Phytochemicals and bioactive compounds effective against acute myeloid leukemia: A systematic review

Abstract This systematic review identified various bioactive compounds which have the potential to serve as novel drugs or leads against acute myeloid leukemia. Acute myeloid leukemia (AML) is a heterogeneous hematopoietic malignancy that arises from the dysregulation of cell differentiation, proliferation, and cell death. The risk factors associated with the onset of AML include long‐term exposure to radiation and chemicals such as benzene, smoking, genetic disorders, blood disorders, advancement in age, and others. Although novel strategies to manage AML, including a refinement of the conventional chemotherapy regimens, hypomethylating agents, and molecular targeted drugs, have been developed in recent years, resistance and relapse remain the main clinical problems. In this study, three databases, PubMed/MEDLINE, ScienceDirect, and Google Scholar, were systematically searched to identify various bioactive compounds with antileukemic properties. A total of 518 articles were identified, out of which 59 were viewed as eligible for the current report. From the data extracted, over 60 bioactive compounds were identified and divided into five major groups: flavonoids, alkaloids, organosulfur compounds, terpenes, and terpenoids, and other known and emerging bioactive compounds. The mechanism of actions of the analyzed individual bioactive molecules differs remarkably and includes disrupting chromatin structure, upregulating the synthesis of certain DNA repair proteins, inducing cell cycle arrest and apoptosis, and inhibiting/regulating Hsp90 activities, DNA methyltransferase 1, and histone deacetylase 1.


| INTRODUC TI ON
Leukemia is a malignant proliferation of white blood cells (leukocytes). In acute leukemia, the cells produced by the bone marrow are abnormal, dysfunctional, and fail to mature, passing into the circulation as immature white blood cells called "blasts." A percentage of ≥20% blasts in the bone marrow is needed to establish the diagnosis of acute leukemia (Chennamadhavuni et al., 2020). Contrastingly, chronic leukemia is characterized by the proliferation of mature, functional leukocytes, and by a small percentage of blasts in the bone marrow (<20%), typically taking months or years. The risk factors for the development of acute leukemia include exposure to ionizing radiation, benzene, chemotherapy (namely topoisomerase inhibitors and alkylating agents), or viral agents (the Epstein-Barr or the human T-cell leukemia virus), a previous hematological cancer, or the presence of a genetic syndrome (e.g., Down syndrome).
The clinical picture of acute leukemia comprises a conundrum of unspecific symptoms and signs, ranging from fatigue, shortness of breath, fever, recurrent infections, weight loss, bruising, bleeding, and heavy menstrual cycles, to bone pain, hepatomegaly, splenomegaly (or both), and (or) enlarged lymph nodes. To establish a final diagnosis of acute leukemia, the physician often needs to perform a bone marrow biopsy, which guides the patient's further management and the employment of chemotherapy regimens and (or) stem cell transplantation. Several treatment options are reported in Table 1. The prognosis differs based on the type of leukemia studied (Chennamadhavuni et al., 2020).
Acute myeloid (or myelogenous) leukemia (AML) is characterized by the abnormal proliferation of blasts of myeloid lineage and has emerged as the most common form of leukemia in the adult population, possessing a bimodal distribution in terms of interested age groups. In 2015, AML affected at least 1 million individuals and caused 147,000 deaths worldwide (Vos et al., 2016). It occurs when a pluripotent hematopoietic stem cell undergoes a malignant transformation and begins to proliferate uncontrollably, giving rise to myeloblasts. Myeloblasts are abnormal white blood cells (Chennamadhavuni et al., 2020), which are immature and poorly differentiated, that are exposed to clonal expansion and proliferation, replacing the normal, healthy cells of the bone marrow. In AML, the bone marrow mostly compromises immature monocytes or granulocytes which in general are positive on the immunohistochemistry tests for markers of myeloid lineage: CD13, CD14, CD15, CD33, CD36, CD61, and CD64 (Chennamadhavuni et al., 2020).
Upon AML diagnosis, other factors are usually considered, such as AML subtypes, age, and the patient's medical history before treatment is scheduled. Usually, the main treatment option for AML is chemotherapy or the use of targeted drugs based on the outcome of medical tests. Some drugs in clinical usage are vadastuximab talirine, gemtuzumab ozogamicin, sorafenib, midostaurin, lestaurtinib, quizartinib, crenolanib, gilteritinib, ivosidenib, enasidenib, venetoclax, guadecitabine, and pracinostat (Beeharry et al., 2019;Bisaillon et al., 2020;Cortes et al., 2018;Galanis et al., 2014;Georgoulia et al., 2020;Ha et al., 2020;Ivosidenib, 2018;Kantarjian et al., 2017;Knapper et al., 2017;Lancet et al., 2018;Muñoz & Coveñas, 2020;Nguyen et al., 2019;Novotny-Diermayr et al., 2012;Ohanian et al., 2018;Sharon et al., 2019;Somers et al., 2020;Stein et al., 2017Stein et al., , 2018Stone et al., 2017;Swaminathan & Cortes, 2023;Wang, Hu, et al., 2020;Weisberg et al., 2020;Zhao et al., 2019; Table 1). Besides drugs, stem cell transplant can also be recommended for treatment. Other conventional forms of cancer treatments such as surgery and radiation therapy are rarely recommended for AML. However, despite the availability of these drugs, the overall survival rate of AML of 5 years is 27.4% according to the National Cancer Institute. This is partly due to drug resistance and increased risk of subsequent cancers and infections. Considering that the current treatment protocols are far from reaching the intended goal, there is an ongoing quest to identify new molecules which could potentially be developed into novel pharmacological agents to battle AML.
Medicinal plants contain chemical compounds called phytochemicals that are good for human health and for the prevention of diseases. The term "phytochemical" is often used to describe chemical substances like antioxidants that may have biological significance but are not recognized as essential nutrients. Some are responsible for color while others are responsible for organoleptic properties in plants. Some phytochemicals have the ability to influence conditions including cancer, stroke, and metabolic syndrome. Thus, this study is aimed at identifying natural bioactive compounds which have been reported to be active against AML.

