Unveiling Therapeutic Potential: Targeting Fusobacterium nucleatum's Lipopolysaccharide Biosynthesis for Endodontic Infections-An In Silico Screening Study.

Complex microbial communities have been reported to be involved in endodontic infections. The microorganisms invade the dental pulp leading to pulpitis and initiating pulp inflammation. Fusobacterium nucleatum is a dominant bacterium implicated in both primary and secondary endodontic infections. Drugs targeting the molecular machinery of F. nucleatum will minimize pulp infection. LpxA and LpxD are early acyltransferases involved in the formation of lipid A, a major component of bacterial membranes. The identification of leads which exhibit preference towards successive enzymes in a single pathway can also prevent the development of bacterial resistance. A stringent screening strategy utilizing physicochemical and pharmacokinetic parameters along with a virtual screening approach identified two compounds, Lomefloxacin and Enoxacin, with good binding affinity towards the early acyltransferases LpxA and LpxD. Lomefloxacin and Enoxacin, members of the fluoroquinolone antibiotic class, exhibit wide-ranging activity against diverse bacterial strains. Nevertheless, their effectiveness in the context of endodontic treatment requires further investigation. This study explored the potential of Lomefloxacin and Enoxacin to manage endodontic infections via computational analysis. Moreover, the compounds identified herein serve as a foundation for devising novel combinatorial libraries with enhanced efficacy for endodontic therapeutic strategies.

Enoxacin-based derivatives: antimicrobial and antibiofilm agent: a biology-oriented drug synthesis (BIODS) approach.

Background: To find alternative molecules against Klebsiella pneumonia, Proteus mirabilis and methicillin-resistant Staphylococcus aureus, new enoxacin derivatives were synthesized and screened. Methods: All derivatives exhibited promising antibacterial activities as compared to standard enoxacin (2 µg/ml) and standard cefixime (82 µg/ml). Compounds 2, 3 and 5 significantly downregulated the gene expression of biofilm-forming genes. Conclusion: Based on our results, these molecules may serve as potential drug candidates to cure several bacterial infections in the future.

Enoxacin Shows Broad-Spectrum Antiviral Activity against Diverse Viruses by Enhancing Antiviral RNA Interference in Insects.

RNA interference (RNAi) functions as the major host antiviral defense in insects, while less is understood about how to utilize antiviral RNAi in controlling viral infection in insects. Enoxacin belongs to the family of synthetic antibacterial compounds based on a fluoroquinolone skeleton that has been previously found to enhance RNAi in mammalian cells. In this study, we show that enoxacin efficiently inhibited viral replication of Drosophila C virus (DCV) and cricket paralysis virus (CrPV) in cultured Drosophila cells. Enoxacin promoted the loading of Dicer-2-processed virus-derived small interfering RNA (siRNA) into the RNA-induced silencing complex, thereby enhancing the antiviral RNAi response in infected cells. Moreover, enoxacin treatment elicited RNAi-dependent in vivo protective efficacy against DCV or CrPV challenge in adult fruit flies. In addition, enoxacin also inhibited the replication of flaviviruses, including dengue virus and Zika virus, in Aedes mosquito cells in an RNAi-dependent manner. Together, our findings demonstrate that enoxacin can enhance RNAi in insects, and enhancing RNAi by enoxacin is an effective antiviral strategy against diverse viruses in insects, which may be exploited as a broad-spectrum antiviral agent to control the vector transmission of arboviruses or viral diseases in insect farming. IMPORTANCE RNAi has been widely recognized as one of the most broadly acting and robust antiviral mechanisms in insects. However, the application of antiviral RNAi in controlling viral infections in insects is less understood. Enoxacin is a fluoroquinolone compound that was previously found to enhance RNAi in mammalian cells, while its RNAi-enhancing activity has not been assessed in insects. Here, we show that enoxacin treatment inhibited viral replication of DCV and CrPV in Drosophila cells and adult fruit flies. Enoxacin promoted the loading of Dicer-generated virus-derived siRNA into the Ago2-incorporated RNA-induced silencing complex and in turn strengthened the antiviral RNAi response in the infected cells. Moreover, enoxacin displayed effective RNAi-dependent antiviral effects against flaviviruses, such as dengue virus and Zika virus, in mosquito cells. This study is the first to demonstrate that enhancing RNAi by enoxacin elicits potent antiviral effects against diverse viruses in insects.

