Effects of 12-O-tetradecanoylphorbol-13-acetate in combination with gemcitabine on Panc-1 pancreatic cancer cells cultured in vitro or Panc-1 tumors grown in immunodeficient mice

In the present study, the effects of 12-O-tetra-decanoylphorbol-13-acetate (TPA) alone or in combination with gemcitabine on the growth of Panc-1 pancreatic cancer cells cultured in vitro or grown in NCr immunodeficient nude mice were investigated. Combinations of TPA and gemcitabine synergi-stically inhibited the growth and induced apoptosis in Panc-1 cells. The combination of TPA (0.16 nM) and gemcitabine (0.5 µM) induced a marked increase in phosphorylated c-Jun NH2-terminal kinase (JNK) in the Panc-1 cells. In animal experiments, NCr nude mice with established Panc-1 tumors received daily intraperitoneal (i.p.) injections of TPA (50 ng/g body weight/day) or gemcitabine (0.5 µg/g body weight/day) alone or in combination for 26 days. Treatment with daily i.p. injections of low doses of TPA or gemcitabine alone had a modest inhibitory effect on the growth of the tumors. However, the combination of low doses of TPA and gemcitabine more potently inhibited the growth of Panc-1 tumors than either agent used individually. Treatment with TPA or gemcitabine alone or in combination did not affect the body weight of the animals. Clinical trials with TPA alone or in combination with gemcitabine on patients with pancreatic cancer are warranted in order to confirm our results.

PDCD2 controls hematopoietic stem cell differentiation during development

Programmed cell death 2 (Pdcd2) is a highly conserved protein of undefined function, and is widely expressed in embryonic and adult tissues. The observations that knockout of Pdcd2 in the mouse is embryonic lethal at preimplantation stages, and that in Drosophila, Zfrp8, the ortholog of Pdcd2, is required for normal lymph gland development suggest that Pdcd2 is important for regulating hematopoietic development. Through genetic and functional studies, we investigated pdcd2 function during the zebrafish ontogeny. Knockdown of pdcd2 expression in zebrafish embryos resulted in defects in embryonic hematopoietic development. Loss of pdcd2 function caused increased expression of progenitor markers, and accumulation of erythroid progenitors during primitive hematopoiesis. Additionally, hematopoietic stem cells (HSCs) failed to appear in the aorta-gonad mesonephros, and were not able to terminally differentiate or reconstitute hematopoiesis. Pdcd2 effects on HSC emergence were cell autonomous and P53-independent, and loss of pdcd2 function was associated with mitotic defects and apoptosis. Restoration of runx1 function(s) and modulation of apoptosis through the inhibition of Jak/Stat signaling rescued the hematopoietic and erythroid defects resulting from pdcd2 knockdown. Our studies suggest that pdcd2 plays a critical role in regulating the transcriptional hierarchy controlling hematopoietic lineage determination. Furthermore, the effects of pdcd2 in regulating mitotic cell death may contribute to its role(s) in directing hematopoietic differentiation during development.

Abstract 4721: Adaptation to histone deacetylase inhibitors attenuates cancer cell growth

Histone deacetylase (HDAC) inhibitors, such as SAHA (suberoylanilude hydroxamic acid) inhibit the growth of multiple cancer cell lines in vitro, and human tumor xenografts in vivo. SAHA has recently been approved for the treatment of human T cell lymphomas and is in clinical trials for a number of other different malignancies. HDAC inhibitors lead to increased acetylation of multiple cellular proteins, including histones, and lead to major changes in cellular gene expression, however the precise mechanisms of their therapeutic effects are not known. HDAC inhibitors have been reported to have multiple effects on different cancer cell lines, ranging from induction of differentiation to induction of apoptosis, DNA damage, senescence, and autophagy. We hypothesized that chronic treatment of malignant cells with HDAC inhibitors, through changes in the program of cancer cell gene expression, would induce differentiation and senescence, and attenuate the malignant phenotype. We have treated a subclone of the SW480 colon cancer cells (S3 cells) with step-wise increasing amounts of SAHA. Chronic treatment with SAHA resulted in adaptation of S3 cells to SAHA, associated with marked decrease in cell growth and tumorigenicity in nude mice. In addition to slow growth, SAHA-adapted SW480 cells (designated SH80), exhibit features of differentiation including gland formation and increased intestinal alkaline phosphatase production (IAP), and increased cell size, associated with multiple nuclei and polyploidy. Interestingly, decreased growth rate and increased expression of alkaline phosphatase were seen even following drug withdrawal, suggesting that drug-adaptation resulted in a relatively stable phenotype. Frequent expression of senescence-associated β-galactosidase was observed in SH80 cells, particularly in giant cells and cell clusters, suggesting on-going senescence. Increased expression of p21 RNA and protein, previously suggested to contribute to the growth inhibition effect of HDAC inhibitors, was observed in the SH80 cells. SH80 cells also exhibited changes in the expression of several microRNAs previously implicated in oncogenesis, suggesting that altered expression of these miRs might contribute to the attenuated malignant phenotype in SH80 cells. These data suggest adaptation of colon cancer cells to HDAC inhibitor therapy may attenuate key aspects of the malignant phenotype, and offer a new therapeutic approach to the long-term control of cancer.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4721. doi:1538-7445.AM2012-4721

