Integrin-Targeted PET Imaging and Therapeutics May Detect and Treat Radiation-Induced Lung Fibrosis Earlier
R&E Foundation–funded study highlights imaging probe’s potential to monitor fibrosis progression and mitigate fibrosis in vivo
Radiation-induced pulmonary fibrosis (RIPF) is a potentially debilitating late adverse effect of radiation therapy (RT), commonly associated with poor clinical outcomes and limited therapeutic options. It can be particularly concerning for patients with lung cancer, breast cancer or thoracic lymphoma, as well as pediatric patients with blood cancers who received total body irradiation.
The development of reliable strategies to predict and prevent RIPF is critical for preserving quality of life, particularly in pediatric patients for whom radiation-related toxicity may have lifelong consequences. Emerging imaging biomarkers and novel therapeutic interventions hold promise for improving risk stratification and mitigating disease progression.
“One of the biggest challenges in detecting RIPF is that conventional imaging does not distinguish RIPF from tumor recurrence. For example, conventional CT can only image structural changes and cannot tell between fibrosis and tumor. PET/CT is also confounded and is unable to tell early development of fibrosis from tumor recurrence,” said William Lo, MD, PhD, assistant professor in the Department of Radiation Oncology at the Fred & Pamela Buffett Cancer Center, Nebraska Medicine in Kearney. “Currently, clinical monitoring of RIPF progression remains challenging given the lack of precise imaging tools that can reliably detect RIPF at an early stage and the difficulty distinguishing RIPF from other pulmonary pathologies.”
In his 2022 R&E Foundation Research Resident Grant, “Integrin-Targeted PET Imaging and Therapeutics To Predict and Mitigate Radiation-Induced Pulmonary Fibrosis,” Dr. Lo and team investigated integrin-targeted PET imaging and integrin antagonism as a promising strategy to predict and mitigate radiation-induced fibrosis in preclinical models of fibrosis in the lung.
One focus was integrin avß6, a protein in the lungs that activates the latent transforming growth factor beta, TGF-ß, a signaling protein that sends instructions between cells.
“In the lung, the integrin cell surface receptors play a key role in the pathogenesis of RIPF. In particular, integrin αvβ6 is expressed at a low level in the alveolar epithelium at baseline, and its expression is significantly upregulated with radiation damage,” Dr. Lo said. “Integrin αvβ6 is a major TGF-β activator in the lung, critical to the pathogenesis of pulmonary fibrosis. Therefore, integrin αvβ6–targeted imaging allows us to specifically probe the early development of RIPF in vivo and is a highly selective marker for RIPF development.”
In addition, the researchers used a specially designed imaging peptide, A20FMDV2, that can attach very specifically to integrin αvβ6. They then used PET scans to track how RIPF develops over time.
“In our study, we investigated an integrin αvβ6–targeted PET imaging probe called 64[Cu]Cu-αvβ6-BP, synthesized with the A20FMDV2 peptide, to study the evolution of RIPF development,” Dr. Lo said.
Whole organ optical tissue clearing with iDISCO and 3-D second harmonic generation (collagen) imaging at 8 weeks post-RT in the focal radiation-induced pulmonary fibrosis model, showing significant attenuation of fibrosis in the irradiated region (blue box, gree = collagen) with the administration of small molecule RGD integrin antagonist (targeting αvβ1 αvβ3 αvβ6) at 50 mg/kg/day vs. control (vehicle alone) from weeks 4-8 (green – SHG; red- autofluorescence).
Murine Model Looks to Identify RIPF
To test the hypothesis, Dr. Lo and team used PET imaging and CT to detect changes in two preclinical models. The first was a focal ablative RIPF model, in which fibrosis developed on an accelerated timeline over eight weeks. The second was a whole lung RIPF model in which fibrosis developed over six months.
The timing of onset of expression of αvβ6 varied depending on the model. In the focal ablative model, the researchers saw uptake as early as four weeks. In the whole lung RIPF model, it took about four to five months before the researchers saw significant uptake.
“While you can see some corresponding changes on CT, with increased opacity in the irradiated areas, it is important to point out αvβ6 imaging can detect fibrosis development much more specifically,” Dr. Lo noted. “CT can only detect changes in morphology, while PET imaging detects changes in function.”
To determine whether PET tracer uptake correlated with histopathology or fibrosis severity, and whether it could serve as a quantitative imaging biomarker, Dr. Lo correlated imaging results at multiple time points with histological comparisons.
The researcher’s hypotheses held true and showed that integrin αvβ6-targeted PET imaging using [64Cu]Cu-αvβ6-BP can serve as a powerful tool to identify RIPF in vivo.
“Since this is a preclinical study in an animal model, future clinical translation of this imaging probe is still needed to test it in patients,” Dr. Lo said. “However, based on the preclinical data, there is a strong translational potential for the use of integrin αvβ6-targeted PET imaging using [64Cu]Cu-αvβ6-BP to detect fibrosis development in patients, which will help address a central problem in distinguishing fibrosis development from tumor recurrence, with implications in monitoring therapeutic response to anti-fibrotic therapies.”
Integrin Antagonism as a Powerful Way to Mitigate RIPF
Dr Lo’s team further demonstrated a novel RGD integrin inhibitor to mitigate RIPF in vivo in the second phase of the study, using insights from the PET imaging study. By targeting the transient increase in αvβ6 expression with integrin antagonism, investigators demonstrated a significant reduction in the later development of fibrosis in irradiated tissue.
Finally, they explored the combination of whole organ tissue clearing, a technique called iDISCO, and second harmonic generation (SHG) imaging. This combination showed the quantification of collagen and assessment of fibrosis in exquisite details at optical resolution in 3D in the optically cleared lungs.
“The ability to quantify collagen in 3D across the entire optically cleared lung using iDISCO-based tissue clearing and volumetric SHG imaging provides a powerful tool for the accurate assessment of response to novel antifibrotic therapeutics, as demonstrated in this work,” Dr. Lo said. “Furthermore, given the central role integrins play in fibrogenesis across a wide range of organs, this study has significant implications for the mitigation of radiation-induced fibrosis, which is an important dose-limiting side effect in radiation therapy.”
The Benefit of R&E Foundation Support
Dr. Lo received a Research Resident Grant, which is designed to allow trainees the opportunity to explore new research methods and techniques while investigating new research hypotheses.
“The R&E Foundation grant provided critical resources to facilitate the pilot work to be completed,” Dr. Lo said. “I am deeply grateful to the foundation for their support during my residency training.”
Following his research, Dr. Lo and team were able to publish their study in the International Journal of Radiation Oncology and the i-DISCO based 3D SHG imaging work was accepted as an oral proffered presentation at the European Society for Radiotherapy and Oncology congress, ESTRO 2024.
For More Information
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