Protective Effects of Curcumin Against Medulloblastoma: A Review

Abstract

Medulloblastoma (MB) is the most common childhood tumor with a poor prognosis. Primary approaches for treating MB comprise surgical resection along with radiotherapy and chemotherapy. However, these methods have not created a promising outlook for subjects with this neuroepithelial tumor due to their low efficiency. On the other hand, these therapeutic strategies are associated with many side effects. So, there is an unmet need to find an alternative way to overcome MB. Currently, there is a significant focus on natural compound-based therapies, particularly curcumin obtained from Curcuma longa, for ameliorating different disorders like cancer. Extensive research has also been conducted to provide evidence supporting the beneficial effects of curcumin in the treatment of MB. This polyphenolic compound can exert its suppressive effects on the proliferation and growth of MB cells by affecting several molecular pathways and agents, such as suppressing Wnt/β-catenin, NF-κB, and SHH signaling pathways, triggering apoptosis-related genetic effectors (eg, Bax, Bcl-2, PARP, caspase-3, and caspase-9), potentiating tubulin acetylation, and decreasing HDAC4 function. Hence, in this literature review, we aimed to debate documents pertaining to MB therapy with curcumin and other formulations in vitro and in vivo with a mechanistic insight.

Introduction

Medulloblastoma (MB), the most common malignant embryonal neuroepithelial tumor, is a type of cancer that stems from a failure in the development of the cerebellum and is known as one of the main causes of morbidity and mortality in pediatric populations.^1–3 MB is responsible for 25% to 30% of pediatric brain tumors and more than 40% of posterior fossa-related childhood tumors. ⁴ MB begins in the hindbrain and cerebellum and subsequently spreads into the spinal cord and leptomeningeal membranes of the forebrain. ⁵ There are several classifications for MB based on genetic changes and histological properties. ¹ For example, genetically, MB is classified into four subgroups, including Sonic Hedgehog-activated (SHH), Wingless-activated (Wnt), and non-Wnt/non-SHH-activated (groups 3 and 4), which are identified based on molecular expression pattern, prognostic features, and clinical manifestations. ⁶ From a clinical viewpoint, MB exhibits some general symptoms, like fatigue, vomiting, headache, and cerebellar impairment. During disease development, symptoms related to elevated intracranial pressure (eg, lethargy, seizures, and behavior and vision changes) are predominant. ⁷ Presently, the primary treatment for this type of cancer is surgical resection accompanied by chemotherapy and radiation therapy; however, the therapeutic effect of the mentioned approach is insufficient, and the survival rate is still very low.^8,9 As a result, researchers are currently looking for a new therapeutic approach. ¹⁰ These days, various dietary natural compounds have been examined, and their anti-neoplastic effects have been approved.^11,12 One of the famous dietary ingredients with a broad therapeutic application is curcumin. This natural compound obtained from the rhizomes of turmeric (Curcuma longa) is a nontoxic polyphenol that serves as an anti-inflammatory, anti-oxidant, anti-fibrosis, anti-bacterial, anti-angiogenesis, and anti-microbial agent.^13,14 Compelling evidence has reflected the importance of curcumin in the amelioration of diverse health-related problems, for instance, neurological, cardiovascular, infectious, musculoskeletal, and immune-associated diseases.^15–19 Among these, the potent ability of curcumin to fight against cancers has significantly been noted.^20–23 For example, it has been demonstrated that curcumin can repress cancer cell proliferation, growth, migration, and invasion of cervical cancer, intestinal adenomas, prostate cancer, colorectal cancer, head and neck squamous cell carcinoma, leukemia, and breast cancer without influencing normal cells in preclinical and clinical investigations. The anti-cancer mechanisms of curcumin have been attributed to several signaling pathways, for instance, Wnt/β-catenin, Janus kinase/signal transducer and activator of transcription (JAK/STAT), phosphatidylinositol 3-kinase (PI3K)/Akt, nuclear factor kappa B (NF-κB), p53, mitogen-activated protein kinase (MAPK), and apoptosis-associated signaling.^23,24 Some studies also suggested that curcumin can considerably target brain tumors, such as MB.^8,25 Given the anti-cancer capacity of this phytochemical, this mini-review summarizes and discusses reports regarding the curative potential of curcumin in MB treatment.

