Plinabulin ameliorates neutropenia induced by multiple chemotherapies through a mechanism distinct from G-CSF therapies.

Purpose: Chemotherapy-induced neutropenia (CIN) increases the risk of infections and mortality in cancer patients. G-CSF therapies are approved for the treatment of CIN, but non-G-CSF therapies are needed to increase efficacy and minimize side effects. Plinabulin is an inhibitor of tubulin polymerization that ameliorates CIN caused in patients by the microtubule stabilizer docetaxel. The present study evaluates the potential of plinabulin to reduce neutropenia induced by chemotherapies of different classes in a manner not dependent on increasing G-CSF.

Methods: The anti-CIN benefits of plinabulin were tested in rodents co-treated with docetaxel, cyclophosphamide or doxorubicin. Effects on G-CSF levels were evaluated in tissues by immunoassay. Flow cytometry was utilized to test treatment effects on femur bone marrow cell counts from immunocompetent mice-bearing orthotopic 4T1 breast cancer tumors.

Results: Plinabulin alleviated neutropenia induced by microtubule stabilizing, DNA cross-linking and DNA intercalating chemotherapies, yet did not affect bone marrow or blood G-CSF levels. The number of lineage/Sca1/c-Kit (LSK) hematopoietic stem/progenitor cells (HSPC) in murine bone marrow collected 2 days after treatment was not affected by docetaxel monotherapy despite increased plasma G-CSF in this group. LSK cell number was, however, increased when plinabulin was combined with docetaxel, without affecting G-CSF.

Conclusions: Results support the clinical testing of plinabulin as a non-G-CSF-based treatment for CIN associated with chemotherapies of different mechanisms. Results also support HSPC as a focal point for future mechanism-of-action work aimed at understanding the ability of plinabulin to reduce this serious side effect of cytotoxic therapy in cancer patients.