Structure–activity relationship and role of oxygen in the potential antitumour activity of fluoroquinolones in human epithelial cancer cells

Advancements in Synthetic Strategies and Biological Effects of Ciprofloxacin Derivatives: A Review

Ciprofloxacin is a widely used antibiotic in the fluoroquinolone class. It is widely acknowledged by various researchers worldwide, and it has been documented to have a broad range of other pharmacological activities, such as anticancer, antiviral, antimalarial activities, etc. Researchers have been exploring the synthesis of ciprofloxacin derivatives with enhanced biological activities or tailored capability to target specific pathogens. The various biological activities of some of the most potent and promising ciprofloxacin derivatives, as well as the synthetic strategies used to develop them, are thoroughly reviewed in this paper. Modification of ciprofloxacin via 4-oxo-3-carboxylic acid resulted in derivatives with reduced efficacy against bacterial strains. Hybrid molecules containing ciprofloxacin scaffolds displayed promising biological effects. The current review paper provides reported findings on the development of novel ciprofloxacin-based molecules with enhanced potency and intended therapeutic activities which will be of great interest to medicinal chemists.

Ciprofloxacin and Norfloxacin Hybrid Compounds: Potential Anticancer Agents

BACKGROUND

The concept of utilizing drug repurposing/repositioning in the development of hybrid molecules is an important strategy in drug discovery. Fluoroquinolones, a class of antibiotics, have been reported to exhibit anticancer activities. Although anticancer drug development is achieving some positive outcomes, there is still a need to develop new and effective anticancer drugs. Some limitations associated with most of the available anticancer drugs are drug resistance and toxicity, poor bio-distribution, poor solubility, and lack of specificity, thereby reducing their therapeutic outcomes.

OBJECTIVES

Fluoroquinolones, a known class of antibiotics, have been explored by hybridizing them with other pharmacophores and evaluating their anticancer activity in silico and in vitro. Hence, this review provides an update on new anticancer drugs containing fluoroquinolones moiety, Ciprofloxacin and Norfloxacin between 2020 and 2023, their structural relationship activity, and the future strategies to develop potent chemotherapeutic agents.

METHODS

Fluoroquinolones were mostly hybridized via the N-4 of the piperazine ring on position C-7 with known pharmacophores characterized, followed by biological studies to evaluate their anticancer activity.

RESULTS

The hybrid molecules displayed promising and interesting anticancer activities. Factors such as the nature of the linker, the presence of electron-withdrawing groups, nature, and position of the substituents influenced the anticancer activity of the synthesized compounds.

CONCLUSION

The hybrids were selective towards some cancer cells. However, further in vivo studies are needed to fully understand their mode of action.

The tale of antibiotics beyond antimicrobials: Expanding horizons

Antibiotics had proved to be a godsend for mankind since their discovery. They were once the magical solution to the vexing problem of infection-related deaths. German scientist Paul Ehrlich had termed salvarsan as the silver bullet to treatsyphilis.As time passed, the magic of newly discovered silver bullets got tarnished with raging antibiotic resistance among bacteria and associated side-effects. Still, antibiotics remain the primary line of treatment for bacterial infections. Our understanding of their chemical and biological activities has increased immensely with advancement in the research field. Non-antibacterial effects of antibiotics are studied extensively to optimise their safer, broad-range use. These non-antibacterial effects could be both useful and harmful to us. Various researchers across the globe including our lab are studying the direct/indirect effects and molecular mechanisms behind these non-antibacterial effects of antibiotics. So, it is interesting for us to sum up the available literature. In this review, we have briefed the possible reason behind the non-antibacterial effects of antibiotics, owing to the endosymbiotic origin of host mitochondria. We further discuss the physiological and immunomodulatory effects of antibiotics. We then extend the review to discuss molecular mechanisms behind the plausible use of antibiotics as anticancer agents.

Effect of four fluoroquinolones on the viability of bladder cancer cells in 2D and 3D cultures

Introduction

The anticancer properties of fluoroquinolones and the high concentrations they achieve in urine may help in bladder cancer therapy. This study aimed to analyze the properties of 4 fluoroquinolones as potential candidates for supportive treatment of bladder cancer.

