Unlocking nature's potential: Soursop in the battle against resistant acute myeloid leukemia

Abstract

Acute Myeloid Leukemia (AML) represents the predominant form of blood cancer in adults and ranks as the second most prevalent in pediatric populations. The disease is heterogeneous, characterized by proliferation and self-renewal, originating in the bone marrow and potentially metastasizing to various body regions. AML arises from a hematopoietic abnormality characterized by the accumulation of myeloblasts, which are immature myeloid cells. Genetic disorders, a medical history of bone marrow disorders, and chemoradiation can lead to genetic mutations that impact hematopoiesis. Leukemic stem cells (LSC) exhibit biological similarities to normal hematopoietic stem cells (HSC), yet they lose the capacity to differentiate progenitor blast cells into mature cells. As a result, progenitor blast cells remain inactive in the G₀ phase of the cell cycle where they proliferate into myeloblasts that are ineffective at differentiation. Standard treatment for AML involves chemotherapy, primarily utilizing cytarabine and daunorubicin. This approach demonstrates initially high remission rates; however, it frequently leads to relapses that are resistant to the drugs. Relapse and resistance are attributed to the survival of stem-cell-like progenitor cells within protective bone marrow niches. This leads to a long-term survival rate of 10–15 % for patients aged sixty and older, and a survival rate of less than 35–45 % for patients under sixty. Natural agents demonstrate potential as therapeutic agents for AML, characterized by low toxicity to normal cells and high toxicity to cancer cells. The plant soursop (Annona muricata) is of particular interest due to its potential application as an anticancer agent. Studies indicate that soursop exhibits cytotoxic effects on leukemic cancer cells through the induction of apoptosis and the inhibition of proliferation. Future research will investigate the mechanism of action and effectiveness of soursop in eliminating AML cells.

Highlights

• •Disease Heterogeneity and Challenges in Treatment: AML is a heterogeneous blood cancer characterized by the proliferation of immature myeloid cells, with standard chemotherapy offering high initial remission rates but leading to frequent relapses due to resistant leukemic stem cells in protective bone marrow niches.
• •Potential of Natural Agents: Soursop (Annona muricata) shows promise as a low-toxicity therapeutic agent for AML, demonstrating cytotoxic effects on leukemic cells by inducing apoptosis and inhibiting proliferation.
• •Future Research Directions: Investigations are required to elucidate the mechanisms of action of soursop and its effectiveness in targeting chemoresistant AML cells, paving the way for alternative or complementary treatments.

1. Introduction

Acute Myeloid Leukemia (AML) is a hematological malignancy originating in the bone marrow, with the capacity for metastasis to other bodily regions. Metastasis commonly occurs in the lymph nodes, liver, spleen, and central nervous system [1]. AML occurs due to genetic abnormalities in hematopoietic stem and progenitor cells, leading to a disruption in normal hematopoietic differentiation [2,3]. This disruption results in the accumulation of myeloblasts and a deficiency of mature hematopoietic cells in both the bone marrow and peripheral blood.

AML accounts for approximately 1.3 % of all cancer cases, constitutes 80 % of adult leukemia cases, and is responsible for around 62 % of deaths caused by leukemia [4,5]. The incidence of new AML cases in the United States is reported at 4.2 per 100,000 population, exceeding 20,000 cases annually. The incidence ratio of cases between males and females is 5:3, indicating a predominance in males [5]. The prevalence of AML is higher in non-Hispanic White populations compared to Hispanic, non-Hispanic Black, and Asian American groups. Furthermore, non-Hispanic White populations typically exhibit a higher age at the onset of AML compared to the other populations mentioned. Although prognosis is generally poorer for older populations due to comorbidities and a more severe response to treatment, non-Hispanic White populations exhibit a higher overall survival rate compared to Hispanic and non-Hispanic Black AML populations. Consequently, although diagnosed at an earlier age, Hispanic and non-Hispanic Black populations exhibit elevated mortality rates [6].

Patients with AML may exhibit symptoms including fatigue, weight loss, fever, anemia, easy bruising, bone pain, recurrent infections, headaches, diaphoresis, and bleeding. Physical examination commonly reveals infection, fever, and hemorrhage. Furthermore, hepatosplenomegaly, splenomegaly, and lymphadenopathy may also manifest. Cytopenia and the presence of circulating myeloblasts are frequently observed in blood examinations. Auer rods in leukemic myeloblasts serve as a diagnostic indicator of AML, although their presence is not universal across all cases [4,5].

Diagnosis criteria established by the 5th edition of the World Health Organization (WHO) necessitate the presence of either the BCR:ABL1 fusion or CEBPA mutation with a blast count of 20 % or greater, an AML-defining genetic abnormality in isolation (excluding the BCR:ABL1 fusion or CEBPA mutation, which requires a specific blast count), or a blast count of 20 % or greater accompanied by either a myelodysplastic syndrome-defining genetic abnormality and/or a history of myelodysplastic syndrome/myeloproliferative neoplasm. The International Consensus Classification (ICC) mandates a blast count of ≥20 % in conjunction with the BCR: ABL1 fusion or CEBPA mutation. In contrast to the WHO, it stipulates a blast count of ≥10 % in the bone marrow or peripheral blood when an AML-defining mutation is present, excluding the BCR:ABL1 fusion and CEBPA mutation [7,8]. Frequent mutations in AML are NPMI (35 %), DNMT3A (20 %), RUNX1 (10–15 %), CEBPA (10 %), TP53 (10 %), and GATA2 (5 %) [9].

