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Converting Intravenous Dosing to Subcutaneous Dosing With Recombinant Human Hyaluronidase
The preferred route of administration for an injected therapeutic agent is subcutaneous (SC), but SC injections are generally limited to no more than 1-2 mL in volume, representing a major challenge, especially for large protein biologics.
Figure 3: The effect of rHuPH20 on spreading and tissue distortion from injection. (a) rHuPH20 (10 U) or carrier control was
co-injected in 50 μL with fluorescein isothiocyanate (FITC)-labeled dextran (2 million Da) in mice and imaged under ultraviolet
light. Area of the tracer was measured with microcalipers at 1-min intervals. (b) Reduction of tissue distortion following
injection of rHuPH20. Saline containing rHuPH20 or carrier control was infused through a 27-gauge needle with a controlled
infusion pump (300 μL/min) for 2 min in both sites. Images were taken at completion of the infusion (time 5 2 min). (FIGURES:
HALOZYME THERAPEUTICS)
The intradermal injection of rHuPH20 with high molecular weight fluorescein isothiocyanate-labeled dextran (2 million Da)
resulted in a significantly increased dispersion area (Figure 3a). This effect was observed with nanogram amounts of the enzyme
(44). Importantly, rHuPH20 injection sites were uniformly dispersed without swelling, in contrast to the significant tissue
distortion in control areas in which saline alone had been infused (Figure 3b). As with HA, the principal substrate for rHuPH20
displays a short half-life in comparison to other ECM molecules such as collagen. The dispersion effects should be temporary,
provided rHuPH20 is catabolized in a short period of time. As shown in Figure 4, the dispersion of tracer dye had returned
to control levels 24 h post-injection (44).
Figure 4: Evaluation of the duration of the rHuPH20 dispersing effect. Fluorescent-dye dispersion following pretreatment with
rHuPH20 or placebo at various times (0.5, 1, and 24 h), * p (p value) <0.05 between rHuPH20 and placebo groups. (FIGURES: HALOZYME THERAPEUTICS)
The possibility existed that the enzymatic degradation of HA with rHuPH20 would produce a variety of breakdown products that
could induce inflammatory mediators. This situation would limit the chronic repeat use of rHuPH20, a situation comparable
with that of the bovine-derived enzyme preparation. Studies have shown that rHuPH20 does not increase vascular permeability
and does not elicit any inflammatory responses in cultures of human microvascular endothelial cells or following SC injection
in primates (38).
As collagen fibrils represent the main structural components of the ECM, it would be expected that rHuPH20 would not facilitate
dispersion of molecules larger than those that could permeate through the 10–300 nm collagen-based fibrous network. Studies
using fluorescent-labeled dextran and latex particles of increasing diameter, and other particles of known size such as recombinant
adenovirus expressing green fluorescent protein, demonstrated that rHuPH20 increased the dispersion in the dermis of molecules
only up to 200 nm in diameter (38).