Medulloblastoma: Risk Factors and Pathogenesis

The male gender is more at risk for the development of MB. ²⁶ Also, subjects with some genetic syndromes, including neurofibromatosis type 1 (NF-1), Li-Fraumeni syndrome, tuberous sclerosis, Turcot syndrome, and Gorlin syndrome, are more susceptible to brain tumors. ²⁷ In addition, certain viral infections can increase the risk of MB development. In this direction, human herpesviruses, for instance, cytomegalovirus and Epstein–Barr virus, showed their role in the pathology of brain tumors such as MB.^28–30 The pathogenesis of MB refers to complex and interconnected molecular processes. ³¹ These mechanisms have not fully been understood; however, several key factors have been identified. These factors include genetic alterations (eg, mutations and chromosomal abnormalities) and dysregulation of key signaling pathways involved in brain development. ³¹ Some genetic alterations have been implicated specifically for each type of MB. In the Wnt subgroup, a common genetic alteration is the activation of the β-catenin pathway due to mutations in the Catenin Beta 1 (CTNNB1) gene. ³² These mutations lead to the stabilization and accumulation of β-catenin protein in the cell nucleus, where it promotes the transcription of target genes involved in cell proliferation and survival. ³³ The SHH subgroup is characterized by genetic abnormalities in the SHH pathway. ³⁴ This kind of MB originates from cerebellar granular neuronal precursors (GNPs), which migrate from the external germinal layer to the internal granule layer during normal brain development.^35,36 In SHH MB, alterations in genes involved in the SHH signaling pathway disrupt this normal migration process and subsequently give rise to the accumulation of GNPs in the external germinal layer. ³⁷ Group 3 MB pertains to amplification or upregulation of the myelocytomatosis oncogene (MYC) gene. ³⁸ The proto-oncogene cellular-MYC (C-MYC) is encoded by the gene MYC and plays a significant role in cell proliferation, differentiation, and metabolism. ³⁹ Group 4 MB is characterized by genetic alterations in genes engaged in chromatin remodeling and histone modification, such as lysine demethylase 6A (KDM6A). Interestingly, around 6% of cases in group 4 MB reflect amplification of the MYCN gene. However, unlike the Wnt and SHH subgroups, there is no single gene mutation in more than 5% to 10% of group 3 or group 4 MB.^40,41 Chromosomal abnormalities, such as lack of chromosome X in females and lack of chromosome 8, have also been detected in MB, dominantly in non-SHH/Wnt subclasses. ³¹ Besides, a multitude of signaling pathways have a substantial action in the occurrence and growth of MB, comprising developmental pathways (Wnt, Notch, and Hedgehog) and Erb-B2 receptor tyrosine kinase 2 (ErbB2), tropomyosin receptor kinase C (TrkC), insulin-like growth factor receptor (IGF-R), the oncoprotein MCY, and the receptor tyrosine kinase (RTK) c-Met. ⁴²

