Nanocarriers are added as colloidal nanosystems loaded with therapeutic agents (anticancer agents or any macromolecules, such as proteins or genes), which allow drugs to selectively accumulate at the site of cancerous tumors. As a result of their unique nanometer range, 1–1000 nm (drug administration is preferable in the 5–200 nm range), they are used for cancer treatment. The main and most promising nanocarriers in the literature are iron oxide, gold, polymers, liposomes, micelles, fullerenes (carbon nanotubes, graphene), dendrimers, quantum dots, and nanodiamonds.
Cancer is a major cause of global morbidity and mortality. It is a disease caused by a variety of factors, and its formation depends on several genetic and epigenetic aspects [1]. Malignant tumors have a specificity that affects other healthy cells in the body [2]. In order to develop more effective methods of diagnosis and treatment without harming the patient, various resources have been widely explored, and current treatment methods used for cancer control include chemotherapy, surgery, radiation, and biological therapies (immunotherapy and hormone therapy) [3][4][5].
However, these therapies have certain disadvantages and, being invasive, have side effects before and after treatment, making the patient uncomfortable. For example, the use of chemotherapeutic drugs can affect the normal and healthy growth of good cells and bring opportunities for tumor recurrence. In addition, resistance to various drugs may develop, and poor biodistribution results in a low concentration of these chemotherapeutic agents at the tumor site, which may reduce the therapeutic effect of anticancer drugs [6][7][8][9]. In this context, it is necessary to research and develop alternative beneficial and effective therapies for the drug delivery system.
Nanotechnology can increase the pharmacological properties of compounds commonly used in the treatment and diagnosis of cancer, which is why it has emerged as an innovative possibility for therapeutic intervention in cancer and in the distribution of drugs [10][11]. This can usually be achieved by different routes of administration, such as oral, nasal, transdermal, intravenous, etc. These nanocarriers can improve the effectiveness of the drug and reduce side effects. They can be encapsulated or used in combination with other drugs [12][13]. In addition, nano-scale transporters can protect drugs or any macromolecules (proteins, peptides, etc.) from degradation, reduce renal clearance, and provide sustained or controlled release kinetics, thereby increasing drug efficacy at steady-state therapeutic levels [14][15][16][17]. Their half-life in the blood improves the therapeutic index, solubility, and stability of the capsules, compared to conventional treatment methods (such as tablets, capsules, and injections) [18][19].
Nanocarriers can be classified into three categories based upon the materials that they are made from (A) lipid-based nanoparticles, (B) inorganic nanoparticles, and (C) polymeric nanoparticles (Figure 1).
Figure 1. Types of nanocarriers used for drug delivery in cancer therapy. (A) Lipid-based nanocarriers; (B) Inorganic nanoparticles; (C) Polymeric nanoparticles.