CellTiter-Glo Luminescent ATP Viability Dose-Response Assay for Doxorubicin Cytotoxicity in MCF-7 Breast Carcinoma Cells

Three independent biological replicates on separate days, each as one 96-well plate with technical triplicate wells per dose. Nine doxorubicin concentrations (10 µM to 1 nM, half-log dilutions) plus vehicle (medium + matched DMSO/water). Outer-perimeter wells filled with PBS (not cells) to mitigate edge evaporation; treatment doses randomized across interior wells to break confounding with plate position. Exposure duration 72 h. Cell-free medium-only wells and maximum-kill (no-cell or lysed) wells included per plate for normalization.

BSL-2 for human MCF-7 cells; biosafety cabinet for culture and dosing. Doxorubicin is a cytotoxic, mutagenic, and vesicant chemotherapeutic — handle as a hazardous drug in a fume hood/biosafety cabinet with double nitrile gloves, sleeve covers, and dedicated cytotoxic-waste containers; spill kit on hand. Staurosporine and digitonin are toxic. CellTiter-Glo reagent is an irritant. Doxorubicin is light-sensitive and stains surfaces red (useful for spill detection). All cytotoxic-drug waste segregated per institutional hazardous-pharmaceutical policy; biological waste bleach-treated or autoclaved.

Vehicle control (0 µM doxorubicin, matched DMSO) defines 100% viability. Medium-only (no cells) wells define luminescence background, subtracted from all wells. Maximum-kill positive control: 1 µM staurosporine or a digitonin/lysed well defines the 0% viability floor. Untreated growth-control wells confirm normal proliferation over 72 h. Edge-evaporation control: perimeter PBS wells protect interior wells. A no-reagent well confirms there is no spontaneous luminescence from medium components.

Vehicle wells should give the highest, consistent RLU (CV <10% across triplicates). The dose-response should be sigmoidal with a clear upper plateau near 100% at low doses and a lower plateau <10% at 10 µM, giving an IC50 around 0.1-1 µM at 72 h. Good data show a Hill slope near 1-2, R^2 >0.95 for the 4PL fit, low intra-plate edge gradient, and reproducible IC50 across the three biological replicates (within ~2-3 fold).

• MCF-7 human breast adenocarcinoma cell line, mycoplasma-tested
• DMEM/EMEM high-glucose, 10% FBS, 1% penicillin/streptomycin, 0.01 mg/mL human insulin
• Doxorubicin hydrochloride, 10 mM stock (in water/DMSO), working 1 nM-10 µM
• CellTiter-Glo 2.0 reagent (luciferase/luciferin ATP assay)
• White opaque-walled, clear-bottom 96-well tissue-culture plates
• 0.05% trypsin-EDTA
• PBS (Ca2+/Mg2+-free) for perimeter wells and washes
• DMSO vehicle (matched, <=0.1% final)
• Staurosporine 1 µM (positive cytotoxicity control)
• ATP standard (optional, for a standard curve / linearity check)

To quantify doxorubicin cytotoxicity in adherent MCF-7 cells by measuring cellular ATP content as a surrogate for viable cell number using the CellTiter-Glo assay. The protocol produces a normalized 9-point log-spaced dose-response curve and a four-parameter logistic IC50 with confidence intervals, controlling for edge effects, plate-position bias, and luminescence drift.

1. Trypsinize and count MCF-7; seed 3,000-5,000 cells/well in 100 µL into interior wells of a white clear-bottom plate; fill perimeter wells with 200 µL PBS.
2. Incubate 24 h (37 C, 5% CO2) to allow attachment.
3. Prepare a half-log doxorubicin dilution series (10 µM-1 nM) at 2x in medium; add 100 µL per well to reach final 1x; include vehicle and 1 µM staurosporine positive-kill wells.
4. Incubate 72 h at 37 C, 5% CO2.
5. Equilibrate plate and CellTiter-Glo 2.0 reagent to RT (~30 min); avoid temperature gradients that cause luminescence variance.
6. Add CellTiter-Glo reagent at 1:1 volume (100 µL) to each well.
7. Mix on an orbital shaker 2 min to lyse cells; incubate 10 min at RT in the dark to stabilize signal.
8. Read luminescence on a plate reader (integration 0.25-1 s/well, no filter).
9. Record raw RLU; include medium-only (background) and maximum-kill wells for normalization.

Independent variable: doxorubicin concentration (1 nM-10 µM, 9 doses). Dependent variable: luminescence (RLU), proportional to viable-cell ATP, normalized to percent viability. Controlled variables: seeding density, attachment time (24 h), exposure duration (72 h), DMSO concentration (matched across all wells), reagent and plate temperature at read, integration time, passage number, plate type (white/clear-bottom), and plate-position randomization. ATP linearity range is verified to ensure RLU tracks cell number.

We hypothesize that doxorubicin reduces MCF-7 viability in a sigmoidal dose-dependent manner with an IC50 in the approximate 0.1-1 µM range after 72 h of exposure, and that the curve reaches a clear lower plateau (<10% residual viability) at the highest dose (10 µM), confirming a full cytotoxic response window.

Raw RLU values are background-subtracted (medium-only mean) per plate. Percent viability is computed as (signal - max-kill mean) / (vehicle mean - max-kill mean) x 100, or simply normalized to vehicle if a max-kill floor is not used. Triplicate technical wells are averaged per dose per plate. Normalized percent viability is fit to a four-parameter logistic (4PL, variable-slope) model in GraphPad Prism or R (drc package) to derive IC50, Hill slope, and plateaus. Z'-factor is computed from vehicle vs max-kill wells to validate assay quality (target Z' >0.5).

1. High triplicate variability / edge effects: fill perimeter wells with PBS, equilibrate plate and reagent to RT, and randomize dose positions. 2. Low or no luminescence: confirm reagent is freshly thawed and not expired, ensure adequate lysis mixing, and verify the reader has no emission filter engaged. 3. Signal drift across the read: allow the full 10 min stabilization and read the whole plate within ~30 min. 4. Curve lacks a lower plateau: extend the top dose or exposure time; confirm the max-kill control truly reaches ~0%. 5. Non-monotonic or noisy curve: check seeding uniformity, exclude wells with visible meniscus/bubbles, and verify ATP signal is within the linear range via a cell-titration check.

IC50 values from the 4PL fit (n = 3 biological replicates) are reported as geometric mean with 95% CI. Curves across conditions (if comparing treatments) are compared by extra-sum-of-squares F-test on shared vs separate IC50 parameters at alpha = 0.05. Per-dose viability differences use two-way ANOVA (dose x replicate) with appropriate correction. Assay robustness is quantified by Z'-factor per plate. With triplicate wells and n = 3 plates, IC50 estimates are typically reproducible within a 2-3 fold window; power is sufficient to distinguish IC50 shifts >2-fold.