In K562 leukemia cells, camptothecin reduced proliferation with a reported 48-hour WST IC50 of 229.4 nM. FL118 was more potent in the parallel comparison. Unlike FL118, camptothecin did not suppress DDX5 expression at 125–500 nM over 24 hours, so the derivative’s DDX5 mechanism should not be assigned to camptothecin. [2]
Site-dependent Topo I break reclosure
Biochemical assay · Purified wheat germ Topo I; rat liver enzyme comparison; isolated end-labeled DNA fragments. [1]
Break enhancement and high-salt reclosure kinetics were compared as one mechanistic design. Sites with stronger enhancement generally reclosed more slowly. The assay supports slowing of reclosure, with site-dependent effects.
Literature-Reported Treatment Conditions
- Treatment concentration
- 2.5 μM CTT lactone
- Exposure duration
- 5 min preincubation at 22 °C; reclosure sampled 0.5–20 min after salt addition
- Method
- Purified enzyme/DNA assay with no-drug and untreated-fragment controls; SDS-stopped products analyzed by sequencing gels.
- Vehicle
- CTT stock in DMSO.
- Co-treatment
- None; CPT and comparator drugs were separate treatments.
- Reported limits
- Independent experimental replicate count not specified in the read methods; triplicate band scans are technical measurements, not biological n. Solvent-matching detail was not established.
Methods and source locations
Compound reported in the paper: Camptothecin; Compound label in the paper: CTT
Mechanistic evidence for camptothecin lactone in a purified system; no universal potency value or cellular exposure inference.
pp. 8522–8524 Materials and Methods; Table 1 p. 8526; Figures 1–4 pp. 8525–8530; Discussion pp. 8529–8531
Association of drug-enhanced breakage with slower break reclosure: Sequencing-gel densitometry; breakage relative to no-drug reaction; reclosure after 0.5 M NaCl addition. — Table 1A and footnotes, p. 8526; Figure 4 and Discussion pp. 8530–8531
Limits of the mechanistic inference: Initial decay used for stable complexes; low-signal time points included detection-limit estimates. — Figure 3 caption p. 8529; Discussion pp. 8529–8531
K562 proliferation after camptothecin
Cell-based study · Human CML-derived K562 cells. [2]
Camptothecin reduced WST proliferation over 48 h. FL118 was more potent in the same comparison; it was tested separately.
Literature-Reported Treatment Conditions
- Treatment concentration
- 15.6, 31.3, 62.5, 125, 250, 500 and 1000 nM.
- Exposure duration
- 48 h
- Method
- Separate CPT and FL118 exposure; WST readout in Figure 5A.
- Vehicle
- CPT solvent/final vehicle not specified in the relevant read methods.
- Co-treatment
- None; CPT and comparator drugs were separate treatments.
- Reported limits
- Methods 4.8 describes 1% or 10% FBS without uniquely assigning the Figure 5A condition; no serum-specific interpretation made. IC50 uncertainty not supplied with the reported value.
Methods and source locations
Compound reported in the paper: Camptothecin; Compound label in the paper: CPT
Cell-assay endpoint for this model and duration; 229.4 nM is an IC50, not an administered treatment dose.
Results 2.4; Figure 5A and caption; Methods 4.1, 4.3, 4.8, 4.11
Reduction of K562 proliferation relative to untreated cells at 48 h: WST assay; untreated cells normalized to 100%; reported fitted value printed in Figure 5A, not inferred from the curve. — Results 2.4; Figure 5A; Methods 4.8
DDX5 expression comparison distinguishes CPT from FL118
Cell-based study · Human K562 cells; DDX5 immunoblot with β-actin loading control. [2]
Under the tested 24-hour conditions, the authors observed suppression of DDX5 expression with FL118 but not with CPT. This negative result limits transfer of the derivative’s DDX5 mechanism to camptothecin.
Literature-Reported Treatment Conditions
- Treatment concentration
- 125, 250 and 500 nM CPT; parallel FL118 comparator at the same nominal concentrations.
- Exposure duration
- 24 h
- Method
- Immunoblot for DDX5 and β-actin; CPT and FL118 separate.
- Vehicle
- CPT solvent/final vehicle not specified in the relevant read methods.
- Co-treatment
- None; CPT and comparator drugs were separate treatments.
- Reported limits
- Serum condition for this specific panel is not uniquely assigned by general Methods 4.6 (1% or 10% FBS). No direct DDX5 binding or helicase assay for CPT is established by this experiment.
Methods and source locations
Compound reported in the paper: Camptothecin; Compound label in the paper: CPT
Condition-specific negative DDX5 finding; no claim that CPT can never affect DDX5 in other models or exposures.
Results 2.3; Figure 3A,C and caption; Methods 4.1, 4.3, 4.6, 4.11
DDX5 protein expression after 24 h: Immunoblot and relative expression analysis with β-actin and 0 nM controls. General reporting: mean ± SD, experiments at least three times; no exact effect sizes transcribed from bars. — Results 2.3; Figure 3C and caption; Methods 4.6, 4.11
