We develop and use in-vivo models for neural cancers to: 1) Identify genetic events that promote tumorigenesis. 2) Study cancer stem and progenitor cells. 3) Evaluate new targets, chemical genetic approaches, and mechanistic rationales for combining targeted agents.
Stem cell biology, genetics, and developmental therapeutics in glioma. Aberrant EGFR signaling features prominently in glioma, the most common primary adult brain tumor. We generated a mouse model for glioma by over-expressing EGFR under the S100 beta promoter (Weiss, 2003). Expression of oncogenes in rare cancer-stem-like cells in the subventricular zone led to differentiation block and aberrant glial differentiation, resulting in astrocytoma (Persson, In revision). In contrast, murine oligodendrogliomas arose from abundant oligodendroglial progenitors in white matter. We described a progenitor origin for this more favorable form of glioma, demonstrating that a progenitor rather than a stem-cell origin underlies the improved outcome in patients (Persson, 2010). We were among the first to describe oncogene addiction driven by activated EGFR (Fan, 2002). We described and characterized dual inhibitors of PI3K and mTOR, demonstrating that these drugs blocked mTOR inhibitor-driven activation of Akt, that EGFR signaling to Akt was dispensable for arrest, that EGFR signaling to Protein Kinase C alpha was central to the ability of PI3K to signal to mTOR, and that blockade of PI3K, mTOR and autophagy converted cytostatic PI3K/mTOR inhibitors into cytotoxic agents (Fan, 2006-2010). Activated alleles of EGFR occur in brain and lung-cancers, yet EGFR inhibitors benefit only lung cancer. We traced this differential response to lower occupancy rates of EGFR inhibitors in brain as compared to lung cancer mutants (Barkovich 2012). EGFR is frequently co-amplified with EGFRvIII. We showed co-expression of EGFR and vIII in individual cells in human tumors, that vIII is a substrate for EGFR, and that co-expression drives STAT signaling (Fan et al, 2013).
Targeted expression of MYCN generate models of neuroblastoma and medulloblastoma in transgenic mice. Neuroblastoma is the third most common tumor of childhood. The proto-oncogene MYCN is amplified in 25% of neuroblastomas, marking incurable disease. We generated transgenic mice that mis-expressed MYCN in neural crest, that developed neuroblastoma, and that remain the standard GEM model used by the community (Weiss et al, 1997). Genome-wide screens revealed genetic alignment with human tumors (Weiss et al, 2002, Hackett et al, 2003). Through systems biology approaches, we identified altered neurotransmitter signaling through GABA as contributing to human and murine neuroblastoma, and described the alternative splicing landscape (Hackett et al, 2014; Chen et al, 2015). Murine neuroblastoma tumors mutant at p53 were therapy resistant, modeling relapsed, drug-resistant neuroblastoma (Chesler, 2006-8). MYCN blockade reduced VEGF signaling, promoting vascular collapse (Chanthery, 2012). We synthesized and solved the co-crystal structure of a new class of MYC/MYCN-degrading drugs that block a kinase-independent MYC/MYCN stabilizing function of Aurora Kinase, potently degrading MYCN in-vivo (Gustafson, Meyerowitz, Cancer Cell, 2014).
MYCN is mis-expresssed in the majority of medulloblastoma tumors. We used the Tet system to regulate MYCN expression and to image tumor-associated firefly luciferase expression in-vivo. Targeted expression of MYCN to the brains of transgenic mice led to luciferase and MYCN-positive medulloblastoma, (Swartling, 2010). We also transduced MYCN into murine neural stem cells, separately cultured from prenatal or postnatal mice, with cells from hindbrain generating medulloblastoma, and from forebrain generating glioma. Orthotopic transduction of prenatal cerebellar stem cells drove SHH-dependent, while both prenatal brainstem and postnatal cerebellar stem cells drove SHH-independent disease (Swartling 2012). Thus, distinct neural stem cell populations generated disparate brain tumors in response to MYCN.
Genome-wide sequencing efforts have generally failed to identify new driver mutations for the majority of high-risk neuroblastoma and medulloblastoma. In contrast, copy number analyses have identified recurrent regions of variation. Regions of gain or loss on any human chromosome correspond to multiple different chromosomes in the mouse, which is challenging to model. Thus, we are incorporating known driver mutations into engineered human induced pluripotent stem cells, and have generated humanized mouse models for neuroblastoma and medulloblastoma. These human based xenograft models represent a genetic platform to test copy number variation as cancer drivers, and to develop therapies.
