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The EGFRx Assay

gdpawel's picture
Posts: 538
Joined: May 2001

A class of anti-cancer drugs, called tyrosine kinase inhibitors (TKIs) or anti-EGFR drugs, selectively targets cells within the body that have a specific molecular defect that is believed to cause dangerous cell behaviors such as uncontrolled proliferative growth and high metastatic potential – behaviors that typically are associated with aggressive cancer. The defect occurs within the interior of the cell in a region that is called the tyrosine kinase domain and it involves a complicated chemical process called EGFR signaling.

When tyrosine kinase inhibitors work, they can be highly beneficial, causing tumor shrinkage or promoting stable disease and extending survival. However, as with most of the newer, targeted therapy drugs, tyrosine kinase inhibitors only work for a small percentage of the patients who receive them. In various studies, response rates in single-agent and combined anti-EGFR drug therapy ranged from around 10% to 66%, depending upon the cancer type and the patient population involved. The drugs are expensive and have been associated with toxic side effects. No molecular (gene-based) test has been proven to tell reliably who will benefit from anti-EGFR treatment.

The EGFRx functional profile has been shown to correlate highly with patient response to anti-EGFR treatment and with overall patient survival. Reported prospectively, EGFRx functional profiling results reliably identify patients who do or do not respond to treatment with anti-EGFR drugs and also those who achieved superior survival after treatment.

The EGFRx targeted therapy profile includes analysis of the following targeted drugs: erlotinib (Tarceva), gefitinib (Iressa), sorafenib (Nexavar), and sunitinib (Sutent). For certain types of cancer, a drug called imatinib (Gleevec), which works in a very different way, may be tested.

As we enter the era of "personalized" medicine, it is time to take a fresh look at how we evaluate treatments for cancer patients. More emphasis should be put on matching treatment to the patient. Patients would certainly have a better chance of success had their cancer been chemo-sensitive rather than chemo-resistant, where it is more apparent that chemotherapy improves the survival of patients, and where identifying the most effective chemotherapy would be more likely to improve survival.

Findings presented at the 41st Annual Meeting of the European Society for Clinical Investigation in Uppsala, Sweden, April 18, 2007, concluded that "functional profiling" with cell culture assays is relevant for the study of both "conventional" and "targeted" anti-neoplastic drug agents (anti-tumor and anti-angiogenic activity of Iressa, Tarceva, Sutent, Nexavar, and Avastin in primary cultures of "fresh" human tumors).

Cell Culture Assays with "cell-death" endpoints can show disease-specific drug activity, are useful clinical and research tools for "conventional" and "targeted" drugs, and provide unique information complementary to that provided by "molecular" tests. There have been more than 25 peer-reviewed publications showing significant correlations between cell-death assay results and patient response and survival.

Many patients are treated not only with a "targeted" therapy drug like Tarceva, Avastin, or Iressa, but with a combination of chemotherapy drugs. Therefore, existing DNA or RNA sequences or expression of individual proteins often examine only one compenent of a much larger, interactive process. The oncologist might need to administer several chemotherapy drugs at varying doses because tumor cells express survival factors with a wide degree of individual cell variability.

There is a tactic of using biopsied cells to predict which cancer treatments will work best for the patient, by taking pieces of live "fresh" tumor tissue, applying different chemotherapy treatments to it, and examining the results to see which drug or combination of drugs does the best job killing the tumor cells. A cell culture assay test with "functional profiling," using a cell-death endpoint, can help see what treatments will not have the best opportunity of being successful (resistant) and identify drugs that have the best opportunity of being successful (sensitive).

"Funtional profiling" measures the response of the tumor cells to drug exposure. Following this exposure, they measure both cell metabolism and cell morphology. The integrated effect of the drugs on the whole cell, resulting in a cellular response to the drug, measuring the interaction of the entire genome. No matter which genes are being affected, "functional profiling" is measuring them through the surrogate of measuring if the cell is alive or dead.

For example, the epidermal growth factor receptor (EGFR) is a protein on the surface of a cell. EGFR-inhibiting drugs certainly do target specific genes, but even knowing what genes the drugs target doesn't tell you the whole story. Both Iressa and Tarceva target EGFR protein-tyrosine kinases. But all the EGFR mutation or amplificaton studies can tell us is whether or not the cells are potentially susceptible to this mechanism of attack. They don't tell you if Iressa is better or worse than Tarceva or other drugs which may target this. There are differences. The drugs have to get inside the cells in order to target anything. So, in different tumors, either Iressa or Tarceva might get in better or worse than the other. And the drugs may also be inactivated at different rates, also contributing to sensitivity versus resistance.

