MMP inhibitor to kill senescent cells

Important work in the understanding and remedy of aging at the Buck Institute’s Systems Biology Symposium of Aging held November 10-13, 2009 was presented by Judith Campisi in a keynote talk, “The Four Horsemen – Damage, Inflammation, Cancer and Aging: Integrating Aging and Age-Related Research.”

Summary
Campisi has found a common biological explanation for the related phenomena of aging, degenerative disease and cancer: the senescence-associated secretory phenotype (SASP). Senescent cells produce the SASP, essentially inflammation, which can then trigger degenerative disease (aging) and hyper-prolific disease (cancer). A potential solution is to remove the 10-15% of senescent cells that are not naturally killed by the immune system by using matrix metalloproteinase (MMP) inhibitors.

Background
Humans are much longer-lived than other organisms such as flies because they have evolved cell-dividing mechanisms for tissue regeneration and repair. However, mistakes in the form of mitotic mutations occur during this process and build-up cumulatively which can cause cancer. To counter the build-up of mutations, tumor suppressor mechanisms evolved. One action of gate-keeper tumor suppression mechanisms is to direct damaged cells to senesce, or lose function.

Senescent cells are not harmless, they amass at sites of inflammation and pre-cancer and secrete up to 40 different cytokines (immunoregulatory proteins) which together can be thought of as the SASP secretome. All major age-related diseases share an inflammatory pathogenesis including atherosclerosis, myocardial infarction, stroke and metabolic syndrome. The build-up of senescent cells can lead to both degenerative disease (aging) and hyper-proliferative disease (cancer).

The purpose of the cytokines is to repair tissue. In the SASP secretome, they are perhaps trying to summon the immune system, communicating to the rest of the tissue that there is a problem. The immune system does arrive and kill most senescent cells, but 10-15% survive, perhaps due to the over-expression of matrix metalloproteinases (MMPs) which can cleave the ligands off the cell surface where natural killer cells would bind, allowing the cell to escape the immune system.

Solution
Extending the existing research and application of matrix metalloproteinase (MMP) inhibitors, chemicals that mimic the binding site, Campisi’s lab has been able to drive senescent cell killing to 95%.