In Vivo Optical Imaging
In our lab, we have examined the PDT-stress-mediated HSP70 activation and its relation to cellular toxicity in a mouse tumor cell line, which was transfected with a plasmid consisting of a fluorescent reporter gene (GFP) under the control of an hsp70 promoter. This has allowed us to study the PDT-mediated inducible expression of HSP70 in living specimens in vitro and in vivo using fluorescence imaging.
hsp70 promoter driven GFP expression in control (a) and PDT-treated (b) tumors
In vivo confocal fluorescence image of neutrophil (red) infiltration in PDT treated tumor. CD31-positive anatomic vasculature is labeled in green.
Several recent studies have established that HSPs may play a pivotal role in antitumor immunity in vivo by activating dendritic cells and enhancing host cell infiltration. With this in mind, our present studies are also focused on using sub-lethal doses of PDT to activate HSP induction in a strategy where PDT is not intended to be curative but is used instead to prime a tumor-specific immune response. Toward this end, we are developing fluorophore-conjugated antibody-targeted imaging of host cell infiltration into tumors in response to PDT and ionizing radiation therapy.
PDT is known to induce hypoxia via photochemical oxygen depletion and by disrupting the tumor vasculature. We have developed two stably-transfected mouse mammary cancer cell lines to investigate the PDT-mediated hypoxia-independent activation of the hypoxia inducible factor 1a (HIF-1a) pathway. In the first of these cell lines, the expression of GFP is under the control of five copies of the hypoxia response element (HRE) promoter of the human VEGF gene. The other cell line is transfected with a vector coding for the expression of a HIF-1a – GFP fusion protein, which enables direct visualization of the nuclear translocation of HIF-1a. Using these two cell lines, we established that PDT initiates both translocation of HIF-1 a and the activation of the HRE promoter under conditions of abundant oxygen.
Translocation of HIF-1a – GFP fusion protein from the cytosol (a) to the nucleus (b) in response to PDT.
Molecular imaging studies with a variety of collaborators are underway.
Mitra S, Modi KD, Foster TH. (2013 Oct 01). Enzyme-activatable imaging probe reveals enhanced neutrophil elastase activity in tumors following photodynamic therapy. J Biomed Opt. 18, 101314.
Mitra S, Mironov O, Foster TH (2012 Jan 01). Confocal fluorescence imaging enables noninvasive quantitative assessment of host cell populations in vivo following photodynamic therapy. Theranostics. 2, 840-9.
S. Mitra, K. Dolan, T.H. Foster, and M. Wellington. Imaging morphogenesis of Candida albicans during infection in a live animal. J. Biomed. Opt. 15, 010504 (2010). [Medline]
S. Mitra and T.H. Foster. In vivo confocal fluorescence imaging of the intratumor distribution of the photosensitizer mono-L-aspartylchlorin-e6 (NPe6). Neoplasia 10, 429-438 (2008). [Medline]
R.J. Cummings, S. Mitra, E.M. Lord, and T.H. Foster. Antibody-labeled fluorescence imaging of dendritic cell populations in vivo. J. Biomed. Opt. 13 , 044041 (2008).
K. Santos, D.A.L. Simon, E. Conway, W.J. Bowers, S. Mitra, T.H. Foster, A. Lugade, E.M. Lord, H.J. Federoff, S. Dewhurst, and J.G. Frelinger. Spatial and temporal expression of HSV-1 amplicon encoded genes: implications for their use as immunization vectors. Hum. Gene Ther. 18, 93-105 (2007). [Medline]