Abstract B12: Centrosome clustering inhibition as a novel strategy to sensitize non-small cell lung cancer to radiation treatment and immunotherapy

The centrosome is a microtubule-organizing center that plays an important role during M-phase and cell division where it organizes the two poles of the bipolar microtubule spindle apparatus from which chromosomes are segregated. In contrast to most normal cells, the vast majority of lung cancers contain extra copies of centrosomes, and a large body of circumstantial evidence links extra centrosomes to the development of cancer. Cells with supernumerary centrosomes form multipolar mitotic spindles, which, if not corrected, lead to lethal multipolar divisions or “mitotic catastrophe.” To overcome this, lung cancer cells cluster their centrosomes into two spindle poles, enabling tumor cells to survive. Thus, inhibition of centrosome clustering (CCi) can force cancer cells into multipolar divisions, lead to chromosomal instability, make cancer cells more sensitive to radiation treatment, and eventually result in the selective killing of cancer cells. At the same time, this approach should spare healthy tissues with normal centrosome numbers, resulting in a favorable therapeutic index. To examine the relationship between CCi and radiation-treatment sensitivity, we first treated three NSCLC cell lines (A549, H460 and H358) and one immortalized primary human bronchial epithelial cell (HBEC) with griseofulvin—a centrosomal clustering inhibitor. Immunofluorescent staining for pericentrin and alpha-tubulin, we observed a significant increase in the number of cells with multipolar spindles in NSCLC cells compared to HBECs (40-80% vs. 15%). Next, we examined the ability of griseofulvin to radiosensitize these cells to radiation treatment. By using clonogenic assays, we saw significantly less clonogenic potential of NSCLC cells following radiation treatment after exposure to 30 uM of griseofulvin, but griseofulvin did not radiosensitize HBECs. To further confirm our results, we genetically targeted KIFC1, a member of kinesin-14 family of motor proteins that have been shown to be essential for clustering centrosomes in cancer cells, but are not required for division in normal cells. In our experiments, knockdown of KIFC1 expression with siRNA also significantly sensitized NSCLC cells to radiation treatment. Finally, when we treated the NSCLC cells with griseofulvin, we saw a significant increase in the formation of micronuclei in cancer cells. Recently, it has been shown that micronuclei are important sources of immunostimulatory DNA via activation of the cGAS-STING pathway. Therefore, inhibition of CC could potentially augment immunogenicity and increase efficiency of immunotherapy (IMT). In conclusion, inhibition of CC resulted in the formation of multipolar spindle in NSCLCs and further sensitized NSCLCs to radiation treatment. CC is not typically required for normal cells, and thus CCi may be a more specific and perhaps less toxic therapy for NSCLCs. The potential of CCi to enhance IMT is under investigation. Citation Format: Hailun Wang, Katriana Nugent, Matthew Ballew, Ghali Lemtiri-Chlieh, Natasha Raman, Michelle Levine, Andrew Holland, Phuoc Tran. Centrosome clustering inhibition as a novel strategy to sensitize non-small cell lung cancer to radiation treatment and immunotherapy [abstract]. In: Proceedings of the Fifth AACR-IASLC International Joint Conference: Lung Cancer Translational Science from the Bench to the Clinic; Jan 8-11, 2018; San Diego, CA. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(17_Suppl):Abstract nr B12.