Abstract
The CXCR4 inhibitor plerixafor in combination with G-CSF disrupts stroma-leukemia interactions, mobilizing leukemia cells from their niche microenvironment. This combination in conjunction with chemotherapy has been investigated in clinical trials in AML. We recently reported a phase 1/2 study of CXCR4 inhibition combined with chemotherapy prior to allogeneic stem cell transplantation (allo-SCT) (G-CSF-plerixafor (G+P) plus busulfan-fludarabine (Bu+Flu), Konopleva, et al. BMT 2015) and confirmed that patients who had not achieved remission at the time of transplant ("non-CR") had poorer outcome than patients who were in remission at the time of allo-SCT ("CR"). Similar results have been reported in other clinical studies. Risk factors, such as the presence of circulating blasts and unfavorable cytogenetics are associated with poor outcome, but the molecular responses in patients treated with CXCR4 inhibitor and conditioning chemotherapy prior to allo-SCT are unknown. We investigated the hypothesis that the CXCR4 inhibition-driven preparative regimen modulates distinct signaling networks, which vary depending on disease status.
Utilizing reverse phase protein array (RPPA), we profiled 157 proteins in 36 cellular signaling and functional groups in samples collected from ten AML patients who were studied in the phase 1/2 trial (Table1). Five CR patients had less than 1% blasts in bone marrow (BM) and no blasts in peripheral blood (PB) before conditioning regimen (baseline, day -9). Five non-CR patients had BM blasts ranging from 10-72% and PB blasts from 0-45%. Here we denote samples from "CR" patients as "normal" and from "non-CR" patient as "AML". All "AML" patients with blasts had persistent blasts after G+P plus conditioning, ranging from 4-64%. However, four of five "AML" and five "normal" patients achieved complete response to allo-SCT. Engraftment was observed in all patients. Disease progression following allo-SCT was observed in four of five "AML" but not in "normal" patients. Overall survival in "AML" was significantly shorter than in "normal" patients (non-CR = 260 ± 55 days, CR = 2028 ± 103 days, P < 0.001).
RPPA analysis of samples prior to conditioning (day -9) revealed that 9 proteins in 9 signaling pathways were expressed differently in "normal" and "AML" samples. Among them, c-KIT, 53BP1, a P53-binding DNA repair protein, and CIAP (a SMAC and IAP family member) had significantly higher expression in "AML".
G+P treatment significantly modulated 7 proteins in 4 pathways in "AML" samples, and 22 proteins in 13 signaling and functional groups in "normal" samples (Fig 1A). As a result, 22 proteins in 14 signaling and functional groups were differentially expressed in "AML" and "normal" samples post G+P treatment (day -7) (Fig 1B). Among the top 10 distinct proteins, PI3Kp110A, P53BP1, SMAD1 and p-C-JUN S73 had higher expression, and P38MAPK, p-HER2 Y1248, P-CADHERIN, SYK, P21 and TAU had lower expression in "AML" samples.
Treatment with G+P plus Bu+Flu conditioning modulated 10 proteins in 7 signaling pathways in "AML" samples, and altered 40 proteins in 13 signaling pathways in "normal" samples (Fig 1C). As a result, G+P plus Bu+Flu conditioning caused significant differences in expression of 16 proteins in 14 signaling and functional groups in "AML" vs. "normal" samples (day -3) (Fig 1D). Among the top 10 distinct proteins, PI3Kp110A, XRCC1, p-ERA S118, 53BP1, and BCL2 had higher expression, and MIG6, SYK, TAU, p-AKT T308 and MEK1 had lower expression in "AML" samples. Notably, c-KIT and 53BP1 in "AML" baseline samples were persistently expressed at high levels in samples from G+P and G+P plus Bu+Flu treated patients, suggesting that c-KIT and 53BP1 mediated signaling might play a role in therapeutic resistance and disease relapse in patients with active disease at the time of transplant.
In summary, CXCR4 inhibition combined with Bu+Flu conditioning triggered distinct molecular responses, resulting in differential signaling between "normal" and "AML" cells prior to allo-SCT. The persistence of c-KIT and 53BP1 might play a role in resistance and contribute to relapse in AML.
No relevant conflicts of interest to declare.
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