Bisphosphonate-enoxacin inhibit osteoclast formation and function by abrogating RANKL-induced JNK signalling pathways during osteoporosis treatment.

Osteoporosis is an age-related disease characterized by low mineral density, compromised bone strength and increased risk of fragility fracture. Most agents for treating osteoporosis focus primarily on anti-resorption by inhibiting osteoclast activity. Bisphosphonate (BP) is a potent anti-resorptive agent that has been used clinically for decades and is proven to be effective. However, BP has a variety of side effects and is far from being an ideal anti-osteoporosis agent. BP selectively binds to calcium crystals, which are subsequently taken up or released by osteoclasts. Based on the action of BP, we previously demonstrated the inhibitory effect of a novel bone-targeting BP derivative, bisphosphonate-enoxacin (BE). In the current study, we used bone marrow-derived osteoclast cultures to further assess the inhibitory effect of BE on osteoclastogenesis and employed reverse transcription PCR and real-time PCR to examine expression of osteoclast-specific genes. Additionally, we used bone resorption and F-actin immunofluorescence assays to evaluate the effect of BE on osteoclast function and investigated the potential mechanisms affecting osteoclast differentiation and function in vitro. Furthermore, an ovariectomized (OVX) rat model was established to evaluate the therapeutic effects of BE on preventing bone loss. Results showed that BE exerted potent inhibitory effects on osteoclast formation and bone resorption by specifically abrogating RANKL-induced JNK signalling, and that it preserved OVX rat bone mass in vivo without any notable side effects. Collectively, these results indicated that the BP derivative BE may have significant potential as a treatment for osteoporosis and other osteolytic diseases.

Identification of a Novel TAR RNA-Binding Protein 2 Modulator with Potential Therapeutic Activity against Hepatocellular Carcinoma.

Imbalance miRNAs contribute to tumor formation; therefore, the development of small-molecule compounds that regulate miRNA biogenesis is an important strategy in oncotherapy. Here, (-)-Gomisin M1 (GM) was found to modulate miRNA biogenesis to inhibit the proliferation, migration, and invasion of hepatocellular carcinoma (HCC) cells. GM modulated expression profiles of miRNA and protein in HCC cells and suppressed tumor growth in a mouse model. Mechanistically, GM affected miRNA maturation by targeting TAR RNA-binding protein 2 (TRBP), with an efficacy higher than that of enoxacin, and promoted the binding of TRBP with Dicer. Structural simplification and a preliminary structure-activity relationship study via the synthesis of 20 GM derivatives showed that compound 9 exhibited more potent inhibitory activity in HCC cell proliferation and affinity for TRBP than did GM. These results suggest that TRBP may be a novel potential therapeutic target in HCC and compound 9 may be a potential drug candidate for the treatment of HCC.

In silico analysis suggests the RNAi-enhancing antibiotic enoxacin as a potential inhibitor of SARS-CoV-2 infection.

COVID-19 has currently become the biggest challenge in the world. There is still no specific medicine for COVID-19, which leaves a critical gap for the identification of new drug candidates for the disease. Recent studies have reported that the small-molecule enoxacin exerts an antiviral activity by enhancing the RNAi pathway. The aim of this study is to analyze if enoxacin can exert anti-SARS-CoV-2 effects. We exploit multiple computational tools and databases to examine (i) whether the RNAi mechanism, as the target pathway of enoxacin, could act on the SARS-CoV-2 genome, and (ii) microRNAs induced by enoxacin might directly silence viral components as well as the host cell proteins mediating the viral entry and replication. We find that the RNA genome of SARS-CoV-2 might be a suitable substrate for DICER activity. We also highlight several enoxacin-enhanced microRNAs which could target SARS-CoV-2 components, pro-inflammatory cytokines, host cell components facilitating viral replication, and transcription factors enriched in lung stem cells, thereby promoting their differentiation and lung regeneration. Finally, our analyses identify several enoxacin-targeted regulatory modules that were critically associated with exacerbation of the SARS-CoV-2 infection. Overall, our analysis suggests that enoxacin could be a promising candidate for COVID-19 treatment through enhancing the RNAi pathway.

Enoxacin Exerts Anti-Tumor Effects Against Prostate Cancer Through Inducing Apoptosis.

