Abstract Enzymatic degradation of hyaluronan (HA), a key component of the extracellular matrix (ECM), can enhance tumor perfusion, improve delivery of chemotherapeutics, and enhance the effects of anti-tumor agents. Recombinant human hyaluronidase (rHuPH20), used clinically to facilitate local dispersion and absorption after subcutaneous delivery, is rapidly cleared from the blood after intravenous (IV) injection. To prolong serum residence time, a pegylated form of rHuPH20 was manufactured and shown to have anti-tumor activities in preclinical models (Thompson et al., Mol Cancer Ther 2010). PEGPH20 is a novel agent in early clinical trials to evaluate the safety and biological activities of hyaluronidase-based therapy. Twenty-three patients enrolled in two Phase 1 trials received IV PEGPH20 (0.5 - 50 μg/kg). To assess PEGPH20 PK, serial blood samples were drawn from patients, and plasma concentrations were measured using an in vitro hyaluronidase activity assay (LLOQ 0.3 U/mL). Plasma levels of HA catabolites were measured using a quantitative HPLC method to characterize PD. After a single 50 μg/kg dose, the PEGPH20 PK profile was well described by a two-compartment open model with a low initial distribution volume (V1 ∼ 60 mL/kg) and a terminal half-life of ∼2 days. Observed Cmax and AUC0-8hr values increased with increasing dose, suggesting linearity within the dose range. Model simulations derived from single-dose PK parameters were predictive of plasma concentrations from patients who received twice weekly dosing. There was no evidence for accumulation of PEGPH20 in the plasma after multiple dosing. Systemic concentrations of HA catabolites were measured to assess the PEGPH20 PD. HA levels detected 24 hours post administration increased with increasing dose of PEGPH20. Observed Cmax and AUC0-168hr values were also dose-dependent. After a 50 μg/kg bolus, HA concentrations increased 100-fold above baseline and persisted for >2 weeks. Repeat dosing with PEGPH20 resulted in sustained plasma concentrations of HA catabolites. Inter-patient variability in PD was notably greater than inter-patient variability in PK. Initial clinical PK/PD analysis indicates that systemic exposure after IV PEGPH20 is proportional to dose and is well described by a two-compartment PK model. Dose-dependent increases in HA catabolites provided a quantitative measure of PEGPH20 PD, consistent with the enzymatic activity of hyaluronidase. These data support continued evaluation of PEGPH20 to enhance delivery of anti-tumor agents via modification of the ECM. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2672. doi:1538-7445.AM2012-2672