Human herpesviruses are known to induce a broad spectrum of diseases, ranging from common cold sores to cancer, and infections with some types of these viruses, known as human oncogenic herpesviruses (HOHVs), can cause cancer. Challenges with viral latency, recurrent infections, and drug resistance have generated the need for finding new drugs with the ability to overcome these barriers. Berberine (BBR), a naturally occurring alkaloid, is known for its multiple biological activities, including antiviral and anticancer effects.
1. Introduction
Herpesviruses are a diverse group of large double-stranded DNA viruses that share a common virion morphology. Herpesviruses, which belong to the
Herpesviridae family, are highly infectious and frequently infect humans for life and persist latently along with the ability to cause recurrent infections
[1][2][1,2]. Some types of herpesvirus that can lead to cancer are recognized to be oncogenic, such as Epstein–Barr virus (EBV, also known as human herpesvirus 4) and Kaposi’s sarcoma-associated herpesvirus (KSHV, also known as human herpesvirus 8)
[3][4][3,4]. On the other hand, some studies have reported other potentially human oncogenic herpesviruses (HOHVs) with an effect on various types of cancer such as herpes simplex virus 1 (HSV-1, also known as human herpesvirus 1), herpes simplex virus 2 (HSV-2, also known as human herpesvirus 2), and human cytomegalovirus (HCMV)
[5][6][7][5,6,7]. It is known that herpesviruses use the infection strategy ‘‘run and hide,’’ and significant complications of these infections can be noticed once the immune system is compromised by various factors that negatively affect the immune system, including physiological and environmental factors
[8][9][8,9]. Infections with herpesviruses are currently challenging to cure, and the clinical drugs used to treat them, such as acyclovir and other nucleoside analogs, do not entirely cure the disease or prevent recurrent infections while blocking the viral replication, thus reducing the duration of symptoms and promoting the healing of epithelial damage, lesions, and other cellular damages that were triggered by virus infection
[10][11][10,11]. On the other hand, the overuse of these drugs has generated the problem of drug resistance, which in turn has adversely affected the treatment efficacy
[12]. Currently, anti-herpesvirus drug development strategies face many challenges, and the most important tasks are linked with developing potent anti-herpesvirus medicines that can conquer the problems of drug resistance, viral latency, and recurrent infections and can also act with diverse mechanisms of action, minimum or no toxicity, and minimum adverse effects
[13][14][13,14]. Most drug discovery strategies rely on natural products as a considerable source of new drug candidates with relatively safe profiles, especially from plant sources
[15].
Berberine (BBR), a secondary metabolite that is biosynthesized by various plant species and is commonly present in the roots, rhizomes, and stem barks of various Chinese herbs as well as several plants of the
Berberis genus
[16]. Chemically, this compound is a quaternary ammonium salt of an isoquinoline alkaloid (PubChem CID: 2353) with a molecular weight of 336.4 g/mol ()
[17]. Biologically, BBR in numerous preclinical and limited human studies has been proven to exert various beneficial bioactivities against several human diseases, including microbial infections, inflammation, various types of cancer, cardiovascular diseases, gastrointestinal disorders, neurodegenerative diseases, depression, and metabolic dysfunctions
[16][18][19][20][16,18,19,20]. More information about berberine’s bioavailability and safety profile is discussed in a later section.
Figure 1. Chemical structure of berberine.
2. Berberine Targets Clinically Recognized Oncogenic Herpesviruses
Herpesviruses are known to employ several immune evasion strategies to cause latent infections in their host cells with the ability to generate certain types of cancer
[21][45]. The potential of developing cancer has been clinically confirmed with EBV and KSHV infections, which are classified as a class I carcinogen
[22][46]. The major carcinogenic mechanisms employed by EBV and KSHV have recently been clarified, where both viruses can repress apoptosis and tumor suppressor pathways, enhance the oncogenic microenvironment, promote cellular migration, metastasis, and angiogenesis, and generate mutagenesis
[3][21][22][3,45,46].
This section records all studies concerning BBR and its protective effects on EBV and KSHV and their associated cancers, with a focus on the mechanisms of action and pathways along with effective concentrations or doses.
2.1. Berberine Targets Epstein–Barr Virus and Its Associated Cancers
EBV is a double-stranded DNA virus that belongs to the
gamma-Herpesviridae subfamily
[23][47] and was first identified in Burkitt’s lymphoma by Sir Anthony Epstein and colleagues in 1964
[24][25][48,49]. This pathogen was the first tumor virus discovered in humans and is principally linked with lymphomas and epithelial cell cancers
[26][50]. Saliva exchange is the most known transmitting method for EBV infection and therefore symptomatic initial infection or infectious mononucleosis was described as ‘’kissing disease’’
[27][51]. There is a strong connection between EBV and the development of cancer, where experimental data confirmed that EBV infection is linked with various human proliferative diseases involving primarily epithelial or lymphoid cells, including nasopharyngeal carcinoma (NPC)
[28][29][52,53]. EBV demonstrates a type II latency mechanism in NPC patients, and this latency is mainly characterized by the expression of Epstein–Barr nuclear antigen 1 (EBNA1), which was observed to be vital for the replication, partition, transcription, and protection of the viral genome
[30][31][32][54,55,56]. Other critical latent membrane proteins and several non-coding RNAs are also expressed by the virus during the latency phase associated with NPC
[33][57]. Therefore, such targets are very crucial in the design of new drug candidates useful in the management of EBV and its linked NPC
[34][58].
