ABSTRACT Osteoporosis directly affects 10 million Americans and another 34 million are osteopenic and at risk for developing osteoporosis. Postmenopausal osteoporosis is most common, but osteoporosis does also frequently affect older men. At MAX BioPharma, we are developing new and improved therapies for osteoporosis that aim to rebalance both bone formation and resorption based on a dual therapy approach. Bisphosphonate drugs, for example, alendronic acid (ALN, Fosamax) can improve bone density and reduce fracture risk by slowing osteoclastic bone resorption; however, many of the existing anti-resorptive therapies are plagued with untoward side effects and limited duration of clinical benefits. Complementary to anti- resorptive therapy, transient activation of anabolic bone formation could become part of a new treatment paradigm. Presently, there are only two FDA approved bone anabolic agents, Forteo and Tymlos, which confer significant clinical benefits in osteoporosis with daily subcutaneous administration, but their use is severely restricted due to safety concerns. Several years ago, we discovered that specific oxysterols induce osteogenesis when applied to mesenchymal stem cells (MSCs) while inhibiting their adipogenesis. The most promising bone anabolic oxysterol to date, OXY133, potently induces osteogenic differentiation in vitro, including in primary rat, rabbit and human MSCs, and stimulates robust localized bone formation in vivo in rat and rabbit spine fusion and cranial and femoral defect models. In the context of osteoporosis, our research has addressed the targeted delivery of Oxy133 to skeletal tissues. We proposed that conjugation of Oxy133 with ALN could selectively deliver both agents to bone tissue, potentially inducing synergistic clinical benefits. Supported by the ongoing NIA-sponsored Phase II SBIR grant, we have examined chemical syntheses and biological properties of numerous Oxy133-ALN conjugates. We have identified Oxy200, a carbamate-linked Oxy133-ALN monoconjugate as a potent osteogenic compound in vitro that is highly water soluble and chemically scalable to multi-gram levels. When administered orally to ovariectomized rats, Oxy200 significantly inhibited bone loss with no evidence of toxicity or ectopic calcification. In this Phase IIB application, we propose detailed studies that seek to further appraise the qualities of Oxy200 as a therapeutic candidate for osteoporosis in IND-enabling studies. According to a therapeutic development plan that we have devised in collaboration with regulatory advisors, these studies will expand on our Phase II grant accomplishments in three Specific Aims: Aim 1: Efficacy and pharmacokinetic studies ? dosing optimization studies will be performed in rats and dogs Aim 2: Genotoxicity studies ? these will include in vitro and in vivo GLP mutagenesis assays to assess safety Aim 3: Acute toxicity and safety pharmacology studies ? these studies will be performed on Albino rats and Beagle dogs following oral administration to further assess safety and tolerability of Oxy200