Abrogation of the hematological and biological activities of the interleukin-3/granulocyte-macrophage colony-stimulating factor fusion protein PIXY321 by neutralizing anti-PIXY321 antibodies in cancer patients receiving high-dose carboplatin

This dose-escalation study was performed to evaluate the hematologic activi ty, biological effects, immunogenicity, and toxicity of PIXY321 (an interle ukin-3/granulocyte-macrophage colony-stimulating factor fusion protein) adm inistered after high-dose carboplatin (CBDCA) treatment. Patients with adva nced cancers received CBDCA at 800 mg/m(2) intravenously on day 0 of repeat ed 28-day cycles. In part A of the study, patients were treated with CBDCA alone during cycle 1 and then received PIXY321 on days 1 through 18 of cycl e 2 and later cycles. In part B, patients received 18 days of PIXY321 begin ning on day 1 of all CBDCA cycles, including cycle 1. PIXY321 was administe red subcutaneously in 2 divided doses. Total doses of 135, 250, 500, 750, a nd 1,000 mu g/m(2)/d were administered to successive cohorts of 3 to 6 pati ents in part: A. In part B, patient groups received PIXY321 doses of 750, 1 ,000, and 1,250 mu g/m(2)/d. The hematologic effects of PIXY321 were assess ed in the first 2 cycles of therapy Anti-PIXY321 antibody formation was ass essed by enzyme-linked immunosorbent assay (ELISA) and neutralization assay . Of the 49 patients enrolled, 31 were fully evaluable for hematologic effi cacy. When comparing the first B cycle (cycle B-1; with PIXY321) with the f irst A cycle (cycle A-1; without PIXY321), the fusion protein had no signif icant effect on platelet nadirs or duration of platelets less than 20,000/m u L but was able to speed the time of recovery of platelet counts to 100,00 0/mu L (15 v 20 days; P = .01) Significant improvements in neutrophil nadir and duration of ANC less than 500 were observed In cycles A-2 and B-l (wit h PIXY321) as compared with cycle A-1 (without PIXY321). Initial PIXY321 pr ophylaxis (cycle A-2 and cycle B-1), enhanced the recovery of ANC to greate r than 1,500/mu L by an average of at least 8 days as compared with cycle A -1 (without PIXY321; P less than or equal to .004). However, positive PIXY3 21 hematologic effects were lost in the second course of PIXY321 among pati ents treated in part B, ELISA analysis showed that 92% of patients had deve loped neutralizing anti-PIXY321 antibodies by the completion of 2 PIXY321-c ontaining cycles. The incidental action of PIXY321 to depress serum cholest erol levels was also abrogated during cycle B-2. We conclude that PIXY321 w as active in speeding hematologic recovery but that neutralizing anti-PIXY3 21 antibody formation suppressed the hematologic and biochemical effects by the second cycle of PIXY321 administration. The immunogenicity of this fus ion protein provides a cautionary warning that clinical development of bioe ngineered human molecules requires thorough testing for immune neutralizati on. This is a US government work. There are no restrictions on its use.