Question: Why do all of the cancer preventing drugs in the pictures you show look like chains?

Josh Meyers answered on 18 Jun 2015:

Those chain links are chemical ring systems! Many modern organic molecules (which is what drugs are) contain ring systems. This is a chemical building block that is easy to link to the next molecular ‘section’.

Some examples of these ring systems are molecules such as benzene, pyridine and imidazole. These can be attached to each other through chemistry to make a larger drug molecule!