Besides fungal bioactive compounds, other structural fungal components are also being incorporated in fabricating nanocarrier, e.g., fungal β glucan. For instance, Meng et al. [241] have developed dendritic nanoparticles derived from fungal β glucan to deliver the cancer drug, Doxorubicin. β-glucans are chiral polysaccharides that occur in the fungal cell wall, and they possess an intrinsic immunostimulatory activity especially on activating macrophages and dendritic cells. Therefore, β -glucans have been widely used as an anti-tumor adjuvant [242]. The unique chiral structure of glucans enables supramolecular interaction with pharmaceutical molecules based on chiral interaction rather than the frequently adopted electrostatic and hydrophobic interactions within the drug delivery systems. Electrostatic and hydrophobic interactions may influence the integrity of tissue proteins and cell membranes [243]. Moreover, β-glucans can self-assemble into nanoparticles making them a potential carrier for many therapeutics. All these features attracted researchers to further investigate β-glucans for drug delivery and anticancer therapeutic applications. Huang et al. [242] β-glucans with different chirality were investigated for DOX drug loading and encapsulation capacity, cellular uptake and immunoactivities activity. Their results have demonstrated that β-glucans can maintain strong immune activation as long as their chirality is maintained. In addition, a subtle variation in their chiral fingerprints may exhibit a considerable influence on the cytokines genes expression. Likewise, chirality played a key role in DOX drug encapsulation efficiency and drug release manner. Nevertheless, free DOX has exhibited higher cell toxicity when compared to the encapsulated DOX. According to Huang et al. [242], this might happen due to the low molecular weight of free DOX which facilitates rapid cell internalization via diffusion, meanwhile, encapsulated DOX is released only under acidic conditions. Certainly, there are more investigations needed to further understand the potential of these structural carbohydrates in developing drug delivery systems for anticancer therapies.

Other fungal structural components have also been explored for the fabricating nano-carriers for drug delivery to target tumors, e.g., extracellular vesicles secreted by fungi [244]. For instance, the EVs secreted by Athrobotrys oligospora were found to provoke the secretion of several proinflammatory cytokines and chemokines, referring to their potential as immunomodulating agents and adjuvants for tumor immune therapies. In association with DOX, these nanocomplex showed higher cytotoxicity than free DOX, when tested in several cancer cell lines [245]. However, in this study, DOX was associated with the nanoparticles outer surface only via simple electrostatic interaction. Thus, healthy cells can still be exposed to the anticancer drug, in addition to the plasma protein interaction with the nanoparticles may cause the drug to dissociate from the NPs causing burst release. Therefore, an alternative setting needs to be established for more efficient in vivo applications.

Despite the several advantages and therapeutic potential fungal-derived compounds show, there are challenges remaining to bring those compounds into clinical translation. More investigating research is needed to further understand the applicability for large scale production. Although several fungal metabolites have passed to the clinical trials [214], they still face difficulties to transform these good preclinical results into anticipated human responses because of their poor pharmacokinetic properties and solubilities [246, 247]. Researchers are constantly trying to reformulate these fungal metabolites and modify their structure to make them more suitable for biomedical applications. However, these formulas need to be examined in animal models and corresponding clinical trials to prove their competency. Eventually, pharma companies would have an essential role to further proceed forward with these formulations to the help patients.

For several years, the main source of medical treatments in developing countries have been plants, used as herbal medicines [248]. Several vegetables, fruits, herbs, and plant extracts have been used for cancer treatment, by inducing cellular apoptosis and inhibiting tumor proliferation [248, 249], since they present bioactive molecules with therapeutical efficacy [249]. For example, paclitaxel and its analogue docetaxel are chemotherapeutic agents used in clinics to treat several types of cancer, due to properties as microtubule disruptors, are plant taxanes [248, 249]. However, several of these phytochemicals, such as curcumin, quercetin, and resveratrol, present several disadvantages, such as low aqueous solubility, poor stability, fast metabolization, poor pharmacokinetics, low bioavailability, and poor target specificity towards cancer cells, with possible toxicity and multidrug resistance [250,251,252]. Besides, although plant compounds have been demonstrated to have antitumor properties in cell culture and animal studies, the results in human clinical trials are conflicting [250]. Therefore, several studies propose the loading of phytochemicals into biocompatible NPs, which can enhance their absorption and bioavailability, protect from liver metabolic degradation, increase the circulation time, and increase the drug uptake in cancer cells compared to healthy cells, reducing the side effects [250, 251]. Therefore, loading phytochemicals into NPs has been shown to increase therapeutic efficiency and decrease toxicity, which translates into better patient compliance [251, 253]. Several nanosystems have been formulated to encapsulate plant molecules or extracts for anticancer therapeutics, such as liposomes, nanoemulsions, SLNs, micelles, among others [250]. For example, ergosterol, a poor soluble plant sterol with anticancer properties, was encapsulated into poly(lactide-co-glycolide) (PLGA) NPs by emulsion/solvent evaporation technique, with increased cytotoxicity against glioma, hepatoma, and breast cancer. The oral administration of these polymeric NPs in mice presented a sustained drug release and a longer circulation time, being distributed specially in the stomach, brain, and liver, in smaller concentrations in the kidney, spleen and lung, and non-existent in the heart and lung. On the other hand, small amounts of sterols were detected in mice administrated with free ergosterol, which indicated that the PLGA NPs can improve the bioavailability, biodistribution and antitumor efficacy of poorly soluble plant compounds [254].