BACKGROUND: Prostate cancer is the most commonly diagnosed cancer and second leading cause of cancer death in men. Enoxacin, a third-generation fluoroquinolone antibiotic, was found with anti-proliferative effects against many cancer types. This study was to further investigate its effects against prostate cancer and explore the underlying molecular mechanisms. METHODS: PC-3 cells were treated with Enoxacin at different concentrations. Tumor model was established by subcutaneously injecting PC-3 cells into nude mice. MTT assay was used to detect cell viability. ELISA assay, Annexin V/PI staining and TUNEL assay were used to detect apoptosis. RT-qPCR and western blot were used to detect the gene and protein expression, respectively. RESULTS: Our data showed that Enoxacin inhibited PC-3 cell proliferation and induced the apoptosis through up-regulating the expression of pro-apoptotic proteins, while down-regulating expression levels of anti-apoptotic proteins. Moreover, Enoxacin increased the gene and protein expression of the autophagy and endoplasmic reticulum stress markers. Treating tumor-bearing mice with Enoxacin significantly inhibited tumor growth in xenograft tumor model. CONCLUSION: Our results suggested that Enoxacin could be developed as a potential anti-tumor agent against prostate carcinoma.

Enoxacin Up-Regulates MicroRNA Biogenesis and Down-Regulates Cytotoxic CD8 T-Cell Function in Autoimmune Cholangitis.

BACKGROUND AND AIMS: Primary biliary cholangitis (PBC) is a prototypical organ-specific autoimmune disease that is mediated by autoreactive T-cell attack and destruction of cholangiocytes. Despite the clear role of autoimmunity in PBC, immune-directed therapies have failed to halt PBC, including biologic therapies effective in other autoimmune diseases. MicroRNA (miRNA) dysregulation is implicated in the pathogenesis (PBC). In the dominant-negative TGF-ß receptor type II (dnTGFßRII) mouse model of PBC, autoreactive CD8 T cells play a major pathogenic role and demonstrate a striking pattern of miRNA down-regulation. Enoxacin is a small molecule fluoroquinolone that enhances miRNA biogenesis, partly by stabilizing the interaction of transactivation response RNA-binding protein with Argonaute (Ago) 2. APPROACH AND RESULTS: We hypothesized that correcting aberrant T-cell miRNA expression with enoxacin in dnTGFßRII mice could modulate autoreactive T-cell function and prevent PBC. Here, we show that liver-infiltrating dnTGFßRII CD8 T cells have significantly decreased levels of the miRNA biogenesis molecules prolyl 4-hydroxylase subunit alpha 1 (P4HA1) and Ago2 along with significantly increased levels of granzyme B and perforin. Enoxacin treatment significantly up-regulated miRNAs in dnTGFßRII CD8 T cells and effectively treated autoimmune cholangitis in dnTGFßRII mice. Enoxacin treatment directly altered T cells both ex vivo and in vitro, resulting in altered memory subset numbers, decreased proliferation, and decreased interferon-γ production. Enoxacin significantly decreased CD8 T-cell expression of the transcription factor, Runx3, and significantly decreased perforin expression at both the mRNA and protein levels. CONCLUSIONS: Enoxacin increases miRNA expression in dnTGFßRII CD8 T cells, reduces CD8 T-cell pathogenicity, and effectively halted progression of autoimmune biliary disease. Targeting the miRNA pathway is a therapeutic approach to autoimmunity that corrects pathological miRNA abnormalities in autoreactive T cells.

1,8-Naphthyridine Derivatives: A Privileged Scaffold for Versatile Biological Activities.

1, 8- Naphthyridine nucleus belongs to significant nitrogen-containing heterocyclic compounds which has garnered the interest of researchers due to its versatile biological activities. It is known to be used as an antimicrobial, anti-psychotic, anti-depressant, anti-convulsant, anti- Alzheimer's, anti-cancer, analgesic, anti-inflammatory, antioxidant, anti-viral, anti-hypertensive, antimalarial, pesticides, anti-platelets, and CB2 receptor agonist, etc. The present review highlights the framework of biological properties of synthesized 1, 8-naphthyridine derivatives developed by various research groups across the globe.

Evolution of resistance to fluoroquinolones by dengue virus serotype 4 provides insight into mechanism of action and consequences for viral fitness.

