, clonogenic assays and EMSA, we investigated the mechanism of apoptosis-inducing effect of garcinol in prostate (LNCaP, C4-2B and PC3) and pancreatic (BxPC-3) cancer cells. We found that garcinol inhibited cell growth of all the cell lines tested with a concomitant induction of apoptosis in a dose-dependent manner. Down-regulation of NF-kappaB signaling pathway appears to be the mechanism of apoptosis-induction because garcinol inhibited constitutive levels of NF-betaB activity, which was consistent with down-regulation of NF-betaB-regulated genes. A significant decrease in the colony forming ability of all the cell lines was also observed, suggesting the possible application of this compound against metastatic disease. In summary, our results provide pre-clinical evidence to support the use of garcinol against human prostate and pancreatic cancer, thus meriting its further investigation as a potential chemo-preventive and/or therapeutic agent.

Up-regulation of sonic hedgehog contributes to TGF-ß1-induced epithelial to mesenchymal transition in NSCLC cells.

BACKGROUND: Lung cancer, especially non-small cell lung cancer (NSCLC) is the major cause of cancer-related deaths in the United States. The aggressiveness of NSCLC has been shown to be associated with the acquisition of epithelial-to-mesenchymal transition (EMT). The acquisition of EMT phenotype induced by TGF-ß1in several cancer cells has been implicated in tumor aggressiveness and resistance to conventional therapeutics; however, the molecular mechanism of EMT and tumor aggressiveness in NSCLC remains unknown. METHODOLOGY/PRINCIPAL FINDINGS: In this study we found for the first time that the induction of EMT by chronic exposure of A549 NSCLC cells to TGF-ß1 (A549-M cells) led to the up-regulation of sonic hedgehog (Shh) both at the mRNA and protein levels causing activation of hedgehog signaling. These results were also reproduced in another NSCLC cell line (H2030). Induction of EMT was found to be consistent with aggressive characteristics such as increased clonogenic growth, cell motility and invasion. The aggressiveness of these cells was attenuated by the treatment of A549-M cells with pharmacological inhibitors of Hh signaling in addition to Shh knock-down by siRNA. The inhibition of Hh signaling by pharmacological inhibitors led to the reversal of EMT phenotype as confirmed by the reduction of mesenchymal markers such as ZEB1 and Fibronectin, and induction of epithelial marker E-cadherin. In addition, knock-down of Shh by siRNA significantly attenuated EMT induction by TGF-ß1. CONCLUSIONS/SIGNIFICANCE: Our results show for the first time the transcriptional up-regulation of Shh by TGF-ß1, which is mechanistically associated with TGF-ß1 induced EMT phenotype and aggressive behavior of NSCLC cells. Thus the inhibitors of Shh signaling could be useful for the reversal of EMT phenotype, which would inhibit the metastatic potential of NSCLC cells and also make these tumors more sensitive to conventional therapeutics.

Anticancer activity of a broccoli derivative, sulforaphane, in barrett adenocarcinoma: potential use in chemoprevention and as adjuvant in chemotherapy.

INTRODUCTION: The incidence of Barrett esophageal adenocarcinoma (BEAC) has been increasing at an alarming rate in western countries. In this study, we have evaluated the therapeutic potential of sulforaphane (SFN), an antioxidant derived from broccoli, in BEAC. METHODS: BEAC cells were treated with SFN, alone or in combination with chemotherapeutic, paclitaxel, or telomerase-inhibiting agents (MST-312, GRN163L), and live cell number determined at various time points. The effect on drug resistance/chemosensitivity was evaluated by rhodamine efflux assay. Apoptosis was detected by annexin V labeling and Western blot analysis of poly(ADP-ribose) polymerase cleavage. Effects on genes implicated in cell cycle and apoptosis were determined by Western blot analyses. To evaluate the efficacy in vivo, BEAC cells were injected subcutaneously in severe combined immunodeficient mice, and after the appearance of palpable tumors, mice were treated with SFN. RESULTS: SFN induced both time- and dose-dependent decline in cell survival, cell cycle arrest, and apoptosis. The treatment with SFN also suppressed the expression of multidrug resistance protein, reduced drug efflux, and increased anticancer activity of other antiproliferative agents including paclitaxel. A significant reduction in tumor volume was also observed by SFN in a subcutaneous tumor model of BEAC. Anticancer activity could be attributed to the induction of caspase 8 and p21 and down-regulation of hsp90, a molecular chaperon required for activity of several proliferation-associated proteins. CONCLUSIONS: These data indicate that a natural product with antioxidant properties from broccoli has great potential to be used in chemoprevention and treatment of BEAC.

Apoptosis-inducing effect of garcinol is mediated by NF-kappaB signaling in breast cancer cells.

