Fig 2: A2 targets MAD2L1 to activate the cGAS‐STING pathway. A) Effect of A2 on aneuploidy formation in T24 and UMUC‐3 cells. B) Representative images showing cGAS subcellular distribution and micronuclei formation (indicated by arrows) in T24 and UMUC‐3 cells treated with 0.064 µm A2 for 48 h. Red: cGAS, green: PicoGreen (DNA stain), Scale bar = 20 µm. C) Quantification of cytosolic DNA in T24 and UMUC‐3 cells treated with 0.32 µm A2 for 48 h (n = 3). D) Western blot analysis of cGAS‐STING pathway protein expression in T24 and UMUC‐3 cells treated with different concentrations of A2 for 48 h. E) Western blot analysis of cGAS‐STING pathway protein expression in MAD2L1‐OE and control cells treated with different concentrations of A2 for 48 h. F) Western blot analysis of cGAS‐STING pathway protein expression in MAD2L1‐KD and control cells treated with different concentrations of A2 for 48 h. G) Apoptotic effects in T24 and UMUC‐3 cells treated with 1.6 µm A2 after STING inhibitor H151‐mediated blockade of the cGAS‐STING pathway. Data are presented as mean ± SD. ****P < 0.0001. Statistical significance was determined by a two‐tailed Student's t‐test (C).

Fig 3: Cytotoxicity of LZU‐WZLYCS01 against BC cells and PDOs, and validation of the bystander effect. A) Cell viability of WT and FGFR3‐KO T24 and UMUC‐3 cells treated with different concentrations of LZU‐WZLYCS01, A2, or FGFR3 antibody for 72 h. B) Apoptotic effects in WT and FGFR3‐KO T24 and UMUC‐3 cells treated with different concentrations of LZU‐WZLYCS01 for 48 h (n = 3). C) Colony formation capacity of T24 and UMUC‐3 cells treated with LZU‐WZLYCS01 for 48 h. D) Schematic diagram of the co‐culture model for assessing the bystander effects. E) Effect of LZU‐WZLYCS01 on the viability of FGFR3‐KO T24 and UMUC‐3 cells in the co‐culture system (n = 3). F) Representative bright‐field and AM/PI‐stained images showing LZU‐WZLYCS01‐induced cytotoxicity in PDOs. Green: viable cells, red: dead cells, scale bar = 50 µm. G) Representative H&E staining of PDOs and matched parental tumor tissues. Scale bar = 25 µm. H) Representative IHC staining of UPK2, FGFR3, and MAD2L1 in PDOs. Scale bar = 25 µm. Data are presented as mean ± SD. *P < 0.05, **P < 0.01, ****P < 0.0001. Statistical significance was determined by two‐way ANOVA followed by Tukey's multiple comparison test (B) and a two‐tailed Student's t‐test (E).

Fig 4: A2 specifically binds to the Lys73 site of MAD2L1. A) Molecular docking simulation of the interaction between A2 and MAD2L1. B) Western blot validation of MAD2L1 expression levels in control, MAD2L1‐KD, and mutant T24 cells. C) Western blot analysis of MAD2L1 expression in pull‐down products from each group. D–F CETSA evaluating the binding of A2 to MAD2L1 in MAD2L1‐KD T24 cells reconstituted with MAD2L1 WT (D), MAD2L1V55A+I62A+V69A (E), and MAD2L1K73A (F) (n = 3). Data are presented as mean ± SD.

Fig 5: A2 induces apoptosis in BC cells by targeting MAD2L1. A) Reaction scheme for biotinylation at the 20th hydroxyl group of A2. B) Overview of differentially expressed proteins identified by MS. C) Top 10 proteins ranked by the A2‐biotin/biotin abundance ratio. D) Western blot analysis of MAD2L1 expression in pull‐down products. E) Western blot detection of soluble MAD2L1 in T24 cells treated with A2 at different temperatures (n = 3). F) SPR analysis of A2‐MAD2L1 binding kinetics and KD value. G) Representative immunofluorescence images showing co‐localization of A2‐biotin and MAD2L1 in T24 cells after 3 h of A2‐biotin treatment. Red: Anti‐MAD2L1, green: A2‐biotin, blue: DAPI, scale bar = 20 µm. H) Western blot analysis of MAD2L1 expression in T24 and UMUC‐3 cells treated with different concentrations of A2 for 24 h. I) Western blot validation of MAD2L1 OE in T24 and UMUC‐3 cells. J) Western blot validation of MAD2L1 KD in T24 and UMUC‐3 cells. K) Colony formation capacity of MAD2L1‐OE and control cells treated with different concentrations of A2 for 48 h. L) Apoptotic effects in MAD2L1‐OE and control cells treated with different concentrations of A2 for 48 h. (n = 3). M) Apoptotic effects in MAD2L1‐KD and control cells treated with different concentrations of A2 for 48 h (n = 3). Data are presented as mean ± SD. ****P < 0.0001. Statistical significance was determined by two‐way ANOVA followed by Tukey's multiple comparison test (L,M).