Retinoic acid enhances the cytotoxic effects of gemcitabine and cisplatin in pancreatic adenocarcinoma cells

The therapeutic potential of vitamins A, C, and D in pancreatic cancer

The pancreatic ductal adenocarcinoma (PDAC) is among the deadliest tumor diseases worldwide. While treatment options have generally become more diverse, little progress has been made in the treatment of PDAC and the median survival time for patients with locally advanced PDAC is between 8.7 and 13.7 months despite treatment. The aim of this review was to explore the therapeutic potential of complementing standard therapy with natural or synthetic forms of vitamins A, C, and D. The therapeutic use of vitamins A, C, and D could be a promising addition to the treatment of PDAC. For all three vitamins and their derivatives, tumor cell-specific cytotoxicity and growth inhibition against PDAC cells has been demonstrated in vitro and in preclinical animal models. While the antitumor effect of vitamin C is probably mainly due to its pro-oxidative effect in supraphysiological concentrations, vitamin A and vitamin D exert their effect by activating nuclear receptors and influencing gene transcription. In addition, there is increasing evidence that vitamin A and vitamin D influence the tumor stroma, making the tumor tissue more accessible to other therapeutic agents. Based on these promising findings, there is a high urgency to investigate vitamins A, C, and D in a clinical context as a supplement to standard therapy in PDAC. Further studies are needed to better understand the exact mechanism of action of the individual compounds and to develop the best possible treatment regimen. This could contribute to the long-awaited progress in the treatment of this highly lethal tumor entity.

Fenretinide induces apoptosis and synergises the apoptosis inducing effect of gemcitabine through inhibition of key signalling molecules involved in A549 cell survival in in silico and in vitro analyses

Fenretinide is a synthetic retinoid compound, which induces apoptosis via generating reactive oxygen species (ROS) and modulating PI3K/Akt/mTOR signalling pathway. We hypothesise that fenretinide's mechanism of action in triggering apoptosis may involve other targets, beside mTOR signalling pathway and it may augment apoptosis inducing effects of chemotherapeutic drugs in lung cancer. Time-lapse microscopy and Western blotting were used to evaluate apoptosis and apoptotic marker cleaved-Caspase 3 in A549 cells. Relative levels of protein phosphorylation and ROS were quantified by Human Phospho-Kinase Array Kit and CellROX® Green Reagent, respectively. Docking and simulation analyses of proteins and fenretinide interactions were identified and visualised by Discovery Studio Visualizer and AutoDock Vina software. Our results showed that fenretinide induced apoptosis in a dose dependant manner and combinations of fenretinide (5 μg/mL) and gemcitabine (1, 2, 4, 8 and 16 μg/mL) synergistically enhanced apoptosis in A549 cells. Fenretinide caused significant increase of cleaved-Caspase 3, de-phosphorylated p-S473 of Akt and failed to inhibit mTORC1 downstream targets. In silico results revealed that Akt required the lowest energy (-10.2 kcal/mol) to interact with fenretinide in comparison with other proteins. In conclusion, Akt may be exploited as a good target for induction of apoptosis in A549 cells and fenretinide has great potentials to fulfil this task. The mechanism by which fenretinide boosts the apoptosis inducing effects of gemcitabine, which is likely expected to be via inhibiting mTORC2 downstream targets. However, docking investigation revealed that fenretinide lacks specificity as it may also interact with several secondary targets beside Akt.

Retinoic acid-loaded PLGA nanocarriers targeting cell cholesterol potentialize the antitumour effect of PD-L1 antibody by preventing epithelial-mesenchymal transition mediated by M2-TAM in colorectal cancer

Tumour-associated macrophages (TAMs) often promote cancer progression through immunosuppression in the tumour microenvironment (TME). However, the signalling pathways crosstalk responsible for this mechanism remain unclear. The aim of our study was to investigate whether the interaction between TAMs and colorectal cancer cells could be down-regulated by nanoparticles (NPs) loaded with retinoic acid (RA) and coated with cholesterol (CHO), in combination with an anti-PD-L1 immune checkpoint inhibitor. Tumours were evaluated by qRT-PCR and immunohistochemistry from allographic tumour growth model. In addition, human tumours were evaluated by Tissue Microarray (TMA) and immunohistochemistry. Complementary analysis of epithelial-mesenchymal transition, cell migration, and macrophage polarisation were evaluated in vitro. We showed that the IL-10R/IL-10 axis is involved in overstimulation of the STAT3 pathway as well as downregulation of the NF-κB signalling pathway, which supports a loop of immunosuppressive cytokines that induces the M2-TAM phenotype. Furthermore, our combined findings suggest that the upregulation of STAT3/NF-κB pathways crosstalk mediated by immunosuppressive cytokines, such as IL-10/PD-L1/TGF-β, via M2-TAMs in the TME, leads to immunosuppression and epithelial-mesenchymal-transition of the colorectal cancer for stimulating Vimentin, CXCL12 and CD163 in the primary tumours. Importantly, NPs holding RA and coated with CHO in combination with anti-PD-L1 were more efficient in blocking this signalling pathway. These results contribute to our understanding of the immunological mechanisms, especially the re-educating of TAMs, and provide a novel management strategy for aggressive colorectal cancers using anti-PD-L1-conjugated nanocarriers.

Pancreatic Ductal Adenocarcinoma: New Insights into the Actions of Vitamin A

BACKGROUND

Pancreatic ductal adenocarcinoma (PDAC) is a gland-forming malignancy arising in the pancreas. It is estimated that in developed countries the incidence of PDAC will continue to rise, and PDAC is now the fourth leading cause of cancer-related deaths in the USA. The mortality of PDAC patients closely parallels the incidence rate, as this malignancy generally remains asymptomatic until it reaches an advanced stage.

SUMMARY

The poor prognosis results from the aggressive nature of the tumor, late detection, and resistance to chemotherapy and radiotherapy. Retinoids, vitamin A (retinol) and its metabolites, such as retinoic acid (RA), play critical roles in important biological functions, including cell growth and differentiation, development, metabolism, and immunity. The actions of retinoids in maintaining normal pancreatic functions have generated considerable research interest from investigators interested in understanding and treating PDAC. Altered expression of retinoid receptors and other RA signaling pathway genes in human cancers offers opportunities for target discovery, drug design, and personalized medicine for distinct molecular retinoid subtypes.

KEY MESSAGES

The goals of this review are to explore the potential activities of retinoids in the pancreas, to assess the evidence that retinoid functions become dysregulated in PDAC, and to describe the actions of retinoids in new therapies developed to increase patient survival.

