Table 1 Summary of Growth Rate Metrics (GR, NDR, and NOGR)
Metric | Assay Technology | Readouts | Controls | Interpretation | Compatibility with Fast/Slow Growing Organoids |
|---|---|---|---|---|---|
GR (Growth Rate Inhibition) | Brightfield and fluorescence imaging | Total Brightfield Organoid Area Total Fluorescence Area (cell death marker) Optional: Label-free Death Organoid Classification | Negative: Vehicle-treated control Positive: None used in GR calculation | > 1, proliferative effect; = 1, normal growth as in vehicle control; = 0, complete growth inhibition; = −1, complete killing as in positive control. | Less accurate for fast-growing organoids as it can underestimate cytotoxicity (GR < 0) due to the lack of a positive control normalisation. |
NDR (Normalised Drug Response) | Brightfield and fluorescence imaging | Total Brightfield Organoid Area Total Fluorescence Area (cell death marker) Optional: Label-free Death Organoid Classification | Negative: Vehicle-treated control Positive: Full cytotoxicity control (e.g., staurosporine) | > 1, proliferative effect; = 1, normal growth as in vehicle control; = 0, complete growth inhibition; = −1, complete killing as in positive control. | Less accurate for fast-growing organoids as it can underestimate the cytostatic effect (1 > NDR > 0) due to its logarithmic fit. Less accurate for slow-growing organoids as it can overestimate cytotoxicity (NDR < 0) at lower growth rates. |
NOGR (Normalized Organoid Growth Rate | Brightfield and fluorescence imaging | Total Brightfield Organoid Area Total Fluorescence Area (cell death marker) Optional: Label-free Death Organoid Classification | Negative: Vehicle-treated control Positive: Full cytotoxicity control (e.g., staurosporine) | > 1, proliferative effect; = 1, normal growth as in vehicle control; = 0, complete growth inhibition; = −1, complete killing as in positive control. | Accurate for both fast and slow-growing organoids, overcoming limitations in GR and NDR. |
