Nanotechnology to Cure Breast Cancer and Obstacles in its Way

    

    

    Graphical Abstract : 
    

The possible factors associated with development of breast cancer include reproductive, menstrual, and hormonal factors. The family history, obesity, high caloric diet, lack of breastfeeding, use of oral contraceptive pills and ingestion of hormones like estrogen in HRT are all contributing factors to breast cancer [4,5].

Traditional treatment of breast cancer involves approaches like surgery, radiotherapy and chemotherapy, all of which have certain limitations and many side effects. Chemotherapy involves the use of anticancer drugs, which are non-specific and cytotoxic. They target not only cancer cells but also healthy cells in the body and leads to Multiple Drug Resistance (MDR). Radiotherapy can also cause side effects due to damage to tissues surrounding the cancer site. This can also cause impairment of immune system and other side effects like fatigue, anemia, diarrhea and vomiting [1]. The use of radiation therapy is also influenced by the presence of breast cancer gene variants. Individuals having pathogenic variants of TP53 are at higher risk of development of new cancers form radiation therapy. The use of radiotherapy and chemotherapy can also cause increase risk of heart disease [6,7]. Surgery can be used for localized cancer removal but it fails in the treatment of metastasized cancer [1]. Nanotherapy on the other provides a solution to all above problems by providing targeted drug delivery to cancer cells with reduced toxicity, enhanced imaging, monitoring and effective drug delivery [8].

Carbon Nanotubes (CNTs) are hollow cylindrical structures of graphene sheets [9]. CNTs are classified as Single-Walled Carbon Nanotubes (SWCNTs) and Multi-Walled Carbon Nanotubes (MWCNTs) [10]. CNTs, in combination with the drugs like doxorubicin, are used extensively as improving agents in cancer therapy and diagnosis because of their large surface area, conjugation ability, and encapsulation of drugs [11,12]. To make CNTs tumorspecific, they can be conjugated with ligands against biomarkers that are over-expressed in cancerous tissues. For example, SWCNTs can be conjugated with CD44 antibodies to target CD44 receptors on breast cancer stem cells [13]. Although CNTs are hydrophobic in nature, they can be functionalized with hydrophilic substances to improve their biocompatibility and solubility [9]. Because of their unique physiochemical properties, CNTs have numerous applications in diagnosis and treatment of different diseases especially cancer [11].

Chemotherapeutic drugs are encapsulated in nano-scale devices to increase the targeted drug delivery and bioavailability of breast cancer drugs [14]. Nanomaterials are nano-carriers of drugs; having the ability of imaging, tracking, and targeting [9].

Nanoparticle is a nanomedicine for cancer treatment and it has been reported by researchers that the uptake of nanoparticles (organic or inorganic) can improve the limitations of traditional therapeutics [15]. Particles having size between 1 and 100nm are referred as nanoparticle [16]. Basically, nanoparticles (NPs) are involved in targeted drug delivery at the tumor site. Micro-particles cannot pass through tiny capillaries having 5-6 microns diameter, so nanoparticle are more suitable to reach remote areas at cancer site [17].

Drug carriers are of several types such as micelles, polymeric dendrimers, microspheres, Quantum Dots (QDs), nano-emulsions, liposomes, hydrogels, and Gold Nanoparticle (GNPs), which adopt diverse methods of drug attachment such as covalent binding, adsorption, and encapsulation [14]. Gold Nanoparticle are considered as a best vaccine vector because they have appropriate payload and are highly biocompatible [16]. Systematic administration of nanoparticle at the tumor site causes accumulation of nanoparticle in the tumor cells through enhanced permeability and retention (EPR) effect; this is due to poor drainage of lymphatic system [18].

In cancer, therapy nano-medicines face certain obstacles in becoming a new paradigm due to incomplete understanding of nano-bio interactions, complexities, heterogeneity of tumor biology, chemistry and good manufacturing practice (GMP). Difference between the efficacies obtained in preclinical studies and the outcomes from clinical trials, is another well-recognized obstacle due to lack of tumor models that can recapitulate human cancers [19]. Enhanced permeability and retention effect (EPR) is one of the example in which small animal models show positive results but such evidences are lacking in humans during clinical trials [20]. In vivo and in vitro toxicity testing assays show that nanomaterials have detrimental effects to biological system at molecular and cellular level because of varying physiochemical properties as, these can impact numerous biological pathways. Because it is impossible to study toxicological properties of all Nano material variants, it is a challenge to testing toxicity of nanomaterials [21].

