In search of the most effective therapy for light chain amyloidosis

Nanobodies counteract the toxicity of an amyloidogenic light chain by stabilizing a partially open dimeric conformation

Light chain amyloidosis (AL) is a systemic disease where fibrillar deposition of misfolded immunoglobulin light chains (LCs) severely affects organ function and results in poor prognosis for patients, especially when heart involvement is severe. Particularly relevant in this context is the cardiotoxicity exerted by still uncharacterized soluble LC species. Here, with the final goal of identifying alternative therapeutic strategies to tackle AL amyloidosis, we produced five llama-derived nanobodies (Nbs) specific against H3, a well-characterized amyloidogenic and cardiotoxic LC from an AL patient with severe cardiac involvement. We found that Nbs are specific and potent agents capable of abolishing H3 soluble toxicity in C. elegans in vivo model. Structural characterization of H3-Nb complexes revealed that the protective effect of Nbs is related to their ability to bind to the H3 VL domain and stabilise an unexpected partially open LC dimer in which the two VL domains no longer interact with each other. Thus, while identifying potent inhibitors of LC soluble toxicity, we also describe the first non-native structure of an amyloidogenic LC that may represent a crucial step in toxicity and aggregation mechanisms.

Advances in the treatment of light chain amyloidosis

PURPOSE OF REVIEW

After many years, the management of systemic light chain (AL) amyloidosis is entering the era of evidence-based medicine, with three recently published randomized clinical trials, a regimen (daratumumab, cyclophosphamide, bortezomib, and dexamethasone, daratumumab-CyBorD) labeled for upfront therapy, more clinical trials ongoing, and published guidelines. In this review, we discuss how current practice is changing based on this data.

RECENT FINDINGS

Daratumumab-CyBorD grants unprecedentedly high rates of hematologic and organ response and became the novel standard-of-care in AL amyloidosis. The International Society of Amyloidosis and the European Hematology Association issued common guidelines for autologous stem cell transplant (ASCT) in this disease. Improved patient selection and effective induction regimens greatly reduced ASCT-related mortality. Venetoclax is emerging as a very effective option in patients harboring the common t(11;14) abnormality. Rapid and profound reduction of the amyloid free light chain can improve survival also at advanced stages.

SUMMARY

Daratumumab-CyBorD is being integrated into the treatment flow-chart whereas the role of ASCT is being redefined. New approaches are being tested in clinical trials. Treatment of daratumumab-refractory patients and validation of criteria of hematologic progression to be used in clinical trials and in individual patient management are current areas of research.