Curcumin and Medulloblastoma

There are some in vitro and in vivo experimental investigations to support the beneficial effects of curcumin in the treatment of MB through different mechanisms.^8,43,44 In this line, He et al explored the anticancer potential of curcumin (0-100 μM for 24, 48, and 72 h) in MB cells (DAOY) by assessing its action in the inhibition of cancer cell proliferation and the regulation of the Wnt/β-catenin pathway using the 2,5-diphenyl-2H-tetrazolium bromide (MTT), immunofluorescence, flow cytometry, reverse transcription polymerase chain reaction (RT-PCR), and western blot tests. The in vitro results of this research group unveiled that this bioactive substance at the concentration of 35 μM for 48 h exerted a 50% inhibitive effect on cancer cell proliferation. Also, following 48 h treatment, curcumin-exposed DAOY cells reflected some morphological alterations, like cell shrinking, rounding, vacuolation, and detachment. From a mechanistic insight, this study justified the antiproliferative effects of curcumin on DAOY cells by arresting the cell cycle at the G2/M stage through inhibition of the Wnt/β-catenin signaling pathway. ⁴⁵ The Wnt signaling pathway plays a fundamental role in embryonic development and maintaining physiological balance, but its deregulation has been associated with the onset and advancement of different types of tumors, notably MB.^46,47 The Wnt/β-catenin signaling pathway can be suppressed in MB cells as a result of curcumin therapy by activating glycogen synthase kinase (GSK)3β (Figure 1), a negative regulator of the Wnt/β-catenin signaling pathway, which in turn suppresses β-catenin and its downstream target cyclin D1. ⁴⁵ In another in vitro study, the significance of SHH signaling pathway suppression in therapeutic events of this component of turmeric (0-40 μM) against MB cells (DAOY, MED-1, MED-4, and MED-5) was highlighted by similar methods to the previous study. ⁴⁴ The obtained data addressed that curcumin targets these MB cells dose-dependently. MED-1 cells showed high resistance to treatment; however, other MB cells exhibited different sensitivity to curcumin. The LC50 values (suppressive concentration for 50% viability) for the MED-4, MED-5, and DAOY cells were 28, 25, and 20 mM, respectively, indicating the cytotoxic potential of curcumin in the majority of MB cell cultures and the most sensitivity of DAOY cells to curcumin. ⁴⁴ From a closer look, curcumin could repress the SHH–glioma-associated oncogene homolog 1 (GLI1) signaling pathway in MB cells by attenuating the SHH protein expression and critical downstream targets, including protein patched homolog1 (PTCH1) and GLI1. ⁴⁴ Curcumin also mitigated NF-κB and β-catenin levels, two key oncogenic transcription factors involved in MB carcinogenesis, as well as the phosphorylated Protein kinase B (Akt), which has an important role in the occurrence of MB induced by the SHH pathway. These mentioned molecular changes resulted in the downregulation of oncoproteins related to MB development, including Cyclin D1, N-MYC, and C-MYC. ⁴⁴ Moreover, curcumin stimulated apoptosis by mitochondrial-dependent pathways by downregulating the anti-apoptotic factor of the SHH pathway (Bcl-2). ⁴⁴ Interestingly, a recent project (2022) accomplished by Gong et al reflected the better function of a curcumin analog, BDDD-721, against MB in vitro and in vivo. The in vitro investigations were performed on different MB cells, including ONS-76, UW473, UW402, and DAOY cells incubated with 5 to 20 μM curcumin or BDDD-721. In vivo evaluations were accomplished in BALB/c-nu/nu nude mice harboring ONS-76 and DAOY cells receiving these two drugs at the dose of 60 mg/kg per day intraperitoneally. In vitro findings showed that BDDD-721 enhances apoptosis and suppresses proliferation, migration, and invasion of MB cells more efficiently than free curcumin. Moreover, in vivo reports confirmed the inhibitory roles of both BDDD-721 and curcumin in the growth of xenografts. However, animals treated with BDDD-721 manifested smaller tumor regions than those animals that received curcumin after 25 days. The molecular aspects of this research indicated that treatment with curcumin analog, BDDD-721, abates the expression of SHH and PTCH1, GLI1, and Smoothened (Smo), as its downstream targets, and activates GLI1. ⁸ Lee and coworkers also scrutinized the antitumor influences of this herbal compound on MB in different concentrations and doses (0-40 μM and 1 g/kg) in vitro and in vivo. The in vitro assessments were carried out on D341 Med, D283 Med, and DAOY cell lines of MB. ⁴³ Also, in vivo assessments have been performed on two mouse models, comprising the Smo/Smo transgenic MB model and subcutaneous DAOY xenografts. The in vitro findings showed that MB cells treated with curcumin have a higher amount of cleaved caspase-3 and poly(ADP-ribose) polymerase (PARP) (a downstream substrate of caspase-3), indicating apoptosis induction in MB cells. This effect was along with elevated tubulin acetylation and diminished histone deacetylase (HDAC)4 activity, causing mitotic catastrophe. ⁴³ Plus, in vivo outcomes in tumor xenografts receiving curcumin (orally) indicated the potential of curcumin for decreasing tumor growth and promoting survivability in MB xenografts and the Smo/Smo transgenic MB model, respectively. ⁴³ Studies regarding curcumin therapy for MB have been summarized in Table 1. In summing up, the present data emphasize the improving influences of curcumin on MB by affecting different cellular and molecular events, such as Wnt/β-catenin and SHH signaling pathways, apoptotic-related events, tubulin acetylation, and HDAC4 function.

