Fibroblast activation in cardio-oncology

Abstract Introduction Carcinoid heart disease is a rare disease affecting the right sided heart valves (1) while anthracycline cardiotoxicity is a dreaded sequelae of a common chemotherapeutic agent that can occur early or even years after exposure (2). Activated fibroblasts, a key factor in these diseases, can be imaged with 68Gallium-fibroblast activation protein inhibitor (68Ga-FAPI). Method 12 patients with carcinoid syndrome, 12 patients with previous anthracycline exposure and 10 healthy volunteers underwent hybrid 68Ga-FAPI positron emission tomography and magnetic resonance imaging. Areas of fibroblast activation were quantified as mean and maximum target-to-background ratios (TBRmean and TBRmax). Results Carcinoid syndrome: 2 of the 12 patients had carcinoid heart disease [mean age 70, 50% female] (CHD) (Figure 1A). 68Ga-FAPI uptake was seen in the liver lesions of all patients with known carcinoid liver tumours. Of the 10 patients without cardiac involvement, 6 had significant tricuspid valve 68Ga-FAPI uptake (CHD- FAPI+) (Figure 1B) and 4 did not (CHD- FAPI-). Median tricuspid TBRmax was significantly higher in CHD + [2.38 (IQR 2.35-2.42)], than CHD- patients [CHD- FAPI+: 1.68 (IQR 1.65-1.73), CHD- FAPI-: 1.55 (IQR 1.53-1.65)], although this was higher than healthy volunteers [1.45 (IQR 1.43- 1.61; p<0.05). CHD- FAPI+ patients had significantly elevated urinary 5-HIAA levels compared to CHD- FAPI- patients [Median =188 mg/24hr (IQR 151-196) in CHD- FAPI+ vs 32mg/24hr ( IQR 12-73); p=0.03]. Anthracycline chemotherapy: 3 of the 12 patients had cardiotoxicity [mean age 61, 67% female]. Anthracycline patients had higher left ventricular myocardial 68Ga-FAPI uptake than healthy volunteers with cardiotoxicity patients having the highest. [TBRmean: Cardiotoxicity 1.46 (IQR 1.36- 1.53), No cardiotoxicity 1.37 (IQR 1.19- 1.49), Healthy volunteers 0.73 (IQR 0.66 - 0.81); p<0.01 (Figure 1E). Across the cohort a moderate negative correlation was observed between Left ventricular ejection fraction and 68Ga-FAPI activity (LV TBRmean r =-0.46 and TBRmax (r= -0.66) Discussion 68 Ga-FAPI provides us the ability to assess fibroblast activation and for the first time demonstrated the key role of these cells in both these cardio-oncology conditions. Increased fibroblast activation is observed around the tricuspid valve in patients with carcinoid syndrome both in those with and without overt clinical disease. Similarly increased myocardial fibroblast activation is observed in patients exposed to anthracyclines even many years after exposure and where there is no overt evidence of cardiotoxicity. Conclusion 68Ga-FAPI imaging holds promise in evaluating the role of activated fibroblasts in the pathology of both carcinoid heart disease and cardiotoxicity, providing information beyond the current resolution of current clinical approaches.