Accelerated blood clearance phenomenon upon cross-administration of PEGylated nanocarriers in beagle dogs

Abstract

The cross-administration of nanocarriers modified by poly(ethylene glycol) (PEG), named PEGylated nanocarriers, a type of combination therapy, is becoming an increasingly important method of long-term drug delivery, to decrease side effects, avoid multidrug resistance, and increase therapeutic efficacy. However, repeated injections of PEGylated nanocarriers induces the accelerated blood clearance (ABC) phenomenon, prevents long circulation, and can cause adverse effects owing to alterations in the biodistribution of the drug. Although the nature of the ABC phenomenon that is induced by repeated injections of PEGylated nanocarriers has already been studied in detail, there are few reports on the immune response elicited by the cross-administration of PEGylated nanocarriers. In this study, we investigated the ABC phenomenon induced by the intravenous cross-administration of various PEGylated nanocarriers, including PEGylated liposomes (PL), PEG micelles (PM), PEGylated solid lipid nanoparticles (PSLN), and PEGylated emulsions (PE), in beagle dogs. The results indicated that the magnitude of the immune response elicited by the cross-administration was in the following order (from the strongest to the weakest): PL, PE, PSLN, PM. It is specifically PEG in the brush structure that elicits a significant immune response, in both the induction phase and the effectuation phase. Furthermore, the present study suggests that there is a considerable difference between the effect of repeated injections and cross-administration, depending on the colloidal structure. This work is a preliminary investigation into the cross-administration of PEGylated nanocarriers, and our observations can have serious implications for the design of combination therapies that use PEGylated vectors.

Keywords:

• ABC phenomenon
• repeated injection
• cross-administration
• immune response
• PEGylated nanocarriers

Supplementary materials

Hematological analysis

Method

Beagle dogs were injected with PE (PEGylated emulsions) via a vein in the right forelimb at a phospholipid dose of 2.5 μmol/kg. Before the injection, a blank blood sample was collected from the left forelimb. Blood samples were collected immediately in the right forelimb after the first injection, regarded as 0 min. At 1, 3, 5, and 10 min after the intravenous injections, blood samples were obtained from the right forelimb, except at 3 and 5 min when blood samples were collected from the left forelimb. All blood samples were collected in bottles containing ethylenediaminetetraacetic acid dipotassium salt (EDTA-2K) and analyzed using a hematology analyzer (LH-750, Beckman Coulter, Inc., Brea, CA, USA). Ratios between measured values and blank blood samples were calculated at each time point, designated Q, which is expressed by the following equation:

$Q\%=\frac{Q_t}{Q_0}\times 100$

where Q_t is the determination of blood samples and Q₀ is the blank blood sample.

Results and discussion

As shown in Figure S1A, immune cells immediately gathered in the injected limb, and the number of monocytes, leukocytes, lymphocytes, and neutrophilic granulocytes at the injection site increased by 467%, 326%, 320%, and 306%, respectively. The amount of immune cells returned to the baseline level within 3–5 min of administration. The number of immune cells on the side opposite to the injection site was reduced to below 50% of the control at 3 min after the injection, whereas the number of immune cells in the injected limb and in limb opposite to the injected limb returned to the baseline levels at 5 min after the injection (Figure S1B).

Figure S1 The percentage change in leucocytes, neutrophilic granulocytes, monocytes, and lymphocytes in left and right limbs after the intravenous injection.

Notes: The beagle dogs were treated with PE at a dose of 2.5 μmol phospholipid/kg. Right limb (A); left limb (B). Data show mean ± standard deviation of three repeats. Q% = (Q_t/Q₀)×100, where Q_t is the value for the blood sample and Q₀ is the control value.

Abbreviation: PE, PEGylated emulsions.

Acknowledgments

This research was supported by the National Natural Science Foundation of China (Grant No 81072602) and the Shenyang Pharmaceutical University Students’ Innovation Undertaking Project of Liao Ning Province (Grant No 201410163006).

Disclosure

The authors report no conflicts of interest in this work.