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University of Colorado Denver

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Translational Bio-Nanosciences Laboratory


General interest

We are interested in mechanisms by which the immune system recognizes and clears nanoparticles from the body. Bio/nano interactions have clinically important outcomes (for example clearance of nanoparticles by liver and spleen, or allergic reactions). We aim to apply the knowledge on bio/nano interactions in order to design better nanosystems for early detection, monitoring and treatment of cancer. Our favorite type of material is iron oxide, which is widely used in biomedical research and as MRI contrast agent. Our additional focus is red blood cells (RBCs), the most abundant and available cell type in the body, in order to convert them into drug delivery, imaging agents and in vivo biosensors. Lastly, we are interested in using gas microbubbles in order to isolate rare cells and biomarkers form blood for ex vivo diagnostics of diseases.


Specific Projects

Project 1: Recognition of nanoparticles by innate immune system

Intravenously injected nanomaterials undergo interactions with plasma components and cell receptors, with subsequent clearance by body macrophages and monocytes. This process is the major problem in nanomedicine since it decreases the dose of nanoparticles in the tumor, limits the efficiency of imaging and therapy, and causes toxicity. There is still insufficient knowledge of the basic mechanisms that lead to nanoparticle recognition and elimination. .

Superparamagnetic crystalline iron oxide (SPIO) is a significant magnetic resonance imaging (MRI) contrast agent by itself and as a component of multifunctional nanomedicines for cancer imaging and treatment (over 4500 citations in PubMed). SPIO consists of magnetite (Fe3O4)-maghemite (gamma-Fe2O3) crystals of 5–10-nm size embedded in a meshwork of polymer (usually dextran, Fig. 1). We are only beginning to unravel the mechanisms of immune recognition and elimination of SPIO. Macrophage scavenger receptors and complement play an important role in this process, but there are potentially other mechanisms involved in nanoparticle elimination. Our current effort is to modify our recently described SPIO nanoworms to in order to prevent complement activation and clearance. Accomplishing these goals will enable to design safe and efficient MRI contrast agents.


Project 2: Engineered red blood cells as long-circulating probes

Red blood cells (RBCs) are natural carriers that can deform and squeeze through capillaries, and the immune system does not readily recognize them as foreign. The unique potential of RBCs due to long half-life, biocompatibility, and large volume capacity has not been fully exploited in diagnostics and therapy.

We optimized RBC surface chemistry to stably incorporate molecules on the RBC surface and demonstrated excellent biocompatibility and targeting in vitro and in vivo (Fig. 2). We are currently working on loading various chemotherapeutic drugs into RBCs. The goals of this project are:

  1. Design targeted theranostic RBCs to treat blood cancers;
  2. Design long-circulating optically coded RBC sensors for detection of diseases;


Project 3: In vitro cancer diangostics and monitoring using microbubbles
Biomarkers such as circulating tumor cells (CTCs), exosomes and DNA could be isolated from biological fluids and analyzed for the diagnosis and prognosis of cancer. Ability to isolate intact biomarkers and tumor cells with high purity and efficiency will facilitate clinical management of malignancies and early diagnostics of asymptomatic cancers. Funded by the NIH R21 grant (Innovative Molecular Analysis) award and a more recent NIH R33 grant, we are developing novel technologies for isolation and enrichment or rare tumor markers from biological fluids. In particular, for isolation of circulating tumor cells (CTCs), we developed buoyant perfluorocarbon microbubbles coated with anti-EpCAM antibody. Microbubbles efficiently target tumor cells in whole blood and isolate the cells after a quick centrifugation step with high purity (Fig. 3).


The goal of these projects is to further develop and test biomarker isolation strategies to enable molecular analysis of cancer samples for personalized molecular diagnostics and early detection.



  1. Chao, Y.; Karmali, P. P.; Mukthavaram, R.; Kesari, S.; Kouznetsova, V. L.; Tsigelny, I. F.; Simberg, D.  Direct recognition of superparamagnetic nanocrystals by macrophage scavenger receptor SR-AI. ACS Nano 2013, 7, (5), 4289-98.
  2. Simberg, D.; Park, J. H.; Karmali, P. P.; Zhang, W. M.; Merkulov, S.; McCrae, K.; Bhatia, S. N.; Sailor, M.; Ruoslahti, E.  Differential proteomics analysis of the surface heterogeneity of dextran iron oxide nanoparticles and the implications for their in vivo clearance. Biomaterials 2009, 30, (23-24), 3926-33.
  3. Chao, Y.; Karmali, P. P.; Simberg, D.  Role of carbohydrate receptors in the macrophage uptake of dextran-coated iron oxide nanoparticles. Adv Exp Med Biol 2012, 733, 115-23.
  4. Karmali, P. P.; Chao, Y.; Park, J. H.; Sailor, M. J.; Ruoslahti, E.; Esener, S. C.; Simberg, D.  Different effect of hydrogelation on antifouling and circulation properties of dextran-iron oxide nanoparticles. Mol Pharm 2012, 9, (3), 539-45.
  5. Chao, Y.; Makale, M.; Karmali, P. P.; Sharikov, Y.; Tsigelny, I.; Merkulov, S.; Kesari, S.; Wrasidlo, W.; Ruoslahti, E.; Simberg, D.  Recognition of Dextran-Superparamagnetic Iron Oxide Nanoparticle Conjugates (Feridex) via Macrophage Scavenger Receptor Charged Domains. Bioconjug Chem 2012.
  6. Shi, G.; Mukthavaram, R.; Kesari, S.; Simberg, D.  Distearoyl Anchor-Painted Erythrocytes with Prolonged Ligand Retention and Circulation Properties In Vivo. Adv Healthc Mater 2013.
  7. Shi, G.; Cui, W.; Benchimol, M.; Liu, Y. T.; Mattrey, R. F.; Mukthavaram, R.; Kesari, S.; Esener, S. C.; Simberg, D.  Isolation of rare tumor cells from blood cells with buoyant immuno-microbubbles. PLoS One 2013, 8, (3), e58017.