Effect of the immunomodulator AS101 on chemotherapy-induced multilineage myelosuppression, thrombocytopenia, and anemia in mice.

The immunomodulator AS101 has previously been found to induce mouse and human hematopoietic cells to secrete cytokines such as interleukin-1 alpha (IL-1 alpha), IL-2, tumor necrosis factor-alpha (TNF-alpha), and gamma interferon (IFN-gamma). The compound was shown to protect mice from lethal and sublethal effects of chemotherapy and irradiation. AS101 prevented the decrease in the number of bone marrow (BM) and spleen myeloid progenitor cells, and increased the survival of lethally treated mice. In this study, we show a dose-dependent response of AS101 in the induction of high secretion levels of IL-6, IL-3, granulocyte-macrophage colony-stimulating factor (GM-CSF), and stem cell factor (SCF). Since these growth factors are known to induce the proliferation and differentiation of multilineage progenitors, including megakaryocytic and erythroid progenitors, we designed this study to evaluate the role of AS101 in attenuating thrombocytopenia, anemia, and multilineage myelosuppression associated with chemotherapy. We demonstrate that pretreatment of mice with AS101 24 hours before intraperitoneal injection of 250 mg/kg cyclophosphamide (CYP) or intravenous injection of 150 mg/kg 5-fluorouracil (5-FU) significantly increased the number of circulating white blood cells (WBC) and platelets. The numbers of both neutrophils and lymphocytes were significantly increased in AS101-treated mice subjected to chemotherapy. In addition, AS101 attenuated erythropenia caused by 5-FU. It could also increase megakaryocyte and erythroid progenitor cells (CFU-MK and CFU-E) in the BM of treated mice severely affected by chemotherapy. We demonstrate that the protective effect of AS101 could be abrogated by treatment with anti-IL-1R or anti-SCF antibodies. We suggest that the endogenous production of cytokines such as IL-1, IL-6, IL-3, SCF, and GM-CSF in mice treated with AS101 offers protection to circulating blood elements and ameliorates the reconstitution of megakaryocytic and erythroid progenitors. The simultaneous protection by AS101 of multilineage cell compartments is probably due to stimulation by AS101 of a selective subpopulation of primitive stem cells resistant to chemotherapy. On the basis of these studies, phase II clinical trials with patients treated with chemotherapy in combination with AS101 have been initiated.