How mesenchymal stem cells interact with tissue immune responses

Mesenchymal stem cells (MSCs), also called multipotent mesenchymal stromal cells, exist in almost all tissues and are a key cell source for tissue repair and regeneration. Under pathological conditions, such as tissue injury, these cells are mobilized towards the site of damage. Tissue damage is usually accompanied by proinflammatory factors, produced by both innate and adaptive immune responses, to which MSCs are known to respond. Indeed, recent studies have shown that there are bidirectional interactions between MSCs and inflammatory cells, which determine the outcome of MSC-mediated tissue repair processes. Although many details of these interactions remain to be elucidated, we provide here a synthesis of the current status of this newly emerging and rapidly advancing field.

Mesenchymal stromal cells protect mantle cell lymphoma cells from spontaneous and drug-induced apoptosis through secretion of B-cell activating factor and activation of the canonical and non-canonical nuclear factor κB pathways

BACKGROUND

There is increasing evidence that stromal cell interactions are required for the survival and drug resistance of several types of B-cell malignancies. There is relatively little information regarding the role of the bone marrow/lymphoid microenvironment in the pathogenesis of mantle cell lymphoma. In this study we investigated the interaction of primary mantle cell lymphoma cells with stromal cells in an ex vivo co-culture system.

DESIGN AND METHODS

The murine stromal cell line MS-5 and human bone marrow mesenchymal stromal cells were each co-cultured with primary mantle cell lymphoma cells for up to 7 months. Mantle cell lymphoma cultures alone or combined with human stromal cells were analyzed for cell number, cell migration, nuclear factor-κB activation and drug resistance.

RESULTS

Co-culture of mantle cell lymphoma cells and human stromal cells results in the survival and proliferation of primary mantle cell lymphoma cells for at least 7 months compared to mantle cell lymphoma cells cultured alone. Mantle cell lymphoma-human stromal cell interactions resulted in activation of the B-cell activating factor/nuclear factor-κB signaling axis resulting in reduced apoptosis, increased mantle cell lymphoma migration and increased drug resistance.

CONCLUSIONS

Direct mantle cell lymphoma-human stromal cell interactions support long-term expansion and increase the drug-resistance of primary mantle cell lymphoma cells. This is due in part to activation of the canonical and non-canonical nuclear factor κB pathways. We also demonstrated the ability of B-cell activating factor to augment CXCL12- and CXCL13-induced cell migration. Collectively, these findings demonstrate that human stromal cell-mantle cell lymphoma interactions play a pivotal role in the pathogenesis of mantle cell lymphoma and that analysis of mantle cell lymphoma-human stromal cell interactions may help in the identification of novel targets for therapeutic use.

Caloric restriction reduces growth of mammary tumors and metastases

We investigated the effects of caloric restriction (CR) on growth of tumors and metastases in the 4T1 mammary tumor model and found that CR, compared with normal diet, reduced the growth of mammary tumors and metastases and the total number of metastases that originated both spontaneously from the primary tumor and also experimentally from i.v. injection of the tumor cells. CR also decreased proliferation and angiogenesis and increased apoptosis in tumors. CR reduced levels of insulin, leptin, insulin-like growth factor 1, insulin-like growth factor binding protein 3 and increased adiponectin in tumors. We also demonstrated that tumors from CR mice possessed lower levels of transforming growth factor-β, lower intratumor deposition of collagen IV and reduced invasiveness due to a decrease in tumor secretion of active matrix metalloproteinase 9. Our results suggest that CR-induced metabolic and signaling changes affect the stroma and the tumor cells resulting in a microenvironment that prevents proliferation of breast tumors and their metastases.

