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An apparently absurd but possibly rational trial: Using anaerobic bacteria as a delivery tool for solid tumors
Shun’ichiro Taniguchi
A groundbreaking trial making use of human intestinal bacteria for treatment of solid cancers is underway in our laboratory. What is the basic idea, and what is its rationality and evidence?
For cancer, early detection and surgical resection are the most effective means of treatment. General chemotherapy is also administered to patients if metastases are detected, and molecular-targeting therapies for this kind of treatment have been progressing thanks to recent advances in molecular oncology. However, improvements are still needed for chemotherapy for solid cancers to reduce side effects, enhance delivery of anticancer drugs to tumor tissues, and overcome cancer cell drug resistance caused by the existence of stem cells and/or heterogenic cancer cell populations. Therefore, in addition to researching the molecular specificities of cancer cells, we maintain that it may be of benefit to also direct our attention to the macroscopic characteristics of cancer tissue microenvironments, such as low pH, hypoxia, and blood vessel abnormalities, to selectively deliver effective doses of anticancer drugs to lesions.
Solid tumor hypoxia, which is believed to be a causative factor of tumor cell resistance to radiation therapy and chemotherapy, has recently been attracting attention as a necessary condition for malignant progression and a niche for cancer stem cells. By taking advantage of these conventionally troublesome anaerobic conditions in tumor tissues, we are now developing a delivery system with non-pathogenic anaerobic bacteria derived from the human intestine to treat solid tumors1.
Administration of bacteria into blood vessels, even if non-pathogenic, has historically been considered absurd in that it may induce sepsis. However, in a recent issue of Nature Cancer Review, an article on the effects of cancer treatment with bacteria appeared2 and brought to light the potential utility of bacteria in cancer treatment. As recombinant technology has made it possible to produce various low-cost drugs using bacteria probiotics are used nowadays not only as drugs for controlling intestinal function, but also for oral cavity care and the skin. We hope the day may be close when the application of probiotics to treat solid cancers is regarded as common sense as well.
Over 50 years ago, it was reported that intravenous administration of pathogenic anaerobic tetanus spores killed tumor-bearing mice, but not normal mice3, thereby biologically demonstrating the existence of an anaerobic condition in solid tumors. This finding inspired our early trials with non-pathogenic bifidobacteria for targeting solid tumors; after intravenous injection of this anaerobic bacterium into tumor-bearing animals, the bacteria disappeared from normal tissues within a few days, growing only in malignant tumor sites4. About 20 years after this observation, an expression vector for bifidobacteria became available, and we succeeded in establishing anaerobic bacteria that expressed an exogenously introduced cytosine deaminase (CD) gene. These genetically modified bifidobacteria proliferated selectively in solid tumors after intravenous injection into tumor-bearing animals. When 5FC (the low toxicity pro-drug of 5FU) was orally administered to these animals, high amounts of 5FU were selectively produced by CD in bacteria present in tumor tissues, resulting in suppression of tumor growth without severe side effects. Serious toxicity, such as anaphylactic shock due to bacterial sepsis, was not observed. Based on these results, a university-based venture company, AnearoPharma Science, Ltd., was established to further develop biologics for the treatment of solid cancers.
In the U.S., Phase 1 clinical trials using salmonella at the NIH and clostridium at Johns Hopkins University were recently performed for cancer treatment (http://www.clinical trials.gov/ct/). Although the pathogenicity of these bacteria was attenuated and caused only mild side effects, bifidobacteria still appear superior in terms of safety and show great promise. We are currently planning to expand our tumor-specific bacterial arsenal to deliver substances like cytokines with antitumor activity, enzymes that convert low toxicity anticancer pro-drugs, anti-angiogenic proteins, shRNA suppressing the expression of oncogenes, and others. The development of combination therapy using bifidobacteria and conventional therapy is also underway. Although we have not observed any severe toxicity from bifidobacteria so far, more detailed and careful analysis from the immunological standpoint is needed.
Literature
1-S. Taniguchi et al.: Cancer. Sci., 101 (9), 1925 (2010)
2-NS Forbes: Nat. Rev. Cancer, 10 (11), 785 (2010)
3- RA Malmgren & CC Flanigan: Cancer Res., 15 (7), 473 (1955)
4- NT Kimura et al.: Cancer Res., 40 (6), 2061 (1980)
Translation of an original essay in Japanese appearing in “Kagaku” on February 19, 2011, published by Iwanami Shoten.
"How and Why" – what I learned in medical science
Originally written on January 1, 2009 by Shun'ichiro Taniguchi
I entered university in Japan at the height of the time of campus unrest, and so my mind soon became filled with disappointment and regret in the rough atmosphere of campus life. All classes were closed because of indefinite protest strikes against government policies, thereby giving students a lot of the free time that they could not have during senior high school life while preparing for college entrance examinations. I used to spend every day alone in my room thinking about the origins and principles of words, materials, and numbers, as well as the significance of thinking itself. It was like that Mickle fails that fools think. When I asked myself about the purpose of learning science and my existence, I always lost my way and wandered into blind alleys with no answers. Furthermore, whenever older students who were enthusiastic about politics criticized me for majoring in physics, from which came the evil atomic bomb, my naïve heart suffered much distress, though such blame seems far too simplistic and unreasonable to me at the present time. Indeed, "my life at 17 and 18 years old was dark," like the words of a very popular Japanese song.
