Abstract
1834
Objectives: Preliminary pharmacokinetic study of a bispecific peptide for pretargeting immunotherapy of amyloidosis using PreClinical SPECT/CT Amyloid deposition in abdominothoracic organs and peripheral nerves results in cytotoxicity and disruption of tissue architecture leading to organ dysfunction. Removal of amyloid would improve organ function, prolong patient survival, and enhance quality of life. Passive immunotherapy, using amyloid-reactive monoclonal antibodies (mAbs) has been shown to improve organ function and reduce amyloid load, but only in a subset of patients evaluated. To enhance the utility of one therapeutic mAb, 11-1F4 (Blood. 2010;116(13):2241-4), which has shown efficacy in ~ 60% of patients with light chain-associated (AL) amyloidosis, but is anticipated to be ineffective in other forms of the disease, we have developed a bifunctional, synthetic “peptope” comprising a pan-amyloid-reactive peptide, p5 (Sci Rep. 2016;6:22695), and a high-affinity, linear epitope for 11-1F4, known as A12. This bispecific synthetic peptide, designated p93, may serve a dual purpose as diagnostic imaging agent, when radiolabeled, and as a therapeutic agent for enhancing 11-1F4-based immunotherapy in many forms of systemic amyloid-associated disorders. Herein we describe data related to two critical factors in the use of the amyloid-bound half-life, which will influence the mAb targeting efficiency and the amyloid-binding specificity, which will affect off-target immunological effects. Peptope p93 was synthetized as an all L-amino acid peptide with a single D-tyrosine residue at position 2 to allow radioiodination that was resistant to dehalogenation in vivo. Female mice (n = 3) with severe, systemic serum amyloid protein A (AA) amyloidosis received 125I-p93 IV in the lateral tail vein and SPECT/CT images acquired under anesthesia at 4 h, 24 h, 72 h and 168 h post injection. Region of interest analyses were performed using SPECT data to quantify the activity associated with the liver and spleen - major sites of amyloid deposition in these mice. The muscle was used a negative control tissue. Following necropsy the liver and spleen at 168 h pi contained 2.2 %ID/g and 2.1 %ID/g, respectively. Specific binding to amyloid at this time point was demonstrated autoradiographically. These data indicate that the bound amyloid bound half-life, estimated using a two-phase exponential was ~8 h and ~37 h for tfast and tslow. Furthermore, given the excellent safety profile a similar amyloid reactive peptide (NOAEL >17 mg/Kg in preclinical studies) this would allow delivery of significant amounts of peptope to amyloid deposits in patients, serving as a pre-targeting agent, prior to delivery of therapeutic mAb 11-1F4. We anticipate that this strategy will enhance and expand the utility of this mAb, or similar reagents, for the treatment of amyloidosis.