A method for identifying a mechanism associated with a cellular response includes identifying molecules participating in the cellular response; accessing a database containing information characterizing molecular interactions; determining pathways connecting the identified molecules participating in the cellular response; and solving an optimization problem that includes determining a subset of the molecules and interactions having a minimum aggregate cost. The pathways include, nodes, each representing a molecule, and edges, each connecting a respective pair of nodes and representing an interaction between a respective pair of molecules represented by the respective pair of nodes. Nodes from a subset of nodes represent molecules identified as participating in the cellular response.