2. Cancer pathways and its role in survival of AML cells

Multiple signaling pathways contribute to the survival and proliferation of AML cells. These include the Janus Kinase/Signal Transducers and Activators of Transcription (JAK/STAT), the pro-inflammatory NF-κB, the PI3K/AKT/mTOR, the PPARγ, the Hedgehog, the Notch, the Wnt/β-catenin, the EGFR, and the TGFβ/SMAD pathway [10]. This review will specifically focus on the JAK/STAT pathway, a significant pathway in the pathogenesis of AML. This pathway regulates various homeostatic and developmental processes, such as hematopoiesis, through the activation of downstream targets that influence cellular proliferation, differentiation, migration, apoptosis, and survival [11]. The JAK/STAT pathway facilitates the entry of extracellular signals into the nucleus, regulating gene expression through the binding of ligands to transmembrane receptors. The binding of ligands, including cytokines and growth factors, induces a conformational change that activates JAK. This activation facilitates the close proximity of intracellular JAKs, enabling their mutual phosphorylation. Phosphorylation of tyrosine residues in the intercellular region of the receptor facilitates the docking of STAT proteins, leading to their activation through phosphorylation. Activated STATs form dimers that translocate to the nucleus to regulate transcription (Fig. 1). STATs play a crucial role in regulating hematopoiesis and influencing the fate of hematopoietic stem cells (HSCs) [12].

Fig. 1.

Schematic representation of the JAK/STAT signaling pathway and its role in oncogenesis. Upon cytokine or growth factor binding to receptors, Janus kinases (JAKs) become activated and phosphorylate the receptor, creating docking sites for STAT proteins. STATs are then phosphorylated, dimerized, and translocate to the nucleus, where they regulate the transcription of genes involved in proliferation, survival, angiogenesis, and immune evasion. Dysregulation of this pathway, via constitutive activation or mutations in JAKs/STATs or upstream receptors, has been implicated in the development and progression of various malignancies. Image was produced in Biorender.com.

STAT5 and STAT3 serve as significant regulators of HSCs. STAT5 is involved in the self-renewal of HSCs, along with their proliferation and survival [11]. A study indicated that a deficiency of STAT5 in HSCs resulted in an increased rate of apoptosis in these cells. Consequently, STAT5 is crucial for safeguarding HSCs against apoptosis. This process involves the activation of BCL-XL transcription, leading to the production of BCL-XL, alongside the upregulation of MCL-1, both of which function as anti-apoptotic proteins [13,14]. Furthermore, the deletion of STAT5 has been demonstrated to influence hematopoiesis, leading to defects in myeloid and lymphoid development [15]. STAT3 is crucial for the formation of mature cells through hematopoiesis, as well as for the survival and proliferation of HSCs. STAT3 is crucial for cell cycle progression, as it upregulates the transcription of positive regulators of cyclin-dependent kinases while downregulating negative regulators [14]. STAT3 also contributes to the suppression of inflammation in mature myeloid cells by inhibiting NF-κB-mediated cytokine production [16].

In many patients with AML, elevated levels of phosphorylated JAK2 are observed in the bone marrow [17]. Moreover, constitutive activation of STAT3 and STAT5 is observed in a significant patient cohort, with persistent STAT3 activation associated with poorer disease outcomes [12]. The upregulation of JAK2, STAT3, and STAT5 facilitates oncogenesis in AML. JAK2 inhibition in AML cells led to apoptosis and reduced growth. This inhibition is proposed to induce apoptosis in dormant leukemia stem cells by targeting CD38+/CD38-cells. The inhibition of the JAK/STAT activator IL-27 led to apoptosis and cell cycle arrest in myeloid cells. Inhibition of JAK2-mediated phosphorylation of STAT3 and STAT5 led to apoptosis and reduced cell growth in AML cell lines [17]. The studies indicate that the upregulation of JAK2 in cancer cells facilitates tumor survival and proliferation. Studies indicate that targeting STAT activity leads to induced apoptosis and reduced proliferation in cancer cells. The overexpression or activation of STAT3 in cancer cells facilitates cell cycle progression, enhances ATP production adaptation in hypoxic tumor conditions, stimulates angiogenesis via VEGF expression induction, and encourages tumor invasion and metastasis through the basement membrane [14]. Therefore, the JAK/STAT pathway is significant not only in normal hematopoiesis but also in the pathogenesis of AML cells. For more comprehensive pathway insights, readers are referred to recent in-depth reviews [18,19].

3. Unraveling mechanisms of drug resistance

The emergence of resistance in AML cells to treatment remains a persistent issue. Resistance arises from factors including bone marrow, tumor microenvironment, chemotherapy, and genetic mutations.

The bone marrow microenvironment (BMM) influences HSCs and hematopoietic progenitor cells (HPCs), impacting their proliferation, differentiation, dormancy, survival, and migration. The BMM in cancer experiences alterations that facilitate the survival and proliferation of leukemic cells. Patients with AML exhibit elevated angiogenesis and vascularization in the bone marrow, attributed to increased levels of VEGF. An increase in angiogenesis leads to enhanced blood supply to leukemic cells, providing essential nutrients and oxygen that facilitate their growth and survival. High expressions of VEGF in AML not only enhance angiogenesis but also lead to a decrease in apoptosis among leukemic cells. Elevated levels of angiogenic growth factors are associated with a poorer response to initial treatment. CXCR4 has been demonstrated to protect myeloblasts in the bone marrow by facilitating pseudo-emperipolesis, enabling the migration of leukemic cells to supportive niches. This process allows the cells to maintain a quiescent state and evade chemotherapy-induced apoptosis. Leukemic initiating cells (LICs) reside within these niches, fostering an environment conducive to their survival [20].

