Simultaneous NF‐κB inhibition and E‐cadherin upregulation mediate mutually synergistic anticancer activity of celastrol and SAHA in vitro and in vivo

Abstract

Suberoylanilide hydroxamic acid (SAHA) is a promising histone deacetylase (HDAC) inhibitor approved by the US Food and Drug Administration (FDA) and whose clinical application for solid tumours is partially limited by decreased susceptibility in cancer cells due to nuclear factor (NF)-jB activation. As an NF-jB inhibitor, celastrol exhibits potent anticancer effects but has failed to enter clinical trials due to its toxicity. In this report, we demonstrated that the combination of celastrol and SAHA exerted substantial synergistic efficacy against human cancer cells in vitro and in vivo accompanied by enhanced caspasemediated apoptosis. This drug combination inhibited the activation of NF-jB caused by SAHA monotherapy and consequently led to increased apoptosis in cancer cells. Interestingly, E-cadherin was dramatically downregulated in celastrol-resistant cancer cells, and E-cadherin expression was closely related to decreased sensitivity to celastrol. However, our combination treatment significantly augmented the expression of E-cadherin, suggesting that mutual mechanisms contributed to the synergistic anticancer activity. Furthermore, the enhanced anticancer efficacy of celastrol combined with SAHA was validated in a human lung cancer 95-D xenograft model without increased toxicity. Taken together, our data demonstrated the synergistic anticancer effects of celastrol and SAHA due to their reciprocal sensitisation, which was simultaneously regulated by NF-jB and E-cadherin; thus, the combination of celastrol and SAHA was superior to other combination regimens that rely on a single mechanism. Our findings not only open new opportunities for the clinical development of SAHA but should also motivate the clinical investigation of celastrol, which has been hampered by its toxicity.Histone deacetylase (HDAC) activity is associated with cancer cell proliferation, survival and maintenance and thus represents an attractive target for cancer therapy. HDAC inhibition triggers a series of cellular responses that interfere with growth-promoting signals, enhances cellular stress and ultimately leads to cancer cell death.1 Suberoylanilide hydroxamic acid (SAHA) is one of the most promising HDAC inhibitors for the treatment of cancer, and it has been approved by the US Food and Drug Administration (FDA) for the treatment of cutaneous T-cell lymphoma.2 In addition, SAHA as a monotherapy or in combination with other chemotherapeutic agents has been used in clinical trials to treat hematologic malignancies and solid tumours, including lung, breast, ovarian and prostate cancers. 3 Moreover, the safety profile of SAHA has been shown to be favourable, particularly compared with traditional cytotoxic chemotherapy, raising the possibility that SAHA may also be a promising drug for the treatment of solid tumours. 2 Nevertheless, early results from a few clinical trials have indicated that SAHA monotherapy has only modest activity

Depletion of runt-related transcription factor 2 (RUNX2) enhances SAHA sensitivity of p53-mutated pancreatic cancer cells through the regulation of mutant p53 and TAp63

“…Theoretically, SAHA facilitates the accumulation of acetylated cellular proteins such as histones and transcription factors, and thus induces the dynamic changes of gene expression in tumor cells. Unfortunately, the extensive clinical trials suggest that SAHA might be sometimes ineffective on certain solid tumors [35]. …”

Pharmacological induction of Heat Shock Protein 70 by celastrol protects motoneurons from excitotoxicity in rat spinal cord in vitro

“…Clinical application of celastrol is rather limited because of its poor solubility and narrow therapeutic window (Zheng et al., ). However, combined therapy of low doses of celastrol with other agents could represent a novel, efficient strategy with acceptable toxicity to treat cancer (Chen et al., ; Zheng et al., ). These data suggest potential avenues to be explored in future also for neuroprotection.…”

ING5‐mediated antineuroblastoma effects of suberoylanilide hydroxamic acid

“…SAHA arrests cancer cell growth by inhibiting classes I and II zinc‐binding HDACs . Substantial evidence indicated that SAHA induced histone acetylation in transcription factor complexes that regulate the genetic expression of molecules associated with malignant phenotypes . Similar to HDACi, ING5 may form MOZ/MORF‐BRPF1/2/3‐ING5‐hEaf6 and JADE1/2/3‐HBO1‐ING4/5‐hEaf6 HAT complexes to acetylate histones H3 and H4, respectively …”

“…5,6 Substantial evidence indicated that SAHA induced histone acetylation in transcription factor complexes that regulate the genetic expression of molecules associated with malignant phenotypes. 7 Similar to HDACi, ING5 may form MOZ/ MORF-BRPF1/2/3-ING5-hEaf6 and JADE1/2/3-HBO1-ING4/5-hEaf6 HAT complexes to acetylate histones H3 and H4, respectively. 8 Suberoylanilide hydroxamic acid suppresses the growth of HeLa cells and induces apoptosis, which is accompanied by PARP cleavage, Caspase-3 activation, potential loss of the mitochondrial membrane, and ROS generation.…”