Review of Experimental Studies to Improve Radiotherapy Response in Bladder Cancer: Comments and Perspectives

Effects of combined radiotherapy with immune checkpoint blockade on immunological memory in luminal-like subtype murine bladder cancer model

MIBC is a highly lethal disease, and the patient survival rate has not improved significantly over the last decades. UPPL is a cell line that can be used to recapitulate the luminal-like molecular subtype of bladder cancer and to discover effective treatments to be translated in patients. Here, we investigate the effects of combinational treatments of radiotherapy and immunotherapy in this recently characterized UPPL tumor-bearing mice. We first characterized the baseline tumor microenvironment and the effect of radiation, anti-PD-L1, and combinatorial treatments. Then, the mice were re-challenged with a second tumor (rechallenged tumor) in the contralateral flank of the first tumor to assess the immunological memory. Radiation slowed down the tumor growth. All treatments also decreased the neutrophil population and increased the T cell population. Anti-PD-L1 therapy was not able to synergize with radiation to further delay tumor growth. Furthermore, none of the treatments were able to generate immune memory. The treatments were not sufficient to induce a significant and lasting pool of memory cells. We show here that anti-PD-L1 treatment added to radiotherapy was not enough to achieve T cell-mediated memory in UPPL tumors. Stronger T cell activation signals may be required to enhance radiation efficacy in luminal-like bladder cancer.

Small-Molecule Polθ Inhibitors Provide Safe and Effective Tumor Radiosensitization in Preclinical Models

PURPOSE

DNA polymerase theta (Polθ, encoded by the POLQ gene) is a DNA repair enzyme critical for microhomology mediated end joining (MMEJ). Polθ has limited expression in normal tissues but is frequently overexpressed in cancer cells and, therefore, represents an ideal target for tumor-specific radiosensitization. In this study we evaluate whether targeting Polθ with novel small-molecule inhibitors is a feasible strategy to improve the efficacy of radiotherapy.

EXPERIMENTAL DESIGN

We characterized the response to Polθ inhibition in combination with ionizing radiation in different cancer cell models in vitro and in vivo.

RESULTS

Here, we show that ART558 and ART899, two novel and specific allosteric inhibitors of the Polθ DNA polymerase domain, potently radiosensitize tumor cells, particularly when combined with fractionated radiation. Importantly, noncancerous cells were not radiosensitized by Polθ inhibition. Mechanistically, we show that the radiosensitization caused by Polθ inhibition is most effective in replicating cells and is due to impaired DNA damage repair. We also show that radiosensitization is still effective under hypoxia, suggesting that these inhibitors may help overcome hypoxia-induced radioresistance. In addition, we describe for the first time ART899 and characterize it as a potent and specific Polθ inhibitor with improved metabolic stability. In vivo, the combination of Polθ inhibition using ART899 with fractionated radiation is well tolerated and results in a significant reduction in tumor growth compared with radiation alone.

CONCLUSIONS

These results pave the way for future clinical trials of Polθ inhibitors in combination with radiotherapy.

Selective inhibition of HDAC6 promotes bladder cancer radiosensitization and mitigates the radiation-induced CXCL1 signalling

BACKGROUND

Although trimodality therapy resecting tumours followed by chemoradiotherapy is emerged for muscle-invasive bladder cancer (MIBC), chemotherapy produces toxicities. Histone deacetylase inhibitors have been identified as an effective strategy to enhance cancer radiotherapy (RT).

METHODS

We examined the role of HDAC6 and specific inhibition of HDAC6 on BC radiosensitivity by performing transcriptomic analysis and mechanism study.

RESULTS

HDAC6 knockdown or HDAC6 inhibitor (HDAC6i) tubacin exerted a radiosensitizing effect, including decreased clonogenic survival, increased H3K9ac and α-tubulin acetylation, and accumulated γH2AX, which are similar to the effect of panobinostat, a pan-HDACi, on irradiated BC cells. Transcriptomics of shHDAC6-transduced T24 under irradiation showed that shHDAC6 counteracted RT-induced mRNA expression of CXCL1, SERPINE1, SDC1 and SDC2, which are linked to cell migration, angiogenesis and metastasis. Moreover, tubacin significantly suppressed RT-induced CXCL1 and radiation-enhanced invasion/migration, whereas panobinostat elevated RT-induced CXCL1 expression and invasion/migration abilities. This phenotype was significantly abrogated by anti-CXCL1 antibody, indicating the key regulator of CXCL1 contributing to BC malignancy. Immunohistochemical evaluation of tumours from urothelial carcinoma patients supported the correlation between high CXCL1 expression and reduced survival.

CONCLUSION

Unlike pan-HDACi, the selective HDAC6i can enhance BC radiosensitization and effectively inhibit RT-induced oncogenic CXCL1-Snail-signalling, thus further advancing its therapeutic potential with RT.

Risk and prognosis of secondary malignant neoplasms after radiation therapy for bladder cancer: A large population-based cohort study

Objective

To investigate the association between radiotherapy and the risk of second malignant neoplasm (SMN) development among patients with bladder cancer (BC). Overall survival (OS) is compared among patients developing SMN and without.

