RAD51 Is Implicated in DNA Damage, Chemoresistance and Immune Dysregulation in Solid Tumors

E2F8-CENPL pathway contributes to homologous recombination repair and chemoresistance in breast cancer

Chemoresistance poses a significant obstacle to the treatment of breast cancer patients. The increased capacity of DNA damage repair is one of the mechanisms underlying chemoresistance. Bioinformatic analyses showed that E2F8 was associated with cell cycle progression and homologous recombination (HR) repair of DNA double-strand breaks (DSBs) in breast cancer. E2F8 knockdown suppressed cell growth and attenuated HR repair. Accordingly, E2F8 knockdown sensitized cancer cells to Adriamycin and Cisplatin. Centromere protein L (CENPL) is a transcriptional target by E2F8. CENPL overexpression in E2F8-knockdowned cells recovered at least in part the effect of E2F8 on DNA damage repair and chemotherapy sensitivity. Consistently, CENPL knockdown impaired DNA damage repair and sensitized cancer cells to DNA-damaging drugs. These findings demonstrate that targeting E2F8-CENPL pathway is a potential approach to overcoming chemoresistance.

In vitro and in vivo induction of ochratoxin A exposure-related micronucleus formation in rat proximal tubular epithelial cells and expression profiling of chromosomal instability-related genes

Ochratoxin A (OTA) is a renal carcinogen in rats, and repeated administration induces karyomegaly in proximal tubular epithelial cells (PTECs) of the outer stripe of the outer medulla (OSOM) before inducing proliferative lesions. To investigate whether OTA induces micronuclei (MN) in PTECs, we performed an in vitro MN assay using rat renal NRK-52E PTECs after treatment for ≤21 days, and an in vivo OSOM MN assay in rats treated with OTA, other renal carcinogens, or non-carcinogenic renal toxicants for 4 or 13 weeks. The in vitro assay revealed an increased frequency of micronucleated cells from the acceptable dose level for cell viability, even after 21 days of treatment. The in vivo assay also revealed a dose- and treatment period-dependent increase in PTECs with γ-H2AX+ MN. OTA-specific gene expression profiling by OSOM RNA sequencing after week 13 revealed the altered expression of genes related to microtubule-kinetochore binding, the kinesin superfamily, centriole assembly, DNA damage repair, and cell cycle regulation. MN formation was also observed with other renal carcinogens that induce karyomegaly similarly to OTA. These results imply that γ-H2AX+ MN formation by OTA treatment is related to the induction of chromosomal instability accompanying karyomegaly formation before proliferative lesions form, providing a new insight into the carcinogenic mechanism that may be relevant to humans.

Rad51 and Systemic Inflammatory Indicators as Novel Prognostic Markers in Esophageal Squamous Cell Carcinoma

BACKGROUND

RAD51 is a central protein involved in homologous recombination, which has been linked to cancer development and progression. systemic inflammatory indicator markers such as neutrophil-to-lymphocyte ratio and lymphocyte-to-monocyte ratio have also been implicated in cancer. However, the relationship between Rad51 and these inflammatory markers in esophageal cancer patients undergoing esophagectomy is not yet understood.

METHODS

We retrospectively observed 320 esophageal cancer patients who underwent esophagectomy. We collected clinical characteristics, postoperative complications, and survival analysis data and analyzed the relationship between Rad51 expression, inflammatory markers, and prognosis.

RESULTS

We found significant linear relationships among the inflammatory markers. There were also close relationships between Rad51 expression and neutrophil-to-lymphocyte ratio or C-reactive protein. Patients with low lymphocyte percentage were more likely to have low Rad51 expression (P = .026), high C-reactive protein (P = .007), and high neutrophil-to-lymphocyte ratio (P = .006). Low lymphocyte-to-monocyte ratio was associated with poor overall survival and was an independent prognostic factor (HR = 2.214; 95% confidence interval: 1.044-4.695, P = .038). In patients without lymph node metastases, low albumin (HR= 0.131; 95% confidence interval: 0.025-0.687, P = .016), high neutrophil-to-lymphocyte ratio (HR = 0.002; 95% confidence interval: 0.000-0.221, P = .009), and high Rad51 expression (HR = 14.394; 95% confidence interval: 2.217-97.402, P = .006) were associated with poor overall survival.

