Receptor-mediated transcytosis across the blood-brain barrier (BBB) may be a useful way to transport therapeutics into the brain. Here we report that transferrin (Tf)-containing gold nanoparticles can reach the brain parenchyma from systemic administration in mice through a receptor-mediated transcytosis pathway. This transport is aided by tuning the nanoparticle avidity to Tf receptor (TfR), which is correlated with nanoparticle size and total amount of Tf decorating the nanoparticle surface. Nanoparticles of both 45 nm and 80 nm diameter reach the brain parenchyma, and their accumulation there (visualized by silver enhancement light microscopy in combination with transmission electron microscopy imaging) is observed to be dependent on Tf content (avidity); nanoparticles with large amounts of Tf remain strongly attached to brain endothelial cells, whereas those with less Tf are capable of both interacting with TfR on the luminal side of the BBB and detaching from TfR on the brain side of the BBB. The requirement of proper avidity for nanoparticles to reach the brain parenchyma is consistent with recent behavior observed with transcytosing antibodies that bind to TfR.E ffective delivery of therapeutics to the brain has remained elusive owing to many factors, including inadequate transport across the blood-brain barrier (BBB). Numerous multidisciplinary-based strategies for transporting therapeutic agents from the blood into the brain have been proposed (1), including the use of receptor-mediated transcytosis. Recently, Yu et al. (2) reported increased accumulation of antibodies to transferrin (Tf) receptor (TfR) in the brain parenchyma when the antibody affinity was reduced. In that work, antibodies with high TfR affinity bound strongly to and remained associated with TfRs in the BBB, whereas antibodies with lower TfR affinity allowed for their detachment from TfRs and subsequent release into the brain parenchyma. These results are consistent with a previous report of a low-affinity (nearly identical to Tf-TfR interaction strength) antibody that significantly accumulated in the brain parenchyma (3).Targeted nanoparticles are finding applications for the delivery of a wide variety of therapeutic agents, and several have already reached the clinical testing stage in humans (4, 5). For example, in a Phase I clinical trial, a Tf-containing nanoparticle was used to deliver siRNA to cancer patients and shown to deliver functional siRNA to melanoma tumors in a dose-dependent manner (6). The results demonstrate that Tf-containing nanoparticles can be administered safely to humans.It is well known that the avidity and receptor selectivity of targeted nanoparticles can be tuned by the choice of targeting ligand and its number density; multivalent nanoparticles can engage multiple cell surface receptors simultaneously (7,8). When an individual targeting ligand is conjugated to a nanoparticle, the affinity of the ligand to the receptor is reduced. However, if the receptor density is such that multiple targeting ligands on...

Nanoparticles are currently being investigated in a number of human clinical trials. As information on how nanoparticles function in humans is difficult to obtain, animal studies that can be correlative to human behavior are needed to provide guidance for human clinical trials. Here, we report correlative studies on animals and humans for CRLX101, a 20-to 30-nm-diameter, multifunctional, polymeric nanoparticle containing camptothecin (CPT). CRLX101 is currently in phase 2 clinical trials, and human data from several of the clinical investigations are compared with results from multispecies animal studies. The pharmacokinetics of polymer-conjugated CPT (indicative of the CRLX101 nanoparticles) in mice, rats, dogs, and humans reveal that the area under the curve scales linearly with milligrams of CPT per square meter for all species. Plasma concentrations of unconjugated CPT released from CRLX101 in animals and humans are consistent with each other after accounting for differences in serum albumin binding of CPT. Urinary excretion of polymer-conjugated CPT occurs primarily within the initial 24 h after dosing in animals and humans. The urinary excretion dynamics of polymer-conjugated and unconjugated CPT appear similar between animals and humans. CRLX101 accumulates into solid tumors and releases CPT over a period of several days to give inhibition of its target in animal xenograft models of cancer and in the tumors of humans. Taken in total, the evidence provided from animal models on the CRLX101 mechanism of action suggests that the behavior of CRLX101 in animals is translatable to humans.nanomedicine | clinical translation | interspecies scaling | pharmacodynamics | Nanoparticles

