Evaluation of Loco-Regional Skin Toxicity Induced by an In Situ Forming Depot after a Single Subcutaneous Injection at Different Volumes and Flow Rates in Göttingen Minipigs

Abstract

The present study aims to investigate the loco-regional tolerability and injection parameters (i.e., flow rate and administration volume) of an in situ forming depot (ISFD) in Göttingen minipigs, to secure both the therapeutic procedure and compliance in chronic medical prescriptions. The ISFD BEPO^® technology (MedinCell S.A.) is investigated over 10 days, after a single subcutaneous injection of test item based on a DMSO solution of diblock and triblock polyethylene glycol-polylactic acid copolymers. Injection sites are systematically observed for macroscopic loco-regional skin reactions as well as ultrasound scanning, enabling longitudinal in vivo imaging of the depot. Observations are complemented by histopathological examinations at 72 h and 240 h post-injection. Overall, no treatment-emergent adverse effects are macroscopically or microscopically observed at the subcutaneous injection sites, for the tested injection flow rates of 1 and 8 mL/min and volumes of 0.2 and 1 mL. The histopathology examination confirms an expected foreign body reaction, with an intensity depending on the injected volume. The depot morphology is similar irrespective of the administration flow rates. These results indicate that the ISFD BEPO^® technology can be considered safe when administered subcutaneously in Göttingen minipigs, a human-relevant animal model for subcutaneous administrations, in the tested ranges.

Keywords: flow rate; in situ forming depots; loco-regional skin tolerability; minipig; subcutaneous injection; sustained release drug delivery.

Figure 1

Macroscopic loco-regional tolerance assessment. Representative images of injection sites from 1 mL treated group along the study.

Figure 2

Longitudinal ultrasound imaging of (A) 0.2 mL and (B) 1 mL test item injection site over the course of the study. Images were acquired between 13 and 15 MHz along the sagittal plane, parallel to the needle insertion orientation. Bolus are highlighted in red post-injection and indicated by an arrow at later time points.

Figure 3

Variation of depot volume over the course of the study (10 days): (a) the calculated volumes from both injections are displayed at both injection sites: site 1 as full line; site 2 as dotted line; (b) the degree of depot swelling is presented for both volumes as the mean of the two injection sites.

Figure 4

Representative H&E histopathology of injection sites: (A) test item injection site at 72 h and (B) test item injection site at 240 h. A focus on the fibrous capsule is presented (C) at 72 h, and (D) at 240 h. ES: poorly defined empty spaces in the subcutis. Green arrow: fibrous capsule. Black arrow: inflammatory cells, including multinucleated macrophages. Red arrow: empty spaces.

Figure 5

H&E histopathology of 1 mL test item depots at 240 h, administered at (A) slow and (B) fast injection flow rate.

Figure 6

Marking of injection sites in the plica inguinalis of a minipig.