Specific netrin proteins, nucleic acids which encode netrin proteins and hybridization reagents, probes and primers capable of hybridizing with netrin genes and methods for screening chemical libraries for lead compounds for pharmacological agents useful in the diagnosis or treatment of disease associated undesirable cell growth are provided. An exemplary screen involves forming a mixture comprising a recombinant netrin protein, a natural intracellular netrin protein binding target, and a candidate pharmacological agent; incubating the mixture under conditions whereby, but for the presence of said candidate pharmacological agent, said netrin protein selectively binds said binding target; and detecting the presence or absence of specific binding of said netrin protein to said binding target.