Radiation therapy is the main therapy chosen for localized pelvic cancers and two thirds of prostate cancer patients. Late radiation cystitis is an adverse event associated with this therapy. It appears in 5-10% of cases, presents with pain and hematuria and can be life threatening. Cellular senescence is a permanent state of cell cycle arrest which is a survival strategy in response to different triggers including telomere shortening with aging, DNA damage due to radiation therapy, or oxidative stress resulting in prevention of cell division and resistance to cell death. This state is not irreversible, and the fate of senescent cells and those around is largely dependent on the microenvironment created by the senescence-associated secretory phenotype (SASP), a variety of proinflammatory cytokines and chemokines released by senescent cells in response to increased NF-. The different paracrine activity of these SASPs determines whether there is continued decreased function as in aging, or cell survival and reemergence as in cancer [1]. Targeting senescent cells following radiotherapy may be a promising strategy to prevent tumor reemergence as well as late radiation cystitis. This can be done either by killing the senescent cells (senolitic agents) or inhibiting all or part of their characteristics (senomorphic agents). It has been demonstrated that cinaciguat can decrease Bcl-2 levels to promote BAX driven apoptotic clearance and decrease inflammation/NF--mediated cytokine release [2]. Thus, it may exhibit both senolitic and senomorphic actions. We have hypothesized that cinaciguat given following radiotherapy can prevent chronic radiation cystitis by reducing the number of senescent cells in the urothelial layer and tested this hypothesis using a mouse model.

For irradiation, mice were anesthetized with avertin (300 mg/kg IP) and placed in X-RAD320 irradiator in a supine position. The radiation beam was collimated to ensure that only the bladder area receives fractionated irradiation (2 Gy x 5 days). 3-4 weeks later, mice were implanted with ALZET osmotic pumps delivering 10 mg/kg/day cinaciguat for 2 weeks. At the conclusion of the treatment, bladder function was tested using cystometry and tissues were saved and processed for histology and p21 and beta-galactosidase (senescence markers) staining evaluation.

Fractionated irradiation induced chronic irradiation cystitis evident as soon as 5-6 weeks post irradiation. Bladders from irradiated mice showed voiding disfunction, decreased compliance, fibrosis and a dramatic increase in p21 and beta-galactosidase stained urothelial cells in comparison to non-irradiated controls. Cinaciguat treatment significantly improved bladder finction, increased the compliance, reversed fibrosis and decreased the number of p21 and beta-galactosidase positive cells in the urothelial layer.

Following irradiation, cenescent cells in the urothelium, releasing proinflammatory cytokines, may be responsible for recurrent inflammation and subsequent fibrosis. Cinaciguat decreased the number of senescent cells in irradiated bladders indicating that this may be the mechanism by which it prevents or reverses development of late radiation cystitis.

We have demonstrated that cinaciguat, a soluble guanylate cyclase activator, has senolitic/senomorphic properties, decreases the number of senescent cells in bladder tissues following irradiation and may be used as an adjuvant therapy to prevent late radiation cystitis.

Yosef R et al, P21 maintains senescent cell viability under persistent DNA damage response by restraining JNK and caspase signaling. EMBO J. 2017 Aug 1; 36(15): 2280–2295. PMID: 28607003
Zabbarova I et al, Benign prostatic hyperplasia/obstruction ameliorated using a soluble guanylate cyclase activator. J Pathol . 2022 Apr;256(4):442-454. PMID: 34936088