Histone deacetylase inhibitors (HDACis) are part of a growing class of epigenetic therapies used for the treatment of cancer. Although HDACis are effective in the treatment of T-cell lymphomas, treatment of solid tumors with this class of drugs has not been successful. Overexpression of the multidrug resistance protein P-glycoprotein (P-gp), encoded by ABCB1, is known to confer resistance to the HDACi romidepsin in vitro, yet increased ABCB1 expression has not been associated with resistance in patients, suggesting that other mechanisms of resistance arise in the clinic. To identify alternative mechanisms of resistance to romidepsin, we selected MCF-7 breast cancer cells with romidepsin in the presence of the P-gp inhibitor verapamil to reduce the likelihood of P-gp-mediated resistance. The resulting cell line, MCF-7 DpVp300, does not express P-gp and was found to be selectively resistant to romidepsin but not to other HDACis such as belinostat, panobinostat, or vorinostat. RNA sequencing analysis revealed upregulation of the mRNA coding for the putative methyltransferase, METTL7A, whose paralog, METTL7B, was previously shown to methylate thiol groups on hydrogen sulfide and captopril. As romidepsin has a thiol as the zinc-binding moiety, we hypothesized that METTL7A could inactivate romidepsin and other thiol-based HDACis via methylation of the thiol group. We demonstrate that expression of METTL7A or METTL7B confers resistance to thiol-based HDACis and that both enzymes are capable of methylating thiol-containing HDACis. We thus propose that METTL7A and METTL7B confer resistance to thiol-based HDACis by methylating and inactivating the zinc-binding thiol.

中文翻译：

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甲基转移酶 METTL7A 和 METTL7B 赋予对基于硫醇的组蛋白脱乙酰酶抑制剂的抗性

组蛋白脱乙酰酶抑制剂 (HDACis) 是用于治疗癌症的越来越多的表观遗传疗法的一部分。尽管HDACis可有效治疗T细胞淋巴瘤，但用此类药物治疗实体瘤尚未成功。已知由 ABCB1 编码的多药耐药蛋白 P-糖蛋白 (P-gp) 的过度表达可在体外赋予 HDACi romidepsin 耐药性，但 ABCB1 表达增加与患者耐药性无关，这表明其他耐药机制出现在诊所。为了确定罗米地辛的替代耐药机制，我们在 P-gp 抑制剂维拉帕米存在下选择了含有罗米地辛的 MCF-7 乳腺癌细胞，以降低 P-gp 介导的耐药性的可能性。所得细胞系 MCF-7 DpVp300 不表达 P-gp，并且被发现对罗米地辛具有选择性耐药性，但对其他 HDACis（如贝利司他、帕比司他或伏立诺他）没有选择性耐药。RNA测序分析显示，编码假定的甲基转移酶METTL7A的mRNA上调，其旁系同源物METTL7B先前已被证明可甲基化硫化氢和卡托普利上的硫醇基团。由于罗米地辛具有硫醇作为锌结合部分，我们假设 METTL7A 可以通过硫醇基团的甲基化来灭活罗米地辛和其他基于硫醇的 HDAC。我们证明 METTL7A 或 METTL7B 的表达赋予对基于硫醇的 HDACis 的抗性，并且这两种酶都能够甲基化含硫醇的 HDACis。因此，我们提出 METTL7A 和 METTL7B 通过甲基化和灭活锌结合硫醇来赋予对基于硫醇的 HDACis 的抗性。