The urinary bladder can develop radiation cystitis when exposed to ionizing radiation during treatment for pelvic malignancies.  The severity and timing at which symptoms develop are highly variable [1], thus, it is difficult to predict the susceptibility of radiation induced bladder dysfunction.  Furthermore, with increasing rates of cancer survivorship consequences of radiation injury are likely to become more pronounced.  We propose that an intravesical radioprotective agent could be used to mitigate collateral damage during treatment of non-bladder tumours.  This possibility was examined by subcutaneous implantation of TRAMPC-1 mouse prostate tumour cells in the lower abdomen of male C57Bl/6 mice.  Mice were subjected to fractionated X-ray irradiation to the tumour following a single bladder instillation with XJB-5-131, a nitroxide free radical scavenger that is conjugated to a hemi-gramicidin-S moiety [2] allowing enrichment in the mitochondria.  The aim was to evaluate if XJB-5-131 could protect the urinary bladder against acute radiation injury without hindering tumour shrinkage.

Ectopic tumour implantation and irradiation protocol.  TRAMPC-1 mouse tumour cells were obtained from ATCC and cultured as instructed.  Male adult C57Bl/6 mice (Envigo, 6 months old) were anesthetized with isoflurane and using sterile surgical methods, subcutaneous injections of TRAMPC-1 cells (1x106 cells in 100 µl) were made 3 to 5 mm bilaterally of the urinary bladder.  Two weeks following implantation, mice were anesthetized (300 mg/kg, 2,2,2-tribromoethanol) and subjected to fractionated irradiation [3] to one of the tumours (8 Gy/day/4 days, Fig 1A, red box denotes the irradiated field, black line indicates location of urinary bladder) using collimated X-ray irradiation (X-RAD320, Precision X-ray Inc.).  On the first day of treatment, mice had their bladders instilled with 1 µM XJB-5-131 (150 µl in saline) or vehicle just prior to irradiation.  There were no further instillations performed during subsequent irradiation events.

Voiding assessments.  Voiding activity was analysed by two-hour urine spot tests starting one week prior to implantation of tumour cells and performed weekly after fractionated radiation treatment commenced.

All mice survived the tumour implantation and radiation treatment up to the experimental endpoint of 14 days after irradiation.  There was significant shrinkage of irradiated tumours compared to those on the untreated side (Fig 1B).  Vehicle instilled mice showed increased urinary frequency and smaller void spots at 14 days after irradiation compared baseline (Fig 1D versus 1C). Instillation of XJB-5-131 prevented development of bladder overactivity/frequent voiding as there was no change from baseline voiding spot profiles (Fig 1E and 1F).  The average void spot areas were significantly smaller (Fig 1G) and greater in number (Fig 1H) in vehicle treated irradiated mice compared to XJB-5-131 treated cohort.

XJB-5-131 did not hinder radiation induced tumour shrinkage and protected against development of radiation cystitis.  The protective effect of XJB-5-131 persisted despite only being administered on the first day of radiation treatment.

This study demonstrates that intravesical radioprotectors may be used as a prophylactic agent against radiation cystitis during treatment of pelvic tumours in the vicinity of the urinary bladder.  This method may have utility in preventing development of the late-stage condition which in many cases manifest years after radiation exposure.

Helissey et al. Chronic Inflammation and Radiation-Induced Cystitis: Molecular Background and Therapeutic Perspectives. Cells, 10(1):21, 2021.
Krainz et al. A Mitochondrial-Targeted Nitroxide Is a Potent Inhibitor of Ferroptosis, ACS Cent. Sci. 2, 9, 653-659, 2016.
Wu et al. The Response of Prostate Cancer to Androgen Deprivation and Irradiation Due to Immune Modulation. Cancers (Basel), 11(1):20, 2019.

Continence 2S2 (2022) 100464
DOI: 10.1016/j.cont.2022.100464