Mitigation of Radiation Fibrosis by CCG-257081

Researchers evaluating the MRTF/SRF transcription pathway inhibitor CCG-257081 as a preventive therapeutic for drug-induced pulmonary fibrosis, using bleomycin as a clinically relevant initiating insult in this research project. The study addresses the unmet need for agents that prevent progression to debilitating lung fibrosis when the timing of injury is known, such as during chemotherapy with bleomycin. The MRTF/SRF pathway is a common downstream node in fibrotic signaling that mediates the fibroblas-to-myofibroblast transition and drives expression of hallmark fibrotic genes. Targeting this transcriptional switch offers a strategy to interrupt fibrosis regardless of the diverse upstream triggers that initiate extracellular matrix deposition and chronic scarring.

In human lung fibroblasts, CCG-257081 effectively reduced mRNA of key MRTF/SRF target genes, including smooth muscle actin and connective tissue growth factor, with half-maximal inhibitory concentrations (IC50s) of approximately 4 μM and 15 μM respectively, demonstrating direct cellular pharmacology consistent with blockade of myofibroblast differentiation programs. The in vivo component assessed the ability of CCG-257081 to prevent inflammation and fibrosis in a murine model in which animals received systemic intraperitoneal bleomycin for four weeks. Concurrent oral dosing with CCG-257081 was evaluated across a dose range (0, 10, 30, and 100 mg/kg PO) and compared to the approved anti-fibrotic nintedanib and to prednisolone, a clinical standard often used to manage symptoms.

Outcomes measured included body weight, pulmonary hydroxyproline content as a quantitative collagen measure, histopathology, and bronchoalveolar lavage fluid biomarkers. At the highest tested dose, 100 mg/kg, mice receiving CCG‑257081 gained weight relative to vehicle controls, whereas mice treated with nintedanib or prednisolone experienced significant weight loss. Importantly, hydroxyproline content and histological assessments in lungs from animals treated with 100 mg/kg CCG‑257081 were not significantly different from naive tissue, indicating successful prevention of bleomycin-induced collagen accumulation and histopathologic fibrosis. Measures of tissue fibrosis were comparable between CCG‑257081 and nintedanib; however, only the MRTF/SRF inhibitor produced a decrease in bronchoalveolar lavage fluid plasminogen activator inhibitor-1 (PAI-1), a biomarker linked to fibrotic processes. By contrast, prednisolone treatment resulted in marked increases in lung fibrosis across metrics, highlighting the limitations of steroid therapy for preventing fibrotic remodeling.

This work provides preclinical evidence that pharmacologic inhibition of the MRTF/SRF transcriptional pathway with CCG-257081 can prevent the development of bleomycin-induced pulmonary fibrosis, preserving lung tissue architecture and avoiding the weight loss associated with other interventions. These results support further development of MRTF/SRF inhibitors as preventive therapies in contexts where the timing of fibrotic insult is known, such as certain chemotherapy regimens, and underscore the potential of targeting a central transcriptional regulator to interrupt diverse fibrotic signaling cascades.