Nanoparticle-based therapeutics are being used to treat patients with solid tumors. Whereas nanoparticles have been shown to preferentially accumulate in solid tumors of animal models, there is little evidence to prove that intact nanoparticles localize to solid tumors of humans when systemically administered. Here, tumor and adjacent, nonneoplastic tissue biopsies are obtained through endoscopic capture from patients with gastric, gastroesophageal, or esophageal cancer who are administered the nanoparticle CRLX101. Both the pre-and postdosing tissue samples adjacent to tumors show no definitive evidence of either the nanoparticle or its drug payload (camptothecin, CPT) contained within the nanoparticle. Similar results are obtained from the predosing tumor samples. However, in nine of nine patients that were evaluated, CPT is detected in the tumor tissue collected 24-48 h after CRLX101 administration. For five of these patients, evidence of the intact deposition of CRLX101 nanoparticles in the tumor tissue is obtained. Indications of CPT pharmacodynamics from tumor biomarkers such as carbonic anhydrase IX and topoisomerase I by immunohistochemistry show clear evidence of biological activity from the delivered CPT in the posttreatment tumors.nanomedicine | clinical trial | gastric cancer | tumor targeting | nanoparticles N anoparticle-based experimental therapeutics are being used to deliver a variety of different drug molecules to patients with solid tumors (1). Nanoparticle delivery seeks to improve pharmacokinetic (PK) properties (e.g., enhanced solubility of the drug, increased circulation times), alter biodistribution of the drug molecules to have low amounts of drugs in nontarget tissues and increased amounts in tumors, and enhance pharmacodynamics (PD) (e.g., tunable release of the drug at the site of action in the tumor) to produce enhanced efficacy while simultaneously reducing side effects (and most importantly, introducing no new side effects due to the nanoparticle) in patients. These properties can: (i) enable drug combinations formerly prohibited by toxicity limits, (ii) enable new classes of drug delivery [for example, short interfering RNAs (siRNAs)], and (iii) provide cell-specific targeting within a tumor.Delivery of drugs to solid tumors using nanoparticle technology relies on the enhanced permeability and retention (EPR) effect. The mechanistic data regarding the EPR effect come from animal models, primarily xenografted human tumors in mice. Because these xenografted tumors poorly recapitulate the architecture of true human tumors, there is skepticism about whether or not intact nanoparticles can localize in human tumors. Radiolabeled liposomes have been used to assess tumor accumulation in humans (2, 3). In those studies, the amounts of radioactivity accumulated in tumors did correlate with the number of microvessels measured from nine patient biopsies (3). Increased microvessel density may be an indication of increasing potential for the EPR effect. Also, Davis et al. demonstrated dose-depe...

Background: CRLX101 is an investigational nanoparticle-drug conjugate with a camptothecin payload.Preclinical evidence indicated preferential uptake in tumors, and tumor xenograft models demonstrate superiority of CRLX101 over irinotecan. A pilot trial was conducted at recommended phase 2 dosing (RP2D) using the bimonthly schedule to assess preferential uptake of CRLX101 in tumor vs. adjacent normal tissue in endoscopically accessible tumors in chemotherapy-refractory gastroesophageal cancer. Results from the biopsies were previously reported and herein we present the clinical outcomes. Methods: Patients initiated CRLX101 dosed at RP2D (15 mg/m 2 ) on days 1 and 15 of a 28-day cycle.Detection of preferential CRLX101 tumor uptake was the primary endpoint and objective response rate (ORR) was a secondary endpoint. With a sample size of ten patients, the study had 90% power to detect ≥1 responder if the true response rate is ≥21%. Results: Between Dec. 2012 and Dec. 2014, ten patients with chemotherapy-refractory (median 2 prior lines of therapy, range 1-4) gastric adenocarcinoma were enrolled. The median time-to-progression was 1.7 months. Best response was seen in one patient with stable disease (SD) for 8 cycles. Only ≥ grade 3 drugrelated toxicity occurred in one patient with grade 3 cardiac chest pain who was able to resume therapy after CRLX101 was reduced to 12 mg/m 2 . Conclusions: Bimonthly CRLX101 demonstrated minimal activity with SD as best response in this heavily pretreated population. Future efforts with CRLX101 in gastric cancer should focus on combination and more dose-intensive strategies given its favorable toxicity profile and evidence of preferential tumor uptake.

44 Background: Camptothecin (CPT) derivatives such as irinotecan have activity in 2nd-line therapy in advanced GEC with reported response rates of 0-15%. CRLX101 is an investigational nanoparticle-drug conjugate (NDC) with a CPT payload. Preclinical evidence indicates preferential uptake in tumors, and animal GEC xenograft models demonstrate superiority of CRLX101 over irinotecan. A pilot trial was conducted at recommended phase 2 dosing (RP2D) to assess preferential uptake of CRLX101 in tumor vs. adjacent normal tissue in endoscopically accessible tumors in patients with chemotherapy-refractory GEC. Data demonstrating preferential tumor uptake of CRLX101 has been presented separately and here we report on the clinical outcomes of patients enrolled. Methods: All pts initiated CRLX101 dosed intravenously at RP2D (15 mg/m2) on days 1 and 15 of a 28-day cycle until disease progression or intolerant toxicity. While detection of preferential CRLX101 tumor uptake was the primary endpoint, with 10 pts enrolled a secondary analysis could be performed with the study having 90% power to detect ≥ 1 responder if the true response rate is ≥ 21%. Responses were assessed using RECIST 1.1. Results: Between Dec. 2012 and Dec. 2014, 10 patients with chemotherapy-refractory (median 2 prior lines of therapy, range 1-4) GEC and adenocarcinoma histology were enrolled and evaluable for response and toxicity. The median time-to-progression was 1.9 mo (range 0.6-8.7 mo). Best response was seen in 1 pt with stable disease (SD) for 8 cycles. Only ≥ grade 3 toxicities related to CRLX101 occurred in a single patient with grade 3 anemia and chest pain who was able to resume therapy without any further toxicity after CRLX101 was reduced to 12 mg/m2. Conclusions: CRLX101 demonstrated minimal activity with SD as best response in this heavily pretreated population. Future efforts with CRLX101 in advanced GEC should focus on combination strategies. Its favorable toxicity profile and evidence of preferential tumor uptake support further clinical research of combining CRLX101 with other targeted therapies such as anti-angiogenesis (ramucirumab) and/or immune checkpoint inhibitors. Clinical trial information: NCT01612546 Clinical trial information: NCT01612546.