Circulating perivascular progenitors: A target of PDGFR inhibition

Abstract

Cancer blood vessels consist of two interacting types of cells: inner lining endothelial cells (ECs) and surrounding perivascular cells (pericytes, vascular smooth muscle cells or mural cells). PDGFRbeta(CD140b)+ progenitor perivascular cells (PPC) can differentiate into pericytes and regulate vessel stability and vascular survival in tumors. Similarly to what we have done with circulating ECs and progenitors, we developed a flow cytometry procedure for the enumeration of circulating PPCs and the study of their viability in murine models of cancer and in cancer patients. DNA+CD45−CD31−CD140b+ cells were enumerated by six‐colour flow cytometry, their morphology was studied by electron microscopy, PPC specificity confirmed by reverse trascription‐PCR (RT‐PCR) expression of CD140b mRNA, and viability assessed by Syto16 and 7AAD. In preclinical marrow transplantation studies, 9 ± 4% of circulating PPCs were derived from the marrow donor. PPCs were increased in cancer‐bearing mice and in patients affected by some types of cancer. At variance with the kinetic of circulating endothelial progenitors, high‐dose cyclophosphamide reduced the number of viable PPCs. The administration of sunitinib, a drug known to inhibit PDGFR, was associated in murine models and in cancer patients with an increase of apoptotic/necrotic circulating PPC, suggesting a direct targeting of these cells. PPC enumeration might be studied as a tool for the definition of the optimal biologic dose of anti‐PDGFR drugs and investigated clinically as a possible predictive/prognostic tool in patients receiving anti‐PDGFR drugs.

The White Adipose Tissue Used in Lipotransfer Procedures Is a Rich Reservoir of CD34+ Progenitors Able to Promote Cancer Progression

“…CD45-CD34 þ progenitor cells were evaluated by 6-color flow cytometry following an approach recently validated for the quantification of circulating EPCs and perivascular progenitors (18,19). The nuclear staining Syto16 was used to discriminate between DNA containing cells, platelets, and cell debris.…”

“…Human bone marrow was obtained from disease-free patients undergoing a follow-up involving bone marrow investigation for hematologic or solid neoplasia. The flow cytometry evaluation included a DNA staining procedure to exclude contamination with platelets and/or micro-and macroparticles, as previously described (18,19).…”

Amelioration of Glucose Control Mobilizes Circulating Pericyte Progenitor Cells in Type 2 Diabetic Patients with Microangiopathy

“…PPCs were evaluated by six-color flow cytometry following an approach recently validated in our laboratory for the enumeration of CECs with some modifications [13]. PPCs were defined as Syto16+CD45−CD31−CD140b+ events.…”

“…These include reduced EPCs [9] and cardiomyocyte differentiation [10], increased generation of smooth muscle progenitor cells [11] and procalcific cells [6], paralleled by a high concentration of circulating shed CECs [12]. Very recent data suggest the existence of circulating pericyte progenitor cells (PPCs) [13]. Pericytes provide a variety of functions, such as capillary blood flow regulation, clearance and phagocytosis of cellular debris, and regulation of vascular permeability.…”

“…They are recruited through the PDGF-B and PDGFR-Beta signaling, while PDGFR-Beta deficient mice display extensive vascular leakage, hemorrhage, and edema due to a defect of capillary coverage by pericytes [15, 16]. Interestingly, PPCs were found to be increased in patients and mice with malignant tumors and also increased after chemotherapy [13]. …”