Neil St. John Forbes

Assistant Professor of Chemical Engineering, University of Massachusetts

N.Forbes Chemical Engineering Web Site

N. Forbes Group Site
N. Forbes PVLSI Web Site

Ph.D.: University of California, Berkeley
Postdoc: Radiation Oncology, Harvard Medical School

Engineering Tumor-Targeting Therapies

Application of chemical engineering principles to the study of tumor formation and treatment is fertile new ground for research and is necessary for the advancement of cancer therapy. Over the last century, researchers have discovered many of the genetic causes of cancer and yet nearly 46,000 people will die this year from cancer in the United States alone. Standard cancer therapies often fail because of spatial heterogeneity of nutrients, wastes, and therapeutics. Transport barriers prevent therapeutic agents from reaching effective concentrations throughout tumors. Models based on mass balance, transport phenomena and reaction kinetics are powerful tools able clarify the connection between the genetic aberrations and the compositional heterogeneity of tumors. Therapeutic strategies designed using engineering principles will be able to overcome transport barriers and create more effective therapies.

Single treatments of radiation or chemotherapy often do not kill all cancer cells within a tumor. Between treatments, surviving cells proliferate and regrow as tumors and metastases, eventually leading to death. Chaotic and irregular tumor vasculature and high interstitial pressure prevent blood-borne chemotherapeutics from diffusing equally throughout all tumor regions. Additionally, non-proliferating cells, distant from vasculature, survive chemotherapeutic therapies specifically targeted to proliferating cells. Radiation therapy is also less effective in the low oxygen regions distant from vasculature because it depends on the formation of oxygen radicals. Furthermore, low oxygen environments have been shown to select for more aggressive and metastatic cells.

In my laboratory we characterize and utilize tumor heterogeneity to develop novel cancer therapies that overcome the limitations of current cancer therapies. Unique three-dimensional tumor models are designed to mimic the metabolic variations observed in tumors in vivo. The metabolic profiles of the tumor models, both in vitro and in vivo, are characterized using fluorescence microscopy, nuclear magnetic resonance spectroscopy and metabolic flux analysis.


Research Projects

In our research we use experimental and computational methods to understand the cellular mechanisms that give rise to drug resistance in tumors and we use engineering methods to design therapeutic strategies to overcome resistance in tumors. These goals are divided into five main projects. A synopsis of each is presented below.

To date the major advances of our group has been 1) determination of the mechanisms that control the localization of therapeutic bacteria in tumors; 2) development of therapeutic bacteria that secrete an anti-cancer protein and dramatically increase survival in mice; 3) quantification of the effects of spatial heterogeneity on tumor metabolism, cell survival, and cell cycle progression; 4) development of computation tools to analyze the interactions of therapeutics with tumors; and 5) demonstration that the properties of nanoparticles can be tuned to enhance  tumor targeting.

Targeted Bacteriolytic Therapy

To specifically target tumors we are investigating motile, facultative anaerobic bacteria that specifically target and accumulate within the therapeutically inaccessible regions of tumors. Over the past 50 years numerous strains of bacteria have been shown to localize and cause lysis in transplanted mouse tumors, but their application has had minimal success in the clinic. By specifically targeting bacteria to specific sub-regions of tumors we hope to dramatically increase their affectivity.

Bacteria selected by these strategies have numerous uses. Administered alone, selected bacteria will compete with the tumor for nutrients, killing cells in inaccessible tumor regions. A combination of bacteriolytic therapy and standard anti-proliferative chemotherapy, which selectively kills proliferating cells growing close to vasculature, will attack tumors from both the inside and out. Additionally, selected bacteria could deliver therapeutic agents or amplification agents (e.g. toxins, prodrug cleaving enzymes or anti-angiogenic factors), or could express markers detectable by MRI, PET, or another imaging device.

Localized Quantification of Tumor Metabolism

In addition to diffusion, cells with different metabolic profiles cause component gradients and distinct regions of proliferation in tumors. Most people over 50 have pre-malignant lesions throughout their breasts and prostates. These lesions are kept small (<1mm) by a balance of cell proliferation and death. Cells at the centers die because of nutrient depletion and waste toxicity. Once the lesions develop vasculature, proliferation exceeds death and the tumor grows. Thus, both metabolism and diffusion play key roles in the early formation of tumors.

In my laboratory we quantify the metabolic state of different tumor regions in order to map nutrient gradients and explain mechanistically why cell growth diminishes away from vasculature. Metabolic flux analysis determines the flow of carbon through the pathways of primary and secondary metabolism using nuclear magnetic resonance spectra of extracted cellular cytoplasm. Whole cell models of metabolism are capable of i) quantifying metabolite transport across biological membranes, ii) quantifying changes in enzyme activity due to extracellular signals and iii) detect inactive pathways. In addition to explaining cancer cell proliferation, metabolic flux analysis will identify enzymatic targets for inhibitors of metabolism and proliferation in the different tumor regions.

