Study Explains How Tumors Outlast Chemotherapy

Beyond defending the body against infection, the immune system also plays a central role in healing injured tissue, prompting cell division to replace what’s been lost and spurring the growth of new blood vessels to deliver extra oxygen and nutrients to the damaged area. This repair process is tightly choreographed, generating new cells only in the places and at the times they’re actually needed.

Tumors have long been known to hijack this same repair system by disguising themselves as injured tissue, persuading the immune system to help them grow and gain resources rather than destroy them—a pattern that has led researchers to call cancers “wounds that do not heal.” Exactly how tumors trigger that wound-healing response, though, has remained unclear.

A new study in Science Advances from Trinity College Dublin’s Smurfit Institute of Genetics, led by Seamus Martin, identifies a piece of that mechanism: a group of molecules called Inhibitor of Apoptosis Proteins, or IAPs, that let tumors survive standard chemotherapy drugs. IAPs do this by blocking “Death Receptors,” molecules that chemotherapy normally switches on in response to DNA damage in order to trigger cell death.

The effect goes further than simple survival. IAPs also push the surviving tumor cells into a state called premature senescence, described as “zombie-like” because the cells stop dividing but remain active, this time as coordinators of wound healing that marshal a helpful immune response and allow the tumor to recover from treatment. These senescent cells transform dramatically within days of chemotherapy exposure, growing to nearly ten times their normal size and switching on genes tied to wound healing, which sharply boosts their ability to release inflammatory signals that draw in immune cells. A similar buildup of senescent cells over time is thought to contribute to age-related inflammation and the gradual decline of tissue function. 

The researchers also found that these chemotherapy-induced senescent cells depend heavily on IAPs simply to stay alive, and that drugs blocking IAPs, known as IAP antagonists, selectively killed off the senescent cells by switching the Death Receptor self-destruct pathway back on inside them.

Tumors that survive chemotherapy remain one of the toughest obstacles in cancer treatment, and better outcomes depend on understanding exactly how tumors manage to persist and where they’re vulnerable. This research points to a previously unrecognized escape route, in which tumors enlist the immune system’s own healing machinery, while also flagging IAP antagonists as a promising way to close off that route.

Professor Martin said: “Discovering how tumors can evade the cell-killing effects of chemotherapy and enter senescence is an important and challenging problem. These new findings suggest ways in which we may be able to lower the defenses of tumors by neutralizing IAPs after the delivery of chemotherapeutic drugs, which should block their entry to senescence and kill more cells of the tumor.”