Abstract LB-271: The CD44high/ALDHhighcell population mediates tumor initiating cell properties through the sonic Hedgehog pathway in lung cancer.
Authors: Wong Maria Pik , Liu Jing , Xiao Zhi-jie 
Published: August 2014

Abstract
In spite of the decreasing lung cancer incidence recently observed in some countries, its mortality has remained high due to late presentation and limited chemotherapy effectiveness. Even for EGFR mutant cancers initially responding to tyrosine kinase inhibitors (TKI), long term patient survival has not been achieved due to the almost universal occurrence of TKI resistance. Tumor initiating cells (TIC) are a subpopulation of cancer cells believed to be capable of self-renewal leading to tumor perpetuation, metastasis and treatment resistance. To identify self-renewing cells in lung cancer and investigate their regulatory pathways, tumor cells with differential expression of the combined CD44 and ALDH1 markers were isolated by flow cytometry for functional comparison. The results showed in established lung cancer cell lines and early passage clinical lung cancer cells, the CD44high/ALDHhigh population had the strongest, while CD44low/ALDHlow the weakest in-vitro cell sphere formation and in-vivo serial xenograft transplantation capacities. The CD44high/ALDHhigh population also showed higher matrigel invasion ability, pluripotency genes expression, cell cycle regulator expression, as well as resistance to tyrosine kinase inhibitor and/or cisplatin treatment. TKI treatment led to increased CD44high/ALDHhigh cell proportions. Simultaneous down-regulation of CD44 by si-RNA and enzymatic inhibition of ALDH1 suppressed stem/progenitor genes expression including OCT4, SOX2 and NANOG, and attenuated cell sensitivity to TKI and cisplatin treatment in different lung cancer cells, indicating CD44 and ALDH were not only surface markers for TIC, but also had functional roles in TIC maintenance. To investigate for phenotypic differences and potential regulatory pathways involved in the maintenance of the two cell populations, the expression microarray profiles of isolated TIC (CD44high/ALDHhigh) and non-TIC (CD44low/ALDHlow) populations were compared. The results showed differential expression of various cell adhesion molecules, HLA markers, and signaling proteins involved in the Sonic Hedgehog (e.g. GLI1, GLI3) and Notch (e.g. DLL4, JAG1) pathways. Differential expression of selective molecules was independently validated by quantitative RT-PCR in an expanded panel of lung cancer cell lines. Pharmacological inhibition of the Hedgehog pathway using cyclopamine decreased TIC proportion in a dose dependent manner and sensitized lung cancer cells to TKI treatment, while Notch inhibition led to less prominent effects. Taken together, these findings indicated that CD44high/ALDHhigh expression characterized a subpopulation of self-renewing and tumorigenic cells in lung cancer. Therapeutic targeting of the Hedgehog pathway might be useful for disrupting TIC and help to achieve lung cancer control.
Citation Format: Maria Pik Wong, Jing Liu, Zhi-jie Xiao. The CD44high/ALDHhigh cell population mediates tumor initiating cell properties through the sonic Hedgehog pathway in lung cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr LB-271. doi:10.1158/1538-7445.AM2013-LB-271