Carbon-ion irradiation overcomes HPV-integration/E2 gene-disruption induced radioresistance of cervical keratinocytes

Basic and translational research on carbon-ion radiobiology

Carbon-ion beam irradiation (IR) has evident advantages over the conventional photon beams in treating tumors. It releases enormous amount of energy in a well-defined range with insignificant scatter in surrounding tissues based on well-localized energy deposition. Over the past 28 years, more than 14,000 patients with various types of cancer have been treated by carbon ion radiotherapy (CIRT) with promising results at QST. I have provided an overview of the basic and translational research on carbon-ion radiobiology including mechanisms underlying high linear energy transfer (LET) carbon-ion IR-induced cell death (apoptosis, autophagy, senescence, mitotic catastrophe etc.) and high radiocurability produced by carbon-ion beams in combination with DNA damaging drugs or with molecular-targeted drugs, micro-RNA therapeutics and immunotherapy. Additionally, I have focused on the application of these treatment in human cancer cells, especially cancer stem cells (CSCs). Finally, I have summarized the current studies on the application of basic carbon-ion beam IR according to the cancer types and clinical outcomes.

Cellular irradiations with laser-driven carbon ions at ultra-high dose rates

Objective.Carbon is an ion species of significant radiobiological interest, particularly in view of its use in cancer radiotherapy, where its large Relative Biological Efficiency is often exploited to overcome radio resistance. A growing interest in highly pulsed carbon delivery has arisen in the context of the development of the FLASH radiotherapy approach, with recent studies carried out at dose rates of 40 Gy s^-1. Laser acceleration methods, producing ultrashort ion bursts, can now enable the delivery of Gy-level doses of carbon ions at ultra-high dose rates (UHDRs), exceeding 10⁹Gy s^-1. While studies at such extreme dose rate have been carried out so far using low LET particles such as electrons and protons, the radiobiology of high-LET, UHDR ions has not yet been explored. Here, we report the first application of laser-accelerated carbon ions generated by focussing 10²⁰W cm^-2intense lasers on 10-25 nm carbon targets, to irradiate radioresistant patient-derived Glioblastoma stem like cells (GSCs).Approach.We exposed GSCs to 1 Gy of 9.5 ± 0.5 MeV/n carbon ions delivered in a single ultra-short (∼400-picosecond) pulse, at a dose rate of 2 × 10⁹Gy s^-1, generated using the ASTRA GEMINI laser of the Central Laser Facility at the Rutherford Appleton Laboratory, Didcot, Oxfordshire, UK. We quantified carbon ion-induced DNA double strand break (DSB) damage using the 53BP1 foci formation assay and used 225 kVp x-rays as a reference radiation.Main Results.Laser-accelerated carbon ions induced complex DNA DSB damage, as seen through persistent 53BP1 foci (11.5 ± 0.4 foci/cell/Gy) at 24 h and significantly larger foci (1.69 ± 0.07μm²) than x-rays induced ones (0.63 ± 0.02μm²). The relative foci induction value for laser-driven carbon ions relative to conventional x-rays was 3.2 ± 0.3 at 24 h post-irradiation also confirming the complex nature of the induced damage.Significance.Our study demonstrates the feasibility of radiobiology investigations at unprecedented dose rates using laser-accelerated high-LET carbon ions in clinically relevant models.

