Kinase inhibitors and cytotoxic drug resistance.
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Antineoplastic Agents↗
Biomedical subjects
Paul Dent
Publications and source records attributed to Paul Dent.
Bortezomib and flavopiridol interact synergistically to induce apoptosis in chronic myeloid leukemia cells resistant to imatinib mesylate through both Bcr/Abl-dependent and -independent mechanisms.
Interactions between the cyclin-dependent kinase (CDK) inhibitor flavopiridol and the proteasome inhibitor bortezomib were examined in Bcr/Abl(+) human leukemia cells. Coexposure of K562 or LAMA84 cells to subtoxic concentration of flavopiridol (150-200 nM) and bortezomib (5-8 nM) resulted in a synergistic increase in mitochondrial dysfunction and apoptosis. These events were associated with a marked diminution in nuclear factor kappaB (NF-kappaB)/DNA binding activity; enhanced phosphorylation of SEK1/MKK4 (stress-activated protein kinase/extracellular signal-related kinase 1/mitogen-activated protein kinase kinase 4), c-Jun N-terminal kinase (JNK), and p38 mitogen-activated protein kinase (MAPK); down-regulation of Bcr/Abl; and a marked reduction in signal transducer and activator of transcription 3 (STAT3) and STAT5 activity. In imatinib mesylate-resistant K562 cells displaying increased Bcr/Abl expression, bortezomib/flavopiridol treatment markedly increased apoptosis in association with down-regulation of Bcr/Abl and BclxL, and diminished phosphorylation of Lyn, Hck, CrkL, and Akt. Parallel studies were performed in imatinib mesylate-resistant LAMA84 cells exhibiting reduced expression of Bcr/Abl but a marked increase in expression/activation of Lyn and Hck. Flavopiridol/bortezomib effectively induced apoptosis in these cells in association with Lyn and Hck inactivation. The capacity of flavopiridol to promote bortezomib-mediated Bcr/Abl down-regulation and apoptosis was mimicked by the positive transcription elongation factor-b (P-TEFb) inhibitor DRB (5,6-dichloro 1-beta-d-ribofuranosylbenzinida-sole). Finally, the bortezomib/flavopiridol regimen also potently induced apoptosis in Bcr/Abl(-) human leukemia cells. Collectively, these findings suggest that a strategy combining flavopiridol and bortezomib warrants further examination in chronic myelogenous leukemia and related hematologic malignancies.
Antineoplastic Agents↗
Activation of MAP kinase pathways by TRAIL: don't expect the obvious.
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Apoptosis↗
Induction of apoptosis in human leukemia cells by the tyrosine kinase inhibitor adaphostin proceeds through a RAF-1/MEK/ERK- and AKT-dependent process.
Effects of the tyrphostin tyrosine kinase inhibitor adaphostin (NSC 680410) have been examined in human leukemia cells (Jurkat, U937) in relation to mitochondrial events, apoptosis, and perturbations in signaling and cell cycle regulatory events. Exposure of cells to adaphostin concentrations > or =0.75 microM for intervals > or =6 h resulted in a pronounced release of cytochrome c and AIF, activation of caspase-9, -8, and -3, and apoptosis. These events were accompanied by the caspase-independent downregulation of Raf-1, inactivation of MEK1/2, ERK, Akt, p70S6K, dephosphorylation of GSK-3, and activation of c-Jun-N-terminal kinase (JNK) and p38 MAPK. Adaphostin also induced cleavage and dephosphorylation of pRb on CDK2- and CDK4-specific sites, as well as the caspase-dependent downregulation of cyclin D1. Inducible expression of a constitutively active MEK1 construct markedly diminished adaphostin-induced cytochrome c and AIF release, JNK activation, and apoptosis in Jurkat cells. Ectopic expression of Raf-1 or constitutively activated (myristolated) Akt also significantly attenuated adaphostin-induced apoptosis, but protection was less than that conferred by enforced activation of MEK. Lastly, antioxidants (e.g., L-N-acetylcysteine; L-NAC) opposed adaphostin-mediated mitochondrial dysfunction, Raf-1/MEK/ERK downregulation, JNK activation, and apoptosis. However, in contrast to L-NAC, enforced activation of MEK failed to block adaphostin-mediated ROS generation. Together, these findings demonstrate that the tyrphostin adaphostin induces multiple perturbations in signal transduction pathways in human leukemia cells, particularly inactivation of the cytoprotective Raf-1/MEK/ERK and Akt cascades, that culminate in mitochondrial injury, caspase activation, and apoptosis. They also suggest that adaphostin-related oxidative stress acts upstream of perturbations in these signaling pathways to trigger the cell death process.
