Functional correlates of N-terminal natriuretic peptide type B (NT-proBNP) response to therapy in cardiac light chain (AL) amyloidosis

Rationale, application and clinical qualification for NT-proBNP as a surrogate end point in pivotal clinical trials in patients with AL amyloidosis

Amyloid light-chain (LC) amyloidosis (AL amyloidosis) is a rare and fatal disease for which there are no approved therapies. In patients with AL amyloidosis, LC aggregates progressively accumulate in organs, resulting in organ failure that is particularly lethal when the heart is involved. A significant obstacle in the development of treatments for patients with AL amyloidosis, as well as for those with any disease that is rare, severe and heterogeneous, has been satisfying traditional clinical trial end points (for example, overall survival or progression-free survival). It is for this reason that many organizations, including the United States Food and Drug Administration through its Safety and Innovation Act Accelerated Approval pathway, have recognized the need for biomarkers as surrogate end points. The international AL amyloidosis expert community is in agreement that the N-terminal fragment of the pro-brain natriuretic peptide (NT-proBNP) is analytically validated and clinically qualified as a biomarker for use as a surrogate end point for survival in patients with AL amyloidosis. Underlying this consensus is the demonstration that NT-proBNP is an indicator of cardiac response in all interventional studies in which it has been assessed, despite differences in patient population, treatment type and treatment schedule. Furthermore, NT-proBNP expression is directly modulated by amyloidogenic LC-elicited signal transduction pathways in cardiomyocytes. The use of NT-proBNP will greatly facilitate the development of targeted therapies for AL amyloidosis. Here, we review the data supporting the use of NT-proBNP, a biomarker that is analytically validated, clinically qualified, directly modulated by LC and universally accepted by AL amyloidosis specialists, as a surrogate end point for survival.

Free light chain testing for the diagnosis, monitoring and prognostication of AL amyloidosis

The disease causing agent in systemic AL amyloidosis is a monoclonal immunoglobulin free light chain, or fragments thereof, circulating in the blood. It is not surprising, therefore, that measurement of serum free light chains plays a central role in the management of this disorder. In this paper, we review the utility of the serum free light chain assay in the investigation, prognostication and monitoring of AL amyloidosis. Data on the two currently available commercial assays is compared and some practical applications of the assay’s use are presented. While there are limitations, it is clear that the availability of the free light chain assay in the laboratory is a major advance and plays an essential role in the management of patients with AL amyloidosis.

What do I need to know about immunoglobulin light chain (AL) amyloidosis?

Immunoglobulin light chain (AL) amyloidosis is the most common acquired systemic amyloidoses. Its presentation is often insidious and progressive, which may delay diagnosis. The interval between first symptoms and actual diagnosis along the intrinsic heterogeneity of tissue tropism create a wide spectrum of presentations, both in terms of scope and depth of symptoms and signs and functional status of patients. In this review, the authors review the pathogenesis, diagnosis and differential diagnosis of AL amyloidosis along with the prognosis and state-of-the-art management for patients with this affliction.