In vitro drug resistance assays have shown efficacy in predicting response to chemotherapeutic drugs in a number of solid tumors. In chronic lymphocytic leukemia (CLL) many assays are limited by the difficulty involved in culturing these cells ex vivo. We have developed a novel, optical-based methodology that is sensitive to broad cellular physical characteristics, such as morphology, size, refractive index, density and surface properties. This measurement, known as Optophoresis, quantifies cell motion induced by exposure to a moving optical gradient, generated from a near-infrared laser beam (Forster AH, et al. Anal Biochem 2004, 327(1):14–22 and Wang MM, et al. Appl Opt 2003, 42(28):5765–73). In Optophoresis small numbers of cells are analyzed intact, in their native state. No labels are required for quantification of functional responses, but cell subpopulations may be identified using fluorescent tags. We have used this assay to predict response to chemotherapeutic agents in patients with CLL.

Methods: We performed Optophoresis with six drugs (fludarabine, chlorambucil, vincristine, cyclophosphamide, cladribine and prednisolone) on 74 CLL patient samples. 68 of these were classic B-CLL; there was one hairy cell variant, two were T-CLL, two evolved to PLL and one evolved to lymphoma. 21 of the samples were from patients for whom clinical data on response to chemotherapy was available for 33 drug treatments. Response to therapy was defined as a decrease in RAI stage.

Results: 21 patients aged 58 to 93 years; 71% Rai stage III or IV were included in this analysis. Six patients were evaluated prospectively, with the assay performed before chemotherapy administration, and 15 patients were evaluated retrospectively with the assay performed after a course of treatment. Optophoresis accurately predicted response to chemotherapy in 88% of the 33 treatments evaluated. In the four instances for which the Optophoresis results did not match the retrospective clinical outcome; the patient was historically sensitive to treatment and Optophoresis results indicated current resistance to the drug. Subsequent resistance to drug therapy is known to occur in a significant percentage of treated CLL patients.

Conclusion: Optophoresis of CLL cells accurately predicts response to chemotherapy in CLL. Further studies using results of Optophoresis to guide CLL treatment are warranted.

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