Adamantane↗
Bile acids enhance the activity of the insulin receptor and glycogen synthase in primary rodent hepatocytes.
Previously, we demonstrated that deoxycholic acid (DCA)-induced ERK1/2 and AKT signaling in primary hepatocytes is a protective response. In the present study, we examined the regulation of the phosphatidylinositol 3 (PI3) kinase/AKT/glycogen synthase (kinase) 3 (GSK3)/glycogen synthase (GS) pathway by bile acids. In primary hepatocytes, DCA activated ERBB1 (the epidermal growth factor receptor), ERBB2, and the insulin receptor, but not the insulin-like growth factor 1 (IGF-1) receptor. DCA-induced activation of the insulin receptor correlated with enhanced phosphorylation of insulin receptor substrate 1, effects that were both blocked by the insulin receptor inhibitor AG1024 and by expression of the dominant negative IGF-1 receptor (K1003R), which inhibited in trans. Expression of the dominant negative IGF-1 receptor (K1003R) also abolished DCA-induced AKT activation. Bile acid-induced activation of AKT and phosphorylation of GSK3 were blunted by the ERBB1 inhibitor AG1478 and abolished by AG1024. Bile acids caused activation of GS to a similar level induced by insulin (50 nM); both were blocked by inhibition of insulin receptor function and the PI3 kinase/AKT/GSK3 pathway. In conclusion, these findings suggest that bile acids and insulin may cooperate to regulate glucose storage in hepatocytes.
Adenoviridae↗
Bile acids induce mitochondrial ROS, which promote activation of receptor tyrosine kinases and signaling pathways in rat hepatocytes.
Previous studies have demonstrated in hepatocytes that deoxycholic acid (DCA) promotes inactivation of protein tyrosine phosphatases (PTPases) and activation of ERBB1 and the extracellular-regulated kinase (ERK) 1/2 pathway. The present studies have determined the biochemical mechanism(s) through which these events occur. DCA and taurodeoxycholic acid (TDCA) (100 micromol/L) caused activation of ERBB1, insulin receptor, and the ERK1/2 and AKT pathways in primary rodent hepatocytes. DCA- and TDCA-induced receptor and signaling pathway activations were blocked by the reactive oxygen species (ROS) scavengers N-acetyl cysteine (NAC) and Trolox (TX), as well as by cyclosporin A (CsA) and bongkrekic acid (BKA). DCA activated the ERK1/2 pathway in HuH7 human hepatoma cells that was blocked by the incubation of cells with an ERBB1 inhibitor, NAC, TX, CsA, or BKA. DCA did not activate the ERK1/2 pathway in mitochondria-defective HuH7 Rho 0 cells. In HuH7 cells and primary hepatocytes, DCA enhanced the production of ROS, an effect that was abolished in Rho 0 cells and by prior incubation of cells with CsA or BKA. In hepatocytes and HuH7 cells, DCA inhibited PTPase activity. Incubation of hepatocytes with either CsA or BKA prevented DCA-induced inhibition of PTPase activity. Loss of mitochondrial function in Rho 0 cells also abolished the inhibitory effects of DCA on PTPase activity. In conclusion, DCA and TDCA cause ROS generation in hepatocytes that is dependent on metabolically active mitochondria. The generation of ROS is essential for PTPase inactivation, receptor tyrosine kinase activation, and enhanced signaling down the ERK1/2 and AKT pathways.
Animals↗
Infectivity enhanced adenoviral-mediated mda-7/IL-24 gene therapy for ovarian carcinoma.
