KEGG

The KEGG collection of online databases dealing with genomes, enzymatic pathways, and biological chemicals. The PATHWAY database records networks of molecular interactions in the cells, and variants of them specific to particular organisms.

NCI-Nature Pathway Interaction Database

The NCI-Nature Pathway Interaction Database is a free biomedical database of human cellular signaling pathways.The database contains information about the molecular interactions and reactions that take place in cells, with aparticular focus on processes that might be relevant to cancer research and treatment.