Methods

Comparative analyses were performed on the cytotoxic effects of norfloxacin, enrofloxacin, moxifloxacin, and ofloxacin on normal and cancer urothelial cell lines. In 2D culture, the cytotoxic properties of fluoroquinolones were evaluated using MTT assay, real-time cell growth analysis, fluorescence and light microscopy, flow cytometry, and molecular analysis. In 3D culture, the properties of fluoroquinolones were tested using luminescence assays and confocal microscopy.

Results and Discussion

All tested fluoroquinolones in 2D culture decreased the viability of both tested cell lines in a dose- and timedependent manner. Lower concentrations did not influence cell morphology and cytoskeletal organization. In higher concentrations, destruction of the actin cytoskeleton and shrinkage of the nucleus was visible. Flow cytometry analysis showed cell cycle inhibition of bladder cancer cell lines in the G2/M phase. This influence was minimal in the case of normal urothelium cells. In both tested cell lines, increases in the number of late apoptotic cells were observed. Molecular analysis showed variable expression of studied genes depending on the drug and concentration. In 3D culture, tested drugs were effective only in the highest tested concentrations which was accompanied by caspase 3/7 activation and cytoskeleton degradation. This effect was hardly visible in non-cancer cell lines. According to the data, norfloxacin and enrofloxacin had the most promising properties. These two fluoroquinolones exhibited the highest cytotoxic properties against both tested cell lines. In the case of norfloxacin, almost all calculated LC values for bladder cancer cell lines were achievable in the urine. Enrofloxacin and norfloxacin can be used to support chemotherapy in bladder cancer patients.

A Study on Repositioning Nalidixic Acid via Lanthanide Complexation: Synthesis, Characterization, Cytotoxicity and DNA/Protein Binding Studies

“Drug repositioning” is a modern strategy used to uncover new applications for out-of-date drugs. In this context, nalidixic acid, the first member of the quinolone class with limited use today, has been selected to obtain nine new metal complexes with lanthanide cations (La³⁺, Sm³⁺, Eu³⁺, Gd³⁺, Tb³⁺); the experimental data suggest that the quinolone acts as a bidentate ligand, binding to the metal ion via the keto and carboxylate oxygen atoms, findings that are supported by DFT calculations. The cytotoxic activity of the complexes has been studied using the tumoral cell lines, MDA-MB-231 and LoVo, and a normal cell line, HUVEC. The most active compounds of the series display selective activity against LoVo. Their affinity for DNA and the manner of binding have been tested using UV–Vis spectroscopy and competitive binding studies; our results indicate that major and minor groove binding play a significant role in these interactions. The affinity towards serum proteins has also been evaluated, the complexes displaying higher affinity towards albumin than apotransferrin.

New promising levofloxacin derivatives: Design, synthesis, cytotoxic activity screening, Topo2β polymerase inhibition assay, cell cycle apoptosis profile analysis

Newly designed levofloxacin analogues were synthesized to act as topoisomerase II beta inhibitors (Topo2β). Their cytotoxic activity was screened against breast, liver, and leukemia cancer cell lines. The best activity against liver cancer cell line (Hep3B) was exhibited by the target compounds 3c, 3e, 4a, and 6d (IC₅₀ = 2.33, 1.38, 0.60 and 0.43, respectively). (L-SR) leukemia cancer cell line was pronouncedly affected by compounds 3b, 3g and 4a (IC₅₀ = 1.62, 1.41 and 1.61, sequentially). 3c possessed the best activity against breast cancer cell line (MCF-7) with IC₅₀ = 0.66. Compounds 3c, 3e, 3g, 4a and 4c exhibited Topo2β inhibition activities exceeding etoposide and levofloxacin as reference drugs and variant cell lines. In DNA-Flow cytometry cell cycle analysis, compound 3c arrested the cell cycle at G2/M phase like etoposide and levofloxacin, while compounds 3e and 4a exhibit its arrest at S phase. In addition, 3c, 3e and 4a showed a significant elevation in active caspase-3 levels (10.01, 8.98 and 10.71 folds, respectively). The effect of the new compounds on normal cells was also investigated including breast (MCF10a), liver (THLE2), and lymphocytic (PCS-800-011) normal cell lines.