OBJECTIVE: Melanoma differentiation associated gene-7 [mda-7/Interleukin (IL)-24] has been identified as a novel anti-cancer agent, which specifically induces apoptosis in cancer cells but not in normal epithelial, endothelial and fibroblast cells. The objective of this study was to evaluate the anti-tumor effect of adenovirus-mediated mda-7/IL-24 (Ad.mda-7) gene therapy in ovarian carcinoma and further improve anti-tumor effect by enhancing infectivity of Ad.mda-7. METHODS: A panel of human ovarian carcinoma cells, OV-4, HEY, SKOV3, SKOV3.ip1 and control normal human mesothelial cells, were infected by a replication deficient recombinant adenovirus encoding mda-7/IL-24 and control virus Ad.CMV.Luc. After 72 h, apoptosis was evaluated by TUNEL and Hoechst staining and further quantified by fluorescent activated cell sorter (FACS) analysis. Infectivity of Ad.mda-7 was enhanced by retargeting it to CD40 or EGF receptors overexpressed on ovarian cancer cells. Subsequently, enhancement in apoptosis of CD40- or epidermal growth factor receptor (EGFR)-retargeted Ad.mda-7 was evaluated. RESULTS: Adenoviral-mediated delivery of mda-7 induces apoptosis ranging from 10-23% in human ovarian cancer cells tested with the highest percentage of apoptosis noted in SKOV3 cells. Minimal apoptosis was noted in normal mesothelial cells. CD40- or EGFR-retargeted Ad.mda-7 increased apoptosis by 10-32% when compared to that achieved with untargeted Ad.mda-7. CONCLUSION: Ad.mda-7 exhibits ovarian cancer-specific apoptosis, but does not affect normal human mesothelial cells. Infectivity enhanced CD40- and EGFR-retargeted Ad.mda-7 augments apoptosis induction, thus increasing the therapeutic index and translational potential of Ad.mda-7 gene therapy.
Adenoviruses, Human↗
Gene profiling and the cyclin-dependent kinase inhibitor flavopiridol: what's in a name?
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Cyclin-Dependent Kinases↗
Deoxycholic acid activates the c-Jun N-terminal kinase pathway via FAS receptor activation in primary hepatocytes. Role of acidic sphingomyelinase-mediated ceramide generation in FAS receptor activation.
We have shown previously that bile acids can activate the JNK pathway and down-regulate cholesterol 7alpha-hydroxylase (CYP7A1), the rate-limiting enzyme in the neutral pathway of bile acid biosynthesis. In this study, the mechanism(s) by which deoxycholic acid (DCA) activates the JNK pathway were examined. FAS receptor (FAS-R) and acidic sphingomyelinase (ASM)-deficient hepatocytes were resistant to DCA-induced activation of the JNK pathway. Activation of the JNK pathway (2-3-fold) in response to tumor necrosis factor-alpha was similar in both wild-type and FAS-R(-/-) hepatocytes. In wild-type and FAS-R(-/-) hepatocytes, ceramide elevation was detected as early as 2 min and peaked at 10 min after DCA treatment. In contrast, ASM(-/-) hepatocytes were defective in DCA-induced ceramide generation. Treatment with DCA resulted in movement of FAS-R to the cell surface, which was blocked upon treatment with brefeldin A. However, brefeldin A failed to block DCA-mediated JNK activation in wild-type hepatocytes. DCA-induced JNK activation was independent of either the epidermal growth factor receptor activation or free radical generation. Addition of ASM to rat hepatocytes activated JNK and down-regulated CYP7A1 mRNA levels. In conclusion, these results show that DCA activates JNK and represses CYP7A1 mRNA levels in primary hepatocytes via an ASM/FAS-R-dependent mechanism that is independent of either the epidermal growth factor receptor or free radical generation.
Alleles↗
Melanoma differentiation associated gene-7, mda-7/interleukin-24, induces apoptosis in prostate cancer cells by promoting mitochondrial dysfunction and inducing reactive oxygen species.
