Download Testing the Role of Non-canonical FAK Signaling

Susan G. Komen for the Cure
Research Grants – Fiscal Year 2011
This research grant was approved by Komen’s national board of directors for FY2011 Research Programs
funding. This grant will be funded upon the execution of grant agreements between Komen and the
grantee institutions.
Testing the Role of Non-canonical FAK Signaling in Breast Cancer Metastasis
Investigator(s): David Schlaepfer, PhD
Fellow: Isabelle Tanjoni, DVM, PhD
University of California at San Diego, California
Awarded: $180,000
Grant Mechanism: Post Doctoral Fellowship - Basic Research
Research Focus: Biology
Public Abstract:
Study hypothesis and how it will be tested. Breast cancer is the second highest cause of cancer-related
death and the most frequent cancer diagnosed in women world-wide. A primary complication of breast
cancer is metastasis (tumor spread to distant sites). While the five-year breast cancer survival rate for
women with localized breast cancer is 98%, this drops to 27% for women with distant organ metastasis.
I have been working with a group of researchers on the development and pre-clinical testing of a small
molecule inhibitor to a protein called focal adhesion kinase (FAK). During breast cancer progression, FAK
expression is elevated, and this is correlated with poor patient prognosis. My research is focused on
elucidating the molecular mechanism of FAK action within tumor cells that provides the push for tumor
growth and spread. Importantly, my recently-published research studies in mice were the first to show
that the chemical FAK inhibitor blocked breast cancer tumor growth and metastasis in mice. This was
associated with the selective death of the tumor cells within the primary tumor. However, the FAK
inhibitor drug was not inherently toxic to the mice (we gave it to them every day in their drinking water).
Thus, my project is to define how this selective killing of the tumor cells is occurring. The standard
way to grow tumor cells in the lab is on plastic dishes and this is termed two dimensional (2D) growth.
However, tumors in the body grow in three-dimensions (3D) and we can partially mimic this the lab by
growing cells as 3D spheroids. I have found that breast carcinoma cells grown as 3D spheroids are very
sensitive to FAK inhibition that results in cell death. Importantly, the same cells grown in 2D are
resistant FAK inhibitor-associated killing. Thus, in this proposal, I will test a specific hypothesis as to how
FAK activity is promoting the selective survival of tumor cells in spheroids. For this, I will investigate a
novel intracellular signaling connection between FAK and two other proteins, NEED9 and Rap1, that are
also involved in promoting cancer progression. I hypothesize that the activity of FAK activates NEDD9Rap1 and this this leads the change in a cell surface receptor called beta1 integrin. This signaling would
be arising from inside the tumor cells as they are growing as spheroids. It is a “non-canonical” signaling
pathway as our current understanding of FAK signaling has shown that beta1-integrin receptor
clustering triggers FAK activation through an outside-in linkage. It is likely that this is a circular pathway
that tumor cells use to grow and spread uncontrollably.
How does this project advance breast cancer
understanding? Many researchers study breast carcinoma tumor cell growth in the lab under 2D
conditions. When testing anti-tumor drugs, the breast carcinoma cells show increased resistance when
grown under 3D conditions compared to 2D. Unfortunately, this is a bad trend that may lead to tumor
resistance to particular drugs. However, I have found that FAK inhibitors trigger the death of breast
cancer cells under 3D but not 2D conditions. Thus, my work may have uncovered a potential “Achilles
heel” for stopping breast cancer tumor growth. In this proposal, I will have 3 specific aims directed at
elucidating the molecular mechanisms linking FAK activity to 3D cell survival and how this may promote
metastatic tumor dissemination. I will test a specific molecular hypothesis as to how FAK promotes the
survival of breast carcinoma cells in 3D environments. I hypothesize that this pathway is acting to
promote activation of a cell surface receptor called beta1 integrin via signaling from inside cells. I also
hypothesize that FAK inhibition preventing beta1 integrin activation is a key event promoting tumor cell
death by a novel process termed entosis (cell death via cell-cell engulfment). Altering this cell survival
pathway may act to prevent tumor metastasis.
The idea that FAK can activate integrins is new, and
how this occurs is not yet known, so my research contributions will advance our understanding of how
breast cancer cells inappropriately grow and survive under 3D conditions. Tumor spheroids are a source
of metastatic spread and recurrent disease, thus it is important that we determine how FAK functions at
the molecular level so that this knowledge may be applied to improving clinical treatment outcomes.
These cellular control pathways are important in breast cancer and have translational potential to
reduce disease-associated morbidity. By working on a translationally-relevant project, I hope that my
work will help bridge the gap between basic research and improvements in clinical care.
Importance
to patients with breast cancer. My research results will be important in understanding modes of action
as current human clinical trials with FAK inhibitors move forward. Most importantly, FAK inhibitors are
not toxic to normal cells (which do not normally grow as spheroids or tumors). Current
chemotherapeutic treatments for breast cancer involve the use of cytotoxic drugs to kill the tumor cells,
which cause several negative side effects in patients. Tumor cells use multiple survival pathways and we
hypothesize that the FAK survival pathway is distinct from those targeted by current chemotherapeutics.
Thus, knowledge of the FAK-survival pathway can be directly applied to future clinical trials, as
inherently non-toxic FAK inhibitor may potently synergize with existing chemotherapeutics to lessen
patient burden as well as drug side-effects.
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