Background The homologous recombination (HR) pathway is involved in DNA damage response (DDR), which is crucial to cancer cell survival after treatment with DNA damage agents. O6-methylguanine DNA methyltransferase (MGMT) is associated with cisplatin (CDDP) resistance in cancer cells; however, the underlying mechanisms remain unclear. Here, we explored the interactions between MGMT and the HR pathway in CDDP-activated DDR and their clinical implications in nasopharyngeal carcinoma (NPC). Methods Human NPC cells were assessed using loss-of-function approaches in vitro. The expression correlations between MGMT and major proteins of the HR pathway were analyzed through Western blotting, quantitative real-time PCR, and bioinformatic analysis by using a public database. The physical interactions between MGMT and HR proteins were studied using co-immunoprecipitation and immunofluorescence analyses. Cell comet tails and γ-H2AX expression levels were examined to evaluate double-strand break (DSB) formation. Established immunofluorescence and reporter analyses were conducted to measure HR activity. Xenograft and cell viability studies were used to assess the therapeutic potential of MGMT inhibition in combination with CDDP and poly(ADP-ribose) polymerase (PARP) inhibitor, respectively. Results Among major proteins of the HR pathway, MGMT suppression inhibited CDDP-induced RAD51 expression. Bioinformatic analyses showed a positive correlation between MGMT and RAD51 expression in patients with NPC. Moreover, MGMT physically interacted with BRCA1 and regulated CDDP-induced BRCA1 phosphorylation (ser 988). In functional assays, MGMT inhibition increased CDDP-induced DSB formation through attenuation of HR activity. NPC xenograft studies demonstrated that MGMT inhibition combined with CDDP treatment reduced tumor size and downregulated RAD51 expression and BRCA1 phosphorylation. Furthermore, MGMT suppression increased PARP inhibitor–induced cell death and DSB formation in NPC cells. Conclusion MGMT is crucial in the activation of the HR pathway and regulates DDR in NPC cells treated with CDDP and PARP inhibitor. Thus, MGMT is a promising therapeutic target for cancer treatments involving HR-associated DDR.
Objectives Adjuvant radiotherapy is the standard of care in locally advanced head and neck cancers. The radiation field is correlated with the surgical field in the adjuvant radiotherapy setting; therefore, tailoring the irradiation field is reasonable. Materials and methods We retrospectively analyzed patients with oral cavity and oropharyngeal cancers included in the cancer registry between 2015 and 2019 in the study hospital. Patients who underwent whole-neck irradiation (WNI) were compared with those who underwent lower-neck–sparing (LNS) irradiation. Results A total of 167 patients with oral cavity and oropharyngeal cancers were included in the study. Cancer recurrence was recorded in 33% of the patients. The rate of recurrence of oral cavity and oropharyngeal cancer at neck level IV was 8%. The 2-year incidence of level IV recurrence was lower in the WNI group than in the LNS group (2% vs. 10%; p = 0.04). The 2-year disease-free survival rates were 75% and 63% in the WNI and LNS groups, respectively (p = 0.08). Conclusion The rate of level IV recurrence was higher in the LNS group than in the WNI group. Trends of improvement in disease-free survival with lower-neck irradiation suggested that it is premature to consider LNS irradiation as daily practice in patients with oral cavity and oropharyngeal cancer.