Garcinol, obtained from Garcinia indica in tropical regions, is used for its numerous biological effects. Its anti-cancer activity has been suggested but the mechanism of action has not been studied in-detail, especially there is no report on its action against breast cancer cells. Here we tested our hypothesis that garcinol may act as an anti-proliferative and apoptosis-inducing agent against breast cancer cell lines. Using multiple techniques such as MTT, Histone-DNA ELISA, Annexin V-PI staining, Western blot for activated caspases and cleaved PARP, homogenous caspase-3/7 fluorometric assay and EMSA, we investigated the mechanism of apoptosis-inducing effect of garcinol in ER-positive MCF-7 and ER-negative MDA-MB-231 cells. We found that garcinol exhibits dose-dependent cancer cell-specific growth inhibition in both the cell lines with a concomitant induction of apoptosis, and has no effect on non-tumorigenic MCF-10A cells. Our results suggested induction of caspase-mediated apoptosis in highly metastatic MDA-MB-231 cells by garcinol. Down-regulation of NF-kappaB signaling pathway was observed to be the mechanism of apoptosis-induction. Garcinol inhibited constitutive NF-kappaB activity, which was consistent with down-regulation of NF-kappaB-regulated genes. This is the first report on anti-proliferative and apoptosis-inducing action of garcinol against human breast cancer cells and the results suggest that this natural compound merits investigation as a potential chemo-preventive/-therapeutic agent, especially against breast cancer.

Suppression of sphingomyelin synthase 1 by small interference RNA is associated with enhanced ceramide production and apoptosis after photodamage.

We have shown that overexpression of SMS1, an enzyme that converts de novo ceramide into sphingomyelin, is accompanied by attenuated ceramide response and apoptotic resistance after photodamage with the photosensitizer Pc 4 (photodynamic therapy; PDT). To test whether SMS1 overexpression-related effects after PDT can be reversed, in this study SMS1 was downregulated in Jurkat T lymphoma/leukemia cells using small inhibitory RNA (siRNA) for SMS1. Compared to scrambled (control) siRNA-transfectants, in SMS1 siRNA-transfected cells the activity of SMS at rest was downregulated with concomitant decrease in sphingomyelin mass. In SMS1 siRNA-transfected cells increases in ceramides were higher than in control siRNA-transfectants after PDT. Similar findings were obtained for dihydroceramides suggesting the involvement of de novo ceramide pathway. PDT-induced DEVDase (caspase-3-like) activation was enhanced in SMS1 siRNA-transfected cells compared to their control counterparts. The data show that RNA interference-dependent downregulation of SMS1 is associated with increased accumulation of ceramide and dihydroceramide with concomitant sensitization of cells to apoptosis after photodamage. Similarly, in SMS2 siRNA-transfected cells, downregulation of SMS activity was accompanied by potentiated DEVDase activation post-photodamage. These findings suggest that SMS is a potential novel molecular target that can augment therapeutic efficacy of PDT.

Sphingomyelin synthase 1 suppresses ceramide production and apoptosis post-photodamage.

The role of sphingomyelin synthase 1 (SMS1), the Golgi membrane isoform of the enzyme, in ceramide metabolism and apoptosis after photodamage with the photosensitizer Pc 4 (PDT) is unclear. In the present study, using electrospray ionization/double mass spectrometry, we show that in Jurkat cells overexpressing SMS1, increases in ceramides were lower than in empty-vector transfectants post-PDT. Similarly, the responses of dihydroceramides and dihydrosphingosine, precursors of ceramide in the de novo synthetic pathway, were attenuated in SMS1-overexpressor after photodamage, suggesting the involvement of the de novo pathway. Overexpression of SMS1 was associated with differential regulation of sphingomyelin levels, as well as with the reduced inhibition of the enzyme post-treatment. Concomitant with the suppressed ceramide response, PDT-induced DEVDase activation was substantially reduced in SMS1-overexpressors. The data show that overexpression of SMS1 is associated with suppressed ceramide response and apoptotic resistance after photodamage.

Ceramide response post-photodamage is absent after treatment with HA14-1.

The oxidative stress induced by photodynamic therapy using the phthalocyanine Pc 4 (PDT) can lead to apoptosis, and is accompanied by photodamage to Bcl-2 and accumulation of de novo ceramide. Similar to PDT, the oxidative stress inducer and Bcl-2 inhibitor HA14-1 triggers apoptosis. To test the specificity of the ceramide response, Jurkat cells were exposed to an equitoxic dose of HA14-1. Unlike PDT, HA14-1 did not induce accumulation of de novo ceramide, although levels of sphingomyelin, phosphatidylserine and phosphatidylethanolamine were below control values after either treatment. In contrast to PDT, (i) the transient inhibition of serine palmitoyltransferase induced by HA14-1 was associated with the initial decrease in de novo ceramide, and (ii) HA14-1-initiated inhibition of sphingomyelin synthase and glucosylceramide synthase did not result in accumulation of de novo ceramide. These results show that the ceramide response to PDT is not induced by another pro-apoptotic stimulus, and may be unique to PDT as described here.