Engineered antibody therapies to counteract mutant huntingtin and related toxic intracellular proteins

Abstract

The engineered antibody approach to Huntington's disease (HD) therapeutics is based on the premise that significantly lowering the levels of the primary misfolded mutant protein will reduce abnormal protein interactions and direct toxic effects of the misfolded huntingtin (HTT). This will in turn reduce the pathologic stress on cells, and normalize intrinsic proteostasis. Intracellular antibodies (intrabodies) are single-chain (scFv) and single-domain (dAb; nanobody) variable fragments that can retain the affinity and specificity of full-length antibodies, but can be selected and engineered as genes. Functionally, they represent a protein-based approach to the problem of aberrant mutant protein folding, post-translational modifications, protein-protein interactions, and aggregation. Several intrabodies that bind on either side of the expanded polyglutamine tract of mutant HTT have been reported to improve the mutant phenotype in cell and organotypic cultures, fruit flies, and mice. Further refinements to the difficult challenges of intraneuronal delivery, cytoplasmic folding, and long-term efficacy are in progress. This review covers published studies and emerging approaches on the choice of targets, selection and engineering methods, gene and protein delivery options, and testing of candidates in cell and animal models. The resultant antibody fragments can be used as direct therapeutics and as target validation/drug discovery tools for HD, while the technology is also applicable to a wide range of neurodegenerative and other diseases that are triggered by toxic proteins.

Experimental Models for Identifying Modifiers of Polyglutamine-Induced Aggregation and Neurodegeneration

“…While current clinical options remain limited for HD and other polyQ diseases, rapid progress in developing focused preclinical models and drug screening technologies for these disorders promises that new generations of drug candidates will be entering clinical evaluation in coming years, including biologic molecules targeting the mutant genes and proteins themselves [10,[140][141][142]. Moreover, emerging robotic and automated imaging technologies, together with powerful new analytic tools, are offering new possibilities for the higher throughput use of complex models in drug discovery, ranging from iPSCs to brain slices to C. elegans and D. melanogaster.…”

“…While we will provide examples of new drug and drug target candidates emerging from such studies, we will regrettably not be able to review the field in a comprehensive manner owing to space limitations. We thus refer the reader to recent and excellent reviews focusing on other aspects of polyQ drug discovery and disease models [7][8][9][10][11][12][13][14].…”

Intrabodies as Neuroprotective Therapeutics

“…These are covered in detail in Butler et al [20]. In summary, in vitro and in situ selection conditions will, of necessity, differ from intracellular conditions, particularly when cells are stressed.…”

“…HD Drosophila models have provided a valuable test system (reviewed in Butler et al [20]). The most extensively utilized HD animal models are transgenic mice.…”

Refolding Technology for scFv Using a New Detergent, N-Lauroyl-L-glutamate and Arginine

“…Conjugation of scFv with cytotoxic agents is particularly attractive for treatments against solid tumors, such as breast cancers [22][23][24][25]. A small size also opens opportunity for the intracellular delivery of therapeutic antibody fragments [26][27][28].…”