The tumor microenvironment facilitates angiogenesis, metastasis, survival, and proliferation of cancer cells. Tumor-associated macrophages (TAMs) suppress immune-mediated apoptosis of tumor cells and upregulate STAT3 activation, thereby promoting tumorigenesis. TAMS, along with natural killer cells (NKs), contribute to the establishment of an acidic and hypoxic environment for tumor cells [20]. In hypoxic conditions, tumor cells transition from mitochondrial oxidative phosphorylation to glycolysis for energy production. The activation of STAT3 leads to enhanced expression of genes associated with glycolysis, thereby facilitating the tumor cell's adaptation to its new environment [14].

The leukemic stem cells (LSCs) exhibit primary and secondary chemotherapy resistance mechanisms that, alongside the microenvironment, contribute to AML relapse. Primary resistance refers to intrinsic mechanisms present in LSCs, whereas secondary resistance pertains to resistance induced by chemotherapy. LSCs can enter a state of dormancy or reversible nonproliferation through both primary and secondary mechanisms, which facilitates evasion of chemotherapy. Cell-cycle specific agents target proliferating LSCs instead of quiescent ones, which contributes to survival and the recurrence of AML. The activation of specific signaling pathways, including Wnt, PI3K/AKT, Hedgehog, and NOTCH, contributes to the maintenance of quiescence in LSCs. Therefore, therapies aimed at signaling pathways that induce quiescence and subsequently activate dormant LSCs into the cell cycle present a potential strategy for eliminating these dormant LSCs. LSCs inherently contain ABC transporters that contribute to chemotherapy resistance, leading to poor prognosis. The transporters facilitate the efflux of cytotoxic drugs from the tumor cell. Certain ABC transporters, including P-glycoprotein, contribute to chemotherapy resistance across multiple drugs. Normal HSCs exhibit elevated levels of ABC transporter expression. Targeting these transporters may reduce chemoresistance in LSCs and disrupt normal hematopoiesis. LSCs can evade apoptosis through the upregulation of anti-apoptotic proteins, specifically BCL-2 and MCL-1. Upregulation correlates with chemotherapy resistance and unfavorable prognosis. In contrast to normal HSCs, LSCs are unable to inhibit DNA damage repair mechanisms after chemotherapy-induced DNA damage. This leads to the repair of DNA damage induced by chemotherapy agents, thereby contributing to chemotherapy resistance [21].

Certain genetic mutations can increase a patient's susceptibility to drug resistance and relapse. Risk groups are classified according to the type of genetic mutation as favorable, intermediate, or adverse. NPM1 mutations occur in roughly 25–30 % of cases and are associated with a favorable prognosis due to their sensitivity to chemotherapy. When this mutation occurs alongside a FLT3-ITD mutation, the prognosis is classified as intermediate due to the increased risk of relapse associated with FLT3-ITD mutations. RUNX1 mutations are associated with a poor prognosis. These mutations exhibit chemoresistance to standard induction therapies and are linked to trisomy 13 and 21 [5]. Additional prevalent mutations, including IDH and DNMT3A, are associated with a negative prognosis [4,[22], [23], [24]]. Understanding the impact of specific genetic mutations on tumor cell properties and their microenvironments is essential for targeting mechanisms that contribute to chemoresistance and relapse.

4. Limitations of treatment and the argument for natural agents

The standard approach for AML generally consists of two phases of chemotherapy: induction therapy followed by post-remission therapy, also known as consolidation therapy [25]. Induction therapy is designed to eradicate active leukemia cells and attain remission, whereas post-remission therapy focuses on addressing residual cells to avert relapse. The treatment strategy is contingent upon the patient's age, overall health, and specific genetic mutations. Intensive regimens, such as the 7 + 3 protocol (cytarabine combined with an anthracycline), are typically administered to younger, fit patients, frequently incorporating additional agents like midostaurin or gemtuzumab. Patients who are older or have lower fitness levels generally receive low-intensity treatments, including low-dose cytarabine or hypomethylating agents such as decitabine and azacitidine, which may be used in conjunction with targeted therapies like venetoclax [26].

Intrathecal chemotherapy or radiation therapy may be employed in instances where acute myeloid leukemia (AML) impacts the central nervous system. Stem cell transplantation can occur after remission or serve as a consolidation strategy in high-risk scenarios; however, it is associated with considerable risks and complications, especially among older individuals. Supportive care, encompassing transfusions and antibiotics, are crucial during treatment because of myelosuppression and heightened risk of infection. The statistics indicate both the aggressiveness of AML and the toxicity and limitations associated with current therapies [27]. Table 1 presents a comprehensive overview of the toxicities associated with treatment.

Table 1.

Current chemotherapeutic agents used in AML treatment, their targeted signaling pathways, and associated toxicities.

