• David A Tess, Tristan S Maurer, Zhenhong Li, Christine Bulawa, James Fleming, and Amy T Moody.
• Department of Pharmacokinetics, Dynamics and Metabolism, Pfizer Inc, Cambridge, MA, USA.
• Amyloid. 2023 Jun 1; 30 (2): 208219208-219.

BackgroundTafamidis inhibits progression of transthyretin (TTR) amyloid cardiomyopathy (ATTR-CM) by binding TTR tetramer and inhibiting dissociation to monomers capable of denaturation and deposition in cardiac tissue. While the phase 3 ATTR-ACT trial demonstrated the efficacy of tafamidis, the degree to which the approved dose captures the full potential of the mechanism has yet to be assessed.MethodsWe developed a model of dynamic TTR concentrations in plasma to relate TTR occupancy by tafamidis to TTR stabilisation. We then developed population pharmacokinetic-pharmacodynamic models to characterise the relationship between stabilisation and measures of disease progression.ResultsModelling individual patient data of tafamidis exposure and increased plasma TTR confirmed that single-site binding provides complete tetramer stabilisation in vivo. The approved dose was estimated to reduce unbound TTR tetramer by 92%, and was associated with 53%, 56% and 49% decreases in the rate of change in NT-proBNP, KCCQ-OS, and six-minute walk test disease progression measures, respectively. Simulating complete TTR stabilisation predicted slightly greater reductions of 58%, 61% and 54%, respectively.ConclusionsThese findings support the value of TTR stabilisation as a clinically beneficial treatment option in ATTR-CM and the ability of tafamidis to realise nearly the full therapeutic benefit of this mechanism.Clinicaltrials.Gov IdentifierNCT01994889.

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