In the meantime, I became interested in life sciences, which made me feel more alive. In particular, I was fascinated in research on cancer, which could be justified as useful work without ever being considered an evil job. Although a professor advised me to continue studying physics, I did not follow his words, and with a twinge of regret for abandoning my chosen major I went on to graduate school to major in biophysics and begin my life of research.
In my new surroundings, I continued reading books on physics and mathematics when I felt good, but studied life sciences when I felt down to rejuvenate myself. When I read the book “The Philosophical Basis of Physics” by Dr. Carnap, I came across the sentence “In science, you should not ask “Why?” in pursuit of the metaphysical significance behind the event, but rather you should ask “How?” to humbly describe the events as you observe them.” This sentence reaffirmed what had been annoying me about my scientific education until that point, and with it I felt a kind of revolution within myself. I heartily agreed with those words and could at last clearly understand that I had been unconsciously confusing physical and metaphysical questions; I knew that science did not give us the answer to “Why?” and thus it felt nihilistic to me. Now, about 35 years later, I feel that it is still important to ask “Why?” as a motive to learn and study science. Without it, science is far less interesting and fascinating. On the other hand, I have learned that science asking “How?” to simply and humbly describe natural phenomena impacts me to such a degree that I often ask myself “Why I am here, and how did I get to this point?”.
Today, it is taken for granted that science deals with physical issues but not metaphysical matters; there are few scientists who consciously distinguish questions with “How?” for physical and “Why?” for metaphysical. The reason why I insist on separating “How?” from “Why?” is that both are unique and important. Questions with “Why?” ask about the significance and purpose of human existence and nature, while those with “How?” ask about the mechanisms of various phenomena and the way to live wisely. I think that it is important to consider and appreciate both approaches in order to understand life more clearly. There are visible (physical) and invisible (metaphysical) truths, and we should be careful not to direct our attention to only one or the other.
One example of the large impact of the question “Why?” on my medical research is about apoptosis, a currently important field in cancer research in which I am deeply involved. "The cell has a nucleus, and therein lies the wisdom of the universe," said Kenji Miyazawa. Today, his words are especially appropriate when we consider the established fact that the information for life is written in DNA, which has maintained the flow of life on earth. Meanwhile, research on apoptosis has revealed that the information for death is written in DNA as well. It was a valuable journey for me to learn about the coexistence of life and death. This coexistence could be discovered through the physical question “How?” by humbly observing the mechanism of life, and yet had a strong impact on the naïve question of “Why?” human beings live and die. The influence of this, at least on me, was profound. Apoptosis, or programmed cell death, is necessary for us to live as healthy individuals. Without apoptosis we would invariably suffer from autoimmune diseases and/or cancer. Furthermore, without human death, life on Earth would not survive. We must realize that the strong current of human life has priority over individual life by means of death. After realizing this, I felt a kind of joy and sense of freedom from the positive significance of death that people are so apt to fear. Learning about apoptosis has been a good way for me to find out that scientific questions of “How?”, which can seem cold and dry, yield warm-feeling answers to the questions of “Why?” for which I usually have no clear answers. I feel heartened that there is feedback and interaction in science by physically asking “How?” and metaphysically asking “Why?” we live and exist in this world. This is an example of how happy I am to be involved in medical science, studying about our lives.
Taken from the preface of the June 2008 issue of “Journal of Medicine Shinshu”
My life of study in cancer metastasis - Yesterday, Today, Tomorrow
Newsletter from JAMR, Shun'ichiro Taniguchi
It was during my posting at the Cancer Research Institute as a graduate student majoring in biophysics at the Kyushu University Graduate School of Science that I began to take an interest in cancer metastasis. I was directed by my supervisor, pathologist Professor Baba, to get practical training by performing autopsies on deceased cancer patients. The experience was so shocking to me that I suffered from stomach ulcers for some time, but it was also one of the most influential and beneficial experiences in my life.
The reason why I was sent to the Cancer Research Institute was that I wanted to engage in research that seemed directly useful to the world. During those years, there was a lot of campus unrest, and I had considerable time to think about the significance of basic research. As a result, I decided to change my general research focus to a more disease-related field. Several senior scientists at the Cancer Research Institute said to me, “You are like a moth drawn to a flame.” How true. Actually, I was quite shocked at the difference in approaches between the laboratories of science and medicine. It seems my attitude of trying to understand phenomena through molecular experiments and articles might have been overly simplistic, as I was quick to generalize everything. It was probably this attitude that irritated Prof. Baba so much that he often yelled to me during discussions “Stop oversimplifying things! Stomach cancer in my stomach is different from your stomach cancer in yours. You must understand that each cancer has its own characteristics.” To which I replied, “Yes, but even though my face is different from yours, there are many points in common. Both of us have two eyes, one nose, and one mouth. Science pursues such common principles, don’t you think?” Exasperated, he scolded, “You are so dull-witted. Get out there and see the patients who died of cancer with your own eyes!” I remember this conversation like it was yesterday.