Chemotherapeutic Agents	Activated Signaling Pathways	Toxicity	References
Cytarabine	Activates Chk1 → S-phase checkpoint → cell cycle arrest; Induces apoptosis in S phase cells; Inhibits DNA polymerase	Cerebellar: gait/motor coordination disorders, ataxia, dysmetria; Gastrointestinal: anorexia, diarrhea, hemorrhage, ulceration; Hematologic: Myelosuppression; Cardiovascular: pericarditis, cardiac tamponade, pericardial effusion; Respiratory: dyspnea, hypoxia, pulmonary infiltrates; Ocular: photophobia, keratitis, conjunctivitis	[[28], [29], [30], [31], [32], [33]]
Anthracyclines: Daunorubicin, Idarubicin	Inhibits topoisomerase II; Intercalates in DNA; Activates p53 → activates PUMA and NOXA → inhibits Bcl-2 → activates BAX/BAK→ release of cytochrome c, SMAC, and AIF; Activates p53 → activates AMPK → autophagy; ROS production; Activates caspase 3/7; Activates NF-kB Activates ERK1/2	Cardiovascular: cardiomyopathy	[[34], [35], [36]]
Cladribine	Induces apoptosis of B and T lymphocytes Inhibits DNA synthesis Inhibits cell proliferation Induces phase G1 arrest Induces apoptosis → decrease c-FLIPʟ expression, increase DR4 and cleaved caspase8 expression; Upregulate BAX expression; Downregulate Mcl-1 and Bcl-2 expression	Hematologic: myelosuppression; Immunologic: infection	[[37], [38], [39]]
Fludarabine	DNA synthesis inhibitor → inhibits ribonucleotide reductase, DNA primase, and DNA polymerase alpha; Decreases expression of p27kip; Inhibits STAT1 phosphorylation	Hematologic: myelosuppression, lymphocytopenia; Respiratory: respiratory tract infections; Gastrointestinal: nausea, vomiting Hepatic: Elevated liver enzymes; Neurologic: encephalopathy, coma, death; Ocular: vision loss	[40,41]
Mitoxantrone	Inhibits topoisomerase II	Hematologic: myelosuppression; Gastrointestinal: nausea, vomiting, mucositis, diarrhea; Cardiovascular: cardiomyopathy; Immunologic: alopecia; Hepatic: elevated liver enzymes	[42,43]
Etoposide	Inhibits topoisomerase II	Hematologic: myelosuppression; Gastrointestinal: nausea, vomiting mucositis; Immunologic: alopecia	[44,45]
Hydroxyurea	Inhibits ribonucleotide reductase → DNA damage Upregulated during S phase of DNA synthesis	Hematologic: myelosuppression, anemia, macrocytosis, leukemic transformation, cutaneous carcinoma; Gastrointestinal: gastritis, mucositis, ulcer; Hepatic: elevated liver enzymes, hepatotoxicity; Pulmonary: interstitial pneumonitis, fibrosis, respiratory failure; Dermatologic: ulcers, erythema, skin infiltration, gangrene; Reproductive: decreased fertility males, pregnancy category D; Neurologic: dizziness, headaches, disorientation, hallucinations, seizures	[46,47]
Corticosteroids: Prednisone, Dexamethasone	Suppresses of inflammatory pathways: toll-like receptor signaling and NF-κB pathway; Reduces eicosanoid and prostaglandin production; Inhibits expression of pro-inflammatory enzymes: IL-1ɑ, IL-1β, IL-2, IL-6, IL-12, IFN-γ, TNF, GM CSF Inhibits expression of E-selectin, VCAM-1, ICAM-1; Decreases secretion of CXCL8 and CCL2 (chemoattractants and chemokines); Decreases secretion of CD44 and integrins (leukocyte adhesion molecules); Impairs T lymphocyte activation	Endocrine: hyperglycemia, Cushing syndrome, adrenal insufficiency; Immunologic Infections; Gastrointestinal: gastritis, ulcer, bleeding, pancreatitis, perforation, hepatic steatosis; Cardiovascular: hypertension, fluid retention, arrhythmias, premature atherosclerosis; Dermatologic: ecchymosis, skin thinning/atrophy, acne, mild hirsutism, facial erythema, stria, impaired wound healing, hair thinning, perioral dermatitis; Ophthalmologic: cataracts, glaucoma; Psychiatric: psychosis, insomnia, akathisia, mild euphoria, anxiety, depression, aggression	[48,49]
Methotrexate	Inhibits dihydrofolate reductase → depletes NADPH → increases oxidative stress	Hematologic: Myelosuppression; Pulmonary: toxicity; Immunologic: Infections; Hepatic: Reversible hepatitis, hyperbilirubinemia; Dermatologic: dermatitis	[50,51]
6-Mercaptopurine (6-MP)	Competitor of hypoxanthine and guanine; Inhibits conversion of IMP to xanthylic acid; Inhibits conversion of IMP to AMP; Incorporates into RNA and DNA	Dermatologic: rash; General: flu-like symptoms Hematologic: myelosuppression; Hepatic: hepatotoxicity; Gastrointestinal: nausea, vomiting, pancreatitis; Nephrotoxicity: acute kidney injury following tumor lysis syndrome, Fanconi syndrome	[52,53]
Azacitidine	Noncompetitive inhibitor of DNA methyltransferase; Direct cytotoxicity to cancer cells	Hematologic: myelosuppression; Immunologic: infection; Gastrointestinal: nausea, vomiting, constipation, diarrhea; Pulmonary: pneumonia, upper respiratory tract infections, pneumonitis; Dermatologic: injection site reaction, necrotizing fasciitis, pyoderma gangrenosum, acute febrile neutrophilic dermatosis, panniculitis; General: fatigue	[33,54]
Decitabine	Inhibits methyltransferase; Induces replication-dependent DNA hypomethylation; High doses: arrests DNA synthesis and results in cytotoxicity	Hematologic: myelosuppression; Dermatologic: rash, dry skin, neutrophilic eccrine hidradenitis; Immunologic: infection; Gastrointestinal: nausea, vomiting, constipation; Cardiovascular: acute myocarditis	[33,55]
Glasdegib	Inhibits hedgehog pathway	Neurologic Dysgeusia; Musculoskeletal: Muscle spasms; Cardiovascular: QT interval prolongation	[56,57]
Venetoclax	Inhibits BCL-2	Gastrointestinal: diarrhea, nausea, vomiting, constipation; Hematologic: neutropenia, anemia, thrombocytopenia; General: fatigue, pyrexia, peripheral edema, hypocalcemia, abdominal pain; Respiratory: upper respiratory tract infection, cough, pneumonia, dyspnea; Neurologic: headache, dizziness; Nephrotic: hyperkalemia, hyperphosphatemia; Musculoskeletal: back pain	[58,59]

