Abstract
<jats:p>FSH, a glycoprotein secreted by the anterior pituitary gland, has for decades been thought to solely regulate estrogen secretion in females and spermatogenesis in males. Through the use of genetically–engineered mouse models and pharmacological approaches, we and others have shown that FSH has an array of direct actions on somatic tissues, including adipose tissue and bone, as well as on the brain. Thus, inhibiting FSH action, genetically in knockout mice or pharmacologically using FSH–blocking antibodies, prevents fat gain, bone loss, and cognitive decline in relevant mouse models. Towards the potential future use of blocking FSH action in people, particularly in post–menopausal women in whom the aforementioned physiologic aberrations track together in the face of elevated FSH levels, we created a therapeutic FSH–blocking monoclonal antibody, MS-Hu6, by humanizing its parent murine version, Hf2. Here, we present an in–depth account of the humanization of Hf2 up to the production of a highly specific, high–affinity antibody. Using X–ray crystallography, we also report a second crystal form of the Fab domain of MS-Hu6 at a 1.98 Ǻ resolution, and its AlfaFold complex with FSHβ. We applied physicochemical testing to a new formulation for MS-Hu6 and Hf2 to establish thermal, colloidal, monomeric, stress–induced, and long–term stability of an ultra–high antibody concentration appropriate for human use. Murine antibody was used to re–test its efficacy in a modified protocol, in which ovariectomized mice were fed on a high–fat diet. The antibody effect in preventing fat accrual and weight gain persisted following its cessation—a finding relevant to its use in people. Finally, with a higher MS-Hu6 dose infused intravenously into African green monkeys, we provide definitive evidence of acute safety in terms of unaltered vitals, serum chemistries, and complete blood counts. This work takes us closer to testing MS-Hu6 in first–in–human studies.</jats:p>