Susan C. Roberts
Susan C. Roberts
Professor; Director, UMass Institute for Cellular Engineering
B.S. in Chemical Engineering with high distinction, Worcester Polytechnic Institute, 1992
Ph.D., Cornell University, 1998
Recognitions & Awards
NSF CAREER Award, 2000-2004
COE Outstanding Junior Faculty Award, 2003
Minority in Engineering Program Recognition Award, 2002
Women in Engineering Program Recognition Award, 2001
Outstanding Advisor Service Award, 2000
Current Focus of Research
Our laboratory focuses on cellular and metabolic engineering. Through the characterization and redirection of metabolism, cellular processes can be optimized for a variety of applications. Our current research focus is in two main areas: (1) plant metabolic engineering for the production of medicinals via plant cell culture and (2) design and utilization of mammalian cell in vitro systems for the development of novel cell encapsulation systems and the study of cellular function.
Plant Metabolic Engineering
The supply of pharmaceuticals is often met through in vitro fermentation and cell culture systems, which can be easily manipulated to yield high quantities of the product of interest. The goals of our program focus on the development and optimization of processes for the production of pharmaceuticals in plant-based systems, with an emphasis on the understanding and control of cellular metabolism. Traditional chemical engineering is combined with modern biotechnology to facilitate the development of such processes.
Our research is directed towards understanding how cellular metabolism can be effectively controlled at both the genetic and cell level. We are developing novel methods (both experimental and theoretical) for studying poorly characterized (both genetic and metabolic) cell systems (e.g., Taxus for Taxol®, paclitaxel, production). We utilize a variety of techniques to characterize cellular metabolism including enzyme elicitation, utilization of metabolic inhibitors, application of radio-labeled and fluorescently-labeled substrates, HPLC-MS for metabolite identification, transcript profiling, 2D-gel electrophoresis, molecular transformation via Agrobacterium, and flow cytometry.
Two projects are described in detail below, and we are working in several additional areas to optimize the plant cell culture process for paclitaxel including design of liquid-liquid extraction processes for improved selectivity and recovery, and characterization of paclitaxel degradation in cell culture.
Metabolic Control of Paclitaxel Accumulation in Taxus Cell Cultures
Collaborators: Elsbeth Walker, Dept. of Biology, Jennifer Normanly, Dept. of Biochemistry and Molecular Biology
The application of molecular approaches to studying plant secondary metabolism is very limited. We are studying the Taxus cell system for production of the anti-cancer agent paclitaxel. The majority of research performed thus far has been directed towards identification and characterization of specific pathway genes with an ultimate goal of enhancing paclitaxel accumulation through specific genetic transformation of Taxus cultures, with no a priori information on whether the particular gene is important in pathway control. We are using significantly different approach, one that combines the use of transcript profiling and proteomics to identify genes involved in global pathway control. We are currently evaluating gene expression in both high- and low-paclitaxel producing states. We utilize the biotic elicitor methyl jasmonate to upregulate expression of secondary metabolic genes, resulting in increased accumulation of paclitaxel.
Plant Cell Population Dynamics
While the production of secondary metabolites by plant cell culture has been studied extensively, most work has been done using whole-flask averages as opposed to studies on individual cells. The isolation of single cells for analysis allows for the rapid collection of information about the behavior of individual cells within a culture population. This data can then be used in the modeling of population dynamics, with an ultimate goal of understanding the regulation of secondary metabolism in plant cell cultures. We are developing novel single cell preparation methods for aggregated plant cell cultures to allow for population analysis via flow cytometry. Current efforts are aimed at characterizing cell populations and sorting these populations for subsequent culture and analysis. Our model system of study is paclitaxel accumulation in Taxus suspension cultures. Additionally, we are concurrently determining the complement of metabolites via HPLC-MS for comparison between distinct cell populations under different conditions (e.g., enzyme elicitation).