Mda-7/IL-24 (Ad.mda-7) is a novel cytokine gene belonging to the interleukin (IL) 10 gene superfamily. Adenoviral-mediated delivery of mda-7/IL-24 causes growth suppression and apoptosis in a wide spectrum of cancer cells, including prostate, without harming normal cells. We now demonstrate that Ad.mda-7 selectively induces apoptosis in prostate cancer cells by promoting mitochondrial dysfunction and reactive oxygen species (ROS) production. Antioxidants (N-acetyl-L-cysteine and Tiron) and inhibitors of mitochondrial permeability transition (cyclosporine A and bongkrekic acid) inhibit Ad.mda-7-induced mitochondrial dysfunction and apoptosis. Conversely, agents augmenting ROS production (arsenic trioxide, NSC656240, and PK11195) facilitate Ad.mda-7-induced apoptosis. Ectopic expression of Bcl-2 and Bcl-x(L) inhibits mitochondrial changes, ROS production, and apoptosis providing additional support for an association between mitochondrial dysfunction and Ad.mda-7 action. These studies present definitive evidence that changes in mitochondrial function and ROS production are key components associated with selective killing of prostate cancer cells by mda-7/IL-24.
Adenoviridae↗
Coadministration of the heat shock protein 90 antagonist 17-allylamino- 17-demethoxygeldanamycin with suberoylanilide hydroxamic acid or sodium butyrate synergistically induces apoptosis in human leukemia cells.
Interactions between the histone deacetylase inhibitors (HDACIs) suberoylanilide hydroxamic acid (SAHA) and sodium butyrate (SB) and the heat shock protein (Hsp) 90 antagonist 17-allylamino-17-demethoxygeldanamycin (17-AAG) have been examined in human leukemia cells (U937). Coadministration of marginally toxic concentrations of 17-AAG with sublethal concentrations of SB or SAHA resulted in highly synergistic induction of mitochondrial damage (i.e., cytochrome c release), caspase-3 and -8 activation, and apoptosis. Similar interactions were noted in human promyelocytic (HL-60) and lymphoblastic (Jurkat) leukemia cells. These events were accompanied by multiple perturbations in signal transduction, cell cycle, and survival-related pathways, including early down-regulation of Raf-1, inactivation of extracellular signal-regulated kinase (ERK) 1/2 and mitogen-activated protein/ERK kinase (MEK) 1/2, diminished expression of phospho-Akt, and late activation of c-Jun-NH(2)-terminal kinase, but no changes in expression of phospho-p38 mitogen-activated protein kinase. Coadministration of 17-AAG blocked SAHA-mediated induction of the cyclin-dependent kinase inhibitor p21(CIP1) and resulted in reduced expression of p27(KIP1) and p34(cdc2). 17-AAG/SAHA-treated cells also displayed down-regulation of the antiapoptotic protein Mcl-1 and evidence of Bcl-2 cleavage. Enforced expression of doxycycline-inducible p21(CIP1) or constitutively active MEK1 significantly diminished 17-AAG/SAHA-mediated lethality, indicating that interference with ERK activation and p21(CIP1) induction play important functional roles in the lethal effects of this regimen. In contrast, enforced expression of constitutively active Akt failed to exert cytoprotective actions. Together, these findings indicate that coadministration of SAHA or SB with the Hsp90 antagonist 17-AAG in human leukemia cells leads to multiple perturbations in signaling, cell cycle, and survival pathways that culminate in mitochondrial injury and apoptosis. They also raise the possibility that combining such agents with Hsp90 antagonists may represent a novel antileukemic strategy.
Antineoplastic Combined Chemotherapy Protocols↗
Bcl-2 and Bcl-x(L) differentially protect human prostate cancer cells from induction of apoptosis by melanoma differentiation associated gene-7, mda-7/IL-24.
