Honokiol in Combination with Radiation Targets Notch Signaling to Inhibit Colon Cancer Stem Cells

Abstract

Cancer stem cells (CSCs) are implicated in resistance to ionizing radiation (IR) and chemotherapy. Honokiol, a biphenolic compound has been used in traditional Chinese Medicine for treating various ailments. In this study, we determined the ability of honokiol to enhance the sensitivity of colon CSCs to IR. The combination of honokiol and IR suppressed proliferation and colony formation while inducing apoptosis of colon cancer cells in culture. There were also reduced numbers and size of spheroids, which was coupled with reduced expression of CSC marker protein DCLK1. Flow cytometry studies confirmed that the honokiol-IR combination reduced the number of DCLK1+ cells. In addition, there were reduced levels of activated Notch-1, its ligand Jagged-1 and the downstream target gene Hes-1. Furthermore, expression of components of the Notch-1 activating γ-secretase complex, Presenilin 1, Nicastrin, Pen2 and APH-1 was also suppressed. On the other hand, the honokiol effects were mitigated when the Notch intracellular domain was expressed. To determine the effect of honokiol-IR combination on tumor growth in vivo, nude mice tumor xenografts were administered honokiol intraperitoneally and exposed to IR. The honokiol-IR combination significantly inhibited tumor xenograft growth. In addition, there were reduced levels of DCLK1 and the Notch signaling-related proteins in the xenograft tissues. Together, these data suggest that honokiol is a potent inhibitor of colon cancer growth that targets the stem cells by inhibiting the γ-secretase complex and the Notch signaling pathway. These studies warrant further clinical evaluation for the combination of honokiol and IR for treating colon cancers.

Targeting Cancer Stem Cells with Small Molecules

“…[41][42] Treatment of colon cancer cells with honokiol, a molecule based on a biphenolic scaffold, suppressed proliferation and colony formation. [43] Reduced numbers and sizes of spheroids were also observed, which was associated with reduced expression of the cancer stem cell marker protein DCLK1 (doublecortin like kinase 1) upon honokiol treatment. [44] Reduced levels of activated NOTCH-1 and its ligand Jagged-1 were observed and expression of the gsecretase complex was also suppressed.…”

c-Myc is a novel target of cell cycle arrest by honokiol in prostate cancer cells

“…Total RNA was extracted using RNeasy mini kit from Qiagen. cDNA was synthesized and reverse transcribed using oligo (dT) 20 primer, 1 mg of RNA, and SuperScript TM III reverse transcriptase. Real-time PCR was done from 1:10 diluted cDNA using DyNAmo HS SYBR Green qPCR kits (Thermo Fisher Scientific) on ABI StepOnePlus PCR Systems.…”

“…18 Other intriguing anticancer properties of HNK include inhibition of epithelial to mesenchymal transition providing mechanistic explanation for its anti-metastatic activity and cancer stem cells. 12,15,19,20 Furthermore, liposomal HNK was shown to sensitize cancer cells to drugs such as cisplatin. 21 In summary, preclinical evidence for anticancer effect of HNK is quite persuasive.…”

Second-Line Intraperitoneal Chemotherapy for Recurrent Epithelial Ovarian, Tubal and Peritoneal Cancer: A Propensity Score-Matching Study

“…Indeed, lines of evidence have supported the existence of ovarian cancer stem cells from both tumor specimens and ascites [26,27]. In preclinical models, IP delivery of therapeutic agents has been shown to effectively eradicate ovarian cancer stem cells [28,29]. In line with the aforementioned explanations, a recent randomized trial of hyperthermic IP chemotherapy (HIPEC) in the treatment of recurrent ovarian cancer has been published, showing a favorable outcome towards the use of HIPEC [30].…”