Abstract 1803: A truncated Plasminogen Activator Inhibitor-1 protein protects from pulmonary fibrosis mediated by irradiation in a murine model

Abstract

Background: Fibrosis can develop as a late side effect of radiation exposure in a variety of tissues, including lung and skin. Late radiation injury and fibrosis are characterized by parenchymal cell depletion, inflammation, senescence, fibroblast proliferation, and excessive deposition of collagen. Plasminogen activator inhibitor 1 (PAI-1) is a critical mediator of cellular senescence and fibrin stabilization, and its expression is increased in experimental fibrosis models. We sought to determine if inhibition of PAI-1 signaling with a recombinant truncated protein (rPAI-123) would protect from the development of radiation-induced lung injury. Methods: C57Bl/6 mice received intraperitoneal injections of rPAI-123 (5.4 μg/kg/day) or vehicle (PBS) for 18 weeks beginning two days prior to radiation exposure. Cohorts of mice treated with rPAI-123 or vehicle were exposed to thoracic irradiation in 5 daily fractions of 6 Gy (RT), and followed for survival (n = 8 per group) and tissue collection (n = 3 per each time point). Histologic changes in irradiated lungs were evaluated by Masson-Trichrome staining at 19 weeks after RT. Senescence was assessed with staining for beta-galactosidase activity in lung tissue and primary pneumocytes. To define the roles of rPAI-123 in the fibroproliferative response, cell proliferation (MTT assay) and collagen deposition (Hydroxyproline assay) were examined in a mouse fibroblast cell line in vitro. Results: Administration of rPAI-123 increased C57Bl/6 mice survival from 37.5% to 62.5% at 19 weeks after radiation exposure. At 19 weeks after irradiation, hydroxyproline content was markedly decreased in mice received rPAI-123 compared to mice received vehicle (RT+rPAI-123: 56.2±10.79, RT+vehicle: 84.97±2.98, μg/lung respectively, p = 0.001 between RT+vehicle and RT+rPAI-123). C57Bl/6 mice exposed to RT+vehicle had dense foci of subplueral fibrosis at 19 weeks, whereas the lungs of mice exposed to RT+rPAI-123 were largely devoid of fibrotic foci. Cellular senescence in response to radiation was significantly decreased by rPAI-123 treatment in primary type2 pneumocyte culture (2-fold reduction at 5 days after RT, p = 0.036), and in lung tissues (>2-fold reduction at 4, 8, and 16 weeks after RT, p<0.001 at each time point). Treatment of NIH-3T3 fibroblasts with rPAI-123 resulted in decreased collagen production, but had no effect on proliferation.Conclusions: These studies identify that rPAI-123 has a novel protection mechanism against radiation-induced fibrosis in murine lungs due to its ability to reduce senescence in type2 pneumocytes, and the potential to be an effective therapy option for radiation induced fibrosis. Citation Format: Eunjoo Chung, Ayla White, Bradley T. Scroggins, Grace B. McKay-Corkum, Mary Jo Mulligan-Kehoe, Deborah E. Citrin. A truncated Plasminogen Activator Inhibitor-1 protein protects from pulmonary fibrosis mediated by irradiation in a murine model. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1803. doi:10.1158/1538-7445.AM2015-1803

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“…To characterize the time dependence of radiationinduced normal tissue senescence in lung, mice were exposed to 5 daily fractions of 6 Gy (6Gyx5) thoracic IR and the number of cells exhibiting SA-β-Galactosidase activity was evaluated at 2, 4, and 8 weeks after IR (n = 10 per group). This dose regimen has been extensively validated as a method to induce fibrosis and senescence in irradiated lung [3,8,10,21]. As previously described, in irradiated lungs, senescent cells increased significantly 4 and 8 weeks after IR compared to age matched unirradiated controls (Figure 1A).…”

“…Expression of the SASP by senescent cells has been shown to propagate normal tissue injury and stimulate tumor growth [19]. Senescence in lung has been demonstrated to contribute to lung injury [3], and targeting senescence with agents that prevent senescence after injury or that selectively clear senescent cells (senolytic) have been shown to reduce lung fibrosis after radiation [3,8,10,20,21].…”

Senescence-associated tumor growth is promoted by 12-Lipoxygenase

“…To characterize the time dependence of radiationinduced normal tissue senescence in lung, mice were exposed to 5 daily fractions of 6 Gy (6Gyx5) thoracic IR and the number of cells exhibiting SA-β-Galactosidase activity was evaluated at 2, 4, and 8 weeks after IR (n = 10 per group). This dose regimen has been extensively validated as a method to induce fibrosis and senescence in irradiated lung [3,8,10,21]. As previously described, in irradiated lungs, senescent cells increased significantly 4 and 8 weeks after IR compared to age matched unirradiated controls (Figure 1A).…”

“…Expression of the SASP by senescent cells has been shown to propagate normal tissue injury and stimulate tumor growth [19]. Senescence in lung has been demonstrated to contribute to lung injury [3], and targeting senescence with agents that prevent senescence after injury or that selectively clear senescent cells (senolytic) have been shown to reduce lung fibrosis after radiation [3,8,10,20,21].…”