The article describes the first human clinical trial using a targeted nanoparticle delivery system to administer siRNA to patients with solid cancers. The study aims to demonstrate the effectiveness of this approach in inducing RNA interference (RNAi) in human tumors. Key findings include: 1. **Evidence of RNAi Mechanism**: Tumor biopsies from melanoma patients treated with the targeted nanoparticles showed the presence of intracellularly localized nanoparticles, correlating with the administered dose levels. This is a significant advancement as it is the first time such evidence has been reported for systemically delivered nanoparticles. 2. **Reduction in mRNA and Protein Levels**: Both the specific messenger RNA (M2 subunit of ribonucleotide reductase (RRM2)) and the protein (RRM2) levels were reduced compared to pre-dosing tissue. Notably, an mRNA fragment was detected, indicating specific mRNA cleavage at the predicted site for an RNAi mechanism. 3. **Clinical Trial Details**: The clinical trial involves patients with solid cancers refractory to standard therapies, administered doses of targeted nanoparticles on specific days of a 21-day cycle. The nanoparticles consist of a synthetic delivery system containing a linear cyclodextrin-based polymer, a human transferrin protein targeting ligand, a hydrophilic polymer (polyethylene glycol (PEG)), and siRNA designed to reduce RRM2 expression. 4. **Biopsy Analysis**: Biopsies from three patients (A, B, and C) were collected after treatment, showing a dose-dependent accumulation of targeted nanoparticles in tumor tissues. Confocal images confirmed the presence of nanoparticles in tumor cells, not in the adjacent epidermis. 5. **Molecular Analysis**: qRT-PCR and western blot analyses demonstrated a reduction in RRM2 mRNA and protein levels, respectively, in post-treatment samples. Immunohistochemical (IHC) data further supported the reduction in RRM2 expression. 6. **RNAi Induced mRNA Cleavage**: A modified 5′-RNA-ligand-mediated RACE (5′-RLM-RACE) PCR technique detected an RRM2 mRNA fragment, confirming that the siRNA delivered by the targeted nanoparticles engaged the RNAi machinery and induced the desired mRNA cleavage. These findings provide the first mechanistic evidence of RNAi in humans from the delivery of siRNA via targeted nanoparticles, highlighting the potential of this approach for therapeutic applications.The article describes the first human clinical trial using a targeted nanoparticle delivery system to administer siRNA to patients with solid cancers. The study aims to demonstrate the effectiveness of this approach in inducing RNA interference (RNAi) in human tumors. Key findings include: 1. **Evidence of RNAi Mechanism**: Tumor biopsies from melanoma patients treated with the targeted nanoparticles showed the presence of intracellularly localized nanoparticles, correlating with the administered dose levels. This is a significant advancement as it is the first time such evidence has been reported for systemically delivered nanoparticles. 2. **Reduction in mRNA and Protein Levels**: Both the specific messenger RNA (M2 subunit of ribonucleotide reductase (RRM2)) and the protein (RRM2) levels were reduced compared to pre-dosing tissue. Notably, an mRNA fragment was detected, indicating specific mRNA cleavage at the predicted site for an RNAi mechanism. 3. **Clinical Trial Details**: The clinical trial involves patients with solid cancers refractory to standard therapies, administered doses of targeted nanoparticles on specific days of a 21-day cycle. The nanoparticles consist of a synthetic delivery system containing a linear cyclodextrin-based polymer, a human transferrin protein targeting ligand, a hydrophilic polymer (polyethylene glycol (PEG)), and siRNA designed to reduce RRM2 expression. 4. **Biopsy Analysis**: Biopsies from three patients (A, B, and C) were collected after treatment, showing a dose-dependent accumulation of targeted nanoparticles in tumor tissues. Confocal images confirmed the presence of nanoparticles in tumor cells, not in the adjacent epidermis. 5. **Molecular Analysis**: qRT-PCR and western blot analyses demonstrated a reduction in RRM2 mRNA and protein levels, respectively, in post-treatment samples. Immunohistochemical (IHC) data further supported the reduction in RRM2 expression. 6. **RNAi Induced mRNA Cleavage**: A modified 5′-RNA-ligand-mediated RACE (5′-RLM-RACE) PCR technique detected an RRM2 mRNA fragment, confirming that the siRNA delivered by the targeted nanoparticles engaged the RNAi machinery and induced the desired mRNA cleavage. These findings provide the first mechanistic evidence of RNAi in humans from the delivery of siRNA via targeted nanoparticles, highlighting the potential of this approach for therapeutic applications.