HER3-Mediated Resistance to Hsp90 Inhibition Detected in Breast Cancer Xenografts by Affibody-Based PET Imaging

Abstract

2 Translational RelevanceCurrently, inter-and intra-tumor heterogeneity is a clinical challenge, as histological techniques can fail to provide a representative indication of molecular variation, due to dependence on the section of tumor that is chosen for sampling. This underscores the need to introduce novel imaging biomarkers that allow the examination of the whole tumor mass and may significantly help to better understand and treat cancer. Therefore, we have developed a novel PET radiotracer that will provide information on heterogeneous HER3 expression and receptor expression changes due to downstream signaling inhibition, which is increasingly being recognized as a key player in therapeutic resistance. This would aid in the selection of patients for novel HER3 targeted therapies and potentially enable patients to be spared ineffective therapies, and, if necessary, being switched sooner to more effective therapeutic regimens.Research. Zr-DFO-Z HER3:8698 can track changes in receptor expression in HER3-positive xenograft models and monitor the outcome of AUY922 treatment. Our in vitro findings showed that MCF-7 cells, which are phenotypically different from BT474, develop resistance to AUY922 through HER3/IGF-1R-mediated signaling. Of note, the lack of response in vitro due to HER3 recovery was confirmed in vivo using 89 Zr-DFO-Z HER3:8698 -based imaging. Upon AUY922 treatment, higher radioconjugate uptake was detected in treated MCF-7 xenografts, correlating with an AUY922-induced HER3 up-regulation concomitant with an increase in IGF-1R expression. Conclusion: These data underline the potential of HER3-based PET imaging to noninvasively provide information about HER3 expression and to identify patients not-responding to targeted therapies due to HER3 recovery.

Benefit of Later-Time-Point PET Imaging of HER3 Expression Using Optimized Radiocobalt-Labeled Affibody Molecules

“…HER3 has evolved into an important molecular target in cancer. We and others have previously investigated the potential of radiolabeled affibody molecules as HER3-targeted imaging agents for PET and SPECT [15,16,[20][21][22]27]. It has been shown that an increase in the negative charge of the radionuclide-chelator complex can improve tumor-to-liver contrast for affibody molecules [26,36].…”

“…[ 89 Zr]Zr-DFO-Z HER3:8698 3 h pi reached a tumor-to-liver ratio of 1.18 ± 0.13. However, some release of the 89 Zr label was observed in vivo, resulting in a two-fold decrease in tumor uptake after 24 and, therefore, a decrease in tumor-to-liver contrast [22]. Compared with [ 111 In]In-Z HER3 -DOTAGA [26], tumor uptake of [ 57 Co]Co-(HE) 3 -Z HER3 -DOTA was slightly lower (3.4 ± 0.5 vs. 2.4 ± 0.4% ID/g at 24 h), but tumor-to-liver contrast of [ 57 Co]Co-(HE) 3 -Z HER3 -DOTA was higher at both time points, providing another argument for using cobalt-55 as a long-lived radiolabel for PET imaging.…”

“…Typically, a high contrast is obtained on the same day as the injection, as early as three to four hours post-injection (pi). We and others have previously shown the feasibility of anti-HER3 affibody molecules for imaging of HER3 expression with different radioisotopes for PET and SPECT [16,[20][21][22].…”

“…The long-lived PET isotope zirconium-89 (t 1/2 = 78.4 h) has been used for preclinical and clinical imaging of HER3 expression in combination with antibodies, and nanobodies [10,13,32]. Recently, a HER3-targeting affibody molecule was labeled with 89 Zr and used to detect changes in HER3 expression in response to treatment of breast cancer xenografts with an HSP90 inhibitor [22]. However, the fast kinetics of affibody molecules would also allow the use of PET isotopes with intermediate half-lives (shorter than 89 Zr but longer than 18 F and 68 Ga).…”

Thiol-Reactive PODS-Bearing Bifunctional Chelators for the Development of EGFR-Targeting [18F]AlF-Affibody Conjugates

“…Mice were administered the radioconjugate (12 µg in 100 µL of 0.9% sterile saline, 1.1-1.8 MBq/mouse) by intravenous tail vein injection and were anesthetized using an isoflurane/O 2 mixture (1.5%-2.0% v/v) approximately 5 min prior to imaging. Whole-body static PET images were acquired 1 h post-radioconjugate injection for the duration of 10 min, with a 358 to 664 keV energy window, followed by CT acquisition as previously described [26]. The image data were processed and reconstructed as previously reported [26].…”