Antibody Mediated "Universal" Osteoclast Targeting Platform

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Abstract

Osteoclasts are the sole cells responsible for bone resorption and their activity is central to the process of bone remodeling. Excessive osteoclast activity leads to increased bone resorption, predisposing individuals to bone conditions such as osteoporosis, Paget’s disease and the focal bone erosions seen in rheumatoid arthritis. Hence, the pharmacological arrest of osteoclasts is the mainstay of treating many bone diseases. However, none of the current antiresorptive therapies for bone loss target osteoclast cells directly. As osteoclasts express the Receptor Activator of Nuclear factor Kappa B (RANK) receptor, the essential signaling receptor for osteoclast differentiation, it was hypothesized that antibody-like molecules generated with specificity against RANK could selectively target and deliver conjugated drug cargo to the osteoclast.

The objectives of this thesis were to generate, characterize and evaluate monoclonal antibodies against the osteoclast RANK receptor, in order to develop a pharmaceutical platform capable of selective and targeted drug delivery to osteoclast cells. Using hybridoma technology, a specific monoclonal antibody against recombinant human RANK receptor was generated. Synthesis of osteoclast-targeting bioconjugates with that antibody was conducted using the antiresorptive peptide hormone calcitonin. Conjugate characterization was undertaken and its efficacy tested on osteoclast cell cultures using various osteoclast specific assays. Both the conjugate as well as the antibody itself showed remarkable inhibition of osteoclast activity. The desirable result obtained with the mere binding of the antibody to the receptor led us towards new research work, focusing on valuable scale-up production and therapeutic use.

As a new research direction, single-chain Fraction variable (scFv) antibody-like molecules was expressed against the human RANK receptor using phage display technology, to circumvent complications associated with murine-derived antibodies. The Anti-RANK scFv showed specificity towards osteoclast RANK receptors and also showed an inhibitory effect on osteoclast activity.

With the increase in development trends for biologics as therapeutics and the growing knowledge on the importance of osteoclast targeted therapy, this novel biologic reagent may find utility as “universal osteoclast targeting platform”. This may provide a meaningful strategy in terms of osteoclast targeting and drug delivery with the aim of treating or controlling the progression of osteoclast related bone disorders.

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