IMPDH2 and HPRT expression and a prognostic significance in preoperative and postoperative patients with osteosarcoma

Abstract

Osteosarcoma is one of the most aggressive bone tumors in children and adolescents. Development of effective therapeutic options is still lacking due to the complexity of the genomic background. In previous work, we applied a proteomics-guided drug repurposing to explore potential treatments for osteosarcoma. Our follow-up study revealed an FDA-approved immunosuppressant drug, mycophenolate mofetil (MMF) targeting inosine-5'-phosphate dehydrogenase (IMPDH) enzymes, has an anti-tumor effect that appeared promising for further investigation and clinical trials. Profiling of IMPDH2 and hypoxanthine-guanine phosphoribosyltransferase (HPRT), key purine-metabolizing enzymes, could deepen understanding of the importance of purine metabolism in osteosarcoma and provide evidence for expanded use of MMF in the clinic. In the present study, we investigated levels of IMPDH2, and HPRT in biopsy of 127 cases and post-chemotherapy tissues in 20 cases of high-grade osteosarcoma patients using immunohistochemical (IHC) analysis. Cox regression analyses were performed to determine prognostic significance of all enzymes. The results indicated that low levels of HPRT were significantly associated with a high Enneking stage (P = 0.023) and metastatic status (P = 0.024). Univariate and multivariate analyses revealed that patients with low HPRT expression have shorter overall survival times [HR 1.70 (1.01-2.84), P = 0.044]. Furthermore, high IMPDH2/HPRT ratios were similarly associated with shorter overall survival times [HR 1.67 (1.02-2.72), P = 0.039]. Levels of the enzymes were also examined in post-chemotherapy tissues. The results showed that high IMPDH2 expression was associated with shorter metastasis-free survival [HR 7.42 (1.22-45.06), P = 0.030]. These results suggest a prognostic value of expression patterns of purine-metabolizing enzymes for the pre- and post-chemotherapy period of osteosarcoma treatment.

Figure 1

Immunohistochemical staining of (A) IMPDH2 and (B) HPRT in osteosarcoma tissues (Χ400). (C) Distribution of IMPDH2 and HPRT levels in osteosarcoma cohort (N = 127). H&E; hematoxylin and eosin.

Figure 2

Kaplan–Meier curves showing overall survival by (A) HPRT and (B) IMPDH2/HPRT ratio in osteosarcoma cases.

Figure 3

Expression levels of IMPDH2 and HPRT enzymes in longitudinal samples. (A) Expression of IMPDH2 and HPRT in biopsy and post-chemotherapy tissues. (B) Metastasis-free survival analysis of IMPDH2 in post-chemotherapy tissues of osteosarcoma.