Gemcitabine-retinoid prodrug loaded nanoparticles display in vitro antitumor efficacy towards drug-resilient human PANC-1 pancreatic cancer cells

The treatment of pancreatic cancer with gemcitabine is hampered by its rapid metabolism in vivo, the dense stroma around the tumor site which prevents the drug from reaching the cancerous cells and drug resistance. To address these challenges, this study describes the preparation of a retinoid prodrug of gemcitabine, GemRA (gemcitabine conjugated to retinoic acid), and its formulation into a nanoparticulate system applicable for pancreatic cancer treatment. Retinoic acid targets stellate cells which are part of the stroma and can thus augment the delivery of gemcitabine. GemRA dissolved in dimethylsulfoxide presented efficacy towards PANC-1 (human) and mT4 (mouse) pancreatic cancer cell lines but its poor solubility in aqueous solution affects its applicability. Thus, the preparation of the nanoparticles was initially attempted through self-assembly of GemRA, which resulted in the formation of unstable aggregates that precipitated during preparation. As a result, encapsulation of the drug into micelles of polyethylene glycol-retinoic acid (PGRA) amphiphilic conjugates was accomplished and resulted in successful incorporation of GemRA into nanoparticles of ca. 33 nm by dynamic light scattering and 25 nm by transmission electron microscopy. The nanoparticles had good stability in aqueous media and protected gemcitabine from the enzymatic action of cytidine deaminase, which converts gemcitabine to its inactive metabolite upon circulation. Cellular uptake of the nanoparticles by PANC-1 cells was confirmed by fluorescence spectroscopy and flow cytometry. Treatment of PANC-1 cells in vitro with the prodrug-loaded nanoparticles resulted in a significant reduction in cell viability (IC50 ca. 5 μM) compared to treatment with gemcitabine (IC50 > 1000 μM). The ability of the GemRA-loaded nanoparticles to induce cellular apoptosis of treated PANC-1 cells was ascertained via a TUNEL assay suggesting these nanoparticles are effective in pancreatic cancer treatment.

Pancreatic Cancer (PDAC): Introduction of Evidence-Based Complementary Measures into Integrative Clinical Management

The most common form of pancreatic cancer is pancreatic ductal adenocarcinoma (PDAC), which comprises some 85% of all cases. Currently, this is the fourth highest cause of cancer mortality worldwide and its incidence is rising steeply. Commonly applied clinical therapies offer limited chance of a lasting cure and the five-year survival rate is one of the lowest of the commonly occurring cancers. This review cultivates the hypothesis that the best management of PDAC would be possible by integrating 'western' clinical medicine with evidence-based complementary measures. Protecting the liver, where PDAC frequently first spreads, is also given some consideration. Overall, the complementary measures are divided into three groups: dietary factors, nutraceutical agents and lifestyle. In turn, dietary factors are considered as general conditioners, multi-factorial foodstuffs and specific compounds. The general conditioners are alkalinity, low-glycemic index and low-cholesterol. The multi-factorial foodstuffs comprise red meat, fish, fruit/vegetables, dairy, honey and coffee. The available evidence for the beneficial effects of the specific dietary and nutraceutical agents was considered at four levels (in order of prominence): clinical trials, meta-analyses, in vivo tests and in vitro studies. Thus, 9 specific agents were identified (6 dietary and 3 nutraceutical) as acceptable for integration with gemcitabine chemotherapy, the first-line treatment for pancreatic cancer. The specific dietary agents were the following: Vitamins A, C, D and E, genistein and curcumin. As nutraceutical compounds, propolis, triptolide and cannabidiol were accepted. The 9 complementary agents were sub-grouped into two with reference to the main 'hallmarks of cancer'. Lifestyle factors covered obesity, diabetes, smoking, alcohol and exercise. An integrative treatment regimen was devised for the management of PDAC patients. This involved combining first-line gemcitabine chemotherapy with the two sub-groups of complementary agents alternately in weekly cycles. The review concludes that integrated management currently offers the best patient outcome. Opportunities to be investigated in the future include emerging modalities, precision medicine, the nerve input to tumors and, importantly, clinical trials.

Cancer Stem Cells: Concepts, Challenges, and Opportunities for Cancer Therapy

Cancer stem cells (CSCs) are a subpopulation of cancer cells with self-renewal capacity, that fuel tumor growth and contribute to the heterogeneous nature of tumors. First identified in hematological malignancies, CSC populations have to date been proposed in solid tumors in various organs. In vitro and in vivo assays, mouse genetic models, and more recently single-cell sequencing technologies and other '-omics' methodologies have not only facilitated the identification of novel CSC populations but also revealed and clarified novel properties of CSCs. Increasingly, both cell-autonomous and CSC niche factors are recognized as important contributors of CSC properties. The deepened understanding of CSC properties and characteristics would enable and facilitate the rational design of CSC-specific therapeutics that would, ideally, have high selectivity for cancer cells, eliminate tumor bulk, and prevent tumor recurrence. Addressing these issues would form some of the key challenges of the CSC research field in the coming years.

Aldehyde dehydrogenases in cancer stem cells: potential as therapeutic targets

Resistance to current chemotherapeutic or radiation-based cancer treatment strategies is a serious concern. Cancer stem cells (CSCs) are typically able to evade treatment and establish a recurrent tumor or metastasis, and it is these that lead to the majority of cancer deaths. Therefore, a major current goal is to develop treatment strategies that eliminate the resistant CSCs as well as the bulk tumor cells in order to achieve complete disease clearance. Aldehyde dehydrogenases (ALDHs) are important for maintenance and differentiation of stem cells as well as normal development. There is expanding evidence that ALDH expression increases in response to therapy and promotes chemoresistance and survival mechanisms in CSCs. This perspective will discuss a paper by Cojoc and colleagues recently published in Cancer Research, that indicates ALDHs play a key role in resistance to radiation therapy and tumor recurrence in prostate cancer. The authors suggest that ALDHs are a potential therapeutic target for treatment prostate cancer patients to limit radiation resistance and disease recurrence. The findings are consistent with work from other cancers showing ALDHs are major contributors of CSC signaling and resistance to anti-cancer treatments. This perspective will address representative work concerning the validity of ALDH and the associated retinoic acid signaling pathway as chemotherapeutic targets for prostate as well as other cancers.

Inhibition of ALDH1A1 activity decreases expression of drug transporters and reduces chemotherapy resistance in ovarian cancer cell lines

The high mortality of ovarian cancer patients results from the failure of treatment caused by the inherent or acquired chemotherapy drug resistance. It was reported that overexpression of aldehyde dehydrogenase A1 (ALDH1A1) in cancer cells can be responsible for the development of drug resistance. To add the high expression of the drug transporter proteins the ALDHA1 is considered as a molecular target in cancer therapy. Therefore, we analysed drug-resistant ovarian cancer cell lines according to ALDHA1 expression and the association with drug resistance. The expression of ALDH1A1, P-glycoprotein (P-gp) or breast cancer resistance protein (BCRP) was determined using a microarray and confirmed by Q-PCR, western blot and fluorescence analysis. ALDH1A1 activity was determined using an Aldefluor assay. The impact of all-trans retinoic acid (ATRA) and diethylaminobenzaldehyde (DEAB) on chemotherapy resistance was assessed by the MTT chemosensitivity assay. The most abundant expression of ALDH1A1 was noted in paclitaxel- and topotecan-resistant cell lines where two populations of ALDH-positive and ALDH-negative cells could be observed. Those cell lines also revealed the overexpression of P-gp and BCRP respectively, and were able to form spheres in non-adherent conditions. Pre-treatment with ATRA and DEAB reduced chemotherapy resistance in both cell lines. ATRA treatment led to downregulation of the ALDH1A1, P-gp and BCRP proteins. DEAB treatment led to downregulation of the P-gp protein and BCRP transcript and protein. Our results indicate that ALDH1A1-positive cancer cells can be responsible for drug resistance development in ovarian cancer. Developing more specific ALDH1A1 inhibitors can increase chemotherapy effectiveness in ovarian cancer.

