ANPEP and acute myeloid leukemia: The other AML cell lines HL-60 (myeloblastic, M2), NB4 (promyelocytic, M3) and THP- 1 (monoblastic, M5) expressed surface CD13 (Figure 3A) and were also sensitive to the NGR-peptide-1's lethal effects as evidenced by cell shrinkage (data not shown), phosphatidylserine externalization and cell membrane disruption (Figure 3B).