Here is a paper (subscription required). It is written by Lee Harland (Pfizer Regenerative Medicine) and Anna Gaulton (ex Pfizer, but now in the ChEMBL group at the EMBL-EBI). It is an overview of Drug Targets, and some of the general principles of 'druggability' and ways to assess target tractability for drug discovery. In particular, the challenges of data integration are discussed.
%A L. Harland %A A. Gaulton %T Drug Target Central %J Expert Opin. Drug. Disc. %V 4 %P 857-872 %D 2009