Acetaldehyde and retinaldehyde-metabolizing enzymes in colon and pancreatic cancers

Colorectal cancer (CRC) and pancreatic cancer are two very significant contributors to cancer-related deaths. Chronic alcohol consumption is an important risk factor for these cancers. Ethanol is oxidized primarily by alcohol dehydrogenases to acetaldehyde, an agent capable of initiating tumors by forming adducts with proteins and DNA. Acetaldehyde is metabolized by ALDH2, ALDH1B1, and ALDH1A1 to acetate. Retinoic acid (RA) is required for cellular differentiation and is known to arrest tumor development. RA is synthesized from retinaldehyde by the retinaldehyde dehydrogenases, specifically ALDH1A1, ALDH1A2, ALDH1A3, and ALDH8A1. By eliminating acetaldehyde and generating RA, ALDHs can play a crucial regulatory role in the initiation and progression of cancers. ALDH1 catalytic activity has been used as a biomarker to identify and isolate normal and cancer stem cells; its presence in a tumor is associated with poor prognosis in colon and pancreatic cancer. In summary, these ALDHs are not only biomarkers for CRC and pancreatic cancer but also play important mechanistic role in cancer initiation, progression, and eventual prognosis.

Activation of AMP-activated protein kinase by retinoic acid sensitizes hepatocellular carcinoma cells to apoptosis induced by sorafenib

To improve the outcome of cancer chemotherapy, strategies to enhance the efficacy of anticancer drugs are required. Sorafenib is the only drug to prolong overall survival of the patients with hepatocellular carcinoma (HCC), however, the outcome is still not satisfactory. Retinoids, vitamin A derivatives, have been known to exhibit inhibitory effects on various cancers including HCC. In this study, we investigated the effects of combined treatment using sorafenib and retinoids including all-trans retinoic acid (ATRA), NIK-333, and Am80 on HCC cells. Cell viability assays in six HCC cell lines, HepG2, PLC/PRF/5, HuH6, HLE, HLF, and Hep3B, revealed that 5 and 10 μM ATRA, concentrations that do not exert cytotoxic effects, enhanced the cytotoxicity of sorafenib, being much more effective than NIK-333 and Am80. We found that ATRA induced AMP-activated protein kinase activation, which was followed by reduced intracellular ATP level. Gene expression analysis revealed that ATRA decreased the expression of glycolytic genes such as GLUT-1 and LDHA. In the combination treatment using ATRA and sorafenib, increased apoptosis, followed by the activation of p38 MAPK and JNK, the upregulation and translocation of Bax to mitochondria, and the activation of caspase-3, was observed. Suppression of AMP-activated protein kinase by siRNA restored the viability of the cells treated with ATRA and sorafenib. Our results thus indicate that ATRA is useful for enhancing the cytotoxicity of sorafenib against HCC cells by regulating the energy metabolism of HCC cells.

All-trans retinoic acid and arsenic trioxide induce apoptosis and modulate intracellular concentrations of calcium in hepatocellular carcinoma cells

We investigated the effects of all-trans retinoic acid (ATRA) and arsenic trioxide (ATO), alone and in combination, on apoptosis and intracellular calcium concentration in hepatocellular carcinoma (HepG2) cells. We used HepG2 cells to test the effects of ATRA and ATO, individually and in combination, on cell proliferation, apoptosis, and intracellular-free calcium concentration. The results indicate that each drug decreased cell proliferation, increased apoptosis, and increased intracellular-free calcium in a time- and dose-dependent manner. We also calculated the coefficients of drug interaction for sub-threshold administration of both drugs in combination (1 μmol/L each). ATRA and ATO acted synergistically in inhibition of cell proliferation and additively in the promotion of apoptosis. All-trans retinoic acid and ATO interacted synergistically to reduce cell proliferation in HepG2 cells.

The role of aldehyde dehydrogenase (ALDH) in cancer drug resistance

Chemotherapy in cancer patients is still not satisfactory because of drug resistance. The main mechanism of drug resistance results from the ability of cancer cells to actively expel therapeutic agents via transport proteins of the ABC family. ABCB1 and ABCG2 are the two main proteins responsible for drug resistance in cancers. Recent investigations indicate that aldehyde dehydrogenase (ALDH) can also be involved in drug resistance. Expression of the ABC transporters and ALDH enzymes is observed in normal stem cells, cancer stem cells and drug resistant cancers. Current chemotherapy regimens remove the bulk of the tumour but are usually not effective against cancer stem cells (CSCs) expressing ALDH. As a result, the number of ALDH positive drug resistant CSCs increases after chemotherapy. This indicates that therapies targeting drug resistant CSCs should be developed. A number of therapies targeting CSCs are currently under investigation. These therapies include differentiation therapy using different retinoic acids (RA) as simple agents or in combination with DNA methyltransferase inhibitors (DNMTi) and/or histone deacetylase inhibitors (HDACi). Therapies that target cancer stem cell signaling pathways are also under investigation. A number of natural compounds are effective against cancer stem cells and lead to decreasing numbers of ALDH positive cells and downregulation of the ABC proteins. Combinations of differentiation therapies or therapies targeting CSC signaling pathways with classical cytostatics seem promising. This review discusses the role of ALDH and ABC proteins in the development of drug resistance in cancer and current therapies designed to target CSCs.

Knock-down of PRAME increases retinoic acid signaling and cytotoxic drug sensitivity of Hodgkin lymphoma cells

The prognosis for patients with Hodgkin lymphoma (HL) has improved in recent decades. On the other hand, not all patients can be cured with the currently established therapy regimes and this therapy is associated with several adverse late effects. Therefore it is necessary to develop new therapy strategies. After treatment of L-540 HL cells with 5′-azacytidine (5AC), we observed increased expression of the preferentially expressed antigen in melanoma (PRAME). In addition, we detected an increased resistance of 5AC-treated cells against cytotoxic drugs. We analyzed the influence of PRAME on cell survival of HL cells by knocking down PRAME in the chemotherapy resistant cell line L-428, a cell line that express PRAME at a high level. After knock-down of PRAME using vector based RNA interference we observed increased sensitivity for cisplatin, etoposide and retinoic acid. DNA microarray analysis of HL cells after PRAME knock-down indicated regulation of several genes including down-regulation of known anti-apoptotic factors. Increased retinoic acid signaling in these cells was revealed by increased expression of the retinoic acid metabolizing cytochrome P450 (CYP26B1), a transcriptional target of retinoic acid signaling. Our data suggest that PRAME inhibits retinoic acid signaling in HL cells and that the knock-down of PRAME might be an interesting option for the development of new therapy strategies for patients with chemo-resistant HL.