Subtraction hybridization identified melanoma differentiation associated gene-7, mda-7, in the context of terminally differentiated human melanoma cells. Based on its structure, cytokine-like properties and proposed mode of action, mda-7 has now been classified as IL-24. When expressed by means of a replication-incompetent adenovirus, Ad.mda-7 induces apoptosis in a broad range of cancer cells, without inducing harmful effects in normal fibroblast or epithelial cells. These unique properties of mda-7/IL-24 suggest that this gene will prove beneficial for cancer gene therapy. We now demonstrate that Ad.mda-7 decreases viability by induction of apoptosis in hormone-responsive (LNCaP) and hormone-independent (DU-145 and PC-3) human prostate carcinomas, without altering growth or survival in early-passage normal human prostate epithelial cells (HuPEC). Ad.mda-7 causes G(2)/M arrest and apoptosis in LNCaP (p53-wildtype), DU-145 (p53 mutant, Bax-negative) and PC-3 (p53-negative) prostate carcinomas, but not in HuPEC. Apoptosis induction correlated with changes in the ratio of pro- to antiapoptotic Bcl-2 protein family members. A potential functional role for changes in bcl-2 family gene expression in Ad.mda-7-induced apoptosis was suggested by the finding that forced overexpression of bcl-x(L) or bcl-2 differentially diminished the apoptotic effect of Ad.mda-7 in prostate carcinomas. These results confirm that induction of apoptosis by the mda-7/IL-24 gene in prostate cancer cells is Bax- and p53-independent and is mediated by mitochondrial pathways involving bcl-2 family gene members. The mda-7/IL-24 gene represents a new class of cancer-specific apoptosis-inducing genes with obvious potential for the targeted gene-based therapy of human prostate cancer.
Adenoviridae↗
Interruption of the NF-kappaB pathway by Bay 11-7082 promotes UCN-01-mediated mitochondrial dysfunction and apoptosis in human multiple myeloma cells.
Interactions between pharmacologic NF-kappaB inhibitors (eg, Bay 11-7082, SN-50) and the checkpoint abrogator UCN-01 have been examined in human multiple myeloma (MM) cells. Exposure of U266 cells to Bay 11-7082 (Bay) in combination with UCN-01 resulted in the abrogation of NF-kappaB/DNA binding activity and the synergistic induction of apoptosis. Comparable synergism was observed in other MM cell lines and patient-derived CD138+ cells and between an inhibitory peptide of NF-kappaB (SN50) and UCN-01. Bay/UCN-01-mediated lethality involved mitochondrial dysfunction, caspase cleavage, and poly adenosine diphosphate-ribose polymerase (PARP) degradation. Although Bay modestly blocked UCN-01-induced extracellular signal-regulated kinase (ERK) phosphorylation, coadministration activated c-Jun N-terminal kinase (JNK) and cdc2/cdk1 and down-regulated Mcl-1, XIAP, and Bcl-xL. Transfection with a constitutively activated mitogen-activated protein kinase kinase (MEK1)/green fluorescent protein (GFP) construct failed to block apoptosis induced by Bay/UCN-01 but significantly attenuated MEK inhibitor (U0126)/UCN-01-induced lethality. Inhibiting JNK activation with SP600125 or D-JNKI1 peptide markedly reduced Bay/UCN-01-mediated mitochondrial dysfunction and apoptosis and the down-regulation of Mcl-1, XIAP, and Bcl-xL but not of cdc2/cdk1 activation. Stable transfection of cells with dominant-negative caspase-9 dramatically diminished Bay/UCN-01 lethality without altering JNK or cdc2/cdk1 activation. Neither interleukin-6 (IL-6)- nor fibronectin-mediated adherence conferred resistance to Bay/UCN-01-induced apoptosis. Together, these findings suggest that a strategy combining UCN-01 with disruption of the IkappaB kinase (IKK)/IkappaB/NF-kappaB pathway warrants attention in MM.
Antigens, CD↗
Inhibition of PI-3 kinase sensitizes human leukemic cells to histone deacetylase inhibitor-mediated apoptosis through p44/42 MAP kinase inactivation and abrogation of p21(CIP1/WAF1) induction rather than AKT inhibition.
