TLK199 is a novel glutathione analog inhibitor of the enzyme GST P1-1. GST P1-1 has been shown to be a negative regulator of c-Jun N-terminal kinase, which has been implicated in the control of cellular growth and differentiation. Studies in rodents have shown that TLK199 treatment increases the levels of circulating white blood cells and stimulates the production of CFU-GM in bone marrow. In a rodent model of 5-FU-induced neutropenia, treatment with TLK199 accelerated the recovery of neutrophil levels at a rate similar to that observed with G-CSF. In a recently reported Phase 2 clinical trial in patients with refractory MDS involving multilineage blood cell dysfunction, treatment with TLK199 resulted in a 65% Hematological Improvement of neutrophils, erythrocytes and/or platelets, confirming the myelorestorative effect of TLK199 in humans. The present study was designed to determine if the myelostimulative effects of TLK199 on neutrophils and their precursors are due in part to increased levels of endogenous G-CSF. TLK199 was tested in normal and neutropenic rodents for its effects on G-CSF production. A single administration of TLK199 (p.o. or i.p.) to normal mice resulted in up to 500% increase in G-CSF serum levels. In a rat model of 5-FU-induced neutropenia, TLK199 administration accelerated the recovery of circulating neutrophils, which corresponded to maximal G-CSF serum levels being observed earlier than vehicle control. The ability of TLK199 to enhance G-CSF production in primary human bone marrow stromal cells was also examined. Treatment of these cells with TLK199 potentiated IL-1b-induced production of G-CSF, GM-CSF and IL-6 from 200 to 400%. These data suggest that the enhancement of G-CSF production may contribute to the accelerated recovery of neutrophils observed with TLK199 treatment under neutropenic conditions. Together with the results from the Phase 2 clinical trial in MDS, these data support further clinical assessment of TLK199 treatment for chemotherapy-induced cytopenia.

Disclosures: Telik, Inc.; Telik, Inc.

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