Angiotensin receptor blockade: a novel approach for symptomatic radiation necrosis after stereotactic radiosurgery

Angiotensin converting enzyme (ACE) inhibitors as radiation countermeasures for long-duration space flights

Angiotensin converting enzyme (ACE) inhibitors are effective countermeasures to chronic radiation injuries in rodent models, and there is evidence for similar effects in humans. In rodent models ACE inhibitors are effective mitigators of radiation injury to kidney, lung, central nervous system (CNS) and skin, even when started weeks after irradiation. In humans, the best data for their efficacy as radiation countermeasures comes from retrospective studies of injuries in radiotherapy patients. We propose that ACE inhibitors, at doses approved for human use for other indications, could be used to reduce the risk of chronic radiation injuries from deep-space exploration. Because of the potential interaction of ACE inhibitors and microgravity (due to effects of ACE inhibitors on fluid balance) use might be restricted to post-exposure when/if radiation exposures reached a danger level. A major unresolved issue for this approach is the sparse evidence for the efficacy of ACE inhibitors after low-dose-rate exposure and/or for high-LET radiations (as would occur on long-duration space flights). A second issue is that the lack of a clear mechanism of action of the ACE inhibitors as mitigators makes obtaining an appropriate label under the Food and Drug Administration Animal Rule difficult.

Radiation Necrosis from Stereotactic Radiosurgery-How Do We Mitigate?

OPINION STATEMENT

Intracranial stereotactic radiosurgery (SRS) is an effective and convenient treatment for many brain conditions. Data regarding safety come mostly from retrospective single institutional studies and a small number of prospective studies. Variations in target delineation, treatment delivery, imaging follow-up protocols and dose prescription limit the interpretation of this data. There has been much clinical focus on radiation necrosis (RN) in particular, as it is being increasingly recognized on follow-up imaging. Symptomatic RN may be treated with medical therapy (such as corticosteroids and bevacizumab) with surgical resection being reserved for refractory patients. Nevertheless, RN remains a challenging condition to manage, and therefore upfront patient selection for SRS remains critical to provide complication-free control. Mitigation strategies need to be considered in situations where the baseline risk of RN is expected to be high-such as large target volume or re-irradiation. These may involve reduction in the prescribed dose or hypofractionated stereotactic radiation therapy (HSRT). Recently published guidelines and international meta-analysis report the benefit of HSRT in larger lesions, without compromising control rates. However, careful attention to planning parameters and SRS techniques still need to be adhered, even with HSRT. In cases where the risk is deemed to be high despite mitigation, a combination approach of surgery with or without post-operative radiation should be considered.

Angiotensin-converting Enzyme Inhibitors Decrease the Incidence of Radiation-induced Pneumonitis Among Lung Cancer Patients: A Systematic Review and Meta-analysis

Background: Angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin receptor blockers (ARBs) have been demonstrated to mitigate radiation-induced lung damage in animal models and preclinical studies. Our study aims to evaluate whether ACEIs or ARBs reduce the incidence of radiation-induced pneumonitis (RP) in lung cancer patients.

Methods: Publications were searched from EMBASE, PubMed and Web of Science databases. Seven studies published from April 2000 to August 2016 met inclusion criteria and included 1412 patients in total. Only patients with grade 2 and above pneumonitis within 12 months after radiotherapy were analyzed.

Results: Patients taking ACEIs had a lower risk of developing radiation pneumonitis compared with non-users (OR = 0.46, 95%CI = 0.31-0.67, p < 0.0001). While the use of ARBs couldn't reduce the incidence of RP (OR = 1.42, 95%CI = 0.94-2.14, p = 0.10). Elderly patients (age ≥ 70) benefited more from ACEIs (OR = 0.12, 95%CI = 0.02-0.67, p = 0.02). In addition, smokers were found to have a lower risk of developing RP than non-smokers (OR = 0.49, 95%CI = 0.30-0.81, p = 0.005), but sex and the use of statin or NSAID had no influence on the appearance of RP (p = 0.59, p = 0.70, p = 0.40, respectively).

Conclusions: ACE inhibitors could decrease the incidence of symptomatic RP among lung cancer patients. However, the use of ARBs has a slight trend to develop RP but not above statistical significance. Elderly patients (age ≥ 70) benefited the most from ACEIs.

Renin-Angiotensin System Inhibitors to Mitigate Cancer Treatment-Related Adverse Events

Treatment-related side effects are a major clinical problem in cancer treatment. They lead to reduced compliance to therapy as well as increased morbidity and mortality. Well-known are the sequelae of chemotherapy on the heart, especially in childhood cancer survivors. Therefore, measures to mitigate the adverse events of cancer therapy may improve health and quality of life in patients with cancer, both in the short and long term. The renin-angiotensin system (RAS) affects all hallmarks of cancer, and blockage of the RAS is associated with an improved outcome in several cancer types. There is also increasing evidence that inhibition of the RAS might be able to alleviate or even prevent certain types of cancer treatment-related adverse effects. In this review, we summarize the potential of RAS inhibitors to mitigate cancer treatment-related adverse events, with a special emphasis on chemotherapy-induced cardiotoxicity, radiation injury, and arterial hypertension. Clin Cancer Res; 24(16); 3803-12. ©2018 AACR.