As an example of this testing, researchers have tested how well a pancreatic cancer patient can be treated successfully with a combination of drugs commonly used to fight lung, pancreatic, breast, and colorectal cancers. The pre-test can report prospectively to a physician specifically which chemotherapy agent would benefit a cancer patient. Drug sensitivity profiles differ significantly among cancer patients even when diagnosed with the same cancer.

The "funtional profiling" technique makes the statistically significant association between prospectively reported test results and patient survival. It can correlate test results that are obtained in the lab and reported to physicians prior to patient treatment, with significantly longer or shorter overall patient survival depending upon whether the drug was found to be effective or ineffective at killing the patient's tumor cells in the laboratory.

This could help solve the problem of knowing which patients can tolerate costly new treatments and their harmful side effects. These "smart" drugs are a really exciting element of cancer medicine, but do not work for everyone, and a test to determine the efficacy of these drugs in a patient could be the first crucial step in personalizing treatment to the individual.

Literature Citation: Eur J Clin Invest 37 (suppl. 1):60, 2007

gdpawel's picture
Posts: 538
Joined: May 2001

Drug Sensitivity and Resistance Assays or Chemosensitivity and Resistance Assays (CSRAs) can help predict which chemotherapy drugs will work best in a cancer patient, by testing different drugs directly against a sample of the tumor to identify which is the most effective. Conventionally, chemotherapy drugs are prescribed based on their overall performance in past clinical trials. However, the best drugs identified may fail to help between 30% and 60% of patients, or more, depending on the disease and the individual. Not all patients will have the same response to the same chemotherapy.

When a cancer patient sees a medical oncologist, they are told that their cancer will be treated with "empiric" or "physician's choice" drugs. However, the average treatment for the average patient cannot possibly work all the time because there are no average cancer patients. Each patient's cancer is unique. Because of this, patients respond differently to the same anticancer drugs. Your treatment should be tailored to your cancer. Assay-testing can help your doctor appreciate how your cancer cells may respond to various anticancer treatments.

With assay-testing, a fresh, surgical specimen is obtained from a viable solid tumor. Less often, it is a malignant effusion, bone marrow, or peripheral blood specimen containing "tumor" cells. These cells are isolated and then cultured in the continuous presence or absence of drugs, most often for 3 to 7 days. At the end of the culture period, a measurement is made of cell injury, which correlates directly with cell death. There is evidence that the majority of available anticancer drugs may work through a mechanism of causing sufficient damage to trigger so-called programmed cell death or apoptosis.

Besides the assays predicting which chemotherapy drugs will work best for the patient, they can also end up confirming that the standard treatment is the best option. In some cases, the tests can return results that show no treatment works. In that case, the patient may be advised to go to a clinical trial or forgo any further, fruitless therapy. Why harm a patient with very toxic and ineffective chemotherapy that would most likely not benefit them, and lower the quality of life that remains.

Some patients may not have easily-accessbile tumors (needle biopsies do not gather enough specimen), making it difficult to harvest a large-enough sample (200mg or 10mm in size). The tests are most reliable before a tumor has been exposed to chemotherapy. However, after a patient fails a previous chemotherapy treatment, the test still can be done once a patient waits at least four weeks.

It is true that what happens in the lab is not necessarily what happens in the patient. Cell death assays are not intended to be scale models of chemotherapy in the patient, anymore than the barometric pressure is a scale model of the weather. But it's always more likely to rain when the barometer is falling than when it is rising, and chemotherapy is more likely to work in the patient when it kills the patient's cancer cells in the laboratory. It is no different than any other medical test in this regard.

The Americain Society of Clinical Oncology (ASCO) suggested in their technology assessment of CSRAs that the study of them should be a top priority. They did not however, recommend its use outside of a clinical study. This recommendation was a result of evaluating a less reliable form of assay-testing. There are two types of CSRAs, one that determines whether a drug stops a cancer from growing (cell-growth) and one that determines whether a drug kills (cell-death) the cancer outright. The ASCO report looked at the cell-growth tests, and not at the cell-death tests, that are a better predictor of whether a drug will work.

The ASCO panel says the cell-death tests weren't included in the review because, to them, there weren't any reliable studies assessing them. Even with the cell-growth analysis, many studies cited in the ASCO report showed twice as many patients who were given assay-directed therapy responded to treatment, compared to patients who were given "empiric-directed" therapies. The researchers claimed that the studies didn't show that using the tests helped people live longer than those prescribed a "standard" treatment. However, they cannot claim that "standard" treatments help people live longer than those that use "assay-directed" treatments.

