Parenteral delivery of recombinant biologic response modifiers (BRMs) remains a challenge because of the brief intravascular half-life of most recombinant proteins and their associated rapid clearance from the circulation. Recombinant derived interleukin-2 (rIL-2) was formulated with Pluronic F-127, N.F. (poloxamer 407, N.F.) and the biological activity determined vs time at 4, 22, and 37-degrees-C. As assessed by rIL-2-induced peripheral blood lymphocyte (PBL) uptake of [H-3]thymidine, storage of rIL-2/poloxamer 407 (33% w/w) for 72 hr at 4 and 22-degrees-C did not result in an overall negative slope of the [H-3]thymidine vs time profiles. However, storage of an rIL2/poloxamer formulation at 37-degrees-C for 72 hr resulted in an approximate 15% reduction in the biological activity as assessed by [H-3]thymidine incorporation. As assessed by bioassay ([H-3]thymidine uptake), the cumulative percentage rIL-2 released in vitro at 22-degrees-C after 8 hr from rIL-2/poloxamer 407 matrices containing either 30% (w/w) or 35% (w/w) poloxamer 407 was 81.8 +/- 1.7 and 82.1 +/- 4.7%, respectively. When ELISA was used to determine the amount of rIL-2 released vs time. the corresponding values for the cumulative percentage rIL-2 released were 82.6 +/- 10.1 and 40.9 +/- 8.8%. Cytotoxicity of rIL-2-stimulated PBLs cultured with poloxamer 407 (0.17%, w/w) toward malignant Daudi cells was significantly (P < 0.05) enhanced compared to controls. Finally, mice injected with the rIL-2/poloxamer 407 formulation (1 x 10(5) U/inj. q.d. x 3 days) demonstrated a bioequivalent effect of rIL-2-induced natural killer (NK) cell activity in vitro toward malignant murine YAC-1 cells at one-half the standard exogenously administered dose of rIL-2 known to generate enhanced NK lytic activity in mice (1 x 10(5) U/inj. b.i.d. x 3 days). No untoward systemic side effects were observed for mice injected i.p. with polymer vehicle alone (30%, w/w) (0.15 ml q.d. x 3 days), pH 7 phosphate-buffered saline (PBS) (0.15 ml q.d. x 3 days), rIL-2 formulated with poloxamer 407 (30%. w/w) (1 x 10(5) U/0. 15 ml q.d. x 3 days and 0.5 x 10(5) U/0. 15 ml q.d. x 3 days), or rIL-2 dissolved in PBS (1 x 10(5) U/0.15 ml b.i.d. x 3 days). Thus, poloxamer 407, N. F., did not denature rIL-2 when the latter was stabilized with human serum albumin (HSA), enhanced the in vitro lytic ability of human rIL-2-stimulated PBLs against malignant Daudi cells, and served as a sustained-release parenteral vehicle for rIL-2 when injected i.p. into mice. Thus. based on these preliminary findings, it appears that poloxamer 407, N.F., may potentially be useful for the formulation and sustained delivery of select protein pharmaceuticals following extravascular administration.
