Remnant living cells that escape cell loss in late-stage tumors exhibit cancer stem cell-like characteristics

Abstract

A balance between cell proliferation and cell loss is essential for tumor progression. Although up to 90% of cells are lost in late-stage carcinomas, the progression and characteristics of remnant living cells in tumor mass are unclear. Here we used molecular imaging to track the progression of living cells in a syngeneic tumor model, and ex vivo investigated the properties of this population at late-stage tumor. The piggyBac transposon system was used to stably introduce the dual reporter genes, including monomeric red fluorescent protein (mRFP) and herpes simplex virus type-1 thymidine kinase (HSV1-tk) genes for fluorescence-based and radionuclide-based imaging of tumor growth in small animals, respectively. Iodine-123-labeled 5-iodo-2′-fluoro-1-beta-𝒟-arabinofuranosyluracil was used as a radiotracer for HSV1-tk gene expression in tumors. The fluorescence- and radionuclide-based imaging using the single-photon emission computed tomography/computed tomography revealed that the number of living cells reached the maximum at 1 week after implantation of 4T1 tumors, and gradually decreased and clustered near the side of the body until 4 weeks accompanied by enlargement of tumor mass. The remnant living cells at late-stage tumor were isolated and investigated ex vivo. The results showed that these living cells could form mammospheres and express cancer stem cell (CSC)-related biomarkers, including octamer-binding transcription factor 4, SRY (sex-determining region Y)-box 2, and CD133 genes compared with those cultured in vitro. Furthermore, this HSV1-tk-expressing CSC-like population was sensitive to ganciclovir applied for the suicide therapy. Taken together, the current data suggested that cells escaping from cell loss in late-stage tumors exhibit CSC-like characteristics, and HSV1-tk may be considered a theranostic agent for targeting this population in vivo.

Identification of genes associated with cortical malformation using a transposon-mediated somatic mutagenesis screen in mice

“…To induce insertional mutagenesis and observe mutant cells, we used the PB-3R-puro construct 18 , 23 , 24 , which encodes a PB transposable element carrying a red fluorescence protein (RFP) for visualization of electroporated cells by fluorescent microscopy. When the brains were electroporated with PB alone or a control pCAG-GFP construct expressing green fluorescence protein (GFP) at E14.5, the fluorescently labeled cells were primarily found within layers 2/3 and 4 of cortex on postnatal day 10 (P10) (Fig.…”

“…The PB transposon system consisted a piggyBac transposon with the PB-tk-mRFP reporter and the Act-PBase helper plasmid of Act-PBase; these were provided by J-Y Lee 18 , 23 , 24 . The shRNA constructs, which are based on the pLKO_TRC001 vector, were obtained from the National RNAi Core Facility in Taiwan (Supplementary Table 4 ).…”

Profiling gene promoter occupancy of Sox2 in two phenotypically distinct breast cancer cell subsets using chromatin immunoprecipitation and genome-wide promoter microarrays

“…In recent years, Sox2 has been discovered to be aberrantly expressed in cancer cells, including those of the lungs, brain, ovaries, bone, colon, skin, and breasts [ 8 ]-[ 15 ]. In many of these studies, Sox2 was found in the cancer stem cell population [ 7 ],[ 12 ],[ 16 ]-[ 22 ], supporting the hypothesis that cancer stemness is related to the aberrant expression of ESC proteins. It has been demonstrated that Sox2 promotes key tumorigenic properties in cancer cells, including enhanced proliferation, invasion, migration, colony formation, non-adherent stem cell-associated sphere formations in vitro , and tumorigenicity in vivo [ 8 ],[ 12 ],[ 19 ]-[ 24 ].…”

Synergistic effects of glycated chitosan with high-intensity focused ultrasound on suppression of metastases in a syngeneic breast tumor model

“…41 We modified this system by adding a firefly luciferase ( luc2 ) gene to the original dual-cistronic PB-2R construct to create a new PB-3R construct for two reasons. First, we wanted to overcome the low sensitivity of mRFP for optical imaging.…”