Abstract
7070 Background: LEN is approved for treatment of del 5q myelodysplastic syndromes and treated multiple myeloma. LEN has potential therapeutic activity in early trials of relapsed CLL. The mechanism(s) whereby this drug is active in CLL is unknown. LEN is not directly cytotoxic to CLL cells in vitro that has stimulated speculation that the activity of LEN might be through modulation of the CLL microenvironment. Cells in the CLL microenvironment, such as Nurse-like cells (NLCs), protect CLL cells from spontaneous and drug mediated apoptosis in vitro and presumably in-vivo. NLCs support CLL survival via multiple mechanisms, including elaboration of SDF-1a and TNF family members BAFF and APRIL. [Burger 2000, Nishio 2005]. Methods: We evaluated the effects of LEN on CLL survival when the CLL cells from different patients were cultured alone, with recombinant SDF-1 or BAFF, or with NLC generated as previously described [Tsukada 2002]. Results: When cultured with NLC, the survival of CLL cells was higher than that of CLL cells cultured alone. LEN at concentrations of 0.1uM and greater to co-cultures of NLC and CLL cells caused specific reductions in CLL cell survival to levels similar to or lower than that of CLL cells cultured without NLC. In the presence of NLC, LEN at 1uM reduced CLL cell viability compared to control (42% vs. 56% ±4% p [<] 0.0005 n=13). CLL B cells from different patients (N=11) were cultured alone or with recombinant cytokines know to be secreted by NLC, all in duplicate in a series of 3 experiments. Both NLC and SDF-1a protected CLL cell viability and it was significantly mitigated in the presence of LEN 0.1–10uM. Under the same conditions, LEN had no significant effect on the survival support provided by rhBAFF at. Subsequent experiments evaluated suprapharmacologic LEN 100uM at days 3–6 and found LEN significantly decreased viability of CLL cells supported by SDF-1, but not recombinant BAFF. CXCR4, the receptor for SDF-1a was downmodulated in 7/8 patients in the presence of lenalidomide versus vehicle control at day 7 (p=0.03 for MFI). Conclusions: LEN might abrogate the protective influence of NLC and SDF-1a on CLL cell survival an effect that was not seen on the survival support provided by rhBAFF. No significant financial relationships to disclose.
Published Version
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