MEOX2 regulates nuclear factor-kappaB activity in vascular endothelial cells through interactions with p65 and IkappaBbeta

AIMS

Tumours secrete proangiogenic factors to induce the ingrowth of blood vessels, the end targets of which are vascular endothelial cells (ECs). The MEOX2 homeoprotein inhibits nuclear factor-kappaB (NF-kappaB) signalling and EC activation in response to serum and proangiogenic factors. We hypothesize that MEOX2 interacts with components of this pathway in vascular ECs to modulate NF-kappaB activity and EC activation and that these interactions depend upon specific domains within the MEOX2 protein.

METHODS AND RESULTS

To test our hypothesis, we transduced ECs with MEOX2 expression constructs. MEOX2 protein localized to the nuclear fraction, as did IkappaBbeta and p65. By co-immunoprecipitation, MEOX2 bound to both p65 and IkappaBbeta. Immunofluorescence demonstrated that MEOX2 colocalizes in the nucleus with both p65 and IkappaBbeta and that this colocalization requires the MEOX2 homeodomain and N-terminal domain. Finally, promoter assays revealed that MEOX2 expression has a biphasic effect on NF-kappaB-dependent promoters. At low levels, MEOX2 stimulates NF-kappaB activity, whereas at high levels, it represses, effects that also depend upon the homeodomain and the N-terminal domain.

CONCLUSION

Our results represent the first report of an interaction between a homeobox protein and IkappaBbeta and suggest that MEOX2 modulates the activity of the RelA complex through direct interaction with its components. These observations implicate MEOX2 as a potentially important regulatory gene inhibiting not only the angiogenic response of ECs to proangiogenic factors, but also their response to chronic inflammatory stimulation that normally activates NF-kappaB, suggesting MEOX2 as a possible molecular target for the therapy of angiogenesis-dependent diseases such as cancer.

Species variation in the mechanisms of mesenchymal stem cell-mediated immunosuppression

Bone marrow-derived mesenchymal stem cells (MSCs) hold great promise for treating immune disorders because of their immunoregulatory capacity, but the mechanism remains controversial. As we show here, the mechanism of MSC-mediated immunosuppression varies among different species. Immunosuppression by human- or monkey-derived MSCs is mediated by indoleamine 2,3-dioxygenase (IDO), whereas mouse MSCs utilize nitric oxide, under the same culture conditions. When the expression of IDO and inducible nitric oxide synthase (iNOS) were examined in human and mouse MSCs after stimulation with their respective inflammatory cytokines, we found that human MSCs expressed extremely high levels of IDO, and very low levels of iNOS, whereas mouse MSCs expressed abundant iNOS and very little IDO. Immunosuppression by human MSCs was not intrinsic, but was induced by inflammatory cytokines and was chemokine-dependent, as it is in mouse. These findings provide critical information about the immunosuppression of MSCs and for better application of MSCs in treating immune disorders.

Inhibition of NF-kappaB by (E)3-[(4-methylphenyl)-sulfonyl]-2-propenenitrile (BAY11-7082; BAY) is associated with enhanced 12-O-tetradecanoylphorbol-13-acetate-induced growth suppression and apoptosis in human prostate cancer PC-3 cells

The effects of 12-O-tetradecanoylphorbol-13-acetate (TPA) alone or in combination with an NF-kappaB inhibitor, (E)3-[(4-methylphenyl)-sulfonyl]-2-propenenitrile (BAY 11-7082; BAY), on the growth and apoptosis of human prostate cancer PC-3 cells cultured in vitro or grown in immunodeficient mice were studied. Treatment of cultured PC-3 cells with TPA (0.2-10 ng/ml) for 96 h resulted in growth inhibition and apoptosis in a concentration-dependent manner. BAY inhibited NF-kappaB activity in PC-3 cells as determined by a luciferase reporter assay and enhanced TPA-induced growth inhibition and apoptosis in cultured PC-3 cells. In animal studies, NCr immunodeficient mice were injected subcutaneously with PC-3 cells in Matrigel. Mice with well-established tumors received daily i.p. injections with TPA (100 ng/g body weight/day), BAY (4 microg/g/day), or a combination of TPA (100 ng/g/day) and BAY (4 microg/g/day) for 36 days. Tumor growth occurred in all of the vehicle-treated control mice. The percent of animals with some tumor regression after 36 days of treatment was 0% for the control group, 40% for the TPA group, 50% for the BAY group and 100% for the TPA + BAY group. Mechanistic studies indicated that treatment of the mice with TPA or TPA + BAY decreased proliferation and increased apoptosis in the tumors. Results from our studies indicate that inhibition of NF-kappaB activity is associated with enhanced TPA-induced growth inhibition and apoptosis in PC-3 cells. Inhibition of NF-kappaB activity by suitable pharmacological inhibitors may be an effective strategy for improving the therapeutic efficacy of TPA in prostate cancer.

