Chemosensitivity Testing – What It Is and What It Isn’t

Several weeks ago I was consulted by a young man regarding the management of his heavily pre-treated, widely metastatic rectal carcinoma. Upon review of his records, it was evident that under the care of both community and academic oncologists he had already received most of the active drugs for his diagnosis. Although his liver involvement could easily provide tissue for analysis, I discouraged his pursuit of an ex vivo analysis of programmed cell death (EVA-PCD) assay. Despite this, he and his wife continued to pursue the option.

As I sat across from the patient, with his complicated treatment history in hand, I was forced to admit that he looked the picture of health. Wearing a pork pie hat rakishly tilted over his forehead, I could see few outward signs of the disease that ravaged his body. After a lengthy give and take, I offered to submit his CT scans to our gastrointestinal surgeon for his opinion on the ease with which a biopsy could be obtained. I then dropped a note to the patient’s local oncologist, an accomplished physician who I respected and admired for his practicality and patient advocacy.

A week later, I received a call from the patient’s physician. Though cordial, he was puzzled by my willingness to pursue a biopsy on this heavily treated individual. I explained to him that I was actually not highly motivated to pursue this biopsy, but instead had responded to the patient’s urging me to consider the option of performing an EVA-PCD assay. I agreed with the physician that the conventional therapy options were limited but noted that several available drugs might yet have a role in his management including signal transduction inhibitors.

I further explained that some patients develop a process of collateral sensitivity, whereby resistance to one class of drugs (platins, for example) can enhance the efficacy of other class of drugs (such as, antimetabolite) Furthermore, patients may fail a drug, then be treated with several other classes of agents, only then a year of two later, manifest sensitivity to the original drug.

Our conversation then took a surprising turn. First, he told me of his attendance at a dinner meeting, some 25 years earlier, where Dan Von Hoff, MD, had described his experiences with the clonogenic assay. He went on to tell me how that technique had been proven unsuccessful finding a very limited role in the elimination of “inactive” drugs with no capacity to identify “active” drugs. He finished by explaining that these shortcomings were the reason why our studies would be unlikely to provide useful information.

I found myself grasping for a handle on the moment. Here was a colleague, and collaborator, who had heard me speak on the topic a dozen times. I had personally intervened and identified active treatments for several of his patients, treatments that he would have never considered without me. He had invited me to speak at his medical center and spoke glowingly of my skills. And yet, he had no real understanding of what I do. It made me pause and wonder whether the patients and physicians with whom I interact on a daily basis understand the principles of our work. For clarity, in particular for those who may be new to my work, I provide a brief overview.

1.    Cancer patients are highly individual in their response to chemotherapies. This is why each patient must be tested to select the most effective drug regimen.
2.    Today we realize that cancer doesn’t grow too much it dies too little. This is why older growth-based assays didn’t work and why cell-death-based assays do.
3.    Cancer must be tested in their native state with the stromal, vascular and inflammatory elements intact. This is why we use microspheroids isolated directly from patients and do not grow or subculture our specimens.
4.    Predictions of response are not based on arbitrary drug concentrations but instead reflect the careful calibration of in vitro findings against patient outcomes – the all-important clinical database.
5.    We do not conduct drug resistance assays. We conduct drug sensitivity assays. These drug sensitivity assays have been shown statistically significantly to correlate with response, time to progression and survival.
6.    We do not conduct genomic analyses for there are no genomic platforms available today that are capable of reproducing the complexity, cross-talk, redundancy or promiscuity of human tumor biology.
7.    Tumors manifest plasticity that requires iterative studies. Large biopsies and sometimes multiple biopsies must be done to construct effective treatment programs.
8.    With chemotherapy, very often more is not better.
9.    New drugs are not always better drugs.
10.  And finally, cancer drugs do not know what diseases they were invented for.

While we could continue to enumerate the principles that guide our practice, one of the more important principles is humility. Medicine is a humbling experience and cancer medicine even more so. Patients often know more than their doctors give them credit for. Failing to incorporate a patient’s input, experience and wishes into the treatment programs that we design, limits our capacity to provide them the best outcome.

