Drug action of ATM inhibitor AZD1390 on nasopharyngeal carcinoma

Abstract

Nasopharyngeal carcinoma (NPC) is a distinct type of malignancy originated from the nasopharynx. NPC has a unique demographic distribution, where it is exceptionally endemic in Southern China regions, including Hong Kong. Undifferentiated subtype of NPC (WHO type III) accounts for more than 98% of the cases, and it is characterized by the type II latency of Epstein-Barr virus (EBV) infection. Apart from radiotherapy, chemotherapy has been a mainstay of treatment regimen in NPC with high responsive rate. Nonetheless, chemoresistance remains a concern in NPC for its elevated risks of cancer relapse and metastasis in NPC patients which is often associated with a low survival rate.

Chromatin-bound high mobility group box (HMGB) family members play a critical role in DNA damage sensing, especially HMGB1 and HMGB2. Apart from the mediation of DNA damage response, our previous study reported that HMGB1 could modulate the activity of B cells which thus promoting angiogenesis and tumorigenesis of NPC. Being highly homologous to HMGB1 in both structure and functions, HMGB2 was also reported to play a role in tumorigenesis, senescence and chemoresistance in various cancers. However, its role played in NPC remains elusive. Since ATM plays a central role governing the DNA damage response by mediating homologous recombination and senescence, we aim to elucidate the effects of ATM inhibition by AZD1390 in combination with cisplatin in NPC via the regulation of HMGB2 and to decipher the underlying mechanism so as to examine the therapeutic potential of AZD1390 towards chemoresistant NPC.

In this study, we first confirmed the relationship between ATM and HMGB2 the potential pathway involved by ATM inhibition by AZD1390 through both transcriptomic and proteomic analysis. We found a higher HMGB2 expression in NPC tumor, compared to normal tissues, and a high HMGB2 expression is associated with poorer progression-free survival. Furthermore, the expression of HMGB2 correlates with ATM in a p53-dependent manner, the downregulation of HMGB2 could possibly bring about therapy-induced premature senescence, while limiting the pro-tumorigenic senescence-associated secretory phenotype (SASP) expressions. With a higher mutation rate in TP53 observed in recurrent and metastatic NPC patients, it might suggest that recurrent and metastatic NPC are amenable to treatment by cisplatin with AZD1390. To confirm, we then tested the effects of the therapeutic combination of AZD1390 with cisplatin in vitro on proliferation, cytotoxicity, cell cycle progression and migration. Our results showed that the therapeutic combination was effective in hindering the efficient repairing of DNA lesions by ATM and the activation of the pRb/E2F1 axis, which leads to HMGB2 suppression and hence DNA damage-induced premature senescence in p53-null NPC cell lines. Besides, ATM inhibition by AZD1390 also limited the expressions of the pro-tumorigenic SASPs and reversed the enhanced migration capability and epithelial mesenchymal transition genotype induced by cisplatin.

In summary, our results highlight the therapeutic effects of AZD1390 towards p53-null NPC by preserving the benefit of senescence limiting the proliferation of tumour cells while minimizing the detrimental effects brought by the chronically inflammatory tumour microenvironment resulted from the release of immunomodulating and pro-metastatic SASPs.