Differential Receptor Tyrosine Kinase PET Imaging for Therapeutic Guidance

Abstract

Inhibitors of the phosphatidylinositol 3-kinase/protein kinase B/mammalian target of rapamycin (PI3K/AKT/mTOR) pathway hold promise for the treatment of breast cancer, but resistance to these treatments can arise via feedback loops that increase surface expression of the receptor tyrosine kinases (RTK) epidermal growth factor receptor 1 (EGFR) and human epidermal growth factor receptor 3 (HER3), leading to persistent growth pathway signaling. We developed PET probes that provide a method of imaging this response in vivo, determining which tumors may use this escape pathway while avoiding the need for repeated biopsies. Methods: Anti-EGFR-F(ab′) 2 and anti-HER3-F(ab′) 2 were generated from monoclonal antibodies by enzymatic digestion, conjugated to DOTA, and labeled with 64 Cu. A panel of breast cancer cell lines was treated with increasing concentrations of the AKT inhibitor GDC-0068 or the PI3K inhibitor GDC-0941. Pre-and posttreatment expression of EGFR and HER3 was compared using Western blot and correlated to probe accumulation with binding studies. Nude mice xenografts of HCC-70 or MDA-MB-468 were treated with either AKT inhibitor or PI3K inhibitor and imaged with either EGFR or HER3 PET probe. Results: Changes in HER3 and EGFR PET probe accumulation correlate to RTK expression change as assessed by Western blot (R 2 of 0.85-0.98). EGFR PET probe PET/CT imaging of HCC70 tumors shows an SUV of 0.32 ± 0.03 for vehicle-, 0.50 ± 0.01 for GDC-0941-, and 0.62 ± 0.01 for GDC-0068-treated tumors, respectively (P , 0.01 for both comparisons to vehicle). HER3 PET probe PET/ CT imaging of MDAMB468 tumors shows an SUV of 0.35 ± 0.02 for vehicle-and 0.73 ± 0.05 for GDC-0068-treated tumors (P , 0.01). Conclusion: Our imaging studies, using PET probes specific to EGFR and HER3, show that changes in RTK expression indicative of resistance to PI3K and AKT inhibitors can be seen within days of therapy initiation and are of sufficient magnitude as to allow reliable clinical interpretation. Noninvasive PET monitoring of these RTK feedback loops should help to rapidly assess resistance to PI3K and AKT inhibitors and guide selection of an appropriate combinatorial therapeutic regimen on an individual patient basis.

89Zr-mAb3481 PET for HER3 tumor status assessment during lapatinib treatment

“… 25 The effects of GDC-0068 effects on HER3 alone were imaged with 64 Cu-anti-HER3-F(ab'), which showed MDA-MB-468 tumor uptake increased from SUV mean of 0.35±0.02 for vehicle to 0.73±0.05 ( P <0.01), three days after treatment initiation. 26 In vitro , 48 hours 5 µM GDC-0068 treatment resulted in 74%, 102%, and 65% increased HER3 surface expression in MDA-MB-468, HCC-70 and MCF-7 human breast cancer cells, respectively. 26 Imaging with lower molecular weight tracers, e.g., affibodies or F(ab) 2 , might be beneficial for imaging of fast or short-lived effects, due to their shorter biological half-life and faster tumor accumulation, compared to full-length antibody tracers.…”

“… 26 In vitro , 48 hours 5 µM GDC-0068 treatment resulted in 74%, 102%, and 65% increased HER3 surface expression in MDA-MB-468, HCC-70 and MCF-7 human breast cancer cells, respectively. 26 Imaging with lower molecular weight tracers, e.g., affibodies or F(ab) 2 , might be beneficial for imaging of fast or short-lived effects, due to their shorter biological half-life and faster tumor accumulation, compared to full-length antibody tracers.…”

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

“…HER3 imaging is challenging due to the relatively low overexpression in malignant lesions and moderate endogenous expression in healthy tissue and potential metastatic sites, especially the liver. Radiolabeled antibodies and antibody fragments have been suggested for imaging of HER3-expression [10][11][12]. For example, the anti-HER3 antibody 89 Zr-lumretuzumab provided good imaging contrast 4-7 days after injection and enabled quantification of the uptake in HER3 positive tumors in a small clinical study.…”

Recent Advances in Nuclear Imaging of Receptor Expression to Guide Targeted Therapies in Breast Cancer

“…Wehrenberg-Klee et al demonstrated in a preclinical study that SUVmean of [ 64 Cu]anti-HER3-F(ab′)2 increased in MDAMB468 xenografts treated with the AKT (Protein Kinase B) inhibitor GDC-0068 when compared to untreated control. The enhancement of tracer uptake in tumor correlated with HER3 levels and resistance to therapy [39].…”