Chemistry: molecular biology and microbiology – Measuring or testing process involving enzymes or... – Involving antigen-antibody binding – specific binding protein...
Reexamination Certificate
2001-07-13
2003-11-11
Huff, Sheela (Department: 1642)
Chemistry: molecular biology and microbiology
Measuring or testing process involving enzymes or...
Involving antigen-antibody binding, specific binding protein...
C435S007100
Reexamination Certificate
active
06645731
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the fields of oncology and diagnostic testing. The invention is useful for cancer screening, staging, monitoring for chemotherapy treatment responses, cancer recurrence or the like. More specifically, the present invention provides reagents, methods and test kits which facilitate analysis and enumeration of tumor cells, or other rare cells isolated from biological samples.
BACKGROUND OF THE INVENTION
Each year in the United States, approximately 600,000 new cases of cancer are diagnosed; one out of every five people in this country will die from cancer or from complications associated with its treatment. Considerable efforts are continually directed at improving treatment and diagnosis of this disease.
Most cancer patients are not killed by their primary tumor. They succumb instead to metastases: multiple widespread tumor colonies established by malignant cells that detach themselves from the original tumor and travel through the body, often to distant sites. If a primary tumor is detected early enough, it can often be eliminated by surgery, radiation, or chemotherapy or some combination of those treatments. Unfortunately, the metastatic colonies are harder to detect and eliminate and it is often impossible to treat all of them successfully. Therefore, from a clinical point of view, metastasis can be considered the conclusive event in the natural progression of cancer. Moreover, the ability to metastasize is the property that uniquely characterizes a malignant tumor.
Cancer metastasis comprises a complex series of sequential events. These are: 1) extension from the primary locus into surrounding tissues; 2) penetration into body cavities and vessels; 3) release of tumor cells for transport through the circulatory system to distant sites; 4) reinvasion of tissue at the site of arrest; and 5) adaptation to the new environment so as to promote tumor cell survival, vascularization and tumor growth.
Based on the complexity of cancer and cancer metastasis and the frustration in treating cancer patients over the years, many attempts have been made to develop diagnostic tests to guide treatment and monitor the effects of such treatment on metastasis or relapse. Such tests presumably could also be used for cancer screening, replacing relatively crude tests such as mammography for breast tumors or digital rectal exams for prostate cancers. Towards that goal, a number of tests have been developed over the last 20 years and their benefits evaluated. One of the first attempts was the formulation of an immunoassay for carcinoembryonic antigen [CEA]. This antigen appears on fetal cells and reappears on tumor cells in certain cancers. Extensive efforts have been made to evaluate the usefulness of testing for CEA as well as many other “tumor” antigens, such as PSA, CA 15.3, CA125, PSMA, CA27.29. These efforts have proven to be somewhat futile as the appearance of such antigens in blood have not been generally predictive and are often detected when there is little hope for the patient. In the last few years, however, one test has proven to be useful in the early detection of cancer, viz., Prostate Specific Antigen [PSA] for prostate cancers. When used with follow-up physical examination and biopsy, the PSA test has played a remarkable role in detecting prostate cancer early, at the time when it is best treated.
Despite the success of PSA testing, the test leaves much to be desired. For example, high levels of PSA do not always correlate with cancer nor do they appear to be an indication of the metastatic potential of the tumor. This may be due in part to the fact that PSA is a component of normal prostate tissue as well as other unknown factors. Moreover, it is becoming clear that a large percentage of prostate cancer patients will continue to have localized disease which is not life threatening. Based on the desire to obtain better concordance between those patients with cancers that will metastasize and those that won't, attempts have been made to determine whether or not prostate cells are in the circulation. When added to high PSA levels and biopsy data, the existence of circulating tumor cells might give indications as to how vigorously the patient should be treated.
The approach for determining the presence of circulating prostate tumor cells has been to test for the expression of messenger RNA of PSA in blood. This is being done through the laborious procedure of isolating all of the mRNA from a blood sample and performing reverse transcriptase PCR. As of this date, (Gomella L G. J of Urology. 158:326-337(1997)) no good correlation exists between the presence of such cells in blood and the ability to predict which patients are in need of vigorous treatment. It is noteworthy that PCR is difficult, if not impossible in many situations, to perform quantitatively, i.e., determine number of tumor cells per unit volume of biological sample. Additionally false positives are often observed using this technique. There is an added drawback which is that there is a finite and practical limit to the sensitivity of this technique based on the sample size examined. Typically, the test is performed on 10
5
to 10
6
cells purified away from interfering red blood cells. This corresponds to a practical lower limit of sensitivity of one tumor cell/0.1 ml of blood. Hence, there needs to be about 10 tumor cells in a ml of blood before signal is detectable. As a further consideration, tumor cells are often genetically unstable. Accordingly, cancer cells having genetic rearrangements and sequence changes may be missed in a PCR assay as the requisite sequence complementarity between PCR primers and target sequences can be lost.
In summary, a useful diagnostic test needs to be very sensitive and reliably quantitative. If a blood test can be developed where the presence of a single tumor cell can be detected in one ml of blood, that would correspond on average to 3000-4000 total cells in circulation. In innoculum studies for establishing tumors in animals, that number of cells can indeed lead to the establishment of a tumor. Further if 3000-4000 circulating cells represents 0.01% of the total cells in a tumor, then it would contain about 4×10
7
total cells. A tumor containing that number of cells would not be visible by any technique currently in existence. Hence, if tumor cells are shed in the early stages of cancer, a test with the sensitivity mentioned above would detect the cancer. If tumor cells are shed in some functional relationship with tumor size, then a quantitative test would be beneficial to assessing tumor burden. Heretofore there has been no information regarding the existence of circulating tumor cells in very early cancers. Further, there are very considerable doubts in the medical literature regarding the existence of such cells and the potential of such information. The general view is that tumors are initially well confined and hence there will be few if any circulating cells in early stages of disease. Also, there are doubts that the ability to detect cancer cells early on will give any useful information.
Based on the above, it is apparent that a method for identifying those cells in circulation with metastatic potential prior to establishment of a secondary tumor is highly desirable, particularly early on in the cancer. To appreciate the advantage such a test would have over conventional immunoassays, consider that a highly sensitive immunoassay has a lower limit of functional sensitivity of 10
−17
moles. If one tumor cell can be captured from a ml of blood and analyzed, the number of moles of surface receptor, assuming 100,000 receptors per cell would be 10
−19
moles. Since about 300 molecules can be detected on a cell such an assay would have a functional sensitivity on the order of 10
−22
moles, which is quite remarkable. To achieve that level of sensitivity in the isolation of such rare cells, and to isolate them in a fashion which does not compromise or interfere with their character
Liberti Paul A.
Racila Emilian V.
Rao Galla Chandra
Terstappen Leon W. M. M.
Uhr Jonathan W.
Dann Dorfman Herrell and Skillman
Huff Sheela
Immunivest Corporation
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