SIRT1 activation enhances HDAC inhibition-mediated upregulation of GADD45G by repressing the binding of NF-κB/STAT3 complex to its promoter in malignant lymphoid cells

We explored the activity of SIRT1 activators (SRT501 and SRT2183) alone and in combination with panobinostat in a panel of malignant lymphoid cell lines in terms of biological and gene expression responses. SRT501 and SRT2183 induced growth arrest and apoptosis, concomitant with deacetylation of STAT3 and NF-κB, and reduction of c-Myc protein levels. PCR arrays revealed that SRT2183 leads to increased mRNA levels of pro-apoptosis and DNA-damage-response genes, accompanied by accumulation of phospho-H2A.X levels. Next, ChIP assays revealed that SRT2183 reduces the DNA-binding activity of both NF-κB and STAT3 to the promoter of GADD45G, which is one of the most upregulated genes following SRT2183 treatment. Combination of SRT2183 with panobinostat enhanced the anti-growth and anti-survival effects mediated by either compound alone. Quantitative-PCR confirmed that the panobinostat in combination with SRT2183, SRT501 or resveratrol leads to greater upregulation of GADD45G than any of the single agents. Panobinostat plus SRT2183 in combination showed greater inhibition of c-Myc protein levels and phosphorylation of H2A.X, and increased acetylation of p53. Furthermore, EMSA revealed that NF-κB binds directly to the GADD45G promoter, while STAT3 binds indirectly in complexes with NF-κB. In addition, the binding of NF-κB/STAT3 complexes to the GADD45G promoter is inhibited following panobinostat, SRT501 or resveratrol treatment. Moreover, the combination of panobinostat with SRT2183, SRT501 or resveratrol induces a greater binding repression than either agent alone. These data suggest that STAT3 is a corepressor with NF-κB of the GADD45G gene and provides in vitro proof-of-concept for the combination of HDACi with SIRT1 activators as a potential new therapeutic strategy in lymphoid malignancies.

Anti-leukemia activity of histone deacetylase (HDAC) inhibitor LBH589 involves depletion of EZH2 and DNA methyltransferase (DNMT) 1 through disruption of their chaperone association with heat shock protein (hsp) 90

10501

Background: LBH589 is a hydroxamate pan-HDAC inhibitor (HA-HDI) that also inhibits HDAC6, which induces acetylation of hsp90 and hsp70. This inhibits the ATP binding and chaperone function of hsp90. We recently reported that treatment with LBH589 depletes the levels of the polycomb repressive complex (PRC) 2 proteins EZH (enhancer of zeste homolog) 2, Suz12 and EED in AML cells. Since EZH2 has been shown to interact with and modulate the DNA methyltransferase activity of DNMT1, which affects its binding to the EZH2-targeted gene promoters, we determined the effects of LBH589 on the levels and interaction between EZH2 and DNMT1 in the CML blast crisis (CML-BC) K562 and LAMA-84 cells as well as in primary AML samples. Methods: Following exposure to 20 to 100 nM of LBH589 for 8 and 24 hours. immunoprecipitation and/or immunoblot analyses were performed to determine hsp90 binding and levels of DNMT1 and EZH2, as well as induction of JunB and loss of clonogenic survival of leukemia cells. Results: Treatment with LBH589 disrupted the chaperone association of DNMT1 and EZH2 with hsp90, resulting in polyubiquitylation and proteasomal degradation of DNMT1. Similar findings were also noted following treatment of leukemia cells with the hsp90 inhibitor, 17-DMAG. DNMT1 depletion by LBH589 was associated with induction of JunB in cultured and primary leukemia cells, which was further enhanced by co-treatment with decitabine. Consistent with this, methylation specific PCR analysis demonstrated increased demethylation of the JunB promoter. Co-treatment with decitabine and LBH589 or DMAG inhibited colony growth of the leukemia cells significantly more than treatment with either agent alone (p<0.05). Conclusions: These findings indicate that in addition to mediating histone acetylation and demethylation, LBH589 treatment induces epigenetic DNA demethylation by targeted depletion of EZH2 and DNMT1 in human leukemia cells. These results support the rationale for testing novel anti- leukemia combinations for epigenetic targeting that include LBH589, decitabine and/or histone methyltransferase inhibitors.

