Acute myeloid leukemia (AML) is generally regarded as a stem cell disease. In CD34-positive AML, the leukemic stem cell has been recognized as CD38 negative. This CD34 þ CD38À population survives chemotherapy and is most probable the cause of minimal residual disease (MRD). The outgrowth of MRD causes relapse and MRD can therefore serve as a prognostic marker. The key role of leukemogenic CD34 þ CD38À cells led us to investigate whether they can be detected under MRD conditions. Various markers were identified to be aberrantly expressed on the CD34 þ CD38À population in AML and high-risk MDS samples at diagnosis, including C-type lectin-like molecule-1 and several lineage markers/marker-combinations. Fluorescent in situ hybridization analysis revealed that marker-positive cells were indeed of malignant origin. The markers were neither expressed on normal CD34 þ CD38À cells in steady-state bone marrow (BM) nor in BM after chemotherapy. We found that these markers were indeed expressed in part of the patients on malignant CD34 þ CD38À cells in complete remission, indicating the presence of malignant CD34 þ CD38À cells. Thus, by identifying residual malignant CD34 þ CD38À cells after chemotherapy, MRD detection at the stem cell level turned out to be possible. This might facilitate characterization of these chemotherapy-resistant leukemogenic cells, thereby being of help to identify new targets for therapy.

Pancreatic ductal adenocarcinoma (PDAC) remains a major unsolved health problem. Most drugs that pass preclinical tests fail in these patients, emphasizing the need of improved preclinical models to test novel anticancer strategies. Here, we developed four orthotopic mouse models using primary human PDAC cells genetically engineered to express firefly-and Gaussia luciferase, simplifying the ability to monitor tumor growth and metastasis longitudinally in individual animals with MRI and high-frequency ultrasound. In these models, we conducted detailed histopathologic and immunohistochemical analyses on paraffin-embedded pancreatic tissues and metastatic lesions in liver, lungs, and lymph nodes. Genetic characteristics were compared with the originator tumor and primary tumor cells using array-based comparative genomic hybridization, using frozen specimens obtained by laser microdissection. Notably, the orthotopic human xenografts in these models recapitulated the phenotype of human PDACs, including hypovascular and hypoxic areas. Pursuing genomic and immunohistochemical evidence revealed an increased copy number and overexpression of c-Met in one of the models; we examined the preclinical efficacy of c-Met inhibitors in vitro and in vivo. In particular, we found that crizotinib decreased tumor dimension, prolonged survival, and increased blood and tissue concentrations of gemcitabine, synergizing with a cytidine deaminase-mediated mechanism of action. Together, these more readily imaged orthotopic PDAC models displayed genetic, histopathologic, and metastatic features similar to their human tumors of origin. Moreover, their use pointed to c-Met as a candidate therapeutic target in PDAC and highlighted crizotinib and gemcitabine as a synergistic combination of drugs warranting clinical evaluation for PDAC treatment. Cancer Res; 73(22); 6745-56. Ó2013 AACR.