Figure 1.

Curcumin therapy for medulloblastoma through different molecular processes. Abbreviations: SHH, Sonic hedgehog; Wnt, Wingless type; PTCH1, protein patched homolog 1; SMO, smoothened; SUFU, suppressor of fused; GSK-3β, glycogen synthase kinase-3 beta; NF-κB, nuclear factor kappa B; GLI1, glioma-associated oncogene homolog 1; PARP, poly(ADP-ribose) polymerase.

Table 1.

Curcumin Influences Medulloblastoma Cell Proliferation, Migration, and Invasion Negatively Through Different Mechanisms In Vitro and In Vivo.

Number	Used curcumin	Dose	Target	Effect/mechanism (s)	In vivo/in vitro	Cell line/species	Reference
1	Curcumin and curcumin analog BDDD-721	0-20 μM and 60 mg/kg.	PARP/c-PARP/Bcl-2/Ki67/PCNA/Smo/GLI1/PTCH1	Stimulating apoptosis and repressing cell proliferation, migration, and invasion by BDDD-721 better than curcumin	Both	DAOY, ONS-76, UW402, and UW473/nude mice	8
2	Curcumin	0-100 μM	β-catenin/Cyclin D1/β-actin/GSK-3β/histone H2	Repressing cell proliferation	In vitro	DAOY	45
3	Curcumin	0-100 μM	CCNE1 (Cyclin E1)/E2F1/CDK2/PTEN/caspase-3 and -7/p53/p21/PARP/Bcl-2	Repressing cell growth and stimulating apoptosis	In vitro	ONS76	48
4	Curcumin	0-200 μg/ml	Bax/Bcl-2/p53/p10	Decreasing cell viability	In vitro	D283	49
5	Curcumin	0-20 μM	Cdc27/PARP/caspase-3/APC-2,7, and 8/cyclin A, B1, D1, and E/GAPDH	Inducing cell cycle arrest and apoptosis	In vitro	DAOY	50
6	Curcumin	0-50 μM and 1 g/kg	Caspase-3/PARP/HDAC 2, 4, 5, 6, and 7/NF-κB/cyclin B1/GAPDH	Stimulating apoptosis and cell cycle arrest and decreasing tumor growth	Both	DAOY, D283 Med, and D341 Med/SCID mice	43
7	Polymeric nanoparticle formulation of curcumin	0-20 μM	PTCH1B/GLI1/Bcl-2/IGF/STAT3/Akt/Shh	Repressing clonogenicity and cell growth and inducing apoptosis and cell cycle arrest	In vitro	DAOY and D283Med	51
8	Curcumin encapsulated with a self-assembling peptide hydrogel	0-20 μM	LDH/caspase-3/PARP	Stimulating apoptosis	In vitro	DAOY	52
9	Curcumin	0-200 μM	Bcl-2/Bcl-xL/caspase-3/PARP	Repressing cell proliferation and migration and colony formation and stimulating apoptosis	In vitro	DAOY	53
10	Curcumin	0-40 μM	C-MYC/N-MYC/cyclin D1/Bcl-2/Bax/β-catenin/SHH/PARP/PTCH1/NF-κB/GLI1/Akt/pro-caspase-3 and -9	Repressing cell proliferation and inducing apoptosis and cell cycle arrest	In vitro	MED-14,5 and DAOY	44

Abbreviations: APC, anaphase-promoting complex; Bcl-2, B-cell lymphoma 2-associated oncogene; IGF, insulin-like growth factor; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; Bax, Bcl-2-associated X protein; PTCH, patched homolog; PCNA, proliferating cell nuclear antigen; E2F2, E2F transcription factor 1; CDK2, cyclin-dependent kinase 2; PTEN, phosphatase and tensin homolog; CDC27, cell division cycle 27.