No significant financial relationships to disclose.

Design and analysis methods for assessing drug synergy: Illustration using histone deacetylase (HDAC) inhibitor LBH589 combined with CDDP in mesothelioma (meso) cell lines

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Background: LBH589 (Novartis) is an investigational agent belonging to a cinnamic hydroxamic acid class of compounds that was shown to inhibit HDAC enzyme activity. LBH589 is in phase I clinical testing and combinations with various agents are being explored in the laboratory. Common experimental designs used for in-vitro cell viability experiments to assess drug synergy in cancer cell lines include complete factorial design (CFD) and fixed dose ratio design (FRD). While CFD provides data for the entire response surface, it can result in unfeasibly large experiments and complex synergy calculations, especially when 3 or more drugs are under evaluation. We investigated the FRD and alternative analysis methods to estimate and test synergy between two or more drugs. Methods: Experiments in meso cell lines were conducted using a colorimetric MTS assay. The FRD included 4 LBH concentrations (10 to 100 nM) and 4 CDDP concentrations (.5 to 5 μM), for each drug alone and in combination at a 50:1 CDDP:LBH ratio. Data were analyzed by applying the median effect equations (Chou, Adv Enzyme Regul, 1984) to the joint modeling approach by Straetemans, Biom. J., 2005. This method provides a straightforward estimate of the combination index (CI) and a statistical test for synergy (CI values less than 1.0 indicate synergy). Results: Results showed CI values significantly less than 1 for cell lines 2052 and MSTO for low to mid effect levels. Additive results were seen in cell line 2452. IC50’s were not greatly exceeded; therefore, CI’s for higher effect levels were not estimated. Conclusions: LBH appears to be synergistic with CDDP in some meso cell lines. The FRD is an efficient method to assess drug synergy and will be used for larger experiments to study 3 drug combinations involving LBH589. We propose a straightforward analysis method based on the median effect equations that jointly models the data, providing confidence intervals and a statistical test for synergy.

[Table: see text]

No significant financial relationships to disclose.

Inhibition of histone deacetylase (HDAC) 6 sensitizes human leukemia and breast cancer cells to antagonists of heat shock protein (hsp) 90 and/or bortezomib (BZ)

13039

Background: HDAC6 is a cytosolic α-tubulin deacetylase, which shuttles misfolded polyubiquitylated proteins into aggresomes. Our studies demonstrated that the hydroxamic acid (HA) analogue pan-HDAC inhibitors (HDIs), e.g., LAQ824 and LBH589, induce α-tubulin and hsp90 acetylation, thereby inhibiting ATP-binding and chaperone function of hsp90. This promotes the polyubiquitylation and degradation of the pro-growth and pro-survival hsp90 client proteins, e.g., Bcr-Abl, mutant FLT-3, c-Raf and AKT in leukemia and Her-2 in breast cancer cells. Methods: Human CML K562 and breast cancer SKBR-3 and BT-474 cells were exposed to LAQ824 (100 nM) or LBH589 (20 to 50 nM) and/or 17-AAG (1 to 5 μM) and/or BZ (5 to 100 nM). K562 and BT-574 cells were also transfected with siRNA to HDAC6. Immunoprecipitation and/or immunoblot analysis were performed to determine the expression or binding of HDAC6 with hsp90, and of hsp90 acetylation and binding with its co-chaperones and client proteins. Immunofluorescent microscopy was utilized to estimate aggresome formation. Cellular cytotoxicity was determined by % inhibition of colony growth. Results: HDAC6 knockdown by its siRNA induced the acetylation of hsp90 and α-tubulin but not of the co-chaperones p23 and hsp40. HDAC6 binds to hsp90. Hsp90 acetylation increased its binding to biotinylated-geldanamycin (GM) and its analogue 17-AAG. Depletion of HDAC6 levels (∼70%) or its activity by treatment with HA-HDI also inhibited the binding of hsp90 to ATP, p23 and hsp90 client proteins, which was augmented by co-treatment with 17-AAG. Knockdown of HDAC6 sensitized the cells to loss of clonogenic survival induced by HA-HDI and/or BZ and/or 17-AAG. Depletion of HDAC6 led to attenuation of Her-2 levels and loss of survival of Her-2 amplified SKBR-3 and BT-474 cells. Co-localization of HDAC6 and polyubiquitylated proteins into aggresomes was enhanced by co-treatment with BZ and/or 17-AAG. This was inhibited by depletion of HDAC6 activity. Conclusions: These findings support the in vivo testing of HDAC6 inhibitors, which through inhibition of hsp90 and aggresome formation sensitizes cancer cells to 17-AAG and/or BZ induced cellular stress due to misfolded and polyubiquitylated proteins.

