Cell Culture Drug Resistance Testing

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The Possible Role of Chemoresistance Testing in the Era of Post Surgical Adjuvant Chemotherapy for Non-Small Cell Lung Cancer (NSCLC)

Ricardo S. Santos, M.D., Amit N. Patel, M.D., Clark T. Gamblin, M.D., Hiran C. Fernando, M.D., James D. Luketich, M.D., and Rodney J. Landreneau, M.D., University of Pittsburg Medical Center, Pittsburgh, PA. CHEST 2004 Meeting, 2004, Abstract #1188: 1

PURPOSE: The role of empiric adjuvant chemotherapy after complete resection of NSCLC (stage Ia-IIIa) is being increasingly recommended by medical oncologists. This opinion is based upon a less than 5% benefit in overall survival with an associated 23% major treatment related toxicity among patients undergoing empiric therapy. Specific resistance and sensitivity testing is routinely utilized in antibiotic management of serious infection. A link between in vitro chemotherapy resistance and clinical outcome has been seen in patients with ovarian and breast cancer. However, current medical oncologic practice for lung cancer continues to utilize empiric drug treatment regimens in spite of potentially variable patient responses to a particular drug. We analyzed the chemotherapy resistance patterns in a consecutive group of patients with completely resected NSCLC.

METHODS: The in vitro extreme chemotherapy resistance (EDR®) profiles were obtained utilizing the Oncotech (Orange County, CA) EDR® assay, in which live cultures of resected tumor cells are incubated with supra-pharmacologic doses of selected chemotherapy agents. Tumors demonstrating proliferation by radioactive thymidine uptake analysis during a three day incubation were considered resistant to the specific agent. Thirty-seven patients following complete resection of stage I(28), stage II(5), stage IIIA(4) NSCLC were evaluated. The percentage of patients with extreme drug resistance occurring with front line chemotherapy agents for NSCLC is shown below.

RESULTS: In vitro resistance patterns seen to first line chemotherapy: LR(%); MR(%); HR(%); MR or HR(%). Platinum=41%;33%;26%;59% Taxanes=47%;41%;13%;54% Etoposide= 46%;19%;35%;54% Gencitabine=26%;12%;64%;76% Navelbine=59%;31%;9%;40% (LR=Low resistance; MR=Moderate resistance; HR=High resistance) .

CONCLUSION: Moderate to high chemoresistance to what is considered "front line" chemotherapy agents for NSCLC is substantial. This should caution thoracic surgeons and medical oncologists against the empiric prescription of these agents as adjuvant therapies for completely resected NSCLC patients.

CLINICAL IMPLICATIONS: Clinical algorithms considering the chemoresistance patterns of the individual patient’s tumor should be formulated in the future in lieu of empiric adjuvant chemotherapy.

In Vitro Extreme Chemotherapy Resistance Patterns for Resected Non-Small Cell Lung Cancer
T. d'Amato1, *R. Landreneau2, *R. McKenna3, R. Santos2, R. Parker4 1University of California, San Diego, San Diego, CA, 2University of Pittsburgh Medical Center, Pittsburgh, PA, 3Cedar Sinai Medical Center, Los Angeles, CA, 4Oncotech Inc, Tustin, CA.Annals of Thoracic Surgery, 2005, Abstract #42: 1

BACKGROUND: Recent reports have suggested adjuvant chemotherapy offers a small but significant survival advantage for patients with completely resected Non-Small Cell Lung Cancer (NSCLC). Little is known of the prevalence of extreme chemotherapy drug resistance (EDR) for the individual NSCLC patient being considered for adjuvant therapy. The EDR assay (Oncotech, Tustin, CA) is highly predictive of clinical unresponsiveness to chemotherapy for ovarian, brain, and breast cancer. This chemo-resistance testing is becoming an increasingly popular way to predict treatment failure, choose alternative agents, and to potentially avoid unnecessary chemotherapy toxicity for patients with these cancers.

METHODS: A total of 3,042 NSCLC specimens were cultured using a soft-agar based proliferation assay and tested for resistance to supra-pharmacologic doses of either CISPLATIN (CPLAT), CARBOPLATIN (CARBO), PACLITAXEL (TAX), ETOPOSIDE (VP16), or DOXORUBICIN (DOXO). Using 3H-Thymidine uptake the percentage of cell-growth inhibition was used to determine extreme drug resistance (EDR), intermediate drug resistance (IDR), or low drug resistance (LDR).

