Correlating preclinical animal studies and human clinical trials of a multifunctional, polymeric nanoparticle

Abstract

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.

Keywords: Nanoparticles; clinical translation; interspecies scaling; nanomedicine; pharmacodynamics.

Conflict of interest statement

Conflict of interest statement: M.E.D. is a consultant to Cerulean Pharma and owns stock in the company.

Figures

Fig. 1.

Schematic diagrams of the assembly and disassembly of CRLX101. (A) Schematic of the cyclodextrin-containing polymer conjugate of CPT and its components. (Right) Cryo-TEM of the CRLX101 nanoparticles formed by self-assembly of the polymer–drug conjugates. (B) Schematic of CRLX101 assembly and disassembly (when the CPT is released).

Fig. 2.

Human plasma PK parameters. (A) Plasma concentrations of conjugated CPT (closed symbols) and unconjugated CPT (open symbols) as a function of time from the phase 1a clinical trial. Data points represent mean, and error bars represent SD (n = 6 per dose level). Circles, 6 mg/m2; squares, 12 mg/m2; triangles, 15 mg/m2; diamonds, 18 mg/m2. (B) AUC as a function of dose level for conjugated CPT (closed symbols) and unconjugated CPT (open symbols). Data points represent mean, and error bars represent SD (n = 6 per data point). CRLX101 lots A and E were used in this study.

Fig. 3.

Interspecies CRLX101 PK comparison. (A and B) Plasma concentrations of conjugated CPT (closed symbols) and unconjugated CPT (open symbols) as a function of time in rats (A) and dogs (B). Circles represent first dose, and squares represent third weekly dose. Data points represent mean, and error bars represent SD (n = 6 per data point). (C) Plasma concentrations of conjugated CPT (closed symbols) and unconjugated CPT (open symbols) as a function of time from the phase 2a clinical trial. Circles represent first dose, and squares represent 11th biweekly dose (cycle 6, day 1). Data points represent mean, and error bars represent SD. (D) AUC as a function of dose level across species for conjugated CPT. The line is a linear regression against all data points (R2 = 0.802). Data points represent mean, and error bars represent SD (n = 6 per data point). Squares, rat; triangles, dog; diamonds, human. Closed symbols, male; open symbols, female.

Fig. 4.

Urinary excretion of conjugated and unconjugated CPT as a function of dose level. Collection periods are 0 to 24 h (A) and 24 to 48 h (B). Total drug content was measured and normalized to the body surface area for each patient. Shaded bars represent conjugated CPT, and open bars represent unconjugated CPT. Data points represent mean, and error bars represent SD.

Fig. 5.

CPT in tumors of mice and humans. (A and B) Fluorescence microscopy demonstrates tumor penetration of CRLX101 over 1 wk following a single dose in NCI-H2122 KRAS mutant non–small-cell lung cancer xenografts. Yellow color is CPT fluorescence (SI Appendix, Fig. S10, shows excitation spectrum), and blue color is (A) nuclei or (B) blood vessels stained with anti-CD31. CPT fluorescence is maximal at 24 h and still detectable at diminished levels at 168 h. CPT fluorescence is more tightly associated with blood vessels at earlier time points. (C) Fluorescence microscopy demonstrates polymer (anti-PEG antibody) and CPT fluorescence colocalization, suggesting that CPT fluorescence signal in the tumor comes from intact CRLX101 nanoparticles. (D) Prolonged tumor exposure to CPT correlates with prolonged inhibition of topoisomerase-1 (SI Appendix, Fig. S11). Mice bearing NCI-H1299 non–small-cell lung cancer tumors were dosed once with 6 mg/kg CRLX101, and tumors were harvested and analyzed at the times indicated for CPT concentration (squares) and topoisomerase-1 expression (circles). CPT concentrations were measurable for >2 wk after a single dose, and topoisomerase-1 inhibition was evident for >1 wk, demonstrating sustained release of CPT in tumors. (E) Detection of CPT fluorescence in a tumor biopsy sample taken from a patient with gastric adenocarcinoma 48 h after CRLX101 treatment. CPT signal is bright green (punctate green dots) and not observed in the pretreatment tumor biopsy.