Rare-Earth Metal Complexes of the Antibacterial Drug Oxolinic Acid: Synthesis, Characterization, DNA/Protein Binding and Cytotoxicity Studies

"Drug repositioning" is a current trend which proved useful in the search for new applications for existing, failed, no longer in use or abandoned drugs, particularly when addressing issues such as bacterial or cancer cells resistance to current therapeutic approaches. In this context, six new complexes of the first-generation quinolone oxolinic acid with rare-earth metal cations (Y³⁺, La³⁺, Sm³⁺, Eu³⁺, Gd³⁺, Tb³⁺) have been synthesized and characterized. The experimental data suggest that the quinolone acts as a bidentate ligand, binding to the metal ion via the keto and carboxylate oxygen atoms; these findings are supported by DFT (density functional theory) calculations for the Sm³⁺ complex. The cytotoxic activity of the complexes, as well as the ligand, has been studied on MDA-MB 231 (human breast adenocarcinoma), LoVo (human colon adenocarcinoma) and HUVEC (normal human umbilical vein endothelial cells) cell lines. UV-Vis spectroscopy and competitive binding studies show that the complexes display binding affinities (K_b) towards double stranded DNA in the range of 9.33 × 10⁴ - 10.72 × 10⁵. Major and minor groove-binding most likely play a significant role in the interactions of the complexes with DNA. Moreover, the complexes bind human serum albumin more avidly than apo-transferrin.

Selected pharmacotherapy agents as antiproliferative and anti-inflammatory compounds

The repurposing of safe therapeutic drugs has emerged as an alternative approach to rapidly identify effective, safe, and conveniently available therapeutics to treat/prevent cancer. Therefore, it was hypothesized that acidic chelator drugs could have a genuine potential as antiproliferative agents. Based on their pKa, the selected 15 acidic drugs of eight classes-namely sulfonylureas, proton pump inhibitors, fluoroquinolones, nonsteroidal anti-inflammatory agents, thiazolidinediones, thienopyridines, statins, and nicotinic acid-were assayed for anticancer HTS against the lung A549, skin A375, breast MCF7 and T47D, pancreatic PANC1, cervical HeLa, and leukemia K562 cancer cell lines and normal fibroblasts. Lipopolysaccharide-prompted inflammation in RAW264.7 macrophages was the potential anticancer mechanism. Atorvastatin exerted remarkably superior cytotoxicity against A375.2S (IC50 value 0.02 μM p < .001 vs. cisplatin 0.07 μM IC50 value). Atorvastatin exhibited an equipotency to cisplatin's T47D growth inhibition (34.6 μM vs. 34.59 μM; p > .05). Levofloxacin as well as ciprofloxacin superbly superseded the antineoplastic cisplatin activity against the K562 cell line (respective IC50 values [μM] 10.4 and 19.5 vs. 29.3; p < .05-<.01). Gemifloxacin and lansoprazole had comparable antiproliferation in K562 to cisplatin's (respective IC50 values [μM] 34.9 and 36.3 vs. 29.3; p > .05). The selected agents lacked cytotoxicity in the panel of MCF7, HeLa, A549, or Panc1 cancer cells. Most notably, LPS prompted RAW264.7 macrophages, atorvastatin, piroxicam, clopidogrel, esomeprazole, and lansoprazole were of higher anti-inflammation potency than indomethacin (p < .01-.001). Evidently, omeprazole, pioglitazone, gemifloxacin, and indomethacin were of comparable anti-inflammation potencies (p > .05). Collectively, this work reveals acidic chelator drugs (atorvastatin, gemifloxacin, and lansoprazole with dual anti-inflammation and antiproliferation propensities) as authentic agents for the repurposing approach in anticancer chemotherapy/prevention.

Repositioning of fluoroquinolones from antibiotic to anti-cancer agents: An underestimated truth

Increasing development costs and higher failure rate in clinical trials has reduced the repertoire of newer drugs in the market for clinical use. The most appropriate approach to end the search for newer drugs is "Repositioning", as it requires less time and money to explore new indication of existing drug or failed drug. In the past, several drugs have been repositioned for different indication but the full potential remains unharnessed. With rise in cancer prevalence and treatment costs, it is imperative to search for newer drugs and the use of repositioning approach may help us. Fluoroquinolones has been used as antibiotics for over four decades now, but recent research highlighted their use as pharmacological compounds with multifaceted implication. Repositioning of fluoroquinolones into anti-cancer molecule seems to be a highly plausible option owing to their profound immunomodulatory, pro-apoptotic, anti-proliferative and anti-metastatic potential. The present review provides a comprehensive account of the recent and past explorations pertaining to the anti-cancer activity of fluoroquinolones and also discusses the various approaches that are being considered to remodel them for the treatment of cancer.

