406

7

Nonmessenger Targets for Drug Action I

Endogenous cellular structures

7.1 Cellular Structures: Relevant Anatomy and Physiology

The goal of medicinal chemistry is to discover and develop novel chemical compounds
(new chemical entities) that will influence the function of the host organism in some
beneficial manner. As discussed in chapters 4–6, the most obvious approach is either to
mimic or to block endogenous messengers used by the organism itself to control its own
biochemistry. These endogenous messengers may be neurotransmitters, hormones, or
immunomodulators working at the electrical, molecular, or cellular level, respectively.
However, not all pathologies afflicting the human organism can be addressed by manip-
ulating these messengers. Accordingly, it becomes necessary to target other cellular
components (this chapter) and/or endogenous macromolecules (chapter 8) that are not
normally directly controlled through binding to endogenous messengers. To identify
such cellular targets for drug design requires an appreciation of cellular structure. The
study of microscopic cellular structure is termed cytology. Cytology should be distin-
guished from histology(the microscopic study of tissues; i.e., functional aggregates of
similar cells, such as neural tissue) and gross anatomy (the study of organs and body
parts, such as the brain).
Cells are the fundamental building blocks of the human body. On average the human
body contains 10^14 cells, ranging in size from nerve cells with a length of 0.5–1.0 m to
red blood cells with a diameter of 7 μm. From a structural perspective, the cell can be
subdivided into three major components:

1. Cell membrane


2. Cytoplasm


3. Nucleus

Each one of these components is composed of a complicated array of substituent
macromolecules and offers targets suitable for drug design (see figure 7.1).