Massachusetts General Hospital

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Jeffrey Settleman
Laurel Schwartz Professor of Medicine
Harvard Medical School

Director
Center for Molecular Therapeutics

Scientific Director
Massachusetts General Hospital Cancer Center

Research Summary Our laboratory is investigating the regulation and biological function of signal transduction pathways in the context of human cancer as they relate to therapeutic opportunities. We are particularly interested in the role of protein kinase-mediated signaling pathways in human tumorigenesis. There are more than 500 kinases encoded by the human genome and many of these have been implicated in cancer. We are exploring mechanisms of molecularly-targeted cancer therapeutics that influence kinase-mediated signaling pathways that become dysregulated during human tumorigenesis. These efforts have led, for example, to the establishment of a link between a class of somatic activating EGF receptor mutations in lung cancer and the response to EGF receptor inhibitor drugs in a subset of treated patients. To begin to identify additional genetic determinants of drug response in human cancers, we have established a large collection of human cancer cell lines that we are testing for sensitivity to targeted kinase inhibitors. We have established a high-throughput fully automated screening platform to test these lines for drug sensitivity and to identify biomarkers that can be used clinically to guide treatment. These studies are providing further insights into the “wiring” of a tumor cell and the relationship between cancer cell genotypes and drug sensitivity, and could therefore lead to the optimization of molecularly targeted therapies.

We are also conducting studies to develop a better understanding of the “oncogene addiction” phenomenon. Oncogene addiction refers to the acquired dependency of cancer cells on a single cellular pathway for survival or sustained proliferation, despite the fact that such cells have accumulated numerous genetic alterations. Moreover, oncogene addiction may account for the dramatic clinical responses reported in some cancer patients treated with the various targeted kinase inhibitors. However, a molecular mechanism to explain oncogene addiction has been elusive. We have conducted studies that reveal a potential mechanism to explain oncogene addiction that involves a shift in the balance of pro-survival and pro-apoptotic signals in oncogene-dependent cancer cells. We are continuing to pursue the specific nature of signaling pathways that contribute to this phenomenon, which may have important implications for the therapeutic use of targeted kinase inhibitors.

Finally, we are interested in understanding the mechanisms by which cancer cells become resistant to targeted drugs that disrupt signaling pathways, which remains an important limitation to their clinical utility. We have developed several in vitro models of drug resistance and we are examining the relationship between a newly identified sub-population of cancer cells that we describe as “drug tolerant” and the more stable forms of genetically-mediated drug resistance.

Jeffrey Settleman, PhD
Principal Investigator

Group Members

Assistant Professor

• Sreenath Sharma, PhD
  

Instructor

• Mike Rothenberg, MD, PhD
  

Research Fellows

• Tim Wilson, PhD
• Anurag Singh, PhD
  
• Nisebita Sahu, PhD
  
• Raju Pusapati, PhD
• Ryan Corcoran, MD, PhD
• Ho-June Lee, PhD
• Rushika Perera, PhD
• Jennifer Lamb, PhD
  

Research Technologists

• Kaitlin McCutcheon
• Diana Lee
• Angela Tam
• Patricia Greninger
• Randy Milano

Research Technicians

• Laury Lucien
• Stephen Lutz
• Michael Sweeney
• Daniel Winokur

Graduate Student

• Annie Phoung Vo

Lab Manager

• Khaleda Haider

Administrative Assistant

• Crystal Amoroso

Research Projects

1. Cancer cell line screening to identify genotype-associated drug sensitivity.
   We are actively investigating better ways to match individual cancer patients with particular targeted drug therapies in order to maximize the likelihood of a positive clinical response. The broad objective of our Center for Molecular Therapeutics is to identify molecular genetic features of a tumor that predict responsiveness to the various molecularly targeted therapies that have either recently been developed or are in early clinical development. Some of these drugs have been found to be highly effective in inducing remissions in a fraction of treated patients, and it is becoming increasingly clear that molecular features, or “biomarkers”, that correlate with drug-responsiveness can be identified in these patients. Such findings can be of great value in designing clinical trials of new cancer drugs as well as in optimizing the clinical benefit of approved drugs. The Center’s platform makes use of a large collection of human cancer cell lines derived from a wide variety of tissue types. The collection now includes more than 1100 cancer cell lines derived from tumors of virtually every tissue. We have optimized automated technologies to screen the collection for sensitivity to drugs and other targeted inhibitory compounds. Drug-sensitive lines are being further analyzed to identify molecular features that are shared among the responsive cell lines and are strongly associated with drug sensitivity. These features include 1) potential mutations in the gene encoding the drug target, 2) amplification of particular genes as assessed by comparative genomic hybridization (CGH) array technology, and 3) gene expression signatures, as assessed by microarray profiling. The identification of such biomarkers is expected to provide important insights into the molecular determinants of sensitivity to potential anti-cancer drugs and should be of great value in the clinical development and clinical use of novel drugs whose appropriate therapeutic setting would be otherwise difficult to predict. Our findings thus far indicate that this cell line screening program provides a powerful model for identifying biomarkers that can be used to predict drug response in cancer patients.


2. Reversible tolerance to cancer drugs.
   Anti-cancer drugs typically produce short-lived remissions due to acquired drug resistance. Notably, drug-responsive patients who subsequently relapse can experience a second response to re-treatment with the same drug following a “drug holiday”, implicating a reversible “drug-tolerant” state. While modeling the acute response of cancer cell populations to a variety of anti-cancer drugs, we have identified a “drug-tolerant” subpopulation of cancer cells. These cells were found to exhibit a distinct chromatin state and exquisite sensitivity to chromatin modifying agents. They arise from a small sub-population of slowly proliferating drug-tolerant cells, and interestingly, this drug-tolerant phenotype is transiently acquired and relinquished by individual cells within the population at a low frequency. We are currently exploring mechanisms underlying reversible drug tolerance and we are developing strategies to target this cancer cell subpopulation therapeutically.


3. A gene expression signature associated with “K-Ras addiction”.
   K-Ras mutations occur frequently in epithelial cancers. Using shRNAs to deplete K-Ras in lung and pancreatic cancer cell lines harboring K-Ras mutations, we identified two classes—cell lines that do or do not require K-Ras to maintain viability. Comparing these two classes of cancer cells revealed a gene expression signature in K-Ras-dependent cells, associated with a well-differentiated epithelial phenotype, which was also seen in primary tumors. Several of these genes encode pharmacologically tractable proteins, such as Syk and Ron kinases and integrin beta6, depletion of which induces epithelial-mesenchymal transformation (EMT) and apoptosis specifically in K-Ras-dependent cells. These findings indicate that epithelial differentiation and tumor cell viability are associated, and that EMT regulators in “K-Ras-addicted” cancers represent candidate therapeutic targets. We are extending these observations to look for K-Ras dependency signatures in other tissue types and to identify additional candidate therapeutic targets associated with K-Ras addiction.

There are no available research positions at this time.

Settleman Lab

Phone: 617-724-9556
Fax: 617-726-7808
Email: settleman@helix.mgh.harvard.edu