Improved photodynamic effect through encapsulation of two photosensitizers in lipid nanocapsules

Photodynamic therapy (PDT) has developed into a new clinical and non-invasive treatment for cancer over the past 30 years. By the combination of three non-toxic partners, i.e. a photosensitizer (PS), molecular oxygen (O₂) and light, cytotoxic reactive oxygen species (ROS) are locally produced leading to irreversible vascular and cellular damage. In the present study, we report for the first time that the combination of two photosensitizers (2 PSs: Protoporphyrin IX, PpIX and Hypericin, Hy) loaded in the same lipid nanocapsules (LNCs) leads to enhanced photodynamic therapy efficiency when compared with previously reported systems. The 2 PS-loaded LNCs are shown to increase the in vitro phototoxicity at the nanomolar range (IC₅₀ = 274 and 278 nM on HeLa and MDA-MB-231 cell lines, respectively), whereas the corresponding single PS-loaded LNCs at the same concentration exhibit a phototoxicity two times lower. Intracellular localization in HeLa cells indicates a subcellular asymmetry of PpIX and Hy, in the plasma, ER membranes and round internal structures. The biodistribution of LNCs was studied upon different routes of injection into Swiss nude mice; based on the obtained data, LNCs were injected intratumorally and used to slow the growth of xenograft tumors in mice. The results obtained in this study suggest that the combination of two or more PSs may be a promising strategy to improve the efficacy of conventional photodynamic therapy as well as to reduce dark toxicity.

GSH depletion, mitochondrial membrane breakdown, caspase-3/7 activation and DNA fragmentation in U87MG glioblastoma cells: New insight into the mechanism of cytotoxicity induced by fluoroquinolones

Fluoroquinolones are a known synthetic group of antibiotics that have been the subject of many research interests. This class of antibiotics was shown to be cytotoxic towards various cancer cell lines, thus representing a potentially important source of new anticancer agents. The present study was designed to examine the effect of ciprofloxacin and moxifloxacin on cell viability, redox balance and apoptosis in U87MG glioblastoma cells. Herein, we found that both fluoroquinolones decrease the viability and exert an anti-proliferative effect on U87MG cells. The EC₅₀ values were found to be as 0.75 µmol/ml, 0.57 µmol/ml, 0.53 µmol/ml for ciprofloxacin and 24, 48, 72 h incubation time, respectively, and 0.48 µmol/ml, 0.22 µmol/ml, 0.15 µmol/ml for moxifloxacin and 24, 48, 72 h incubation time, respectively. Ciprofloxacin and moxifloxacin have also induced the intracellular GSH depletion and apoptosis as shown by externalization of phosphatidylserine, caspase-3/7 activation, S and sub-G₁ cell cycle arrest, nuclear morphological changes induction and DNA fragmentation. The mechanism of apoptosis was related to the loss of mitochondrial membrane potential suggesting activation of the intrinsic mitochondrial pathway. This is the first study that may provide the basis for understanding potential cellular and molecular mechanism underlying ciprofloxacin and moxifloxacin cytotoxic and pro-apoptotic effect towards U87MG glioblastoma cells, suggesting that these fluoroquinolone derivatives may have value for the development as anti-glioma agents.

Red grape (Vitis vinifera L.) flavonoids down-regulate collagen type III expression after UV-A in primary human dermal blood endothelial cells

Red grape (Vitis vinifera L.) flavonoids including flavan-3-ols (eg, catechin and epicatechin), flavonols (eg, quercetin) and anthocyanins (eg, malvidin) exert anti-inflammatory and antioxidant activities. In the skin they also have a photoprotective action, and their effects have been extensively investigated in keratinocytes, melanocytes and fibroblasts. Despite their known effects also on blood vasculature, little is known on their activities on human dermal blood endothelial cells (HDBECs), which are critically involved in skin homeostasis as well as in the pathogenesis of neoplastic and inflammatory skin diseases. We sought to study the biological effects of selected red grape flavonoids in preventing the consequences of ultraviolet (UV)-A irradiation in vitro. Our results show that red grape flavonoids prevent UV-A-induced sICAM-1 release in HDBECs, suggesting that this cell type could represent an additional target of the anti-inflammatory activity of flavonoids. In addition, flavonoids effectively inhibited UV-A-induced synthesis of collagen type III at both RNA and protein level, indicating that dermal blood microvasculature could be actively involved in ECM remodelling as a consequence of skin photo-ageing, and that this can be prevented by red grape flavonoids.

