Ursolic acid inhibits proliferation and reverses drug resistance of ovarian cancer stem cells by downregulating ABCG2 through suppressing the expression of hypoxia-inducible factor-1α in vitro

Abstract

Hypoxia in tumors is closely related to drug resistance. It has not been verified whether hypoxia-inducible factor-1α (HIF-1α) or ABCG2 is related to hypoxia-induced resistance. Ursolic acid (UA), when used in combination with cisplatin can significantly increase the sensitivity of ovarian cancer stem cells (CSCs) to cisplatin, but the exact mechanism is unknown. The cell growth inhibitory rate of cisplatin under different conditions was evaluated using Cell Counting Kit-8 (CCK-8) in adherence and sphere cells (SKOV3, A2780, and HEY). The expression of HIF-1α and ABCG2 was tested using quantitative PCR, western blotting, and immuno-fluorescence under different culture conditions and treated with UA. Knockdown of HIF-1α by shRNA and LY294002 was used to inhibit the activity of PI3K/Akt pathway. Ovarian CSCs express stemness-related genes and drug resistance significantly higher than normal adherent cells. Under hypoxic conditions, the ovarian CSCs grew faster and were more drug resistant than under normoxia. UA could inhibit proliferation and reverse the drug resistance of ovarian CSC by suppressing ABCG2 and HIF-1α under different culture conditions. HIF-1α inhibitor YC-1 combined with UA suppressed the stemness genes and ABCG2 under hypoxic condition. The PI3K/Akt signaling pathway activation plays an important functional role in UA-induced downregulation of HIF-1α and reduction of ABCG2. UA inhibits the proliferation and reversal of drug resistance in ovarian CSCs by suppressing the expression of downregulation of HIF-1α and ABCG2.

Tyrphostin RG14620 selectively reverses ABCG2-mediated multidrug resistance in cancer cell lines

“…Next, the effect of tyrphostin RG14620 on ABCG2 protein expression was determined in ABCG2-overexpressing H460-MX20 cancer cells, as it has been shown that drug-induced transient down-regulation of ABCG2 can also lead to the re-sensitization of ABCG2-overexpressing multidrug-resistant cancer cells to chemotherapeutic agents [12, 33, 62]. Cells were treated with increasing concentrations (0 – 2 μM) of tyrphostin RG14620 for 72 h and processed by immunoblotting as described in Materials and methods .…”

An ABCG2 non-substrate anticancer agent FL118 targets drug-resistant cancer stem-like cells and overcomes treatment resistance of human pancreatic cancer

“…This is highly possible, because survivin [ 31 – 38 ], Mcl-1 [ 39 – 47 ], XIAP [ 35 , 36 , 38 , 44 , 48 – 55 ], and cIPA2 [ 55 ] play critical roles in pancreatic cancer resistance to treatment, and it is also known that survivin [ 56 – 69 ], Mcl-1 [ 70 , 71 ] and XIAP [ 54 ] are involved in latent CSC drug resistance and function. Furthermore, it is well documented that ABCG2 as a critical efflux pump protein plays a vital role in maintaining viability of latent stem-like cancer cells [ 23 – 29 ], and the increase of ABCG2 [ 13 – 17 ], Pgp [ 18 – 21 ] expression is important for pancreatic cancer resistance to commonly used pancreatic cancer drugs in the clinic. In this regard, FL118 is not a substrate of these efflux pump proteins [ 12 , 22 ] and can bypass these protein expression-induced treatment resistance [ 22 ].…”

“…FL118 exhibits a favorable pharmacokinetics profile, accumulating and residing in tumors [ 12 ]. Since ABCG2 is a critical efflux pump that maintains viability of latent stem-like cancer cells [ 23 – 29 ], the capability of FL118 bypassing ABCG2 resistance makes it effective in killing latent, stem-like cancer cell populations and may also overcome the effect of desmoplasia-mediated limitation of drug access to pancreatic tumors. Therefore, development of novel drugs that can overcome ABCG2-mediated treatment resistance is one of the pressing issues in the field of anticancer drug development [ 30 ].…”

Ursolic acid sensitized colon cancer cells to chemotherapy under hypoxia by inhibiting MDR1 through HIF-1α

“…Since MDR1 is an HIF-1α target gene and it was reported that UA was capable of inhibiting HIF-1α (Wang et al, 2016), we wondered whether HIF-1α mediates UA-induced MDR1 down-regulation. We observed that under hypoxia, inhibition of HIF-1α resulted in lower MDR1 levels, while MDR1 inhibition did not influence the expression of HIF-1α, confirming the transcriptional regulation of MDR1 by HIF-1α (Figs.…”