Search

Understanding a drug's whole-body biodistribution and tumor targeting can provide important information regarding efficacy, safety, and dosing parameters. Current methods to evaluate biodistribution include in vivo imaging technologies like positron electron tomography and single-photon emission computed tomography or ex vivo quantitation of drug concentrations in tissues using autoradiography and standard biochemical assays. These methods use radioactive compounds or are cumbersome and do not give whole-body information. Here, for the first time, we show the utility of fluorescence molecular tomography (FMT) imaging to determine the biodistribution and targeting of an antibody–drug conjugate (ADC). An anti–5T4-antibody (5T4-Ab) and 5T4-ADC were conjugated with a near-infrared (NIR) fluorophore VivoTag 680XL (VT680). Both conjugated compounds were stable as determined by SEC-HPLC and plasma stability studies. Flow cytometry and fluorescence microscopy studies showed that VT680-conjugated 5T4-ADC specifically bound 5T4-expressing cells in vitro and also exhibited a similar cytotoxicity profile as the unconjugated 5T4-ADC. In vivo biodistribution and tumor targeting in an H1975 subcutaneous xenograft model demonstrated no significant differences between accumulation of VT680-conjugated 5T4-Ab or 5T4-ADC in either normal tissues or tumor. In addition, quantitation of heart signal from FMT imaging showed good correlation with the plasma pharmacokinetic profile suggesting that it (heart FMT imaging) may be a surrogate for plasma drug clearance. These results demonstrate that conjugation of VT680 to 5T4-Ab or 5T4-ADC does not change the behavior of native biologic, and FMT imaging can be a useful tool to understand biodistribution and tumor-targeting kinetics of antibodies, ADCs, and other biologics. Mol Cancer Ther; 15(10); 2530–40. ©2016 AACR.

Supplemental Figure 1: Standard curve of VT680 showing the 3-D quantitation and linearity by FMT imaging; Supplemental Figure 2: Evaluation of VT680 conjugated 5T4-Ab and 5T4-ADC; Supplemental Figure 3: Determination of antibody binding capacity (ABC) and receptor saturation in H1975 and MDA-MB-468 cells by flow cytometry; Supplemental Figure 4: Ex vivo FMT imaging showing the accumulation of 5T4-Ab-VT680, 5T4-ADC-VT680, Isotype control-Ab-VT680 and VT680 alone 48 h post-injection in tumor (A) and liver (B).

P-cadherin-LP-DART is a bispecific antibody targeting P-cadherin expressed on the tumor cells and CD3 on the T-cells. Previously we demonstrated the development and efficacy of P-cadherin-LP-DART in in vitro and in vivo models. Here, we evaluated the three pillars: exposure, targeting specificity and pharmacodynamic modulation for P-cadherin-LP-DART using fluorescence molecular tomography (FMT). Bispecific antibodies and T-cells were conjugated with a near-infrared fluorophores: VivoTag®680XL (VT680) and CellVue®NIR815 (CV815), respectively. In vitro binding and cytotoxic T-lymphocyte assay demonstrated that P-cadherin-LP-DART significantly retained its properties after VT680 conjugation. In vivo FMT imaging was performed to determine the bispecific biodistribution and T-cell trafficking in HCT-116 xenograft model. Peak tumor exposure (2.71%ID) was observed at 96 hr post-injection with measurable quantity even at 240 hr (1.46%ID) (Pillar 1). P-cadherin-LP-DART accumulation in tumor was 20-25 fold higher compared to Control-LP-DART demonstrating the targeting specificity (Pillar 2). Imaging after engraftment of CV815 labeled T-cells showed P-cadherin-LP-DART mediated T-cell trafficking in tumors (Pillar 3). This study harnessed the multichannel capability of FMT and demonstrated the targeting of drug and trafficking of T cells to tumors, simultaneously. Our results show the impact of molecular imaging in demonstrating three pillars of pharmacology, longitudinally and non-invasively.

Age-related Macular Degeneration (AMD) is the leading cause of visual impairment and blindness in the elderly in developed countries. Neovascular/exudative (wet) AMD is the aggressive form of AMD and can involve choroidal neovascularization and vascular leakage. Anti-vascular endothelial growth factor (anti-VEGF) medications have significantly improved treatment of wet-AMD. However, only approximately 40% of patients obtain full benefit from anti-VEGF therapy and the medications are given by intravitreal injection. Axitinib, a small molecule multi-receptor tyrosine kinase inhibitor used for the treatment of advanced renal cell carcinoma, is taken orally and inhibits VEGF activity by blocking VEGF receptors. Axitinib also has the advantage of blocking platelet derived growth factor (PDGF) receptors which play a role in neovascularization. Using in vitro human retinal microvascular endothelial cells (HRMVECs), human brain vascular pericytes (HBVRs), 3D co-culture vessel sprout assay, and in vivo laser induced rat choroidal neovascularization (CNV) models, the effect of axitinib on neovascularization was evaluated. Axitinib inhibited neovascularization better than anti-VEGF and/or anti-hPDGF-B mAb in the in vitro models demonstrating that combined inhibition of both VEGF and PDGF pathways may be synergistic in treating wet-AMD. Additionally, axitinib showed good efficacy at a low dose (0.875 mg/day) in laser-induced CNV model in rats. In conclusion our data shows that axitinib, an inhibitor of VEGF and PDGF-B pathways may be useful in ameliorating wet-AMD therapy.

Understanding a drug's whole-body biodistribution and tumor targeting can provide important information regarding efficacy, safety, and dosing parameters. Current methods to evaluate biodistribution include in vivo imaging technologies like positron electron tomography and single-photon emission computed tomography or ex vivo quantitation of drug concentrations in tissues using autoradiography and standard biochemical assays. These methods use radioactive compounds or are cumbersome and do not give whole-body information. Here, for the first time, we show the utility of fluorescence molecular tomography (FMT) imaging to determine the biodistribution and targeting of an antibody–drug conjugate (ADC). An anti–5T4-antibody (5T4-Ab) and 5T4-ADC were conjugated with a near-infrared (NIR) fluorophore VivoTag 680XL (VT680). Both conjugated compounds were stable as determined by SEC-HPLC and plasma stability studies. Flow cytometry and fluorescence microscopy studies showed that VT680-conjugated 5T4-ADC specifically bound 5T4-expressing cells in vitro and also exhibited a similar cytotoxicity profile as the unconjugated 5T4-ADC. In vivo biodistribution and tumor targeting in an H1975 subcutaneous xenograft model demonstrated no significant differences between accumulation of VT680-conjugated 5T4-Ab or 5T4-ADC in either normal tissues or tumor. In addition, quantitation of heart signal from FMT imaging showed good correlation with the plasma pharmacokinetic profile suggesting that it (heart FMT imaging) may be a surrogate for plasma drug clearance. These results demonstrate that conjugation of VT680 to 5T4-Ab or 5T4-ADC does not change the behavior of native biologic, and FMT imaging can be a useful tool to understand biodistribution and tumor-targeting kinetics of antibodies, ADCs, and other biologics. Mol Cancer Ther; 15(10); 2530–40. ©2016 AACR.