[PARP inhibitors and radiotherapy: rational and prospects for a clinical use]

Enhancing anti-tumour innate immunity by targeting the DNA damage response and pattern recognition receptors in combination with radiotherapy

Radiotherapy is one of the most effective and frequently used treatments for a wide range of cancers. In addition to its direct anti-cancer cytotoxic effects, ionising radiation can augment the anti-tumour immune response by triggering pro-inflammatory signals, DNA damage-induced immunogenic cell death and innate immune activation. Anti-tumour innate immunity can result from recruitment and stimulation of dendritic cells (DCs) which leads to tumour-specific adaptive T-cell priming and immunostimulatory cell infiltration. Conversely, radiotherapy can also induce immunosuppressive and anti-inflammatory mediators that can confer radioresistance. Targeting the DNA damage response (DDR) concomitantly with radiotherapy is an attractive strategy for overcoming radioresistance, both by enhancing the radiosensitivity of tumour relative to normal tissues, and tipping the scales in favour of an immunostimulatory tumour microenvironment. This two-pronged approach exploits genomic instability to circumvent immune evasion, targeting both hallmarks of cancer. In this review, we describe targetable DDR proteins (PARP (poly[ADP-ribose] polymerase); ATM/ATR (ataxia-telangiectasia mutated and Rad3-related), DNA-PKcs (DNA-dependent protein kinase, catalytic subunit) and Wee1 (Wee1-like protein kinase) and their potential intersections with druggable immunomodulatory signalling pathways, including nucleic acid-sensing mechanisms (Toll-like receptors (TLR); cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) and retinoic acid-inducible gene-I (RIG-I)-like receptors), and how these might be exploited to enhance radiation therapy. We summarise current preclinical advances, recent and ongoing clinical trials and the challenges of therapeutic combinations with existing treatments such as immune checkpoint inhibitors.

Post-mastectomy Radiation Therapy in Triple-Negative Breast Cancer Patients: Analysis of the BEATRICE Trial

PURPOSE

Post-mastectomy radiation therapy (PMRT) improves locoregional control and overall survival in patients with breast cancer. With the evolution of systemic therapy, the benefit of PMRT in patients with triple-negative disease requires further evaluation.

PATIENTS AND METHODS

BEATRICE is a phase III randomized clinical trial that examined the efficacy of bevacizumab in patients with triple-negative breast cancer (TNBC). The current study is a retrospective analysis of data on patients enrolled and treated with mastectomy and systemic therapy. The primary endpoint was determining the effect of PMRT on locoregional recurrence rates (LRR). Hazard ratios were estimated using Cox regression, and LRR curves were generated by the Kaplan-Meier method.

RESULTS

In total, 940 patients were included in our analysis, of whom 359 (38.2%) received PMRT while 581 (61.8%) did not. At median follow-up of 5 years, no significant difference in LRR was noted between the PMRT and no PMRT groups in node-negative patients (HR = 1.09). Patients with N1 disease had 5-year LRR-free survival of 96% for PMRT versus 91% for no PMRT (HR = 0.46). Most N2 patients received PMRT and had 5-year LRR-free survival of 76%.

CONCLUSION

PMRT benefit in TNBC patients treated with modern systemic therapy is lower than historical reports. Delivery of PMRT in patients with N1 disease enrolled in the BEATRICE trial was not shown to improve local control. As this might be due to patient selection for PMRT, future randomized controlled trials are required to assess the role of PMRT in this patient population.

DNA damage response signaling pathways and targets for radiotherapy sensitization in cancer