The effects of chemotherapeutic agents on differentiated chordoma cells

OBJECT

Chordoma is a rare type of malignant bone tumor and is known to arise from the remnants of the notochord. Resistance to chemotherapy makes the treatment of chordoma difficult; therefore, new approaches need to be developed to cure this disease. Differentiation therapy, using various differentiating agents, is attracting oncologists as a common therapeutic method to treat other tumors. Based on forcing cells to mature into other lineages, differentiation therapy might be an available method to treat chordomas in addition to conventional therapies.

METHODS

In this study a chordoma cell line, U-CH1, was exposed to several chemotherapeutic agents including vincristine, doxorubicin, cisplatin, etoposide, fludarabine, methotrexate, nilotinib, and imatinib mesylate under appropriate conditions. The first group of U-CH1 cells was exposed to drugs only and the second group of cells was exposed to the simultaneous treatment of 1 μM all-trans retinoic acid (ATRA) and chemotherapeutic agents in differentiation therapy. The efficacy of the differentiation method was assessed by measuring the viability of U-CH1 cells.

RESULTS

Vincristine, doxorubicin, etoposide, cisplatin, and fludarabine, each at a concentration of 10 μM, decreased the number of chordoma cells when given alone down to 11%, 0%, 30%, 67%, and 3%, respectively. Etoposide and cisplatin, each at a concentration of 10 μM, reduced the percentage of viable chordoma cells in a more effective way when given with 1 μM ATRA simultaneously, reducing the number of viable cells to 14% and 9%, respectively. On the other hand, imatinib and nilotinib, each at a concentration of 3 μM, as well as 10 μM methotrexate, showed no decrease in the number of cancer cells.

CONCLUSIONS

The results suggest that chordoma cells may be treated using the differentiation method in a more effective way than when they are treated with chemotherapeutic agents alone. This new approach may be an alternative method to conventional therapies in the treatment of chordoma.

Genotoxicity of all-trans retinoic acid (ATRA) and its steroidal analogue EA-4 in human lymphocytes and mouse cells in vitro

The aim of our study is to: (a) investigate whether ATRA and its steroidal analogue EA-4 enhance micronucleation in human lymphocytes and mouse cells in vitro and clarify the micronucleation mechanism by FISH and CREST analysis respectively, and (b) analyze their effect on spindle organization by immunofluorescence of β- and γ-tubulin in mouse cells. We found that they: (a) induce micronucleation mainly via chromosome breakage and chromosome delay in a lesser extent, (b) disturb microtubule network, chromosome orientation and centrosome duplication/separation, (c) accumulate cell cycle at ana-telophases, which exert micronucleation, multiple γ-tubulin signals, nucleoplasmic bridges and multinucleation, and (d) generate multinucleated and multimicronucleated interphase cells.

An oxidative analogue of gambogic acid-induced apoptosis of human hepatocellular carcinoma cell line HepG2 is involved in its anticancer activity in vitro

The objective of this study was to investigate the apoptosis-inducing effect of an oxidative analogue of gambogic acid (GA) on the human hepatocellular carcinoma cell line HepG2 and explore the related molecular mechanisms. HepG2 cells were treated with the analogue of GA and the growth inhibition was analysed by MTT assay. The morphological changes in cells were observed under an inverted light microscope and a fluorescence microscope. In addition, both the cell-cycle arrest and the apoptosis rate were detected by flow cytometry. Western blot was used to evaluate the alteration of protein expression. The viability of HepG2 cells was markedly inhibited in a concentration-dependent manner and obvious morphological changes were confirmed, including condensed chromatin and reduced volume. Increased percentage of apoptotic cells was displayed and altered expression level of several apoptosis-associated proteins, P53, Bcl-2, Bax and pro-caspase-3, was obtained. The newly synthesized analogue of GA exhibited potential anticancer activity, induced remarkable apoptosis in HepG2 cells, probably through the intrinsic mitochondrial pathway, and promised to be a new candidate for future cancer therapy.

Antiproliferative effects of CC-8062 and CC-8075 in pancreatic cancer cells

OBJECTIVES

Pancreatic cancer is one of the leading causes of cancer related deaths in the western world. It is also resistant to most chemotherapeutic modalities. Phosphodiesterase-4 inhibitors (PDE4is) have found applications in the treatment of respiratory diseases. The aim of this study is to investigate the cytotoxic effect of 2 novel PDE4is, the CC-8075 and CC-8062 compounds in pancreatic cancer cells.

METHODS

Cell proliferation was measured using the sulforhodamine B protein dye. Induction of apoptosis was detected using enzyme-linked immunosorbent assay. Regulation of proteins and posttranslational modifications were determined using immunoblotting.

RESULTS

Treatment of pancreatic cancer cells with CC-8075 and CC-8062 reduces their proliferation and increases apoptosis that is caspase dependent in T3M4 cells. Furthermore, PDE4is increase phosphorylation of p38MAPK, mitogen-activated protein kinase (MAPK) kinase 3/6,MAPKYactivated protein kinase 2, Atf2, and Hsp27. The use of thep38MAPK-specific inhibitors SB202190 and SB203580 results in a modest reduction in PDE4i-induced apoptosis in T3M4 cells. Also, retinoids enhance apoptosis induced by CC-8075 and CC-8062 in GER cells.

CONCLUSIONS

These results highlight the antiproliferative effects of the phosphodiesterase inhibitors CC-8075 and CC-8062 in pancreatic cancer cells and suggest that activation of p38MAPK signaling pathway may be associated with this process.

Neuronal differentiation of synovial sarcoma and its therapeutic application

Synovial sarcoma is a rare sarcoma of unknown histologic origin. We previously reported the gene expression profile of synovial sarcoma was closely related to that of malignant peripheral nerve sheath tumors, and the fibroblast growth factor (FGF) signal was one of the main growth signals in synovial sarcoma. Here we further demonstrate the neural origin of synovial sarcoma using primary tumors and cell lines. The expression of neural tissue-related genes was confirmed in synovial sarcoma tumor tissues, but the expression of some genes was absent in synovial sarcoma cell lines. Treatment of synovial sarcoma cell lines with BMP4 or FGF2 enhanced or restored the expression of neural tissue-related genes and induced a neuron-like morphology with positive Tuj-1 expression. Treatment with all-trans-retinoic acid also induced the expression of neural tissue-related genes in association with growth inhibition, which was not observed in other cell lines except a malignant peripheral nerve sheath tumor cell line. A growth-inhibitory effect of all-trans-retinoic acid was also observed for xenografted tumors in athymic mice. The simultaneous treatment with FGF signal inhibitors enhanced the growth-inhibitory effect of all-trans-retinoic acid, suggesting the combination of growth signaling inhibition and differentiation induction could be a potential molecular target for treating synovial sarcoma.

