Selection strategies for anticancer antibody discovery: searching off the beaten path.

Antibody-based drugs represent one of the most successful and promising therapeutic approaches in oncology. Large combinatorial phage antibody libraries are available for the identification of therapeutic antibodies and various technologies exist for their further conversion into multivalent and multispecific formats optimized for the desired pharmacokinetics and the pathological context. However, there is no technology for antigen profiling of intact tumors to identify tumor markers targetable with antibodies. Such constraints have led to a relative paucity of tumor-associated antigens for antibody targeting in oncology. Here we review novel approaches aimed at the identification of antibody-targetable, accessible antigens in intact tumors. We hope that such advanced selection approaches will be useful in the development of next-generation antibody therapies for cancer.

Chloroquine targets pancreatic cancer stem cells via inhibition of CXCR4 and hedgehog signaling.

Pancreatic ductal adenocarcinoma is one of the deadliest carcinomas and is characterized by highly tumorigenic and metastatic cancer stem cells (CSC). CSCs evade available therapies, which preferentially target highly proliferative and more differentiated progenies, leaving behind CSCs as a putative source for disease relapse. Thus, to identify potentially more effective treatment regimens, we screened established and new compounds for their ability to eliminate CSCs in primary pancreatic cancer (stem) cells in vitro and corresponding patient-derived pancreatic cancer tissue xenografts in vivo. Intriguingly, we found that in vitro treatment with the antimalarial agent chloroquine significantly decreased CSCs, translating into diminished in vivo tumorigenicity and invasiveness in a large panel of pancreatic cancers. In vivo treatment in combination with gemcitabine was capable of more effectively eliminating established tumors and improved overall survival. The inhibitory effect of chloroquine was not related to inhibition of autophagy, but was due to inhibition of CXCL12/CXCR4 signaling, resulting in reduced phosphorylation of ERK and STAT3. Furthermore, chloroquine showed potent inhibition of hedgehog signaling by decreasing the production of Smoothened, translating into a significant reduction in sonic hedgehog-induced chemotaxis and downregulation of downstream targets in CSCs and the surrounding stroma. Our study demonstrates that via to date unreported effects, chloroquine is an effective adjuvant therapy to chemotherapy, offering more efficient tumor elimination and improved cure rates. Chloroquine should be further explored in the clinical setting as its success may help to more rapidly improve the poor prognosis of patients with pancreatic cancer.

Raising antibodies against circulating foetal cells from maternal peripheral blood.

OBJECTIVE: Cells of foetal origin circulating in the maternal peripheral bloodstream present a unique source for non-invasive prenatal diagnostics. The aims of this study were to raise antibodies against identified circulating foetal cells from the maternal blood, test the properties of these antibodies and to determine the foetal cell type recognised by the antibodies. METHOD: Cells from a male foetus were identified in a maternal blood sample by FISH analysis of the X- and Y- chromosomes. The identified cells were subjected to phage display selection using a novel single cell selection strategy. Selected antibodies were tested by immunocytochemistry on foetal and adult tissue arrays, an endothelial cell line, and peripheral blood mononuclear cells. RESULTS: Three identified foetal cells subjected to antibody selection, yielded a total of 12 antibodies. Three antibodies gave distinct staining patterns on tissue arrays, and endothelial cells. One antibody, SF1.3, shows specific staining of a subpopulation of peripheral blood mononuclear cells, including a fraction of CD34 positive cells. CONCLUSION: These findings indicate that the identified foetal cells could have been progenitor cells of haematopoietic origin. The antibody SF1.3 could be a potential tool toward non-invasive prenatal diagnostics.

Selection of antibodies against a single rare cell present in a heterogeneous population using phage display.

Here we describe a new method applying phage-displayed antibody libraries to the selection of antibodies against a single identified cell on a glass slide. This is the only described method that has successfully achieved selection of antibodies against a single rare cell in a heterogeneous population of cells. The phage library is incubated with the slide containing the identified rare cell of interest; incubation is followed by UV irradiation while protecting the target cell with a minute disc. The UV light inactivates all phages outside the shielded area by cross-linking the DNA constituting their genomes. The expected yield is between one and ten phage particles from a single cell selection. The encoded antibodies are subsequently produced monoclonally and tested for specificity. This method can be applied within a week to carry out ten or more individual cell selections. Including subsequent testing of antibody specificity, a specific antibody can be identified within 2 months.

