Kit for the preparation of 111In-labeled pertuzumab injection for imaging response of HER2-positive breast cancer to trastuzumab (Herceptin)

Formulation of a kit under Good Manufacturing Practices (GMP) for preparing [111In]In-BnDTPA-trastuzumab-NLS injection: a theranostic agent for imaging and Meitner-Auger Electron (MAE) radioimmunotherapy of HER2-positive breast cancer

BACKGROUND

¹¹¹In[In]-BnDTPA-trastuzumab-NLS is a radiopharmaceutical with theranostic applications for imaging and Meitner-Auger electron (MAE) radioimmunotherapy (RIT) of HER2-positive breast cancer (BC). Nuclear localization sequence (NLS) peptides route the radiopharmaceutical to the nucleus of HER2-positive BC cells following receptor-mediated internalization for RIT with subcellular range MAEs. The γ-photons emitted by ¹¹¹In permit tumour imaging by SPECT. Our aim was to formulate a kit under Good Manufacturing Practices conditions to prepare ¹¹¹In[In]-BnDTPA-trastuzumab-NLS injection for a first-in-human clinical trial.

RESULTS

Trastuzumab was derivatized with p-SCN-BnDTPA to introduce Bn-DTPA for complexing ¹¹¹In, then modified with maleimide groups for conjugation to the thiol on cysteine in NLS peptides [CGYGPKKKRKVGG]. BnDTPA-trastuzumab-NLS (5 mg in 1.0 mL of 0.05 M ammonium acetate buffer, pH 5.5) was dispensed into unit dose sterile glass vials to produce kits for labeling with 100-165 MBq of ¹¹¹In[In]Cl₃. The kits met specifications for protein concentration (4.5-5.5 mg/mL), volume (0.95-1.05 mL), pH (5.5-6.0), appearance (clear, pale-yellow, particulate-free), BnDTPA substitution level (2.0-7.0 BnDTPA/trastuzumab), purity and homogeneity (SDS-PAGE and SE-HPLC), ¹¹¹In labeling efficiency (> 90%), binding to HER2-positive SK-BR-3 human breast cancer cells (K_a = 1-8 × 10⁸ L/mmol; B_max = 0.5-2 × 10⁶ sites/cell), NLS peptide conjugation (upward band shift on SDS-PAGE), sterility (USP Sterility Test) and endotoxins (USP Bacterial Endotoxins Test). ¹¹¹In-BnDTPA-trastuzumab-NLS injection met specifications for pH (5.5-6.5), radiochemical purity (≥ 90%), radionuclide purity (≥ 99%), appearance (clear, colourless, particle-free) and sterility (retrospective USP Sterility Test). Kits were stable stored at 2-8 °C for up to 661 days (d) meeting all key specifications. Protein concentration remained within or just slightly greater than the specification for up to 139 d. ¹¹¹In[In]-BnDTPA-trastuzumab-NLS injection was stable for up to 24 h. An expiry of 180 d was assigned for the kits and 8 h for the final radiopharmaceutical.

CONCLUSION

A kit was formulated under GMP conditions for preparing ¹¹¹In[In]-BnDTPA-trastuzumab-NLS injection. This radiopharmaceutical was safely administered to 4 patients with HER2-positive BC to trace the uptake of trastuzumab into brain metastases before and after MRI-guided focused ultrasound (MRIg-FUS) by SPECT imaging.

A comparison of DFO and DFO* conjugated to trastuzumab-DM1 for complexing 89Zr - In vitro stability and in vivo microPET/CT imaging studies in NOD/SCID mice with HER2-positive SK-OV-3 human ovarian cancer xenografts

INTRODUCTION

Desferrioxamine (DFO) is conjugated to antibodies to chelate ⁸⁹Zr for PET, but DFO forms a hexadentate complex with Zr⁴⁺ that exhibits instability contributing to bone uptake of ⁸⁹Zr, while the cationic charge of the Zr⁴⁺-DFO complex may promote normal tissue uptake of the radioimmunoconjugates (RICs). DFO* is a novel chelator that forms a more stable octadentate and neutral complex with ⁸⁹Zr. Our aim was to compare the in vitro stability of [⁸⁹Zr]Zr-DFO*-human IgG (hIgG) and [⁸⁹Zr]Zr-DFO-hIgG RICs, and the in vivo PET imaging properties of the antibody-drug conjugate (ADC), trastuzumab-DM1 (T-DM1), labeled with ⁸⁹Zr by conjugation to DFO or DFO*.

