In a recent study (August of 2010) conducted
by researchers at Thomas Jefferson University’s Kimmel Cancer Center, scientists found
evidence to suggest that cancer cells use recycled nutrients from normal
supporting cells in order to support their own growth and be able to
metastasize to other parts of the body. The supporting cells are fibroblasts,
which form the connective tissue surrounding tumor cells (stroma). Through the
process of oxidative stress, cancer cells trick these fibroblasts to
essentially eat themselves (the process of autophagy, which we will soon
discuss in class) and leave the nutrients behind for the cancer cells (which
would explain why patients tend to lose weight with the onset of cancer).
Senior investigator, Michael P.
Lisanti, claims, “We think we have finally figured out how cancer really works
– and this reverses 85 years of dogma, upon which current cancer research and
therapy is based.” One particular concept in oncology that this study
challenges is the Warburg Effect (developed by Otto Warburg in 1924). Warburg
claimed that tumor cells changed their metabolism in order to fuel their growth
and cited the fact that the cells had no mitochondria as evidence for his
claim. However, Lisanti and his team argue that the explanation for Warburg’s
findings are due to the fact that he studied the cells in vitro rather than in vivo.
When the researchers at the Kimmel Cancer Center mixed fibroblasts and cancers
cells together, they found that cancer cells had mitochondria while the
fibroblasts did not have any. They concluded that the fibroblasts were essentially
“eating” their mitochondria, and the cancer cells were using their own mitochondria
to process all the nutrients created by the fibroblasts (a process they termed “The Reverse Warburg
Effect”). The fibroblasts were being induced through oxidative stress to
undergo autophagy (a full discussion of the mechanism of how this process works
can be found here:
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3041164/?tool=pubmed). Additionally,
researchers found that oxidative stress in fibroblasts stimulated the production
of reactive oxygen species (ROS), which in turn promoted mutations in cancer cells
that favored their development toward becoming fully invasive (something similar to a positive feedback loop we
discussed in class).
As a result of this evidence,
researchers at the Kimmel Cancer Center have begun investigation of certain
anti-oxidants that can prevent oxidative stress in fibroblasts, thereby
eliminating the source of nutrients for cancer cells. As an interesting aside,
I’m not sure if this might be a possible correlation between diet and cancer,
as certain foods (especially fruits and vegetables) are known to have a variety
of natural anti-oxidants. The researchers also identified two metabolites,
lactate and ketones, produced by fibroblasts which serve as a high-energy food
for cancer cells. I want to highlight ketones only because it relates to a blog
entry someone posted earlier this week with respect to diabetes. It seems that
diabetes produces elevated levels of ketones in fibroblasts, which again
promotes cancer cell growth. This could explain why 80% of pancreatic cancer
patients (and perhaps there are similar numbers for other cancers as well), as indicated in the blog, were also found to have
diabetes.
In addition, the researchers also
claimed that their new theory implies that angiogenesis (one of the hallmarks
of cancer we have studied) is not necessary for cancer cells to be able to metastasize
to other parts of the body. According to them, this would explain why
angiogenesis inhibitors (manufactured drugs) have failed to produce successful results in clinical
trials. However, I am not so sure if this aspect of their study is necessarily
accurate (or backed up with enough evidence for that matter). I know we have
yet to discuss this in detail, but I found an article (http://www.cancer.gov/cancertopics/factsheet/Therapy/angiogenesis-inhibitors)
from the National Cancer Institute, which still contends that angiogenesis is
essential for tumors to be able to “grow beyond a few millimeters in size.” I
am not entirely sure what to make of these conflicting opinions, but I think I
will stay on the side of the latter argument (considering that many sources,
including our own textbook, have argued this as well).
Another issue that this article
brings up, which I think is important is the fact that if much cancer research is in fact
done in vitro, then we need to begin to study cancer in vivo (considering that the interactions that take place between cancer
cells and the cells in the surrounding environment - the tumor microenvironment -
contribute to the growth and spread of cancer cells).
References:
“Angiogenesis Inhibitors.” National Cancer Institute Factsheet. National Cancer Institute.
Web. 19 Apr. 2012. <http://www.cancer.gov/>
“'How & Why’ Cancer Cells Eat Us Alive.” Jefferson University Hospitals. Thomas
Jefferson University Hospitals, 31 Aug. 2010. Web. 19 Apr. 2012. <http://www.jeffersonhospital.org/>► 1:55