Drugs against flaviviruses such as dengue (DENV) and Zika (ZIKV) virus are urgently needed. We previously demonstrated that three fluoroquinolones, ciprofloxacin, enoxacin, and difloxacin, suppress replication of six flaviviruses. To investigate the barrier to resistance and mechanism(s) of action of these drugs, DENV-4 was passaged in triplicate in HEK-293 cells in the presence or absence of each drug. Resistance to ciprofloxacin was detected by the seventh passage and to difloxacin by the tenth, whereas resistance to enoxacin did not occur within ten passages. Two putative resistance-conferring mutations were detected in the envelope gene of ciprofloxacin and difloxacin-resistant DENV-4. In the absence of ciprofloxacin, ciprofloxacin-resistant viruses sustained a significantly higher viral titer than control viruses in HEK-293 and HuH-7 cells and resistant viruses were more stable than control viruses at 37 °C. These results suggest that the mechanism of action of ciprofloxacin and difloxacin involves interference with virus binding or entry.

Fluoroquinolone Antibiotics Exhibit Low Antiviral Activity against SARS-CoV-2 and MERS-CoV.

Repurposing FDA-approved drugs that treat respiratory infections caused by coronaviruses, such as SARS-CoV-2 and MERS-CoV, could quickly provide much needed antiviral therapies. In the current study, the potency and cellular toxicity of four fluoroquinolones (enoxacin, ciprofloxacin, levofloxacin, and moxifloxacin) were assessed in Vero cells and A549 cells engineered to overexpress ACE2, the SARS-CoV-2 entry receptor. All four fluoroquinolones suppressed SARS-CoV-2 replication at high micromolar concentrations in both cell types, with enoxacin demonstrating the lowest effective concentration 50 value (EC50) of 126.4 µM in Vero cells. Enoxacin also suppressed the replication of MERS-CoV-2 in Vero cells at high micromolar concentrations. Cellular toxicity of levofloxacin was not found in either cell type. In Vero cells, minimal toxicity was observed following treatment with ≥37.5 µM enoxacin and 600 µM ciprofloxacin. Toxicity in both cell types was detected after moxifloxacin treatment of ≥300 µM. In summary, these results suggest that the ability of fluoroquinolones to suppress SARS-CoV-2 and MERS-CoV replication in cultured cells is limited.

Enoxacin induces oxidative metabolism and mitigates obesity by regulating adipose tissue miRNA expression.

MicroRNAs (miRNAs) have been implicated in oxidative metabolism and brown/beige adipocyte identity. Here, we tested whether widespread changes in miRNA expression promoted by treatment with the small-molecule enoxacin cause browning and prevent obesity. Enoxacin mitigated diet-induced obesity in mice, and this was associated with increased energy expenditure. Consistently, subcutaneous white and brown adipose tissues and skeletal muscle of enoxacin-treated mice had higher levels of markers associated with thermogenesis and oxidative metabolism. These effects were cell autonomous since they were recapitulated in vitro in murine and human cell models. In preadipocytes, enoxacin led to a reduction of miR-34a-5p expression and up-regulation of its target genes (e.g., Fgfr1, Klb, and Sirt1), thus increasing FGF21 signaling and promoting beige adipogenesis. Our data demonstrate that enoxacin counteracts obesity by promoting thermogenic signaling and inducing oxidative metabolism in adipose tissue and skeletal muscle in a mechanism that involves, at least in part, miRNA-mediated regulation.

Affordable automated phenotypic antibiotic susceptibility testing method based on a contactless conductometric sensor.

User-friendly phenotypic antibiotic susceptibility testing (AST) methods are urgently needed in many fields including clinical medicine, epidemiological studies and drug research. Herein, we report a convenient and cost-effective phenotypic AST method based on online monitoring bacterial growth with a developed 8-channel contactless conductometric sensor (CCS). Using E. coli and V. parahaemolyticus as microorganism models, as well as enoxacin, florfenicol, ampicillin, kanamycin and sulfadiazine as antibiotic probes. The minimum inhibitory concentration (MIC) determination was validated in comparison with standard broth microdilution (BMD) assay. The total essential agreements between the CCS AST assays and the reference BMD AST assays are 68.8-92.3%. The CCS has an approximate price of $9,000 (USD). Requiring neither chemical nor biotic auxiliary materials for the assay makes the cost of each sample < $1. The MICs obtained with the automated CCS AST assays are more precise than those obtained with the manual BMD. Moreover, in 72 percent of the counterpart, the MICs obtained with the CCS AST assays are higher than that obtained with the BMD AST assays. The proposed CCS AST method has advantages in affordability, accuracy, sensitivity and user-friendliness.