Considering these challenges, there is an increasing focus on investigating natural agents as supplementary or alternative options in the treatment of AML. Natural products frequently exhibit reduced systemic toxicity, engage multiple mechanisms of action, and demonstrate improved tolerability, positioning them as favorable options for long-term or maintenance strategies [60,61]. Matrine is a natural derivative that demonstrates anti-tumor effects on AML. Matrine is an alkaloid extracted from Sophora species, including Sophora flavescens and Sophoraalopecuroides, among others [62]. Research indicates that matrine induces autophagy and apoptosis in AML cancer cells by inhibiting the PI3K/AKT/mTOR and JAK/STAT3 pathways [63,64]. Matrine was found to inhibit the proliferation of AML cells and the expression of pro-inflammatory cytokines [63]. Parthenolideserves as another example of a natural agent exhibiting anti-cancer properties. Parthenolide is found in the plant known as feverfew, scientifically classified as Tanacetum parthenium. Parthenolide promotes apoptosis in both AML stem cell and progenitor cell populations [60]. Parthenolide exhibited lower toxicity to healthy normal cells compared to cytarabine, while demonstrating increased toxicity to AML cells. Further research on enhancing the bioavailability of parthenolide indicates that this plant may serve as a promising agent in AML chemotherapy [60]. Numerous natural products demonstrate significant potential in the treatment of AML. This review specifically examines soursop (Annona muricata) and its demonstrated anticancer activity across various malignancies, as summarized in Table 2. This underscores the potential of natural compounds in enhancing safer and more effective treatment options for AML.

Table 2.

The effects of soursop in a variety of cancers and the pathways affected.

Cancer Type	Effects of Soursop	Pathways Affected by Soursop	References
Breast	Reduction of tumors Cell proliferation inhibition	Caspase-3 activation; Reactive oxygen species (ROS) activation	[65,66]
Colorectal	Regression of tumors	Caspase-3 activation; intrinsic apoptosis activation	[65,67,68]
Lung	Regression of tumors; inhibition of cancer marker carcinoembryonic antigen (CEA); decreased lipid peroxidation; increased levels of superoxide dismutase (SOD), glutathione (GSH), and catalase (CAT)	Upregulation of Bax, and downregulation of Bcl-2; cell cycle arrest; inhibition of NF-κB signaling	[65,67,68]
Hematologic	Reduction of tumors; inhibiting formation of new cancer cells	Cell cycle arrest in G0/G1 phase; upregulation of reactive oxygen species (ROS); and disruption of Mitochondrial Membrane Potential	[69]

5. Soursop: a tropical ally in targeting AML

Soursop (Annona muricata) is an evergreen tree native to tropical and subtropical areas globally. The structure comprises four primary components: bark, leaves, edible fruit, and flowers [67]. The tree has a height ranging from 5 to 10 m and a diameter between 15 and 83 cm [70]. Soursop has historically served as a food source and has been utilized for pharmacological purposes. The fruit is frequently utilized in the production of juice, candy, syrups, and desserts, including ice cream. All components of the plant possess ethnomedicinal properties and are utilized for the prevention, management, and treatment of various ailments [67]. The fruit serves not only as a food source but has also been utilized in traditional medicine for the treatment of diarrhea, dysentery, arthritis, rheumatism, neuralgia, fever, malaria, parasites, helminths, skin rashes, and heart and liver diseases [60]. The fruit has been traditionally administered to mothers post-childbirth to enhance breast milk production [65,67]. The leaves are utilized internally as an extract or decoction and externally as dried or cooked leaves. Dried leaves have been utilized topically for the treatment of rheumatism, skin abscesses, and as an analgesic. The leaves are utilized internally for the treatment of rheumatism, headaches, fever, inflammation, insomnia, cystitis, neuralgia, diabetes, hypertension, dysentery, liver issues, cancer, and serve as an antispasmodic agent [65,67,70]. The leaves, in conjunction with fruit, have been utilized for the treatment of gastrointestinal issues, as well as liver, kidney, and heart diseases [71]. The seeds are utilized to combat parasitic and helminthic infections [65,67]. The bark is utilized alongside other plant components, including leaves and roots, to address conditions such as inflammation, dysentery, helminth infections, glycemia, insomnia, hypertension, muscle tension, and muscle spasms [65,67,70]. The flower and fruit have been utilized in the treatment of catarrh, or mucus accumulation [67].

