Identification of an antilaminin-1 scFv that preferentially homes to vascular solid tumors.

The tumor vasculature and extracellular matrix make attractive targets for distinguishing solid tumors from normal cells. In solid tumors, the processes of angiogenesis and metastasis potentially give rise to unique epitopes not usually accessible in homeostatic organs. Specific targeting of solid tumors for radioimmunotherapy requires that the targeting agent accumulate rapidly and at high levels at the tumor site. This study involved the selection of scFvs that recognize laminin-1 in vitro from the Tomlinson I and J phage display libraries. Selected, purified scFvs were radioiodinated and injected in tumor-bearing mice. One of these, scFv 15-9, exhibited preferential accumulation at subcutaneous tumors when compared to other antilaminin scFvs or to a control scFv. Autoradiographic analysis indicated that scFv15- 9 also displayed a higher vessel:parenchyma ratio than did two other antilaminin scFvs, scFv 15-6 and scFv 15-1, indicating a preferential accumulation of scFv 15-9 around vessel structures. Immunohistochemistry confirmed that scFv 15-9 accumulated at sites of endothelial cells lining vessel structures where significant levels of laminin were present. These data demonstrate that scFv 15-9 binds to a specific epitope on laminin and has potential for tumor endoradiotherapy in subcutaneous tumors.

Mutations in the clathrin-assembly gene Picalm are responsible for the hematopoietic and iron metabolism abnormalities in fit1 mice.

Recessive N-ethyl-N-nitrosourea (ENU)-induced mutations recovered at the fitness-1 (fit1) locus in mouse chromosome 7 cause hematopoietic abnormalities, growth retardation, and shortened life span, with varying severity of the defects in different alleles. Abnormal iron distribution and metabolism and frequent scoliosis have also been associated with an allele of intermediate severity (fit14R). We report that fit14R, as well as the most severe fit15R allele, are nonsense point mutations in the mouse ortholog of the human phosphatidylinositol-binding clathrin assembly protein (PICALM) gene, whose product is involved in clathrin-mediated endocytosis. A variety of leukemias and lymphomas have been associated with translocations that fuse human PICALM with the putative transcription factor gene AF10. The Picalmfit1-5R and Picalmfit1-4R mutations are splice-donor alterations resulting in transcripts that are less abundant than normal and missing exons 4 and 17, respectively. These exon deletions introduce premature termination codons predicted to truncate the proteins near the N and C termini, respectively. No mutations in the genes encoding Picalm, clathrin, or components of the adaptor protein complex 2 (AP2) have been previously described in which the suite of disorders present in the Picalmfit1 mutant mice is apparent. These mutants thus provide unique models for exploring how the endocytic function of mouse Picalm and the transport processes mediated by clathrin and the AP2 complex contribute to normal hematopoiesis, iron metabolism, and growth.