Effects of the PI-3 kinase inhibitor LY294002 (LY) have been examined in relation to responses of human leukemia cells to histone deacetylase inhibitors (HDIs). Coexposure of U937 cells for 24 h to marginally toxic concentrations of LY294002 (e.g., 30 microM) and sodium butyrate (SB; 1 mM) resulted in a marked increase in mitochondrial damage (e.g., cytochrome c and Smac/DIABLO release, loss of DeltaPsi(m)), caspase activation, and apoptosis. Similar results were observed in Jurkat, HL-60, and K562 leukemic cells and with other HDIs (e.g., SAHA, MS-275). Exposure of cells to SB/LY was associated with Bcl-2 and Bid cleavage, XIAP and Mcl-1 downregulation, and diminished CD11b expression. While LY blocked SB-mediated Akt activation, enforced expression of a constitutively active (myristolated) Akt failed to attenuate SB/LY-mediated lethality. Unexpectedly, treatment of cells with SB+/-LY resulted in a marked reduction in phosphorylation (activation) of p44/42 mitogen-activated protein (MAP) kinase. Moreover, enforced expression of a constitutively active MEK1 construct partially but significantly attenuated SB/LY-induced apoptosis. Lastly, cotreatment with LY blocked SB-mediated induction of p21(CIP1/WAF1); moreover, enforced expression of p21(CIP1/WAF1) significantly reduced SB/LY-mediated apoptosis. Together, these findings indicate that LY promotes SB-mediated apoptosis through an AKT-independent process that involves MEK/MAP kinase inactivation and interference with p21(CIP1/WAF1) induction.
Apoptosis↗
MAPK pathways in radiation responses.
Within the last 15 years, multiple new signal transduction pathways within cells have been discovered. Many of these pathways belong to what is now termed 'the mitogen-activated protein kinase (MAPK) superfamily.' These pathways have been linked to the growth factor-mediated regulation of diverse cellular events such as proliferation, senescence, differentiation and apoptosis. Based on currently available data, exposure of cells to ionizing radiation and a variety of other toxic stresses induces simultaneous compensatory activation of multiple MAPK pathways. These signals play critical roles in controlling cell survival and repopulation effects following irradiation, in a cell-type-dependent manner. Some of the signaling pathways activated following radiation exposure are those normally activated by mitogens, such as the 'classical' MAPK (also known as the ERK) pathway. Other MAPK pathways activated by radiation include those downstream of death receptors and procaspases, and DNA-damage signals, including the JNK and P38 MAPK pathways. The expression and release of autocrine growth factor ligands, such as (transforming growth factor alpha) and TNF-alpha, following irradiation can also enhance the responses of MAPK pathways in cells and, consequently, of bystander cells. Thus, the ability of radiation to activate MAPK signaling pathways may depend on the expression of multiple growth factor receptors, autocrine factors and Ras mutation. Enhanced basal signaling by proto-oncogenes such as K-/H-/N-RAS may provide a radioprotective and growth-promoting signal. In many cell types, this may be via the PI3K pathway; in others, this may occur through nuclear factor-kappa B or multiple MAPK pathways. This review will describe the enzymes within the known MAPK signaling pathways and discuss their activation and roles in cellular radiation responses.
Animals↗
EGFRvIII-mediated radioresistance through a strong cytoprotective response.
The constitutively active, truncated epidermal growth factor receptor EGFRvIII lacks the ability of EGF binding due to a deletion of the NH(2)-terminal domain. EGFRvIII confers increased tumorigenicity, is coexpressed with EGFR wild type (wt) in human carcinoma and malignant glioma cells when grown as xenografts, but is not expressed in vitro. The effects of EGFRvIII expression on cellular radiation responses were studied in Chinese hamster ovary (CHO) cells transfected with plasmids expressing EGFRvIII (CHO.EGFRvIII) or EGFRwt (CHO.EGFRwt). CHO cells expressing similar levels of either receptor were employed to define their roles in response to EGF and ionizing radiation. EGF activated EGFRwt with no effect on EGFRvIII. In contrast, a single radiation exposure of 2 Gy resulted in a 2.8- and 4.3-fold increase in Tyr phosphorylation of EGFRwt and EGFRvIII, respectively. Downstream consequences of this radiation-induced activation were examined by inhibiting EGFRwt and EGFRvIII with AG1478 (kinase inhibitor). The radiation-induced 8.5-fold activation of the pro-proliferative mitogen-activated protein kinase and the 3.2-fold stimulation of the antiapoptotic AKT/phosphatidylinositol-3-kinase pathways by EGFRvIII far exceeded that in CHO.EGFR wt cells. Thus, based on colony formation and apoptosis assays, EGFRvIII expression conferred a stronger cytoprotective response to radiation than EGFRwt, resulting in relative radioresistance. Therefore, disabling EGFRvIII in addition to EGFRwt needs to be considered in any therapeutic approach aimed at targeting EGFR for tumor cell radiosensitization.