Radiotherapy is one of the most common countermeasures for treating a wide range of tumors. However, the radioresistance of cancer cells is still a major limitation for radiotherapy applications. Efforts are continuously ongoing to explore sensitizing targets and develop radiosensitizers for improving the outcomes of radiotherapy. DNA double-strand breaks are the most lethal lesions induced by ionizing radiation and can trigger a series of cellular DNA damage responses (DDRs), including those helping cells recover from radiation injuries, such as the activation of DNA damage sensing and early transduction pathways, cell cycle arrest, and DNA repair. Obviously, these protective DDRs confer tumor radioresistance. Targeting DDR signaling pathways has become an attractive strategy for overcoming tumor radioresistance, and some important advances and breakthroughs have already been achieved in recent years. On the basis of comprehensively reviewing the DDR signal pathways, we provide an update on the novel and promising druggable targets emerging from DDR pathways that can be exploited for radiosensitization. We further discuss recent advances identified from preclinical studies, current clinical trials, and clinical application of chemical inhibitors targeting key DDR proteins, including DNA-PKcs (DNA-dependent protein kinase, catalytic subunit), ATM/ATR (ataxia–telangiectasia mutated and Rad3-related), the MRN (MRE11-RAD50-NBS1) complex, the PARP (poly[ADP-ribose] polymerase) family, MDC1, Wee1, LIG4 (ligase IV), CDK1, BRCA1 (BRCA1 C terminal), CHK1, and HIF-1 (hypoxia-inducible factor-1). Challenges for ionizing radiation-induced signal transduction and targeted therapy are also discussed based on recent achievements in the biological field of radiotherapy.

Low-Dose and Long-Term Olaparib Treatment Sensitizes MDA-MB-231 and SUM1315 Triple-Negative Breast Cancers Spheroids to Fractioned Radiotherapy

The Triple-Negative Breast Cancer subtype (TNBC) is particularly aggressive and heterogeneous. Thus, Poly-ADP-Ribose Polymerase inhibitors were developed to improve the prognosis of patients and treatment protocols are still being evaluated. In this context, we modelized the efficacy of Olaparib (i.e., 5 and 50 µM), combined with fractioned irradiation (i.e., 5 × 2 Gy) on two aggressive TNBC cell lines MDA-MB-231 (BRCAness) and SUM1315 (BRCA1-mutated). In 2D cell culture and for both models, the clonogenicity drop was 95-fold higher after 5 µM Olaparib and 10 Gy irradiation than Olaparib treatment alone and was only 2-fold higher after 50 µM and 10 Gy. Similar responses were obtained on TNBC tumor-like spheroid models after 10 days of co-treatment. Indeed, the ratio of metabolic activity decrease was of 1.2 for SUM1315 and 3.3 for MDA-MB-231 after 5 µM and 10 Gy and of only 0.9 (both models) after 50 µM and 10 Gy. MDA-MB-231, exhibiting a strong proliferation profile and an overexpression of AURKA, was more sensitive to the co-treatment than SUM1315 cell line, with a stem-cell like phenotype. These results suggest that, with the studied models, the potentiation of Olaparib treatment could be reached with low-dose and long-term exposure combined with fractioned irradiation.

Preclinical Studies Comparing Efficacy and Toxicity of DNA Repair Inhibitors, Olaparib, and AsiDNA, in the Treatment of Carboplatin-Resistant Tumors

Purpose: Carboplatin is used to treat many cancers, but occurrence of drug resistance and its high toxicity remain a clinical hurdle limiting its efficacy. We compared the efficacy and toxicity of DNA repair inhibitors olaparib or AsiDNA administered alone or in combination with carboplatin. Olaparib acts by inhibiting PARP-dependent repair pathways whereas AsiDNA inhibits double-strand break repair by preventing recruitment of enzymes involved in homologous recombination and non-homologous end joining. Experimental Design: Mice with MDA-MB-231 tumors were treated with carboplatin or/and olaparib or AsiDNA for three treatment cycles. Survival and tumor growth were monitored. Toxicities of treatments were assayed in C57BL/6 immunocompetent mice. Circulating blood hematocrits, bone marrow cells, and organs were analyzed 10 and 21 days after end of treatment using flow cytometry and microscopy analysis. Resistance occurrence was monitored after cycles of treatments with combination of AsiDNA and carboplatin in independent BC227 cell cultures. Results: Olaparib or AsiDNA monotherapies decreased tumor growth and increased mean survival of grafted animals. The combination with carboplatin further increased survival. Carboplatin toxicity resulted in a decrease of most blood cells, platelets, thymus, and spleen lymphocytes. Olaparib or AsiDNA monotherapies had no toxicity, and their combination with carboplatin did not increase toxicity in the bone marrow or thrombocytopenia. All animals receiving carboplatin combined with olaparib developed high liver toxicity with acute hepatitis at 21 days. In vitro, carboplatin resistance occurs after three cycles of treatment in all six tested cultures, whereas only one became resistant (1/5) after five cycles when carboplatin was associated to low doses of AsiDNA. All selected carboplatin-resistant clones retain sensitivity to AsiDNA. Conclusion: DNA repair inhibitor treatments are efficient in the platinum resistant model, MDA-MB-231. The combination with carboplatin improves survival. The association of carboplatin with olaparib is associated with high liver toxicity, which is not observed with AsiDNA. AsiDNA could delay resistance to carboplatin without increasing its toxicity.

