The drug inhibits a protein called MEK, part of a molecular signaling chain that relays genetic instructions to the cell nucleus to promote cell growth. Researchers decided to test the drug after conducting a cross-species bioinformatics computer analysis of mouse and human NF1 tumors. The analysis identified genes and molecules that regulate cell signals driving the growth of neurofibromas and MPNSTs in both species.The drug is currently being tested in human clinical trials for cancers that involve molecular components similar to those in NF1, in particular the MEK protein. MEK is a downstream molecular target for a group of cell signaling proteins called Ras-GTPase. The proteins work together in a molecular relay to activate normal cell growth. In the instance of genetic mutation, Ras-GTPase can get stuck in the "on" position and promote hyperactive cell growth, tumor formation or cancer. Overactive Ras-GTPase signaling has been linked to a number of cancers. In the case of mouse and human NF1 tumors, bioinformatics computer analysis suggested that deregulated Ras-GTPase signaling prompted MEK to stimulate the sustained activity of an enzyme called ERK. To confirm whether this molecular pathway is critical to NF1 tumor growth, researchers tested the MEK-blocking drug in genetically engineered mice. The mice lacked expression of the NF1 gene and its tumor suppressing protein, causing the animals to develop benign neurofibromas. Scientists also transplanted human malignant peripheral nerve sheath tumor cells into a separate group of genetically receptive mice, which developed their own cancerous tumors. Researchers then tested different doses of the drug to identify an optimal dose – one that would achieve the maximum amount of tumor shrinking efficiency with the least amount of toxicity. Treatment with PD0325901 reduced the abnormal growth of cells in both benign neurofibromas and malignant peripheral nerve sheath tumors (MPNSTs). It also reduced the volume of tumor feeding blood vessels.