How does cancer use normal cells for its needs?

Cunning cancer cells often know what works and what doesn’t when it comes to thriving and surviving. While rogue cells break the rules of normal cellular behavior to divide, grow, and sometimes travel to distant organs, they also adopt certain normal functions that healthy cells use to further their nefarious agenda. “These cellular functions are good for us, but they’re also good for cancer cells,” says Justin Chura, MD, chief of surgery and director of gynecological oncology and robotic surgery at our Hospital in Philadelphia.

To stop this behavior in cancer cells, doctors can use drugs called inhibitors. True to their name, inhibitors are designed to block certain actions within cells, and in most cases target specific enzymes. Playing with these enzymes can lead to a wide range of side effects that must be managed or treated, from skin rashes and digestive upset to high blood pressure and autoimmune diseases.

What are inhibitory drugs?

Inhibitory medications are used to treat a variety of diseases and conditions. Omeprazole (Prilosec® ⁾ , for example, is a proton pump inhibitor that blocks the enzyme that releases acid in the stomach. It is used to treat some stomach ulcers and acid reflux disease. In recent years, the US Food and Drug Administration has approved new cancer-fighting inhibitor drugs. Checkpoint inhibitors, first approved in 2010, have shown promising results in fighting some hard-to-treat cancers, such as skin cancer and lung cancer. These drugs block the signaling receptors that help cancer cells hide from the immune system. Common checkpoint inhibitors are pembrolizumab (Keytruda® ⁾ and nivolumab (Opdivo® ⁾ .

Examples of other common inhibitory drugs that may be used to treat cancer include:

PARP inhibitors:A new treatment for ovarian cancer, these drugs are designed to prevent cancer cells from repairing damage to their DNA. When the damage is not repaired, cells can die. Cells are constantly under attack from external forces, such as chemicals or sunlight, which can damage their DNA. Cell division can also cause errors in DNA replication. Cells, whether normal or cancerous, can monitor damage with a protein called poly-ADP-ribose polymerase (PARP) and invoke genes to repair the damage. PARP inhibitors are designed to stop the repair process in cancer cells, allowing damaged cells to die. Common PARP inhibitors used to treat ovarian cancer are olaparib (Lynparza®), which received FDA approval in December 2014, and rucaparib (Rubraca®), which was approved by the FDA in 2016.

Proteasome inhibitors: These drugs are designed to prevent cancer cells from recycling old proteins into new ones, resulting in a toxic increase in proteins that can damage the cell. Proteasomes are tube-like structures within cells that break down proteins so that they can be recycled. Cancer cells may rely on proteasomes more than other cells, because their uncontrolled growth often leads to overproduction of the protein. Proteasome inhibitors are also thought to increase levels of proteins that promote cell death, a normal process in healthy cells called apoptosis. A common proteasome inhibitor approved for the treatment of multiple myeloma is bortezomib (Velcad® ⁾ .

Angiogenesis inhibitors: These medications can be used to prevent cancer cells from developing a new blood supply. Angiogenesis is the process by which cells create new blood vessels. When tumors reach a certain size, they use proteins called growth factor receptors to reach the body’s vascular system and create a constant flow of blood that can help drive tumor growth. Angiogenesis inhibitors look for growth factor proteins and prevent them from working, cutting off the tumor’s nutritional supply. Inhibitors of angiogenesis commonly used to treat cancer are bevacizumab (Avastin®), which can be used to treat many cancers, and cetuximab (Erbitux®), which can be used to treat colorectal cancer.

Tyrosine kinase inhibitors: These block signals are sent to the cell nucleus, which can cause the cell to grow or multiply. Tyrosine kinases are often overactive in cancer cells, and when activated by the signaling molecule, they can lead to uncontrolled growth or cell division. Tyrosine kinase inhibitors block these enzymes and can stop or slow tumor growth. Tyrosine kinase inhibitors commonly used to treat cancer are imatinib (Gleevec®), which can be used to treat leukemia, and crizotinib (Xalkori®), which can be used to treat cell-cell lung cancer.