Bacterial Migration and Segregation in Solid Tumors

In collaboration with Baystate Medical Center we are investigating how bacteria segregate in tumors. The ability of bacteria to migrate within a tumor defines their usefulness for drug delivery. We use surgical, histological and standard staining techniques to measure the rate of bacterial spread throughout subcutaneous tumors in mice following systemic injection. These experiments were designed to determine the mechanism of specific bacterial localization in tumors

Representative publications:

St. Jean AT, Swofford CA, Brentzel ZJ, Jan Panteli, Forbes NS. Bacterial delivery of Staphylococcus aureus alpha-hemolysin causes tumor regression and necrosis in murine tumors. Molecular Therapy Website

Kasinskas RW, Venkatasubramanian R, and Forbes NS. Rapid uptake of glucose and lactate, and not hypoxia, induces apoptosis in three-dimensional tumor tissue culture. Integrative Biology PDF Website

Swofford CA, St. Jean AT, Panetli JT, Brentzel ZJ†, Forbes NS. 2014. Identification of Staphylococcus aureus α-hemolysin as a protein drug that is secreted by anticancer bacteria and rapidly kills cancer cells. Biotechnology and Bioengineering PDF Website

Zhang M, Swofford CA, Forbes NS. 2014. Lipid A controls the robustness of intratumoral accumulation of attenuated Salmonella in mice. International Journal of Cancer PDF Website

Toley BJ, Tropeano-Lovatt Z, Harrington JL, Forbes NS. 2013. Microfluidic technique to measure intratumoral transport and calculate drug efficacy shows that binding is essential for doxorubicin and release hampers Doxil. Integr. Biol. 5:1184-96 PDF Website

Dai Y, Toley BJ, Swofford CA, Forbes NS. 2013. Construction of an inducible cell-communication system that amplifies Salmonella gene expression in tumor tissue. Biotechnol Bioeng. 110:1769-81 PDF Website

Toley BJ, Forbes NS. 2012. Motility is critical for effective distribution and accumulation of bacteria in tumor tissue. Integr. Biol. 4:165-76

Toley BJ, Park J, Kim BJ, Venkatasubramanian R, Maharbiz MM, Forbes NS. 2012. Micrometer-scale oxygen delivery rearranges cells and prevents necrosis in tumor tissue in vitro. Biotechnol Prog. 28:515-25.

Toley BJ, Ganz DE, Walsh CL, Forbes NS. 2011. Microfluidic device for recreating a tumor microenvironment in vitro. J Vis Exp. DOI: 10.3791/2425.

Ganai S, Arenas RB, Sauer JP, Bentley B, Forbes NS. 2011. In tumors Salmonella migrate away from vasculature toward the transition zone and induce apoptosis. Cancer Gene Ther. 18:457-66

Forbes NS. 2010. Engineering the perfect (bacterial) cancer therapy. Nature Reviews Cancer. 10:785–794

Venkatasubramanian R, Arenas RB, Henson MA, Forbes NS. 2010. Mechanistic modeling of dynamic MRI data predicts that tumor heterogeneity decreases therapeutic response. Br J Cancer. 103:486-97

Kim BJ, Han G, Rotello VM, Forbes NS. 2010. Tuning payload delivery in tumor cylindroids using gold nanoparticles. Nat Nanotechnol. 5:465-72

Hunnewell M, Forbes NS. 2010. Active and inactive metabolic pathways in tumor spheroids: determination by GC-MS. Biotechnol Prog. 26:789-96

Ganai S, Arenas RB, Forbes NS. 2009. Tumor-targeted delivery of TRAIL using Salmonella typhimurium enhances breast cancer survival in mice. Br J Cancer. 101:1683

Walsh CL, Babin BM, Kasinskas RW, Foster JA, McGarry MJ, Forbes NS. 2009. A multipurpose microfluidic device designed to mimic microenvironment gradients and develop targeted cancer therapeutics. Lab on a Chip. 9:545-554

Ghosh PS, Kim CK, Han G, Forbes NS, Rotello VM. 2008. Efficient gene delivery vectors by tuning the surface charge density of amino-acid functionalized gold nanoparticles. ACS Nano. 2:2213-8
Forbes NS. 2008. A module to foster engineering creativity: an interpolative design problem and an extrapolative research project. Chemical Engineering Education 42:166172

