Ivermectin has powerful antitumor effects, including the inhibition of proliferation, metastasis, and angiogenic activity, in a variety of cancer cells. This may be related to the regulation of multiple signaling pathways by ivermectin through PAK1 kinase. On the other hand, ivermectin promotes programmed cancer cell death, including apoptosis, autophagy and pyroptosis. Ivermectin induces apoptosis and autophagy is mutually regulated. Interestingly, ivermectin can also inhibit tumor stem cells and reverse multidrug resistance and exerts the optimal effect when used in combination with other chemotherapy drugs.
Abstract
Ivermectin is a macrolide antiparasitic drug with a 16-membered ring that is widely used for the treatment of many parasitic diseases such as river blindness, elephantiasis and scabies. Satoshi ōmura and William C. Campbell won the 2015 Nobel Prize in Physiology or Medicine for the discovery of the excellent efficacy of ivermectin against parasitic diseases. Recently, ivermectin has been reported to inhibit the proliferation of several tumor cells by regulating multiple signaling pathways. This suggests that ivermectin may be an anticancer drug with great potential. Here, we reviewed the related mechanisms by which ivermectin inhibited the development of different cancers and promoted programmed cell death and discussed the prospects for the clinical application of ivermectin as an anticancer drug for neoplasm therapy.
1. Introduction
Ivermectin(IVM) is a macrolide antiparasitic drug with a 16-membered ring derived from avermectin that is composed of 80% 22,23-dihydroavermectin-B1a and 20% 22,23-dihydroavermectin-B1b [1]. In addition to IVM, the current avermectin family members include selamectin, doramectin and moxidectin [[2], [3], [4], [5]] (Fig. 1 ). IVM is currently the most successful avermectin family drug and was approved by the FDA for use in humans in 1978 [6]. It has a good effect on the treatment of parasitic diseases such as river blindness, elephantiasis, and scabies. The discoverers of IVM, Japanese scientist Satoshi ōmura and Irish scientist William C. Campbell, won the Nobel Prize in Physiology or Medicine in 2015 [7,8]. IVM activates glutamate-gated chloride channels in the parasite, causing a large amount of chloride ion influx and neuronal hyperpolarization, thereby leading to the release of gamma-aminobutyric acid (GABA) to destroy nerves, and the nerve transmission of muscle cells induces the paralysis of somatic muscles to kill parasites [9,10]. IVM has also shown beneficial effects against other parasitic diseases, such as malaria [11,12], trypanosomiasis [13], schistosomiasis [14], trichinosis [15] and leishmaniasis [16].
IVM not only has strong effects on parasites but also has potential antiviral effects. IVM can inhibit the replication of flavivirus by targeting the NS3 helicase [17]; it also blocks the nuclear transport of viral proteins by acting on α/β-mediated nuclear transport and exerts antiviral activity against the HIV-1 and dengue viruses [18]. Recent studies have also pointed out that it has a promising inhibitory effect on the SARS-CoV-2 virus, which has caused a global outbreak in 2020 [19]. In addition, IVM shows potential for clinical application in asthma [20] and neurological diseases [21]. Recently scientists have discovered that IVM has a strong anticancer effect.
Since the first report that IVM could reverse tumor multidrug resistance (MDR) in 1996 [22], a few relevant studies have emphasized the potential use of IVM as a new cancer
treatment [[23], [24], [25], [26], [27]]. Despite the large number of related studies, there are still some key issues that have not been resolved. First of all, the specific mechanism of IVM-mediated cytotoxicity in tumor cells is unclear; it may be related to the effect of IVM on various signaling pathways, but it is not very clear overall. Second, IVM seems to induce mixed cell death in tumor cells, which is also a controversial issue. Therefore, this review summarized the latest findings on the anticancer effect of IVM and discussed the mechanism of the inhibition of tumor proliferation and the way that IVM induces tumor programmed cell death to provide a theoretical basis for the use of IVM as a potential anticancer drug. As the cost of the research and development of new anticancer drugs continues to increase, drug repositioning has become increasingly important. Drug repositioning refers to the development of new drug indications that have been approved for clinical use [28]. For some older drugs that are widely used for their original indications and have clinical data and safety information, drug repositioning allows them to be developed via a cheaper and faster cycle and to be used more effectively in clinical use clinically [29]. Here, we systematically summarized the anticancer effect and mechanism of IVM, which is of great significance for the repositioning of IVM for cancer treatment.