[Table: see text]

LBH589, a novel histone deacetylase inhibitor (HDACi), treatment of patients with cutaneous T-cell lymphoma (CTCL). Changes in skin gene expression profiles related to clinical response following therapy

7501

Background: LBH589 is a novel histone deacetylase inhibitor in Phase I trials. Since other HDACi have induced disease regression in CTCL, we evaluated the activity of LBH589 and resulting changes in gene expression of LBH589 in CTCL patients (pts). Methods: Pts with advanced-stage CTCL, who had progressed following prior systemic therapy were entered into the DLT dose level 30mg M,W,F cohort (n = 1) or the subsequent MTD dose level 20mg M,W, F weekly (n = 10). LBH589 was continued until disease progression or unacceptable toxicity. The first three pts had 3mm punch biopsies from CTCL-involved skin lesions at 0, 4, 8 and 24h after administration, which were subjected to gene expression profiling using Affymetrix U133 plus 2.0 GeneChips with 47,000 probesets. Results: Eleven pts with CTCL have been entered to date. Two of the pts attained a complete response (CR), 3 attained a partial response (PR), 2 achieved stable disease (SD) with ongoing improvement, and 4 progressed on treatment (PD). Of particular interest, 2 pts who were initially SD required discontinuation because of toxicities (Grade III diarrhea at week 4, Grade II fatigue at week 12). Both had ongoing improvement in their disease achieving a CR and PR, respectively 3 months later. Of the 5 responding pts, one with a CR (discontinued after 10 doses due to Grade III diarrhea) progressed at 8m. Microarray data on the first 3 pts (2CR and 1PD) demonstrated distinct gene expression response profiles between the 3 pts. Surprisingly, the pt with PD showed the greatest transcriptional response with more than 16,000 genes activated or repressed over the 24 hr time course. Of these responsive genes, close to 60% were activated while 40% were repressed. In contrast, less than 1000 genes showed a 2-fold change in expression in the 2 pts with a CR with greater than 85% of the genes being repressed. Conclusions: LBH589 induce CR’s in CTCL pts. Regression of disease can occur some weeks after discontinuation of therapy. Preliminary microarray analysis of tumor samples indicated that LBH589 mediates changes in gene expression in vivo with an unexpected observed inverse relationship between the number of genes altered and clinical outcome.

[Table: see text]

Combined effects of novel tyrosine kinase inhibitor AMN107 and histone deacetylase inhibitor LBH589 against unmutated or mutant Bcr-Abl-expressing human leukemia cells

