*4.2. Proliferation Assay with Cell Counting Kit-8*

Cell proliferation was measured using a Cell Counting Kit-8 (CCK-8) (Enzo Life Sciences, Farmingdale, NY, USA) as described in the supplier's protocol. Cells were seeded into 96-well plates (1 × <sup>10</sup>**<sup>4</sup>** cells/well) and pre-treated with GTX (5 μM) for 8 h and then treated with PTX (100 nM) for an additional 48 h. For comparison, non-treated control cells were cultured with media in the presence of DMSO. After drug treatment, the cells were stained with 10 μL of CCK-8 dye in 90 μL of culture medium for 2 h at 37 ◦C. The absorbance was measured at 450 nm.

#### *4.3. Analysis of Apoptosis by Flow Cytometry*

The percentages of cells undergoing apoptosis were measured by flow cytometry with fluorescein isothiocyanate (FITC)-labeled annexin-V (BD Biosciences, San Diego, CA, USA) and 7-amino actinomycin D (7-AAD) (BD Biosciences). The cells were suspended in 100 μL of 1× annexin-V binding buffer; then, FITC-conjugated annexin-V (3 μL) and 7-AAD (3 μL) were added to the suspensions, and the cells were kept at room temperature for 15 min in the dark. The stained cells were monitored with a BD Accuri**TM** C6 (BD Biosciences).
