Predoctoral trainees are selected on a competitive basis from current graduate students in the following graduate programs at the University of Minnesota:
- Microbiology, Immunology & Cancer Biology (MICaB)
- Molecular, Cellular, and Developmental Biology & Genetics (MCDB&G)
- Biochemistry, Molecular Biology & Biophysics (BMBB)
Students in the MCDB&G and BMBB programs begin their training in a combined program in Molecular, Cellular and Structural Biology (MCSB).These programs provide broad training in core disciplines that are essential to cancer research: biochemistry, cell biology, immunology, microbiology and genetics. The curriculum within each program allows the student and faculty preceptor the opportunity to design a program of training that incorporates core knowledge in these disciplines, while allowing for specialization in a specific area. Specific graduate-level courses in Biology of Cancer and Translational Cancer Research are offered by the MICaB graduate program and are required for all trainees supported by the Cancer Biology Training Grant.
Current Predoctoral Trainees
Jose Valentin Lopez
Prostate Cancer (PCa) is the leading cause of cancer cases in U.S. men and the second leading cause of male cancer death. An advanced form the disease, termed castration-resistant prostate cancer (CRPC), is incurable, and accounts for most PCa mortality. A western diet increases the incidence of PCa and the risk of advanced PCa. The mechanisms by which a western diet – rich in fatty acids – leads to these outcomes remains to be elucidated. Previous work done by our laboratory and collaborators has shown that PCa cell line models are dependent on endogenous lipid synthesis through fatty acid synthase (FASN). The objective is to study requirements for endogenously-synthesized vs. endogenous lipids, and identify therapeutic targets in lipid metabolism pathways for treatment of CRPC. Preliminarily, I have observed that while all CRPC cell line models are sensitive to exogenous lipid depletion, the growth of only a subset of these can be rescued by replenishing the medium with fatty acids. Additionally, I have also observed that this rescue is specific to certain fatty acids.
Natasha Roman Ortiz
Breast cancer is the second leading cause of cancer deaths among women in the United States. Estrogen receptor positive [ER+] breast cancer has a more favorable prognosis; however, patients can experience recurrence for many years after initial diagnosis. Breast cancer stem cells (BCSC), which are dormant and exist as a minority sub-population (0-5%), drive recurrence, metastasis and resistance to therapies that primarily target rapidly proliferating tumor cells. Current treatments are insufficient to cure metastatic ER+ breast cancer and there are no FDA approved therapeutics that target BCSC. Mammalian orthoreovirus (MRV) is an oncolytic virotherapy tested in clinical trials for many cancer types including metastatic breast cancer. MRV was found to be safe, but efficacy limited as a monotherapy. In our studies we compared several laboratory MRV strains (T1L, R2) to the strain most similar to Reolysin, which is being tested in clinical trials (i.e. T3D). Our studies suggest that T3D, strain used in clinical trials is less effective in killing ER+ breast cancer cells and BCSCs. We propose to generate a novel MRV strain with enhanced BCSC-targeting capacity by serially passaging MRV strains in BCSC enriched 3D tumorsphere cultures. Our preliminary data have shown that serially passaged (SP) MRV strains (T1L SP, R2 SP) are more effective in decreasing MCF-7 paclitaxel resistant (TaxR) cells viability and inhibiting tumorsphere formation compared to the parental (P) strains (T1L P, R2 P). MRV induces cell death by different mechanisms (apoptosis, necroptosis) depending on the cell type. The mechanisms of MRV-induced cell death in BCSC and non-BCSC populations are unknown. We aim to define the effects of MRV-induced death comparing parental vs MRV serially passaged strains on BCSC and non- BCSC cell populations using single cell mass cytometry, flow cytometry, and cell death assays. We anticipate these studies will lead to an improved MRV oncolytic virotherapy that will be combined with clinically relevant inhibitors, such as CDK4/6 inhibitors and anti-estrogens, to prevent and treat therapy-resistant ER+ breast cancer.
My work focuses on examining the role of APOBECs in the development of secondary resistance to breast cancer treatment. APOBECs are a large family of deaminase enzymes whose upregulation has been documented in many cancers to cause significant DNA damage. Within this deaminase family of enzymes, APOBEC3B (A3B) has been demonstrated to have increased expression levels in breast cancer. A3B is unique among the larger APOBEC family for its nuclear localization. As a result, A3B has direct access to endogenous DNA, giving it a greater opportunity to act as a driver of tumor formation. This increased level has been known to cause tumor heterogeneity and drug resistance in animal models. To examine if A3B drives treatment resistance in breast cancer, we have generated A3B inducible plasmid that we have transfected into various cancer cell lines. These A3B-induced cells are being exposed to long-term standard-of-care breast tumor treatment and time to resistance is currently being studied. As a complementary approach, we are also screening clinical data sets to determine if A3B has any prognostic value and if it is predictive of treatment response. The results of this study may identify how A3B status may be leveraged to improve the outcomes of breast cancer patients.
