Enhanced Histone Deacetylase Activity in Malignant Melanoma Provokes RAD51 and FANCD2-Triggered Drug Resistance

Abstract

DNA-damaging anticancer drugs remain a part of metastatic melanoma therapy. Epigenetic reprogramming caused by increased histone deacetylase (HDAC) activity arising during tumor formation may contribute to resistance of melanomas to the alkylating drugs temozolomide, dacarbazine, and fotemustine. Here, we report on the impact of class I HDACs on the response of malignant melanoma cells treated with alkylating agents. The data show that malignant melanomas in situ contain a high level of HDAC1/2 and malignant melanoma cells overexpress HDAC1/2/3 compared with noncancer cells. Furthermore, pharmacologic inhibition of class I HDACs sensitizes malignant melanoma cells to apoptosis following exposure to alkylating agents, while not affecting primary melanocytes. Inhibition of HDAC1/2/3 caused sensitization of melanoma cells to temozolomide in vitro and in melanoma xenografts in vivo. HDAC1/2/3 inhibition resulted in suppression of DNA double-strand break (DSB) repair by homologous recombination because of downregulation of RAD51 and FANCD2. This sensitized cells to the cytotoxic DNA lesion O 6 -methylguanine and caused a synthetic lethal interaction with the PARP-1 inhibitor olaparib. Furthermore, knockdown experiments identified HDAC2 as being responsible for the regulation of RAD51. The influence of class I HDACs on DSB repair by homologous recombination and the possible clinical implication on malignant melanoma therapy with temozolomide and other alkylating drugs suggests a combination approach where class I HDAC inhibitors such as valproic acid or MS-275 (entinostat) appear to counteract HDAC-and RAD51/FANCD2-mediated melanoma cell resistance. Cancer Res; 76(10); 3067-77. Ó2016 AACR.

The multifaceted influence of histone deacetylases on DNA damage signalling and DNA repair

“…Inhibition of HDACs has been shown to abolish drug-resistance in cancer cells (36). In support of this finding, HDAC inhibition sensitizes neuroblastoma cells to the genotoxins etoposide, melphalan, carboplatin and vincristine (37), melanoma cells to temozolomide, psoralen and UVA, fotemustine and ionizing radiation (16,38,39), prostate cancer cells to bleomycin, doxorubicin, etoposide, hydroxyurea, cisplatin and ionizing radiation (40,41), breast cancer cells to etoposide and olaparib (42,43) and head and neck cancer cells to cisplatin (44). In addition, HDAC inhibition sensitizes squamous cell carcinoma, non-small cell lung cancer, osteosarcoma, rhabdomyosarcoma and cervical cancer cells to ionizing radiation (45–48).…”

“…Apart from the role of SIRT1 in NER, the overexpressed HDACs in melanoma cells (16,26) (Table 1) seem to also play a role in stimulating NER, as HDAC inhibition by sodium butyrate, an inhibitor of class I and class IIA HDACs (84), inhibits removal of bulky lesions by NER in these cells (38). Contrary to melanoma cells, HDAC inhibition with sodium butyrate in normal human fibroblasts enhances NER upon UV irradiation (85).…”

“…Inhibition of class I HDACs by MS-275 or knockdown of HDAC2 decreases RAD51 expression and impedes HR in melanoma cells (16). In osteosarcoma and rhabdomyosarcoma cells the pan-HDACi SAHA caused downregulation of RAD51 (47) while in prostate cancer cells inhibition of class I HDACs by valproic acid also decreased RAD51 expression, which the authors ascribed to a decrease in E2F1 promoter binding following HDAC inhibition (40).…”

“…Monoubiquitinated FANCD2 recruits nucleases that very likely promote dual incision and unhooking of the ICL by the structure-specific endonucleases SLX4-SLX1, ERCC1-XPF and MUS81-EME1, as well as the Fanconi-associated nuclease 1 (192). Exposing melanoma cells to the HDACi MS-275, that inhibits HDAC1, 2 and 3 (84), caused a transcriptional downregulation of FANCD2 and sensitized these cells to the chloroethylating agent fotemustine (16). The unhooking of the ICL allows for the HR-mediated restart of the replication fork that proceeds across the unhooked lesion with the help of the translesion polymerases REV1 and polymerase ζ (POLζ) (192).…”

Targeting Histone Deacetylases in Malignant Melanoma: A Future Therapeutic Agent or Just Great Expectations?

“…Malignant melanomas in situ contain a high level of HDAC-1, 2 and malignant melanoma cells overexpress HDAC-1, -2, -3 compared with non-cancer cells. Furthermore, pharmacologic inhibition of class I HDAC sensitizes malignant melanoma cells to apoptosis following exposure to alkylating agents, while not affecting primary melanocytes (24)(25)(26). West et al (27) showed that the immune system is absolutely necessary for the anticancer effect of HDACI (9,11,24,28).…”