Cardiac Amyloid Detection by PET/CT Imaging of Iodine (124I) Evuzamitide (124I-p5+14): A Phase 1/2 Study

Positron emission tomography in cardiac amyloidosis: current evidence and future directions

The increasing recognition of cardiac amyloidosis (CA) as a cause of heart failure, coupled with advancements in therapeutic options, has underscored the need for early detection. Positron emission tomography (PET) imaging emerged as a promising non-invasive tool for diagnosing and managing CA. This review provides a comprehensive analysis of current PET imaging techniques, focusing on radiotracers, including [11C]Pittsburgh Compound B, [18F]Flutemetamol, [18F]Florbetapir, [18F]Florbetaben, [18F]-sodium fluoride, and [124I]Evuzamitide. PET imaging's ability to differentiating CA subtypes and quantify amyloid burden contributes defining prognosis and aids in monitoring treatment response. However, standardizing imaging protocols and establishing definitive diagnostic thresholds remain challenging. As PET imaging continues to evolve, it promises to improve patient outcomes by facilitating earlier diagnosis, more accurate subtype differentiation, and better treatment monitoring in CA.

Etiological Treatment of Cardiac Amyloidosis: Standard of Care and Future Directions

PURPOSE OF REVIEW

Cardiac amyloidosis (CA) is a condition caused by interstitial infiltration of misfolded proteins structured into amyloid fibrils. Transthyretin (ATTR) and immunoglobulin light chain (AL) amyloidosis represent the most common forms of CA. CA was traditionally perceived as a rare and incurable disease, but diagnostic and therapeutic advances have undermined the conventional paradigm.

RECENT FINDINGS

The standard of care for ATTR-CA include agents capable of selectively stabilizing the precursor protein (e.g., tafamidis), whereas the plasma cell clone is the main target of chemotherapy for AL-CA. For long, tafamidis represented the only drug approved for patients with ATTR-CA. Recent data from ATTRibute-CM led to the approval of acoramidis, whereas patisiran received refusal based on the APOLLO-B trial. Novel CRISPR-Cas9-based drugs (i.e., NTLA-2001) hold great potential in the setting of ATTR-CA. Several hematological regimens are available to treat AL-CA. The main limit of current therapies is their inability to trigger removal of amyloid from tissues. However, the investigation of monoclonal antibodies targeting misfolded ATTR (e.g., PRX004, NI301A) or AL (e.g., birtamimab, anselamimab) has led to encouraging results. Various cutting-edge strategies are being tested for treatment of CA and may change the prognostic landscape of this condition in the next years.

Hereditary transthyretin amyloidosis (ATTRv)

Hereditary transthyretin (TTR) amyloidosis (ATTRv amyloidosis) is a devastating disease characterized by broad range of clinical manifestations, including predominantly neurological, predominantly cardiac, and mixed phenotypes. This wide phenotypic variability hindered timely disease diagnosis and risk stratification in the past, especially in individuals with absent or uncharted family history. However, recent advances in noninvasive testing have led to greater awareness and earlier diagnosis. Further, medications have been discovered which proved effective in controlling the disease and improving outcomes including stabilizing TTR, silencing TTR variants, and removing TTR amyloid from affected tissues. Importantly, CRISPR gene editing, a groundbreaking technology, offers the unique potential to cure ATTRv amyloidosis, transforming lives and opening new doors in medical science. This review provides an update on ATTRv amyloidosis mechanisms, diagnosis, and management emphasizing the importance of early diagnosis as the steadfast underpinning for the capitalization of the advances in medical treatment to the benefit of the patients.

