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Justin M. Drake, Ph.D.
University of California, Los Angeles
RESEARCH STATEMENT
Pre-clinical and Translational Approaches to Assess Activated Signaling Pathways in Prostate Cancer
The goal of my research program will be to generate more effective, rational, and personalized treatment options
for advanced prostate cancer patients. I will do this through the mechanistic understanding of the signaling
pathways and therapeutic resistance mechanisms underlying advanced prostate cancer. My lab will combine my
experience using in vitro (Drake et al., 2010a; Drake et al., 2009) and in vivo (Drake et al., 2005; Drake et al.,
2012) models of mouse and human prostate cancer (graduate and postdoctoral studies) with phosphoproteomic
(Drake et al., 2013; Drake et al., 2012) and other mass spectrometry-based ‘omics’ technologies (postdoctoral
studies). My research laboratory will openly collaborate with clinical, basic, and computational scientists to
facilitate productive science towards my overall research program goals. The use of mass spectrometry for
proteomics will be conducted through the collaboration with other labs and core facilities. Finally, my expertise
is in prostate cancer and my studies will be initiated using prostate cancer models, but these approaches would
be applicable to numerous other cancer types and model systems increasing the collaboratory potential of my
research.
OVERVIEW
Prostate cancer is an androgen regulated disease that is the second-leading cause of cancer death for men in
the United States. The standard of care for aggressive prostate cancer patients is androgen deprivation therapy
(Fig. 1). Unfortunately, these tumors inevitably recur resulting in castration resistant prostate cancer (CRPC)
concomitant with metastatic disease. The development of new, potent anti-androgen agents have provided
increased survival benefit in CRPC patients, although the development of resistance to these therapies is
common, often leading to the development of a highly lethal variant termed small cell neuroendocrine carcinoma
(SCNC). These clinical findings have prompted the intense investigation into other signaling mechanisms beyond
the androgen receptor (AR) that are driving the progression of metastatic CRPC in patients who fail these antiandrogen therapies. My work and others suggest that enhanced tyrosine kinase signaling develops as a result
of acquired resistance to anti-androgens in CRPC patients and should be evaluated further as viable therapeutic
targets (Fig. 1) (Drake et al., 2013; Drake et al., 2012).
The identification of genetically altered tyrosine kinases
has transformed the way we treat cancers. Typically,
these genetic lesions render the kinase constitutively
active resulting in hyperactive pathways that lead to
continued cancer growth and survival. Hence, the
development of targeted therapies designed to block the
kinase’s activity have resulted in significant clinical
benefits. The history of genetic alterations in prostate
cancer, however, has revealed a paucity of activating
mutations in kinase genes (Grasso et al., 2012) although
kinase activity is elevated (Drake et al., 2012).
Accordingly, there are examples where non-mutated,
overactive kinases can drive disease such as BTK
tyrosine kinase in hematopoietic malignancies (Rawlings
et al., 1996) or SRC tyrosine kinase in prostate and colon
cancer (Cai et al., 2010; Cartwright et al., 1990). Recently, the approval of a BTK specific inhibitor for chronic
lymphocytic leukemia provides evidence that non-mutated hyperactive pathways can be therapeutically targeted
with clinical success (Byrd et al., 2013).
PREVIOUS AND CURRENT RESEARCH
During my Ph.D. training in the laboratory of Dr. Michael Henry at the University of Iowa, I investigated the cellular
and molecular mechanisms of metastatic prostate cancer. To understand the metastatic process in more detail,
I initially developed and characterized an in vivo xenograft model of metastatic disease by monitoring prostate
cancer cell dissemination via intracardiac injection coupled with bioluminescence imaging (BLI) (Drake et al.,
2005). I was able to show that dissemination of prostate cancer cells resembled metastatic tissue tropism that is
Justin M. Drake, Ph.D.
University of California, Los Angeles
observed clinically. Using this model, I investigated the efficacy of an endothelin receptor antagonist, atrasentan,
on prostate cancer cell metastasis (Drake et al., 2010b). Antagonism with atrasentan resulted in striking
differences in metastatic prostate cancer cell growth as tumor cells that seeded bone were growth repressed
while cells that seeded soft tissues (such as the liver) grew unimpeded. I also developed a new in vitro model of
metastasis, transendothelial migration, and found that the epithelial-to-mesenchymal (EMT) transcription factor,
ZEB1, regulated the transendothelial migration and in vivo metastatic potential of prostate cancer cells (Drake
et al., 2009). I was able to expand upon these findings and demonstrate that ZEB1 regulated the expression of
key basement membrane attachment proteins known as laminins and integrins, thereby promoting metastatic
disease (Drake et al., 2010a).
