Nitro-Deficient Niclosamide Confers Reduced Genotoxicity and Retains Mitochondrial Uncoupling Activity for Cancer Therapy

Abstract

Niclosamide is an oral anthelmintic drug, approved for use against tapeworm infections. Recent studies suggest however that niclosamide may have broader clinical applications in cancers, spurring increased interest in the functions and mechanisms of niclosamide. Previously, we reported that niclosamide targets a metabolic vulnerability in p53-deficient tumours, providing a basis for patient stratification and personalised treatment strategies. In the present study, we functionally characterised the contribution of the aniline 4′-NO2 group on niclosamide to its cellular activities. We demonstrated that niclosamide induces genome-wide DNA damage that is mechanistically uncoupled from its antitumour effects mediated through mitochondrial uncoupling. Elimination of the nitro group in ND-Nic analogue significantly reduced γH2AX signals and DNA breaks while preserving its antitumour mechanism mediated through a calcium signalling pathway and arachidonic acid metabolism. Lipidomics profiling further revealed that ND-Nic-treated cells retained a metabolite profile characteristic of niclosamide-treated cells. Notably, quantitative scoring of drug sensitivity suggests that elimination of its nitro group enhanced the target selectivity of niclosamide against p53 deficiency. Importantly, the results also raise concern that niclosamide may impose a pleiotropic genotoxic effect, which limits its clinical efficacy and warrants further investigation into alternative drug analogues that may ameliorate any potential unwanted side effects.

Structural investigations on the mitochondrial uncouplers niclosamide and FCCP

“…The FCCP analogues (12,13) were synthesized via a one-step reaction by using the same procedure (Fig. 1B).…”

“…C1-CCP (12) was obtained in 83% yield as a yellow solid. 1 H NMR (400 MHz, CDCl 3 ) d 10.20 (s, 1H), 7.34-7.26 (m, 2H), 7.01-6.92 (m, 2H), 3.85 (s, 3H).…”

The Antifungal Potential of Niclosamide and Structurally Related Salicylanilides

“…CYP1A1 and Cnr nitroreductase were shown to be responsible for the bioactivation of niclosamide in Salmonella species [ 33 ]. Strategies to mask the hydroxy group by acylation and to remove the nitro group were applied to overcome these pharmacological drawbacks and were able to conserve the biological activities of niclosamide [ 38 , 39 ]. A water-soluble phosphate ester prodrug of niclosamide was also described [ 40 ].…”

“…Fluorine substituents were less tolerated in tests with Candida albicans [ 51 ]. Although the absence of the para -nitro group retained the inhibition of oxidative phosphorylation, a more recent study disclosed a distinctly reduced activity of the niclosamide analog lacking the para -nitro substituent [ 39 , 101 ]. Bulky para -substituents were also tolerated in active salicylanilides such as rafoxanide.…”

Exploring Structure–Activity Relationships of Niclosamide-Based Colistin Potentiators in Colistin-Resistant Gram-Negative Bacteria

“…Niclosamide is composed of a 5-chlorosalicylic acid ring linked to a 2-chloro-4-nitroaniline ring via an amide bond. The nitro group has been demonstrated to contribute to genotoxicity [14], as well as serving as a target for bacterial nitroreductases resulting in resistance to niclosamide [13]. These factors, in addition to reports that structurally similar salicylanilides such as rafoxanide (Figure 1) which lack the nitro group can also synergize with colistin [15], led to us targeting this site for most of our modifications.…”