Carbon Nanotubes in Breast Cancer Treatment

The promising size, needle-like structure and unique physiochemical properties of carbon nanotubes make them a good tool for fighting breast cancer [9]. CNTs are mostly used for targeted drug delivery and photothermal therapy for breast cancer [11].

One of the major causes of treatment resistance in breast cancer is hypoxia. This is because tumor cells initiate multiple adaptation processes under hypoxic conditions, which results in treatment failure. In 2017, Jia, Weng et al. determined the increase in chemosensitivity and radiosensitivity of MDA MB 231 and ZR 75 1 human breast cancer cell lines by synthesizing a new functionalized single walled carbon nanotube carrying oxygen. They synthesized an oxygen carrying tombarthite modified folic acid conjugated chitosan (R O2 FA CHI) SWCNT nanocarrier and treated cancer cell lines with this nanocarrier along with chemotherapy drugs or radiotherapy. It was observed that the R O2 FA CHI SWCNTs significantly enhanced the chemosensitivity and radiosensitivity of human breast cancer cell lines by downregulating the expression of B cell lymphoma 2 (Bcl 2), survivin, hypoxia inducible factor 1a (HIF 1a), multidrug resistance associated protein 1 (MRP 1), P glycoprotein (P gp), RAD51 and Ku80 [22].

Targeted drug delivery

In order to make carbon naotubes tumor-specific, they can be conjugated with monoclonal antibodies (mAb) or aptamers [10]. In 2015, Al Faraj, Shaik et al. determined the efficiency of SWCNTs to improve the clinical utility of doxorubicin (DOX) in breast cancer murine model. They synthesized Iron-tagged SWCNTs conjugated with Endoglin/CD105 antibody with or without DOX. After characterizing the nanoparticles for biocompatibilty, they were actively and magnetically targeted to tumor sites in murine model. It was observed that DOX-loaded SWCNTs induced significant increases in apoptosis, DNA damage, and oxidative stress. These results showed enhanced therapeutic efficacy of DOX delivered through antibody-conjugated magnetic SWCNTs [23].

Another approach to control the cancer cell proliferation and metasis to other tissues is by blocking certain molecular pathways through small molecules or monoclonal antibody. Trastumzumab an anti-HER monoclonal antibody is considered to be the besttargeted therapy so far. The nanodelivery of trastuzumab can be done by decorating the surfaces of nanocarriers with antibody and allowing targeted delivery of trastuzumab to HER2+ cells. Antibody conjugated with gold sulfide nanoparticles can be used for photoablation therapy and ln-labeled trastuzumab conjugated to modified gold nanoparticles can be used for radiation therapy [24].

Abraxane, also called as nab-paclitaxel or nanoparticle albumin bound paclitexal, is another example of targeted drug delivery to breast cancer cells [24]. Paclitaxel (PTX) has been an important contribution to the treatment of breast cancer. A Single Walled Carbon Nanotube Based Drug Delivery System (SWNT-HAS) was established using human albumin proteins. This combination displayed 80% of intracellular drug delivery in MCF-7 breast cancer cell along with high growth inhibition; suggesting high delivery efficiency and effectiveness [25].

A cisplatin modified poly(d,1-lactide-co-glycolide) (PLGA) has shown significant efficacy in breast cancer patients [14].

Photothermal therapy

Because of the intrinsic hyperthermic property of CNTs induced by near infrared (NIR) irradiation, several attempts have been made to use them for the photothermal ablation of cancer cells [26]. In 2016, Han, Han et al. synthesized SWCNTs conjugated with PEG and thioaptamer and determined their effect in human breast cancer targeted photothermal therapy in-vivo and in-vitro. In vivo testing was performed via injection to the caudal vein to subcutaneous breast cancer mice models while HCC1937 human breast cancer cells were used for in vitro testing. In vitro results showed that SWCNT-PEG-TA significantly decreased the cell viability. Similar results were observed in in vivo study as well [27]. In another study carried out by Oh, Jin et al. in 2017, MDA-MB-231 cell death promoted by SWCNTs-Dox was investigated. Dox-release from SWCNTs was accelerated by NIR irradiation. It was observed that Dox released from SWNTs- Dox effectively localized into the MDA-MB-231 cell nucleus and accumulated inside the cells at high concentration. SWNTs-Dox and PPT together promoted an effective cell death in MDA-MB- 231 cells by mitochondrial disruption and Reactive Oxygen Species (ROS) generation [28].