Chemotherapeutic/chemopreventive role of retinoids in chemically induced skin carcinogenesis in albino mice

OBJECTIVE

To determine the chemotherapeutic effect of retinoids on albino mouse skin.

METHODS

Eighty albino mice were selected for this study and were divided into four groups (A-D, 20 mice in each group). 7,12-Dimethylbenz(a)anthracene (DMBA) and tetradecanoylphorbal-13-acetate (TPA) were given for 15 weeks to produce tumors. Retinoids were given topically and orally after the development of tumors for the following 15 weeks.

RESULTS

Of the 80 mice, 69 (86.25%) developed different types of lesion and 11 (13.75%) remained lesion free. Of the 69 mice that developed lesions, 50 (62.50%) developed benign lesions and 19 (23.75%) developed malignant lesions. In all groups of mice, treatment with retinoids was effective against all benign lesions and the early stages of carcinogenesis of the skin. The chemotherapeutic effect against malignant tumors was not satisfactory.

CONCLUSION

This study demonstrates that retinoids are effective as chemopreventive agents in premalignant lesions of the skin, but have a very weak chemotherapeutic role in malignant neoplasms. If retinoids are given at an early stage, they can cause regression of premalignant lesions of the skin. They are best administered both orally and parenterally. These agents should be recommended as they reduce the potential effects of carcinogenesis.

Novel azolyl-(phenylmethyl)]aryl/heteroarylamines: potent CYP26 inhibitors and enhancers of all-trans retinoic acid activity in neuroblastoma cells

The synthesis and potent inhibitory activity of novel 4-[(imidazol-1-yl and triazol-1-yl)(phenyl)methyl]aryl-and heteroaryl amines versus a MCF-7 CYP26A1 cell assay is described. Biaryl imidazole ([4-(imidazol-1-yl-phenyl-methyl)-phenyl]-naphthalen-2-yl-amine (8), IC(50)=0.5 microM; [4-(imidazol-1-yl-phenyl-methyl)-phenyl]-indan-5-yl-amine (9), IC(50)=1.0 microM) and heteroaryl imidazole derivatives ((1H-benzoimidazol-2-yl)-{4-[(5H-imidazol-1-yl)-phenyl-methyl]-phenyl}-amine (15), IC(50)=2.5 microM; benzooxazol-2-yl-{4-[(5H-imidazol-1-yl)-phenyl-methyl]-phenyl}-amine (16), IC(50)=0.9 microM; benzothiazol-2-yl-{4-[(5H-imidazol-1-yl)-phenyl-methyl]-phenyl}-amine (17), IC(50)=1.5 microM) were the most potent CYP26 inhibitors. Using a CYP26A1 homology model differences in activity were investigated. Incubation of SH-SY5Y human neuroblastoma cells with the imidazole aryl derivative 8, and the imidazole heteroaryl derivatives 16 and 17 potentiated the atRA-induced expression of CYP26B1. These data suggest that further structure-function studies leading to clinical development are warranted.

13-cis-Retinoic acid in combination with gemcitabine in the treatment of locally advanced and metastatic pancreatic cancer--report of a pilot phase II study

AIMS

Adenocarcinoma of the pancreas is a cancer with extremely poor prognosis and limited therapeutic options. Retinoids are derivatives of vitamin A involved in the control of many biological functions, including cell growth and differentiation and the induction of apoptosis. On the basis of pre-clinical evidence and some clinical data, we conducted a phase II study of 13-cis-retinoic acid (13-cis-RA) in combination with gemcitabine in patients with unresectable pancreatic carcinoma.

MATERIALS AND METHODS

Patients with histologically confirmed unresectable pancreatic carcinoma were treated with gemcitabine 1000 mg/m2 on days 8, 15, 22 plus 13-cis-RA 1 mg/kg on days 1-14 for six cycles. The end points included the objective response rate and median survival.

RESULTS

Thirty patients were recruited, 15 men and 15 women; 20 patients were evaluable. The median age was 65 years (range 44-79 years) and the median Karnofsky performance status was 80% (range 60-100%). The median follow-up was 21 months. One patient achieved a partial remission, seven patients had stable disease and 12 patients developed progressive disease. Toxicity was mainly haematological, with eight cases of grade 3 and four cases of grade 4 neutropenia, thrombocytopenia and anaemia. The median survival was 7.8 months (range 2.6-21.6 months).

CONCLUSIONS

The combination of gemcitabine and 13-cis-RA was well tolerated, but we did not see improvement in the response rate. Further studies with other retinoids may be beneficial to patients with unresectable pancreatic cancer.

Sequence-dependent antitumor effects of differentiation agents in combination with cell cycle-dependent cytotoxic drugs

PURPOSE

Combination of two differentiation agents such as phenylbutyrate (PB) and 13-cis-retinoic acid (CRA) has been shown to have an additive inhibitory effect on tumor growth in preclinical studies. In this report we explored the hypotheses that these "cytostatic" agents may have a greater antitumor activity in combination with "cytotoxic" compounds and their biological effect may be sequence-dependent.

METHODS

The antitumor activity of combination of PB and CRA with paclitaxel (TX ) and doxorubicin (DOXO) on human prostate and colon carcinoma cell lines was assessed both in vitro and in vivo. The effect on cell cycle, apoptotic rate, cyclin expression and induction of p21 expression was also determined.

RESULTS

Following treatment of tumor cells with PB + CRA + TX or DOXO, inhibition of tumor cell growth was greatly enhanced as compared to PB + CRA, TX or DOXO alone, with >90% growth inhibition. However, when the cells were pretreated with PB + CRA followed by TX or DOXO, the enhanced inhibition was abolished suggesting a protective effect to this sequence. Interestingly treatment with PB + CRA restored sensitivity to DOXO in PC-3 human prostate cancer cell line. PB + CRA induced p21 expression and cell-cycle arrest in G1 phase, while TX and DOXO induced G2/M arrest. p21 and p53-deficient colon carcinoma cell lines were more sensitive to the effect of PB + CRA and TX as single agents and in combination, as compared to the wild type cells. When p21-deficient cells were pretreated with PB + CRA followed by TX the protective effect was still observed. Treatment of tumor cells with combination of these drugs induced cell cycle delay at multiple mitotic checkpoints before undergoing apoptosis. Tumor growth was significantly inhibited and delayed in animals treated with either TX or concomitantly with TX and PB + CRA as compared to control. Animals treated with all three agents demonstrated further growth inhibition or delay than the TX alone or PB + CRA arm.

CONCLUSIONS

These results suggest a rational therapeutic approach for combination of differentiation-inducing agents with cytotoxic drugs given concomitantly, but not sequentially.

