Improved Enzymes for Prodrug Reduction
New Prodrug (CNOB)
Use of Magnetatatic bacteria to detect cancer by MRI
Mechanism of bacterial anti-tumor activity
We have discovered that many of the enzymes we initially characterized as 'chromate reductases' (now termed ChrR) and subsequently showed to have the biological role of two-electron quinone reduction (see Molecular Bioremediation) can also reduce prodrugs. These are compounds such as mitocycin C and CB1954 that are innocuous but upon reduction become highly toxic alkylating agents. By DNA shuffling combined with rational approaches, and using a novel screening method, we have enhanced the prodrug reducing activity of these enzymes (e.g., ChrR6). Work in collaboration with Dr. Chris Contag's group (BioX) shows that these enzymes are effective in vivo in enhancing prodrug effectiveness. In fact, one of the improved versions of these enzymes is the most effective agent currently available for this purpose. We have recently crystallized ChrR.
We have also discovered a new prodrug (CNOB), which too is activated highly efficiently by our improved enzymes. The prodrug as well as its reduced (activated) product (MCHB) fluoresce at a wavelength that can be visualized within the animal and solid tumors by non-invasive imaging. This makes it possible to follow its activation in vivo, spot penetration barriers in solid tumors and devise countermeasures to overcome them without having to sacrifice the experimental animal and using labor-intensive procedures. See the folllowing publications for further details:
For delivering the enzyme and the drug specifically to tumors, we are using nanoparticles in collarboration with Dr. Richard Zare (Chemistry). These fluorescent nanoparticles encapsulate either the drug or the enzyme. Work underway in collaboration with oncologists is directed to label these nanoparticles with ligands specific to a patient's cancer by using subtractive phage display.
Yoram Barak, Stephen H. Thorne, David F. Ackerley, Susan V. Lynch, Christopher H. Contag, and A. Matin. 2006. New enzyme for reductive cancer chemotherapy (YieF) and its improvement by directed evolution. Molecular Cancer Therapeutics 5(1): 97-103. [PDF]
Barak, Y., Y. Nov., D. Ackerley, and A. Matin. 2008. Enzyme improvement in the absence of structural knowledge - a novel approach. ISME Journal, 2: 171-179 [PDF]
Steve H. Thorne, Yoram Barak, Wenchuan Liang, Michael H. Bachmann, Jianghong Rao, Christopher H. Contag and A. Matin. 2009. CNOB/ChrR6, a new prodrug enzyme cancer chemotherapy.- Molecular Cancer Therapeutics 8(2): 333-341 Ms [PDF]; Suppl. Tables [PDF]; Suppl. Figures [PDF]; Video [PDF]
Magnetotactic bacteria in cancer diagnosis
It has been known for some time that attenuated pathogenic bacteria can target tumors and can also act as cancer treatment. In a new twist to this theme, we show in the following paper that environmental bacteria can also selectively target tumors. The bacteria we chose naturally produce Fe3O4 particles (the ‘magnetotactic bacteria’), which we hypothesized, could act as contrast agent in MRI for cancer detection. We report that one such bacterium, AMB-1, localizes exclusively in tumors and can be manipulated to generate positive contrast, greatly facilitating tumor detection in mice.
Michael R Benoit, Dirk Mayer, Yoram Barak, Ian Y Chen, Wei Hu, Zhen Cheng, Shan X Wang, Daniel M Spielman, Sanjiv S Gambhir, A Matin. 2009. Visualizing implanted tumors in mice with MRI using magnetotactic bacteria. In press, Clinical Cancer Research: Manuscript [PDF] Suppl mat. [PDF]
Antitumor activity of bacteria
We show that an important mechanism for the toxicity of bacteria to tumors in their generation of nitric oxide radical:
Yoram Barak, Frank Schreiber, Steve H Thorne, Christopher H Contag, Dirk deBeer, A Matin. Role of nitric oxide in Salmonella typhimurium-mediated cancer cell killing. Submitted.
Matin, A., Y. Barak, S. Lynch, and D. Ackerley, S. Thorne, C. Contag, and J. Rao. Improved enzymes for reductive prodrug cancer chemotherapy and a novel prodrug that can be visualized in vivo. S06-096