Dual PI3K/mTOR Inhibitor NVP-BEZ235 Leads to a Synergistic Enhancement of Cisplatin and Radiation in Both HPV-Negative and -Positive HNSCC Cell Lines

Establishment and Application of Novel Hypoxia-driven Dual-reporter Model to Investigate Hypoxic Impact on Radiation Sensitivity in Human Nasopharyngeal Carcinoma Xenografts

Background: Tumor hypoxia has been frequently detected in nasopharyngeal carcinoma (NPC) and is intently associated with therapeutic resistance. The aim of the study is to establish a clonogenically stable hypoxia-inducible dual reporter model and apply it to investigate the effect of tumor hypoxia on DNA double strand break (DSB) and synergistic effect of irradiation in combination with chemotherapy or targeted therapy. Methods: The plasmid vector consisting of hypoxia response elements to regulate HSV1-TK and GFP genes, was constructed and stably transfected into human NPC cells. The expected clone was identified and validated by in vivo and in vitro assay. DSB repair was measured by γH2AX foci formation. Tumor growth delay assay and spatial biodistribution of various biomarkers was designed to investigate the anti-tumor effect. Results: The system has the propensity of high expression of reporter genes under hypoxia and low to no expression under normoxia. Intratumoral biodistributions of GFP and classic hypoxic biomarkers were identical in poor-perfused region. Upon equilibration with 10% O2, the xenografts showed higher expression of hypoxic biomarkers. Cisplatin radiosensitized SUNE-1/HRE cells under hypoxia by suppressing DSB repair while the addition of PI3K/mTOR inhibitor further enhanced the anti-tumoral therapeutic efficacy. Combination of IR, DDP and NVP-BEZ235 exhibited most effective anti-tumor response in vivo. These observations underline the importance of dual reporter model for imaging tumor hypoxia in therapeutic study. Conclusions: Our preclinical model enables the investigation of heterogeneous tumor hypoxic regions in xenograft tissues and explores the treatment efficacy of combinations of various therapeutic approaches to overcome hypoxia.

PTEN and P-4E-BP1 might be associated with postoperative recurrence of rectal cancer patients undergoing concurrent radiochemotherapy

BACKGROUND

Local recurrence after surgery and radiochemotherapy seriously affects the prognosis of locally advanced rectal cancer (LARC) patients. Studies on molecular markers related to the radiochemotherapy sensitivity of cancers have been widely carried out, which might provide valued information for clinicians to carry out individual treatment.

AIM

To find potential biomarkers of tumors for predicting postoperative recurrence.

METHODS

In this study, LARC patients undergoing surgery and concurrent radiochemotherapy were enrolled. We focused on clinicopathological factors and PTEN, SIRT1, p-4E-BP1, and pS6 protein expression assessed by immunohistochemistry in 73 rectal cancer patients with local recurrence and 76 patients without local recurrence.

RESULTS

The expression of PTEN was higher, while the expression of p-4E-BP1 was lower in patients without local recurrence than in patients with local recurrence. Moreover, TNM stage, lymphatic vessel invasion (LVI), PTEN and p-4E-BP1 might be independent risk factors for local recurrence after LARC surgery combined with concurrent radiochemotherapy.

CONCLUSIONS

This study suggests that PTEN and p-4E-BP1 might be potential biomarkers for prognostic prediction and therapeutic targets for LARC.

Nicaraven attenuates the acquired radioresistance of established tumors in mouse models via PARP inhibition

Nicaraven has been reported to inhibit the activity of poly (ADP-ribose) polymerase (PARP). In this study, we investigated the probable ability of nicaraven to attenuate cancer radioresistance during fractionated radiotherapy. Tumor models were established in C57BL/6 mice and BALB/c nude mice by subcutaneous injection of Lewis mouse lung carcinoma cancer cells and A549 human lung cancer cells, respectively. When the tumors had grown to approximately 100 mm3, we initiated fractionated radiotherapy. Nicaraven or saline was administered immediately after each irradiation exposure. Compared to saline treatment, nicaraven administration significantly induced gamma-H2AX foci formation and cell apoptosis in tumors at 1 or 3 days after an additional challenge exposure to 10 Gy and inhibited tumor growth during the short-term follow-up period, suggesting increased radiosensitivity of cancer cells. Moreover, the expression of PARP in tumor tissue was decreased by nicaraven administration. Our data suggest that nicaraven likely attenuates the acquired radioresistance of cancers through PARP inhibition.

Human papillomavirus associated XPF deficiency increases alternative end joining and cisplatin sensitivity in head and neck squamous cell carcinoma

OBJECTIVES

Human papillomavirus (HPV) positive head and neck squamous cell carcinoma (HNSCC) showed a considerably better prognosis with greater cisplatin sensitivity compared to their HPV-negative counterparts. Deciphering the underlying molecular mechanisms for HPV-induced cisplatin sensitivity is imperative to improve the prognosis of HPV-negative HNSCC.

MATERIALS AND METHODS

The Fanconi anemia (FA) pathway status in HNSCC cells was analysed by detecting the cell cycle and chromosomal aberrations. XPF expression was validated using PCR, western blot, and immunohistochemistry. Droplet digital PCR and GFP expressing reporter assay were used to analyse the changes in alternative end-joining (alt-EJ) levels. The cisplatin sensitization was verified by cell proliferation assay, clonogenic cell survival assay, and TUNEL.

RESULTS

HPV-positive HNSCC cells showed significant prolonged G2-M cell cycle arrest and aberrant chromosome formation under interstrand crosslinker treatment. Both mRNA and protein expression of XPF were considerably decreased in HPV-positive HNSCC, according to the analysis of cellular and clinical data. XPF inhibition upregulated the activity of the alt-EJ pathway in HPV-negative HNSCC cells by 32.02% (P < 0.001) but had little effect on HPV-positive HNSCC. Consistent with this, simultaneous suppression of XPF and alt-EJ enhanced cisplatin sensitivity of HPV-negative HNSCC in vitro and in vivo.

CONCLUSION

HPV-positive HNSCC cells exhibit a profound FA pathway deficiency associated with reduced XPF expression. HNSCC cells with compromised XPF function are more reliant on the alt-EJ pathway for genomic stability. Combining FA and alt-EJ inhibition may be used to cope with the hard-to-treat HPV-negative HNSCC.