Homology model of human retinoic acid metabolising enzyme cytochrome P450 26A1 (CYP26A1): active site architecture and ligand binding

Homology models of cytochrome P450 RA1 (CYP26A1) were constructed using three human P450 structures, CYP2C8, CYP2C9 and CYP3A4 as templates for the model building. Using MOE software the lowest energy CYP26A1 model was then assessed for stereochemical quality and side chain environment. Further active site optimisation of the CYP26A1 model built using the CYP3A4 template was performed by molecular dynamics to generate a final CYP26A1 model. The natural substrate, all-trans-retinoic acid (atRA), and inhibitor R 15866, were docked into the model allowing further validation of the active site architecture. Using the docking studies structurally and functionally important residues were identified with subsequent characterisation of secondary structure. Multiple hydrophobic interactions, including the side chains of TRP112, PHE299, PHE222, PHE84, PHE374 and PRO371, are important for binding of atRA and R115866. Additional hydrogen bonding interactions were noted as follows: atRA-- C==O of the atRA carboxylate group and ARG86; R115866--benzothiazole nitrogen and the backbone NH of SER115.

Oroxylin A induced apoptosis of human hepatocellular carcinoma cell line HepG2 was involved in its antitumor activity

We previously reported that wogonin, a flavonoid compound, was a potent apoptosis inducer of human hepatoma SMMC-7721 cells and murine sarcoma S180 cells. In the present study, the effect of oroxylin A, one wogonin structurally related flavonoid isolated from Scutellariae radix, on human hepatocellular carcinoma cell line HepG2 was examined and molecular mechanisms were also investigated. Oroxylin A inhibited HepG2 cell proliferation in a concentration- and time-dependent manner measured by MTT-assay. Treatment with an apoptosis-inducing concentration of oroxylin A caused typical morphological changes and apoptotic blebbing in HepG2 cells. DNA fragmentation assay was used to examine later apoptosis induced by oroxylin A. FACScan analysis revealed a dramatic increase in the number of apoptotic and G(2)/M phase arrest cells after oroxylin A treatment. The pro-apoptotic activity of oroxylin A was attributed to its ability to modulate the concerted expression of Bcl-2, Bax, and pro-caspase-3 proteins. The expression of Bcl-2 protein and pro-caspase-3 protein was dramatically decreased after treatment with oroxylin A. These results demonstrated that oroxylin A could effectively induce programmed cell death and suggested that it could be a promising antitumor drug.

Involvement of bax/bcl-2 in wogonin-induced apoptosis of human hepatoma cell line SMMC-7721

The molecular mechanisms of wogonin-induced apoptosis of human hepatoma SMMC-7721 cells are reported. Wogonin treatment resulted in significant inhibition of SMMC-7721 cells in a time-dependent and concentration-dependent manner. Typical morphological changes and apoptotic blebbing in SMMC-7721 cells were observed after treatment with 1x10(-4) mol/l wogonin for a period of 0-48 h. Flow cytometry and Annexin-V/propidium iodide double-staining experiments revealed a dramatic increase in the number of apoptotic and G0/G1 phase cells after wogonin treatment. The proapoptotic activity of wogonin is attributed to its ability to modulate the expression of bcl-2 and bax proteins. It is observed that the expression of bax protein is dramatically increased whereas the synthesis of bc1-2 protein is significantly decreased when cells are treated with wogonin. The results presented in this paper suggested an important relationship between gene regulation and wogonin-induced apoptosis, and indicated the possibility of developing naturally occurring monoflavonoids as novel anticancer agents for better management of human cancers.

Synthesis and CYP26A1 inhibitory activity of 1-[benzofuran-2-yl-(4-alkyl/aryl-phenyl)-methyl]-1H-triazoles

Methodology previously described by our group was applied to the preparation of a series of 4-alkyl/aryl-substituted 1-[benzofuran-2-yl-phenylmethyl]-1H-triazoles. The [1,2,4]-triazole derivatives were prepared for a range of alkyl and aryl substituents, and for the 4-methyl, 4-ethyl, 4-(i)propyl, 4-(t)butyl, 4-phenyl and 4-chlorophenyl derivatives, the minor [1,3,4]-triazole isomer also isolated. All the triazole derivatives were evaluated for CYP26A1 inhibitory activity using a MCF-7 cell-based assay. The 4-ethyl and 4-phenyl-1,2,4-triazole derivatives displayed inhibitory activity (IC(50) 4.5 and 7 microM, respectively) comparable with that of the CYP26 inhibitor liarozole (IC(50) 7 microM). Using a CYP26A1 homology model (based on CYP3A4) template, docking experiments were performed with MOE with multiple hydrophobic interactions observed in addition to coordination between the triazole nitrogen and the haem transition metal.

RNAi-mediated knockdown of aldehyde dehydrogenase class-1A1 and class-3A1 is specific and reveals that each contributes equally to the resistance against 4-hydroperoxycyclophosphamide

PURPOSE

Aldehyde dehydrogenases class-1A1 (ALDH1A1) and class-3A1 (ALDH3A1) have been associated with resistance to cyclophosphamide (CP) and its derivatives. We have previously reported the downregulation of these enzymes by all-trans retinoic acid (ATRA).

METHODS

In this study, we used siRNA duplexes as well as retrovirally expressed siRNA to knockdown one or both enzymes together in A549 lung cancer cell line in order to investigate the role of each one in mediating the resistance and the effect of the addition of ATRA.

RESULTS

The results show that significant and specific knockdown of each enzyme can be achieved and that each one contributes similarly to cell resistance to 4-hydroperoxycyclophosphamide (4-HC), an active derivative of CP. Added effects were seen when both enzymes were inhibited. The addition of ATRA also exhibited additional inhibitory effects on ALDH activity and increased 4-HC toxicity when added to single siRNA aimed at one of the enzymes. On the other hand, ATRA had minimal and insignificant additional inhibitory effects on ALDH enzyme activity when added to a combination of siRNAs against both enzymes, but still increased 4-HC toxicity beyond that seen with RNAi-mediated inhibition of both enzymes together.

CONCLUSIONS

We conclude that both enzymes, ALDH1A1 and ALDH3A1 will need to be blocked in order to achieve the highest sensitivity to 4-HC. Furthermore, ATRA increases 4-HC toxicity even when added to a combination of siRNAs against both enzymes, thus suggesting additional mechanisms by which ATRA can increase drug toxicity.

All-trans retinoic acid induces XAF1 expression through an interferon regulatory factor-1 element in colon cancer

BACKGROUND & AIMS

X-linked inhibitor of apoptosis protein (XIAP)-associated factor 1 (XAF1) is a novel tumor suppressor and interferon (IFN)-stimulated gene. All-trans retinoic acid (ATRA) exerts an antiproliferative effect on tumor cells through up-regulation of IFN regulatory factor 1 (IRF-1) and the downstream IFN-stimulated genes. The aim of this study was to determine the effect and mechanism of ATRA on XAF1 expression and the role of XAF1 in ATRA-induced growth inhibition in colon cancer.

