Molecular Mechanism of SAHA on Regulation of Autophagic Cell Death in Tamoxifen-Resistant MCF-7 Breast Cancer Cells

Objective: Tamoxifen is currently used for the treatment of estrogen receptor-positive breast cancer patients, but acquired resistance to tamoxifen is a critical problem in breast cancer therapy. Suberoylanilide hydroxamic acid (SAHA) is a prototype of the newly developed HDAC inhibitor. The aim of this study is to investigate the anticancer effects of SAHA in tamoxifen-resistant MCF-7 (TAMR/MCF-7) cells.Methods: Cytotoxicity, apoptosis and autophagic cell death induced by SAHA were studied. A TAMR/MCF-7 cells xenograft model was established to investigate the inhibitory effect of SAHA on tumor growth in vivo.Results: SAHA inhibited the proliferation of TAMR/MCF-7 cells in a dose-dependent manner. SAHA significantly reduced the expression of HDAC1, 2, 3, 4 and 7 and increased acetylated histone H3 and H4. Although SAHA induced G2/M phase arrest of cell cycle, apoptotic cell death was very low, which is correlated with the slight change in the activation of caspases and PARP cleavage. Interestingly, expression of the autophagic cell death markers, LC3-II and beclin-1, was significantly increased in TAMR/MCF-7 cells treated with SAHA. Autophagic cell death induced by SAHA was confirmed by acridine orange staining and transmission electron microscopy (TEM) in TAMR/MCF-7 cells. In mice bearing the TAMR/MCF-7 cell xenografts, SAHA significantly reduced the tumor growth and weight, without apparent side effects.Conclusion: These results suggest that SAHA can induce caspase-independent autophagic cell death rather than apoptotic cell death in TAMR/MCF-7 cells. SAHA-mediated autophagic cell death is a promising new strategy to treatment of tamoxifen-resistant human breast cancer.     

MuLV IN mutants responsive to HDAC inhibitors enhance transcription from unintegrated retroviral DNA

For Moloney murine leukemia virus (M-MuLV), sustained viral infections require expression from an integrated provirus. For many applications, non-integrating retroviral vectors have been utilized to avoid the unwanted effects of integration, however, the level of expression from unintegrated DNA is significantly less than that of integrated provirus. We find that unintegrated DNA expression can be increased in the presence of HDAC inhibitors, such as TSA, when applied in combination with integrase (IN) mutations. These mutants include an active site mutation as well as catalytically active INs bearing mutations of K376 in the MuLV C-terminal domain of IN. MuLV IN K376 is homologous to K266 in HIV-1 IN, a known substrate for acetylation. The MuLV IN protein is acetylated by p300 in vitro, however, the effect of HDAC inhibitors on gene expression from unintegrated DNA is not dependent on the acetylation state of MuLV IN K376.     

Modulation of cell sensitivity to antitumor agents by targeting survival pathways

The advent of drugs targeting tumor-associated prosurvival alterations of cancer cells has changed the interest of antitumor drug development from cytotoxic drugs to target-specific agents. Although single-agent therapy with molecularly targeted agents has shown limited success in tumor growth control, a promising strategy is represented by the development of rational combinations of target-specific agents and conventional antitumor drugs. Activation of survival/antiapoptotic pathways is a common feature of cancer cells that converge in the development of cellular resistance to cytotoxic agents. The survival pathways implicated in cellular response to drug treatment are primarily PI3K/Akt and Ras/MAPK, which also mediate the signalling activated by growth factors and play a role in the regulation of critical processes including cell proliferation, metabolism, apoptosis and angiogenesis. Inhibitors of PI3K, Akt and mTOR have been shown to sensitize selected tumor cells to cytotoxic drugs through multiple downstream effects. Moreover, the MAPK pathway, also implicated in the regulation of gene expression in response to stress stimuli, can interfere with the chemotherapy-induced proapoptotic signals. Targeting Hsp90, which acts as a molecular chaperone for survival factors including Akt, may have the potential advantage to simultaneously block multiple oncogenic pathways. Overall, the available evidence supports the interest of rationally designed approaches to enhance the efficacy of conventional antitumor treatments through the inhibition of survival pathways and the notion that the concomitant targeting of multiple pathways may be a successful strategy to deal with tumor heterogeneity and to overcome drug resistance of tumor cells.     

Histone deacetylase inhibitors: a survey of recent patents

Histone deacetylase (HDAC) inhibitors have been the subject of an intense drug discovery effort in the pharmaceutical industry and in some academic institutions over the last few years. Although, at present, only a small number of compounds have progressed to human clinical trials, the prospect of finding safe compounds useful in therapy, particularly in cancer and inflammatory processes, is still a strong motivating factor for further research efforts. A patent literature review of small organic molecules as HDAC inhibitors is presented here, as many of the major pharmaceutical companies have shown a continued effort in the field [1]. This paper provides an update on the patenting activity in 2004 – 2005 related to HDAC inhibitors.     

Patent status of histone deacetylase inhibitors

Histone deacetylase (HDAC) has emerged as an important therapeutic target for the treatment of cancer and other diseases. Several HDAC inhibitors that target class I and II HDACs are currently in clinical trials. The initial results from these studies indicate that HDAC inhibitors show great promise for the treatment of cancer. To date, more than 30 research organisations are named as applicants on published patent applications claiming structures of HDAC inhibitors. This review summarises the patent literature published from mid-2002 to early 2004 containing claims directed towards HDAC inhibitor structures, together with discussion of the related primary literature.     

Mocetinostat (MGCD0103): a review of an isotype-specific histone deacetylase inhibitor

Introduction: HDAC inhibitors (HDACIs) have the potential to restore gene expression and display antitumor effects in vitro. As single agents, HDACIs have clinical activity in lymphoma. In myeloid leukemias, combinations of DNA methylation inhibitors and HDACIs are promising. Other combinations are being studied in solid tumors.

Areas covered: This article covers basic information and an update on preclinical and clinical experience with the oral isotype-selective HDACI MGCD0103 (mocetinostat) in hematological malignancies and solid tumors. It also examines data concerning MGCD0103 from recent conferences and articles through to November 2010, including new data regarding responses in lymphoma and toxicities.

Expert opinion: MGCD0103 is well-tolerated and exhibits favorable pharmacokinetic and pharmacodynamic profiles, demonstrating target inhibition and clinical responses. It induces cell death and autophagy, synergizes with proteasomal inhibitors and affects non-histone targets, such as microtubules. In 2008, new patient enrollment in trials was temporarily suspended due to potential cardiac complications. This restriction was lifted in 2009 as no correlation between MGCD0103 exposure and pericardial effusions was found. New patient enrollment in MGCD0103 clinical trials requires the exclusion of patients diagnosed with significant cardiac abnormalities prior to enrollment. Clinical and pharmacodynamic data support a three-times-weekly administration at a 90 mg fixed dose. MGCD0103 displays promising antitumor activity in several hematological diseases.