| Search strategy
The PubMed/MEDLINE, ScienceDirect, and Google Scholar databases/search engines were searched using the following key terms: ("bioactive compounds" OR "natural compounds" OR "phytochemicals") AND ("acute myeloid leukemia" OR "AML").

| Inclusion criteria
To be eligible for inclusion, the selected articles had to meet the following inclusion criteria. To begin, the article must have used generally recognized research models (human cell lines and laboratory K E Y W O R D S acute myeloid leukemia, drug discovery, leukemia, natural products, secondary metabolites TA B L E 1 Selective drugs against acute myeloid leukemia.  Somers et al. (2020) animals) and reported on the effects of the bioactive compound(s) against AML. Second, the article must have been published in English.

| Exclusion criteria
We excluded studies that investigated other types of cancers.
Duplicate articles from different databases were screened and only one was retained. Two authors evaluated the title and abstract and references of each article.

| Results
A total of 518 articles were identified through database search-

| Discussion
Based on the data obtained from this study (Table 2), we identified a myriad of promising bioactive compounds that have the potential to be used as novel drugs or serve as leads for the discovery and development of new pharmacological agents to target AML cells.
Although the majority of the analyzed research consisted of cell models of AML (leukemic cells, in vitro), the effort is commendable and might represent a leading step for future drug discovery studies involving in vivo AML models. From the extracted data, we found that the majority of the compounds belong to one of the following compound classes: polyphenols (mainly flavonoids), alkaloids, organosulfur compounds, and terpenoids.
The cytotoxicity of the flavagline family on AML cells, which occurs via several mechanisms, has been studied and established (Menezes et al., 2016;Saraei et al., 2019). Epigallocatechin-3-gallate has been reported to be effective against AML. The significant reduction in the xenograft capability of rocaglamide-treated AML cells shows that rocaglamide targets leukemia stem cells (LSCs) and has an insignificant influence on hematopoietic stem cells (HSCs).