The Last Decade in Cardiac Amyloidosis: Advances in Understanding Pathophysiology, Diagnosis and Quantification, Prognosis, Treatment Strategies, and Monitoring Response

Cardiac amyloidosis represents a unique disease process characterized by amyloid fibril deposition within the myocardial extracellular space. Advances in multimodality cardiac imaging enable accurate diagnosis and facilitate prompt initiation of disease-modifying therapies. Furthermore, rapid advances in multimodality imaging have enriched understanding of the underlying pathogenesis, enhanced prognostication, and resulted in the development of imaging-based markers that reflect the amyloid burden, which is of increasing importance when assessing the response to treatment. Whereas conventional therapies have focused on reducing amyloid formation and subsequent stabilization of the cardiac disease process, novel agents are being developed to accelerate the immune-mediated removal of amyloid fibrils from the heart. In this context, the ability to track changes in the amyloid burden over time is of paramount importance. Although advanced imaging techniques have shown efficacy in tracking the treatment response, future research focused on improved precision through use of artificial intelligence may augment the detection of changes earlier in the course of treatment.

Cardiac PET Imaging for Coronary Artery Disease and Heart Failure: An Overview

Cardiac PET imaging is an important noninvasive modality for the diagnosis and management of heart failure. Cardiac PET myocardial perfusion imaging can identify coronary artery disease with high accuracy and also detect myocardial viability, offering crucial information for the treatment of ischemic cardiomyopathy. Additionally, cardiac PET can help diagnose nonischemic cardiomyopathies including sarcoidosis, amyloidosis, and myocarditis. Improved PET scanner technology combined with emerging radiotracers will, in the future, offer disease-specific molecular imaging that will further assist in the diagnosis, prognosis, and treatment selection for a variety of cardiovascular pathologies.

Transthyretin amyloid cardiomyopathy: a paradigm for advancing precision medicine

Development of specific therapies addressing the underlying diseases' mechanisms constitutes the basis of precision medicine. Transthyretin cardiac amyloidosis (ATTR-CM) is an exemplar of precise therapeutic approach in the field of heart failure and cardiomyopathies. A better understanding of the underlying pathophysiology, more precise data of its epidemiology, and advances in imaging techniques that allow non-invasive diagnosis have fostered the development of new and very effective specific therapies for ATTR-CM. Therapeutic advances have revolutionized the field, transforming a rare, devastating, and untreatable disease into a more common disease with several therapeutic alternatives available. Three main types of therapies (stabilizers, suppressors, and degraders) that act at different points of the amyloidogenic cascade have been developed or are currently under investigation. In this review, the key advances in pathophysiology and epidemiology that have occurred in the last decades along with the different therapeutic alternatives available or under development for ATTR-CM are described, illustrating the role of precision medicine applied to cardiovascular disorders. Pending questions that would need to be answered in upcoming years are also reviewed.

Recent Advances in Positron Emission Tomography Radiotracers to Image Cardiac Amyloidosis

Cardiac amyloidosis includes a group of protein-misfolding diseases characterized by fibril accumulation within the extracellular space of the myocardium and cardiac dysfunction. Cardiac amyloidosis has high mortality. Emerging radionuclide techniques have helped us to better understand disease pathogenesis, prognostication, and treatment response in cardiac amyloidosis. PURPOSE OF REVIEW: To review recent advances in molecular imaging of cardiac amyloidosis using amyloid PET radiotracers. RECENT FINDINGS: Multiple single center studies have shown that amyloid PET radiotracers allow definitive diagnosis and quantification of cardiac amyloid burden. These amyloid targeting tracers may provide means to improve early disease detection, risk stratification and treatment monitoring. Amyloid PET imaging may inform definitive imaging-based diagnosis for therapeutic decisions, risk stratification, and treatment monitoring. More research in unselected cohorts of patients with suspected cardiac amyloidosis is needed to optimize the clinical implementation of amyloid PET imaging.