Microselection--affinity selecting antibodies against a single rare cell in a heterogeneous population.

Rare cells not normally present in the peripheral bloodstream, such as circulating tumour cells, have potential applications for development of non-invasive methods for diagnostics or follow up. Obtaining these cells however require some means of discrimination, achievable by cell type specific antibodies. Here we have generated a microselection method allowing antibody selection, by phage display, targeting a single cell in a heterogeneous population. One K562 cell (female origin) was positioned on glass slide among millions of lymphocytes from male donor, identifying the K562 cell by FISH (XX). Several single cell selections were performed on such individual slides. The phage particles bound to the target cell is protected by a minute disc, while inactivating all remaining phage by UV-irradiation; leaving only the phage bound to the target cell viable. We hereby retrieved up to eight antibodies per single cell selection, including three highly K562 cell type specific.

Epsilon haemoglobin specific antibodies with applications in noninvasive prenatal diagnosis.

Invasive procedures for prenatal diagnosis are associated with increased risk of abortion; thus, development of noninvasive procedures would be beneficial. Based on the observation that embryonic nucleated red blood cell (NRBC) crosses the placenta and enters the circulation of pregnant women, the ability to identify such cell would allow development of such procedures. Identification of NRBCs in blood samples would be possible provided that specific antibodies are available. Here we have isolated recombinant antibodies using phage display. From the panel of antibody fragments specifically recognising epsilon-Hb, one was chosen for further characterization, DAb1. DAb1 binds to epsilon-Hb both in Western blots and immunocytochemistry. Several epsilon-Hb positive cells were detected in a blood sample taken as postchorionic villus sampling (CVS). To evaluate the sensitivity of the method, K562 cells (which express epsilon-Hb) were spiked in a blood sample followed by staining in solution and FACS analysis.

Identification of genes involved in healthy aging and longevity.

Studies suggest that the region around microsatellite marker D4S1564 on chromosome 4 is in some way linked to longevity. As a part of the integrated European project Genetics of Healthy Aging (GeHA), we set out to investigate the genes found in this region using a proteomics approach. Here, we report the cloning of six candidate genes.

Phage-displayed antibodies for the detection of glycated proteasome in aging cells.

Accumulation of posttranslationally damaged proteins during aging could explain the decline of cell performance with age. N(epsilon)-carboxymethyllysine (CML) is the major glycation product on damaged proteins, causing dysfunction and cross-linking. The proteasome, a multicatalytic degradation complex, is one of the pathways for eliminating damaged proteins, and thus regulating their accumulation within the cell. However, the proteinase activities of the proteasome decline during aging. This may be due to posttranslational modifications of the subunits forming the proteasome complex. Using phage display technology, we have selected 16 single-chain variable fragments (scFv) recognizing the CML-modified alpha7 subunit of the proteasome. Using one of them, Ab3, we have observed a five-fold increase of CML-alpha7 in old human skin fibroblasts in comparison with young fibroblasts and telomerase-immortalized bone marrow cells (hTERT-BMCs).

Severe acute respiratory syndrome (SARS): development of diagnostics and antivirals.

The previously unknown coronavirus that caused severe acute respiratory syndrome (SARS-CoV) affected more than 8,000 persons worldwide and was responsible for more than 700 deaths during the first outbreak in 2002-2003. For reasons unknown, the SARS virus is less severe and the clinical progression a great deal milder in children younger than 12 years of age. In contrast, the mortality rate can exceed 50% for persons at or above the age of 60. As part of the Sino-European Project on SARS Diagnostics and Antivirals (SEPSDA), an immune phage-display library is being created from convalescent patients in a phagemid system for the selection of single-chain fragment variables (scFv) antibodies recognizing the SARS-CoV.