Old Drugs with New Tricks: Efficacy of Fluoroquinolones to Suppress Replication of Flaviviruses.

Repurposing FDA-approved compounds could provide the fastest route to alleviate the burden of disease caused by flaviviruses. In this study, three fluoroquinolones, enoxacin, difloxacin and ciprofloxacin, curtailed replication of flaviviruses Zika (ZIKV), dengue (DENV), Langat (LGTV) and Modoc (MODV) in HEK-293 cells at low micromolar concentrations. Time-of-addition assays suggested that enoxacin suppressed ZIKV replication at an intermediate step in the virus life cycle, whereas ciprofloxacin and difloxacin had a wider window of efficacy. A129 mice infected with 1 × 105 plaque-forming units (pfu) ZIKV FSS13025 (n = 20) or phosphate buffered saline (PBS) (n = 11) on day 0 and treated with enoxacin at 10 mg/kg or 15 mg/kg or diluent orally twice daily on days 1-5 did not differ in weight change or virus titer in serum or brain. However, mice treated with enoxacin showed a significant, five-fold decrease in ZIKV titer in testes relative to controls. Mice infected with 1 × 102 pfu ZIKV (n = 13) or PBS (n = 13) on day 0 and treated with 15 mg/kg oral enoxacin or diluent twice daily pre-treatment and days 1-5 post-treatment also did not differ in weight and viral load in the serum, brain, and liver, but mice treated with enoxacin showed a significant, 2.5-fold decrease in ZIKV titer in testes relative to controls. ZIKV can be sexually transmitted, so reduction of titer in the testes by enoxacin should be further investigated.

LZ-106, a potent lysosomotropic agent, causing TFEB-dependent cytoplasmic vacuolization.

Cytoplasmic vacuolization usually occurs in cells treated with different agents and substances. We found that LZ-106, an analog of enoxacin, is a potent lysosomotropic agent, contributing to the formation of cytoplasmic vacuoles in cells. Studies of LZ-106-induced vacuolization in H460 cells showed acid environment inside these vacuoles. Further study demonstrated that markers in the late endosomes and lysosomes, like LAMP1 and RAB7, on the surface of the vacuoles, implying that these vacuoles might derive from endosomes and/or lysosomes. By studying the fluorescence intensity of LZ-106, we discovered that LZ-106 tended to locate in acid organelles, and Bafilomycin A1, a V-ATPase inhibitor, was able to suppress its acid organelles localization. Also, we noticed that LZ-106 could induce lysosome stress, involving pH increment and lysosomal membrane damage. Moreover, the expression levels of some lysosome-related proteins, like LAMP1, EEA1, and Cathepsin B, were also altered upon LZ-106 treatment. At last, we confirmed LZ-106 can activate TFEB, a key regulator of lysosomes. Knockdown of TFEB could also reverse LZ-106's effect on vacuolization in H460 cells. Taken together, due to LZ-106's lysosomotropic properties, it is able to accumulate in the acid organelles and induce lysosomal dysfunction in H460 cells, leading to TFEB activation and the following cytoplasmic vacuolization.

RNAi-mediated control of CRISPR functions.

CRISPR-Cas9 has become a versatile tool for genome editing and regulation, and strategies to effectively control its activity have attracted much attention. RNAi, also a gene-regulating tool, is used as another mechanism by which eukaryotes resist the invasion of foreign genetic material. Methods: In this study, we analyzed the quantitative inhibition of the CRISPR system by using artificial miRNAs (amiRNAs) combined with the RNAi enhancer enoxacin to improve the targeting specificity of the CRISPR system. Furthermore, we examined the feasibility of improving the efficiency of gene editing and regulation by blocking the effects of natural intracellular miRNAs on sgRNAs. Results: amiRNAs targeting the sgRNA were used to control its expression, and the small molecule drug denoxacin was utilized to enhance this effect, especially in the presence of Cas9. amiRNA/enoxacin inhibited CRISPR-mediated gene editing and regulation both in vitro and in vivo and could tune sgRNA-targeting specificity. Furthermore, CRISPR efficiency was increased by blocking the effects of endogenous miRNAs. Conclusion: Our study provides an efficient molecular switch for conditional regulation of CRISPR activities in mammalian cells and also presents potentially useful approaches for solving current key issues of off-target effects and low targeting efficiency.

