The Primacy of Microspheroids

After incorporating the realization that cancer biology was predicated on cell survival and not cell growth into our laboratory platform, we moved away from proliferative end points to cell death measures, and then redoubled our efforts to recreate the human tumor micro-environment in tissue culture. We immediately recognized that this required the preservation of cell-cell interactions found normally in the body as cellular clusters.

These cellular clusters better known as microspheroids, represent cohesive populations that interact directly with stroma, vasculature, inflammatory cells, and other tumor cells. Thus, the microspheroid recapitulates the human tumor environment. By applying cell death endpoints (the most rigorous of predictive measures) to these microspheroids, we have overcome most of the pitfalls encountered by earlier technologies. And, for the first time, a truly predictive human tumor model has been developed.

Of the two fundamental changes that we as a laboratory have brought to the field of chemosensitivity-resistance testing, the maintenance of cancerous tumor cells in their “native state” as microspheroids has been fundamental to our success.

Despite these important advances, many physicians have not grasped their significance. Falling back on their out-dated understanding of chemosensitivity studies that used growth-based endpoints (clonogenic, growth-to-confluence, and H₃* thymidine incorporation, etc.) many physicians have failed to incorporate the use of these highly validated methodologies into their clinical practices.

A review of the published literature, correlating these more rigorous predictive methodologies with clinical outcomes, clearly establishes the validity of cell death in microspheroids as an important breakthrough in cancer treatment.

Chemosensitivity Testing That Makes Sense

Much of the controversy that has surrounded chemosensitivity-resistance assays (CSRA), reflects the fact that the majority of these tests were developed based on the erroneous belief that cancer was driven by its proliferative capacity and that the most active drugs could be chosen based upon their capacity to inhibit cancer cell growth. This led to a long series of unsuccessful attempts to predict clinical response based on cell proliferation endpoints.  Since the 1980’s we have come to realize that cancer represents a dysregulation of cell death and that effective drugs must kill cells outright (not inhibit their growth) in order to provide clinical response to patients.

The Ex Vivo Analysis of Programmed Cell Death (EVA-PCD) ^® assay developed by Rational Therapeutics pioneered the application of drug induced cell death for the prediction of clinical response in cancer patients.  The EVA-PCD^® assay was the first to incorporate this new understanding of cancer biology. By expanding the application of the EVA-PCD^® platform to targeted therapies, RTI is now exploring new classes of compounds that function by inhibiting survival signals in cancer cells.  Many signaling pathways like the epidermal growth factor receptor (EGFr) have extracellular domains that function as cellular switches activating downstream phosphorylations following receptor ligation by proteins like EGF, amphiregulin and TGF alpha.

These mitogen activated protein kinases (MAPK) induce additional cascades of phosphorylations ultimately signaling transcription factors at the level of DNA. While these phenomena were originally thought to represent mitotic events, it is now recognized that most cells are not actively dividing, yet require all of these signaling pathway activations to remain alive. Thus, what was once described as growth factors are more likely better described as anti-death factors.

If indeed cancer doesn’t grow too much but dies too little, it is evident that effective therapies induce cell death, not growth inhibition in the patient.  This is why it is critical to apply lab analyses that measure cell death. Furthermore, as most of the signals for cell survival emanate from the extracellular environment, it is clear that cancer cells must be maintained in their native state to provide clinically relevant information. This is the basis of RTI’s human tumor microspheroid assay platform.

There is a Better Way

With several hundred compounds currently in development for the treatment of cancer, how will we scientists and clinical oncologists match these drugs to patients  in need?

Only 8 percent of drugs entering Phase I ever make it through the highly unproductive Phase II and Phase III trial mechanisms to win FDA approval, with 50 percent failing at the Phase III final stage of development!

We can stop this self-defeating strategy and apply selective methodologies to identify the best disease targets for these compounds. According to Joanne Woodcock of the FDA, modern science has provided much more information about the origin of cancer than about its treatment. She has called for a developmental effort in the pursuit of a “critical path,” from bench to bedside.

I believe that Ex Vivo Analysis of Programmed Cell Death (EVA-PCD)® is that critical pathway and can serve to streamline drug development.

Truly Personalized Cancer Care

In the mid 1980s, it became apparent to me that cancer did not result from uncontrolled cell proliferation, but instead from the lack of cell death. Yet, cancer research labored for almost a century under the erroneous belief that cancer represented dysregulation of cell proliferation. Today, we confront another falsehood: the complexities and redundancies of human tumor biology can be easily characterized based on genomic analyses.

The process of carcinogenesis reflects the accumulation of cellular changes that provide a selective survival advantage to transformed cells.  However, the intricate circuitry that provide these survival advantages, reflect harmonic osolations between DNA, RNA and protein. Put simply, Genotype does not equal Phenotype. It is the phenotype that determines biological behavior and clinical response in cancer. Thus, it is ridiculously simplistic to imagine that a DNA profile by itself can provide more than a fraction of the information required to make individual patient treatment decisions.

When therapies are based on genomic analysis, only a portion of the patient’s profile is taken into consideration. These analyses disregard the environmental, epigenetic and proteomic factors that make each of us individuals. Though useful prognostically and applicable in select circumstances where a unique genetic perturbation leads to a clinical response (c-ABL and Imatinib response in CML), genomic analyses provide only a veneer of information.

The Rational Therapeutics Ex Vivo Analysis – Programmed Cell Death™ (EVA-PCD) assay focuses upon the complexity of human tumors by measuring cell death, the end result of all cellular mechanisms of response and resistance acting in concert. By incorporating cell-cell, vascular, stromal and inflammatory elements into the tumor response assessment, the EVA-PCD platform provides a robust surrogate for human tumor response. While much of modern cancer research pursues the question of “Why” cancer arises, the clinical oncologist must confront the more practical question of “How” the best outcome can be achieved.

Assay-directed therapy is truly personalized cancer care providing treatments unique to the individual.