The protein p53, often called the ‘guardian of the genome,’ is a transcription factor that is activated in response to cellular stress (low oxygen levels, heat shock, DNA damage, etc.) and acts to prevent further proliferation of the stressed cell by promoting cell cycle arrest or apoptosis. Its role as a tumor suppressor is evident by the observation that approximately 50% of human tumors have mutated or non-functional p53. Mdm2, a key negative regulator of p53, which is over-expressed in many human tumors, functions by binding to and targeting p53 for proteasomal degradation. MI-77301 binds to MDM2 with a Ki value of 0.88 nM and blocks the MDM2-p53 interaction. It activates wild-type p53 in vitro and in xenograft tumor tissue of leukemia and solid tumors, leading to p53-dependent cell cycle arrest and/or apoptosis. In an SJSA-1 xenograft model of osteosarcoma, a single dose of 200 mg/kg MI-77301 induces complete tumor regression in mice by upregulating the pro-apoptotic protein PUMA.
