Dissolving erythromycin: Dissolve the erythromycin compound in an appropriate solvent. Common solvents include DMSO (for water-insoluble compounds) or sterile water. Ensure that the concentration in the solution is appropriate for the subsequent MTT assay. Generally, using a smaller volume of solvent for dissolution allows for easier concentration control.

Filter sterilization: If the solution is to be used in a cell-based assay, it is recommended to filter sterilize it after dissolution, typically using a 0.22 µm filter, to ensure that the solution is sterile and suitable for addition to cell culture.

Dilution and concentration: Dilute the erythromycin solution using cell culture medium or PBS to achieve an appropriate concentration range. For the MTT assay, it is recommended to prepare different concentration gradients to evaluate their effects on cell viability.

MTT assay: Add different concentrations of erythromycin solution to MCF-7 cell culture and incubate for a period of time (usually 24-48 hours). Then follow the standard MTT assay procedure, add MTT solution, incubate for a period of time to dissolve the formed formazan, and read the OD value on a microplate reader (usually at 570 nm wavelength).

Data analysis: Calculate cell viability based on OD value, and draw a concentration-viability curve to determine the cytotoxic effect of erythromycin.