5.1. Active ingredients of soursop

Soursop comprises various compounds that contribute to its bioactivity. In 2017, soursop was identified to contain 212 bioactive compounds [71]. Approximately half of these compounds are acetogenins (AGEs). AGEs are considered the primary bioactive component of soursop [65]. These compounds are derivatives of long-chain fatty acids characterized by a lengthy aliphatic chain attached to a γ-lactone ring. They are terminally substituted with β-unsaturated methyl groups (ketolactone) and may contain one or two tetrahydrofurans (THF) along the hydrocarbon chain, in addition to oxygen functional groups [65,71]. Among the AGEs, annonacin was identified as the most prevalent in both the fruit and the leaves. Annonacin is also found in the roots, seeds, and peel [65]. Besides AGEs, soursop contains vitamins, flavonoids, alkaloids, megastigmanes, phenolics, triglycerides, essential oils, and cyclopeptides [67]. Soursop contains essential minerals such as potassium, calcium, sodium, copper, iron, and magnesium [65,67]. Alkaloids constitute roughly 26 % of the compounds found in soursop, with reticuline and coreximine being the most prevalent alkaloids [65]. Leaves exhibited higher concentrations of alkaloids compared to other plant parts. Previous studies indicate that alkaloids in Annona species exhibit antidepressant-like effects through their role in dopamine biosynthesis and interaction with serotonin 5-HT1A receptors. Alkaloids and acetogenins exhibit neuronal cytotoxicity through the induction of apoptosis in neuronal cells. Studies indicate that neurotoxicity is not a significant concern, given the low bioavailability of this compound and the requirement for prolonged exposure to produce such effects [71]. Flavonoids constitute 19 % of the compounds found in soursop. The leaves contain a high concentration of flavonoids, specifically rutin and quercetin [65]. Flavonoids, as phenolic compounds, significantly contribute to the antioxidant properties of soursop. Many of these compounds exhibit water solubility, a crucial factor to consider in the medicinal use of soursop [71]. Six percent of the compounds in soursop consist of other substances [65]. The leaves were found to contain eighty essential oils, which may contribute to the bioactivity of soursop [71].

5.2. Soursop's potential in other cancer treatment

Prior research has delineated mechanisms through which soursop exerts its anti-cancer properties. Soursop has been shown to induce apoptosis, necrosis, and cytotoxicity in cancer cells, while also inhibiting their proliferation and migration [72]. Acetogenins, the primary bioactive component in soursop, have demonstrated selective cytotoxic effects across more than fifteen cancer cell lines, including those resistant to chemotherapy (Fig. 2) [68,71]. Acetogenins induce apoptosis in cancer cells by targeting oxidative phosphorylation and ATP synthesis through the inhibition of mitochondrial complex I and ubiquinone-linked NADH oxidase in the plasma membrane of these cells. This mechanism is effective due to the higher ATP requirements of tumor cells relative to normal cells for survival [66,71,72]. Research indicates that soursop extracts exhibit greater toxicity towards cancer cells compared to conventional drugs, while also enhancing the viability of healthy cells [66]. Annona muricata leaf extract contains the one form of acetogenin, Annomuricin E, which induces apoptosis through a mitochondrial-mediated pathway. Annomuricin E specifically induced the release of cytochrome c from the mitochondria to the cytosol by decreasing the mitochondrial membrane potential (MMP). The release of cytochrome c subsequently activated caspases 9, 3, and 7, which function as pro-apoptotic proteins. Annomuricin E induces apoptosis through the upregulation of the pro-apoptotic protein Bax and the downregulation of the anti-apoptotic protein Bcl-2 [71].

Fig. 2.

The main bioactive compound of soursop, acetogenins, induce apoptosis in cancer cells. The pie chart depicts the pharmacological activities of soursop. Image was produced in Biorender.com.

Soursop extract reduces the proliferation and survival of pancreatic cancer cells by inhibiting the extracellular signal-regulated kinase (ERK) pathway and the phosphatidylinositol 3-kinase (PI3K/AKT) pathway. Furthermore, the extract was observed to decrease ATP production and glucose uptake in pancreatic cancer cells by inhibiting the expression of glucose transporters and glycolytic enzymes [71]. Leaf extract was observed to induce necrosis in pancreatic cancer cells. In necrosis, caspase activation is not necessary for cell death. The rupture of the cancer cell's plasma membrane leads to the activation of an immune response. Consequently, cellular metabolism is suppressed, leading to necrosis of factors associated with glycolysis and hypoxia. Treatment of pancreatic cancer cells with soursop leaf extracts led to a reduction in the motility of these cells, a critical factor in cancer metastasis [72]. Previous research indicates that capsules containing soursop leaf and stem powder, which is high in flavonoids, exhibit antitumor and antimetastatic properties, including cell cycle arrest, apoptosis, reduced motility, and decreased invasion of pancreatic cancer cells [68,71]. In comparing crude leaf extract to flavonoid-rich extract, the crude extract demonstrated a greater inhibitory effect on the proliferation and growth of prostate cancer cells. The synergistic interaction between acetogenins and flavonoids is responsible for this finding [71].

