Aim

MEK and AKT inhibitors inhibit signaling down steam of KRAS and are being evaluated as single agents or in combination with other anticancer drugs for the treatment of KRAS mutant adenocarcinoma of the lung (adeno-NSCLC). We investigated whether increased PD-L1 expression with functional T cell inhibitory consequences were a common mechanism of resistance to these drugs in this setting.

Material and Methods

A panel of 10 KRAS mutant adeno-NSCLC cell lines were studied. Cells were exposed to GI50 concentrations of a MEK (trametinib) and AKT (AZD5363) inhibitor for 6hrs, 24hrs and 3 weeks. PD-L1 expression on cell lines was studied by immunofluorescence. Immunofluorescence at various time points were expressed as a ratio of values in drug treated cells compared to untreated control. Functional consequences of PD-L1 expression were studied using a T cell cancer cell line (Jurkat) transfected with a luciferase reporter where co-culture of cancer cells expressing PD-L1 led to reduction in luminescence. Luminescence at various time points were expressed as ratio of luminescence values of drug treated cells compared to untreated controls.

Results

Following characterization of expression of PD-L1 in 10 KRAS mutant adeno-NSCLC cell lines, 5 cell lines with the highest expression of PD-L1 was chosen for functional assays (H441, H2291, H23, H2030 and A549). When exposed to trametinib for 3 weeks, 3/5 cell lines (H23, H2030 and A549) showed an statistically significant increase in expression of PD-L1 (range 1.1-2.4) however significant reduction of luciferase activity was only observed in H23 and H2030, 0.93 and 0.75, p= 0.018 and p=0.01 respectively. When exposed to AZD5363 for 3 weeks, 3/5 cell lines (H441, H23 and H2030) showed a statistically significant increase in PD-L1 expression (range 1.3-1.9) however significant reduction in luciferase reduction was seen in only H441 and H23, 0.86 and 0.76, p= 0.03 and p= 0.04 respectively.

Conclusion

Chronic exposure of KRAS mutant cell lines to MEK and AKT inhibitors cause minor increases in PD-L1 expression but this does not result in functional inhibition of T cells in all instances. Consequently, a functional increase in PD-L1 expression is unlikely to be a common mechanism of resistance to MEK and AKT inhibitors in KRAS mutant adeno-NSCLC.

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Citation Format: Anna R. Minchom, Parames Thavasu, Zai Ahmad, Adam Stewart, Alexandros Georgiou, Mary ER O'Brien, Sanjay Popat, Jaishree Bhosle, Timothy A. Yap, Johann de Bono, Udai Banerji. A study of dynamic changes in PD-L1 expression in KRAS mutant adenocarcinoma of the lung exposed to signal transduction inhibitors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2627. doi:10.1158/1538-7445.AM2017-2627