Enoxacin and Epigallocatechin Gallate (EGCG) Act Synergistically to Inhibit the Growth of Cervical Cancer Cells in Culture.

Cervical cancer is a major cause of death in females worldwide. While survival rates have historically improved, there remains a continuous need to identify novel molecules that are effective against this disease. Here, we show that enoxacin, a drug most commonly used to treat a broad array of bacterial infections, is able to inhibit growth of the cervical cancer cells. Furthermore, our data show that epigallocatechin gallate (EGCG), a plant bioactive compound abundant in green tea, and known for its antioxidant effects, similarly functions as an antiproliferative agent. Most importantly, we provide evidence that EGCG functions synergistically against cancer cell proliferation in combined treatment with enoxacin. These data collectively suggest that enoxacin and EGCG may be useful treatment options for cases of cervical cancer.

Pharmacological boost of DNA damage response and repair by enhanced biogenesis of DNA damage response RNAs.

A novel class of small non-coding RNAs called DNA damage response RNAs (DDRNAs) generated at DNA double-strand breaks (DSBs) in a DROSHA- and DICER-dependent manner has been shown to regulate the DNA damage response (DDR). Similar molecules were also reported to guide DNA repair. Here, we show that DDR activation and DNA repair can be pharmacologically boosted by acting on such non-coding RNAs. Cells treated with enoxacin, a compound previously demonstrated to augment DICER activity, show stronger DDR signalling and faster DNA repair upon exposure to ionizing radiations compared to vehicle-only treated cells. Enoxacin stimulates DDRNA production at chromosomal DSBs and at dysfunctional telomeres, which in turn promotes 53BP1 accumulation at damaged sites, therefore in a miRNA-independent manner. Increased 53BP1 occupancy at DNA lesions induced by enoxacin ultimately suppresses homologous recombination, channelling DNA repair towards faster and more accurate non-homologous end-joining, including in post-mitotic primary neurons. Notably, augmented DNA repair stimulated by enoxacin increases the survival also of cancer cells treated with chemotherapeutic agents.

Zika virus infection induces RNAi-mediated antiviral immunity in human neural progenitors and brain organoids.

The re-emergence of Zika virus (ZIKV) in the Western Hemisphere has resulted in global public health crisis since 2015. ZIKV preferentially infects and targets human neural progenitor cells (hNPCs) and causes fetal microcephaly upon maternal infection. hNPCs not only play critical roles during fetal brain development, but also persist in adult brain throughout life. Yet the mechanism of innate antiviral immunity in hNPCs remains largely unknown. Here, we show that ZIKV infection triggers the abundant production of virus-derived small interfering RNAs in hNPCs, but not in the more differentiated progenies or somatic cells. Ablation of key RNAi machinery components significantly enhances ZIKV replication in hNPCs. Furthermore, enoxacin, a broad-spectrum antibiotic that is known as an RNAi enhancer, exerts potent anti-ZIKV activity in hNPCs and other RNAi-competent cells. Strikingly, enoxacin treatment completely prevents ZIKV infection and circumvents ZIKV-induced microcephalic phenotypes in brain organoid models that recapitulate human fetal brain development. Our findings highlight the physiological importance of RNAi-mediated antiviral immunity during the early stage of human brain development, uncovering a novel strategy to combat human congenital viral infections through enhancing RNAi.

Apoptosis Induced by Ultraviolet A Exposure in the Presence of Enoxacin in HL-60 Cells.

BACKGROUND: The ultraviolet A (UVA) spectrum mainly includes the region associated with the phototoxicity of fluoroquinolone antimicrobial agents. This study investigated apoptosis induced with UVA light and enoxacin in HL-60 cells. MATERIALS AND METHODS: HL-60 cells were irradiated by UVA (1.1 mW/cm2) for 20 min in the presence or absence of enoxacin. The induction of apoptosis was investigated by analysing cell morphology, flow cytometry of annexin V-positive cells, DNA ladder formation, and caspase-3 activation. RESULTS: Significant induction of apoptosis, DNA fragmentation, and caspase-3 activation were observed in cells treated with both UVA and enoxacin. UVA-induced apoptosis was significantly suppressed when NaN3, a singlet oxygen scavenger, was present. CONCLUSION: Apoptosis was induced by the combination of UVA and enoxacin in HL-60 cells, and singlet oxygen appears to play an important role in photodynamically-induced apoptosis.