Targeting multidrug resistant tumor cells with a recombinant single-chain FV fragment directed to P-glycoprotein.

The MDR1 gene product P-glycoprotein (Pgp) plays a key role in multidrug resistance of cancer cells. Pgp is an ATP-driven efflux pump that extrudes a variety of dissimilar hydrophobic cytotoxic compounds. P-glycoprotein overexpression results in multidrug resistance (MDR) of tumor cell lines in vitro as well as in cancer patients. To selectively target and eliminate MDR tumor cells, we have isolated a monoclonal antibody that specifically reacts with the first extracellular loop of the human Pgp. We have cloned the variable domain genes of this antibody and assembled a functional single-chain Fv fragment capable of specifically targeting various Pgp-expressing MDR carcinoma cells lines. Targeting and specific elimination of Pgp-dependent MDR human cancer cells was achieved by constructing a single-chain immunotoxin in which the scFv fragment was fused to a truncated form of Pseudomonas exotoxin (PE38). We conclude that recombinant Fv-immunotoxins or other Fv-based molecules armed with potent cytotoxins represent an effective tool in targeted cancer therapy aimed at specific elimination of MDR tumor cell sub-populations. Recombinant antibody fragments targeting MDR proteins such as Pgp may be also used for intracellular expression and consequent phenotypic knockout of MDR.

Antibody engineering for targeted therapy of cancer: recombinant Fv-immunotoxins.

Recombinant Fv-immunotoxins are a new class of biologic anticancer agents composed of a recombinant antibody fragment linked to a very potent bacterial toxin. These potent molecules are designed to specifically bind and kill cancer cells that express a specific target antigen on their cell surface. Recombinant Fv-immunotoxins are an excellent example for the concept of rational drug design. They combine the progress in understanding cancer biology, -the recent knowledge on the mechanisms of malignant transformation and the special properties of cancer cells, -with the enormous developments in recombinant DNA technology and antibody engineering. Recombinant Fv immunotoxins were developed for solid tumors and hematological malignancies and have been characterized intensively for their biological activity in vitro and in vivo in animal models. The excellent in vitro and in vivo activities of recombinant Fv-immunotoxins have lead to their pre-clinical development and to the initiation of clinical trial protocols. Recent trials have demonstrated potent clinical efficacy in patients with malignant diseases that are refractory to traditional modalities of cancer treatment. It is thus suggested that this strategy can be developed into a separate modality of cancer treatment with the basic rationale of specifically targeting cancer cells on the basis of their unique surface markers combined with potent effective biological toxic agents that directly kill the cancer cell. Efforts are now being made to improve the current molecules and to develop new agents with better clinical efficacy. In this review, we will describe the rationale in designing Fv-immunotoxins and will review current progress made in using these agents for cancer treatment.

Data predictability for compression of digital fluorography images.

Images obtained by digital fluorography were checked for compressability. These images include images of coronary vessels and images of peripheral vessels. These images have a very low signal-to-noise ratio compared to the optical images usually used for developing compression methods. Configurational entropy was used to represent the information content of these images. Reversible prediction algorithms were extensively checked in a search for minimal residual information, enabling more efficient reversible compression. Optimal results were obtained for algorithms based on two or three neighboring pixels and a semiempirical rule, based on the noise level, was found which decides on the best approach. It was found that raw data images are more predictable than subtracted images although the latter are visually preferred.