2.11. Preparation of CM

5637 and T24 cells were seeded in 6‐well plates with RPMI‐1640 medium supplemented with 10% FBS. When cells reached confluence, they were washed with 1× PBS and cultured in serum‐free medium (1 ml/well). After an incubation for 4–6 h, the supernatant was replaced with fresh RPMI‐1640 medium containing 25% FBS and the STAT3 inhibitor Stattic (2 or 2.5 μM; #9983‐44‐9, MedChemExpress, NJ, USA). After 24 h, the medium was replaced with fresh RPMI‐1640 medium containing 10% FBS, and then the supernatant was collected after 24 h. After the cells were cultured with recombinant human IL8 (1 × 10⁻⁴ g/L; Peprotech, CI6217, Princeton Business Park, NJ, USA) and human antibody IL8 (5×10⁻⁴ g/L; Biotechne, MAB208‐SP, Minneapolis, MN, USA) for 24 h separately, they were switched to fresh RPMI‐1640 medium containing 10% FBS, and the supernatant was collected after 24 h.