Expansion of Bone Marrow (BM) Progenitors and Mobilization of Multilineage Progenitor Cells Associated with Once Per Cycle Administration of Long-Acting Growth Factors Neulasta and Aranesp with Chemotherapy (CT): Biology and Nature of Response.

Hematopoietic growth factors (HGF) G-CSF and GM-CSF have been utilized widely to facilitate mobilization of progenitor cells that can be used to support high dose CT. Recently long-acting HGF neulasta (pegfilgrastim) and aranesp (darbepoetin alfa) were developed to reduce the frequency of administration. While these agents are effective in reducing CT-induced neutropenia and anemia similar to their parent compounds, very little is known about their efficiency in mobilizing progenitor cells. The purpose of this study was to evaluate biologic effects of these agents, used in combination with CT, on progenitor cells. Chemo-naïve sarcoma patients receiving adriamycin and ifosfamide (AI) were treated once per cycle with aranesp (500 mcg) SC prior to initiating CT (day 0) and neulasta (6 mg) SC after completion of CT (day 4). BM and peripheral blood (PB) samples were studied at the baseline and around day 14 (at the time of WBC recovery) for progenitors and mediators of response. The treatment was associated with a significant increase in PB CD 34 + cells (median increase 36-fold, p=0.005) and marked mobilization (p=0.003) of CFU-GM (24-fold), BFU-E (22-fold), and CFU-GEMM (62-fold) (n=14). To better understand the biology and nature of response, we examined BM before and at the time of mobilization (n=12). There was an expansion of multi-lineage BM progenitors (p=0.06) and CD 34+ cells (P=0.001). BM exam at the time of recovery showed increased cellularity (2-fold) with increased granulopoietic elements. An increased expression of MMP-9 but unchanged expression of TIMP-1 was observed by Immunohistochemistry (IHC). c-kit ligand level by Elisa was decreased in the BM supernatant. In addition, phospho c-kit (phospho site 568) was increased in the myeloid and erythroid precursors by IHC but phospho site 823 was unaltered, indicating the specificity of activation of the downstream pathway in response to c-kit ligand-receptor activation, possibly leading to expansion of progenitor cells. Interestingly, expression of CXCR4 at the protein level (flow cytometry and western blot) and RNA level (RT-PCR) was decreased (p<0.05) in the BM at the time of mobilization (day 14) as compared to the baseline. These findings indicate that long-acting HGFs, administered once per cycle of CT, are a potent stimulus for mobilization of myeloid, erythroid, and multipotential progenitors. Our findings also suggest that increased myelopiesis in the regenerating BM may be associated with increased protease activity such as MMP-9 that may result in the cleavage of c-kit leading to activation of c-kit receptors and expansion of progenitors, and the cleavage of CXCR-4 leading to release of progenitors from the BM anchorage and mobilization into PB.