Hyaluronan (HA) is a component of the extracellular matrix that frequently accumulates in human cancers. The quantity of HA produced by the tumor cells directly correlates with increased tumor growth and metastasis and it has been linked with tumor progression and poor prognosis. Previous clinical trials of bovine hyaluronidase showed promise in enhancing chemotherapy regimens using adjunctive systemic hyaluronidase in chemo-refractory patients. In animal studies the removal of HA from tumors with recombinant human hyaluronidase has demonstrated improved survival, suppression of tumor growth, and enhanced efficacy of certain anti-cancer drugs. Chemotherapeutic agents may be able to better penetrate the tumor once the HA has been removed.
We have also observed significant reduction of tumor interstitial fluid pressure (IFP) following the administration of rHuPH20 in solid tumors grown in mice. Tumor interstitial pressure is widely believed to be an important factor limiting the access of cytostatic regimens to solid tumors. By digesting the HA gel, rHuPH20 may reduce IFP in the tumor and promote more effective delivery of chemotherapy throughout the tumor. This could potentially lead to better patient outcomes and increased survival.
Our PEGPH20 program utilizes PEGylated hyaluronidase that allows for intravenous administration to degrade the HA that surrounds tumor cells. The Chemophase program applies the rHuPH20 enzyme along with mitomycin C directly into the bladder where the enzyme can hydrolyze the HA produced by the cancerous bladder cells. Unlike tumor cells, normal cells do not produce HA in this manner and appear not to be adversely affected by the enzyme.
We are investigating PEGylated-rHuPH20, or PEGPH20, a new molecular entity, as a candidate for the systemic treatment of tumors rich in hyaluronan, or HA. PEGylation refers to the attachment of polyethylene glycol to our rHuPH20 enzyme, which extends its half life from less than one minute to approximately 48 to 72 hours. Numerous solid tumors, including prostate, breast, pancreas, colon and non-small cell lung, accumulate HA that forms a halo like coating over the surface of the tumor cell.
In preclinical studies, PEGPH20 has been shown to remove the HA coating surrounding several tumor cell lines. Treatment of PC3 (a prostate cancer cell line that produces HA) tumor-bearing mice with PEGPH20 as a single agent demonstrated approximately 70% tumor growth inhibition relative to controls. Repeat dosing with PEGPH20 produced a sustained depletion of HA in the tumor microenvironment. For tumor models that do not produce HA, the presence of PEGPH20 has no effect. An estimated 20% to 40% of certain solid tumors may produce HA.
Administration of the combination of PEGPH20 with docetaxel, liposomal doxorubicin, or gemcitabine, in HA producing animal tumor models showed a significant survival advantage for the combination relative to either chemotherapeutic agent alone. Therefore, based on these animal studies and other tests conducted by Halozyme, PEGPH20 may represent a potentially innovative treatment approach against tumors that produce HA.
PEGPH20 began its first Phase 1 clinical trial in 2009 which will evaluate the agent over a range of doses. The study is enrolling advanced cancer patients who receive intravenous administration of PEGPH20 as a single agent. The primary outcome measures of the study will be to evaluate safety and tolerability of PEGPH20 and to determine the recommended dose for future studies. Secondary objectives will be to determine pharmacokinetics, obtain dose limiting toxicities, and observe patients for any evidence of anti-tumor activity.
Chemophase is a chemoadjuvant we have investigated for possible use in the treatment of patients with superficial bladder cancer. The Chemophase program combines our PH20 enzyme with mitomycin C, a cytotoxic drug, for direct administration into the bladder immediately after transurethral resection of bladder tumors (TURBT), a standard surgical treatment for the disease. Many bladder tumor cells produce high quantities of HA and thus treatment to remove the HA coating could increase their exposure to mitomycin C. This may lead to a lower recurrence of the cancer and a better prognosis for patients.
During 2009, we decided to reallocate certain resources previously budgeted for Chemophase to other higher priority programs. We are currently exploring strategic alternatives that will allow the Chemophase program to continue its clinical development.