As a Postdoctoral Fellow in the laboratory of Dr. Owen Witte at the University of California, Los Angeles (UCLA),
I have focused on uncovering non-mutated kinases and kinase pathway targets in metastatic CRPC using
unbiased phosphopeptide enrichment strategies coupled with quantitative mass spectrometry in collaboration
with Dr. Thomas Graeber at UCLA. My recent work has revealed that tyrosine phosphorylation is heightened in
a panel of advanced non-tyrosine kinase-driven mouse tumors with SRC, JAK2, and EGFR tyrosine kinase
activity (Drake et al., 2012). A follow up to this work confirmed that human CRPC tissues also display robust
tyrosine phosphorylation when compared to organ confined, treatment naïve prostate tissues (Drake et al.,
2012). In collaboration with Dr. Kenneth Pienta and the University of Michigan I acquired rare lethal human
metastatic CRPC tissues via a rapid autopsy program to identify the activated tyrosine kinases. I observed that
these kinase activation patterns were highly conserved in multiple anatomically distinct metastatic lesions from
the same patient, but differed between patients and that co-targeting the SRC and MAPK pathways may be
clinically beneficial (Drake et al., 2013). These findings support clonally derived metastatic disease and that
matching activation patterns in an individual to a specific inhibitor or inhibitor combinations would be fruitful
clinically. Currently, I am assessing phosphoserine and phosphothreonine kinase activities in these clinical
tissues to identify more candidate kinases and kinase pathway targets for diagnostic and functional evaluation.
In collaboration with Dr. Josh Stuart at the University of California, Santa Cruz, we are developing computational
approaches to delineate the predominant kinase networks within this dataset for subsequent functional analysis.
FUTURE RESEARCH
Project 1: Evaluation of the signaling pathways that distinguish adenocarcinoma and small cell
neuroendocrine carcinoma (SCNC) using pre-clinical models of prostate cancer. Background: Prostate
SCNC is very rare in untreated adenocarcinomas. However, frequency of SCNC increases to greater than 20%
after resistance to anti-androgens with low survival rates. The identification of candidate kinases driving SCNC
may lead to new diagnostic and predictive biomarkers that will classify which patients are at a greater risk of
developing this highly lethal variant prior to selective therapy. This project is an extension of my currently funded
Department of Defense Exploration-Hypothesis Development Award.
Approach: I will use phosphoproteomic enrichment and
quantitative mass spectrometry to evaluate the differential
kinase signaling pathways between the neuroendocrinebased transgenic adenocarcinoma of the mouse prostate
(TRAMP) mouse model (Greenberg et al., 1995) compared
to transgenic adenocarcinoma mouse models such as
PTEN-/- (Wang et al., 2003) and MYC (Ellwood-Yen et al.,
2003) (Fig. 2A). Candidate kinases activated in the TRAMP
model, but not in the adenocarcinoma models, would then
be evaluated for their capability to induce SCNC using mouse or human tissue recombination cancer models
alone or in combination with other oncogenes or anti-androgens (such as abiraterone acetate or enzalutamide)
which drives the phenotype clinically (Fig. 2B). Further, I will evaluate clinical SCNC tissues for the candidate
kinase’s activity and diagnostic biomarker potential.
Project 2: Evaluation of therapeutic resistance in advanced prostate cancer. Background: I plan to evaluate
therapeutic resistance mechanisms in aggressive primary mouse and human tissue recombination cancer
models via 3 ways: (1) Define the resistance mechanisms that arise upon administration of anti-androgens
(primary resistance and data already collected from CRPC patients, Drake et al., 2013), (2) Pharmacologically
Justin M. Drake, Ph.D.
University of California, Los Angeles
target the primary resistance mechanisms in combination with anti-androgens, and (3) Evaluate new resistance
mechanisms to these combination therapies (secondary resistance). Once the mechanisms of primary and
secondary resistance to specific combinations of pharmacologic agents are understood, clinicians will then be
able to better predict which inhibitors to use early in the tumor life cycle. This project is the focus for my submitted
K22 Transition Career Development Award.
Approach: Several genetic mouse models
exist for prostate cancer but I will focus
initially on the PTEN-/- or MYC mouse
models as my source for prostate epithelial
cells. Initially, the mouse prostate
recombination cancer model will be utilized
to infect prostate epithelial cells from the
genetic mouse models (i.e. PTEN-/-) with
lentivirus expressing oncogenes such as the androgen receptor (AR) to develop aggressive prostate cancer
(Drake et al., 2012; Xin et al., 2006) (Fig. 3A). Aggressive prostate tumors will be re-implanted into castrated
mice at which point kinase activity will be assessed (Fig. 3B). Since I have previously shown that tyrosine kinase
activity is robust in aggressive mouse prostate tumors expressing oncogenes relevant to metastatic CRPC and
have utilized phosphoproteomics to characterize the activated kinases in these tumors, I can begin to perturb
the tumors with kinase inhibitors in combination with other agents (e.g. anti-androgens or PI3K inhibitors). During
perturbation, I would plan to monitor tumor response using in vivo imaging such as positron emission tomography
(PET) or BLI as well as evaluate the acute biochemical resistance mechanisms to these therapies via
phosphoproteomic and metabolomic enrichment methods coupled to quantitative mass spectrometry (Fig. 3C).
