CXCR4 blocker · stem cell mobilizer
Motixafortide (Aphexda) is a hematopoietic stem cell mobilizer: a synthetic peptide, ring-closed by a disulfide bond, that inhibits the chemokine receptor CXCR41. Given with filgrastim (G-CSF), it releases blood-forming stem cells from the bone marrow into the blood, where they are harvested for later autologous transplantation in multiple myeloma1.
Blood-forming stem cells stay anchored in the bone marrow partly because their CXCR4 receptors bind a chemokine called CXCL12 (also known as SDF-1α), which helps hold them to the marrow. Motixafortide binds CXCR4 with very high affinity and stays on the receptor for a long time, blocking that signal so stem cells loosen their hold and move into the blood. It is used after several days of filgrastim, another stem-cell mobilizer; together they raise the number of CD34+ stem cells in the circulation, where an apheresis machine collects them. The collected cells are later given back to the same patient in an autologous transplant to rebuild the marrow. The same action also raises circulating white blood cell counts.
The key human evidence is GENESIS, a phase 3, double-blind, placebo-controlled trial in 122 adults with multiple myeloma preparing for autologous transplant2. After filgrastim, a single motixafortide administration let 67.5% of patients reach the stem-cell collection goal within two apheresis sessions by central-lab count, versus 9.5% with placebo, according to the FDA label1. The published trial report, using its own analysis, gave 92.5% versus 26.2%, and found the mobilized cells were enriched for more primitive stem-cell types2. Times to neutrophil and platelet engraftment after transplant were similar between groups1. In rodent transplant models, cells mobilized by motixafortide repopulated the marrow long term1.
FDA-approved in 2023 as Aphexda, in combination with filgrastim, to mobilize blood-forming stem cells for collection and autologous transplantation in people with multiple myeloma.
The label lists injection-site reactions (pain, redness, itching) in most patients, plus generalized itching, flushing and back pain. Anaphylactic shock occurred in under 1% of patients, so premedication and close monitoring are required. Other warnings: rising white cell counts, possible mobilization of leukemia or tumor cells (it is not for use in leukemia), and fetal harm. The label also reports concentration-dependent QT prolongation in a healthy-volunteer study.
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