A biopsy-based pilot clinical study: monitoring the effectiveness of tafamidis treatment of patients with transthyretin amyloid cardiomyopathy

Abstract

Abstract Background Transthyretin amyloid cardiomyopathy (ATTR-CM) is a rare and progressive disease associated with high mortality. It is caused by the accumulation of TTR amyloid protein in various tissues, including the myocardium. Tafamidis is currently the only approved therapy for ATTR-CM. The results of the phase III ATTR-ACT trial showed lower rates of mortality and hospitalization, besides lower rate of decline for both quality of life (QoL), and 6-minute walk test (6mwt) distance [1]. Whether the reported clinical outcomes represent a change in myocardial ATTR-accumulation and remodeling remains unclear. Here we monitor the clinical outcome and the corresponding myocardial histological changes of tafamidis-treated patients using endomyocardial biopsy (EMB). Methods Eleven patients with EMB-proven ATTR-CM, 10 wild type, 1 hereditary, 9 males, 2 females age= 77±9 years, were prescribed with 61 mg tafamidis once daily indefinitely. The course of the disease was evaluated via EMB, 99mTc-DPD scintigraphy, cardiac magnetic resonance imaging (cMRI), echocardiography, 6mwt, Minnesota QoL questionnaire and serum N-terminal pro brain natriuretic peptide (NT-proBNP) analysis, at baseline and after 321±72 days of treatment (ethics application number EA2/140/16). EMBs were examined via immunohistochemistry and Imaging mass spectrometry. All patients received standard heart failure medications. Paired clinical measurements were compared via paired t test for parametric data or Wilcoxon rank test for non-parametric data. Results Following the course of treatment, EMB ATTR-positive area measured via immunohistochemistry increased by 7.7±9.5% (p<0.05). Myocardial CD3+ and CD68+ cell counts remained within normal limits. The EMB peak intensities of ATTR, collagen and macrophage migration inhibitory factor, measured via imaging mass spectrometry were increased by 23% (AUC= 0.677, p<0.001), 25% (AUC= 0.620, p<0.001) and 18% (AUC= 0.609, p<0.001), respectively. Echocardiography measured left ventricular (LV) ejection fraction and LV end-diastolic diameter, as well as 6mwt distance, QoL and serum NT-proBNP showed no significant changes. cMRI did not show any significant changes in fibrosis/amyloidosis markers (N=9). 99mTc-DPD scintigraphy-derived Perugini score (N=10) improved by one-point in two patients and remained stable in the rest. The New York Heart Association (NYHA) functional class improved in one patient and remained stable in 10/11 patients. Conclusion Our findings demonstrate, for the first time, the persistence of myocardial ATTR-accumulation and remodeling despite a clinically stable disease course. Whether this finding is relevant in terms of disease-progression or indicate a need for more intensive treatment warrants further investigation.