Nanoparticles - An Emerging Nanomaterial to Treat Breast Cancer

Conventional chemotherapeutics have systemic toxicity and adverse effects on normal cells. Nanotechnology has revolutionized the treatment of breast cancer by targeted drug delivery. Nanoparticles have some important parameters such as size, charge, and shape. These parameters are significant in targeted drug delivery at cancer site. There are many advantages concerned with nanoparticles: (1) prevention of early degradation of drug, (2) absorption rate of drug is increased in selected tumor areas, (3) intracellular penetration of drug is increased by nanosystem, (4) lowers the rate of systemic toxicity, (5) premature interaction of drug and biological system is inhibited, (6) have capacity to absorb or load more than one therapeutic drugs, (7) Nanomedicine are more stable as compared to conventional ones. So Nanomedicine are easily accessible to tumor site and have great potential to treat cancer [29] [30].

Nanoscale dispersions of solid particles are referred as nanoparticles. According to American society for Testing and Materials, nanoparticles are three dimensional small bits of matter, having size from 1-100nm [31]. Nanoparticle are classified into different types; nanospheres, nanorings, nanoshells, nanocapsules, fullerenes, liposomes, dendrimers and quantum dots [32].

Cancer treatment by nano-system

Tumor is optimally treated by using Nanoparticles (NPs), either organic or inorganic in nature. Organic nanoparticles are composed of organic and inorganic materials. Nanoparticles are made from components of particular metals having specific physicochemical properties and these properties are related to that particular metal [15].

Inorganic nanoparticles

Inorganic nanoparticles are made up of two basic parts: shell and core. Core of inorganic NP is made up of metals such as gold, silver, quantum dots, and iron oxides. Shell is composed of either organic polymers or metals. The function of shell is to protect the inner core from chemical interactions and act as a binding substrate for biomolecules [15].

Gold nanoparticle

Gold nanoparticles are highly selective anti-cancerous nanodrugs having unique biological compatibility, and increased payload efficiency. Various biomolecules are coated over gold nanoparticles to make their surface functionalized and more stable in biological environment. Gold nanoparticles are pharmaceutical cargos for targeted drug delivery at tumor site [34].

Characteristics of gold nanoparticles

Gold nanoparticles are found in different sizes, shapes, compositions, and structures. Gold nanospheres (AuNPs) are solid gold balls, which are synthesized by the reduction of chloroauric acid, having diameter from few to more than 100nm. Gold nanoshells (AuNSs) are composed of silica cores and thin gold shells protecting that silica cores, having size between 50-150nm. [31]. Inorganic Nanoparticle such as nanoshells and GNPs are used in combination with MIR and high-resolution superconducting quantum interference devices to enhance the therapeutic effect [35].

Gold nanoparticles conjugated with trastuzumab increases the uptake of AuNPs by breast cancer cells and trastuzumab conjugated AuNPs is potentially strong therapeutic agent to treat breast cancer [31] (Figure 1).

    

    

    Figure 1: AuNPs (Gold Nanoparticles) to treat/kill breast cancer. (a) Normal
amount of HER2 in normal breast cell. HER2 Receptors sending signals to
breast cell to grow and divide in normal fashion as in mitotic cell division. (b)
Huge amount of HER2+ in cancerous breast cell. Too much HER2 receptors
sending more signals, causing cell to grow and divide quickly in uncontrolled
manner by losing mitotic mechanism. (c) Trastuzumab (Antibody) is
chemically conjugated with AuNP (Gold Nanoparticle) via a protein called
a linker molecule. Trastuzumab is used to treat breast cancer that is HER2
receptor positive, where AuNP has a huge payload efficiency. (d) Gold
Nanoparticle is pharmaceutical cargo and able to transport drug at targeted
tumor site and thus blocking the HER2+ receptors from signaling the cell to
divide and grow in uncontrolled manner.