Background

Glioblastoma (GBM), characterized by wild-type isocitrate dehydrogenase (IDH), is the most aggressive and fatal primary brain tumor in adults [1, 2]. Despite substantial efforts, the standard of care for GBM, maximum surgical resection followed by ionizing radiation (IR) and temozolomide adjuvant therapy, has only a minor clinical benefit [3, 4]. Due to the transcriptional plasticity and heterogeneity of GBM, radiotherapy resistance and eventual recurrence are inevitable [5].

According to bulk expression profiles, there are three phenotypes of GBM, termed proneural (PN), classical (CL) and mesenchymal (MES). GBM patients with the MES phenotype exhibit worse survival and enhanced resistance to radiotherapy than patients with the PN phenotype [6, 61].

Additionally, intrinsic nuclear DNA damage also causes activation of STING and innate immune responses, which are independent of the cGAS signaling pathway. IFI16 together with ATM and PARP-1 mediates the noncanonical activation of STING. Meanwhile, activated STING signaling is further implicated in the activation of NF-κB signaling. In addition to the function of IFI16 in the STING/NF-κB axis, Cindy et al. found that activation of the ATR/CHK1 pathway was related to an increased number of cytoplasmic ssDNA and micronuclei, which further activated the IFI16/STING pathway [58]. Their work revealed the upstream ATR of IFI16, which provided insights for our subsequent drug design and analysis.

HuR is reported to counteract miR-330 to promote STAT3 translation [49]. In addition, HuR is responsible for IL-6 mRNA stability, which further activates the JAK1/STAT3 signaling pathway [62]. In terms of the regulation of HuR, Hyeon et al. reported that the function of HuR was regulated by ATM/ATR through Chk1 and Chk2 [59]. It is clear that the upstream regulation of both IFI16 and HuR is implicated in the activation of ATR. Intriguingly, the drug we screened based on the expression profile of ARPC1B, AZD6738, is also coincidentally an inhibitor of ATR.

ATR is implicated in coordinating the DNA damage response (DDR) induced by DNA replication-related stress and cell cycle checkpoints [33]. The activation of ATR is essential for fork stabilization in response to replication stress and adverse stress-induced DNA damage [63]. Therefore, targeting ATR has exhibited promising antitumor effects, and a variety of ATR inhibitors have been developed. AZD6738, an oral inhibitor of ATR, has been studied as a monotherapy or in combination with radiotherapy, chemotherapy or immunotherapy. Our results indicated that AZD6738 in combination with radiotherapy exhibited excellent antitumor activity in vitro and in vivo. As previously discussed, the regulation of IFI16 and HuR is involved in the ATR pathway, whereas AZD6738 has been validated to target ATR-induced activation of IFI16 and HuR. Therefore, AZD6738 has the potential to counteract ARPC1B-induced resistance to radiotherapy in GSCs. We demonstrated that AZD6738 was implicated in the suppression of two downstream molecules of ARPC1B, IFI16 and HuR. That is, in addition to the cellular sensitivity to AZD6738 being reflected by the expression of ARPC1B, AZD6738 also has the potential to inhibit PMT and resistance to radiotherapy by affecting IFI16 and HuR.

Conclusions

In conclusion, we identified ARPC1B, which is significantly upregulated in MES-GBM/GSCs and is correlated with a poor prognosis. ARPC1B promotes PMT and radiotherapy resistance by inhibiting TRIM21-mediated degradation of IFI16 and HuR, thereby activating the NF-κB and STAT3 signaling pathways, respectively. AZD6738 in combination with radiotherapy exhibited potent anti-GSC effects. Our findings expand the understanding of the heterogeneity and plasticity of GBM and provide a potential therapeutic strategy for GBM treatment.