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Background: AMN107 has potent in vitro and in vivo activity against the un-mutated and most mutant forms of Bcr-Abl tyrosine kinase (TK). We have previously demonstrated that in CML cells the pan-histone deacetylase inhibitor LBH589 depletes both unmutated and mutated Bcr-Abl, as well as attenuates p-AKT and Raf-1 levels. In the present studies we determined the effects of AMN107 and/or LBH589 in unmutated or mutated Bcr-Abl-expressing mouse BaF3 cells, or human CML K562 and LAMA-84 cells, as well as in primary CML cells procured from patients with imatinib mesylate (IM)-refractory CML. Methods: Cultured and primary CML cells were exposed to 20 to 100 nM AMN107 and/or LBH589 for 24 to 48 hours. Following this, the % of apoptotic cells was determined, as well as immunoblot analyses were performed to determine Bcr-Abl, p-STAT5, p-AKT, p-CrkL, Bim, Bcl-xL and p27 levels. Synergy between the apoptotic effects was determined by the median dose-effect isobologram analysis. Results: AMN107 was 20-fold more potent than IM, and was more potent in inhibiting Bcr-Abl TK activity and attenuating p-STAT5, p-AKT, Bcl-xL, and c-Myc levels in K562 and LAMA-84 cells. Co-treatment with LBH589 and AMN107 exerted synergistic apoptotic effects against human CML (but not the normal bone marrow progenitor cells), with more attenuation of p-STAT5, p-ERK1/2, c-Myc and Bcl-xL and increased p27 and Bim levels. LBH589 attenuated Bcr-Abl levels and induced apoptosis of mouse pro-B BaF3 cells containing ectopic expression of unmutated Bcr-Abl or the IM-resistant Bcr-AblT315I and Bcr-AblE255K. Treatment with LBH589 also depleted Bcr-Abl levels and induced apoptosis in IM-resistant primary human CML cells, including those with expression of Bcr-AblT315I. As compared to either agent alone, co-treatment with AMN107 and LBH589 induced more loss of cell viability of primary IM-resistant CML cells. Conclusions: These findings support in vivo testing of the combination of LBH589 and AMN107 against IM naïve or resistant CML, with the goal to eradicate IM sensitive or resistant CML.

[Table: see text]

Histone deacetylase inhibitor NVP-LAQ824 has significant activity against myeloid leukemia cells in vitro and in vivo

NVP-LAQ824 is a novel potent hydroxamic acid-derived histone deacetylase inhibitor that induces apoptosis in nanomolar concentrations in myeloid leukemia cell lines and patient samples. Here we show the activity of NVP-LAQ824 in acute myeloid leukemia cells and BCR/ABL-expressing cells of mouse and human origin, both sensitive and resistant to imatinib mesylate (Gleevec, STI-571). Whereas imatinib inhibited overall cellular tyrosine phosphorylation in Ba/F3.p210 cells, NVP-LAQ824 did not inhibit tyrosine phosphorylation, and did not affect BCR/ABL or ABL protein expression. Neither compound was able to inhibit cellular tyrosine phosphorylation in the imatinib-resistant Ba/F3.p210-T315I cell line. These data taken together suggest that BCR/ABL kinase activity is not a direct target of NVP-LAQ824. Synergy between NVP-LAQ824 and imatinib was demonstrated against BCR/ABL-expressing K562 myeloid leukemia cell lines. In addition, we show that NVP-LAQ824 was well tolerated in vivo in a pre-clinical murine leukemia model, with antileukemia activity resulting in significant prolongation of the survival of mice when treated with NVP-LAQ824 compared to control mice. Taken together, these findings provide the framework for NVP-LAQ824 as a novel therapeutic in myeloid malignancies.

Altered activity of MDR-reversing agents on KB3-1 cells transfected with Gly(185)-->Val human P-glycoprotein

P-glycoprotein (P-gp) is a transmembrane glycoprotein that confers multidrug resistance (MDR). It has been demonstrated that the Gly185 residue within the cytoplasmic loop between predicted transmembrane portions 2 and 3 plays an important role in substrate specificity of human P-gp. Derivatives of cyclosporin interact with and reverse the ability of P-gp to act as a drug efflux pump. To determine if the Gly185 residue of human P-gp is also important for the interaction of P-gp with closely related cyclosporin derivatives, we examined the effect of PSC-833 and CsA on P-gp in KB3-1 cells transfected with human wild-type P-gp (GSV-2) or with the mutant P-gp (VSV-1) that habored the Gly185-->Val substitution. While the ability of CsA to sensitize VSV-1 cells to anticancer agents was enhanced, no changes in the potency of PSC-833 against cells transfected with either the wild-type or mutant P-gp were observed. In addition, VSV-1 transfected cells were more sensitive to CsA inhibition of verapamil-stimulated ATPase activity than cells transfected with wild-type P-gp. Furthermore, the intracellular accumulation of CsA was low in GSV-2 P-gp-expressing cells, compared with its accumulation in VSV-1 cells and it was found to be as high as in non-P-gp expressing KB3-1 cells. These results indicated an enhanced sensitivity of Val185-P-gp expressing cells to CsA that correlated with increased intracellular accumulation in these cells. In contrast, no significant difference in the accumulation of PSC-833 was observed among the parental, wild-type or resistant cells. Since PSC-833 was found to be more potent than CsA, these studies provided insight into the effects of the structure of MDR modulators in mediating sensitivity to anticancer drugs.