Chondrodendron platyphyllum
Increased the apoptotic cell number.

Ecdysteroid hormone Bark of Dacrycarpus imbricatus
Induced dose-dependent reduction in the cell proliferation activity of the OCI leukemia cell line tested.

Indirubin
Another study by Ye et al. (2016) showed that the novel amaryllidaceae alkaloid named N-amaryllidaceae chloride (NMHC) extracted from Zaphyranthes candida possesses an enhanced ability to inhibit AML in vivo. The authors hypothesized that this alkaloid caused an aberrant activation of the Notch signaling pathway by docking into the hydrophobic cavity to promote the NOTCH1 proteolytic cleavage via the NOTCH1-negative regulatory region (Ye et al., 2016).
On the same hand, Huang, Pan, et al. (2019) reported that a novel Bruton's tyrosine kinase (BTK) inhibitor named abivertinib (another alkaloid) possesses antileukemia properties and synergistic effects against AML cells along with homoharringtonine. In a different study by Li, Yan, et al. (2018), it was stated that a natural alkaloid named nitidine chloride possesses an enhanced ability to arrest the cell cycle and induce apoptosis in AML cells. The study revealed that nitidine chloride possesses a dose-and time-dependent growth inhibition activity against AML cells after 48 h of treatment by downregulating the cyclins B1, BCL-2, and cyclin-dependent kinase-1 (CDK-1; Li, Yan, et al., 2018). Nitidine also upregulates the p27-and bcl-2-like protein 4 (Bax) while inactivating the poly-(ADP ribose) polymerase (PARP; Li, Yan, et al., 2018). It also activates caspase-3 as well as inhibits the phosphorylation of protein kinase B (AKT) and extracellular signal-regulated kinase (ERK; Li, Yan, et al., 2018). It is evident from all these studies that alkaloids exhibit an enhanced potential to inhibit the growth and development of AML cells.
Organosulfur compounds (OSCs) are sulfur-containing organic compounds ( Figure 4) found abundantly in nature-plants and animals. Sulfur-containing compounds are essential for human life, for example, amino acids like cysteine and methionine contain sulfur in their chemical structure. Organosulfur compounds extracted from allium species (chives, garlic, leek, onion, scallions, and shallots) showed antiproliferative and apoptotic effects in human cell lines (U97, NB4, HL-60, and MonoMac-6; Auger et al., 2008). OSCs from garlic have been the most studied in the management of AML.
Garlic OSCs can be classified as thiosulfinates and sulfides. Alliin, a (+)S-allyl-L-cysteine sulfoxide, is present in the intact garlic clove and is converted into the corresponding thiosulfinate (Allicin) by the enzyme allinase when the garlic clove is cut, crushed, chopped, or chewed. Allicin is unstable, it rapidly degrades and rearranges to stable derivatives. The anti-AML activity is related to the disulfide functional group present in these compounds (Kaschula et al., 2011).
Ajoene in combination with conventional chemotherapeutic agents has shown promising effects in AML therapy (Hassan, 2004).
Organosulfur compounds such as diallyl sulfide ( (Wu et al., 2005). DADS promoted the apoptosis of HL-60 cells via an increased expression of the GTPase Ras-related C3 botulinum toxin substrate 2 (Rac2). Furthermore, research has shown that Rac2, NADPH oxidase, and ROS have important roles in the apoptosis induced by DADS in HL-60 cells . DADS-induced apoptosis in human leukemia HL-60 cells is triggered by caspase-3 activation, poly(adenosine diphosphate-ribose) polymerase (PARP) degradation, and DNA fragmentation (Kwon et al., 2002). Moreover, the DADS-mediated apoptosis in HL-60 cells also involves the activation of JNK via ROS generation (Novotny-Diermayr et al., 2012). Other evidence suggests that ERK signaling pathway inhibition and activation of the p38 signaling pathway in DADS leads to apoptosis (Tan et al., 2008).

