Design Rationale and Development Approach for Pegfilgrastim as a Long-Acting Granulocyte Colony-Stimulating Factor

Filgrastim, a recombinant methionyl human granulocyte colony-stimulating factor (G-CSF) (r-metHuG-CSF), is efficacious in stimulating neutrophil production and maturation to prevent febrile neutropenia (FN) in response to chemotherapy. Because of its relatively short circulating half-life, daily filgrastim injections are required to stimulate neutrophil recovery. In an effort to develop a long-acting form of filgrastim that was as safe and efficacious as filgrastim but had a longer in vivo residence time, a number of strategies were considered. Ultimately, fusion of filgrastim to polyethylene glycol (PEG) was selected. Following extensive analysis of conjugation chemistries as well as in vitro and in vivo characterization of a panel of PEGylated proteins, a construct containing a 20 kDa PEG moiety covalently conjugated to the N-terminus of filgrastim was chosen for advancement as pegfilgrastim. Pegfilgrastim is primarily cleared by neutrophils and neutrophil precursors (rather than the kidneys), meaning that clearance from the circulation is self-regulating and pegfilgrastim is eliminated only after neutrophils start to recover. Importantly, addition of PEG did not alter the mechanism of action and safety profile compared to filgrastim. Clinical evaluation revealed that a single 6 mg dose effectively reduces the duration of neutropenia and risk of FN in patients receiving chemotherapy. This work demonstrates the benefit of using PEGylation to generate pegfilgrastim, which allows for once-per-chemotherapy cycle administration while maintaining similar safety and efficacy profiles as those for multiple daily administration of filgrastim. Approaches that may provide advances for therapeutic agonists of G-CSF receptor are also discussed.

Efficacy, effectiveness and safety of long-acting granulocyte colony-stimulating factors for prophylaxis of chemotherapy-induced neutropenia in patients with cancer: a systematic review

PURPOSE

Pegfilgrastim was introduced over a decade ago. Other long-acting granulocyte colony-stimulating factors (G-CSFs) have recently been developed. We systematically reviewed the efficacy, effectiveness and safety of neutropenia prophylaxis with long-acting G-CSFs in cancer patients receiving chemotherapy.

METHODS

We performed a systematic literature search of the MEDLINE, EMBASE and Cochrane Library databases, and abstracts from key congresses. Studies of long-acting G-CSFs for prophylaxis of chemotherapy-induced neutropenia (CIN) and febrile neutropenia (FN) were identified by two independent reviewers. Abstracts and full texts were assessed for final inclusion; risk of bias was evaluated using the Cochrane's tool. Effectiveness and safety results were extracted according to study type and G-CSF used.

RESULTS

Of the 839 articles identified, 41 articles representing different studies met the eligibility criteria. In five randomised controlled trials, 11 clinical trials and 17 observational studies across several tumour types and chemotherapy regimens, pegfilgrastim was used alone or compared with daily G-CSF, no G-CSF, no upfront pegfilgrastim or placebo. Studies generally reported lower incidence of CIN (4/7 studies), FN (11/14 studies), hospitalisations (9/13 studies), antibiotic use (6/7 studies) and adverse events (2/5 studies) with pegfilgrastim than filgrastim, no upfront pegfilgrastim or no G-CSF. Eight studies evaluated other long-acting G-CSFs; most (5/8) were compared to pegfilgrastim and involved patients with breast cancer receiving docetaxel-based therapy. Efficacy and safety profiles of balugrastim and lipegfilgrastim were comparable to pegfilgrastim in phase 3 studies. Efficacy and safety of other long-acting G-CSFs were mixed.

CONCLUSIONS

Pegfilgrastim reduced the incidence of FN and CIN compared with no prophylaxis. Most studies showed better efficacy and effectiveness for pegfilgrastim than filgrastim. Efficacy and safety profiles of lipegfilgrastim and balugrastim were similar to pegfilgrastim.

Survival efficacy of the PEGylated G-CSFs Maxy-G34 and neulasta in a mouse model of lethal H-ARS, and residual bone marrow damage in treated survivors

In an effort to expand the worldwide pool of available medical countermeasures (MCM) against radiation, the PEGylated G-CSF (PEG-G-CSF) molecules Neulasta and Maxy-G34, a novel PEG-G-CSF designed for increased half-life and enhanced activity compared to Neulasta, were examined in a murine model of the Hematopoietic Syndrome of the Acute Radiation Syndrome (H-ARS), along with the lead MCM for licensure and stockpiling, G-CSF. Both PEG-G-CSFs were shown to retain significant survival efficacy when administered as a single dose 24 h post-exposure, compared to the 16 daily doses of G-CSF required for survival efficacy. Furthermore, 0.1 mg kg of either PEG-G-CSF affected survival of lethally-irradiated mice that was similar to a 10-fold higher dose. The one dose/low dose administration schedules are attractive attributes of radiation MCM given the logistical challenges of medical care in a mass casualty event. Maxy-G34-treated mice that survived H-ARS were examined for residual bone marrow damage (RBMD) up to 9 mo post-exposure. Despite differences in Sca-1 expression and cell cycle position in some hematopoietic progenitor phenotypes, Maxy-G34-treated mice exhibited the same degree of hematopoietic stem cell (HSC) insufficiency as vehicle-treated H-ARS survivors in competitive transplantation assays of 150 purified Sca-1+cKit+lin-CD150+cells. These data suggest that Maxy-G34, at the dose, schedule, and time frame examined, did not mitigate RBMD but significantly increased survival from H-ARS at one-tenth the dose previously tested, providing strong support for advanced development of Maxy-G34, as well as Neulasta, as MCM against radiation.