Radionuclide Imaging of Cardiac Amyloidosis: An Update and Future Aspects

Cardiac amyloidosis (CA) is caused by the misfolding, accumulation and aggregation of proteins into large fibrils in the extracellular compartment of the myocardium, leading to restrictive cardiomyopathy, heart failure and death. The major forms are transthyretin (ATTR) CA and light-chain (AL) CA, based on the respective precursor protein. Each of them requires early diagnosis for a timely treatment initiation that will improve patient outcomes. For this, radionuclide imaging is essentially used as single-photon emission computed tomography (SPECT) with bone-avid radiotracers or as positron emission tomography (PET) with amyloid-binding radiotracers. Both offer unprecedented specificity for the diagnostic of CA. SPECT has even revolutionized the diagnosis of ATTR-CA by making it non-invasive. Indeed, SPECT has now entered the standard diagnostic pathway to CA and has led to earlier diagnosis of the disease. SPECT also modified the epidemiology of ATTR-CA, highlighting that the disease is much more frequent than previously believed, and showing that ATTR-CA plays a substantial role in HFpEF and aortic stenosis, particularly among elderly patients. In parallel, amyloid-binding radiotracers for PET have accumulated a substantial amount of evidence, but are not approved for clinical use in CA yet. Further studies are needed to refine acquisition protocols and validate results in broader populations. Unlike bone-avid SPECT radiotracers, PET radiotracers have been specifically created to bind to amyloid fibrils. Thus, PET is the only imaging method that is truly specific for amyloid deposits and very sensitive to any amyloid type. Indeed, PET can not only detect ATTR-CA, but also AL-CA and rare hereditary forms. For both SPECT and PET, advances in quantitation of myocardial uptake have generated more granular and reproducible findings, paving the way for progress in earlier diagnosis, risk stratification and therapeutic response monitoring. Encouraging findings have shown that SPECT and PET are sensitive to early CA when other diagnostic methods are negative. Both radionuclide imaging techniques can predict adverse outcomes, but more evidence is needed to determine how to use them in conjunction with usual prognostic staging scores. Studies on follow-up imaging after therapy suggested that SPECT and PET can capture myocardial changes in CA, but again, more data are needed to meaningfully interpret such changes. Based on all these promising results, radionuclide imaging has the potential to further impact the landscape of CA in diagnosis, prognosis and follow-up, but also to substantially contribute to the assessment of novel therapies that will improve the lives of patients with CA.

Nuclear imaging techniques for cardiac amyloidosis

PURPOSE OF REVIEW

Cardiac amyloidosis is a condition marked by the misfolding of precursor proteins into insoluble amyloid fibrils, leading to restrictive cardiomyopathy and heart failure symptoms. This review discusses advancements in nuclear imaging techniques that enhance the diagnosis and guide the management of cardiac amyloidosis, addressing the critical need for early and accurate detection in clinical practice.

RECENT FINDINGS

Recent studies and guidelines emphasizes the pivotal role of nuclear imaging techniques in diagnosing cardiac amyloidosis. Cardiac scintigraphy, using bone-avid tracers like 99mTc-PYP, 99mTc-DPD, and 99mTc-HMDP, is instrumental in distinguishing between transthyretin amyloidosis and light chain amyloidosis. PET, with tracers such as 11C-Pittsburgh Compound B (11C-PiB) and 18F-Florbetapir, offers significant potential in measuring amyloid burden and monitoring disease progression, providing detailed insights into the myocardial involvement.

SUMMARY

The advancements in nuclear imaging techniques significantly impact the management of cardiac amyloidosis. These methods allow for a more accurate diagnosis, detailed assessment of disease extent, and better differentiation between amyloidosis types, which are crucial for tailoring treatment approaches. The integration of these techniques into clinical practice is essential for improving patient outcomes and advancing research in cardiac amyloidosis.

Prognostic Value of Left Ventricular 18F-Florbetapir Uptake in Systemic Light-Chain Amyloidosis

BACKGROUND

Positron emission tomography/computed tomography (PET/CT) with 18F-florbetapir, a novel amyloid-targeting radiotracer, can quantify left ventricular (LV) amyloid burden in systemic light-chain (AL) amyloidosis. However, its prognostic value is not known.

