Background: Tyrosine Kinase Inhibitors (TKIs) such as Erlotinib (ER) and Osimertinib (OR) are being used to treat lung cancer patients with EGFR mutations; however, patients develop resistance to these drugs within 10-18 months. EGFR-TKI resistance may be mediated by epithelial-mesenchymal transition (EMT), which causes a motile and invasive phenotype similar to mesenchymal cells. Sphingosine kinase 2 (SphK2), which is upregulated in Non-Small Cell Lung Cancer (NSCLC), phosphorylates sphingosine to sphingosine-1-phosphate (S1P) and increases cell proliferation, tumor survival and cell migration. The sphingolipid rheostat controls the cell fate by maintaining a balance between pro-survival and pro-apoptotic sphingolipids, which is regulated by SphK2. However, the role of SphK2 in TKI resistance and EMT is not well understood.

Hypothesis: We hypothesize that the inhibition/downregulation of SphK2 will reverse EMT, reduce tumorigenicity and overcome ER and OR resistance. Study design and

Results: We studied expression of SphK2 in both drug resistant (OR and ER) and drug sensitive (parental) H358, H2170, H3255 and PC9 NSCLC cell lines. In drug resistant cells, qPCR and immunoblotting studies showed that SphK2 was upregulated by 1.5-1.7 and 1.5-3.3 fold in ER and OR resistant cell lines respectively compared to parental cells. 48 hours after SphK2 knockdown with siRNA treatment, SphK2 was downregulated by 4.6-fold and EMT mediator E-cadherin expression was upregulated by 2.9-fold. EMT proteins Vimentin and N-cadherin were downregulated by 3.8 and 2.2 fold respectively (p≤0.01). Using an MTT assay, differences in percentage viability of cells with different treatments were calculated with respect to their viability in the presence of OR. We found that 81.43% of H358OR and 76.35% of the H3255OR cells were inhibited by a combination of Opaganib, a Sphk2 inhibitor, and OR, this is 27.74% and 12.28% higher compared to the additive effect of drug and inhibitor in H358OR and H3255 cells respectively. Furthermore, transwell migration assays, wound healing assays and spheroid assays were performed in OR resistant cells and the results indicated inhibition of the above assays by 94.97%, 82.36%, 88.67% respectively when treated with a combination of Opaganib and OR as compared to the diluent. This indicates the potential of SphK2 inhibition to overcome TKI resistance and EMT. To analyze the role of SphK2 expression in cancer progression, IHC was performed on 63 early and 48 late-stage lung cancer patient sections. We observed upregulation of SphK2 in late-stage lung cancer (p≤0.05), indicating its role in cancer progression.

Conclusion: In this study, SphK2 was shown to decrease tumor survival, cancer cell proliferation, and expression of EMT markers. Thus, SphK2 may be a promising clinical target for overcoming EGFR-TKI resistance and NSCLC tumor progression.

Citation Format: S M Nasifuzzaman, Namrata Dube, Katie Lam, Robert J. Hillwig, Neelu Puri. The role of sphingosine kinase 2 in overcoming EGFR-tyrosine kinase inhibitor resistance, EMT and NSCLC tumor progression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 428.