The induction of apoptosis in human leukemia K562 cells by DADS
involves the activation of the Fas/FasL pathway which is associated with an increased expression of the Fas gene and caspase-8 and a decreased expression of FasL and Bag-1 genes (Lin et al., 2007;Xiao et al., 2011;Yin & Peng, 2011). DATS inhibited the growth of U937 leukemia cells by apoptosis induction in a concentration-and timedependent manner. DATS-induced apoptosis was associated with the downregulation of the protein levels of Bcl-2, XIAP, and cIAP-1, the cleavage of Bid proteins, the activation of caspases, and the collapse of the mitochondrial membrane potential. Furthermore, the data showed that DATS increased the generation of intracellular ROS, which was attenuated by pretreatment with N-acetyl-Lcysteine (NAC), an antioxidant that acts as a ROS scavenger (Agassi et al., 2020;Choi & Park, 2012). Furthermore, NAC administration resulted in a major inhibition of the DATS-induced apoptosis by inhibiting caspase activation. Apoptosis induction in HL-60 cells treated with moderate doses of DADS may be associated with the expression of DJ-1 (also known as Parkinsonism-associated deglycase-7, PARK-7) in the mitochondria (Li, Tang, et al., 2016). Moreover, the aforementioned effect is extrapolated to the activation of caspase-9, an initiator caspase of the mitochondrial-mediated intrinsic pathway, and caspase-3, accompanied by the proteolytic degradation of poly(ADP-ribose)-polymerase. In one of the investigations, the DADS lead to apoptosis and autophagy via mTOR (mammalian target of rapamycin) activation in K562 and NB4 myeloid leukemia cell lines (Suangtamai & Tanyong, 2016). In several cell lines of leukemia, for example, U937, K562, and Jurkat, since they lack a wild-type p53, NF-κB-mediated pathways might play another putative role in the apoptosis mediated by the DADS treatment. DADS induced reversible G2/M arrest via an increased nuclear translocation of NF-κB and its specific binding to the p21 promoter (Tiong & Wei, 2019).
In animal models, terpenoids have been shown to possess chemopreventive properties as well as in the treatment of cancer (Haider et al., 2014;Tiong & Wei, 2019). The plant-derived molecule, helenalin (sesquiterpene lactone) has been investigated against doxorubicinresistant AML HL-60 cells. It was found to induce apoptosis, cell inhibition, cell migration, and Akt/PI3K/mTOR signaling pathway inhibition . Helenalin strongly inhibited HL-60 cell growth and displayed an IC 50 of 23.5 μM. It was noted that helenalin's anticancer effects are due to the activation of mitochondrialinduced apoptosis which has also been associated with an increase  Oridonin may have the capacity to suppress human AML cell invasion and metastasis and is likely to be effective in inhibiting the development of drug-resistant AML cells. Combination treatment with oridonin and cisplatin has become a useful way of treating human AML cells resistant to cisplatin. Both compounds exerted synergistic antitumor effects, and cisplatin tolerance in human AML cells was essentially reversed. Meanwhile, under these laboratory conditions, opioid toxicity had to be minimized (Zhang, Wang, et al., 2017).

| CON CLUS ION
Acute myeloid leukemia is one of the most common kinds of leukemia, resulting in significant human mortality in both children and adults. It is a type of hematological malignancy characterized by dysregulation of cell differentiation, proliferation, and death induced by epigenetic and genetic changes in hematopoietic progenitor or stem cells. Despite the development of innovative treatments in recent years, such as modifications in conventional chemotherapies, hypomethylating medicines, and molecular targeted medications, resistance and relapse remain the key clinical concerns of AML care.
As a result, there is an urgent need for ongoing research on better alternatives. This study has identified various promising bioactive compounds, many of which pertain to the class of flavonoids and polyphenols. Other important groups are alkaloids, organosulfur compounds and terpenoids. All of the identified compounds showed promising effects on AML cells.  (Alves et al., 2018;Folmer et al., 2010;Schwartsmann et al., 2001;Sithranga Boopathy & Kathiresan, 2010;Wali et al., 2019;Wang, Sorolla, et al., 2020).