Ciprofloxacin Potentiates RSL3-Induced Ferroptosis via Mitochondrial Zinc Accumulation

Study Background and Research Question

Regulated cell death modalities, including apoptosis, pyroptosis, necroptosis, and ferroptosis, have become focal points in the development of innovative cancer therapies. Ferroptosis, characterized by iron-dependent lipid peroxidation, offers unique opportunities for targeting therapy-resistant malignancies. Ciprofloxacin (CFX), a fluoroquinolone antibiotic, has previously been implicated in modulating cell death pathways, but its context-dependent effects on ferroptosis remain incompletely understood. The reference study (Hu Tang et al., J. Biol. Chem. 2025) addresses the critical question of how CFX influences ferroptosis induced by distinct small-molecule triggers — specifically, its effect on RSL3-induced ferroptosis and the underpinning molecular mechanisms.

Key Innovation from the Reference Study

The central innovation of this work lies in the discovery that CFX, despite previously being shown to inhibit erastin-induced ferroptosis via stabilization of glutathione peroxidase 4 (GPX4), exhibits the opposite effect when combined with RSL3. Here, CFX enhances RSL3-induced ferroptosis in cancer cells by promoting mitochondrial Zn²⁺ accumulation. This potentiation is mediated through a signaling cascade involving topoisomerase 2β inhibition, mitochondrial DNA stress, and activation of the STING1–CAV2 pathway, ultimately leading to disruption of zinc homeostasis and mitochondrial reactive oxygen species (ROS) overload. This duality underscores the importance of context in ferroptosis modulation and opens avenues for targeted manipulation of regulated cell death in cancer therapy (Hu Tang et al., 2025).

Methods and Experimental Design Insights

The authors employed a systematic antibiotic screening approach in various cancer cell lines to identify agents that synergize with ferroptosis inducers. Using viability assays, mitochondrial ROS detection, and zinc-specific probes, they dissected the molecular sequence from CFX exposure to the enhancement of RSL3-induced ferroptosis. Key methodologies included:

• Pharmacological Treatments: Cancer cells were exposed to low-dose CFX with or without RSL3, a GPX4 inhibitor known to trigger ferroptosis.
• Viability and Cell Death Assays: Quantitative measurement of cell viability and death following drug treatments, likely employing ATP-based luminescent methods for high sensitivity.
• Mitochondrial Stress and Zinc Accumulation: Live-cell fluorescence imaging and atomic absorption were used to assess mitochondrial DNA stress and the subcellular distribution of Zn²⁺.
• Pathway Dissection: RNA interference and pharmacological inhibitors were leveraged to probe the involvement of topoisomerase 2β, STING1, CAV2, and mitochondrial zinc transporters.

This multi-pronged approach enabled the authors to map the signaling events from CFX/topoisomerase inhibition to mitochondrial dysfunction and ferroptotic cell death.

Protocol Parameters

• assay | ATP-based luminescent viability assay | 10–30,000 cells/well (linear detection range) | applicability: cell viability measurement in low- to high-density formats | rationale: optimal for detecting viability shifts during ferroptosis and cytotoxicity studies | source_type: product_spec | source_link: https://www.apexbt.com/luminescent-atp-cell-viability-assay-kit-i.html
• assay | CFX concentration | 1–10 μM (as used in in vitro synergy screens) | applicability: cancer cell ferroptosis modulation | rationale: effective for observing synergistic effects with RSL3 | source_type: paper | source_link: https://doi.org/10.1016/j.jbc.2025.110653
• assay | Ferroptosis induction (RSL3) | 0.1–2 μM | applicability: GPX4-targeted ferroptosis models | rationale: standard concentration range for robust cell death induction | source_type: paper | source_link: https://doi.org/10.1016/j.jbc.2025.110653
• assay | Mitochondrial Zn²⁺ detection | live-cell fluorometric Zn²⁺ probes | applicability: mechanistic studies of metal ion homeostasis | rationale: quantifies mitochondrial zinc accumulation during ferroptosis | source_type: paper | source_link: https://doi.org/10.1016/j.jbc.2025.110653
• assay | Cell viability assay incubation time | 10–30 min post-reagent addition | applicability: rapid detection in kinetic cell death assays | rationale: enables time-resolved measurement of acute cytotoxicity | source_type: product_spec | source_link: https://www.apexbt.com/luminescent-atp-cell-viability-assay-kit-i.html

Core Findings and Why They Matter

The study's pivotal findings can be summarized as follows:

• CFX alone does not induce ferroptosis but markedly enhances RSL3-induced cell death in a dose-dependent manner.
• This potentiation is not observed with erastin, establishing a stimulus-selective effect.
• Mechanistically, CFX inhibits topoisomerase 2β, causing mitochondrial DNA stress, which activates the STING1–CAV2 signaling pathway.
• STING1–CAV2 activation leads to intracellular zinc redistribution and accumulation of Zn²⁺ in mitochondria via SLC25A25, driving excessive mitochondrial ROS and amplifying ferroptosis (Hu Tang et al., 2025).
• This dual role of CFX — suppressing erastin-induced ferroptosis but enhancing RSL3-triggered ferroptosis — demonstrates that drug effects on cell death are highly context and pathway dependent.

These insights highlight the therapeutic potential of manipulating zinc homeostasis and STING1–CAV2 signaling as adjuncts to ferroptosis-based cancer treatments. The data also caution that antibiotic use in cancer patients may have unanticipated consequences on cell death responses, depending on the microenvironment and molecular context.

Comparison with Existing Internal Articles

Recent thought-leadership articles, such as "Redefining Cell Viability Measurement: Mechanistic Insight" and "Integrating Mechanistic Insight and High-Sensitivity Tool", have contextualized the importance of high-sensitivity cell viability measurement in the study of regulated cell death modalities, including ferroptosis. These resources underscore how ATP-based luminescent detection, such as that provided by luciferase-based assays, enables precise resolution of cell health changes during drug perturbation and mechanistic dissection. The current reference study exemplifies this approach, as subtle cell viability shifts during CFX and RSL3 co-treatment would be most accurately captured by quantitative assays with a broad dynamic range and rapid readout. Notably, these internal articles also discuss the evolving landscape of cell metabolism and cytotoxicity assays, reinforcing the necessity for robust and scalable platforms in translational research workflows.

Limitations and Transferability

While the study provides compelling mechanistic evidence for the CFX–RSL3–zinc axis in cultured cancer cell models, several limitations should be considered:

• The findings are currently restricted to in vitro systems; the relevance of mitochondrial zinc accumulation to ferroptosis in vivo remains to be validated.
• The study focuses on cancer cell lines, and transferability to non-malignant cells or diverse tumor types requires further investigation.
• Potential off-target effects of CFX or pathway-specific compensatory mechanisms in complex biological contexts may limit direct translation.

Nevertheless, the mechanistic framework established here is likely to inform future studies in ferroptosis regulation and therapeutic design.

Research Support Resources

High-sensitivity, rapid cell viability measurement is critical for dissecting regulated cell death mechanisms such as ferroptosis and for validating small-molecule effects in high-throughput screens. The Luminescent ATP Cell Viability Assay Kit I (SKU K2041) from APExBIO offers a robust, luciferase luminescence detection platform optimized for quantitative cell viability, cytotoxicity, and cell metabolism assays [source_type: product_spec | source_link: https://www.apexbt.com/luminescent-atp-cell-viability-assay-kit-i.html]. Researchers aiming to replicate or extend the findings of context-dependent ferroptosis modulation can leverage this tool to achieve ultra-sensitive and reproducible results in diverse experimental systems.