Bacteria in Cancer Research

One of the most important things a researcher has to do is justify their existence; explain why they should continue to be paid for the work they're doing. When working with bacteria finding a reason isn't too difficult (although getting it accepted can be another matter). Most researchers can draft something up about medical superbugs, or industrial chemical production and then get back to ferreting out just how these amazing organisms function, in their little cellular world.

However sometimes research can be justified with more than just a passing nod to the realms of General Usefulness. Ananda Chakrabarty, possibly best known for patenting a bacteria capable of metabolising oil, and therefore eating up oil spills has been producing papers for about ten years concerning bacterial chemicals that have the potential to induce apoptosis (cell death). Most interestingly, they seem to bind preferentially to certain cells, in particular cancerous cells.

Azurin was first discovered as the toxin that attacks cellular macrophages. It's produced by the bacteria Pseudomonas aeruginosa the 8821M strain of which was found to produce a high concentration of Azurin. When applied to both normal and cancerous cells (taken from a breast cell carcinoma) the Azurin preferentially entered the cancerous cells, as shown below:



The picture on the right shows the carcinoma cells while normal epithelial cells are on the left. Cells are stained blue, which Azurin is stained green. Both cells are shown twenty four hours after the Azurin treatment. The cancerous cells have taken up the Azurin and are starting to be degraded by it.

The exact mechanism for Azurin-mediated cell death is not yet fully certain, but it does interact with p53, a cell cycle control protein which can lead to cell death in normal cells if overactivated. The graph below shows cytoxicity (cell killing) levels in cells containing p53 (B) and cells that did not (C):


In both cases the wild type Azurin (in contrast to the mutated Azurin, which is non-functional) leads to some cytoxicity, but when p53 is present the effects are far greater, suggesting a role for the p53 protein, which is usually upregulated in cancer cells.

Further research managed to isolate the active component of Azurin; the section of the protein that was actually binding to p53 and causing the cancer cells to die. By simply chopping bits off the protein and seeing which parts were essential for it's activity, they managed to isolate a region between amino acids 50-77 and subsequently called it p21 (p usually stands for 'protein' in these circumstances, because bacteriologists are not always very imaginative about names). p21 is currently undergoing stage I clinical trials for cancer treatment; first stage of testing in human subjects.

Azurin isn't just useful as a potential cancer treatment however, it also has several other potentially quite amazing properties. Azurin is able to bind to the surface protein MSP1 of the malarial parasite Plasmodium falciparum and significantly reduces parasitemia (the number of parasites found in the blood). Azurin also forms an attachment with CD4 receptors of HIV, the sites of attachment of the T4 cells, and leads to suppressed HIV-1 growth at early stages in the infection.

All of this is very exciting, as it shows that despite the drop-off in antibiotic discovery, molecules produced by bacteria still have plenty of applications that are waiting to be discovered. As to why the bacteria might have evolved to kill cancer cells and malarial parasites as yet there's no idea! Probably the best explanation at the moment is that like antibiotics they were originally intended for something completely different, yet they have properties which allow them to be more useful too us than they can ever have imagined.

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Yamada, T. (2002). Bacterial redox protein azurin, tumor suppressor protein p53, and regression of cancer Proceedings of the National Academy of Sciences, 99 (22), 14098-14103 DOI: 10.1073/pnas.222539699

Punj V, Bhattacharyya S, Saint-Dic D, Vasu C, Cunningham EA, Graves J, Yamada T, Constantinou AI, Christov K, White B, Li G, Majumdar D, Chakrabarty AM, & Das Gupta TK (2004). Bacterial cupredoxin azurin as an inducer of apoptosis and regression in human breast cancer. Oncogene, 23 (13), 2367-78 PMID: 14981543

Chaudhari A, Fialho AM, Ratner D, Gupta P, Hong CS, Kahali S, Yamada T, Haldar K, Murphy S, Cho W, Chauhan VS, Das Gupta TK, & Chakrabarty AM (2006). Azurin, Plasmodium falciparum malaria and HIV/AIDS: inhibition of parasitic and viral growth by Azurin. Cell cycle (Georgetown, Tex.), 5 (15), 1642-8 PMID: 16861897