Method

We identified patients diagnosed with BC from the Surveillance, Epidemiology, and End Results (SEER) database. The development of an SMN is defined as any SMN occurring more than 5 years after the diagnosis of BC. The Fine-Gray competing risk regression is used to estimate the probability of SMN. The radiotherapy-associated risk (RR) for SMNs is assessed by Poisson regression. The Kaplan–Meier method was used to evaluate the OS of patients with SMNs. Propensity score matching (PSM) is performed.

Results

A total of 76575 BC patients are enrolled in our study. The probability of SMNs in the radiotherapy cohort is statistically higher than in the non-radiotherapy cohort. In competing risk regression analysis, radiotherapy is proven to be associated with a higher risk of SMN (Hazard ratio: 1.23; 95% CI: 1.102–1.368). The radiotherapy-associated risks significantly increase in the radiotherapy cohort (RR: 1.28; 95% CI: 1.14–1.43). In site-specific analysis, statistically significant results are observed in lung and bronchus (LAB) cancer and hematological malignancies. The OS rate in patients developing SMN is significantly lower than that among matched patients with primary BC.

Conclusion

Radiotherapy for BC is associated with SMN. Radiotherapy increases the risk of secondary low-dose area cancer development, including LAB cancer or hematological malignancies. Notably, this effect is not observed in the high-dose area involving pelvic tumors. Patients developing SMN showed poorer OS.

Tyro3 Targeting as a Radiosensitizing Strategy in Bladder Cancer through Cell Cycle Dysregulation

Bladder cancer is a common cancer; it is the tenth most common cancer in the world. Around one fourth of all diagnosed patients have muscle-invasive bladder cancer (MIBC), characterized by advanced tumors and which remains a lethal disease. The standard treatment for MIBC is the bladder removal by surgery. However, bladder-preserving alternatives are emerging by combining chemotherapy, radiotherapy and minimal surgery, aiming to increase the patient’s quality of life. The aim of the study was to improve these treatments by investigating a novel approach where in addition to radiotherapy, a receptor, TYRO3, a member of TAM receptor tyrosine kinase family known to be highly expressed on the bladder cancer cells and involved in the control of cell survival is targeted. For this, we evaluated the influence of TYRO3 expression levels on a colony or cell survival assays, DNA damage, γH2AX foci formation, gene expression profiling and cell cycle regulation, after radiation on different bladder cell models. We found that TYRO3 expression impacts the radiation response via the cell cycle dysregulation with noeffets on the DNA repair. Therefore, targeting TYRO3 is a promising sensitization marker that could be clinically employed in future treatments.

Case report: Bladder preserving after maximal transurethral resection of the bladder tumor combined with chemotherapy and immunotherapy in recurrent muscle-invasive bladder cancer patients: A report of two cases

Background

Cisplatin-based neoadjuvant chemotherapy combined with radical cystectomy (RC) plus pelvic lymph node dissection (PLND) is the preferred treatment option for muscle-invasive bladder cancer (MIBC). However, some patients are unable to tolerate RC or may have postoperative complications after RC. And most patients have a strong desire for bladder-preserving treatment. There are no reports on the efficacy of maximal transurethral resection of the bladder tumor (TURBT) in combination with chemotherapy plus tislelizumab for bladder-preserving in recurrent MIBC patients.

Case presentation

We report two cases diagnosed with recurrent MIBC who achieved pathological complete response (pCR) and bladder-preserving after maximal TURBT combined with chemotherapy plus tislelizumab.

Conclusion

Postoperative immunotherapy should be considered for all patients with recurrent MIBC who are eligible for immunotherapy. In addition, high programmed death ligand-1 (PD-L1) expression, high tumor mutation burden (TMB), and TP53 mutation level can be combined to predict tislelizumab efficacy.

EZH2 targeting to improve the sensitivity of acquired radio-resistance bladder cancer cells

Among the many treatments for Bladder cancer (BCa) patients, radiotherapy is an effective way to preserve the bladder. However, as the frequency of irradiation increases, the tumor cells appear "acquired radio-resistance" (ARR) and loss the sensitivity to radiotherapy. To explore the molecular mechanism of ARR, two BCa cell lines, 5637 and T24, were enrolled here and their ARR counterparts, 5637R and T24R, were obtained by exposure to γ-ray of 2 Gy for 30 times. Compared to parental cells, ARR cells have significantly enhanced stem cell-like phenotype, robust DNA damage repair capabilities and elevated expression of zeste homolog 2 (EZH2). Decreasing EZH2 expression, both parental and ARR cells exhibited reduced abilities of forming microsphere and repairing DNA damage, but enhanced cells radio-sensitivity and intracellular autophagy compared to untreated cells. Down-regulation the expression of EZH2 induced an increasing of both LC3 and P62 in parental cells, while in ARR cells, only LC3 increased upon EZH2 reduction. On the other hand, UNC1999 treatment caused the increasing of LC3B and P62 in all cells, suggested that siEZH2 and UNC1999 affect ARR cells autophagy through different mechanisms. In vivo study showed that pre-treated with UNC1999 greatly enhanced T24R cells sensitivity to IR, and knocking down the expression of EZH2 significantly suppressed the tumor growth. Combined with bioinformatics data analysis, we speculate that EZH2 is an important biomolecule linking the diagnosis, radiotherapy and prognosis of BCa. EZH2 targeted therapy may be an effective way to overcome ARR of BCa, and is worthy of in-depth study.