Mammalian Cell In Vitro Systems
The collection of scientific and engineering data for in vivo applications is highly dependent on animal studies. To better design such studies so as to minimize animal testing, we are utilizing in vitro systems for the high-throughput testing of multiple designs/parameters as well as interactions between variables. An effective in vitro system will mimic human physiology. We are developing novel reactor configurations and cell culture techniques as well as applying relevant metabolic assays to evaluate cellular responses. We utilize a variety of equipment/techniques in our studies including UV-vis spectroscopy, fluorescence microscopy, TEM, application of radio-labeled and fluorescently-labeled substrates, HPLC-MS for metabolite identification, and flow bioreactors.
Cell Encapsulation Technologies
Collaborator: Surita Bhatia, Dept. of Chemical Engineering
This program is aimed at developing new approaches for the formulation and design of structured materials for cell encapsulation, specifically for signal-responsive cells with a high metabolic rate and oxygen demand. Our efforts are focused specifically on characterizing cell growth and metabolism and cell-material interactions in encapsulated systems through the application of novel in vitro techniques. We are specifically studying hydrogel systems (e.g., alginate and Pluronic® F127) with oxygen reservoirs to promote high cell viability and functionality over extended periods of time.
Optimizing Energy Metabolism for Diabetic Patients During Exercise
Collaborators: Surita Bhatia, Dept. of Chemical Engineering, Barry Braun, Dept. of Exercise Science, Stuart Chipkin, M.D., Baystate Medical Center
A core component of the underlying defect in diabetes is the barrier to effectively delivering necessary fuel (in the form of either starch or fat) to cells for energy production. Although much emphasis has been placed on the study of insulin and its impact on cellular glucose uptake and biochemistry, relatively little is known about how modifications in the composition, delivery and utilization of the "fuel" itself could influence the efficiency and effectiveness of energy metabolism. As part of this collaboration, our laboratory is developing in vitro evaluated systems to characterize fuel metabolism. To test the performance of new candidate energy formulations, metabolic responses of specific relevant tissue types (e.g., skeletal muscle, hepatic, adipose and b-cells) are being evaluated. This new collaboration brings together expertise
Naill, M., and Roberts, S. (2005) "Cell cycle analysis of Taxus suspension cultures at the single cell level as an indicator of culture heterogeneity," Biotechnology and Bioengineering , 90(4) : 491-500.
Naill, M., and Roberts, S. (2005) "Flow cytometric identification of paclitaxel accumulating subpopulations," Biotechnology Progress , 21 : 978-9834.
Naill, M., and Roberts, S. (2005) "Flow cytometric analysis of protein content in Taxus protoplasts and single cells as compared to aggregated suspension cultures," Plant Cell Reports , 23(8) : 528-533.
Naill, M., and Roberts, S. (2005) "Culture of isolated single cells from Taxus suspensions for the propagation of superior cell populations," Biotechnology Letters , in press.
Khattak, S., Bhatia, S.R., and Roberts, S.C. (2005) "Pluronic F127 â as a cell encapsulation material: Utilization of membrane stabilizing agents," Tissue Engineering , 11(5-6): 974-983.
Agrawal, S.K., Chin, K.S., Sanabria-Delong, N., Aamer, K.A., Sardinha, H., Tew, G.N., Roberts, S.C., and Bhatia, S.R. (2005) "Rheology and biocompatibility of Poly(lactide)-poly(ethylene oxide)-poly(lactide) hydrogels," MRS Symp. Proc. v. 844 – Mechanical Properties of Bio-Inspired and Biological Materials, Y9.8.1-Y.9.8.6.
Bhatia, S.R., Khattak, S., and Roberts, S.C. (2005) "Polyelectrolytes for cell encapsulation," Current Opinion in Colloid and Interface Science , 10: 45-51
Nims, E., Dubois, C., Roberts, S.C., and Walker , E.L. (2005) "Expression profiling of genes involved in paclitaxel biosynthesis for targeted metabolic engineering," Metabolic Engineering , in revision.
Roberts, S.C., (2005) "A successful introduction to ChE first-semester course focusing on connection, communication and preparation," Chemical Engineering Education , summer 2005: 222-227.
Khattak, S., Spatara, M., Roberts, L., and Roberts, S.C. "Application of colorometric assays to assess viability, growth and metabolism of hydrogel-encapsulated HepG2 cells," Biotechnology and Applied Biochemistry.