Immune and Tumor Genome Signatures Associated with Response to Radiotherapy and Chk-1 Inhibition in a Phase 1b Clinical Trial for Patients with Head and Neck Squamous Cell Carcinoma

Purpose/Objective(s)

Prexasertib is a checkpoint kinase 1 (Chk-1) inhibitor that induces tumor cell apoptosis through bypassing DNA repair checkpoints. We and others have shown that prexasertib in combination with chemotherapy with or without radiation (RT) has significant antitumor effects in both in vitro and in vivo models of head and neck squamous cell carcinoma (HNSCC). Recently, we reported the results of a phase 1b trial assessing the safety and efficacy of prexasertib in combination with cetuximab-RT or cisplatin-RT (Yang et al. Radiotherapy and Oncology 2021). In this study, we report tumor and immune biomarker analyses from this trial.

Materials/Methods

Gene expression profiling using multiplex analysis platform and panels was performed on archival tumor tissue obtained prior to administration of prexasertib in combination with RT and either cisplatin or cetuximab from 17/25 patients with locally advanced HNSCC enrolled in a Phase 1b study (NCT02555644). Differentially expressed genes were compared between patients with complete response (CR) and not complete response (NCR; includes partial response, progressive and stable disease), as defined by RECIST criteria.

Results

Immune gene signatures that correlated with prexasertib clinical response involved Th1 T cell and M1 macrophage phenotypes. While exhausted CD8⁺ T and Treg cell gene scores, as well as PD-L1 mRNA levels, were higher in tumors from CR patients, we found significantly higher immune tolerogenic M2 macrophage-associated gene expression and increased CSF1 tumor cell signaling in NCR patients. Gene expression of functional markers of T and NK cells, including IL-2, IFN-γ, granzyme and perforin, were similarly elevated in CR patients with correspondingly increased tumor mRNA levels of JAK/STAT signaling elements such as JAK2, STAT1/3, and IFNG. Conversely, Wnt/β-catenin pathway mediators CTNNB1 and AXIN2, as well as IL-6 mRNA levels, which may mediate immune exclusion, were upregulated in NCR patients. Consistent with our prior preclinical observations, Notch signaling activators JAG1/2, which are implicated in maintaining cancer stem cells, apoptosis inhibition and tumor growth, were found to be elevated in NCR patients.

Conclusion

Gene expression analysis found that baseline immune and tumor gene signatures correlated with Chk-1 inhibitor sensitivity in patients receiving chemo-RT. Findings suggest that oncogenic pathway activity and intact immune surveillance may be important in response to combination of prexasertib with RT, and that baseline immunosuppressive tumor microenvironments may impede maximal Chk-1 inhibitor efficacy. Future studies aimed to validate tumor and immune signatures as biomarkers of efficacy of Chk-1 inhibition and to identify targetable mediators to enhance responsiveness are warranted.