Chemosensitivity Testing Captures Attention of “Nature Biotechnology”

An interesting editorial appeared in the February 2013 issue of Nature Biotechnology titled “Dishing out cancer treatment.” The lead line reads, “Despite their limitations, in-vitro assays are a simple means for assessing the drug sensitivity of a patient’s cancer . . . we think assays deserve a second look.”

The author describes the unequivocal appeal of laboratory analyses that are capable of selecting drugs and combinations for individual patients. At a time when 100’s of new drugs are in development, drug discovery platforms that can mimic human tumor response in the laboratory are becoming increasingly attractive to patients and the pharmaceutical industry. While the author, rooted in contemporary molecular biology, examines the field through the lens of genomic, transcriptomic, proteomic and metabolomic profiling, he recognizes that these analyte-based approaches cannot capture the tumor in its microenvironment, yet we now recognize that these micro-environmental influences are critical to accurate response prediction.

As one reads this piece, it is instructive to remember that no other platform can examine the dynamic interaction between cells and their microenvironment. No other platform can examine drug synergy. And no other platform can examine drug sequence.

It is these complexities however, that will guide the next generation of drug tests and ultimately the process of drug discovery. Even the most ardent adherents to genomic profiling must ultimately recognize that genotype does not equal phenotype. Yet, it is the tumor phenotype that we must study.

I am gratified that the editors of so august a journal as Nature Biotechnology have taken the time to reexamine this important field. Perhaps, if our most scientific colleagues are beginning to recognize the importance of functional analyses, it may be only a matter of time before the clinical oncology community follows suit.

The editor’s final line is poignant, “After years spent on the sidelines, perhaps in-vitro screening methods deserve another look.” We couldn’t agree more.

Cancer Explained – The Role of Cell Death

Following a recent blog, I received an inquiry from one of our readers. The individual asked whether I could better explain my oft repeated statement that “cancer doesn’t grow too much, it dies too little.” The questioner was puzzled by my assertion that chemotherapy drugs acted to stop cells from growing, while she had come to believe that this was synonymous with killing them. This dichotomy is at the crux of our modern understanding of cancer.

In response, I would like to examine the very basis of what is known as carcinogenesis, the process by which cancer comes to exist.

For more than a century, scientists believed that cancer cells were growing more rapidly than normal cells. They based this on serial measurements of patient’s tumors, which revealed that tumor dimensions increased. A small lump in the breast measuring one-half inch in diameter would be found six months later to be one inch in diameter. And six months after that it was two inches in diameter. This was growth, plain and simple, and so it was reasoned that cancer cells must be growing too much. As such, cancer therapies, per force of necessity, would need to stop cancer cells from growing if they were to work at all.

And then, in 1972, a paper was published in the British Journal of Cancer that described the phenomenon of apoptosis, a form of programmed cell death. Although it would be almost a decade before cancer researchers fully grasped the implications of this paper, it represented a sea change in our understanding of human tumor biology.

Let’s use the example of a simple mathematical equation. Every child would recognize the principles of the following formula:
Tumor mass = growth rate – death rate
This simple equation represents the principle of modern cancer biology. Where cancer researchers went wrong was that they mistakenly posited that the only way a tumor mass could increase was through an increase in the growth rate. However, as any child will tell you, a negative of a negative is a positive. That is, at a given growth rate, the tumor mass can also increase if you reduce the death rate. Thus, the “growth” so obvious to earlier investigators did not reflect an increase in proliferation but instead a decrease in cell attrition. Cancer didn’t grow too much it died too little, but the end result was exactly the same.

It should now be abundantly clear exactly why chemotherapy drugs, designed to stop cells from growing, didn’t work. Yes, the drugs stopped cells from growing, and yes any population of “growing cells” would suffer the effect. But they didn’t cure cancers because the cancers weren’t growing particularly fast. Indeed, the fact that chemotherapy works at all is almost an accident. Contrary to our long held belief that we were inhibiting cell proliferation, chemotherapy drugs designed to damage DNA and disrupt mitosis, were actually working (when they did at all) by forcing the cells to take inventory and decide whether they could continue to survive. If the injury were too extreme, the cells would commit suicide through the process of cell death. If the cells were not severely damaged or could repair the damage, then they carried on to fight another day. None of this, however, had anything to do with cell growth.

