Perivascular localized cells commit erythropoiesis in PDGF-B-expressing solid tumors

Background:Tumors possess incessant growth features,and expansion of their masses demands sufficient oxygen supply by red blood cells(RBCs).In adult mammals,the bone marrow(BM)is the main organ regulating hematopoiesis with dedicated manners.Other than BM,extramedullary hematopoiesis is discovered in various pathophysiological settings.However,whether tumors can contribute to hematopoiesis is completely unknown.Accumulating evidence shows that,in the tumor microenvironment(TME),perivascular localized cells retain progenitor cell properties and can differentiate into other cells.Here,we sought to better understand whether and how perivascular localized pericytes in tumors manipulate hematopoiesis.Methods:To test if vascular cells can differentiate into RBCs,genome-wide expression profiling was performed using mouse-derived pericytes.Genetic tracing of perivascular localized cells employing NG2-CreERT2:R26R-tdTomato mouse strain was used to validate the findings in vivo.Fluorescence-activated cell sorting(FACS),single-cell sequencing,and colony formation assays were applied for biological studies.The production of erythroid differentiationspecific cytokine,erythropoietin(EPO),in TME was checked using quantitative polymerase chain reaction(qPCR),enzyme-linked immunosorbent assay(ELISA,magnetic-activated cell sorting and immunohistochemistry.To investigate BM function in tumor erythropoiesis,BM transplantation mouse models were employed.Results:Genome-wide expression profiling showed that in response to plateletderived growth factor subunit B(PDGF-B),neural/glial antigen 2(NG2)+perivascular localized cells exhibited hematopoietic stem and progenitor-like features and underwent differentiation towards the erythroid lineage.PDGF-B simultaneously targeted cancer-associated fibroblasts to produce high levels of EPO,a crucial hormone that necessitates erythropoiesis.FACS analysis using genetic tracing of NG2+cells in tumors defined the perivascular localized cell-derived subpopulation of hematopoietic cells.Single-cell sequencing and colony formation assays validated the fact that,upon PDGF-B stimulation,NG2+cells isolated from tumors acted as erythroblast progenitor cells,which were distinctive from the canonical BM hematopoietic stem cells.Conclusions:Our data provide a new concept of hematopoiesis within tumor tissues and novel mechanistic insights into perivascular localized cell-derived erythroid cells within TME.Targeting tumor hematopoiesis is a novel therapeutic concept for treating various cancers that may have profound impacts on cancer therapy.

Phage display screening of therapeutic peptide for cancer targeting and therapy

Recently,phage display technology has been announced as the recipient of Nobel Prize in Chemistry 2018.Phage display technique allows high affinity target-binding peptides to be selected from a complex mixture pool of billions of displayed peptides on phage in a combinatorial library and could be further enriched through the biopanning process;proving to be a powerful technique in the screening of peptide with high affinity and selectivity.In this review,we will first discuss the modifications in phage display techniques used to isolate various cancer-specific ligands by in situ,in vitro,in vivo,and ex vivo screening methods.We will then discuss prominent examples of solid tumor targeting-peptides;namely peptide targeting tumor vasculature,tumor microenvironment(TME)and overexpressed receptors on cancer cells identified through phage display screening.We will also discuss the current challenges and future outlook for targeting peptidebased therapeutics in the clinics.