Herein, we access the recent research concerning the enhanced anticancer properties of plant compounds when encapsulated with NPs, being that the plant compounds are divided by chemical classes – alkaloids, polyphenols, benzophenones, quinones, terpenes. Also, we describe the properties of NPs loaded with plant extracts and oils, as well as the NPs produced by biogenesis.

Alkaloids are a class of naturally organic compounds with nitrogen containing heterocycles [255], and have demonstrated anti-inflammatory, neuroprotective, antimicrobial, and anticancer properties [255, 256]. However, their poor water solubility and the lack of specificity towards cancer cells [255, 257], leads to inadequate tissue discrimination and several side effects connected to their toxicity [255]. The use of nanocomposites, such as nanoemulsions, polymeric NPs [257] and lipidic NPs has shown to surpass these limitations and increase the anticancer potential of alkaloids, improving their bioavailability and providing passive and active targeting strategies. Therefore, in vitro and in vivo studies shown that loading several alkaloids into NPs increases their cytotoxicity for cancer cell lines and reduces the tumor growth and systemic toxicity, respectively (Table 5) [255, 257].

Berberine (BBR) is a natural isoquinoline alkaloid which main sources are Phellodendron amurense, Coptis chinesis, and Hydrastis canadensis. This compound has antimicrobial, anti-inflammatory, antidiabetic, and chemotherapeutic properties [259, 261, 266]. BBR has presented anticancer properties due to its ability to induce apoptosis and cell cycle arrest and inhibit cell migration and invasion [266], while having less side effects when compared with other chemotherapeutic drugs [264]. However, its low absorption rate, stability and targeting delivery are some factors that disable BRR therapeutic use [259, 263].

For that reason, several studies have been encapsulating BBR in several types of NPs. For example, Wang et al. have demonstrated that BRR loaded into Chitosan NPs functionalized with FA modulated the migration, proliferation, and apoptosis of human nasopharyngeal carcinoma CNE-1 cells both in vitro and in vivo. The produced NPs presented pH-dependent release, inducing cancer cells apoptosis while restricting their mobility, resulting in a reduced tumor volume in mice [258]. BBR-loaded chitosan NPs also presented in vivo anticancer properties towards urethane-induced lung cancer. While control groups injected intraperitoneally with urethane presented increased levels of nitric oxide, NF-kB and HIF1-α and decrease glutathione (GSH), SOD, caspase 9 in the lung tissue, and high serum levels of Vascular Endothelial Growth Factor (VEGF) receptror-2, alanine aminotransferease, aspartate aminotransferase, urea, and creatinine, oral treatment with Chitosan NPs loaded with BBR (ChitosanNPs@BBR) modulated serum Bax and VEGF receptor-2 expressions, and lung caspase 9 and HIF 1 gene expressions, reducing cancer growth and promoting apoptosis, while inhibiting tumor angiogenesis (Fig. 11) [259]. BBR also demonstrated chemotherapeutic potential against non-small cell lung cancer when encapsulated into liquid crystalline NPs composed of monoolein and poloxamer 407. In vitro studies demonstrated and antiproliferative properties towards A549 cancer cell line (IC50 of 10.1 µM), as well as anti-migratory and colony formation properties, probably due to the inhibition of epithelial-mesenchymal transition (EMT)-related proteins, such as SNAIL, P27 and vimentin, as well as other proteins involved in the promotion of tumor proliferation and migration, such as PDGF-AA, Axl, BCLx, Cathepsin S, Galectin-3, Survivin, CEACAM5, Pro-granulin, and ERBB3 [260]. Another study concerning the BBR therapeutic potential against lung cancer produced liquid crystalline NPs produced by ultrasonication using poloxamer 407 and phytantriol as vehicle for BBR delivery. This nanocompound reduced A549 cells viability, due to the modulation of P53, PTEN, and KRT18 genes, and the downregulation of proteins associated with cell proliferation such as AXL, CA9, ENO2, HER1, HER3, HER3, PRGN, and PDGF-AA. Besides, A549 cell migration and colony formation were also inhibited due to the downregulation of DKK1, CTSB, CTSD, BCLX, CSF1, and CAPG proteins [261].