METHODS

Gene expression is detected by reverse-transcription polymerase chain reaction and immunoblotting. The transcription activity of XAF1 promoter is examined by luciferase reporter assay. The activity of IFN regulatory factor binding element (IRF-E) is assessed by electrophoretic mobility shift assay and chromatin immunoprecipitation assay. Cell growth is evaluated by both in vitro and in vivo in nude mice xenografts.

RESULTS

IFN-alfa stimulates XAF1 promoter activity in the colon cancer cells Lovo and SW1116 dose-dependently. An IRF-1 binding element (IRF-E-XAF1) is found in the -30 to -38 nucleotide region upstream of the ATG initiator codon of the XAF1 gene. Site-directed mutagenesis of IRF-E-XAF1 abrogates native and IFN-induced promoter activity and binding capacity. ATRA induces XAF1 expression both in vitro and in vivo through interaction with IRF-E-XAF1. Overexpression of XAF1 increases cell susceptibility to ATRA-induced growth suppression both in vitro and in vivo. Furthermore, the effect of ATRA on XAF1 expression is independent of the promoter methylation and the subcellular distribution of XIAP.

CONCLUSIONS

XAF1 participates in ATRA-induced growth suppression through IRF-1-mediated transcriptional regulation.

Antitumor effects of all-trans-retinoic acid on cultured human pancreatic cancer cells

BACKGROUND AND AIM

Although it is uncommon, pancreatic cancer is known to have a poor prognosis. The aim of the present study was to determine the inhibitory effects of all-trans-retinoic acid (ATRA) on cell growth, cell cycle and alkaline phosphatase (ALP) activity in the human pancreatic cancer cell line PANC-1 in vitro.

METHODS

Human pancreatic cancer PANC-1 cells were treated by various concentrations of ATRA, and then the cell growth was determined by MTT viability assay. Cell cycle distribution and ALP activity were analyzed by flow cytometry and chemical analyzer, respectively.

RESULTS

ATRA inhibited the growth of PANC-1 cells grown in culture; a dose-dependent inhibitory influence was found. ATRA arrested PANC-1 cells at G2/M phase. The ALP activity of PANC-1 cells was significantly increased by 1-50 micromol/L ATRA.

CONCLUSIONS

The antitumor effects of ATRA on human pancreatic cancer cells are associated with G2/M phase arrest and increased ALP activity.

Novel tetralone-derived retinoic acid metabolism blocking agents: synthesis and in vitro evaluation with liver microsomal and MCF-7 CYP26A1 cell assays

The potent inhibitory activity of novel 2-benzyltetralone and 2-benzylidenetetralone derivatives vs liver microsomal retinoic acid metabolizing enzymes and a MCF-7 CYP26A1 cell assay is described. In the liver microsomal assay, the 2-biphenylmethyl-6-hydroxytetralone derivatives 16a and 16b were found to be potent inhibitors (IC50 = 0.5 and 0.8 microM) compared with the broad spectrum P450 inhibitor ketoconazole and the retinoid mimetic R115866 (IC50 = 18.0 and 9.0 microM, respectively). In the MCF-7 CYP26A1 cell assay, the 2-(4-hydroxybenzyl)-6-methoxytetralone 5 and unsaturated benzylidene precursor 6 were found to be the most potent (IC50 = 7 and 5 microM, respectively), which was comparable with liarozole (7 microM) but considerably less active than R115866 (IC50 = 5 nM). With a CYP26A1 homology model, the tetralones were shown to be positioned in a hydrophobic tunnel with additional interactions, e.g., transition metal coordination and hydrogen-bonding interactions with GLY300, observed for the potent 4-hydroxyphenyl substituted inhibitors.

Investigation of the mechanisms by which EB1089 abrogates apoptosis induced by 9-cis retinoic acid in pancreatic cancer cells

OBJECTIVES

Previous research has shown that the retinoid 9-cis retinoic acid (RA) promotes apoptosis in pancreatic cancer cells. The vitamin D analog EB1089 does not. Furthermore, cotreatment of cells with 9-cis RA and EB1089 abrogates apoptosis. To explain this, we studied the regulation of proteins involved in apoptotic signaling pathways in pancreatic cancer cells.

METHODS

The pancreatic adenocarcinoma cell line T3M4 was used. Cell proliferation was measured using the SRB protein dye assay. Induction of apoptosis was evaluated using an ELISA assay. Caspase activation was detected using a colorimetric assay based on cleavage of a caspase-associated substrate. Regulation of protein levels and posttranslational events were detected using immunoblotting.

RESULTS

We confirm that EB1089 diminishes apoptosis induced by 9-cis RA in T3M4 cells. We extend the study to show that EB1089 abrogates increases, induced by 9-cis RA, in caspase activation, p27Kip1 protein levels, Bim and Bax protein levels and in Bax/Bcl2 ratio. In addition, the CDKI p21Waf1 and CAII, a differentiation marker for pancreatic cancer cells are also differentially regulated.

CONCLUSIONS

These results suggest that the inhibitory effects of EB1089 on 9-cis RA-induced apoptosis lie upstream of caspase activation and could be associated with reduction of p27Kip1 protein levels.

The Anticancer Activities of Wogonin in Murine Sarcoma S180 both in Vitro and in Vivo

The anticancer effects of wogonin on murine sarcoma S180 both in vitro and in vivo were investigated, and its pro-apoptotic molecular mechanism was further studied. Wogonin treatment resulted in significant inhibition of S180 cells in a concentration-dependent manner detected by MTT assay. The IC50 value for 48 h was (7.37+/-1.53) x 10(-5) M. Typical morphological changes and apoptosis bleb phenomenon in S180 cells exposed to wogonin were distinctly observed by the inverted light microscope and the fluorescence microscope, respectively. According to protocols of transplanted tumor research, mice were transplanted with tumor cells S180. The weight of tumor and the peripheral leucocyte count were observed after the treatment of wogonin. The significant suppression of tumor growth was observed, and the peripheral leucocyte count of S180-bearing mice remained no significant changes compared with control group. After the treatment of 40 mg/kg wogonin, the inhibitory rate of tumor weight was 53.01%. Additional DNA fragmentation assay showed that wogonin induced apoptosis on murine sarcoma S180 tissue. RT-PCR results indicated that the increasing mRNA levels of bax and p53 and the decreasing mRNA level of bcl-2 were induced by wogonin. Western-blot assay showed that the increasing protein level of bax and the decreasing protein level of bcl-2 were induced by wogonin. Collectively, wogonin could induce apoptosis in murine sarcoma S180 thereby inhibiting the tumor growth both in vitro and in vivo. The pro-apoptotic effects might be related to the improvement of mRNA level of p53, the improvement of mRNA and protein levels of bax, and the reduction of mRNA and protein levels of bcl-2.