By observing the autopsies of 5 or 6 cadavers with lung metastases and peritoneal carcinomatosis, I finally realized that cancer was indeed complex and individualized, and that the most important question in the fight against this disease was how to control metastasis. I also began to understand the notions of pathologists regarding cancer as a complicated systemic disease. Their sense had been completely different from mine, a mere student learning only of generalized molecular matters. After that, I became a quiet researcher devoted to experiments without any intense discussions, but with the inner desire simply to understand the complex disease of cancer at the molecular level, which was curiously strengthened through this painful but valuable experience.
Some time later, I had the chance to study under the supervision of the late Dr. Kakunaga at NCI in Bethesda. There, I experienced an active and bustling atmosphere due to the discovery of many new oncogenes at the time. When I returned to Prof. Baba’s lab, I felt that genes relating to metastasis were more important than those for carcinogenesis, and I started to search for and identify genes relating to metastasis while simultaneously engaging in Dr. Baba’s chemotherapy projects. Over time, I learned that gene manipulation of cytoskeletal actin could modify the motility of cancer cells, leading to the suppression of metastasis, and that the fos oncogene could regulate cancer metastasis by affecting multiple gene expression. Furthermore, I found out that the cytoskeletal systems of blood vessels and peritoneal mesothelial cells became fragile through the paracrine effects of factors excreted from cancer cells, and I proved that this fragility enhanced cancer metastasis by developing knockout mice for cytoskeletal genes, such as calponin.
Today, since molecular experiments and studies using genetically modified animals have become routine, all oncologists agree that cancer is a disease of the genes; the accumulation of structural changes and/or expression of multiple genes is necessary for carcinogenesis and progression. In addition, it has become commonly known that individual cancers stem from changes in individual genes, which has led to the idea of individual therapies. Prof. Baba was correct, but it was the molecular biologists, who were trying to simplify and generalize, that came up with the idea of individual therapy. Without our kinds of activities, the idea of individual therapy would not have been obtained, so recently I said to Prof. Baba, “You were absolutely right, but what you said was proven by the molecular techniques that I had told you about. So it looks like we were both right, weren’t we?”
Meanwhile, Dr. J. Fidler pointed out the important concept that a fundamental problem of cancer is the heterogeneity of cancer cells. Heterogeneous cell populations are considered to be produced because of the genetic instability of cancer cells. Today, it is also thought that this heterogeneity may be due to the presence of cancer stem cells.
If cancer stem cells create heterogeneity by producing differentiated cells, it is logical to think that treatment of cancer should target the regenerative stem cells only. It remains to be proven, however, whether cancer stem cells actually do exist, as well as whether cancer cells other than stem cells would be able to differentiate and die naturally without treatment. Recently, it appears likely that differentiated cancer cells might revert back to stem-like cells through EMT.
Although the ideal target of cancer treatment may be cancer stem cells, it seems to me that there remains several other problems to overcome, such as the drug-resistant dormant state of cancer stem cells and the discrimination of cancer stem cells from normal stem cells. Whatever the cause of cancer heterogeneity is, I think a major concept shift in the future search for effective ways to selectively destroy heterogeneous cancer populations will be to target the cancer tissue as a whole by directing our attention to the characteristics of the microenvironment.
Whenever I think about treating solid tumors, an analogy flashes in my mind: to fully see and/or understand the meaning of a picture, one has to stand at just the right distance from it. If we are too far from the picture, we cannot see what it is, and if we are too close, we can only see only colored paints and silver particles. This may be the case when searching for targets to treat cancer as well; I believe that we should also direct our attention to the broader specificities of the cancer tissue and its microenvironment, such as hypoxia, low pH, inflammatory reactions, and blood vessel fragility, in addition to molecular targets in cancer cells. I myself have been focusing on the inflammatory state, hypoxia, fragility of the vascular system, and peritoneal mesentery interactions with cancer cells to develop methods of treating cancers.
Lastly, I think that since the Japanese Association of Metastasis Research (JAMR) has many experts on the cancer microenvironment, it has a great potential to make discoveries in this area useful for the treatment of cancer in addition to its activities on revealing molecular targets in cancer cells. In this way, we can start to differentiate our activities and mission from those of the Japanese Association for Molecular Target Therapy of Cancer. The dream of the founders of JAMR, such as the late Drs. Akedo and Tsuruo, was for JAMR to contribute to the understanding and triumph over cancer metastasis in collaboration with academia and the pharmaceutical industry. Through this vision, we look forward to making further progress in metastasis research towards a tomorrow with new hopes.