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Histological photomicrograph of transverse lung sections: A control mice presented normal alveoli architecture with thin interalveolar septa constituted of simple squamous epithelial cells and normal interstitial tissues and alveolar sacs; B mice treated with urethane presented alveolar adenoma, cellular alterations (cells tend to be round, with stained cytoplasm, poor defined borders) and mildly differentiated squamous cell carcinoma; C mice treated with urethane also presented a defined alveolar adenoma demarcated from surrounding parenchyma as well as a mass of inflammatory cells infiltration, with damaging potential for the lung tissue; D mice treated with urethane and BBR displayed a partial alleviation of lung tissue degradation, with mild aggregations areas; E Mice treated with urethane and BBR-loaded chitosan NPs presented a significant reduction of the lung tissue degradation Reproduced with permission [259].

NPs loaded with BRR have also shown therapeutic potential against breast cancer [262, 263]. For example, a BBR loaded into nanocomposites of gold and collagen (Au-Col-BB) have demonstrated higher toxicity for Her-2 cancer cell line than to BAEC. This nanosystem presented were internalized into the cancer cells mainly via clathrin-mediated endocytosis and cell autophagy, inducing cancer cell apoptosis, by upregulating both Bax and p21 proteins, while suppressing anti-apoptosis proteins, such as Bcl-2 and cyclin D1, as well as reduced cancer cell migration by downregulating both metalloproteinase-9 (MMP-9) activity. Au-Col-BB also presented therapeutic properties in vivo, by reducing tumor size and increasing the time of survival [262]. Another study encapsulated BBR on citrate-capped silver NPs through electrostatic interactions, which were afterwards conjugated with conjugated with polyethylene glycol-functionalized folic acid (FA-PEG@BBR-AgNPs) to target the folate receptors, overexpressed in cancer cells. The resultant nanosystem presented higher toxicity against MDA-MB-231 breast cancer cells than HBL-100, a healthy breast cancer, inducing mitochondria dysfunction and increased reactive oxygen species (ROS) production, activating the pro-apoptotic factors cytochrome c, caspase-9, caspase- and Bax, while downregulating the antiapoptotic protein Bcl-2. On the other hand, FA-PEG@BBR-AgNPs also modulated the expression levels of proteins associated with tumor progression (PI3K, AKT, Ras, Raf, and ERK), angiogenesis (VEGF) and hypoxia (HIF-1α). Consequently, the nanosystem induced apoptosis, with nuclear alterations, such as nuclear shrinkage and bulging, nuclei fragmentation. Furthermore, in vivo studies showed that FA-PEG@BBRAgNPs inhibited tumor growth, without presenting any significant lesions in the lungs, liver, kidneys, heart, and brain [263].

Other studies have shown the potential of BBR-loaded NPs for liver cancer treatment. Li et al. [264] loaded BBR into Janus Au silica NPs conjugated with FA. This nanosystem presented dose-dependent cytotoxicity against SMMC-7721 cells and HL-7702 cells. Also, in vivo studies demonstrated the nanosystem synergic potential with X-ray radiation and photothermal therapy, reducing the tumor volume, without major side effects [264]. Yue et al. also loaded BRR into mesoporous silica NPs (MSNs) for the treatment of liver cancer. These NPs where then coated with human liver cancer HepG2 cell membranes to increase their targeting and reduce the blood clearance. The resulting nanosystem demonstrated antitumor properties both in vitro and in vivo, promoting the accumulation of BBR in tumor tissue, reducing the tumor volume and weight, without presenting relevant toxicity [265]. Additionally, BBR encapsulated into PLGA-HA copolymeric NPs presented anticancer properties in both HeLa and MCF-7 cancer cells, although the NPs uptake was higher in MCF-7 cells, due to the higher CD44 receptor density, which is targeted by HA. In vivo studies demonstrated that these NPs increase the ROS levels in EAC cells, with consequent mitochondria dysfunction, apoptosis, and cell cycle arrest at sub-G1, increasing the mice life span and decreasing the decreasing the tumor-burden in tumor-bearing mice [266]. Other polymeric NPs, composed of polylactic acid, were also studied for BBR delivery towards HCT116 colon cancer cells. The loaded NPs increased the cellular drug accumulation when compared with dree BBR, presented pH-dependent release and increased cytotoxicity towards cancer cells compared to NIN3T3, a non-neoplastic fibroblast call line [267].