A study on breast cancer indicated that fruit extract exhibits anticancer properties in certain cancer cell lines. After five weeks of treatment with soursop fruit extract, researchers observed a reduction in breast tumors in rats [71]. In breast cancer cells, leaf extracts induce apoptosis through the upregulation and activation of caspase-3. A separate study indicated that leaf extract reduced Bcl-2 expression while increasing caspase-3 and caspase-9 expression, thereby inducing apoptosis in cancer cells [65]. Moreover, leaf extract was observed to induce G0/G1 cell cycle arrest in breast cancer cell lines. More than twenty purified acetogenins demonstrated cytotoxic effects on breast cancer cells, with enhanced therapeutic outcomes observed when acetogenins were administered in combination [72]. Leaf extract demonstrated a growth inhibitory effect on the proliferation of breast cancer cells, with no significant impact on noncancerous cells. A study demonstrated that MCF-7 breast cancer cells, when treated with leaf extract, exhibited morphological changes indicative of apoptosis upon staining. These changes included chromatin condensation, bleb formation in the nucleus, alterations in cell membrane shape, nuclear fragmentation, and reduced proliferation rates. This study also identified a dose-dependent increase in reactive oxygen species (ROS) in treated breast cancer cells, leading to the activation of apoptosis [66].

Soursop leaf extract downregulates Bcl-2 and PCNA proteins, upregulates Bax protein, and restores antioxidant enzyme levels in colorectal cancer. Patients with colorectal cancer often exhibit elevated levels of malondialdehyde (MDA), a lipid radical resulting from excessive reactive oxygen species (ROS) production. In colon tissue treated with extract, MDA formation decreased, indicating that soursop may protect against oxidative stress [71]. Furthermore, it was demonstrated that leaf extract increased the expression of caspase-3 in colorectal cell lines, leading to the induction of apoptosis [65]. Soursop leaf extract induces apoptosis in colon cancer cells through the mitochondrial-mediated pathway [67]. Leaf extract inhibited the proliferation of colorectal cancer cells through various mechanisms, including the disruption of matrix metalloproteinases (MMPs), induction of cytochrome c leakage, and activation of pro-apoptotic proteins caspase-3, caspase-7, and caspase-9 [65]. Soursop extract also induced G1 cell cycle arrest and inhibited the migration and invasion of colon cancer cells [67]. A study demonstrated that the administration of 300 mg of soursop leaf extract in patients with colorectal cancer inhibited cancer cell growth without impacting normal cells. Annocherimolin, an acetogenin, demonstrated cytotoxic activity against HT-29 colon cancer cells [65]. A study indicated that daily intake of 5 g of soursop leaf extract, combined with lifestyle changes, led to complete regression of colon tumors [68].

Soursop has demonstrated efficacy in the treatment of lung cancer. The ethyl acetate extract of soursop induces apoptosis in lung cancer cell lines by upregulating Bax and downregulating Bcl-2 expression [65]. Soursop, akin to colon cancer, promotes apoptosis in lung cancer cells through the mitochondrial-mediated pathway and suppresses proliferation by inducing cell cycle arrest in the G1 phase [67]. Soursop extracts induce apoptosis in lung cancer cells through the upregulation of reactive oxygen species (ROS) formation and the reduction of mitochondrial membrane potential (MMP) by increasing Bax expression and decreasing Bcl-2 expression [72]. Treatment with soursop in lung cancer was observed to inhibit NF-κB signaling. A study induced lung cancer using the carcinogen benzo [a]pyrene (BPa), and findings indicated that oral administration of methanolic soursop leaf extract exhibited protective and anticancer properties. The extract was administered one week prior to treatment with BPa and continued for sixteen consecutive weeks thereafter. The findings indicated that methanolic soursop leaf extract significantly diminished the incidence and burden of lung tumors, reduced the expression of the serum cancer marker carcinoembryonic antigen (CEA), lowered lipid peroxidation, and enhanced levels of superoxide dismutase (SOD), glutathione (GSH), and catalase (CAT) in comparison to control groups treated solely with BPa. Furthermore, normal lung gross morphology was noted following treatment with soursop. The results indicate that soursop possesses a protective mechanism against cancer-related cellular damage and free radicals [68].

5.3. Soursop's potential in AML and hematological malignancies

Soursop has significant anti-leukemic effects through numerous complementary pathways targeting cancer cell survival, proliferation, and metabolic balance as shown in Fig. 3. [72,73]. Acetogenins, alkaloids, flavonoids, and phenolic compounds are their main bioactive ingredients, which have shown cytotoxicity against hematological malignancies. A study demonstrated that stem methanolic extract caused cytotoxic effects in U-937 cells [72]. Soursop extract inhibits Complex I (NADH dehydrogenase) in mitochondria, causing ATP depletion and ROS production. Extracts from soursop leaves, roots, and twigs have been demonstrated to disrupt matrix metalloproteinases (MMPs), elevate reactive oxygen species (ROS), and induce G0/G1 cell cycle arrest, resulting in the inhibition of proliferation and growth of HL-60 leukemia cells [65,69,74]. Leukemia cells, which depend more on oxidative metabolism, are selectively injured and metabolically collapsed by oxidative stress, which destroys lipids, proteins, and DNA.

Fig. 3.

