Role of Topoisomerases in Pediatric High Grade Osteosarcomas: TOP2A Gene Is One of the Unique Molecular Biomarkers of Chemoresponse

Abstract

Currently, the treatment of pediatric high-grade osteosarcomas systematically includes one topoisomerase IIα inhibitor. This chemotherapy is usually adapted to the response to the neo-adjuvant therapy after surgery. The current and unique marker of chemoresponsiveness is the percentage of viable residual cells in the surgical resection. This late patient management marker has to be evaluated earlier in the therapeutic history of the patients on initial biopsy. Therefore, new biomarkers, especially those involved in the topoisomerase IIα inhibitor response might be good candidates. Therefore, our study was designed to target TOP1, TOP2A and TOP2B genes in 105 fresh-frozen diagnostic biopsies by allelotyping and real-time quantitative PCR. Our analyses in those pediatric osteosarcomas, homogeneously treated, highlighted the frequent involvement of topo-isomerase genes. The main and most important observation was the statistical link between the presence of TOP2A amplification and the good response to neo-adjuvant chemotherapy. Compared to adult cancers, the 17q21 amplicon, including TOP2A and ERBB2 genes, seems to be differentially implicated in the osteosarcoma chemoresponsiveness. Surprisingly, there is no ERBB2 gene co-amplification and the patients harboring TOP2A amplification tend to show a worse survival, so TOP2A analyses remain a preliminary, but a good molecular approach for the evaluation at diagnosis of pediatric osteosarcoma chemoresponsiveness.

Mutations in TOP2B cause autosomal‐dominant hereditary hearing loss via inhibition of the PI3K‐Akt signalling pathway

“…There are two TOP2 enzymes, TOP2A and TOP2B, in mammalian cells. TOP2A is located on chromosome 17q21-22 while TOP2B is located on chromosome 3p24 [18]. Although TOP2A and TOP2B have structural and catalytic similarities, they are not genetically identical and functionally redundant [19].…”

Molecular Reclassification in Pediatric Osteosarcomas at Surgical Resection is a Potential Helpful Prognostic Marker

“…Most of the studies, even in our Lab, were focusing on diagnostic samples to determine really early the chemoresistant osteosarcomas [5][6][7][8][13][14][15][16][17]. Nevertheless, this risk re-stratification is necessary to adapt the treatment but, for instance, was mostly based on clinical features [18][19][20][21].…”

“…Comparing normal and tumor DNAs, the allelotyping analyses are identifying directly the presence of chromosomal alterations and is able to detect either chromosomal (allelic imbalance or AI) or microsatellite instabilities (MSIs). In the entire previously published cohort of 105 pediatric osteosarcomas [14], no MSIs, identifying usually a repair error phenotype, were detected, but only AIs were observed on biopsy's DNA. Twenty-three different microsatellites were analyzed on all specimens to screen tumor response to chemotherapy at a molecular level based on the presence or not of diagnostic AIs.…”

“…The data were analyzed with the Genemapper Software (Applied Biosystems). This technique detects two types of rearrangements: a modification of the allele ratio in tumor or biopsy DNA compared to the paired blood DNA, which is described as an allelic imbalance (AI), and the microsatellite instability (MSI), which was not described in the entire French osteosarcoma cohort [13][14][15][16][17]. The AI is the witness of a deletion or an amplification of the targeted locus.…”

“…DNAs originated from blood, biopsy and tumor samples (10 ng) were amplified by PCR in a total volume of 25 µL using 0.125 µL of Taq polymerase and 4 pmol of both forward and Cy5 labeled reverse primers. PCR was carried out in an Omnigen Hybaid Thermocycler (Hybaid Ldt, Ashford, UK) using the protocols already described in our previous publications [13][14][15][16][17]. The PCR products were analyzed by capillary electrophoresis on ABI PRISM® Genetic Analyzer 3100 (Applied Biosystems, Foster City, CA, USA).…”