across an extensive network by kinases, ultimately resulting
in changes in the cell’s behavior (see Figure 15, p. 53).
Antibodies are also proteins that are naturally made by a
type of immune cell, called a B-cell. Their role in normal
cells is to identify and kill foreign invaders, such as viruses
and bacteria. Researchers undertook a strategy to block the
activity of the specific receptors driving certain cancers by
developing therapeutic antibodies that block receptor
function and thereby halt tumor growth (see Figure 16, pp.
54-55). The increased function of these receptors and their
signaling networks are the result of genetic changes specific
to the cancers in which they occur. Therapeutic antibodies
can be used alone, or in combination with chemotherapy, to
treat different types of cancers. Researchers have also
devised ways to attach chemotherapy drugs or radiation-emitting particles to therapeutic antibodies in order to
deliver them directly to the cancer cells and avoid
damaging normal cells.
Figure 15: Receptor Tyrosine Kinase Cell Signaling. One way in which
cells communicate is through growth factors. These growth factors (blue
and purple spheres) bind to specific receiving proteins, called receptors
(orange and yellow cup-like structures). These receptors sit on the
surface of cells and, working in clusters, relay the growth factor signal
into the cell. Within the cell, the signal is further relayed across an
extensive network of proteins by kinases (lightly-colored blob shapes),
eventually changing the activity of genes (DNA) in the nucleus (N) and
thus, ultimately, cell behavior. Many identified oncogenes are kinases
within these networks, and both they and their receptors are very
effective drug targets; see Tables 2 and 3, pp. 40-41 and 42.