CONCLUSIONS

Our study found a close correlation between elevated Rad51 expression and inflammatory markers. High Rad51 expression, high neutrophil-to-lymphocyte ratio, and low lymphocyte-to-monocyte ratio are associated with lower survival rates. The combined assessment of Rad51 and inflammatory markers can be useful for preoperative assessment and prognostic evaluation in esophageal squamous cell carcinoma patients.

Mechanistic study of dual-function inhibitors targeting topoisomerase II and Rad51-mediated DNA repair pathway against castration-resistant prostate cancer

BACKGROUND

Castration-resistant prostate cancer (CRPC) is refractory to hormone treatment and the therapeutic options are continuously advancing. This study aims to discover the anti-CRPC effects and underlying mechanisms of small-molecule compounds targeting topoisomerase (TOP) II and cellular components of DNA damage repair.

METHODS

Cell proliferation was determined in CRPC PC-3 and DU-145 cells using anchorage-dependent colony formation, sulforhodamine B assay and flow cytometric analysis of CFSE staining. Flow cytometric analyses of propidium iodide staining and JC-1 staining were used to examine the population of cell-cycle phases and mitochondrial membrane potential, respectively. Nuclear extraction was performed to detect the nuclear localization of cellular components in DNA repair pathways. Protein expressions were determined using Western blot analysis.

RESULTS

A series of azathioxanthone-based derivatives were synthesized and examined for bioactivities in which WC-A13, WC-A14, WC-A15, and WC-A16 displayed potent anti-CRPC activities in both PC-3 and DU-145 cell models. These WC-A compounds selectively downregulated both TOP IIα and TOP IIβ but not TOP I protein expression. WC-A13, WC-A14, and WC-A15 were more potent than WC-A16 on TOP II inhibition, mitochondrial dysfunction, and induction of caspase cascades indicating the key role of amine-containing side chain of the compounds in determining anti-CRPC activities. Furthermore, WC-A compounds induced an increase of γH2AX and activated ATR-Chk1 and ATM-Chk2 signaling pathways. P21 protein expression was also upregulated by WC-A compounds in which WC-A16 showed the least activity. Notably, WC-A compounds exhibited different regulation on Rad51, a major protein in homologous recombination of DNA in double-stranded break repair. WC-A13, WC-A14, and WC-A15 inhibited, whereas WC-A16 induced, the nuclear translocation of Rad51.

CONCLUSION

The data suggest that WC-A compounds exhibit anti-CRPC effects through the inhibition of TOP II activities, leading to mitochondrial stress-involved caspase activation and apoptosis. Moreover, WC-A13, WC-A14, and WC-A15 but not WC-A16 display inhibitory activities of Rad51-mediated DNA repair pathway which may increase apoptotic effect of CRPC cells.

Quantifying the impact of immunotherapy on RNA dynamics in cancer

BACKGROUND

Checkpoint inhibitor (CPI) immunotherapies have provided durable clinical responses across a range of solid tumor types for some patients with cancer. Nonetheless, response rates to CPI vary greatly between cancer types. Resolving intratumor transcriptomic changes induced by CPI may improve our understanding of the mechanisms of sensitivity and resistance.

METHODS

We assembled a cohort of longitudinal pre-therapy and on-therapy samples from 174 patients treated with CPI across six cancer types by leveraging transcriptomic sequencing data from five studies.

RESULTS

Meta-analyses of published RNA markers revealed an on-therapy pattern of immune reinvigoration in patients with breast cancer, which was not discernible pre-therapy, providing biological insight into the impact of CPI on the breast cancer immune microenvironment. We identified 98 breast cancer-specific correlates of CPI response, including 13 genes which are known IO targets, such as toll-like receptors TLR1, TLR4, and TLR8, that could hold potential as combination targets for patients with breast cancer receiving CPI treatment. Furthermore, we demonstrate that a subset of response genes identified in breast cancer are already highly expressed pre-therapy in melanoma, and additionally we establish divergent RNA dynamics between breast cancer and melanoma following CPI treatment, which may suggest distinct immune microenvironments between the two cancer types.

CONCLUSIONS

Overall, delineating longitudinal RNA dynamics following CPI therapy sheds light on the mechanisms underlying diverging response trajectories, and identifies putative targets for combination therapy.