Atorvastatin and celecoxib inhibit prostate PC-3 tumors in immunodeficient mice

PURPOSE

To investigate the effects and mechanisms of atorvastatin and celecoxib administered individually or in combination on human prostate cancer PC-3 cells cultured in vitro or grown as xenograft tumors in immunodeficient mice.

EXPERIMENTAL DESIGN

Human prostate cancer PC-3 cells in culture were treated with atorvastatin and celecoxib alone or in combination. Severe combined immunodeficient (SCID) mice were injected s.c. with PC-3 cells. The mice received daily i.p injections starting 2 days before tumor cell inoculation and continuing during the course of treatment with atorvastatin (10 microg/g body weight/d), celecoxib (10 microg/g/d), a combination of atorvastatin (10 microg/g/d) and celecoxib (10 microg/g/d), or a combination of atorvastatin (5 microg/g/d) and celecoxib (5 microg/g/d).

RESULTS

Atorvastatin in combination with celecoxib had stronger effects on growth inhibition and apoptosis of PC-3 cells than either agent used individually. Atorvastatin and celecoxib in combination also had a stronger inhibitory effect on activation of nuclear factor-kappaB and extracellular signal-regulated kinase 1/2 in PC-3 cells than either agent alone. Treatment of SCID mice with combinations of atorvastatin and celecoxib more effectively inhibited the formation and growth of PC-3 tumors in the mice than either agent administered alone.

CONCLUSIONS

A combination of atorvastatin and celecoxib had a more potent inhibitory effect on the growth of PC-3 cells cultured in vitro or grown in SCID mice than either agent alone. A combination of atorvastatin and celecoxib may be an effective strategy for the prevention of prostate cancer.

Effects of 12-O-tetradecanoylphorbol-13-acetate (TPA) in combination with paclitaxel (Taxol) on prostate Cancer LNCaP cells cultured in vitro or grown as xenograft tumors in immunodeficient mice

PURPOSE

To investigate the effects of 12-O-tetradecanoylphorbol-13-acetate (TPA) in combination with paclitaxel (Taxol) on prostate cancer cells cultured in vitro or grown as tumors in immunodeficient mice.

EXPERIMENTAL DESIGN

Human prostate cancer LNCaP cells in culture were treated with TPA alone or in combination with paclitaxel. NCr immunodeficient mice with well-established LNCaP tumors received i.p. injections with vehicle or with TPA, paclitaxel, or TPA in combination with paclitaxel. The animals either received daily treatment for 5 consecutive days followed by a 2-day intermission, which was repeated for a total of 28 days (experiment 1), or continuous daily treatment for 28 days (experiment 2).

RESULTS

Treatment of LNCaP cells with a combination of TPA and paclitaxel synergistically inhibited the growth and induced apoptosis in cultured LNCaP cells, and this treatment also induced a marked increase in phosphorylated c-Jun-NH2-kinase (JNK). In animal experiments, tumor growth occurred in all mice treated with vehicle. When treated with TPA alone, the percentage of animals with some tumor regression was 33% in experiment 1 and 100% in experiment 2. Treatment of animals with paclitaxel alone caused some tumor regression in 17% and 57% of the animals in experiments 1 and 2, respectively. All animals treated with TPA + paclitaxel in both experiments had some tumor regression.

CONCLUSIONS

TPA and paclitaxel in combination had a stronger inhibitory effect on the growth of LNCaP cells in culture or as xenograft tumors in immunodeficient mice than either agent alone. Clinical trials with TPA alone or in combination with paclitaxel in patients with prostate cancer may be warranted.

