Osteosarcoma is a heterogeneous disease with regard to its histology, chemotherapy response and clinical outcomes12,13. In this study, whole exome and transcriptome sequencing were conducted in 25 patients with osteosarcoma. A clinicopathologic integrated rating scale was developed to evaluate the chemotherapy response. In addition, clinical, genomic and transcriptomic features relevant to chemotherapy response were explored and a chemotherapy response classifier was constructed. To our knowledge, this is the first study to comprehensively investigate the clinical and molecular characteristics of chemotherapy response in osteosarcoma using multi-omics techniques, which expands our knowledge of this complex disease.
In multiple previous studies14–16, osteosarcoma was mainly characterized by diverse variants, recurrent structural variants, high frequencies of TP53 and RB1 mutations. Similarly, our study revealed that the genetic variants in osteosarcoma were dispersedly distributed. In terms of mutation type, single nucleotide variants and small insertions and deletions were atypical events, whereas CNVs, especially amplification, were common in osteosarcoma. PHOX2B mutations were firstly identified in osteosarcoma in our study, which encodes a transcription factor participating in the development of the peripheral nervous system and is known to be related to neuroblastoma and congenital central hypoventilation syndrome17. Our study also found that osteosarcoma had the extremely low level of TMB and relatively high level of chromosomal CNV burden. In addition, it seemed that patients with high chromosomal CNV burden had a nonsignificantly better response to chemotherapy, which required to be verified in further studies. Consistent with the previous study15, mutations in osteosarcoma were mainly caused by the dysfunctional DNA damage repair in this study. Moreover, this study suggested that chemotherapy responders had more homologous recombination repair deficiency - induced mutations, which may be explained by the administration of platinum-based chemotherapy regimens in osteosarcoma and the favorable response to platinum in defective homologous recombination repair ovarian cancer18.
In this study, 11 genes were significantly up-regulated in responders and 18 genes were significantly up-regulated in non-responders. Both KEGG and GSEA enrichment analyses suggested that 4 pathways relative to cardiomyopathy were significantly enriched in responders and neuroactive ligand-receptor interaction pathway was significant in non-responders. The recommended neoadjuvant chemotherapy regimen for osteosarcoma included high-dose methotrexate, doxorubicin, cisplatin and ifoshamide. Doxorubicin can induce clinically symptomatic cardiac toxicity in 1.5%-1.7% of patients with osteosarcoma and the incidence of subclinical cardiac abnormalities may be higher19. The enrichment of cardiomyopathy-related pathways in chemotherapy responders may be related to the treatment of doxorubicin, which reminds clinicians of the occurrence of cardiac toxicity in chemotherapy responders. In a previous study, transcriptomic analysis was performed in breast cancer to investigate biomarkers related to chemotherapy sensitivity. KEGG analysis indicated that a great number of DEGs in neuroactive ligand-receptor interaction and the number of DEGs in neuroactive ligand-receptor interaction pathway subexpressed in chemotherapy resistant group was more than overexpressed genes. However, whether the entire pathway was up-regulated or down-regulated was not analyzed20. In another study in breast cancer, the relationship between neuroactive ligand-receptor interaction pathway and pathological complete response to chemotherapy was not clearly elucidated21. One study used the paclitaxel-induced peripheral neuropathy rat model to understand the transcriptomic level of the dorsal root ganglia neurons and found that neuroactive ligand-receptor interaction was majorly involved in sensory neurons of rats with paclitaxel-induced peripheral neuropathy22. Therefore, the enrichment of neuroactive ligand-receptor interaction pathway in chemotherapy non-responder group in our study might be related to chemotherapy-induced peripheral neuropathy. PPI analysis identified ACTN2, TTN and MYH6 as hub genes resulting in chemotherapy responsiveness. ACTN2 encoded protein links the anti-parallel actin filaments, contributes to sarcomere stability and is related to cardiomyopathy23. TTN encoded protein plays an important role in skeletal and in heart muscles24. MYH6 gene provides instructions for making a protein known as the cardiac alpha (α)-myosin heavy chain, which forms part of type II myosin in cardiac muscles25. All of them were overexpressed in chemotherapy responders and involved in pathways enriched in chemotherapy responders, which confirmed the pathway enrichment findings.
In clinics, multiple methods are used to evaluate the neoadjuvant chemotherapy response in osteosarcoma, including symptoms and signs, laboratory tests, imaging examinations and evaluation of tumor necrosis rate. Our study suggested that changes of tumor margin and circumference after chemotherapy were more related to chemotherapy response. Zeng et.al. developed a chemoresistant risk model using markers ontained from bulk RNA and single-cell RNA sequencing with the area under the curve of 0.82 in the TARGET-OS training cohort and 0.84 in the GSE33382 validation cohort26. Our study used the limited internal data to develop a random forest-based classifier, and performance of the model was comparative to the previous study. Due to the inaccessible clinical information in TARGET-OS dataset and limited overlapping genes between GSE33382 dataset and our internal dataset, no suitable external dataset could be used to validate our classifier. A potential limitation of this study was the small amount number of participants, which may reduce the representativeness of certain findings and need to be further verified in large-scale studies.
In conclusion, multi-omics sequencing techniques help us better understand the molecular characteristics of osteosarcoma. Osteosarcoma is a highly heterogeneous disease with frequent occurrence of CNVs at the genomic level. Transcriptomic analysis identified several signaling pathways associated with chemotherapy responsiveness to osteosarcoma, including pathways related to cardiomyopathy and neuroactive ligand-receptor interaction. Additionally, the performance of chemotherapy response classifier was acceptable, which requires to be validated using more data before utilizing in clinics.