Abstract 2136: Doublecortin-like Kinase 1 (DCLK1) correlates with the cell proliferation in malignant pleural mesothelioma

Background: Malignant pleural mesothelioma (MPM) is a refractory disease with poor prognosis despite multimodality therapy. Because standard therapy is unsatisfactory, it is expected to establish a novel strategy such as molecular-targeting therapy for MPM. Doublecortin-like kinase 1 (DCLK1), a microtubule-associated protein, is one of the tumor-specific stem cell marker and is revealed that the cell survival is reduced by inhibiting this protein in pancreatic and colorectal cancers. DCLK1 is known to have several isoforms named as isoform #1-#4, although the significance of them in MPM has not been clarified. We hypothesized that DCLK1 was a potential therapeutic target for MPM. Methods: Immunohistochemical staining was performed using surgically resected formalin-fixed paraffin-embedded tissue of MPM to evaluate the expression of DCLK1. Additionally, MPM cell lines were analyzed to characterize the protein and mRNA expression of DCLK1 by western blotting and RT-PCR. The expression of DCLK1 isoforms were selectively knocked down by small interfering RNA (siRNA) and cell viability was analyzed by colony formation and cell count assays. Results: Immunohistochemical staining demonstrated that the expression of DCLK1 in MPM specimens was positive in 24 out of 27 samples (89%). Western blotting and RT-PCR revealed that DCLK1 was expressed in seven out of nine MPM cell lines. The results of RT-PCR revealed that isoform #2 and isoform #4 of DCLK1 were expressed in H2052, isoform #4 was expressed in H28, and isoform #2 was expressed in YUMC44 cell lines. Expressions of DCLK1 isoforms were selectively suppressed by isoform-specific siRNAs. Colony formation and cell count assays revealed that siRNA-mediated knockdown of both isoforms #2 and #4 suppressed cell growth compared to knockdown by negative control siRNA and knockdown of only isoform #2 or #4. Conclusion: Our results demonstrate that simultaneous knockdown of both isoforms #2 and #4of DCLK1 results in the inhibition of cell growth and suggest its potential as a therapeutic target in MPM. Citation Format: Akihiro Miura, Hiromasa Yamamoto, Hiroyuki Tao, Ken Suzawa, Syunsaku Miyauchi, Kota Araki, Yuta Takahashi, Eisuke Kurihara, Yusuke Ogoshi, Kazuhiko Shien, Junichi Soh, Kazunori Okabe, Shuta Tomida, Masakiyo Sakaguchi, Shinichi Toyooka. Doublecortin-like Kinase 1 (DCLK1) correlates with the cell proliferation in malignant pleural mesothelioma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2136.