Project 3: Development of a diagnostic and predictive biomarker platform for CRPC. Background: Due to
the increasing resistance to anti-androgen therapies in metastatic prostate cancer, the development of
biomarkers that can either predict disease progression or stratify cancer patients for personalized therapy are
urgently needed. I plan to use targeted selected ion monitoring (SIM) mass spectrometry to evaluate druggable
kinase targets as diagnostic or predictive biomarkers for personalized therapy in prostate cancer. Targeted SIM
mass spectrometry will provide a viable alternative to traditional immunohistochemistry by increasing the
sensitivity and eliminating the need for an application specific antibody toward the kinase of interest (Fig. 4A, B).
In addition, this approach has the capability to evaluate dozens of kinase activation states simultaneously from
one tissue source. This project is the focus for my submitted Department of Defense Idea Development Award.
Approach: To develop the most clinically
relevant and actionable phosphopeptide list for
targeted SIM mass spectrometry, I plan to
identify and list the FDA-approved kinase
inhibitors indicated for cancer treatment. Once
identified,
I
can
then
construct
phosphopeptides flanking the activation site of
each kinase of interest. Initially, test runs will be
performed using established prostate cancer
cell line-derived xenograft tumors and then
subject them to phosphoproteomic enrichment
techniques coupled to targeted mass
spectrometry identification (Fig. 4C-F). The
ability to biopsy organ confined, treatment
naïve prostate tumors or metastatic CRPC
lesions for activated kinases would be the
ultimate goal of this project. The capability to
evaluate kinase activities in real time using this
approach could aid in diagnostic, prognostic,
predictive, or pharmacologic biomarker
detection and help stratify CRPC patients for personalized, inhibitor combinations.
Justin M. Drake, Ph.D.
University of California, Los Angeles
REFERENCES
Byrd, J. C., Furman, R. R., Coutre, S. E., Flinn, I. W., Burger, J. A., Blum, K. A., Grant, B., Sharman, J. P.,
Coleman, M., Wierda, W. G., et al. (2013). Targeting BTK with ibrutinib in relapsed chronic lymphocytic leukemia.
N Engl J Med 369, 32-42.
Cai, H., Babic, I., Wei, X., Huang, J., and Witte, O. N. (2010). Invasive prostate carcinoma driven by c-Src and
androgen receptor synergy. Cancer Res.
Cartwright, C. A., Meisler, A. I., and Eckhart, W. (1990). Activation of the pp60c-src protein kinase is an early
event in colonic carcinogenesis. Proc Natl Acad Sci U S A 87, 558-562.
Drake, J. M., Barnes, J. M., Madsen, J. M., Domann, F. E., Stipp, C. S., and Henry, M. D. (2010a). ZEB1
coordinately regulates laminin-332 and {beta}4 integrin expression altering the invasive phenotype of prostate
cancer cells. J Biol Chem 285, 33940-33948.
Drake, J. M., Danke, J. R., and Henry, M. D. (2010b). Bone-specific growth inhibition of prostate cancer
metastasis by atrasentan. Cancer Biol Ther 9.
Drake, J. M., Gabriel, C. L., and Henry, M. D. (2005). Assessing tumor growth and distribution in a model of
prostate cancer metastasis using bioluminescence imaging. Clin Exp Metastasis 22, 674-684.
Drake, J. M., Graham, N. A., Lee, J. K., Stoyanova, T., Faltermeier, C. M., Sud, S., Titz, B., Huang, J., Pienta,
K. J., Graeber, T. G., et al. (2013). Metastatic castration-resistant prostate cancer reveals intrapatient similarity
and interpatient heterogeneity of therapeutic kinase targets. Proc Natl Acad Sci U S A 110, E4762-4769.
Drake, J. M., Graham, N. A., Stoyanova, T., Sedghi, A., Goldstein, A. S., Cai, H., Smith, D. A., Zhang, H.,
Komisopoulou, E., Huang, J., et al. (2012). Oncogene-specific activation of tyrosine kinase networks during
prostate cancer progression. Proc Natl Acad Sci U S A 109, 1643-1648.
Drake, J. M., Strohbehn, G., Bair, T. B., Moreland, J. G., and Henry, M. D. (2009). ZEB1 Enhances
Transendothelial Migration and Represses the Epithelial Phenotype of Prostate Cancer Cells. Mol Biol Cell.
