Abstract 425: Doxorubicin Upregulation of the Fibrotic Transforming Growth Factor-beta Pathway

Abstract

Childhood cancer survivors are at an increased risk of heart disease as a result of their cancer treatments. Drugs like doxorubicin (DOX) are an effective part of treatment regimens, but have been proven to cause acute and chronic cardiotoxicity (DOX tox). An under-investigated aspect of DOX tox is the interstitial fibrosis that the majority of patients develop. This project aims to better understand the pathology of DOX-induced cardiac fibrosis and the role of the pro-fibrotic transforming growth factor-beta (TGFb) signaling pathway. Research in the area of fibrosis and the effect of DOX on cardiac fibroblasts will increase our understanding of DOX tox. This understanding will allow for improved treatment of pediatric cancer patients by reducing the cardiotoxic sequelae of many standard chemotherapy regimens. Cardiac fibroblasts, isolated from 3 week old mice and treated with 5 μM DOX, showed an increase in nuclear pSMAD compared to control cells via fluorescent immunocytology (2.06 ± 0.26 vs 1.13 ± 0.15, p<0.05). Mice treated with 3 mg/kg DOX injections from 2 weeks to 6 weeks of age showed increased TGFb staining in the left ventricle (1.83 ± 0.34 vs 0.87 ± 0.28, p<0.05) a week after treatment ceased. A subset of mice were followed into old age and sacrificed at 80 weeks. A clear increase in TGFb was seen with age. However, 80 week mice that were exposed to DOX early in life showed a greater increase in TGFb staining compared to untreated 80 week old mice (44.50 ± 2.48 vs 30.93 ± 2.30, p<0.001). Early DOX exposure causes chronic molecular changes as evidenced by acute and chronic changes in signaling molecules in cardiac tissue. Changes in collagen seen in earlier studies and increases in MMP-2 from the literature suggest a cardiac remodeling phenotype in DOX-exposed animals. This project demonstrates that DOX initiates changes to pro-fibrotic pathways, seemingly driven by the TGFb signaling pathway.