The application of CRISPR/Cas9 system in cervical carcinogenesis

Integration of high-risk HPV genomes into cellular chromatin has been confirmed to promote cervical carcinogenesis, with HPV16 being the most prevalent high-risk type. Herein, we evaluated the therapeutic effect of the CRISPR/Cas9 system in cervical carcinogenesis, especially for cervical precancerous lesions. In cervical cancer/pre-cancer cell lines, we transfected the HPV16 E7 targeted CRISPR/Cas9, TALEN, ZFN plasmids, respectively. Compared to previous established ZFN and TALEN systems, CRISPR/Cas9 has shown comparable efficiency and specificity in inhibiting cell growth and colony formation and inducing apoptosis in cervical cancer/pre-cancer cell lines, which seemed to be more pronounced in the S12 cell line derived from the low-grade cervical lesion. Furthermore, in xenograft formation assays, CRISPR/Cas9 inhibited tumor formation of the S12 cell line in vivo and affected the corresponding protein expression. In the K14-HPV16 transgenic mice model of HPV-driven spontaneous cervical carcinogenesis, cervical application of CRISPR/Cas9 treatment caused mutations of the E7 gene and restored the expression of RB, E2F1, and CDK2, thereby reversing the cervical carcinogenesis phenotype. In this study, we have demonstrated that CRISPR/Cas9 targeting HPV16 E7 could effectively revert the HPV-related cervical carcinogenesis in vitro, as well as in K14-HPV16 transgenic mice, which has shown great potential in clinical treatment for cervical precancerous lesions.

Biology of the Radio- and Chemo-Responsiveness in HPV Malignancies

In multiple anatomic sites, patients with cancers associated with the Human Papillomavirus (HPV) experience better locoregional control and overall survival after radiotherapy and/or chemoradiotherapy than patients with HPV-negative cancers. These improved outcomes suggest that relatively unique biological features in HPV-positive cancers may increase sensitivity to DNA damaging agents as well as an impaired DNA damage response. This review will address potential biological mechanisms driving this increased sensitivity of HPV-positive cancer to radiation and/or chemotherapy. This review will discuss the clinical and preclinical observations that support the intrinsic radiosensitivity and/or chemosensitivity of HPV-positive cancers. Furthermore, this review will highlight the molecular mechanisms for increased radiation sensitivity using the classical "4 Rs" of radiobiology: repair, reassortment, repopulation, and reoxygenation. First, HPV-positive cancers have increased DNA damage due to increased oxidative stress and impaired DNA damage repair due to the altered activity TP53, p16, TIP60, and other repair proteins. Second, irradiated HPV-positive cancer cells display increased G2/M arrest leading to reassortment of cancer cells in more radiosensitive phases of the cell cycle. In addition, HPV-positive cancers have less radioresistant cancer stem cell subpopulations that may limit their repopulation during radiotherapy. Finally, HPV-positive cancers may also have less hypoxic tumor microenvironments that make these cancers more sensitive to radiation than HPV-negative cells. We will also discuss extrinsic immune and microenvironmental factors enriched in HPV-positive cancers that facilities responses to radiation. Therefore, these potential biological mechanisms may underpin the improved clinical outcomes often observed in these virally induced cancers.

DNA repair gene expression is associated with differential prognosis between HPV16 and HPV18 positive cervical cancer patients following radiation therapy

Cervical cancers are almost always induced by HPV infections, of which HPV16 and HPV18 are predominant. Cancers associated with these strains are induced through DNA repair factors and have a differential response to radiation therapy. Hence this study focuses on finding DNA repair gene expression differences in HPV16 and HPV18 positive cervical cancers after radiation therapy. A higher number of somatic mutations were observed in HPV16 positive cervical tumours for patients that were disease free when compared to those who recurred/progressed. Moreover, hierarchal clustering of RNAseq data from The Cancer Genome Atlas was conducted to identify groups of DNA repair genes associated with a differential prognosis for cervical cancer following postoperative radiation therapy. TP53BP1, MCM9 (at higher than mean levels), POLR2F and SIRT6 (at lower than mean levels), were associated with an increase in patients experiencing cervical cancer recurrence/progression following postoperative radiation therapy when HPV18 positive, but not HPV16 positive. The expression patterns of these genes provide an explanation for the higher rate of postoperative radiation therapy resistance associated with HPV18 positive cervical cancer patients. Therefore, HPV18 positive cervical tumours may be more likely retain a greater non-homologous end joining and homologous recombination pathway activity, which could dampen the effect of postoperative radiation therapy. Moreover, greater susceptibility to postoperative radiation therapy could be caused by the reliance of cervical cancer cells upon the single-strand annealing and nucleotide excision pathways for repair of DNA damage.