A 15 Hour Dosing-Collection Interval for Plerixafor Is at Least as Effective as the Standard 10 Hour Interval.
Authors: Rosenbaum Eric R , Nakagawa Mayumi , Pesek Gina , Theus John , Barlogie Bart , Cottler-Fox Michele H. 
Published: October 2019

Abstract
Abstract 2152
Poster Board II-129

Introduction:
Plerixafor (formerly AMD3100) is a reversible CXCR4 inhibitor used to mobilize CD34+ cells for collection and use in hematopoietic transplant. Since beginning phase I trials, the drug has been given at 10 pm and collection initiated 10h later at 8 am. After recent FDA approval, we examined use of a dosing-collection interval of 15h (5 pm administration/8 am collection) for patient (pt) convenience. Here we compare results retrospectively from phase I and II trials at our institution using the 10h interval with post-approval collections using the 15h interval. We also evaluated prechemotherapy platelet (plt) count as a predictor of response to plerixafor+G-CSF.

Materials and Methods:
We reviewed data for all pts (n=107) at our institution who received plerixafor using the 10h (n=79) and 15h (n=34) intervals. This group was reduced to only those who received 4 consecutive days of plerixafor (n=76), of which 67 had the 10h interval and 21 had the 15h interval. The age range of the 10h group was 30-79y (median 62) and the range of the 15h group was 45-78y (median 57). The primary disease in both groups was multiple myeloma, but included 2 NHL in the 10h group, and 5 NHL in the 15h group. Chemotherapy given prior to mobilization for both the 10h and 15h interval groups were similar and plerixafor was administered with G-CSF in all pts. CD34+ cells collected on days 1-4 were quantified by flow cytometry. Finally, some patients (n=9) underwent mobilization with plerixafor two or more times, of which 4 did so on both the 10h and 15h intervals. These instances were recorded as separate events. Prechemotherapy plt counts were also reviewed for each patient and subcategorized into 3 groups: <100, 100-150, and >150,000/uL. Mean CD34+ cells collected were compared between the plt subcategories for both the 10h and 15h groups.

Results:
The mean number of CD34+ cells collected for the 10h group on days 1-4 of plerixafor administration was 1.26, 1.04, 0.71, and 0.55 ×10e6 CD34+ cells/kg, respectively, with total average collection of 3.56 × 10e6 CD34+ cells/kg. For the 15h group, the average number of CD34+ cells collected on days 1-4 were 2.20, 1.61, 1.44, and 1.01 × 10e6 CD34+ cells/kg, respectively, with total average collection of 6.26 × 10e6 CD34+ cells/kg. The two groups were compared using two-tailed student's t-tests. There was no statistically significant difference between the quantity of CD34+ cells collected on days 1 or 2 for the 10h and 15h groups, however there was a statistically significant difference on days 3 and 4. On these latter two days, the 15h group collected a significantly higher number of CD34+ cells compared to the 10h group. The difference in average total collection for the two groups over all 4 days was statistically significant at an alpha level of 0.05 (p-value: 0.03). The different prechemotherapy plt groups were compared using one-way ANOVA statistical analysis. Within the 10h group the <100 group had the least amount collected (mean 2.46×10e6 CD34+/kg), the 100-150 had an intermediate amount (mean 3.30×10e6CD34+/kg), and the >150 group the most (4.30×10e6CD34+/kg; p-value 0.02). The same comparison within the 15h group showed similar findings but the number of patients in each subcategory was too small to be statistically significant.

Conclusion:
Administration of plerixafor with the 15h interval (5 pm dosing/8 am collection) appears to be equivalent to the standard 10h interval with regard to quantity of CD34+ cells collected over the first 2 days, and is superior to the 10 h schedule if the collection continues for 4 days. Further, prechemotherapy plt count is predictive of ability to mobilize CD34+ cells with perixafor+G-CSF for the 10h interval, as has been previously shown by our group for G-CSF alone in a similar population. Additional pts are needed to demonstrate conclusively the same finding for the 15h dosing/collection interval.

Disclosures:
No relevant conflicts of interest to declare.