|
Mignon Loh, M.D. |
|
Loh Lab |
|
My research would be categorized as clinical-translational studies in pediatric leukemia. My interests are split between two diseases, juvenile myelomonocytic leukemia (JMML) and acute lymphoblastic leukemia (ALL). My research broadly involves the identification, significance, and function of genetic mutations in pediatric leukemia. The laboratory develops and uses laboratory based assays to conduct cohort studies in primary human cells that interrogate the role of specific genetic mutations in human leukemia. For instance, in 2004 and 2005, I co-authored a number of publications that established the spectrum of PTPN11 mutations in various malignancies. The role of mutated PTPN11, which encodes SHP-2, cannot be overstated since this is one of the first examples of a phosphatase to function as an oncogene. Importantly, we published one of the first publications that established that these point mutations exists in 35% of patients with de novo JMML {Loh, 2004 #1467}. We then continued to report that PTPN11 mutations existed in 5% of pediatric AML (collaboration with the Children’s Oncology Group (COG)), were rare in CMML/MDS (collaboration with MD Anderson Cancer Center and investigators in Italy), and were rare in other solid tumors (collaboration with multiple adult oncology groups with investigators from Harvard University) {Loh, 2005 #1493;Loh, 2004 #1467;Loh, 2004 #1313;Bentires-Alj, 2004 #1466}. In another international collaboration, we also reported the most comprehensive analysis of these mutations in patients with syndromic JMML (patients with Noonan Syndrome) as well as in patients with de novo JMML {Kratz, 2005 #1491}.
As a follow-up to this work, we focused on integrating novel mutations into clinical use (e.g. assessing prognostic significance or minimal residual disease) as well as yield insights that lead to more scientific questions about the pathogenesis and mechanisms of disease. First, we developed a novel assay to monitor JMML patients undergoing chemotherapy or hematopoietic stem cell transplant by exploiting a PCR-based technique called mismatched amplification of the mutated allele (MAMA). Designing a fluorescent PCR strategy on top of this, we are able to quantitate levels of mutant PTPN11 or NRAS/KRAS alleles in patients{Archambeault, 2008 #1510}. Given the difficulties with following JMML patients on therapy, this has proven to be an extremely useful clinical tool that will be incorporated into future clinical trials sponsored by COG. Importantly, we have exported our reagents to our colleagues in Germany, where they are also using it to monitor their patients.
Secondly, we have noticed that rare patients harbor two detectable mutations in Ras pathway molecules. One characteristic feature of JMML is the hypersensitive growth of the mononuclear cells to low doses of GM-CSF. We have developed human colony assays and can easily demonstrate this hypersensitivity. In addition, we have picked colonies (representing the outgrowth of a single progenitor cell) and have demonstrated that patients with single mutations almost never have any normal hematopoietic progenitors grow out in these colony assays at diagnosis. For patients with double mutations, we have been able to strictly order the acquisition of these somatic mutations, which is a novel finding. This data will be prepared shortly for a manuscript.
A third area of interest has focused on using phosphoflow signaling tools in collaboration with a graduate student in Garry Nolan’s laboratory to dissect the aberrant signal transduction pathways that arise in response to mutations in the Ras pathway in juvenile myelomonocytic leukemia (JMML). We have determined that CD38 intermediate, CD33/CD14+ cells hyperphosphorylate Stat5 in response to low doses of GM-CSF, mimicking the CFU-GM assays. This data was recently published as a cover article in Cancer Cell (October 2008). We continue to assess signaling abnormalities in the stem and progenitor cell compartments of JMML and hope to rationally select targeted agents to treat these patients with an otherwise fatal disease. We are currently testing such agents in accurate mouse models of JMML.
A final area of interest is the development of phosphosignaling in Acute Lymphoblastic Leukemia, the most common childhood cancer. While much of the genomic landscape has been mapped out for ALL, relatively little is know about the functional consequences of these genetic lesions on aberrant B-precursor cell signaling. By developing a map of these perturbed networks we hope to identify characteristic nodes that can be further exploited therapeutically, particularly in patients who can be identified to do poorly based on the presence of residual leukemia cells in their bone marrow at the end of their first month of therapy. |
