An atlas of bloodstream-accessible bone marrow proteins for site-directed therapy of acute myeloid leukemia.

The concept of arming antibodies with bioactive payloads for a site-specific therapy of cancer has gained considerable interest in recent years. However, a successful antibody-based targeting approach critically relies on the availability of a tumor-associated target that is not only preferentially expressed in the tumor tissue but is also easily accessible for antibody therapeutics coming from the bloodstream. Here, we perfused the vasculature of healthy and acute myeloid leukemia (AML)-bearing rats with a reactive ester derivative of biotin and subsequently quantified the biotinylated proteins to identify AML-associated bone marrow (BM) antigens accessible from the bloodstream. In total, >1400 proteins were identified. Overall, 181 proteins were >100-fold overexpressed in AML as compared with normal BM. Eleven of the most differentially expressed proteins were further validated by immunohistochemistry and confocal microscopic analyses, including novel antigens highly expressed in AML cells (for example, adaptor-related protein complex 3 ß2) and in the leukemia-modified extracellular matrix (ECM) (for example, collagen-VI-α-1). The presented atlas of targetable AML-associated BM proteins provides a valuable basis for the development of monoclonal antibodies that could be used as carriers for a site-specific pharmacodelivery of cytotoxic drugs, cytokines or radionuclides to the BM in AML.

A monoclonal antibody prevents aggregation of the NBD1 domain of the cystic fibrosis transmembrane conductance regulator.

The homozygous deletion of the phenylalanine at position 508 (DeltaPhe508) in the first nucleotide-binding domain (NBD1) of the cystic fibrosis transmembrane conductance regulator (CFTR) is the most common CF-causing genetic defect. It has been proposed that the propensity of NBD1 to aggregate may lead to a lower display of the CFTR chloride channel to the cell membrane and to the disease, thus opening an avenue for the pharmacological development of CFTR folding correctors. Here, we show that a human monoclonal antibody fragment specific to the folded conformation of NBD1 inhibits the aggregation of NBD1 in vitro. However, in contrast to the previously published observations, we proved experimentally that NBD1 of wild-type and DeltaPhe508 version of CFTR display comparable propensities to aggregate in vitro and that the corresponding full-length CFTR protein reaches the cell membrane with comparable efficiency in mammalian cell expression systems. On the basis of our results, the 'folding defect' hypothesis seems unlikely to represent the causal mechanism for the pathogenesis of CF. A solid understanding of how the DeltaPhe508 deletion leads to the disease represents an absolute requirement for the development of effective drugs against CF.