23^rd International Conference on
Cancer Research & Pharmacology

During tumor progression, transformed cells accumulate mutations and gain malignancy. By now, it is unclear how easily this

process can be undertaken and if it can be considered the main bottleneck in tumorigenesis. To measure the probability of

glioma progression, we used a well-characterized murine model of gliomagenesis, induced by overexpressing PDGF-B in embryonic

Neural Progenitor Cells (NPC), mimicking a possible first hit of tumorigenesis. In order to univocally tag each PDGF-transduced cell,

we added a degenerated barcode sequence to the PDGF-B transducing vector and we produced high complexity libraries of barcoded

retroviruses that had been injected in mouse embryos. After the development of gliomas, tumor masses were analyzed by NGS and

compared to embryonic brains few days post infection. By using in-house developed software, we successfully retrieved barcodes

from tumor masses and reconstructed the clonal composition of several independent tumors in different progression stages. Our

data shows that even though low grade, partially progressed tumor masses are clonally heterogeneous and composed by about one

thousand independent clones each, they are the result of a strong selection because the number of oncogene-transduced cells is more

than 10 times higher. Still, high grade and fully progressed gliomas are characterized by a very low clonal complexity and often are

composed by a single clone, suggesting another great bottleneck in glioma progression divides these two stages. More strikingly, fully

progressed tumors derived from in vivo transplant the same pool of thousands different transduced NPCs are composed by the same

clones, suggesting that a predetermined cell state is required to gain malignancy.