Curcumin downregulates the constitutive activity of NF-κB and induces apoptosis in novel mouse melanoma cells

Melanoma, the most deadly form of skin cancer, is very aggressive and resistant to present therapies. The transcription factor nuclear factor-kappa B (NF-kappaB) has been reported to be constitutively active in many types of cancer. Constitutively active NF-kappaB seen in melanoma likely plays a central role in cell survival and growth. We have established and characterized novel cell lines from our murine melanoma model. Here we report the constitutive activity of NF-kappaB in these melanoma-derived cells, as shown by electrophoretic mobility shift assay and reporter assays. We hypothesized that agents that inhibit NF-kappaB may also inhibit cell proliferation and may induce apoptosis in such melanoma cells. Curcumin has been shown to inhibit NF-kappaB activity in several cell types. In our system, curcumin selectively inhibited growth of melanoma cells, but not normal melanocytes. Curcumin induced melanoma cells to undergo apoptosis, as shown by caspase-3 activation, inversion of membrane phosphatidyl serine, and increases in cells in the sub-G1 phase. A curcumin dose-dependent inhibition of NF-kappaB-driven reporter activity correlated with decreased levels of phospho-IkappaBalpha, and decreased expression of NF-kappaB-target genes COX-2 and cyclin D1. This study demonstrates that the use of cells from our model system can facilitate studies of signaling pathways in melanoma. We furthermore conclude that curcumin, a natural and safe compound, inhibits NF-kappaB activity and the expression of its downstream target genes, and also selectively induces apoptosis of melanoma cells but not normal melanocytes. These encouraging in-vitro results support further investigation of curcumin for treatment of melanoma in vivo.

Alternative pathways of NF-kappaB activation: a double-edged sword in health and disease

While the classical pathway of NF-kappaB activation plays critical roles in a wide range of biological processes, the more recently described "non-canonical" NF-kappaB pathway has important but more restricted roles in both normal and pathological processes. The non-canonical NF-kappaB pathway, based on processing of the nf-kappab2 gene product p100 to generate p52, appears to be involved in B-cell maturation and lymphoid development. Deregulated activation of this pathway has been observed in a variety of malignant and autoimmune diseases, thus inhibitors that specifically target p100 processing might be predicted to have potential roles as immunomodulators and in the therapy of malignant diseases. We review current understandings of NF-kappaB activation, particularly the mechanisms of p100 processing under both physiological and pathological conditions.

Novel multi-component nanopharmaceuticals derived from poly(ethylene) glycol, retro-inverso-Tat nonapeptide and saquinavir demonstrate combined anti-HIV effects

Background

Current anti-AIDS therapeutic agents and treatment regimens can provide a dramatically improved quality of life for HIV-positive people, many of whom have no detectable viral load for prolonged periods of time. Despite this, curing AIDS remains an elusive goal, partially due to the occurrence of drug resistance. Since the development of resistance is linked to, among other things, fluctuating drug levels, our long-term goal has been to develop nanotechnology-based drug delivery systems that can improve therapy by more precisely controlling drug concentrations in target cells. The theme of the current study is to investigate the value of combining AIDS drugs and modifiers of cellular uptake into macromolecular conjugates having novel pharmacological properties.

Results

Bioconjugates were prepared from different combinations of the approved drug, saquinavir, the antiviral agent, R.I.CK-Tat9, the polymeric carrier, poly(ethylene) glycol and the cell uptake enhancer, biotin. Anti-HIV activities were measured in MT-2 cells, an HTLV-1-transformed human lymphoid cell line, infected with HIV-1 strain Vbu 3, while parallel studies were performed in uninfected cells to determine cellular toxicity. For example, R.I.CK-Tat9 was 60 times more potent than L-Tat9 while the addition of biotin resulted in a prodrug that was 2850 times more potent than L-Tat9. Flow cytometry and confocal microscopy studies suggest that variations in intracellular uptake and intracellular localization, as well as synergistic inhibitory effects of SQV and Tat peptides, contributed to the unexpected and substantial differences in antiviral activity.

Conclusion

Our results demonstrate that highly potent nanoscale multi-drug conjugates with low non-specific toxicity can be produced by combining moieties with anti-HIV agents for different targets onto macromolecules having improved delivery properties.