RESULTS: EDR or IDR to CPLAT in 1,409/2227 (63%), to CARBO in 1,056/1,565 (68%), to VP-16 in 1581/2505 (63%), and to DOXO in 1,101/1471 (75%) of NSCLC cultures.

CONCLUSIONS: Chemotherapy resistance is highly variable and individualized among NSCLC clinical cell cultures. This may account for the marginal results seen with empiric use of “First Line” chemotherapy agents in the adjuvant setting. The use of viable tumor culture in vitro analysis for EDR to these agents should be considered when formulating a plan of adjuvant therapy for resected NSCLC. Future trials comparing patient survival following tailored versus empiric adjuvant therapy appear justified.

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The traditional criteria ever used to evaluate laboratory tests has been the predictive 'accuracy' of the test. The American Society of Clinical Oncology (ASCO) reviews of cell culture assay tests specifically excluded all studies reporting the predictive 'accuracy' of the tests. In other words, they excluded reports that only reported correlations between assay results and clinical outcomes.

Instead, ASCO reviews included old, previously-reviewed studies comparing outcomes of patients who had treatment based on assay results versus patients with empirically chosen therapy. The criteria of laboratory assay 'efficacy', as opposed to laboratory assay 'accuracy' sound reasonable, but it is unprecendented with regard to any other laboratory test ever evaluated.

None of the available laboratory tests used in the selection of treatments for cancer patients have ever been tested for 'efficacy'. This includes estrogen receptor, progesterone receptor, Her2/neu, immunohistochemical staining for tumor classification, bacterial culture and sensitivity testing, CT, MRI and Pet Scans to measure tumor response to treatment. The only data supporting any of them relate to test 'accuracy', and there is a total lack of information regarding test 'efficacy'. (randomized trials with outcome measurements for diagnostic tests)

Also, no one is seriously proposing that any of the molecular tests now available (Oncotype DX, EGFR amplification/mutation) should have to be proven 'efficacious', as opposed to merely 'accurate', before they are used in clinical decisions regarding treatment selection.

ASCO says that there is no literature establishing clinical 'efficacy' of assay tests, because the costs of such clinical trials are prohibitive, granting agency support is non-existent, and no other analogous tests have been or will likely ever be subjected to such an unreasonably high bar criterion for clinical use.

Cell culture assay tests have been well proven to have predictive 'accuracy' with that of estrogen receptor, progesterone receptor, Her2/neu and the newer molecular tests. In light of the precious little in the way of guidance from clinical trials with respect to best empiric therapy (where the only thing that has been proven to correlate with treatment decisions is reimbursement to the prescribing oncologist) and the importance of basing cancer treatment at least in part on patient preferences, it is entirely reasonable to support judicious application of laboratory tests which have been well characterized with respect to test 'accuracy'. This is a diagnostic test and should be held to that criteria, and not to that of therapy.

This laboratory test is a tool for the oncologist. The oncologist should take advantage of all the tools available to him/her to treat a patient. And since studies show that only 25-30% of patients do respond to chemotherapy that is available to them, there should be due consideration to looking at the advantage of human tissue assay tests to the resistance that has been found to chemotherapy drugs.

Cell culture drug resistance testing is for preventing use of known anti-cancer drugs that are not likely effective in the specific tumor. Cell culture drug sensitivity testing tries to determine specific drug and dose effectiveness. The distinction between sensitivity and resistance is more semantic than substantive.

In virtually all forms of cancer, clinical trials have failed to identify best drug regimens for use in all individuals with a given form of cancer.

Oncologists have been documented to use reimbursement (payment to the oncologist) as the most important criterion for selecting between the large array of otherwise equally acceptable regimens.

The established criterion on which to judge all laboratory tests used to help in the selection of cancer treatment is test 'accuracy' and not test 'efficacy'.

Cell culture assay tests with cell-death endpoints have been exceedingly and reproducibly well established to be usefully 'accurate' in correlation with and predicting for clinical outcomes, including tumor response and patient survival.

Molecular assays have established absolutely no data relating to assay 'efficacy', and with much less data relating to assay 'accuracy' than exist to support the application of cell culture assays.

ASCO is an organization which has been zealous in its support of an inherently corrupt system which won't allow drugs to be chosen on the basis of tumor biology but instead protects the ability of oncologists to choose drugs largely on the basis of profit margin or least inconvenience to research clinics.

There should an expansion of reimbursement to promote even greater utilization and development of laboratory-based mechanisms for improving the match between tumors and an ever-increasing number of partially effective and very expensive drug therapies.