It has been shown that estrogen receptor-mediated signaling drives macrophages to take on a pro-tumor (M2-like) phenotype and that this exacerbates cell proliferation and tumor associated macrophage (TAM) infiltration. It has also been suggested that TAMs express aromatase and produce estrogens locally in the tumor microenvironment (TME). Together, this suggests a positive feedback loop between estrogen signaling and M2 TAM infiltration. My current predoctoral research focuses on elucidating the molecular mechanism of estrogen-receptor (ER) signaling in TAMs. Estrogens bind either ERα or ERβ at the cell membrane which activates Src and other downstream targets, such as PI3K, Erk1/2, and Akt. Macrophages express several Src family members, including Lyn. Our lab has used CRISPR/Cas9 to generate Lyn isoform-specific knockout mice, allowing us to study the signaling differences between LynA and the shorter splice form, LynB. Preliminary data from our lab suggests that LynB, not LynA, plays an inhibitory role in the non-genomic pathway when bone marrow-derived macrophages (BMDMs) are treated with 17β-estradiol (E2). My ongoing research focuses on the mechanistic differences between LynA and LynB signaling in macrophages under physiological conditions (BMDMs) and in TAMs. Elucidating this positive feedback mechanism between the E2 pathway and TAM proliferation and infiltration is crucial for developing more effective breast cancer therapies that would be TAM-specific allowing all other ER-mediated signaling, in other cell types, to remain functional.
Previous Predoctoral Trainees
Solid tumors consist of malignant cells and a heterogeneous mixture of supporting stromal cells that are essential for tumor growth beyond a few millimeters. This complex and immunosuppressive tumor microenvironment remains a significant challenge to cancer treatment. Non-malignant stromal cells called cancer-associated fibroblasts exist exclusively in the tumor stroma and modulate adaptations to the microenvironment that promote survival and progression of the disease. Castration-resistant prostate cancer (CRPC) has a high stromal composition and the presence of highly reactive stroma enriched with cancer-associated fibroblasts directly correlates with poor prognosis. My work in the laboratory of Dr. Aaron LeBeau aims to address CRPC treatment limitations by developing a stroma- targeted chimeric antigen receptor (CAR) natural killer (NK) cell immunotherapy. This approach is based upon the hypothesis that eliminating the aiding and abetting tumor stroma with CAR NK cells will lead to reduction in tumor burden and tumor-mediated immunosuppression. In contrast to healthy tissues, cancer-associated fibroblasts over-express the membrane-bound serine protease fibroblast activation protein alpha (FAP) in the tumor microenvironment. This expression pattern is characteristic of 90% of all epithelial tumors, including CRPC, which makes FAP an attractive target for CAR NK cell immunotherapy. Existing immunotherapies for solid tumors have limited efficacy and more work is needed to understand the intricacies of the tumor microenvironment and to tailor CAR-based therapeutic approaches to these types of cancer. My research will contribute to a better understanding of the interactions among tumor, stromal, and CAR NK cells and could facilitate the development of immunotherapies for other refractory solid tumors containing supportive stromal cells. Because my approach targets genetically-stable stromal tissue, and not antigens expressed on mutation-prone cancer cells, FAP-CAR NK cells could be an effective therapy to kill heterogeneous tumor populations.
Cyclin dependent kinase 2 (Cdk2) is a mitotic checkpoint protein, the aberrant activation of which is implicated in triple negative breast cancer, high grade serous ovarian cancer, and glioblastoma (among other types of cancer). Cdk2 comprises an attractive therapeutic target because it is not essential in mitosis, and thus inhibition of Cdk2 can theoretically be accomplished without the expense of normally functioning cells. Despite significant efforts, however, selective inhibition of Cdk2 has remained elusive, most likely due to the inability of ATP-competitive inhibitors to differentiate between Cdk2 and the closely related and indispensable Cdk1. This is a result of an insufficient understanding of the mechanisms and the degree to which molecules that bind to Cdk2 affect its conformation. Abir’s project involves the use of a number of spectroscopic tools to tease apart the dynamic mechanism of activation of Cdk2 and understand the contributions of biochemical effectors to its conformation. Using a combination of EPR spectroscopy and high-throughput FRET assays, Abir and the Levinson Lab have shown that 1) Cdk2 exists in a delicate conformational balance between the active and inactive states, 2) that Cdk2 requires independent inputs (cyclin binding and phosphorylation) for a full shift to the active state, and 3) ATP-competitive inhibitor candidates that have failed in clinical trials dramatically tilt the conformational balance towards the structurally conserved active state, leading to the problem of poor selectivity. This research has demonstrated that an understanding of the biochemical context of kinase inhibition is critical in kinase inhibition, and successful completion of this project will provide an important understanding of protein dynamics and facilitate screening for selective inhibitors of Cdk2 that alter the conformational equilibrium in a more productive manner.
Hendrickson and Bielinsky Laboratories
Homologous recombination (HR) is a key pathway for the precise repair of DNA double-stranded breaks and other DNA replication-associated lesions. HR promotes repair of lesions by using the non-damaged sister chromatid as a template for repair. Due to its essential role in maintaining genome stability, the HR pathway is tightly regulated and both loss of HR and illegitimate hyper-recombination are associated with genomic instability and carcinogenesis. Our main objective is to understand how the HR pathway is regulated by RAD18, a RING-type E3 ubiquitin ligase that is best known for its role in promoting DNA damage tolerance. This objective is based in part on preliminary data from our laboratory demonstrating that human RAD18 -/- cells exhibit abnormally high levels of sister chromatid recombination and chromosomal radial formations, indicators of genomic instability. Additionally, a survey of The Cancer Genome Atlas (TCGA) revealed that RAD18 inactivating deletions occur in human cancers at high frequencies, with a particularly high prevalence in cervical and renal cell tumors. We aim to understand the molecular mechanism(s) by which RAD18 suppresses hyper-recombination in human cells and protects normal cells from genome instability. This research will provide long sought-after insight into how hyper-recombination is suppressed and should open new therapeutic avenues of treating patients harboring RAD18 mutations.