2. The role of IVM in different cancers
2.1. Breast cancer
Breast cancer is a malignant tumor produced by gene mutation in breast epithelial cells caused by multiple carcinogens. The incidence of breast cancer has increased each year, and it has become one of the female malignant tumors with the highest incidence in globally. On average, a new case is diagnosed every 18 seconds worldwide [30,31]. After treatment with IVM, the proliferation of multiple breast cancer cell lines including MCF-7, MDA-MB-231 and MCF-10 was significantly reduced. The mechanism involved the inhibition by IVM of the Akt/mTOR pathway to induce autophagy and p-21-activated kinase 1(PAK1)was the target of IVM for breast cancer [32]. Furthermore, Diao’s study showed that IVM could inhibit the proliferation of the canine breast tumor cell lines CMT7364 and CIPp by blocking the cell cycle without increasing apoptosis, and the mechanism of IVM may be related to the inhibition of the Wnt pathway [33].
Triple-negative breast cancer (TNBC) refers to cancer that is negative for estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2(HER2) and is the most aggressive subtype of breast cancer with the worst prognosis. In addition, there is also no clinically applicable therapeutic drug currently [34,35]. A drug screening study of TNBC showed that IVM could be used as a SIN3-interaction domain (SID) mimic to selectively block the interaction between SID and paired a-helix2. In addition, IVM regulated the expression of the epithelial mesenchymal-transition (EMT) related gene E-cadherin to restore the sensitivity of TNBC cells to tamoxifen, which implies the possibility that IVM functions as an epigenetic regulator in the treatment of cancer[36].
Recent studies have also found that IVM could promote the death of tumor cells by regulating the tumor microenvironment in breast cancer. Under the stimulation of a tumor microenvironment with a high level of adenosine triphosphate (ATP) outside tumor cells, IVM could enhance the P2 × 4/ P2 × 7/Pannexin-1 mediated release of high mobility group box-1 protein (HMGB1) [37]. However, the release of a large amount of HMGB1 into the extracellular environment will promote immune cell-mediated immunogenic death and inflammatory reactions, which will have an inhibitory effect on the growth of tumor cells. Therefore, we believe that the anticancer effect of IVM is not limited to cytotoxicity, but also involves the regulation of the tumor microenvironment. IVM regulates the tumor microenvironment and mediates immunogenic cell death, which may be a new direction for research exploring anticancer mechanisms in the future.
2.2. Digestive system cancer
Gastric cancer is one of the most common malignant tumors worldwide. In the past year, more than one million patients with gastric cancer have been diagnosed worldwide [38]. Nambara’s study showed that IVM could significantly inhibit the proliferation of gastric cancer cells in vivo and in vitro and that the inhibitory effect of IVM depended on the expression of Yes-associated protein 1(YAP1)[39]. The gastric cancer cell lines MKN1 and SH-10-TC have higher YAP1 expression than MKN7 and MKN28 cells, so MKN1 and SH-10-TC cells are sensitive to IVM, while MKN7 and MKN28 are not sensitive to IVM.YAP1 plays an oncogenic role in tumorigenesis, indicating the possibility of the use of IVM as a YAP1 inhibitor for cancer treatment [40].
In a study that screened Wnt pathway inhibitors, IVM inhibited the proliferation of multiple cancers, including the colorectal cancer cell lines CC14, CC36, DLD1, and Ls174 T, and promoted apoptosis by blocking the Wnt pathway [41]. After intervention with IVM, the expression of caspase-3 in DLD1 and Ls174 T cells increased, indicating that IVM has an apoptosis-inducing effect and inhibits the expression of the downstream genes AXIN2, LGR5, and ASCL2 in the Wnt/β-catenin pathway. However, the exact molecular target of IVM that affects the Wnt/β-catenin pathway remains to be explored.
Hepatocellular carcinoma is the fourth leading cause of cancer death worldwide. Approximately 80% of cases of liver cancer are caused by hepatitis B virus (HBV) and hepatitis C virus (HCV) infection [42]. IVM could inhibit the development of hepatocellular carcinoma by blocking YAP1 activity in spontaneous liver cancer Mob1b-/- mice [43].Cholangiocarcinoma is a malignant tumor that originates in the bile duct inside and outside the liver. Intuyod’s experiment found that IVM inhibited the proliferation of KKU214 cholangiocarcinoma cells in a dose- and time-dependent manner [44]. IVM halted the cell cycle in S phase and promoted apoptosis. Surprisingly, gemcitabine-resistant KKU214 cells showed high sensitivity to IVM, which suggested that IVM shows potential for the treatment of tumors that are resistant to conventional chemotherapy drugs.