Lomefloxacin Induces Oxidative Stress and Apoptosis in COLO829 Melanoma Cells

Although some fluoroquinolones have been found to exert anti-tumor activity, studies on the effect of these drugs on melanoma cells are relatively rare. The aim of this study was to examine the effect of lomefloxacin on cell viability, reactive oxygen species production, redox balance, cell cycle distribution, DNA fragmentation, and apoptosis in COLO829 melanoma cells. Lomefloxacin decreases the cell viability in a dose- and time-dependent manner. For COLO829 cells treated with the drug for 24, 48, and 72 h, the values of IC50 were found to be 0.51, 0.33, and 0.25 mmol/L, respectively. The analyzed drug also altered the redox signaling pathways, as shown by intracellular reactive oxygen species overproduction and endogeneous glutathione depletion. After lomefloxacin treatment, the cells were arrested in S- and G2/M-phase, suggesting a mechanism related to topoisomerase II inhibition. DNA fragmentation was observed when the cells were exposed to increasing lomefloxacin concentrations and a prolongation of incubation time. Moreover, it was demonstrated that the drug induced mitochondrial membrane breakdown as an early hallmark of apoptosis. The obtained results provide a strong molecular basis for the pharmacologic effect underlying the potential use of lomefloxacin as a valuable agent for the treatment of melanoma in vivo.

Dual Inhibition of Topoisomerase II and Tyrosine Kinases by the Novel Bis-Fluoroquinolone Chalcone-Like Derivative HMNE3 in Human Pancreatic Cancer Cells

Both tyrosine kinase and topoisomerase II (TopII) are important anticancer targets, and their respective inhibitors are widely used in cancer therapy. However, some combinations of anticancer drugs could exhibit mutually antagonistic actions and drug resistance, which further limit their therapeutic efficacy. Here, we report that HMNE3, a novel bis-fluoroquinolone chalcone-like derivative that targets both tyrosine kinase and TopII, induces tumor cell proliferation and growth inhibition. The viabilities of 6 different cancer cell lines treated with a range of HMNE3 doses were detected using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Cellular apoptosis was determined using Hoechst 33258 fluorescence staining and the terminal deoxynucleotidyl transferase (TdT) dUTP nick-end labeling (TUNEL) assay. The expression of activated Caspase-3 was examined by immunocytochemistry. The tyrosine kinase activity was measured with a human receptor tyrosine kinase (RTK) detection kit using a horseradish peroxidase (HRP)-conjugated phosphotyrosine (pY20) antibody as the substrate. The topoisomerase II activity was measured using agarose gel electrophoresis with the DNA plasmid pBR322 as the substrate. The expression levels of the P53, Bax, Bcl-2, Caspase-3, -8, -9, p-cSrc, c-Src and topoisomerase II proteins were detected by western blot analysis. The proliferation of five of the six cancer cell lines was significantly inhibited by HMNE3 at 0.312 to 10 μmol/L in a time- and dose-dependent manner. Treatment of the Capan-1 and Panc-1 cells with 1.6 to 3.2 μM HMNE3 for 48 h significantly increased the percentage of apoptotic cells (P<0.05), and this effect was accompanied by a decrease in tyrosine kinase activity. HMNE3 potentially inhibited tyrosine kinase activity in vitro with an IC50 value of 0.64±0.34 μmol/L in Capan-1 cells and 3.1±0.86 μmol/L in Panc-1 cells. The activity of c-Src was significantly inhibited by HMNE3 in a dose- and time-dependent manner in different cellular contexts. Compared with the control group, HMNE3 induced increased expression of cellular apoptosis-related proteins. Consistent with cellular apoptosis data, a significant decrease in topoisomerase IIβ activity was noted following treatment with HMNE3 for 24 h. Our data suggest that HMNE3 induced apoptosis in Capan-1 and Panc-1 cells by inhibiting the activity of both tyrosine kinases and topoisomerase II.

Understanding the structure–activity relationship between quercetin and naringenin: in vitro

The interactions of quercetin and naringenin with DNA have been studied at molecular level, which may throw light on their structure–activity relationships, helpful for the design of analogs flavonoids and their application in drug industries.