Research ArticleCombination therapy for hepatocellular carcinoma: Additive preclinical efficacy of the HDAC inhibitor panobinostat with sorafenib
Introduction
Hepatocellular carcinoma (HCC) remains a major health problem worldwide as the third cause of cancer-related mortality and the primary cause of death among cirrhotic patients [1]. Hepatitis B and C, alcohol, and aflatoxin have been identified as major risk factors leading to the development of HCC [2], [3]. Resection and transplantation are the only curative treatments available but are greatly hampered by high recurrence rates [3]. Currently, the multi-kinase inhibitor sorafenib is the only FDA-approved treatment for patients with advanced disease, necessitating the development of novel compounds that are effective against this devastating disease [4], [5]. A new class of histone deacetylase (HDAC) inhibitors is currently considered to be among the most promising anticancer agents in drug development, most likely due to their potent anti-tumoral effects demonstrated in preclinical studies of hematological malignancies and solid tumors and their promising therapeutic potential in early-phase clinical trials [6]. Vorinostat and romidepsin are HDAC inhibitors (HDACi) that recently received FDA approval for the treatment of cutaneous T cell lymphoma [7].
HDAC inhibitors execute their anti-tumoral activities through hyperacetylation of histone and non-histone proteins, such as the molecular chaperone heat shock protein 90 (HSP90). Histone acetylation leads to decreased affinity for DNA and increased access of transcription factors, while HSP90 acetylation blocks its chaperone function and causes destabilization of client proteins implicated in several important signaling pathways [8]. In addition, HDACi can repress transcriptional activity directly or through destabilization and accelerated decay of mature transcripts. These different mechanisms of action lead to various anti-tumoral effects including the induction of apoptosis, autophagy and differentiation, cell cycle arrest and inhibition of tumor vascularization [9]. Although several key factors in cancer-related signaling pathways have been identified to be regulated by the HDAC family, no exclusive targets have been reported so far. HDACs are known to regulate the expression of some of the pivotal players of hepatocarcinogenesis including the apoptosis inhibitor BIRC5 (survivin), the tumor suppressor gene and Wnt-pathway regulator CDH1 (E-Cadherin), and the cyclin-dependent kinase inhibitor CDKN1A (p21) known to be implicated in growth arrest, senescence and apoptosis [10], [11], [12], [13], [14].
Panobinostat (LBH589) is a novel pan-HDAC-inhibitor with high efficacy in several preclinical models of cancer [15] and synergistic anti-tumoral activity when administered in combination with chemotherapy or molecular targeted therapies [14], [16]. Early clinical trials recently reported promising results with feasible tolerance and side effects, even indicating anti-tumoral activity in patients with lymphoma [17].
Further evidence of the importance of the HDAC machinery in cancer is their observed dysregulation in tumoral tissues and their close correlation with aggressive tumoral behaviour. In cancer, aberrant expression of several of the 11 known classical HDAC family members (HDAC1-11, class I, II, IV) often correlates with disease progression and patient’s outcomes [18]. Overexpression of HDAC1 and 2 has been described in gastric and colorectal cancer [19], [20], and HDAC3 has recently been proposed as a potential biomarker for recurrence following liver transplantation in hepatits B (HBV)-associated HCC [21].
Herein, we show that several HDAC-family members are aberrantly expressed in HCC with significant correlation of HDAC3 and 5 upregulation to DNA copy number gains. In addition, we provide evidence that panobinostat has consistent anti-tumoral efficacy in preclinical models of HCC, which is further enhanced when combined with sorafenib. Significantly decreased tumor volume and increased survival in vivo in response to this combination establish a rationale for clinical studies with this novel combination.
Section snippets
Human samples, mRNA expression array and SNP analysis
A total of 230 human samples were obtained from patients with HCC treated with resection or liver transplantation within the HCC Genomic Consortium (Mount Sinai School of Medicine, New York; Hospital Clinic, Barcelona; Istituto Nazionale dei Tumori in Milan) as previously reported [22], [23], [24], [25]. After patient’s informed consent and Institutional Review Board approvals were obtained, samples were collected and gene expression and SNP array studies were performed as described elsewhere
Aberrant HDAC expression
Gene expression levels of all 11 classic HDACs were analyzed by microarray in a training set of 91 HCC samples, 18 dysplastic nodules, 10 normal and 13 cirrhotic liver samples (Fig. 1A). A subset of HDAC mRNAs (HDAC1, 2, 4, 5, and 11) was significantly upregulated compared to the normal liver, cirrhosis and dysplastic nodules, with the highest expression levels for HDAC2, 4 and 11 (Fig. 1B). HDAC3 was significantly upregulated in HCC compared to cirrhosis. By contrast, HDAC6 and HDAC7 were
Discussion
After sorafenib approval in advanced HCC, the scientific community aimed at further enhancing the survival benefit with combination therapies and/or novel drugs [28], [29]. Combination therapies are currently tested in one phase III study (sorafenib with erlotinib) and in several phase II studies [5]. Nonetheless, none of them is testing the efficacy of an HDAC inhibitor in this difficult-to-treat cancer, a family of drugs already approved in other malignancies [6].
This study provides
Conflict of interest
Prof. Llovet has a Consultancy Agreement and received research support from Bayer Pharmaceutical. The other authors have no conflict of interest to declare.
The underlying research reported in this study was funded by the NIH Institutes of Health.
Financial support
Josep M Llovet is supported by grants from the US National Institutes of Diabetes and Digestive and Kidney Diseases (1R01DK076986-01), the European Commission’s Framework Programme 7 (HEPTROMIC, proposal No. 259744), the Samuel Waxman Cancer Research Foundation and the Spanish National Health Institute (SAF-2010-16055). The study was supported by the Landon Foundation-American Association for Cancer Research Innovator Award for International Collaboration in Cancer Research. Scott Friedman has
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