## 4 Advances in Nanotechnology towards Development of Nano-Based Therapies  
Pharmacotherapy, the use of drugs for disease treatment, is the cornerstone of numerous disease management protocols. It is designed to either kill pathological cells or alter the affected biological processes to reverse the disease's effects. The major drawbacks of these therapies are non-specificity and off-target side effects [10; 11]. Non-specific drug distribution within the body can result in insufficient drug dosage reaching the desired target, as well as toxicity towards healthy cells and tissues. Some of the potent drugs have been withdrawn from the market due to these limitations. Ideally, the drugs should only be able to target and reach the pathological tissues with minimal toxicity to healthy cells, escape bio-degradation, retain drug activity while circulating in the body, and only induce their activity on the diseased cells [11].  
Nanotechnology-based systems have the potential to address these issues, using nanomaterials as drug-delivery systems, photothermal, radiosensitizers, and therapeutic agents. Nanomaterials have a larger surface area-to-volume ratio, which increases their capacity to load multiple molecules, and this feature is widely exploited for biomedical applications. Bioactive molecules can either be encapsulated in or attached to the NP surface for diagnostic, therapeutic, and/or theranostic purposes [10; 12; 13]. Therapeutic strategies using nanomaterial-based delivery systems to treat cancer take advantage of the enhanced permeability and retention effect in the vasculature of the diseased tissues (passive targeting) or use targeting moieties (active targeting) [14]. Targeted nanotherapy has been extensively used to target and increase drug specificity toward diseased tissues [10; 15]. Nanosystems have been shown to improve cancer patient survival rates and quality of life and have enhanced efficacy [12]. Targeting moieties also help to reduce systemic and toxic bystander effects, thus, maximizing the efficacy of nanotherapy [16].  
The use of nanomaterials as drug-delivery vehicles has been the highlight of nanomedicine and has successfully improved drug efficacy and encouraged the repurposing of conventional drugs [11; 12; 13]. The earliest application of nanomedicine was in cancer research, where biodegradable NPs were used to deliver chemotherapeutic drugs to tumors [17]. Abraxane (albumin-bound paclitaxel NPs) was the first chemotherapeutic nanordug to be approved by the Food and Drug Administration (FDA) for the treatment of metastatic breast cancer [11]. Dosil (liposome-encapsulated doxorubicin) is also FDA-approved for the treatment of refractory ovarian cancer, breast cancer, and [PERSON]'s sarcoma. These nanodrugs (Abraxane and Dosil) showed enhanced drug efficacy with improved safety profiles compared to anti-cancer drugs on their own [11].  
Metallic nanoparticles (MNPs) have also found their way into clinical use as drug delivery and photothermal agents. Aurimmune (CYT-6091) and Aurolase are two FDA-approved AuNPs-formulations used for the treatment of solid tumors. Aurimmune uses cAuNPs as delivery agents of tumor necrosis factor (TNF)-\(\alpha\) for the treatment of cancer patients who are unresponsive to chemotherapy and in the late stages of pancreatic, breast, colon, melanoma, sarcoma, and lung cancers. Aurimmune achieved safety and targeted biological response at the tumor site at a dose significantly lower than that required for TNF-\(\alpha\) alone [12]. Aurolase, nanoshells with a 15 nm gold shell, is used for the treatment of head and neck tumors and is in clinical trials for the photothermal treatment of prostate cancer [13]. Although only a few AuNPs formulations are in anti-cancer clinical trials, AuNPs possess unique physicochemical properties that are also beneficial for the treatment of chronic diseases.