OBJECTIVES

The authors' aim was to evaluate the prognostic value of LV amyloid burden quantified by 18F-florbetapir PET/CT, and to identify mechanistic pathways mediating its association with outcomes.

METHODS

A total of 81 participants with newly diagnosed AL amyloidosis underwent 18F-florbetapir PET/CT imaging. Amyloid burden was quantified using 18F-florbetapir LV uptake as percent injected dose. The Mayo stage for AL amyloidosis was determined using troponin T, N-terminal pro-B-type natriuretic peptide (NT-proBNP), and free light chain levels. Major adverse cardiac events (MACE) were defined as all-cause death, heart failure hospitalization, or cardiac transplantation within 12 months.

RESULTS

Among participants (median age, 61 years; 57% males), 36% experienced MACE, increasing from 7% to 63% across tertiles of LV amyloid burden (P < 0.001). LV amyloid burden was associated with MACE (HR: 1.46; 95% CI: 1.16-1.83; P = 0.001). However, this association became nonsignificant when adjusted for Mayo stage. In mediation analysis, the association between LV amyloid burden and MACE was mediated by NT-proBNP (P < 0.001), a marker of cardiomyocyte stretch and heart failure, and a component of Mayo stage.

CONCLUSIONS

In this first study to link cardiac 18F-florbetapir uptake to subsequent outcomes, LV amyloid burden estimated by percent injected dose predicted MACE in AL amyloidosis. This effect was not independent of Mayo stage and was mediated primarily through NT-proBNP. These findings provide novel insights into the mechanism linking myocardial amyloid deposits to MACE.

PET and Cardiac Amyloidosis: Which Possible Role?

PET has recently demonstrated promising capabilities in the diagnosis and differentiation of various forms of CA. Tracers labeled with 18F, such as 18F-flutemetamol, 18F-florbetapir, and 18F-florbetaben, are being increasingly researched due to their extended half-life, eliminating the requirement for on-site cyclotrons. Unlike bone tracers, PET amyloid-binding tracers exhibit a higher affinity for light-chain fibrils, potentially enabling accurate differentiation between various types of CA. The methodology for measuring tracer uptake in PET imaging, whether dynamic or static, facilitates the quantification of disease severity and could act as a marker for monitoring the disease, assessing treatment response.

Immunoglobulin light chain amyloidosis: 2024 update on diagnosis, prognosis, and treatment

DISEASE OVERVIEW

Immunoglobulin light chain amyloidosis is a clonal, nonproliferative plasma cell disorder in which fragments of immunoglobulin light or heavy chain are deposited in tissues. Clinical features depend on organs involved but can include heart failure with preserved ejection fraction, nephrotic syndrome, hepatic dysfunction, peripheral/autonomic neuropathy, and "atypical smoldering multiple myeloma or MGUS."

DIAGNOSIS

Tissue biopsy stained with Congo red demonstrating amyloid deposits with apple-green birefringence is required for the diagnosis of AL amyloidosis. Organ biopsy is not required in 85% of patients. Verification that amyloid is composed of immunoglobulin light chains is mandatory. The gold standard is laser capture mass spectroscopy.

PROGNOSIS

N-terminal pro-brain natriuretic peptide (NT-proBNP or BNP), serum troponin T(or I), and difference between involved and uninvolved immunoglobulin free light chain values are used to classify patients into four stages; 5-year survivals are 82%, 62%, 34%, and 20%, respectively.

THERAPY

All patients with a systemic amyloid syndrome require therapy to prevent deposition of amyloid in other organs and prevent progressive organ failure. Current first-line therapy with the best outcome is daratumumab, bortezomib, cyclophosphamide, and dexamethasone. The goal of therapy is a ≥VGPR. In patients failing to achieve this depth of response options for consolidation include pomalidomide, stem cell transplantation, venetoclax, and bendamustine.

FUTURE CHALLENGES

Delayed diagnosis remains a major obstacle to initiating effective therapy prior to the development of end-stage organ failure. Trials of antibodies to deplete deposited fibrils are underway.