Retraction Note: Anti-cancer effects of grailsine-al-glycoside isolated from Rhizoma Sparganii

An embryonic toxicity of Rhizoma
 sparganii was observed in mice. This study was
 aimed to evaluate the anticancer effects of
 Grailsine-Al-glycoside, the bioactive component of Rhizoma sparganii, on estrogen
 receptor-positive (ER+) and estrogen
 receptor-negative (ER-) cancer cell
 lines. After A549, HeLa, HepG-2 and MCF-7 cells were treated with
 Grailsine-Al-glycoside, cell proliferation was analyzed by MTT,
 cell cycle and apoptosis by flow cytometry, and morphology with
 an immunofluorescence microscope. Grailsine-Al-glycoside strongly suppressed cell proliferation
 in a dose-dependent fashion in A549, MCF-7, HepG2, and HeLa
 cells, though this growth inhibitory effect on HepG2 cells was
 not as strong and long lasting. Compared to the control,
 Grailsine-Al-glycoside caused a significant increase of
 apoptosis in A549, MCF-7 and Hela cells. A549 and MCF-7 cells
 were arrested at the G2/S phase whereas HepG2 cells were
 arrested at the G1 phase by a high concentration of
 Grailsine-Al-glycoside . Cell shapes were also changed by the
 presence of Grailsine-Al-glycoside. Grailsine-Al-glycoside from Rhizoma
 sparganii inhibited the proliferation of
 ER+ and some
 ER- cancer cells.
 Grailsine-Al-glycoside may be used as a chemotherapeutic agent
 against ER+ and ERRα-expressing
 ER- cancers.


Background
It is well known that many cancers have a number of receptors that are suitable targets for therapy. In particular, anti-estrogen therapy is a highly effective treatment for patients with estrogen receptor-positive (ER + ) breast cancer, emphasizing the central role of estrogen activity in the development of this disease [1]. Estrogen-estrogen receptor complexes can bind directly to specific sequences of DNA, mediate transcription (gene expression), and affect various biological actions [2,3]. Proliferation of a subset of breast, lung, and liver cancers is reportedly mediated through the estrogen-estrogen receptor mechanism [4][5][6][7][8].
The dried rhizome of Sparganium stoloniferum Buch.-Ham. (Rhizoma Sparganii, RS) is frequently used in traditional Chinese medicine. An aqueous extract of RS (RS-W) is widely used in the treatment of blood stasis, amenorrhea, functional dyspepsia, and early stages of tumors especially for hysteromyoma in China [9]. A new N-heterocyclic Al complex glycoside, Grailsine-Alglycoside, was isolated from RS-W by column chromatography and its structure was determined by spectroscopic methods (Figure 1) [10].
RS is contraindicated during pregnancy and during profuse menstrual flow. RS-W also showed anti-estrogenic and anti-angiogenesis effects in the reproductive system of rodents (unpublished data, Wei et al). Pregnant mice receiving RS showed reduced fibroblast growth factor (FGF) protein level but enhanced toxicity to ER + cells in the embryos during mice embryonic development. As embryos and tumors share many similarities in endocrine, angiogenesis, and gene expression profile, we hypothesize that RS-W may exert a anti-tumor effect on ER + tumors through similar anti-estrogen/anti-angiogenic activity. This study was intended to determine the anticancer activities of Grailsine-Al-glycoside from RS-W on ER + cancer cell lines, A549 and MCF-7, and ERcancer cell lines, HeLa, and HepG-2.

Extracting grailsine-Al-glycoside
The dried herb, Sparganium stoloniferum (Rhizoma Sparganii, RS) was purchased from Yi-Kang Chain Medicine Co. (Xi'an, China). Standardization of this drug was consistent with the regulations of the State Food and Drug Administration. The pure compound Grailsine-Al-glycoside ( Figure 1) was purified from aqueous extract of RS (RS-W) through the silica gel (SiO 2 ; 230-400 mesh, Merck, Shanghai, China) and Sephadex G-25 (Sigma, St. Louis, MO) column chromatography [10]. 3 H and 13 C spectra were recorded on a Varian INOVA-400 MHz system (Varian, Palo Alto, CA). TOF-MS spectra were obtained on an AXIMA-CFR™ plus MALDI-TOF Mass Spectrometer (SHIMADZU, Beijing, China). Elements were analyzed on a Vario EL III (Elementar Analysensysteme GmbH, Hanau, Germany), and monosaccharide composition was analyzed using the general method.