Ellwood-Yen, K., Graeber, T. G., Wongvipat, J., Iruela-Arispe, M. L., Zhang, J., Matusik, R., Thomas, G. V., and
Sawyers, C. L. (2003). Myc-driven murine prostate cancer shares molecular features with human prostate
tumors. Cancer Cell 4, 223-238.
Grasso, C. S., Wu, Y. M., Robinson, D. R., Cao, X., Dhanasekaran, S. M., Khan, A. P., Quist, M. J., Jing, X.,
Lonigro, R. J., Brenner, J. C., et al. (2012). The mutational landscape of lethal castration-resistant prostate
cancer. Nature 487, 239-243.
Greenberg, N. M., DeMayo, F., Finegold, M. J., Medina, D., Tilley, W. D., Aspinall, J. O., Cunha, G. R., Donjacour,
A. A., Matusik, R. J., and Rosen, J. M. (1995). Prostate cancer in a transgenic mouse. Proc Natl Acad Sci U S
A 92, 3439-3443.
Rawlings, D. J., Scharenberg, A. M., Park, H., Wahl, M. I., Lin, S., Kato, R. M., Fluckiger, A. C., Witte, O. N., and
Kinet, J. P. (1996). Activation of BTK by a phosphorylation mechanism initiated by SRC family kinases. Science
271, 822-825.
Wang, S., Gao, J., Lei, Q., Rozengurt, N., Pritchard, C., Jiao, J., Thomas, G. V., Li, G., Roy-Burman, P., Nelson,
P. S., et al. (2003). Prostate-specific deletion of the murine Pten tumor suppressor gene leads to metastatic
prostate cancer. Cancer Cell 4, 209-221.
Xin, L., Teitell, M. A., Lawson, D. A., Kwon, A., Mellinghoff, I. K., and Witte, O. N. (2006). Progression of prostate
cancer by synergy of AKT with genotropic and nongenotropic actions of the androgen receptor. Proc Natl Acad
Sci U S A 103, 7789-7794.
Justin M. Drake, Ph.D.
University of California, Los Angeles
TEACHING STATEMENT
Great teachers create the foundation for a prosperous community. Throughout my student life, I have been very
fortunate to be exposed to excellent teachers in all disciplines and that has directly influenced my career path
and impacted how I teach and will teach in the future.
My primary goal as a teacher will be to get the students excited about the course material. To do this, I must first
demonstrate my own enthusiasm for the topic as well as teach the material in a stimulating and logical manner.
From my experiences, I find students become more engaged if the topic you are discussing can be connected
to their everyday experiences and can demonstrate value that links the knowledge gained to their career goals
such as getting into professional school or being successfully employed. As a teacher, it will be my duty to convey
that consistently.
At the University of Iowa I was afforded 2 excellent teaching opportunities: (1) Teaching assistant for graduate
level human physiology and (2) Ambassador for the University of Iowa Health Sciences Program. The human
physiology course taught dental and graduate students, and my responsibilities included leading weekly research
paper discussions with graduate students to develop scientific comprehension, weekly review sessions on topics
pertaining to human physiology, and writing exam questions. As a result of my instruction, I received the 2008
Dr. Byron A. Schottelius Teaching Award, which is presented annually to a graduate student who shows
exceptional promise as a teacher in the physiological sciences.
Further, as an ambassador for the University of Iowa in 2008, I traveled to high schools to educate junior high
and high school students on the day to day activities of being a scientist, the truths and stereotypes of scientists,
and the wide array of career paths that a Ph.D. can take. I took pride in both of these opportunities as I realized
that my instruction, demeanor, and advice may positively influence the students I was teaching.
I have also had the opportunity to mentor several undergraduate and graduate students during my postdoctoral
studies at the University of California, Los Angeles in the laboratory of Dr. Owen Witte. As a mentor, my
responsibilities were to train my students to become better scientists, through the development of critical thinking
skills and knowledge of experimental design, and also to help them achieve their career goals. Excellent mentors
realize that each student is unique and can adjust their teaching/mentoring style accordingly. Students can reach
their full potential only if they are put into an environment that is best suited for that particular student. As I have
a background in athletics, I find that academic teachers and coaches are very similar. In either case, the
teacher/coach must be able to recognize the strengths and weaknesses of each individual to ultimately position
that individual into a position of success.
My scientific background is broad, and this is reflected in my teaching interests. Further, my research program
in cancer biology will directly influence my enthusiasm about teaching courses related to Biochemistry, Cell and
Molecular Biology, Physiology, and Cancer Biology to undergraduate, graduate, and medical students. As my
life has been directly impacted by good teachers, I am committed to the education of young scientists.