P1.01-01 Clinical Relevance of Targeting Proteins Required for Mitotic Progression to Improve Chemotherapy Response in Non-Small Cell Lung Cancer

Abstract

Lung cancer is the leading cause of cancer-related mortality worldwide with a ∼14% 5-year survival rate. Patients with non-small cell lung cancer (NSCLC), may undergo surgery followed by platinum-based chemotherapy for resectable disease, chemoradiotherapy for locally advanced disease, systemic treatment for advanced disease and palliative care. The primary issue with chemotherapy is that only 20-40% of patients have responsive disease. Although combinations with immunotherapy can enhance drug response in advanced disease, new strategies are needed to (1) identify which patients are most likely to benefit from platinum based therapy and (2) enhance the effectiveness of the current drug strategies. Herein we describe cell division cycle associated protein-3 (CDCA3) and CDCA8 as a novel prognostic factors and therapeutic targets to delay or prevent platinum resistance in NSCLC. Both CDCA3 and CDCA8 are key regulators of the cell cycle mediating mitotic entry and progression. CDCA3 functions to enable cell entry into mitosis through degradation of the mitosis inhibitory factor WEE1. Whereas, CDCA8 promotes mitotic progression functioning in concert with the chromosomal passenger complex to ensure accurate chromosomal segregation. Tissue microarray (TMA), immunohistochemistry, Bioinformatics, Western blot, siRNA library, CRISPR-Cas9 knockout, cell viability, mass spectrometry. Our preliminary data point to CDCA3 and CDCA8 as novel therapeutic options in NSCLC. CDCA3 and CDCA8 protein are markedly elevated in NSCLC cases with heterogeneous staining associated with Ki67+ cases and strongly prognostic in adenocarcinoma cases. Bioinformatics analysis of clinical trial data (UT Lung SPORE cohort; observation arm vs adjunct chemotherapy arm) indicated that NSCLC patients with elevated CDCA3 and CDCA8 and treated with adjuvant chemotherapy had a poorer outcome than CDCA3low/CDCA8low patients. Accordingly, in vitro analysis of CDCA3 and CDCA8 expression in NSCLC cell lines identified a strong correlation with cisplatin sensitivity whereby CDCA3/CDCA8high cell lines have greater cisplatin IC50 values. Consistently, silencing of either CDCA3 or CDCA8 significantly enhanced cisplatin sensitivity. As a means to reduce either CDCA3 or CDCA8 levels in tumours, we identified that, for CDCA3 in particular, cisplatin induces phosphorylation of CDCA3 (Ser222) which is dependent upon casein kinase 2 (CK2). Inhibition of CK2 with the small molecule CX-4945 (Senhwa Biosciences) abrogated CDCA3 phosphorylation and consequently suppressed CDCA3 levels. CK2 inhibition also suppressed CDCA8 levels whereby CDCA8 protein stability is dependent upon CDCA3. The sensitivity of cisplatin was enhanced by CX-4945 across a panel of 11 NSCLC cell lines, particularly in CDCA3/CDCA8low cell lines. Cisplatin efficacy was further enhanced in CDCA3 or CDCA8 depleted NSCLC cells. Our data highlight CDCA3 and CDCA8 as novel factors mediating NSCLC cell proliferation and sensitivity to cisplatin. Our data also suggest that novel strategies to suppress CDCA3/CDCA8 protein levels, using agents such as CX-4945, might ultimately benefit NSCLC patient outcome by delaying or preventing cisplatin resistance.