POLQ and DNA-PK inhibition in muscle-invasive bladder cancer : Enhancing radiosensitivity with novel DNA damage response inhibitors to improve radiotherapy outcomes.

BACKGROUND

Muscle-invasive bladder cancer (MIBC) includes histological subtypes such as urothelial carcinoma (UC) and the rarer, prognostically unfavorable, squamous cell carcinoma (SCC). Standard treatment is radical cystectomy, while alternatives like chemotherapy or radiotherapy are particularly limited in SCC. Radiosensitizers, such as DNA-dependent protein kinase (DNA-PK) and DNA polymerase theta (POLQ) inhibitors, could selectively enhance radiotherapy effects in tumor cells and represent promising approaches for clinical translation.

OBJECTIVE

This study analyzed the radiosensitizing effects of DNA-PK and POLQ inhibition ex vivo in patient-derived MIBC cell lines of UC and SCC subtypes.

MATERIALS AND

METHODS

The DNA-PK inhibitor AZD7648 (DNA-PKi) and the POLQ inhibitor ART558 (POLQi) were tested ex vivo in patient-derived SCC (p-SCC; n = 3) and UC (p-UC; n = 3) cell cultures. Effects were assessed in combination with ionizing radiation (IR) using XTT cell viability assays (IC50), clonogenic survival assays, γH2AX immunofluorescence, and comet assays.

RESULTS

DNA-PKi strongly radiosensitized MIBC cultures ex vivo, reducing IC50-XTT values by 74-99% and survival rates by 34-64%. Under POLQi +2 Gy, IC50 decreased by 7-13%, whereas under POLQi +8 Gy it increased by 11-24%, with only ~5% reduction in survival. DNA-PKi markedly delayed DNA repair (comet tail moments 38-40%, γH2AX foci increased 11.9-13.1-fold), while POLQi showed minimal effects (comet tail moments 22-33%, γH2AX foci increased 5.4-6.0-fold).

CONCLUSION

DNA-PKi radiosensitized MIBC cells more effectively than POLQi, particularly SCC. DNA damage response (DDR) inhibitors thus have therapeutic potential in MIBC, depending on the target protein and tumor subtype.