2.3. Urinary system cancer
Renal cell carcinoma is a fatal malignant tumor of the urinary system derived from renal tubular epithelial cells. Its morbidity has increased by an average of 2% annually worldwide and the clinical treatment effect is not satisfactory [[45], [46], [47]]. Experiments confirmed that IVM could significantly inhibit the proliferation of five renal cell carcinoma cell lines without affecting the proliferation of normal kidney cells, and its mechanism may be related to the induction of mitochondrial dysfunction [48]. IVM could significantly reduce the mitochondrial membrane potential and inhibit mitochondrial respiration and ATP production. The presence of the mitochondrial fuel acetyl-L-carnitine (ALCAR), and the antioxidant N-acetyl-L-cysteine (NAC), could reverse IVM-induced inhibition. In animal experiments, the immunohistochemical results for IVM-treated tumor tissues showed that the expression of the mitochondrial stress marker HEL was significantly increased, and the results were consistent with those of the cell experiments.
Prostate cancer is a malignant tumor derived from prostate epithelial cells, and its morbidity is second only to that of lung cancer among men in Western countries [49]. In Nappi’s experiment, it was found that IVM could enhance the drug activity of the anti-androgen drug enzalutamide in the prostate cancer cell line LNCaP and reverse the resistance of the prostate cancer cell line PC3 to docetaxel [50]. Interestingly, IVM also restored the sensitivity of the triple-negative breast cancer to the anti-estrogen drug tamoxifen [36], which also implies the potential for IVM to be used in endocrine therapy. Moreover, IVM was also found to have a good inhibitory effect on the prostate cancer cell line DU145 [51].
2.4. Hematological cancer
Leukemia is a type of malignant clonal disease caused by abnormal hematopoietic stem cells [52]. In an experiment designed to screen potential drugs for the treatment of leukemia, IVM preferentially killed leukemia cells at low concentrations without affecting normal hematopoietic cells [51]. The mechanism was related to the increase in the influx of chloride ions into the cell by IVM, resulting in hyperpolarization of the plasma membrane and induction of reactive oxygen species (ROS) production. It was also proven that IVM has a synergistic effect with cytarabine and daunorubicin on the treatment of leukemia. Wang’s experiment found that IVM could selectively induce mitochondrial dysfunction and oxidative stress, causing chronic myeloid leukemia K562 cells to undergo increased caspase-dependent apoptosis compared with normal bone marrow cells [53]. It was also confirmed that IVM inhibited tumor growth in a dose-dependent manner, and dasatinib had improved efficacy.
2.5. Reproductive system cancer
Cervical cancer is one of the most common gynecological malignancies, resulting in approximately 530,000 new cases and 270,000 deaths worldwide each year. The majority of cervical cancers are caused by human papillomavirus (HPV) infection [54,55]. IVM has been proven to significantly inhibit the proliferation and migration of HeLa cells and promote apoptosis [56]. After intervention with IVM, the cell cycle of HeLa cells was blocked at the G1/S phase, and the cells showed typical morphological changes related to apoptosis.
Ovarian cancer is a malignant cancer that lacks early clinical symptoms and has a poor therapeutic response. The 5-year survival rate after diagnosis is approximately 47% [27,57]. In a study by Hashimoto, it found that IVM inhibited the proliferation of various ovarian cancer cell lines, and the mechanism was related to the inhibition of PAK1 kinase [58]. In research to screen potential targets for the treatment of ovarian cancer through the use of an shRNA library and a CRISPR/Cas9 library, the oncogene KPNB1 was detected. IVM could block the cell cycle and induce cell apoptosis through a KPNB1-dependent mechanism in ovarian cancer [59]. Interestingly, IVM and paclitaxel have a synergistic effect on ovarian cancer, and combined treatment in in vivo experiments almost completely inhibited tumor growth. Furthermore, according to a report by Zhang, IVM can enhance the efficacy of cisplatin to improve the treatment of epithelial ovarian cancer, and the mechanism is related to the inhibition of the Akt/mTOR pathway [60].