The incidence of nasopharyngeal carcinoma (NPC) in Southeast Asia and Taiwan is high due to epidemiological factors. Cisplatin-based chemoradiotherapy is an important treatment strategy with excellent outcomes for patients with NPC. However, the outcomes for patients who are refractory to cisplatin-based therapy are poor. Methods for risk stratification of patients with NPC undergoing cisplatin-based chemoradiotherapy require to be investigated. A previous study indicated that ubiquitin-conjugating enzyme E2 B (UBE2B) was able to regulate alkylating drug sensitivity in NPC cells. In the present study, the clinical significance of UBE2B expression in patients with NPC was analyzed. Analysis of the two available NPC datasets containing the UBE2B expression profile (GSE12452 and GSE68799) was performed to evaluate the UBE2B expression levels in NPC tissues compared with nasopharyngeal mucosal epithelial tissues. Furthermore, immunohistochemical staining was performed using anti-UBE2B antibodies on samples from 124 patients with NPC who underwent cisplatin-based chemoradiotherapy. Disease-specific survival (DSS), distant metastatic-free survival (DMeFS) and local recurrence-free survival (LRFS) of patients with high and low UBE2B expression was analyzed. Furthermore, the associations between UBE2B expression and the biological behavior of NPC cells were investigated in vitro. Using public NPC datasets and in vitro studies, it was identified that UBE2B expression levels were increased in NPC tumor tissues compared with those in mucosal epithelial tissues. The cell proliferation ability was decreased in UBE2B-deficient NPC cells as compared with that in UBE2B-proficient cells. Immunohistochemical analysis of 124 NPC tissues from patients who underwent cisplatin-based chemoradiotherapy indicated that high UBE2B expression levels were associated with poor DSS, DMeFS and LRFS. Multivariate regression analysis of factors influencing survival also confirmed that high UBE2B expression levels were a statistically significant independent risk factor for poor clinical outcomes in terms of DSS [hazard ratio (HR), 1.955; 95% CI 1.164-3.282], DMeFS (HR, 2.141; 95% CI 1.206-3.801) and LRFS (HR, 2.557;.In vitro analysis indicated that O6-methylguanine-DNA methyltransferase attenuated cisplatin sensitivity induced by knockdown of UBE2B in NPC cells. In conclusion, the present study demonstrated that high UBE2B expression is associated with poor clinical outcomes for patients with NPC treated with cisplatin-based chemoradiotherapy.
3102 Background: Senaparib (or IMP4297) is a PARP inhibitor with a novel chemical structure. Preliminary data demonstrate senaparib has significant anti-tumor activity with good tolerability in some patients with advanced solid tumors. DNA damage caused by temozolomide, a non-classic oral alkylating agent, can sensitize tumors to the effects of PARP inhibitors. In a xenograft model, synergistic antitumor effect was observed with the combination of senaparib and temozolomide, supporting this trial (NCT04434482). Methods: This is a phase Ⅰb/Ⅱ dose-escalation and dose-expansion study. Patients with advanced solid tumors were enrolled for dose escalation to evaluate the safety, tolerability using a modified “3+3” design. Low dose temozolomide (20 to 30 mg, once daily, days 1 to 21) in combination with continuous senaparib (40 to 80 mg, once daily, days 1 to 28) of each 28-day cycle was evaluated. Dose expansion will establish anti-tumor activity and safety of the combination in patients with extensive stage small cell lung cancer (ES-SCLC). Results: A total of 14 patients were enrolled for dose escalation as follows: Cohort 1 (1 patient; senaparib 40 mg plus temozolomide 20 mg), Cohort 2 (3 patients; senaparib 60 mg plus temozolomide 20 mg), Cohort 3 (7 patients; senaparib 80 mg plus temozolomide 20 mg), Cohort 4 (3 patients; senaparib 80 mg plus temozolomide 30 mg). One DLT (Grade 4 thrombocytopenia) was observed in Cohorts 3 and 4. The MTD and RP2D were determined as: senaparib 80 mg plus temozolomide 20 mg. Anaemia, neutropenia and thrombocytopenia were the only Grade ≥3 TEAEs occurring in > 1 patient. All AEs were manageable, and no treatment related deaths were reported. The ORR was observed in 3 of 12 (25.0%) evaluable patients, including 2 confirmed PR and 1 unconfirmed PR. The DCR was 83.3% (10 of 12 evaluable patients). Two patients remain on treatment for more than 1 year. Conclusions: Preliminary results suggest that low dose temozolomide (D1-21 of a 28-day cycle) in combination with continuous senaparib is generally well tolerated with encouraging anti-tumor activity. Recruitment for dose expansion for ES-ECLC patients has commenced (Sep 2021). Clinical trial information: NCT04434482.
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