The direct suppression effect of BBR on EBV infection has been revealed in limited experiments, while its potent antitumor impacts have been explored in numerous in vitro and in vivo studies evaluated in multiple EBV positive-cancerous cells. For instance, in preclinical investigations (in vitro and in vivo), Wang and coauthors
[35][59] showed the capacity of BBR to inhibit the latent and lytic replication of EBV-positive NPC cells and reduce cell proliferation, cause cell cycle arrest, and promote apoptosis in the EBV-positive NPC cells (). Their results unveiled diverse mechanisms of action at multiple molecular and cellular levels, suggesting BBR as a promising drug for the therapies of EBV infection and EBV-associated tumors such as NPC. In an in vivo experiment using athymic nude mice, BBR was observed to efficiently hinder the tumorigenicity and growth of EBV-positive NPC cells. The mechanism has been found to correlate with successful inhibition of signal transducer and activator of transcription 3 (STAT3) activation in NPC cells
[36][60]. On the other hand, this study did not determine the inhibitory action of BBR against EBV. NPC could also be generated in the absence of EBV infection
[37][61]. Since various drugs could work in a synergistic manner and provide enhanced treatment efficacy
[38][62], BBR in combination with ginsenoside Rg3 (Rg3; an active molecule from
Panax ginseng) was evaluated for improved anticancer properties and was detected to induce remarkable inhibition of NPC cell proliferation (in the absence of EBV infection) in vitro and in vivo. The underlying mechanism has been revealed to affect the mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) signaling pathways
[39][63]. In another research performed on EBV-transformed B cells and cancerous B cells, treatment with BBR led to significant induction of mitochondrial apoptosis, clarifying that the role of X-linked inhibitor of apoptosis protein-associated factor 1 (XAF1) as a supporter of the mitochondrial apoptosis pathway might offer a novel target for cancer therapy, mainly for cancers with wild-type p53 expression
[40][64].
Table 1. Protective effects of berberine against Epstein–Barr virus and its linked tumors.
Type of Study, Assay, Virus, and Cells/Animals |
Outcomes |
Mechanism of Action |
Reference |
In vitro. Viral titer and Western blotting assays. EBV. EBV-positive NPC cells (HONE1 and HK1-EBV cells). |
At a concentration of 50 µM, BBR effectively reduced the production of virions in HONE1 and HK1-EBV cells, thus inhibiting latent and lytic replication of EBV in EBV-positive NPC cells. |
BBR decreased the expression of the EBV transcription factor BZLF1. |
[35] | [59] |
In vitro and in vivo. Various biochemical assays. EBV-positive NPC cells (HONE1 and HK1-EBV cells). NOD/SCID mice. |
At various concentrations in micromolar ranges, BBR successfully inhibited the viability of EBV-positive NPC cells and exposed cell cycle arrest and apoptosis in the EBV-positive NPC cells, providing a significant antitumor effect against NPC. |
Reduction of EBNA1 expression and inhibition of STAT3 activation. |
[35] | [59] |
In vivo. Tumorigenicity, Western blot, and immunohistochemistry analyses. EBV-positive NPC cells (C666-1) in athymic nude mice. |
Treatment with BBR at doses of 5 and 10 mg/kg significantly suppressed the tumorigenicity and growth of NPC cells. |
Inhibition of STAT3 activation. Inhibition of IL-6-activated STAT3. |
[36] | [60] |
In vitro and in vivo. Cell proliferation, cell apoptosis, and Western blot assays. Xenograft tumor models of human NPC analysis. Male nude mice (BALB/C-NU). |
Combined treatment of BBR (10 mg/kg) with Rg3 (5 mg/kg) remarkably diminished tumor growth in NPC CNE2 xenograft nude mice. |
Enhancement of the expression of the apoptosis-associated protein Bax. Inhibition of survivin, PCNA, and anti-apoptotic protein Bcl-2 expressions via targeting the MAPK/ERK signaling pathways. |
[39] | [63] |
In vitro. Multiple biochemical assays. EBV-transformed B cells and cancerous B cells. |
Treatment with BBR (50 µM) lessened cell viability and demonstrated apoptosis through a mitochondria-dependent pathway in EBV-transformed B cells and cancerous B cells. |
The mechanism has been elucidated through p53-mediated regulation of XAF1 and GADD45α expressions. |
[40] | [64] |