A novel retinoid-related molecule inhibits pancreatic cancer cell proliferation by a retinoid receptor independent mechanism via suppression of cell cycle regulatory protein function and induction of caspase-associated apoptosis

Retinoid-related molecules are important potential agents for the treatment of cancer. In the present study, we test the effect of a novel retinoid-related ligand, AGN193198 (4-[3-(1-heptyl-4,4-dimethyl-2-oxo-1,2,3,4-tetrahydroquinolin-6-yl)-3-oxo-prophenyl] benzoic acid), on pancreatic cancer cell proliferation and survival. AGN193198 treatment reduces BxPC-3 cell proliferation more efficiently than high-affinity retinoid acid receptor (RAR)- or retinoid X receptor (RXR)-selective retinoids. Moreover, AGN193198 does not activate transcription from RAR or RXR response elements and its effects on cell survival are not reversed by treatment with RAR- or RXR receptor-selective antagonists. These results suggest that the AGN193198-dependent inhibition of BxPC-3 cell function is not mediated via activation of the classical retinoid receptors. Cell cycle analysis of AGN193198-treated BxPC-3 cells indicates that AGN193198 causes accumulation of cells in G2/M. This change is associated with a marked reduction in regulators of S (cyclin A, cyclin-dependent kinase (cdk)2), G2/M (cyclin B1, cdk1, cdc25c) and G1 (cyclin D1, cyclin E, cdk2, cdk4) phase, and an increase in p21 and p27 level. Kinases assays reveal that cdk1, cdk2 and cdk4 activity are suppressed in AGN193198-treated cells. In addition, reduced cell proliferation is associated with enhanced procaspase (3, 8 and 9) and PARP cleavage. Z-VAD-FMK, a pancaspase inhibitor, inhibits AGN193198-dependent caspase activation and attenuates cell death. Z-VAD-FMK inhibits PARP cleavage, but does not alter the AGN193198-dependent reduction in cell cycle regulatory protein expression and activity, suggesting that caspase activation and suppression of cell cycle regulatory protein levels are independent processes. AGN193198 produces similar responses in other pancreatic cancer cell lines including AsPC-1 and MIA PaCa-2. These studies suggest that AGN193198 may be useful for the treatment of pancreatic cancer.

Retinoic acid down-regulates aldehyde dehydrogenase and increases cytotoxicity of 4-hydroperoxycyclophosphamide and acetaldehyde

Multiple prior studies have identified aldehyde dehydrogenases (ALDH) that are capable of oxidizing retinal to retinoic acid. In this study, we test the hypothesis that the accumulation of intracellular retinoic acid may lead to the suppression of ALDH expression and thus increase cytotoxicity to 4-hydroperoxycyclophosphamide (4-HC) in vitro. Mainly A549, but also other lung cancer cell lines, were used in our experiments, with the former having high levels of two ALDH isozymes expressed. Dose-response and time-course experiments were performed by incubating the cells with all-trans retinoic acid (ATRA) as well as other commercially available retinoids. The results show that incubation of A549 cells with any of the retinoids at pharmacologic doses for > or =48 h results in a significant decrease in ALDH-1A1 and ALDH-3A1 enzyme activity and protein levels but not the corresponding mRNAs. Such a decrease in ALDH activity was seen in all cell lines tested and results in a significant increase in toxicity of 4-HC and acetaldehyde, both of which are substrates for the enzymes. Prior incubation with ATRA also results in increased cytotoxicity, although to a lesser degree, of phenylketophosphamide and melphalan, neither of which is a substrate for ALDHs. These results suggest a post-translational mechanism through which retinoids decrease both ALDH expression, which results in increased cytotoxicity of 4-HC and acetaldehyde, although other previously described effects of these retinoids may contribute to the slight increase in cytotoxicity seen with other chemotherapy agents. These results may have clinical implications in regard to the use of retinoids in lung cancer prevention and treatment.

Thioredoxin is downstream of Smad7 in a pathway that promotes growth and suppresses cisplatin-induced apoptosis in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive human malignancy in which Smad7 is commonly overexpressed. Analysis by differential display identified thioredoxin-1 (TRX) as a gene whose basal expression is increased in COLO-357 pancreatic cancer cells engineered to overexpress Smad7. To delineate the biological consequences of TRX overexpression, we assessed TRX mRNA levels in PDAC and studied the effects of increased TRX levels in Smad7-overexpressing cells. By northern blotting, TRX mRNA levels were increased in PDAC samples by comparison with the normal pancreas. Moreover, analysis of laser-captured pancreatic cancer cells revealed parallel increases in Smad7 and TRX mRNA levels. Retroviral infection of an antisense TRX cDNA suppressed TRX protein levels and blunted the increased capacity of Smad7-overexpressing cells to form colonies in soft agar. 1-Methyl-propyl-2-imidazolozyl disulfide, a TRX inhibitor, markedly suppressed the growth of sham-transfected COLO-357 cells and enhanced the growth inhibitory actions of cis-diamminedichloroplatinum(II) (CDDP). CDDP also induced apoptosis, as evidenced by induction of DNA laddering, PARP cleavage, and caspase-3/9 activities. These pro-apoptotic actions were greatly attenuated in Smad7-overexpressing cells, which exhibited a more prolonged association of TRX with the apoptosis inducer apoptosis signal-regulating kinase-1, and enhanced nuclear factor kappaB activation in response to CDDP. These findings suggest that TRX is downstream of Smad7 in a pathway that confers a growth advantage to pancreatic cancer cells and that increases their resistance to CDDP-mediated apoptosis, implying novel regulatory functions for Smad7.

Retinoids cause apoptosis in pancreatic cancer cells via activation of RAR-gamma and altered expression of Bcl-2/Bax

All-trans-retinoic acid and 9-cis-retinoic acid have been reported to have inhibitory effects on pancreatic adenocarcinoma cells and we have shown that this is partly due to induction of apoptosis. In this study, the mechanisms whereby 9-cis-retinoic acid induces apoptosis in these cells were investigated. An involvement of the Bcl-2 family of proteins was shown, such that 9-cis-retinoic acid causes a decrease in the Bcl-2/Bax ratio. Overexpression of Bcl-2 also resulted in inhibition of apoptosis induced by 9-cis-retinoic acid. Furthermore, two broad-range caspase inhibitors blocked DNA fragmentation induced by 9-cis-retinoic acid, but had no effect on viability defined by mitochondrial activity. Using synthetic retinoids, which bind selectively to specific retinoic acid receptor subtypes, we further established that activation of retinoic acid receptor-gamma is essential for induction of apoptosis. Only pan-retinoic acid receptor and retinoic acid receptor-gamma selective agonists reduced viability and a cell line expressing very low levels of retinoic acid receptor-gamma is resistant to the effects of 9-cis-retinoic acid. A retinoic acid receptor-beta/gamma selective antagonist also suppressed the cytotoxic effects of 9-cis-retinoic acid in a dose-dependent manner. This study provides important insight into the mechanisms involved in suppression of pancreatic tumour cell growth by retinoids. Our results encourage further work evaluating the clinical use of receptor subtype selective retinoids in pancreatic carcinoma.