## 4 Advances in Nanotechnology towards Development of Nano-Based Therapies
### AuNPs in the Targeted Treatment of Obesity and Cancer
#### 4.1.1 Targeted AuNPs as Drug-Delivery Agents for Anti-Obesity Drugs  
The most widely studied biomarker in targeted therapy for obesity is prohibitin (PHB), a protein found to be differentially expressed by endothelial cells (ECs) in the vasculature of the white adipose tissues (WATs) of obese rodents [24; 25], monkeys [26], and humans [25]. The protein is intracellularly expressed by various cells and organs but exclusively expressed on the cell surface of the WAT ECs of obese subjects. Obesity is a disease that stems from the uncontrolled growth of WATs and associated angiogenesis. Anti-angiogenic treatments targeted to the WAT vasculature have been recognized as a feasible therapeutic strategy for the treatment of obesity. Targeting molecules that bind to PHB with high affinity and specificity include flavagines, miR-361, and adipose-homing peptide (AHP). AHP, a 9 amino acid peptide (CKGGRAKDC), has been studied extensively in the PHB-targeted treatment of obesity [24; 25; 26]. AHP fused/conjugated to a proapoptotic \(\mathrm{d}\)(KLAKLAK)\({}_{2}\) peptide (AHP-KLA) selectively targeted and killed the PHB-expressing cells in the WAT vasculature of obese mice [25] and monkeys [26] and reduced their body weights [25]. These effects were enhanced by using liposomes as delivery agents, which protected the treatment from bio-degradation and thus increased its circulation time [27]. The BRN used AuNPs as drug-delivery systems using the same targeting (AHP) and therapeutic (KLA) peptides for the treatment of diet-induced obesity in rats. Taking advantage of the unique physicochemical properties of AuNPs, i.e., their size and increased drug loading capacity, the citrate-capped AuNPs (cAuNPs) were chemically synthesized [28] and functionalized with AHP and KLA using methodologies developed at Mintek (Figure 1) [10]. Surface modifications of the cAuNPs were made to ensure the biocompatibility of the nanosystems in order to resolve noncompliance when used in vivo. Since PHB is upregulated in obese WAT vasculature compared to the normal blood vessels, the cAuNPs bio-functionalized with AHP alone (AG), and both AHP and KLA (AGK) were hypothesized to selectively bind and accumulate in these tissues. KLA peptides have been shown to induce cell death via apoptosis only when internalized by the cells [25]. The internalization of AGK by ECs of the WATs will cause the apoptotic cell death of these cells, resulting in anti-angiogenesis and reduced WAT mass and total body weight. The binding efficiency of AG was investigated on ECs isolated from the subcutaneous WATs that were obtained from lean and diet-induced obese Wistar rats. After 24 h exposure to cAuNPs and AG, increased gold content was observed in the cells isolated from the obese rats. Furthermore, Figure 2 shows that AG preferentially accumulated in the tissues that express PHB, mainly the WATs, while the unfunctionalized cAuNPs accumulated mostly in the reticuloendothelial system organs, such as liver, lungs, spleen, and kidney [24]. This  
Figure 1: Chemical synthesis and bio-functionalization of AuNPs with AHP (AG), and both AHP and KLA (AGK) peptides. study substantiated that AuNPs can serve as effective drug-delivery vehicles to the target tissues without compromising their functions [24]. The bio-distribution and anti-obesity effects of AGK following the mechanism described in Figure 3 have been further evaluated in diet-induced obese Wistar rats after 4 weeks of treatment (manuscript in preparation). Great strides have been taken throughout the world to develop targeted nanotechnology-based treatments for obesity, where nanocarriers were used as drug-delivery vehicles to improve the pharmacokinetics and pharmacodynamics of anti-obesity treatments [10; 24]. As experts in this area, the BRN recently published an extensive review of the three PHB-targeting strategies for the treatment of obesity [7].