With regard to my colleague who seemed so utterly unfamiliar with these concepts, indeed for a large swath of the oncologic community as a whole, I am reminded of the saying “There’s none so blind as those who will not see.”

Reposted from March 23, 2012

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.

Why Oncologists Don’t Like In Vitro Chemosensitivity Tests

In human experience, the level of disappointment is directly proportional to the level of expectation. When, for example, the world was apprised of the successful development of cold fusion, a breakthrough of historic proportions, the expectations could not have been greater. Cold fusion, the capacity to harness the sun’s power without the heat and radiation, was so appealing that people rushed into a field about which they understood little. Those who remember this episode during the 1990s will recall the shock and dismay of the scientists and investors who rushed to sponsor and support this venture only to be left out in the cold when the data came in.

Since the earliest introduction of chemotherapy, the ability to select active treatments before having to administer them to patients has been the holy grail of oncologic investigation. During the 1950s and 60s, chemotherapy treatments were punishing. Drugs like nitrogen mustard were administered without the benefit of modern anti-emetics and cancer patients suffered every minute. The nausea was extreme, the bone marrow suppression dramatic and the benefits – marginal at best. With the introduction of cisplatin in the pre Zofran/Kytril era, patients experienced a heretofore unimaginable level of nausea and vomiting. Each passing day medical oncologists wondered why they couldn’t use the same techniques that had proven so useful in microbiology (bacterial culture and sensitivity) to select chemotherapy.

And then it happened. In June of 1978, the New England Journal of Medicine (NEJM) published a study involving a small series of patients whose tumors responded to drugs selected by in vitro (laboratory) chemosensitivity. Eureka! Everyone, everywhere wanted to do clonogenic (human tumor stem cell) assays. Scientists traveled to Tucson to learn the methodology. Commercial laboratories were established to offer the service. It was a new era of cancer medicine. Finally, cancer patients could benefit from effective drugs and avoid ineffective ones. At least, it appeared that way in 1978.

Five years later, the NEJM published an update of more than 8,000 patients who had been studied by clonogenic assay. It seemed that with all the hype and hoopla, this teeny, tiny little detail had been overlooked: the clonogenic assay didn’t work. Like air rushing out of a punctured tire, the field collapsed on itself. No one ever wanted to hear about using human tumor cancer cells to predict response to chemotherapy – not ever!

In the midst of this, a seminal paper was published in the British Journal of Cancer in 1972 that described the phenomenon of apoptosis, a form of programmed cell death.  All at once it became evident exactly why the clonogenic assay didn’t work. By re-examining the basic tenets of cancer chemosensitivity testing, a new generation of assays were developed that used drug induced programmed cell death, not growth inhibition. Cancer didn’t grow too much, it died too little. And these tests proved it.

Immediately, the predictive validity improved. Every time the assays were put to the test, they met the challenge. From leukemia and lymphoma to lung, breast, ovarian, and even melanoma, cancer patients who received drugs found active in the test tube did better than cancer patients who received drugs that looked inactive. Eureka! A new era of cancer therapy was born. Or so it seemed.

I was one of those naive investigators who believed that because these tests worked, they would be embraced by the oncology community. I presented my first observations in the 1980s, using the test to develop a curative therapy for a rare form of leukemia. Then we used this laboratory platform to pioneer drug combinations that, today, are used all over the world. We brought the work to the national cooperative groups, conducted studies and published the observations. It didn’t matter. Because the clonogenic assay hadn’t worked, regardless of its evident deficiencies, no one wanted to talk about the field ever again.

In 1600, Giordano Bruno was burned at the stake for suggesting that the universe contained other planetary systems. In 1634, Galileo Galilei was excommunicated for promoting the heliocentric model of the solar system. Centuries later, Ignaz Semmelweis, MD, was committed to an insane asylum after he (correctly) suggested that puerperal sepsis was caused by bacterial contamination. A century later, the discoverers of helicobacter (the cause of peptic ulcer disease) were forced to suffer the slings and arrows of ignoble academic fortune until they were vindicated through the efforts of a small coterie of enlightened colleagues.

