Selection of the optimal chemotherapeutic agent is one of the major problems in oncology. Even with the advent of large multicenter therapeutic trials for the determination of chemotherapeutic efficacy, individual variability in tumor characteristics often leads to a poor therapeutic outcome. A major cause of failure to many of the natural products used as chemotherapeutic agents is multiple drug resistance (MDR). The over expression of P-glycoprotein and other proteins involved in cellular transport is a frequent cause of MDR, although detoxification by biochemical means, DNA replication and repair, or other mechanisms may be involved.
In conjunction with immunocytochemistry and molecular techniques, flow cytometry has been essential for measuring the expression of cell surface and intracellular markers of MDR, assessing the intracellular accumulation and efflux of chemotherapeutic drugs, and studying the other mechanisms leading to MDR.The identification of intrinsic or acquired MDR is potentially of significant clinical value in planning chemotherapy, and several clinical trials of drug efflux blockers are underway.The reliable in vitro prediction of tumor cell sensitivity to radiation and antineoplastic agents prior to therapy in individual cancer patients is a long-sought goal of oncologists.
A variety of flow cytometric techniques have also been explored as alternatives to the clonogenic assay, including microdrop encapsulation and assays of proliferative survival using bromodeoxyuridine (BrdU) incorporation. Flow cytometric measurements of cell viability or apoptosis have been used to design drug treatment protocols and improve the accuracy and reliability of the conventional clonogenic assay. Ligand, antigen, or molecule-targeted biological therapy utilizing monoclonal antibodies is the most rapidly growing area of pharmacology for a wide variety of human diseases, including cancer and autoimmune disease. These agents work through a number of mechanisms. Some directly disrupt cell proliferation and anti-apoptosis by blocking the cell membrane receptors and circulating ligands associated with signal transduction, while others serve as the targeting system for other cytotoxic products.The first of this new class of pharmaceutical agents was anti-CD3 (OKT3), developed for the immunosuppressive therapy of solid organ transplant rejection. More recently developed monoclonal antibodies are directed against CD20, CD33, CD25, CD45, and CD52. Prior to treatment, flow cytometric analysis is critical for confirming that the antigen is expressed by the aberrant cells. During and after treatment, flow cytometry is utilized to verify binding of the antibody and to monitor the efficacy of tumor cell eradication.