St. Jean A, Zhang M Forbes NS. 2008. Bacterial therapies: completing the cancer treatment toolbox. Current Opinions in Biotechnology. 19:511-517

Kim BJ, Forbes NS. 2008.Single cell sorting in cylindroids demonstrates how nutrient deprivationcreates apoptotic and quiescent cell populations in tumors. Biotechnology and Bioengineering. 101:797-810

Venkatasubramanian R, Henson MA, Forbes NS. 2008. Incorporating cell cycle progression and drug penetration into metabolic models of multicellular tumor spheroid growth. Journal of Theoretical Biology. 253:98–117

Kasinskas RW, Forbes NS. 2007. Salmonella typhimurium lacking ribose chemoreceptors localize in tumor quiescence and induce apoptosis. Cancer Res. 67:3201-9

Kim BJ, Forbes NS. 2007. Flux analysis shows that hypoxia-inducible-factor-1-alpha minimally affects intracellular metabolism in tumor spheroids. Biotechnol Bioeng. 96:1167-82
Ganai S, Arenas RB, Bentley B, Forbes NS. 2007. Targeting bacteriolytic therapy of solid tumors using Salmonella typhimurium. Annuls Surgical Oncology 14:71-71

Forbes NS. 2006. Profile of a bacterial tumor killer. Nat. Biotech. 24:1484-1485
Forbes NS*, Meadows AL, Clark DS, Blanch HW. 2006. Estradiol stimulates the biosynthetic pathways of breast cancer cells: detection by metabolic flux analysis. Metabolic Engineering. 8:639-652

Venkatasubramanian R, Henson MA, Forbes NS. 2006. Incorporating energy metabolism into a growth model of multicellular tumor spheroids. J Theor Biol. 242:440-453

Kasinskas RW, Forbes NS. 2006. Salmonella typhimurium specifically chemotax and proliferate in heterogeneous tumor tissue in vitro. Biotechnology Bioengineering, 94:710-721

Han G, You CC, Kim BJ, Turingan RS, Forbes NS, Martin CT, Rotello VM. 2006. Light-regulated release of DNA and its delivery to nuclei by means of photolabile gold nanoparticles. Angew Chem Int Ed Engl. 45:3165-3169

Hong R, Han G, Fernandez JM, Kim BJ, Forbes NS, Rotello VM. 2006. Glutathione-mediated delivery and release using monolayer protected nanoparticle carriers. J Am Chem Soc. 128:1078-9

Pinelis M, Kasinskas RW, Borno RT, Park JH, Chu E, Forbes NS, Maharbiz MM. 2006. Microfluidic devices for the assembly and culture of three-dimensional multi-cellular constructs with diffusion-limited microenvironments. Proceedings of the 10th International Conference on Miniaturized Systems for Chemistry and Life Sciences (μTAS2006). Japan

Han G, Hong R, Fernandez J, Kim BJ, Forbes NS, Rotello VM. 2006. Glutathione-mediated drug release using monolayer protected nanoparticle carriers. Abs Amer Chem Soc. 231:176

Han G, You CC, Kim BJ, Forbes NS, Martin CT, Rotello VM. 2006. Light-regulated DNA transcription and delivery using photolabile gold nanoparticles. Abs Amer Chem Soc. 231:266

Crichton MA, Forbes NS, Bhatia SR. 2005. USANS as a probe of large-scale structure in attractive colloidal glasses of block copolymer micelles.  MRS Symp. Proc. v. 840 - Neutron and X-Ray Scattering as Probes of Multiscale Phenomena. Q7.11.1-Q7.11.6

Forbes NS, Munn LL, Fukumura D, Jain RK. 2003. Sparse initial entrapment of systemically injected Salmonella typhimurium leads to heterogeneous accumulation within tumors. Cancer Res. 63:5188-5193

Helmlinger G, Sckell A, Dellian M, Forbes NS, Jain RK. 2002. Acid production in variant, glycolysis-deficient and parental tumors in vivo: support for hypothesized tumor metabolism. Clin. Cancer Res. 8:1284-1291

Jain RK, Forbes NS. 2001. Can engineered bacteria help control cancer? PNAS 98:14748-14750

Forbes NS, Clark DS, Blanch HW. 2001. Using isotopomer path tracing to quantify metabolic fluxes in pathway models containing reversible reactions. Biotech. Bioeng. 74:196-211

Forbes NS, Clark DS, Blanch HW. 2000. Analysis of metabolic fluxes in mammalian cells. Chap 4.4 in: Schügerl K, Bellgardt KH, editors. Bioreaction Engineering: Modeling and Control. Berlin: Springer Verlag