Proposed mechanisms of Soursop-induced cytotoxicity and cell death in hematologic malignancies. Soursop exerts multifaceted anticancer effects through four major mechanistic modes: (1) Cell-cycle arrest and inhibition of proliferative signaling. (2) Soursop phytochemicals enhance intracellular reactive oxygen species (ROS) generation, causing mitochondrial dysfunction and oxidative damage. Elevated ROS and disrupted mitochondrial membrane potential lead to cytochrome c release, activation of caspase-9 and caspase-3, and cleavage of PARP, collectively driving intrinsic apoptotic signaling (3) Soursop downregulates pro-survival pathways (e.g., PI3K/AKT/mTOR and MAPK). and upregulates tumor suppressors such as p53 and Bax, resulting in G1/S or G2/M phase arrest and inhibition of DNA synthesis. (4) Final outcome is programmed cell death. The combined oxidative, mitochondrial, and signaling perturbations culminate in apoptotic and necrotic cell death, characterized by nuclear condensation, membrane blebbing, and loss of cell viability. Image was produced in Biorender.com.

Soursop induces mitochondrial apoptosis by decreasing ΔΨm and releasing cytochrome c into the cytoplasm [75]. This triggers caspase-9 and caspase-3, cleaving PARP and causing programmed cell death. Bax, Bak, Bcl-2, and Mcl-1 upregulation and downregulation enhance the apoptotic cascade. Some acetogenins also activate apoptotic genes via p53 signaling. Moreover, soursop disrupts ATP synthesis and generates excessive ROS, causing irreversible mitochondrial damage and necrotic cell death at higher concentrations or extended exposure. Some studies show that soursop causes autophagic vacuole formation, indicating that apoptotic and necrotic mechanisms work together to destroy resistant leukemia.

Soursop extract inhibits DNA synthesis and produces cell cycle arrest at G0/G1 or G2/M phases, depending on cell type and concentration. This action is caused by suppressing cyclin D1, CDK2, and CDK4, and activating p21^Cip1 and p27^Kip1, preventing excessive growth. Inhibiting critical signaling pathways such PI3K/Akt/mTOR, NF-κB, and MAPK/ERK reduces leukemia cell survival and proliferation. Importantly, soursop doesn't harm normal peripheral blood mononuclear cells. Cancerous and normal cells differ in metabolic rate, mitochondrial activity, and redox homeostasis, causing selectivity.

Although the in vitro results are promising, research on the specific effects of soursop in AML remains limited. Our laboratory is expanding research to investigate the efficacy of soursop in in vivo models and AML-resistant cell lines. We are also preparing a clinical trial to assess the therapeutic potential of soursop in chemotherapy-resistant acute myeloid leukemia, with the objective of establishing it as a viable clinical option. Ongoing studies may reinforce the anti-leukemic effects of soursop and highlight its potential role in overcoming treatment resistance, providing a natural, complementary approach for AML therapy.

6. Final insights and future directions

AML continues to present significant challenges in treatment, characterized by elevated rates of drug resistance and relapse that adversely affect patient outcomes. To achieve substantial progress in the treatment of AML, it is essential to thoroughly investigate the molecular mechanisms that underpin the disease, along with a comprehensive understanding of the limitations associated with existing treatments. This understanding will offer essential insights for formulating strategies that can efficiently target and eradicate the resilient, resistant cancer cells that remain following conventional therapies.

In the quest for innovative treatment alternatives, natural agents have surfaced as a promising area of exploration. Compounds derived from nature, such as matrine and parthenolide, have demonstrated significant efficacy in targeting AML cells, including progenitor and stem cell populations. These natural agents frequently demonstrate a reduced toxicity profile in comparison to synthetic chemotherapies, potentially alleviating the severe side effects commonly linked to traditional cancer treatments. Soursop is distinguished among these natural agents for its significant anticancer properties. Research indicates that soursop has the potential to induce apoptosis, inhibit proliferation, and disrupt cellular pathways that contribute to the survival of leukemic cells. The complete mechanism through which soursop effectively targets and eliminates AML cells is not yet fully understood and represents a critical area for additional research.

Our laboratory is committed to exploring the therapeutic potential of soursop by broadening investigations into its effectiveness in resistant AML models and in vivo systems. Our objective is to accurately ascertain the mechanisms by which soursop demonstrates its anticancer properties, with the intention of clarifying the molecular pathways it affects and pinpointing the active compounds that contribute to its cytotoxic effects. Acquiring a thorough understanding of soursop's mechanism of action will enable us to advance toward clinical trials assessing its efficacy in treating AML patients. The long-term vision is to position soursop as a viable, less toxic alternative to traditional chemotherapy, aimed at not only eradicating AML cells but also preventing relapse and minimizing side effects, thereby enhancing patient quality of life. Through these efforts, we aim to establish soursop as a significant asset in the fight against AML and potentially other resistant cancers.

Funding

The work was supported by intramural fund of Department of Biomedical Sciences, Cooper Medical School of Rowan University.

CRediT authorship contribution statement

Sabrina M. Paparo: Conceptualization, Methodology, Writing – original draft. Rebeca M. Mendoza: Methodology, Visualization, Writing – original draft. Sahil Jethi: Writing – review & editing. Michael Brister: Writing – review & editing. Subash C. Jonnalagadda: Resources, Writing – review & editing. Tulin Budak-Alpdogan: Conceptualization, Visualization, Writing – review & editing. Roger Strair: Visualization, Writing – review & editing. Manoj K. Pandey: Conceptualization, Resources, Supervision, Visualization, Writing – original draft, Writing – review & editing.

Declaration of competing interest

The authors do not report any conflicts of interest.

Data availability

No data was used for the research described in the article.