Microarray, Gene Expression and Cell-Lines
There have been attempts to develop molecular-based tests to examine a broader range of chemotherapeutic drugs. New technologies for measuring the expression (biological activity) of literally hundreds to thousands of genes as part of a single test. There are two main technologies involved: RT-PCR (reverse transcription polymerase chain reaction) and DNA microarray.
The Microarray (gene chips) is a device that measures differences in gene sequence, gene expression or protein expression in biological samples. Microarrays may be used to compare gene or protein expression under different conditions, such as cells found in cancer.
Hence the headlong rush to develop tests to identify molecular predisposing mechansims whose presence still does not guarantee that a drug will be effective for an individual patient. Nor can they, for any patient or even large group of patients, discriminate the potential for clinical activity among different agents of the same class.
Genetic profiles are able to help doctors determine which patients will probably develop cancer, and those who will most likely relapse. However, it cannot be suitable for specific treatments for "individual" patients. The NCI has concluded (J Natl Cancer Inst. March 16, 2010), it cannot determine treatment plans for patients. It cannot test sensitivity to any of the targeted therapies. It just tests for "theoretical" candidates for targeted therapy.
Some molecular tests do utilize living cells, but generally of individual cancer cells in suspension, sometimes derived from tumors and sometimes derived from circulating tumor cells. This was tried with the human clonogenic assay, which had been discredited long ago. Traditionally, in-vitro (in lab) "cell-lines" have been studied in 2 dimensions (2D) which has inherent limitations iin applicability to real life 3D in-vivo (in body) states. Recently, other researchers have pointed to the limitations of 2D "cell-line" study and chemotherapy to more correctly reflect the human body.
All DNA or RNA-type tests are based on "population" research (not individuals). They base their predictions on the fact that a higher percentage of people with similar genetic profiles or specific mutations may tend to respond better to certain drugs. This is not really "personalized" medicine, but a refinement of statistical data.
The cell "function" method is not hampered by the problems associated with gene expression tests. That is because they measure the net effect of all processes within the cancer, acting with and against each other in real time, and it tests living cells actually exposed to drugs and drug combinations of interest.
Cancer is already in 3D conformation. Cell-based functional profiling cultures "fresh" live tumor cells in 3D conformation and profiles the function of cancer cells (is the whole cell being killed regardless of the targeted mechanism or pathway). It distinguishes between susceptibility of cancer cells to different drugs in the same class and the susceptibility to combinations. In other words, which combinations are best and in what sequence would they be most effective.
The key to understanding the genome is understanding how cells work. The ultimate driver is a "functional" assay (is the cell being killed regardless of the mechanism) as opposed to a "target" assay (does the cell express a particular target that the drug is supposed to be attacking). While a "target" assay tells you whether or not to give "one" drug, a "functional" assay can find other compounds and combinations and can recommend them from the one assay.
The core of the functional assay is the cell, composed of hundreds of complex molecules that regulate the pathways necessary for vital cellular functions. If a "targeted" drug could perturb any one of these pathways, it is important to examine the effects of the drug within the context of the cell. Both genomics and proteomics can identify potential new therapeutic targets, but these targets require the determination of cellular endpoints.
Cell-based functional assays are being used for screening compounds for efficacy and biosafety. The ability to track the behavior of cancer cells permits data gathering on functional behavior not available in any other kind of assay.
The reason for at least a "tru-cut" biopsied tumor specimen is that "real life" 3D analysis makes functional profiling indicative of what will happen in the body. It tests fresh "live" cells in their 3 dimensional (3D), floating clusters (iin their natural state). Upgrading clinical therapy by using drug sensitivity assays measuring cell-death of 3 dimenionsl microclusters of live "fresh" tumor cells can improve the conventional situation by allowing more drugs to be considered.
We are forced to confront the realization that genotype does not equal phenotype. The particular sequence of DNA that an organism possess (genotype) does not determine what bodily or behaviorial form (phenotype) the organism will finally display. Among other things, environmental influences can cause the suppression of some gene functions and the activation of others. Out knowledge of genomic complexity tells us that genes and parts of genes interact with other genes, as do their protein products, and the whole system is constantly being affected by internal and external environmental factors.
The gene may not be central to the phenotype at all, or at least it shares the spotlight with other influences. Environmental tissue and cytoplasmic factors clearly dominate the phenotypic expression processes, which may in turn, be affected by a variety of unpredictable protein-interaction events. This view is not shared by all molecular biologists, who disagree about the precise roles of genes and other factors, but it signals many scientists discomfort with a strictly deterministic view of the role of genes in an organism's functioning.
Until such time as cancer patients are selected for therapies predicated upon their own unique biology (and not population studies), we will confront one targeted drug after another. The solution to this problem has been to investigate the targeting agents in each individual patient's tissue culture, alone and in combination with other drugs, to gauge the likelihood that the targeting will favorably influence each patient's outcome. Functional profiling results to date in patients with a multitude type of cancers suggest this to be a highly productive direction.
JNCI J Natl Cancer Inst (2010) doi: 10.1093/jnci/djq306
J Thorac Cardiovasc Surg 2007;133:352-363. Chemotherapy Resistance and Oncogene Expression in NSCLC.
J Clin Onco, 2006 ASCO Annual Meeting Proceedings Part 1. Vol 24, No. 18S (June 20 Supplement), 2006: 17117. Genfitinib-induced cell death in short term fresh tumor cultures predicts for long term patient survival in previously-treated NSCLC.
Eur J Clin Invest, Volume 37(suppl. 1):60, April 2007. Functional profiling with cell culture-based assays for kinase inhibitors and anti-angiogenic agents.
Weisenthal Cancer Group, Huntington Beach, CA and Departments of Clinical Pharmacology and Oncology, Uppsala University, Uppsala, Sweden. Current Status of Cell Culture Drug Resistance Testing (CCDRT) May, 2002.
Gregory D. Pawelski
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