Role of NF-kappaB in regulation of PXR-mediated gene expression: a mechanism for the suppression of cytochrome P-450 3A4 by proinflammatory agents

It is a long-standing observation that inflammatory responses and infections decrease drug metabolism capacity in human and experimental animals. Cytochrome P-450 3A4 cyp304 is responsible for the metabolism of over 50% of current prescription drugs, and cyp3a4 expression is transcriptionally regulated by pregnane X receptor (PXR), which is a ligand-dependent transcription factor. In this study, we report that NF-kappaB activation by lipopolysaccharide and tumor necrosis factor-alpha plays a pivotal role in the suppression of cyp3a4 through interactions of NF-kappaB with the PXR.retinoid X receptor (RXR) complex. Inhibition of NF-kappaB by NF-kappaB-specific suppressor SRIkappaBalpha reversed the suppressive effects of lipopolysaccharide and tumor necrosis factor-alpha. Furthermore, we showed that NF-kappaB p65 disrupted the association of the PXR.RXRalpha complex with DNA sequences as determined by electrophoretic mobility shift assay and chromatin immunoprecipitation assays. NF-kappaB p65 directly interacted with the DNA-binding domain of RXRalpha and may prevent its binding to the consensus DNA sequences, thus inhibiting the transactivation by the PXR.RXRalpha complex. This mechanism of suppression by NF-kappaB activation may be extended to other nuclear receptor-regulated systems where RXRalpha is a dimerization partner.

Regulation of Bcl-3 through interaction with the Lck tyrosine kinase

bcl-3 is a protooncogene which undergoes chromosomal translocation in a subset of chronic B-cell lymphocytic leukemia cells. Bcl-3 is a unique IkappaB family protein that regulates transcription of a number of NF-kappaB target genes through interactions with NF-kappaB dimers. Based on previous studies, suggesting that Bcl-3 interacts with the Fyn tyrosine kinase in platelets, we investigated possible interactions of Bcl-3 with Lck, a related tyrosine kinase important in lymphoid cells. Protein-protein interactions between Bcl-3 and the Lck tyrosine kinase were identified both in vitro and in vivo. Lck enhanced Bcl-3-mediated activation of a p52/Bcl-3-responsive promoter in reporter gene assays independent of its tyrosine kinase activity, but requiring the Lck SH3 protein interaction domain. These studies suggest that Bcl-3 might participate in oncogenic pathways involving Lck.

Adenovirus infection and cytotoxicity of primary mantle cell lymphoma cells

Mantle cell lymphoma (MCL) is a distinct form of non-Hodgkin's lymphoma (NHL) derived from CD5+ B cells. MCL cells overexpress cyclin D1 as a consequence of translocation of the gene into the immunoglobulin heavy-chain gene locus. MCL is an aggressive form of NHL with frequent relapses after standard-dose chemotherapy. In this context, a variety of novel therapies for patients with MCL have been investigated. In this study, we use an expanded panel of attenuated adenoviruses to study adenovirus-mediated cytotoxicity of MCL cells. Our results demonstrate: 1) adenovirus infection of MCL cells despite the absence of receptor/coreceptor molecules known to be important for adenovirus infection of other cells types; 2) cytotoxicity of MCL cells after infection with specific adenovirus mutants; 3) a high degree of cytotoxicity after infection of some patient samples with viruses lacking the E1B 19k "antiapoptotic" gene; and 4) cytotoxicity after infection with viruses containing mutations in E1A pRb or p300 binding. The extent of cytotoxicity with the panel of viruses demonstrated interpatient variability, but 100% cytotoxicity, as determined by molecular analysis, was detected in some samples. These studies provide the foundation for: 1) the development of adenoviruses as cytotoxic agents for MCL and 2) analyses of key regulatory pathways operative in MCL cells.