Camptothecin (CPT), an alkaloid existent in the wood, bark, and fruit of the Asian tree Camptotheca acuminate, inhibits topoisomerase I, an enzyme involved in DNA replication that is overexpressed in several tumors, resulting in cell cycle arrest and apoptosis [268]. Therefore, CPT is an extremely cytotoxic chemotherapeutic compound, although it was poor water-solubility and is non-specific, failing in clinical trials due to its toxicity [271]. McCarron et al. loaded CPT into polymeric PLGA NPs, covalently attached to antibodies targeting the Fas receptor (CD95/Apo-1), overexpressed in colorectal cancer. It was found that, while CPT presented an IC50 of 21.8 ng/mL against HCT116 cancer cells after 72 h incubation, The polymeric CPT-loaded NPs exhibited an increased cytotoxic effect, with an IC50 of 0.37 ng/mL [268]. Studies have demonstrated that PLGA NPs loaded with CPT also presented antitumor potential against glioma, increasing the payload to 10 times higher in tumor compared to healthy brain tissue. The treatment of the NPs at 20 mg/Kg b.w. increase at CPT levels in the tumor site, decreasing the tumor growth and increased the time of survival compared to treatment with saline, free CPT, and NPs at 10 mg/Kg b.w, without adverse effects [269]. CPT have also presented increased antitumor potential when encapsulated within solid lipid NPs prepared using a lipid (cetyl palmitrate) and a surfactant (polysorbate 60 or 80). The encapsulation of CPT in NPs increased the drug uptake by an endocytic pathway and cell death in human glioma cell lines (A172, U251, U373, and U87), reducing the IC50 value compared to free CPT (A172: 93 × lower; U251: 99 × lower; U373; 896 × lower; U87: 129 × lower). Further in vivo experiments supported that the use of NPs as drug vehicle increased CPT concentration in serum and brain. Moreover, the CPT could be detected in brain until 24 h after i.v. administration, while free CPT could only be detected until 8 h after administration. On the other side, the accumulation of CPT increased in organs of the reticuloendothelial system, such as lungs, liver and spleen, responsible for NPs clearance [270]. More recently, Landgraf et al. prepared porous silicon NPs functionalized with cetuximab, an antibody targeting the epidermal growth factor receptor (EGFR), for CPT delivery. The produced NPs presented pH-responsive properties and have demonstrated anticancer properties in vivo against breast cancer induced by injection of MDA-MB-231 cells in the murine mammary fat pad. Overall, the tumor growth rate of mice treated with the loaded NPs was reduced compared with mice treated with unloaded groups, especially after the weeks 18 and 19, reducing the metastases in lung, liver and murine bone [271].

Capsaicin (CAP) is the main active compound of chili pepper (Capsicum annuum) and it is responsible for its hot taste [274]. Studies revealed the CAP plays a role at tumor development, as a carcinogen or as a cancer preventive substance [272, 282]. CAP has shown therapeutic properties against bladder, lung, breast, colorectal, stomach, prostate cancers, a nasopharyngeal carcinoma, among others [272, 274, 282], by inducing both mitochondrial intrinsic apoptosis and extrinsic death receptor pathways [272]. Besides, CAP has presented antitumor synergy with other chemotherapeutic agents (for example, 5-fluorouracil, cisplatin, pirarubicin, sorafenib) have been proved [282]. However, CAP therapeutic use is limited by its hydrophobicity, low affinity, and short half-life [273, 282]. Also, CAP is very irritant, causing skin and gastrointestinal pain and burn [274]. Therefore, its encapsulation into NPs and micelles have been studied to prolong the drug retention in the blood circulation, while increasing its targeting towards the tumor site and decrease the side effects [282]. Similarly, CAP loaded into lipid NPs produced by thin-film hydration technique, using 1,2-Distearoyl-sn-glycero-3-phosphoethanolamine-N- [methoxy (polyethylene glycol)-2000] folate presented more cytotoxicity towards SKOV-3 ovarian cancer cells than in healthy cells, probably due to the overexpression of folate receptors in cancer cells, increasing the receptor-mediated endocytosis of these lipid NPs. Moreover, the lipid NPs increased the CAP pharmacokinetics, probably due to the presence of PEG in the NPs structure [272]. More recently, Xu et al. [273] produced calcium carbonate NPs to load CAP, providing an additional efflux of extracellular calcium ions to cause cancer cell death. The resulting NPs presented pH-responsive properties, activating the TRPV1 channel on the Hepg-2 cells membrane, resulting in an excessive influx of calcium ions, with consequent mitochondria dysfunction and increase of intracellular ROS. In vivo studies have shown that the tumor growth of mice treated with loaded NPs was significantly decreased when compared with no treated mice, or mice treated with free drug, with elevation of the caspase-3 levels and the calcium weight per gram of tumor tissue, with no relevant tissue damage [