2.6. Brain glioma
Glioma is the most common cerebral tumor and approximately 100,000 people worldwide are diagnosed with glioma every year. Glioblastoma is the deadliest glioma, with a median survival time of only 14-17 months [61,62]. Experiments showed that IVM inhibited the proliferation of human glioblastoma U87 and T98 G cells in a dose-dependent manner and induced apoptosis in a caspase-dependent manner [63]. This was related to the induction of mitochondrial dysfunction and oxidative stress. Moreover, IVM could induce apoptosis of human brain microvascular endothelial cells and significantly inhibit angiogenesis. These results showed that IVM had the potential to resist tumor angiogenesis and tumor metastasis. In another study, IVM inhibited the proliferation of U251 and C6 glioma cells by inhibiting the Akt/mTOR pathway [64].
In gliomas, miR-21 can regulate the Ras/MAPK signaling pathway and enhance its effects on proliferation and invasion [65]. The DDX23 helicase activity affects the expression of miR-12 [66]. IVM could inhibit the DDX23/miR-12 signaling pathway by affecting the activity of DDX23 helicase, thereby inhibiting malignant biological behaviors. This indicated that IVM may be a potential RNA helicase inhibitor and a new agent for of tumor treatment. However, here, we must emphasize that because IVM cannot effectively pass the blood-brain barrier [67], the prospect of the use of IVM in the treatment of gliomas is not optimistic.
2.7. Respiratory system cancer
Nasopharyngeal carcinoma is a malignant tumor derived from epithelial cells of the nasopharyngeal mucosa. The incidence is obviously regional and familial, and Epstein-Barr virus (EBV) infection is closely related [68]. In a study that screened drugs for the treatment of nasopharyngeal cancer, IVM significantly inhibited the development of nasopharyngeal carcinoma in nude mice at doses that were not toxic to normal thymocytes [69]. In addition, IVM also had a cytotoxic effect on a variety of nasopharyngeal cancer cells in vitro, and the mechanism is related to the reduction of PAK1 kinase activity to inhibit the MAPK pathway.
Lung cancer has the highest morbidity and mortality among cancers [70]. Nishio found that IVM could significantly inhibit the proliferation of H1299 lung cancer cells by inhibiting YAP1 activity [43]. Nappi’s experiment also proved that IVM combined with erlotinib to achieved a synergistic killing effect by regulating EGFR activity and in HCC827 lung cancer cells [50]. In addition, IVM could reduce the metastasis of lung cancer cells by inhibiting EMT.
2.8. Melanoma
Melanoma is the most common malignant skin tumor with a high mortality rate. Drugs targeting BRAF mutations such as vemurafenib, dabrafenib and PD-1 monoclonal antibodies, including pembrolizumab and nivolumab have greatly improved the prognosis of melanoma [71,72]. Gallardo treated melanoma cells with IVM and found that it could effectively inhibit melanoma activity [73]. Interestingly, IVM could also show activity against BRAF wild-type melanoma cells, and its combination with dapafinib could significantly increase antitumor activity. Additionally, it has been confirmed that PAK1 is the key target of IVM that mediates its anti-melanoma activity, and IVM can also significantly reduce the lung metastasis of melanoma in animal experiments. Deng found that IVM could activate the nuclear translocation of TFE3 and induce autophagy-dependent cell death by dephosphorylation of TFE3 (Ser321) in SK-MEL-28 melanoma cells [74]. However, NAC reversed the effect of IVM, which indicated that IVM increased TFE3-dependent autophagy through the ROS signaling pathway.
3. IVM-induced programmed cell death in tumor cells and related mechanisms
3.1. Apoptosis
IVM induces different programmed cell death patterns in different tumor cells (Table 1). As shown in Table 1, the main form of IVM induced programmed cell death is apoptosis. Apoptosis is a programmed cell death that is regulated by genes to maintain cell stability. It can be triggered by two activation pathways: the endogenous endoplasmic reticulum stress/mitochondrial pathway and the exogenous death receptor pathway [75,76]. The decrease in the mitochondrial membrane potential and the cytochrome c is released from mitochondria into the cytoplasm was detected after the intervention of IVM in Hela cells [56].Therefore, we infer that IVM induces apoptosis mainly through the mitochondrial pathway. In addition, morphological changed caused by apoptosis, including chromatin condensation, nuclear fragmentation, DNA fragmentation and apoptotic body formation were observed. Finally, IVM changed the balance between apoptosis-related proteins by upregulating the protein Bax and downregulating anti-apoptotic protein Bcl-2, thereby activating caspase-9/-3 to induce apoptosis [48,53,63] (Fig. 2 ).
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