ImmunoPET imaging identifies the optimal timepoint for combination therapy in preclinical models of triple negative breast cancer
Authors: Li Ziqi , Belitzky Erika , Blaha Ondrej , Cavaliere Alessandra , Aboian Mariam , Katz Samantha , Rajabimoghadam Khashayar , Melegari Lindy , Kurpiewski Stephen , Zhu Xiaohua , Marquez-Nostra Bernadette 
Published: November 2022

Abstract
Purpose To quantify the degree and identify the timeframe of glycoprotein nonmetastatic melanoma B (gpNMB) upregulation in vivo after treatment with the Src tyrosine kinase inhibitor, dasatinib, by longitudinal PET imaging with the 89Zr-labeled anti-gpNMB antibody ([89Zr]Zr-DFO-CR011). The goal is to identify the timepoint at which to administer the corresponding antibody drug conjugate, CDX-011 following treatment with dasatinib to enhance therapeutic efficacy of sequential targeted treatments using noninvasive imaging to guide therapy.
Methods First, TNBC cell lines that either express gpNMB (MDA-MB-468) or do not express gpNMB (MDA-MB-231) were treated with dasatinib in vitro for 48 h followed by western blot analysis to determine differences in gpNMB expression. MDA-MB-468 xenografted mice were treated with dasatinib. Subgroups of mice were euthanized at 0-, 7-, 14-, and 21-days post treatment, and tumors were harvested for western blot analysis of gpNMB. In a different cohort of MDA-MB-468 xenograft models, longitudinal PET imaging with [89Zr]Zr-DFO-CR011 was performed before treatment at 0- (baseline), and at 14- and 28-days after treatment with dasatinib, CDX-011, or their combination, to determine changes in gpNMB expression in vivo relative to baseline. As a gpNMB-negative control, MDA-MB-231 xenograft models were imaged at 21 days after treatment with dasatinib, combination of CDX-011 and dasatinib, and vehicle control.
Results Western blot analysis of MDA-MB-468 cell and tumor lysates validated that dasatinib increased expression of gpNMB in vitro and in vivo at 14 days post treatment initiation. In PET imaging studies of different cohorts of MDA-MB-468 xenografted mice, [89Zr]Zr-DFO-CR011 uptake in tumors (SUVmean = 3.2 ± 0.3) was greatest at 14 days after treatment with dasatinib (SUVmean = 4.9 ± 0.6) or combination of dasatinib and CDX-011 (SUVmean= 4.6 ± 0.2) compared with that at baseline (SUVmean = 3.2 ± 0.3). The highest tumor regression after treatment was observed in the combination-treated group with a percent change in tumor volume relative to baseline (%CTV) of -54 ± 13 compared with the vehicle control-treated group (%CTV = +102 ± 27), CDX-011 group (%CTV = -25 ± 9.8), and dasatinib group (%CTV = -23 ± 11). In contrast, the PET imaging of MDA-MB-231 xenografted mice indicated no significant difference in the tumor uptake of [89Zr]Zr-DFO-CR011 between treated (dasatinib alone or in combination with CDX-011) and vehicle-control groups.
Conclusions Dasatinib upregulated gpNMB expression in gpNMB-positive MDA-MB-468 xenografted tumors at 14 days post treatment initiation, which can be quantified by PET imaging with [89Zr]Zr-DFO-CR011. Furthermore, combination therapy with dasatinib and CDX-011 appears to be a promising therapeutic strategy for TNBC and warrants further investigation.