Drug Delivery Systems for Improving Curcumin Therapy Against Medulloblastoma

Despite the considerable anti-MB impacts of curcumin reported in several studies, there are still some pharmacological challenges hindering its clinical applications, such as insolubility in water and instability resulting in its weak bioavailability in tumor cells. ²¹ In order to better utilize the curative abilities of curcumin for combating MB, some drug delivery systems have been fabricated and recommended. In this regard, Altunbas and colleagues designed a self-assembling peptide hydrogel, constructing a solid physical hydrogel in physiological situations for controlled and sustained delivery of curcumin. ⁵² The results of in vitro tests on an MB cell line (DAOY cells) demonstrated that encapsulated curcumin (0-4 mM) with the hydrogel does not have a negative effect on its bioactivity. In this scientific work, the capability of curcumin released from the hydrogel to induce cell death was scrutinized by appraising the levels of lactate dehydrogenase (LDH), an enzyme secreted into the cell culture medium following cell plasma membrane damage, and the activity of PARP and caspase-3 (apoptosis markers). ⁵² Finally, the analyzed data implicated that with an increase in the concentration of curcumin encapsulated with the mentioned hydrogel, the release of LDH is elevated. Following 24 h of the culture of DAOY cells on 0.5 wt% hydrogels loaded with 0- and 4-mM curcumin, morphological changes related to cell death (ie, cytoplasm shrinkage, cell rounding, and separation from tissue culture plate) were observed; however, hydrogels without curcumin addressed spread and attached morphologies without obvious cytotoxic effects on these tumoral cells. The immunoblotting outcomes also approved that in DAOY cells subjected to 0.5, 1, and 2 wt% hydrogels encapsulating 0 to 4 mM curcumin (for 24 h), cleaved PARP and caspase-3 are elevated dose-dependently. This study inferred that hydrogel-released curcumin can stimulate apoptosis through similar molecular and cellular processes as curcumin without encapsulation. ⁵² In the study of Lim and colleagues, this polyphenolic compound was encapsulated with polymeric nanoparticles (NPs), and its effectiveness was inspected on D283Med and DAOY cells. ⁵¹ In this work, decreased cell viability upon nanocurcumin usage was observed and attributed to the apoptotic stimulation and cell cycle arrest at the G2/M stage. ⁵¹ Also, nanocurcumin diminished CD133-positive stem-like cells and clonogenic growth. CD133 is a renowned cancer stem cell marker for MB. ⁵⁴ From a detailed look, nanocurcumin, containing 5 and 10 µM curcumin, dramatically decreased the normalized clonogenicity of MB cells (DAOY) from 100% to 10% and 1.8%, respectively. In addition, nanocurcumin-treated DAOY cells reflected reduced total Signal transducer and activator of transcription α (STAT3α) protein levels, ⁵¹ whose activation leads to triggering oncogenic pathways like cell proliferation, survival, and maturation. ⁵⁵ However, the nano-based formulation of curcumin did not repress SHH signaling in another MB cell line, D283Med. ⁵¹ Overall, it seems that drug delivery systems, especially those based on nanocarriers, can elevate the effectiveness of curcumin on MB, but more in-depth studies are demanded to vindicate this report.

Conclusion

MB is known as the most prevalent pediatric malignant brain tumor, consisting of four molecular subclasses, which typically occurs in the posterior fossa and primarily affects children who are under the age of 15 years. ⁵⁶ Despite the extensive efforts of scientists, there is not a bright landscape for treating patients with MB yet. However, some herbal-based approaches unveiled a potent therapeutic capacity against various disorders such as cancer. In this respect, it is thought that curcumin obtained from the Curcuma longa can act as an anti-MB compound through different mechanisms, including attenuation of Wnt/β-catenin, NF-κB, and SHH signaling pathways, induction of apoptosis-pertained agent (ie, Bax, Bcl-2, PARP, caspase-3, and caspase-9), elevation of tubulin acetylation, and reduction of HDAC4 activity. Besides, it seems that using some drug delivery vehicles, namely, a self-assembling peptide hydrogel and polymeric NPs, not only solves the pharmacological restrictions of this polyphenolic agent but also causes the stimulation of cell death and reduction of cell survival and oncogenic mediators (eg, STAT3α) in MB cells. However, more experimental studies are deemed necessary to support our reports.