There have been over 40 publications in peer-reviewed medical literature showing correlations between cell-death assay test results and the results of clinical chemotherapy in more than 2,000 patients. In every single study, patients treated with drugs active in the assays had a higher response rate than the entire group of patients as a whole. In every single study, patients treated with drugs inactive in the assays had lower response rates than the entire group of patients. In every single study, patients treated with active drugs were much more likely to respond than patients treated with inactive drugs, with assay-active drugs being 7 to 9 times more likely to work than assay-inactive drugs. A large number of peer-review publications also reported that patients treated with assay-tested 'active' drugs enjoyed significantly longer survival of cancer than patients with assay-tested 'negative' drugs.

The tumors of different patients have different responses to chemotherapy. It requires individualized treatment based on testing the individual properties of each patient's cancer. The hallmark of cancer is its heterogeneity, yet the powers that be insist on trying to homogenize it, rather than tailoring treatment to the individual nature of the disease.

Resources: Various Bio-Assay Journals

gdpawel's picture
Posts: 538
Joined: May 2001

The EGFR (or HER1) signaling pathway is a promising and widely studied interventional target. EGFR signaling involves a cascade of chemical reactions that serve to drive cell behaviors. In a healthy cell, EGFR signaling helps to perform a variety of useful functions such as regulating normal cell growth, facilitating wound healing, and helping to resist damage from toxins.

However, abnormal signaling along the EGFR pathway has been associated with numerous dangerous cell behaviors such as tumor growth and progression, metastasis, resistance to chemotherapy, and generally poorer patient prognosis. Because of the high cost of anti-EGFR drugs and the fact that only a relatively small percentage of patients benefit from them - about 10% in most studies - there is great urgency to develop laboratory tests that identify patients who are good candidates for anti-EGFR treatments.

Three types of tests have been studied most extensively. These include tests that measure EGFR protein expression, a test for EGFR gene amplification, and a test for EGFR-related gene mutations. The EGFR gene amplification test is the only one of the three approaches shown to date to predict for improved survival among patients who receive anti-EGFR drugs.

However, questions concerning this approach remain unanswered and even the principal developer of the test says that it is still too early to recommend his test for routine use. In one retrospective study of the gene mutation approach, a certain mutation was associated with a modest survival benefit from anti-EGFR treatment, particularly in Asian patients, who seem to have higher incidences of that particular EGFR mutation.

A follow-up study failed to reproduce the results. EGFR protein expression tests have not been shown to correlate reliably either with response or survival. The Medical Director of Genzyme, a laboratory company that markets a gene-based EGFR test, has stated that a panel consisting of several different tests that collectively assess several, different factors probably will be necessary for meaningful patient selection.

There was a cell-based assay test that was developed which is based upon the Functional Profiling method. Functional Profiling is a laboratory method in which fresh "living" tumor cells are obtained from individual cancer patients and are exposed to different chemotherapy drugs in order to see which of the drugs are effective at killing or stopping the growth of the cancer cells and which of the drugs are not effective.

The purpose of Functional Profiling is to personalize therapy design by identifying chemotherapy drug treatments that have the greatest likelihood of helping each patient as an individual. This is the opposite of empirical therapy selection in which patients are treated blindly with drugs that worked in the past for some percentage of patients who received them.

Functional Profiling is based upon the principle that no cancer patient is "average" but rather that each patient's illness is unique in its response to treatment. This is supported by the clinical observation that different cancer patients often respond very differently to the same treatments.

In a study of 60 non-small lung cancer cell patients, the EGFRx assay, prospectively identified patients who not only responded to gefitinib (Iressa) and erlotinib (Tarceva) but who also achieved significantly longer survival periods than patients whose tumors were resistant in vitro to treatment with EGFR-based therapies.

The extent of the survival advantage among patients prospectively identified as likely candidates for anti-EGFR therapy in EGFR assay greatly exceeds that which has been published to date for any other EGFR-related test. Importantly, patients who were resistant in the EGFRx assay but who received anti-EGFR therapy in spite of their negative assay results lived no longer than patients who did not receive anti-EGFR therapy.

The findings were presented at the 2006 American Society of Clinical Oncology (ASCO) annual international meeting (above). The EGFRx assay is applicable to all patients and does not require a panel of different tests. The advantage of the Functional Profiling approach, is that it evaluates drug activity in the whole cell, as opposed to individually assessing some number of individual of surrogate markers, as in molecular tests, each of which provides only one piece of the puzzle.

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