Veliparib in combination with whole-brain radiation therapy for patients with brain metastases from non-small cell lung cancer: results of a randomized, global, placebo-controlled study

Veliparib is a potent, orally bioavailable, poly (adenosine diphosphate-ribose) polymerase (PARP) inhibitor that crosses the blood-brain barrier and has been shown to potentiate the effects of radiation in preclinical and early clinical studies. This phase 2, randomized, global study evaluated the efficacy and safety of veliparib in combination with whole-brain radiation therapy (WBRT) in patients with brain metastases from non-small cell lung cancer (NSCLC). Three-hundred and seven patients with brain metastases from NSCLC were randomized 1:1:1 to WBRT (30 Gy in 10 fractions) plus 50 mg veliparib twice daily (BID; n = 103), 200 mg veliparib BID (n = 102), or placebo BID (n = 102). Treatment began within 28 days of diagnosis. Tumor response and safety were assessed; the primary endpoint was overall survival (OS). Patients who received ≥1 dose of treatment were included in the safety analysis. All randomized patients were included in the efficacy endpoint analyses. Patient characteristics were well balanced between treatment arms. Median OS was 185 days for patients treated with WBRT plus placebo and 209 days for WBRT plus veliparib (50 or 200 mg). No statistically significant differences in OS, intracranial response rate, and time to clinical or radiographic progression between any of the treatment arms were noted. No differences were observed in adverse events (all grades) across treatment arms; nausea, fatigue, alopecia, and headache were the most commonly reported. No new safety signals were identified for veliparib. A significant unmet need for therapies that improve the outcomes of patients with brain metastases from NSCLC remains.

New treatment option for ovarian cancer: PARP inhibitors

Poly(ADP-ribose) polymerase (PARP), which was first described over 50 years ago by Mandel, are a family of protein enzymes involved in DNA damage response and works by recognizing the single-strand DNA break (ssDNA) and then effecting DNA repair. A double-strand DNA (dsDNA) break can be repaired by one of two different pathways: homologous recombination (HR) or non-homologous end joining (NHEJ). Homologous recombination occurs in the G2 or M phase of the cell cycle when a sister chromatid is available to use as a template for repair. Because a template is available, HR is a high fidelity, error-free form of DNA repair. With NHEJ there is not a template and the DNA is trimmed and ligated which is a very error-prone process of repair which can lead to genetic instability. Exploiting these mechanism led to development of PARP inhibitors with the idea of utilizing synthetic lethality, where two deficiencies each having no effect on the cellular outcome become lethal when combined, as single agent in BRCA deficient patients or as chemotherapy/radiotherapy combinations to inhibit ssDNA repair. The recent approval of olaparib in BRCA deficient ovarian cancer patients in US and Europe has opened up a whole new treatment option for ovarian cancer patients. This review will discuss the different PARP inhibitors in development and the potential use of this class of agents in the future.

Radiation therapy (RT) after breast-conserving surgery (BCS) in 2015--The year of radiation therapy advances

Surgery associated with radiation therapy is the standard treatment for early breast cancer. This paper reviews the new evidence on local control and survival, the indications of lymph-node irradiation, and the long-term results of large prospective trials. New shorter fractionation schemes allow a reduction in the constraints of daily treatment courses over several weeks, and recent technical improvements in treatment delivery will improve cancer outcomes in terms of local control, decreased toxicity and long-term sequelae. Research should focus on identifying molecular markers for radiation sensitivity while designing specific, targeted modulators of the radiation response in early breast cancer.