Effect of porphyrins on the hematopoietic recovery of mice treated with gamma-radiation

Photofrin increases murine spleen cell transferrin receptor expression and responsiveness to recombinant myeloid and erythroid growth factors

When given to normal male mice, the photochemotherapeutic agent Photofrin (porfimer sodium), a complex mixture of monomeric and oligomeric non-metallic porphyrins, significantly increased relative spleen weight, spleen cell numbers, DNA replication, levels of granulocyte-macrophage and erythroid progenitors and cellular responsiveness to different recombinant (r) myeloid growth factors. In contrast, monomeric hematoporphyrin had no effect on spleen weight, cellularity, erythroid progenitor levels or spleen cell cycle status. Photofrin significantly increased spleen cell expression of the receptor (CD71) for the iron transport protein transferrin by 72 h post-injection but did not affect levels of a receptor (CD25) for the T-cell growth factor interleukin-2 (IL-2) or spleen cell responsiveness to rIL-2. Further evidence of increased splenic erythropoietic activity in Photofrin-treated mice was provided by double color flow cytometric studies which indicated that the treatment elevated the number of nucleated spleen cells recognized by the erythroid lineage-specific monoclonal antibody TER-119. A majority of TER-119+ cells also expressed CD71 and the heat stable antigen, a marker of developing hematopoietic cells as well as mature erythrocytes. The capacity of Photofrin to stimulate murine hematopoietic activity appears to be a property not shared by other porphyrin photosensitizers.

Accelerated myelopoietic recovery in irradiated mice treated with Photofrin

The porphyrin photosensitizer, Photofrin porfimer sodium (Photofrin), has been widely studied for its capacity to evoke destruction of malignant tissues. In addition to its photosensitizing properties, Photofrin may exert myelostimulatory effects in normal and immunosuppressed mice in the absence of activating light. In the present set of experiments, we examined the effect of Photofrin upon the immunohematopoietic axis of sublethally irradiated DBA/2 mice. Administration of Photofrin (10 mg/kg) 1 and 4 days following irradiation (4 Gy) significantly enhanced the recovery of spleen cellularity, spleen and bone granulocyte/macrophage progenitors (colony-forming units, CFU-GM) and peripheral blood leukocytes levels. Proliferative responses to the T-cell mitogen concanavalin A by spleen cells prepared from Photofrin-treated mice were significantly less than those of cells from irradiated control mice 8 and 15 days post-irradiation. Photofrin given 1, 4 and 7 days following irradiation elevated splenic CFU-GM 3 to 4-fold 10 days post-irradiation relative to the irradiated controls and mice given only two injections of Photofrin. In contrast to the effect of two injections, multiple (three or four) injections of Photofrin did not elevate bone marrow CFU-GM above control levels beyond 8 days post-irradiation. In addition, splenic CFU-GM levels in animals receiving three or four injections of Photofrin were no different than those of the irradiated controls later than 10 days post-irradiation. These findings indicate that prolonged exposure to Photofrin in sublethally irradiated mice may induce regulatory factors which dampen the enhanced myelopoietic recovery stimulated by only two injections of the drug.