Unveiling the Potential of Unfused Bichromophoric Naphthalimide To Induce Cytotoxicity by Binding to Tubulin: Breaks Monotony of Naphthalimides as Conventional Intercalators

Abstract

In the development of small-molecule drug candidates, naphthalimide-based compounds hold a very important position as potent anticancer agents with considerable safety in drug discoveries. Being synthetically and readily accessible, naphthalimide compounds with planar architecture have been developed mostly as DNA-targeting intercalators. However, in this article, it is demonstrated, for the first time, that an unfused naphthalimide-benzothiazole bichromophoric compound 2-(6-chlorobenzo[ d] thiazol-2-yl)-1 H-benzo[ de] isoquinoline-1,3(2 H)-dione (CBIQD), seems to expand the bioactivity of naphthalimide as anti-mitotic agent also. Preliminary studies demonstrate that CBIQD interferes with human lung cancer (A549) cell proliferation and growth and causes cellular morphological changes. However, the underlying mechanism of its antitumor action and primary cellular target in A549 cells remained skeptical. Confocal microscopy in A549 cells revealed disruption of interphase microtubule (MT) network and formation of aberrant multipolar spindle. Consistent with microscopy results, UV-vis, steady-state fluorescence, and time-resolved fluorescence (TRF) studies demonstrate that CBIQD efficiently binds to tubulin ( K = 2.03 × 10 M ± 1.88%), inhibits its polymerization, and depolymerizes preformed microtubules (MTs). Low doses of CBIQD have also shown specificity toward tubulin protein in the presence of a nonspecific protein like bovine serum albumin as well as other cytoskeleton component, actin. The in vitro determination of binding site coupled with in silico studies suggests that CBIQD may prefer to occupy the colchicine binding site. Further, CBIQD perturbed tubulin conformation to some extent and protected ∼1.4 cysteine residues toward chemical modification by 5,5'-dithiobis-2-nitrobenzoic acid. We also suggest the possible mechanism underlying CBIQD-induced cancer cell cytotoxicity: CBIQD, when bound to tubulin, may prevent it to maintain a straight conformation; consequently, the α- and β-heterodimers might be no longer available for MT growth. Thus, the consolidated spectroscopic research described herein explores the potential of CBIQD as a new paradigm in the design and development of novel unfused or nonring-fused naphthalimide-based antimitotic cancer therapeutics in medicinal chemistry research.

Potent and Selective Benzothiazole-Based Antimitotics with Improved Water Solubility: Design, Synthesis, and Evaluation as Novel Anticancer Agents

“…Furthermore, the benzothiazole moiety is a versatile scaffold for the development of new anticancer drugs [ 27 , 28 ] that are able to act on different targets [ 29 ]. It has played an important role in the design of new polar compounds targeting tubulin [ 30 ], as reported 2-anilinopyridinyl-benzothiazole [ 31 ], triazole-benzothiazole [ 32 ], naphthalimide-benzothiazole [ 33 ], isoxazole-benzothiazole [ 34 ], trimethoxyphenyl-benzothiazole [ 35 ], and bis-benzothiazole [ 36 ] derivatives; most of them are adapted to bind at the A–B zones of the colchicine site. The benzothiazole scaffold was also used to develop photoswitchable tubulin polymerization inhibitors that are able to spatiotemporally control the microtubule dynamics and target different regions of the colchicine domain depending on a photoisomerization process of styrylbenzothiazole derivatives [ 37 ].…”

1O2 Generating Luminescent Lanthanide Complexes with 1,8-Naphthalimide-Based Sensitizers

“…1,8-Naphthalimide-based compounds are also efficient photosensitizers of 1 O 2 , with reported ϕ 1O2 in the range 5–82%, − and are proposed for biological sensing, − as anti-inflammatory drugs, and as anticancer therapeutics. − For example, the derivatives amonafide and mitonafide were tested in clinical trials as anticancer agents. , 1,8-Naphthalimide and its derivatives intercalate between DNA base pairs and form strong van der Waals interactions, resulting in reduced gene expression . Selected derivatives are reported to bind and disable topoisomerase II (the enzyme responsible for DNA packaging) or tubulin, or nitroreductase, considerably hindering cell function. Naphthalimide derivatives are often used as fluorescent reporters. ,,,, Hideg and co-workers described an example used to infiltrate chlorophyll-containing mesophyll cells of tobacco leaves and to detect 1 O 2 in vitro by luminescence in the range 500–600 nm …”

“…29,30 1,8-Naphthalimide and its derivatives intercalate between DNA base pairs and form strong van der Waals interactions, 31 resulting in reduced gene expression. 32 Selected derivatives are reported to bind and disable topoisomerase II (the enzyme responsible for DNA packaging) 33 or tubulin, 34 or nitroreductase, 35 considerably hindering cell function. Naphthalimide derivatives are often used as fluorescent reporters.…”

Switching of the Polarity-Sensitive Aggregation Pattern of a Thiosemicarbazone-Based Anticancer Luminophore and Its Involvement in Cellular Apoptosis of the Human Lung Cancer Cell Line

“…By maintaining DAHTS exposure for 24 and 48 h, the cells were observed using an inverted optical microscope (Nikon Eclipse TS 100), and the pictures were taken using a compact digital camera (Canon) attached to the microscope. 47 2.2.4.5. Cytotoxicity Assay.…”