Chemosensitivity Testing: Lessons Learned

Like all physicians and scientists engaged in the study of cancer biology and cancer treatment, I had accepted that cancer was a disease of abnormal cell growth. I remember reading the lead article in the New England Journal of Medicine (NEJM) that described the clonogenic assay (Salmon, S. E., Hamburger, A. W., Soehnlen, B. S., et al. 1978. Quantitation of differential sensitivity of human tumor stem cells to anticancer drugs. N Engl J Med 298:1321–1327).

I sat in a laboratory at Georgetown University reading about a lab test that could accurately predict the outcome of cancer patients, without first having to give patients toxic drugs. It seemed so logical, so elegant, so inherently attractive. Sitting there as a medical student, far removed from my formal cancer training, I thought to myself, this is a direction that I would like to pursue.

But I was only a first year student and there were miles to go before I would treat cancer patients. Nonetheless, selecting drugs based on a laboratory assay was something I definitely wanted to do. At the time I had no idea just how difficult that could prove to be.

After medical school I found myself in California. There I met an investigator from the National Cancer Institute who had recently joined the faculty at the University of California, Irvine. He too had read the NEJM paper. Being several years ahead of me in training he had applied the clonogenic technique at his laboratory at the National Cancer Institute. Upon his arrival in California, he had continued his work with the clonogenic assay.

All was going along swimmingly until the NEJM published their report documenting the results of five years experience with the clonogenic assay.  It wasn’t a good report card. In fact the clonogenic assay got an “F.”

Despite the enthusiastic reception that the assay had previously enjoyed, the hundreds of investigators around the world who had adopted it and the indefatigable defense of its merits by leading scientists, it seemed that something was very wrong with the clonogenic assay and I desperately needed to know what that was.

It so happens that in parallel to clonogenic assays, my colleague was working on a simpler, faster way to measure drug effects. Using the appearance of cells under the microscope and their staining characteristics, one could skip the weeks of growth in tissue culture and jump right to the finish line. The simple question to be answered was: Did the drugs and combinations kill cancer cells in the test tube? And if they did kill cancer cells in the test tube, would those drugs work in the patient? The answer was, “YES!”

Despite the clonogenic assay’s supporters, it turned out that killing cancer cells outright in the test tube was a much, much better way to predict patient’s outcomes. It would be years before I understood the depth of this seemingly simple observation and the historical implications it would have for cancer therapy.

In Chapter 7 of my soon-to-be-released book, Outliving Cancer I examine the impact of programmed cell death on human biology.

What is Cancer?

This is a question that has vexed scientific investigators for  centuries, and for the last century, our belief was predicated upon physical observation that cancer reflected altered  cell growth. After all, to the untrained eye, or even to the rather sophisticated eye, the mass in the pelvis or the lymph node under the arm, or the abnormality on a chest x-ray, continued to expand upon serial observation. This was “growth” (at least since the time of Rudolph Virchow); and growth it was reasoned represented cell division.

Based upon the cell growth model, cancer therapists devised drugs and treatments that would stanch cellular proliferation. If cells were growing, then cells needed to reproduce the genetic elements found in chromosomes leading to the duplication of the cell through mitosis. If chromosomes were made of DNA, then DNA would be the target of therapy. From radiation to cytotoxic chemotherapy, one mantra rang through the halls of academia, “Stop cancer cells from dividing and you stop cancer.”

As in many scientific disciplines, nothing spoils a lovely theory more than a little fact. And, the fact turned out to be that cancer does not grow too much, it dies too little. Cancer doesn’t “grow” its way into becoming a measurable tumor, it “accumulates” its way to that end.

In 1972, we realized that the most basic understanding of cancer biology up to that point was absolutely, positively wrong.

Working in a laboratory during my fellowships, I began to realize that something was wrong with the principles that guided cancer therapeutics. My first inkling came from the rather poor outcomes that many of my patients experienced despite high-dose, aggressive drug combinations.

Then, it was the failure of the clonogenic assay to predict clinical outcomes that further raised my suspicions. I began to ponder cell growth – cell death, cell growth – cell death. With each passing day the laboratory analysis that I conducted identified active treatments that worked.  Using short-term measures of cell death (not cell growth),. I could predict which of my patients would get better.  All of the complicated and inefficient clonogenic assay investigations could not. Cell growth – cell death – what was I missing?

It would be years before I would attend a special symposium on the topic of cell death that it all became abundantly clear.

My “eureka” moment is captured in Chapter 6 of my soon-to-be-released book, Outliving Cancer.