Enhancement of TPA-induced growth inhibition and apoptosis in myeloid leukemia cells by BAY 11-7082, an NF-kappaB inhibitor

The phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (TPA) is a potent stimulator of differentiation and apoptosis in myeloid leukemia cells. In the present study, we investigated the role of the transcription factor NF-kappaB in TPA-induced growth inhibition and apoptosis in the myeloid leukemia HL-60 cell line and its TPA-resistant cell variant HL-525. Unlike the parental cell line, HL-525 cells are protein kinase C (PKC)-beta deficient and resistant to TPA-induced differentiation and apoptosis. We found that treatment of HL-60 cells with TPA resulted in a concentration-dependent growth inhibition and an increase in apoptotic cells. TPA only had a small effect on growth and apoptosis in HL-525 cells. Treatment of HL-60 cells with TPA (0.64-3.2 nM) caused a rapid activation of NF-kappaB as determined by electrophoresis mobility shift assay (EMSA) and immunocytochemistry. Although the basal level of NF-kappaB activity was low in HL-60 cells, TPA-resistant HL-525 cells had a high basal level of NF-kappaB activity. Treatment of HL-525 cells with higher concentrations of TPA (16-80 nM) resulted in a further increase in NF-kappaB activity. (E)3-[(4-methylphenyl)-sulfonyl]-2-propenenitrile (BAY 11-7082; BAY), which inhibits IkappaB alpha phosphorylation and thus decreases NF-kappaB activation, was found to decrease TPA-induced nuclear translocation of NF-kappaB. Furthermore, BAY enhanced TPA-induced growth inhibition and apoptosis in both HL-60 and HL-525 cells. Results from the present study indicate that inhibition of NF-kappaB by BAY was associated with enhanced TPA-induced growth inhibition and apoptosis in human myeloid leukemia cells. TPA in combination with pharmacological inhibitors of NF-kappaB may improve the therapeutic efficacy of TPA and overcome the resistance to TPA in some myeloid leukemia patients.

Activation of human T cell leukemia virus type 1 LTR promoter and cellular promoter elements by T cell receptor signaling and HTLV-1 Tax expression

Human T cell leukemia virus 1 (HTLV-1) gene expression is regulated by both the viral Tax protein and by cellular transcriptional factors. We have previously shown that immune activation stimuli such as phorbol esters (PMA) and phytohemagglutinin (PHA) cooperate with HTLV-1 Tax expression to enhance HTLV-1 gene expression in infected T cells through increased activity of the HTLV-1 LTR. We now extend these studies to demonstrate roles for the T cell receptor complex, Lck, and Ras molecules in the coactivation of the HTLV-1 LTR by Tax and T cell activation stimuli. We also observe coactivation of Tax-responsive cellular promoter elements containing NF-kappaB and serum response factor (SRF) binding sites by Tax and T cell activation stimuli. These results suggest a model whereby T cell receptor stimulation and Tax expression coactivate HTLV-1 gene expression and cellular gene expression, enhancing activation of latent HTLV-1 and expression of cellular genes involved in disease pathogenesis.

Inhibitory effects of 12-O-tetradecanoylphorbol-13-acetate alone or in combination with all-trans retinoic acid on the growth of cultured human pancreas cancer cells and pancreas tumor xenografts in immunodeficient mice

Treatment of cultured PANC-1, MIA PaCa-2, and BxPC-3 human pancreatic adenocarcinoma cells with 0.1 to 1.6 nM 12-O-tetradecanoylphorbol-13-acetate (TPA) for 96 h inhibited the proliferation of these cells in a dose-dependent manner, and PANC-1 and MIA PaCa-2 cells were more sensitive to TPA than BxPC-3 cells. Inhibition of proliferation by TPA in PANC-1 cells was associated with an increase in the level of p21, but this was not observed in MIA PaCa-2 or BxPC-3 cells. The TPA-induced increase of p21 in PANC-1 cells was blocked by bisindolylmaleimide or rottlerin (inhibitors of protein kinase C). Studies in NCr-immunodeficient mice with well established PANC-1 tumor xenografts indicated that daily i.p. injections of TPA strongly inhibited tumor growth, increased the percentage of caspase-3-positive cells, and decreased the ratio of mitotic cells to caspase-3-positive cells in the tumors. Studies with BxPC-3 tumors in NCr mice receiving daily i.p. injections of vehicle, TPA, all-trans retinoic acid (ATRA), or a TPA/ATRA combination showed that TPA had an inhibitory effect on tumor growth, but treatment of the animals with the TPA/ATRA combination had a greater inhibitory effect on tumor growth than TPA alone. Treatment with the TPA/ATRA combination resulted in a substantially decreased ratio of the percentage of mitotic cells to the percentage of caspase-3-positive cells in the tumors compared with tumors from the vehicle-treated control animals. The inhibitory effects of TPA on tumor growth occurred at clinically achievable blood levels.