PSC-833, a frontier in modulation of P-glycoprotein mediated multidrug resistance

The expression of drug efflux mechanisms by cancer cells during chemotherapy leads to multidrug resistance (MDR) and constitutes a major obstacle in the effective treatment of cancer. The most widely characterized drug effluxes pump is P-glycoprotein (P-gp) and efforts are being directed towards identifying agents that reverse P-gp mediated drug resistance. PSC-833 is a non-immunosuppressive cyclosporin derivative that potently and specifically inhibits P-gp. The current review focuses on the elucidation of the mechanism of action of PSC-833 as a potential MDR reversing agent, using syngeneic multidrug resistant sublines of MDA435 human breast adenocarcinoma cell line that express increasing levels of P-gp. In vitro experiments indicate that PSC-833 interacts directly with P-gp with high affinity and probably interferes with the ATPase activity of P-gp. Studies in multidrug resistant tumor models confirm P-gp as the in vivo target of PSC-833 and demonstrate the ability of PSC-833 to reverse MDR leukemias and solid tumors in mice. Presently, PSC-833 is being evaluated in the clinic.

Regulation of transcription factor activity during cellular aging

Several lines of evidence suggest that the limited replication potential of normal human cells is due to the presence of an intrinsic genetic programme. This "senescence programme" is believed to reduce the incidence of cancer by limiting the growth of most of the transformed cells arising in vivo, although some cells do escape senescence becoming both immortalized and transformed. Here we review the literature that describes the senescence process in terms of gene expression and the regulation of gene expression by a variety of mechanisms affecting transcription factor activity. We focus on regulation of the c-fos gene through posttranslational modification of the serum response factor (SRF) as an example of altered gene expression during cellular aging.

Increased activity of p53 in senescing fibroblasts

The p53 tumor-suppressor protein binds DNA and activates the expression of a 21-kDa protein that inhibits both the activity of cyclin-dependent kinases and the function of proliferating cell nuclear antigen. Since p21 expression has been reported to increase 10- to 20-fold as human diploid fibroblasts lose the ability to replicate, we examined the expression and activity of p53 during replicative aging. Similar levels of total p53 mRNA and protein were expressed in low-passage (young) and high-passage (old) cells but both DNA binding activity in vitro and transcriptional activity of p53 in vivo were increased severalfold in high-passage cells. While the basis of increased p53 activity is presently unclear, it is not correlated with differential phosphorylation or changes in p53-mouse double minute 2 gene product interactions. These results provide evidence for the activation of a protein involved in the control of cell cycle checkpoints during cellular aging, in the absence of increased expression.

Overexpression of cyclin D1 blocks proliferation of normal diploid fibroblasts

Human cyclin D1 forms complexes with several Cdks, with proliferating cell nuclear antigen, and with a recently discovered 21-kDa inhibitor of Cdk activity. Substrates for cyclin D1/Cdks have not been identified in vivo, but it has been proposed that the D class of cyclins might play a role in regulating the activity of the retinoblastoma gene product p105Rb. Here we report that normal human diploid fibroblasts that endogenously or ectopically express high levels of cyclin D1 are unable to enter S phase in response to normally mitogenic stimuli. Fibroblasts that have reached the end of their in vitro life span (senescent cells) express five-fold higher levels of cyclin D1 protein than low-passage cells and individual cells in mass culture that fail to initiate DNA synthesis in response to serum addition have severalfold higher levels of this cyclin than proliferation-competent cells. These observations provide evidence that cyclin D1 is involved with the regulation of cell proliferation by more than one mechanism.