Abstract
PurposeIn a departure from conventional strategies to improve treatment outcome for myeloid malignancies, we report the isolation of leukemia-specific peptides using a phage display library screened with freshly obtained human myeloid leukemia cells.ResultsA phage display library was screened by 5 rounds of biopanning with freshly isolated human AML cells. Individual colonies were randomly picked and after purification, biologic activity (growth and differentiation) on fresh AML cells was profiled. Ten peptides were synthesized for further biological studies. Multiple peptides were found to selectively bind to acute myeloid leukemia (AML) cells. The peptides bound to leukemia cells, were internalized and could induce proliferation and/or differentiation in the target patient cells. Two of the peptides, HP-A2 and HP-G7, appeared to have a novel mechanism of inducing differentiation since they did not cause G1 arrest in cycling cells even as the expression of the differentiation marker CD11b increased.ConclusionPeptide induced differentiation of leukemia cells offers a novel treatment strategy for myeloid malignancies, whereas their ability to induce proliferation could be harnessed to make cells more sensitive to chemotherapy. Conceptually, these leukemia specific peptides can also be used to refine diagnosis, document minimal residual disease, and selectively deliver toxins to malignant cells.
Highlights
We proposed to isolate leukemia specific peptides that have the potential to target and deliver toxins to acute myeloid leukemia cells (AML) or to modify the biological behavior of the cells to which they bind using a phage display library
Peptides that are specific for surface expressed immunoglobulins isolated from chronic lymphocytic leukemia (CLL) cells [8] and multiple myeloma cells [9] have been identified for potential patient specific targeted therapy
Cell preparation The peripheral blood (PB) or bone marrow (BM) cells were subjected to density cut centrifugation over FicollHypaque
Summary
Isolation of phage able to bind cells from leukemia patients Phage clones that bind to leukemia cells were isolated by incubating a library of M13 phage bearing 8 mer peptides with BM mononuclear cells from CML-BC patients. Among the 450 clones, 129 (28%) were positive for 3 different CML-BC patients These clones were profiled with AML and normal cells. The 6 peptides that did not bind normal bone marrow cells together with the peptide HP-A2A (alanine substituted for arginine of HP-A2) and HP-A6 (both used in further studies) were profiled on mononuclear cells from patients with AML (Table 3). While binding properties of the mutated peptide were not changed (Table 3), the number of patients in whom proliferation was stimulated was significantly lower (from 40 to 22%) This peptide inhibited proliferation in a number of samples (16%) (Figure 5)
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