LEADERSHIP. I am Professor of Neurology, Pediatrics, and Neurosurgery at UCSF, Director of Clinical Child Neurology at San Francisco General Hospital, Co-Leader of the Helen Diller Family Comprehensive Cancer Center’s Pediatrics Malignancies Program and Chair of the weekly seminar series in UCSF’s Helen Diller Family Comprehensive Cancer Center, and Project PI in UCSF’s Pediatric Brain Tumor Foundation Program. I edit Breaking Advances for Cancer Research, am associate editor of the NeuroOncology, Molecular and Cellular Biology, and Scientific Reports, serve on the Neuroblastoma Biology Committee for the Children’s Oncology Group, and am advise Research Programs at Stanford and at Saint Jude Children’s Research Hospital. I have organized two international meetings on mouse models for neural cancers for the NCI, was co-organizer of the Cold Spring Harbor Models and Mechanisms of Cancer meeting (2009-2014), and was founding organizer of the now annual Medulloblastoma in the Mountains, and Pediatric Infiltrating Glioma Meeings (which bring together international basic and clinical thought leaders to translate scientific findings into patient care). I was co-chair of the program meeting for the 2007 centennial AACR meeting, and have organized basic science sessions at annual AACR meetings for many years. I was an external advisor for programs at CHLA, Mayo Clinic and University of Calgary; and have been external reviewer of NCI’s Mouse Cancer Genetics Program (2003 and 2008) and of the Departments of Genetics and of Tumor Cell Biology at St. Jude’s Children’s Research Hospital (2009). I have been a good citizen of the NIH for many years, and was a permanent member of both the NINDS NSDA study section. I was also a permanent member of the Cancer Prevention and Research Institute of Texas (under Chuck Sherr).
MENTORING RECORD. I formally mentor neurologists Li Gan (Associate Prof of Neurology at UCSF) Hannah Green, MD (Associate Prof of Neurology at UCSF), and Audrey Foster-Barber (Associate Prof of Pediatric Neurology at UCSF), David Young (fellow in Child Neurology), Christopher McGraw (resident in Neurology), and Abrar Choudhury (first year MSTP). Other mentees include Clay Gustafson, MD-PhD (K08 recipient and Alex Lemonade Stand Career Awardee, Asst Prof of Pediatrics at UCSF), Anders Persson, PhD (independent investigator and Assistant Professor of Neurology at UCSF), Theo Nicolaides, MD, (K08 recipient, independent investigator and Assistant Professor of Pediatrics at UCSF), Qi-Wen Fan, MD-PhD, (up for promotion to Associate Professor of Neurology at UCSF), and Lou Chesler (former K08 recipient and Professor at ICR in London). I was formally a mentor to Jonathan Hecht, MD-PhD (Assistant Prof of Pediatric Neurology, Stanford), Manu Hegde MD-PhD (Assistant Prof of Neurology, UCSF), Sabine Mueller, MD-PhD (Assistant Professor of Pediatric Neurology at UCSF), Kendall Nash, MD (Assistant Professor of Pediatric Neurology at UCSF), Kyle Steinman, MD (Assistant Prof of Pediatric Neurology, Univ of Washington) and Raquel Gardner (Assistant Professor at UCSF). In addition to Drs. Fan, Gustafson, Nicolaides, and Persson, above, my former postdoctoral fellow mentees also include Yvan Chanthery, PhD (now Asst Professor at Santa Clara University), Lou Chesler, MD-PhD (former K08 recipient and now full Professor and independent investigator at the Royal Marsden Hospital, ICR, UK), and Fredrik J. Swartling, PhD, (Assistant Professor and independent investigator at Uppsalla University, Sweden). I mentor on average 4-5 postdocs in my lab. Miller Huang, a postdoc in my lab, was awarded a K99 in 2016. I have mentored 4 PhD students (all have graduated) and three MD-PhD student (one graduated) in my own lab, as well as a large number of medical students and undergraduates. In addition, I mentor a large number of graduate students as a non-thesis advisor, and through sitting on qualifying exam and thesis committees.