Animals↗
Melanoma differentiation-associated 7 (interleukin 24) inhibits growth and enhances radiosensitivity of glioma cells in vitro and in vivo.
PURPOSE: Despite therapeutic interventions including surgery, chemotherapy, and radiotherapy, glioblastoma multiforme (GBM) has a very poor prognosis and novel therapies are required. EXPERIMENTAL DESIGN: Melanoma differentiation-associated 7 (mda-7) (interleukin 24), when expressed via a recombinant replication-defective adenovirus, adenovirus (Ad).mda-7, has profound antiproliferative and cytotoxic effects in a variety of tumor cells but not in nontransformed cells. The present studies examined the combined impact of Ad.mda-7 and ionizing radiation on the proliferation and survival of GBM cell lines. RESULTS: Ad.mda-7 caused a dose-dependent reduction in the proliferation of glioma cells in 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays. The antiproliferative effects of Ad.mda-7 were enhanced by radiation in a greater than additive fashion. These effects were not observed in cultures of nontransformed primary astrocytes. Purified MDA-7 protein caused a similar dose-dependent reduction in GBM cell growth that was enhanced after radiation exposure. The enhanced reduction in growth correlated with increased necrosis and DNA degradation. These modifications in cell phenotype correlated with reduced expression of Bcl-(XL) and enhanced expression of BAX. Overexpression of Bcl-(XL) protected cells from the antiproliferative and cytotoxic effects of Ad.mda-7 + radiation. Incubation of cells with N-acetyl cysteine abolished the enhancing effects of radiation. In vitro, Ad.mda-7 and radiation reduced colony formation ability, which was significantly increased when the two treatments were combined. In vivo, Ad.mda-7 enhanced the survival of Fischer 344 rats implanted intracranially with glioma cells. Radiation did not alter survival in control infected animals, whereas it prolonged survival in those infected with Ad.mda-7. CONCLUSIONS: These findings demonstrate that mda-7 reduces the proliferation and enhances the radiosensitivity of GBM cells in vitro and in vivo.
Acetylcysteine↗
The proteasome inhibitor bortezomib interacts synergistically with histone deacetylase inhibitors to induce apoptosis in Bcr/Abl+ cells sensitive and resistant to STI571.
Interactions between the proteasome inhibitor bortezomib and histone deacetylase inhibitors (HDIs) have been examined in Bcr/Abl+ human leukemia cells (K562 and LAMA 84). Coexposure of cells (24-48 hours) to minimally toxic concentrations of bortezomib + either suberoylanilide hydroxamic acid (SAHA) or sodium butyrate (SB) resulted in a striking increase in mitochondrial injury, caspase activation, and apoptosis, reflected by caspases-3 and -8 cleavage and poly(adenosine diphosphate-ribose) polymerase (PARP) degradation. These events were accompanied by down-regulation of the Raf-1/mitogen-induced extracellular kinase (MEK)/extracellular signal-related kinase (ERK) pathway as well as diminished expression of Bcr/Abl and cyclin D1, cleavage of p21CIP1 and phosphorylation of the retinoblastoma protein (pRb), and induction of the stress-related kinases Jun kinase (JNK) and p38 mitogen-activated protein kinase (MAPK). Transient transfection of cells with a constitutively active MEK construct significantly protected them from bortezomib/SAHA-mediated lethality. Coadministration of bortezomib and SAHA resulted in increased reactive oxygen species (ROS) generation and diminished nuclear factor kappa B (NF-kappa B) activation; moreover, the free radical scavenger L-N-acetylcyteine (LNAC) blocked bortezomib/SAHA-related ROS generation, induction of JNK and p21CIP1, and apoptosis. Lastly, this regimen potently induced apoptosis in STI571 (imatinib mesylate)-resistant K562 cells and CD34+ mononuclear cells obtained from a patient with STI571-resistant disease, as well as in Bcr/Abl- leukemia cells (eg, HL-60, U937, Jurkat). Together, these findings raise the possibility that combined proteasome/histone deacetylase inhibition may represent a novel strategy in leukemia, including apoptosis-resistant Bcr/Abl+ hematologic malignancies.
Antineoplastic Agents↗