Synthesis and biological evaluation of novel quinolone derivatives dual targeting histone deacetylase and tubulin polymerization as antiproliferative agents

A strategy to develop chemotherapy agents by combining two complimentary chemo-active groups into a single molecule may have higher efficacy and fewer side effects than that of single-target drugs. In this article, we describe the synthesis and evaluation of a series of novel dual-acting levofloxacin–HDACi conjugates to target both histone deacetylase (HDAC) and tubulin polymerization. These bifunctional conjugates exhibited potent inhibitory activities against HDACs and tubulin polymerization. In docking analysis provides a structural basis for HDACs inhibition activities. Moreover, these conjugates showed selective anticancer activity that is more potent against MCF-7 compared to other four cancer cells A549, HepG2, PC-3, HeLa, but they had no toxicity toward normal cells.

Synthesis of a series of novel dual-acting levofloxacin–HDACi conjugates, which show potent inhibitory activities against HDACs, tubulin polymerization, and significant antiproliferative effect on MCF-7 cells.

Cancer is a highly complex multifactorial disease involving multiple cross-talking between signaling networks. Almost all single-target-based drugs suffer from severe toxicities or other undesirable side effects. In contrast, combination therapy, which combines multiple anticancer agents working with different mechanisms, might have superior efficacy and fewer side effects compared to single-target treatments.^1,2Histone deacetylases (HDACs) are epigenetic enzymes that are capable of removing acetyl groups from ε-amino groups of lysine residues in histone or other nonhistone proteins.³ Abnormal expression of HDACs has been observed in various types of cancer,^4–6 and these enzymes have emerged as important targets in the development of anticancer drugs. Consequently, inhibition of HDAC activity is now recognized as a powerful strategy for cancer therapy. There are 18 human HDAC isoforms categorized into four major classes: class I (HDACs 1, 2, 3, 8), class IIa (HDACS 4, 5, 7, 9), class IIb (HDACs 6 and 10), and class IV (HDAC 11) are Zn²⁺-dependent metalloenzymes, while class III (SirTs 1–7) are NDA⁺-dependent sirtuins.^7,8 Of these HDAC isoforms, only HDACs 1, 2, 3, and 6 have shown biologically relevant deacetylation ability.⁹ Specially, selective inhibition of HDAC6 may have fewer side effects than pan-HDAC and class I isoform.^10–12To date, more than twenty HDAC inhibitors have been initiated in clinical trials, and four HDAC inhibitors vorinostat (SAHA),¹³ romidepsin (FK-228),¹⁴ belinostat (PXD-101),^15,16 panobinostat (LBH-589),¹⁷ have been approved by FDA for the treatment of T-cell lymphoma, cutaneous T-cell lymphoma and multiple myeloma. However, most of them are pan-HDAC (SAHA, LBH-589) or class I selective (FK-228, PXD-101) inhibitors, which usually lead to several mild to severe side effects.^16,18,19 In addition, most of HDAC inhibitors lack visible efficacy against solid tumor,^14,20 the doses given in clinical are much higher, which severely limit their clinical utility for the treatment of broad spectrum of cancer. Therefore, preclinical evaluation of new HDAC inhibitors will need to focus on improving HDAC isoform selectivity and enhancing potency against solid tumors. One strategy may be able to ameliorate the shortcomings of current inhibitors, which is to develop a dual-acting HDAC inhibitor (HDACi) by incorporation of the surface recognition group of prototypical HDACi into other anticancer drugs, forming a single molecule that can modulate intracellular multiple targets, other than various HDAC isoforms. So far, a few examples of bifunctional HDACi-derived conjugates have been obtained.^21–26 Expansion of the diversity of such bifunctional conjugates could lead to broad acting, therapeutically viable anticancer drugs.In another aspect, fluoroquinolones (FQs) have recently been proven as an excellent class of broad-spectrum anticancer drugs against a variety of cancer cells such as bladder cancer,²⁷ non-small cell lung carcinoma,²⁸ colorectal carcinoma cells,²⁹etc. For instance, it has been demonstrated that levofloxacin (Lv) displays antiproliferative activity against various cancer cells.^30,31 Additionally, many of fluoroquinolones were potent inhibitors of tubulin polymerization and exhibited selective activity against some tumor cell types.^32,33 More importantly, fluoroquinolones have favorable pharmacokinetic profiles and good adsorption, which possess an established record of safety.³⁴ Therefore, on the basis of therapeutic effectives of aforementioned HDACi as well as fluoroquinolone, we conceived that concurrent inhibition of HDAC and tubulin polymerization would be a viable alternative approach for cancer treatment.In this work, we describe the design, synthesis and biological evaluation of novel dual-action levofloxacin–HDACi conjugates, which can be prepared conveniently by direct connection of levofloxacin with a triazole-liked SAHA (Fig. 1). The levofloxacin–SAHA conjugates (compounds 8a–c and 9a–c) of this design not only have HDACi unit but also have a second pharmacologically quinolone scaffold. Thus, they expand the exploration of bifunctional HDACi-derived conjugates. For comparison, the carboxylic acid analogues (by replacing the hydroxamic acid (–CONHOH) group with (–COOH), compounds 6a–c and 7a–c) were also prepared and evaluated for their HDAC and tubulin polymerization inhibition activity, antiproliferative activity and cell-type selectivity, etc.Open in a separate windowFig. 1Design of dual-acting levofloxacin–HDACi conjugates.