Radiation quality and cellular oxygen concentration have a substantial impact on DNA damage, reproductive cell death and, ultimately, the potential efficacy of radiation therapy for the treatment of cancer. To better understand and quantify the effects of radiation quality and oxygen on the induction of clustered DNA lesions, we have now extended the Monte Carlo Damage Simulation (MCDS) to account for reductions in the initial lesion yield arising from enhanced chemical repair of DNA radicals under hypoxic conditions. The kinetic energy range and types of particles considered in the MCDS have also been expanded to include charged particles up to and including (56)Fe ions. The induction of individual and clustered DNA lesions for arbitrary mixtures of different types of radiation can now be directly simulated. For low-linear energy transfer (LET) radiations, cells irradiated under normoxic conditions sustain about 2.9 times as many double-strand breaks (DSBs) as cells irradiated under anoxic conditions. New experiments performed by us demonstrate similar trends in the yields of non-DSB (Fpg and Endo III) clusters in HeLa cells irradiated by γ rays under aerobic and hypoxic conditions. The good agreement among measured and predicted DSBs, Fpg and Endo III cluster yields suggests that, for the first time, it may be possible to determine nucleotide-level maps of the multitude of different types of clustered DNA lesions formed in cells under reduced oxygen conditions. As particle LET increases, the MCDS predicts that the ratio of DSBs formed under normoxic to hypoxic conditions by the same type of radiation decreases monotonically toward unity. However, the relative biological effectiveness (RBE) of higher-LET radiations compared to (60)Co γ rays (0.24 keV/μm) tends to increase with decreasing oxygen concentration. The predicted RBE of a 1 MeV proton (26.9 keV/μm) relative to (60)Co γ rays for DSB induction increases from 1.9 to 2.3 as oxygen concentration decreases from 100% to 0%. For a 12 MeV (12)C ion (681 keV/μm), the 'predicted RBE for DSB induction increases from 3.4 (100% O(2)) to 9.8 (0% O(2)). Estimates of linear-quadratic (LQ) cell survival model parameters (α and β) are closely correlated to the Monte Carlo-predicted trends in DSB induction for a wide range of particle types, energies and oxygen concentrations. The analysis suggests α is, as a first approximation, proportional to the initial number of DSBs per cell, and β is proportional to the square of the initial number of DSBs per cell. Although the reported studies provide some evidence supporting the hypothesis that DSBs are a biologically critical form of clustered DNA lesion, the induction of Fpg and Endo III clusters in HeLa cells irradiated by γ rays exhibits similar trends with oxygen concentration. Other types of non-DSB cluster may still play an important role in reproductive cell death. The MCDS captures many of the essential trends in the formation of clustered DNA lesions by ionizing radiation and provides useful information to probe the mu...

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BackgroundAutoimmunity is a common cause of pulmonary fibrosis and can present either as a manifestation of an established connective tissue disease or as the recently described entity of interstitial pneumonia with autoimmune features. The rate of progression and responsiveness to immunosuppression in these illnesses are difficult to predict. Circulating fibrocytes are bone marrow-derived progenitor cells that home to injured tissues and contribute to lung fibrogenesis. We sought to test the hypothesis that the blood fibrocyte concentration predicts outcome and treatment responsiveness in autoimmune interstitial lung diseases.MethodsWe compared the concentration of circulating fibrocytes in 50 subjects with autoimmune interstitial lung disease and 26 matched healthy controls and assessed the relationship between serial peripheral blood fibrocyte concentrations and clinical outcomes over a median of 6.25 years.ResultsAs compared to controls, subjects with autoimmune interstitial lung disease had higher circulating concentrations of total fibrocytes, the subset of activated fibrocytes, and fibrocytes with activation of PI3K/AKT/mTOR, TGF-beta receptor, and IL4/IL13 receptor signalling pathways. Over the follow-up period, there were episodes of marked elevation in the concentration of circulating fibrocytes in subjects with autoimmune interstitial lung disease but not controls. Initiation of immunosuppressive therapy was associated with a decline in the concentration of circulating fibrocytes. For each 100 000 cell·mL−1 increase in peak concentration of circulating fibrocytes, we found a 5% increase in odds of death or lung function decline.ConclusionIn patients with autoimmune interstitial lung disease, circulating fibrocytes may represent a biomarker of outcome and treatment response.

Idiopathic pulmonary fibrosis (IPF) is a progressive disease associated with poor prognosis. Fibrocytes are a novel population of bone marrow-derived circulating cells that traffic to the lungs and contribute to fibrosis in animal models of pulmonary fibrosis via the interaction of the chemokine CXCL12, made in the lung, and the chemokine receptor CXCR4, expressed on fibrocytes. In human interstitial lung disease, the concentration of CXCR4+ circulating fibrocytes correlates with survival. The expression of fibrocyte CXCR4 is dependent on the mTOR pathway, and is reduced by in vitro treatment with the mTOR inhibitor, sirolimus. In animal models of lung fibrosis, sirolimus therapy reduces both the trafficking of fibrocytes to the lungs and the extent of lung fibrosis. The effect of sirolimus in human IPF has not been examined. We hypothesized that therapy with the mTOR inhibitor sirolimus reduces the number of circulating fibrocytes in patients with idiopathic pulmonary fibrosis and is associated with an acceptable side-effect profile. METHODS:We performed a short-term randomized double-blinded placebo-controlled crossover study of 30 subjects diagnosed with IPF by consensus definition. Subjects were randomized to placebo or sirolimus for a 1-3 week run-in period with dose adjustment to achieve therapeutic drug levels, followed by 4 weeks of dose maintenance, and then a 4 week washout period. Subjects were then crossed over to the alternate treatment (placebo or sirolimus) for same length run-in, maintenance and washout periods. The concentration of circulating fibrocytes plasma chemokine ligands, pulmonary function tests, and adverse events were measured at specific time points. Adverse events were classified as serious per the NCI CTCAE criteria and were adjudicated as unrelated or possibly related to the study drug by an independent DSMB. RESULTS:We enrolled 30 subjects between 2011 and 2015; 2 withdrew prior to randomization. The remaining 28 had a median age of 69 (IQR 65-73), 22 were men and 8 were on concurrent therapy with pirfenidone or nintedanib. Sirolimus therapy resulted in a statistically significant reduction in the concentration of circulating fibrocytes (median change -62%, IQR -40% to -29%) whereas placebo did not (median change -32%; IQR -47% to +6%). A total of 49 adverse events occurred during treatment with sirolimus and 29 with placebo, of which 35 (2 serious: elevated liver enzymes and angioedema) were adjudicated as possibly related to therapy during sirolimus and 15 (1 serious: worsened dyspnoea) during placebo treatments. The incidence of total adverse events, serious adverse events, and total and serious adverse events that were potentially related to therapy did not differ significantly during therapy with drug and placebo.CONCLUSIONS: As compared with placebo, short-term treatment with sirolimus resulted in reduction of circulating fibrocyte concentrations in subjects with IPF and was associated with an acceptable safety profile.CLINICAL IMPLICATIONS: Given the benefit of sirolimus in...

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