Effects of PIXY321, a granulocyte-macrophage colony-stimulating factor/interleukin-3 fusion protein, on chemotherapy-induced multilineage myelosuppression in patients with sarcoma

Purpose: To evaluate the clinical safety and ability of PIXY321, a novel fusion protein of recombinant human granulocyte-macrophage colony- stimulating factor (GM-CSF) and interleukin-3 (IL-3), to ameliorate chemotherapy-induced multilineage myelosuppression. Patients and Methods: PIXY321 was administered by subcutaneous injection twice daily (25 to 1,000 μg/m²/d) over 14 days to 24 chemotherapy-naive patients with sarcoma in a phase I/II study. Three weeks from the initiation of PIXY321, the first cycle of chemotherapy with cyclophosphamide, doxorubicin, and dacarbazine (DTIC) (CyADIC) was administered over 3 days. Four weeks later, a second cycle of CyADIC was administered, followed by 14 days of PIXY321. Results: Treatment with PIXY321 was well tolerated. Local skin reactions and constitutional symptoms were the main side effects. The dose-limiting toxicity was not encountered; however, headache and fatigue were more frequent at the highest dose (1,000 μg/m²). PIXY321 before chemotherapy elicited a modest increase in the WBC count (consisting mainly of mature neutrophils), platelets, and corrected reticulocyte counts (all P < .001). Following chemotherapy, PIXY321 at effective doses (500 to 1,000 μg/m²/d), significantly reduced both the degree (mean nadir, 70 v 310/μL; P = .016) and duration (mean days < 500/μL, 6.6 v 3.9 days; P = .002) of neutropenia. Cumulative thrombocytopenia was not observed during the first two cycles of CyADIC (mean nadir platelet count, 103 v 95 x 10³/μL, in cycles no. 1 and 2, respectively; P = NS). Compared with our historic control data, the mean nadir platelet count in cycle no. 2 was significantly higher after PIXY321 (1.7-fold, P < .05) than with CyADIC alone or with GM-CSF support. There was a suggestion for a dose response, since the mean percentage change in nadir platelet values from cycle no. 1 to cycle no. 2 increased with the PIXY321 dose (P < .02), with the peak effect observed at 750 μg/m²/d. Conclusion: These results suggest a potential clinical role for PIXY321 in attenuating the cumulative multilineage hematopoietic toxicity of chemotherapy.