Innovations are not suffered lightly by those who prosper under established norms. To disrupt the standard of care is to invite the wrath of academia. The 2004 Technology Assessment published by Blue Cross/Blue Shield and ASCO in the Journal of Oncology and ASCO’s update seven years later, reflect little more than an established paradigm attempting to escape irrelevance.

Cancer chemosensitivity tests work exactly according to their well-established performance characteristics of sensitivity and specificity. They consistently provide superior response and, in many cases, time to progression and even survival. They can improve outcomes, reduce costs, accelerate research and eliminate futile care. If the academic community is so intent to put these assays to the test, then why have they repeatedly failed to support the innumerable efforts that our colleagues have made over the past two decades to fairly evaluate them in prospective randomized trials? It is time for patients to ask exactly why it is that their physicians do not use them and to demand that these physicians provide data, not hearsay, to support their arguments.

Ovarian Cancer National Alliance 2011

The July meeting of the OCNA included a lecture by John Hays, MD, from the National Cancer Institute (NCI), entitled “Decision time: what is the right choice of chemotherapeutic agent(s)? Dr. Hays, part of the molecular signaling section at the NCI, reviewed literature on the topic. He described the need for prospective clinical trials to validate retrospective and in vitro results.

He then examined data from three technologies, the Oncotech extreme drug resistance test, Precision Therapeutics ChemoFX test and the ATP-based chemosensitivity test.

I found it odd that Dr. Dr. Hays spent time examining the EDR technology of Oncotech in as much as it is no longer offered and reflects proliferation-based studies, which have since largely been discredited.

The ATP assay was reviewed using the results of a study published by Dr. Ian Cree in which 180 patients received either assay-directed (ATP) or physician choice. This study actually provided an improvement for patients who received the ATP-based treatment but failed to achieve significance. Thus, it failed largely because it was underpowered.

But this reflected a more concerning aspect of the study.  It seems that the “physician choice” arm increasingly applied the best drug regimens developed in Dr. Cree’s own laboratory. As the trial continued to accrue, an increasing proportion of patients received Gemcitabine-based doublets (which were very new at the time) based upon Dr. Cree’s observation of activity for these novel combinations. This had the uncomfortable effect of forcing Dr. Cree to compete with himself. Had Dr. Hays been truly interested in examining this study as I have, he might have noticed the good control group response rate partly reflected the application of Dr. Cree’s’ own observations.

Indeed, when during my many attempts to conduct a prospective study with the GOG, I was at the very last moment confronted with a study design similar to Dr. Cree’s, (e.g. they could incorporate any treatment they chose, including those that I developed), my statistician demanded that I forego the pleasure, as he could see only too well that the trial had become impossible to power. You see, there was no true control arm for statistical comparison.

The final portion of Dr. Hays’ presentation was the ChemoFX assay. This technology propagates tissue biopsies to confluence and then conducts measurement of drug-induced cell death. With substantial funding largely provided by venture capital, Precision Therapeutics has leapt into the GOG with a series of trials. Should this hybrid technology fail to provide prospective results that meet significance, it will be a damaging blow to this unfairly maligned area of investigation. While I wish the ChemoFX investigators luck, a failure on their part could be harmful to the field. Their reliance on propagated, sub-cultured tissues grown to monoculture has been a concern to me since they first arose in the last few years as participants in the field. We await the results of their trials with great anticipation.

What is interesting in Dr. Hays’ review is not so much what he said, but what he didn’t say.

First, he did not mention the seminal work of Dr. Larry Weisenthal, a pioneer in the field.

Second, he did not describe the nearly 2,000 retrospective, yet statistically significant correlations in the literature in a wide variety of diseases. He neglected to mention that one of the most widely used regimens for breast and ovarian cancer was developed using the same human tumor culture analyses that he decries. If he actually treats patients, he no doubt uses the cisplatin gemcitabine doublets developed using one of these platforms.

Finally, Dr. Hays has failed evidence-based medicine 101. He has forgotten that in life-threatening illnesses where prospective clinical trial data is not available, in accordance with the dictates of evidence-based medicine, one should use the best available data to guide treatments.

There is a wealth of data supporting laboratory based drug selection.  Presentations like that described do not add to the discourse.