Of all the risk factors associated with cancer: obesity, smoking, sun exposure etc., there is none more universal than aging. According to a 2011 report on Global Health and Aging, the number of people aged 65 or older is projected to reach 1.5 billion by 2050 and correspondingly the yearly number of new cancer cases alone is estimated to reach 27 million by 2030. Therefore it is of paramount importance to develop new anti-cancer approaches to meet the humanitarian and economic challenges associated with our aging global population.
One such approach is to target cancers that employ a particular mechanism to achieve cellular immortality — Alternative Lengthening of Telomeres, or “ALT”.
Every time a normal somatic cell divides, the DNA at the ends of its chromosomes, called telomeres, gets shorter. When the telomeres shorten too much, the cell permanently stops dividing and either enters senescence or undergoes apoptosis (programmed cell death). Telomere shortening thus acts as a biological mechanism for limiting cellular life span. Most cancer cells bypass this failsafe by synthesizing new telomeres using the enzyme telomerase.
Several therapies targeting this well-described telomerase-based pathway are in the advanced stages of clinical development, but as with any cancer therapy there is the potential for development of resistance against telomerase-based strategies to defeat cancer. Studies using mice and human cancer cell lines have demonstrated that cancer can overcome the loss of telomerase by using a telomerase-independent mechanism called alternative lengthening of telomeres (ALT).
There are currently no ALT-targeted anti-cancer therapeutics, however, largely because this process is much less well understood. In contrast to telomerase-driven telomere lengthening, which does occur in the stem cells of healthy tissues and organs, ALT activity is not found in normal human postnatal tissues. A positive side of this fact is that this would allow for more-effective dosing with minimal side effects. ALT is present in some of the most clinically challenging cancers to treat, such as pediatric and adult brain cancers, soft tissue sarcoma, osteosarcoma, and lung cancers. Clearly, targeting ALT is a very attractive strategy in the development of novel cancer therapies.
Decades of research in aging people and experimental animals has established that there are no more than seven major classes of such cellular and molecular damage, shown in the table below. We can be confident that this list is complete, first and foremost because of the fact that scientists have not discovered any new kinds of aging damage in nearly a generation of research, despite the increasing number of centers and scientists dedicated to studying the matter, and the use of increasingly powerful tools to examine the aging body. In its own way, each of these kinds of damage make our bodies frail, and contribute to the rising frailty and ill-health that appears in our sixth decade of life and accelerates thereafter.
Cell Loss and Atrophy