Flow cytometry (FCM) test
Cells were treated for 36 hr with Grailsine-Al-glycoside before being fixed with methyl alcohol and stained with propidium iodide. DNA content was determined by flow cytometry (EPICS @ XL, Beckman Coulter, Brea, CA), and the data was analyzed with FlowJo 5.7.2.

Grailsine-Al-glycoside suppressed the proliferation of cancer cells
Grailsine-Al-glycoside strongly inhibited the proliferation of HeLa, MCF-7, and A549 cells. The treatment of 20 μg/ml of Grailsine-Al-glycoside significantly inhibited the cell proliferation in those three cell lines after 48 hr and 72 hr while the dosage of 40 μg/ml had an even stronger inhibition (Figure 2). On the other hand, Grailsine-Al-glycoside could only inhibit the proliferation of HepG2 cells for up to 48 hr at 40 μg/ml dosage ( Figure 2).

Grailsine-Al-glycoside promoted apoptosis of cancer cells
The 4 cell lines showed different apoptotic responses upon Grailsine-Al-glycoside treatment ( Figure 3). Hela, A549, and MCF7 cells all had more than 2-fold increases of apoptotic cells in the presence of 20 μg/ml of Grailsine-Al-glycoside over that of the control (Figure 3  A, B & D). The increase of apoptosis caused by Grailsine-Al-glycoside treatment in HepG2 cells was much more modest ( Figure 3C).

Grailsine-Al-glycoside induced cell cycle arrest in some cancer cells
HeLa cells showed no cell cycle abnormalities at any concentrations of Grailsine-Al-glycoside after 36 hr treatments. Grailsine-Al-glycoside increased the number of G2/S phase cells of A549 in a dose dependent fashion ( Figure 4). MCF-7 had a higher ratio of G 2 /S phase cells only with Grailsine-Al-glycoside treatment at a high  concentration (40 μg/ml) (Figure 4) while HepG-2 had a higher amount of G 1 phase cells at the same high concentration (Figure 4).

Cell morphology
Grailsine-Al-glycoside-treated A549 and HepG2 cells showed a condensed cytoplasm and spindle shape with increased α-tubulin density while MCF-7 cells had swollen cytoplasm without loss of α-tubuin density upon the treatment of Grailsine-Al-glycoside ( Figure 5). The Grailsine-Al-glycoside treatment did not induce obvious morphological change of Hela cells ( Figure 5).

Discussion
Grailsine-Al-glycoside showed strong inhibitory effects on ER + human lung cancer cell line A549 and breast cell line MCF-7, by inhibiting cell proliferation and inducing apoptosis. Surprisingly, Grailsine-Al-glycoside exhibited the same inhibitory effects on ERhuman cervical cell line Hela and liver cancer cell line HepG2, indicating that Grailsine-Al-glycoside could exert its anti-cancer effects through a different pathway other than ER.
The number of HeLa cells was severely suppressed by Grailsine-Al-glycoside (40 μg/ml) due to growth inhibition and apoptosis but cells showed moderate morphological changes and no cell cycle abnormality was observed at 36 h treatment. HepG2 cells showed different changes in response to Grailsine-Al-glycoside treatment, which had modest inhibition of proliferation and increase of apoptosis but significant G1 phase arrest at a concentration of 40 μg/ml. Such changes might be resulted from the inhibition of estrogen-related receptor α (ERRα) [11]. ERRα is one of the orphan nuclear receptors which is constitutively active, and it does not respond to estradiol (E2) or natural estrogens. ERRα is expressed in various types of cancer, such as breast [12], endometrial [13], cervical [11], and colorectal cancers [14]. Increased ERRα levels are associated with a higher risk of recurrence and poor clinical outcome in breast cancer, suggesting that ERRα could be a negative prognostic factor [11]. Grailsine-Al-glycoside showed the ability to suppress the growth of both ER + breast cancers and ERbut ERRα-expressing cancers.

Conclusions
Grailsine-Al-glycoside from RS showed anti-cancer effects on both ER + and ERcancer cells by inhibiting proliferation, triggering apoptosis, and / or cell cycle arrest.