The present invention provides inhibitors of protein kinases comprising a molecule having at least a first moiety competent for penetration of the molecule into cells, and a second moiety for having a protein kinase inhibiting effect within the cells. The first moiety is joined to the second moiety through a linker or a spacer. The complex molecules are preferably peptide conjugates having improved cell-permeability, serum stability and kinase selectivity compared to known protein kinase inhibitors. Pharmaceutical compositions that include these protein kinase inhibitors, and methods of using such compositions for treatment of cancers and other diseases associated with protein kinase activity are also disclosed.