METHODS

SCN-pPhe-DFO and SCN-pPhe-DFO* were reacted with hIgG at a 14.6-fold excess or with T-DM1 at a 4.1-fold or 10-fold excess, respectively, purified and labeled with ⁸⁹Zr. The number of DFO* introduced was determined by measuring the absorbance at 245/252 nm and the protein concentration was measured at 280 nm. The stability of [⁸⁹Zr]Zr-DFO*-hIgG was studied in vitro in human plasma, and by challenge with a 385-fold excess (0.1 mM) of DFO or EDTA. An inverse stability study was performed with [⁸⁹Zr]Zr-DFO-hIgG challenged with 0.1 mM DFO*. The HER2 binding affinity of [⁸⁹Zr]Zr-DFO*-T-DM1 was measured in a direct (saturation) binding assay using SK-BR-3 human breast cancer cells or SK-OV-3 human ovarian cancer cells. The biodistribution of [⁸⁹Zr]Zr-DFO*-T-DM1 and [⁸⁹Zr]Zr-DFO-T-DM1 were compared in non-tumor bearing Balb/c mice and in NOD/SCID mice with s.c. SK-OV-3 xenografts at 96 h post-intravenous injection (p.i.). MicroPET/CT images were obtained at 96 h p.i. of the RICs.

RESULTS

hIgG and T-DM1 were conjugated to 4.5-5.3 and 3.1 chelators (DFO or DFO*), respectively, and labeled with ⁸⁹Zr to a final radiochemical purity of 91-99%. [⁸⁹Zr]Zr-DFO*-hIgG was stable in vitro in human plasma or to challenge with 0.1 mM EDTA, but incubation with 0.1 mM DFO caused 26.0 ± 2.1% loss of ⁸⁹Zr after 5 days. In contrast, incubation of [⁸⁹Zr]Zr-DFO-hIgG with 0.1 mM DFO* resulted in 77.0 ± 3.9% loss of ⁸⁹Zr after 5 days. [⁸⁹Zr]Zr-DFO*-T-DM1 retained high affinity binding to HER2 on SK-BR-3 and SK-OV-3 cells with a K_d = 2.2 ± 0.3 nM and 1.9 ± 0.3 nM, respectively, and B_max = 3.4 ± 0.1 × 10⁵ and 1.1 ± 0.04 × 10⁵ receptors/cell, respectively. Biodistribution studies of [⁸⁹Zr]Zr-DFO-T-DM1 and [⁸⁹Zr]Zr-DFO*-T-DM1 in Balb/c and NOD/SCID mice revealed significantly lower uptake in bone, liver, kidneys, and spleen for [⁸⁹Zr]Zr-DFO*-T-DM1 than [⁸⁹Zr]Zr-DFO-T-DM1. Uptake of [⁸⁹Zr]Zr-DFO*-T-DM1 and [⁸⁹Zr]Zr-DFO-T-DM1 in SK-OV-3 tumors was moderate [5.0 ± 1.8% injected dose/g (%ID/g) and 6.3 ± 0.6%ID/g, respectively; P = 0.18]. Tumors were imaged with both RICs.

CONCLUSION

We conclude that DFO* conjugated to T-DM1 provides more stable complexation of ⁸⁹Zr and therefore, [⁸⁹Zr]Zr-DFO*-T-DM1 would be more useful than [⁸⁹Zr]Zr-DFO-T-DM1 to probe the delivery of T-DM1 to tumors by PET, which we previously found is correlated with response to treatment with T-DM1 in mouse tumor xenograft models.

ADVANCES IN KNOWLEDGE AND IMPLICATION FOR PATIENT CARE

This study is the first to directly compare the PET imaging properties of [⁸⁹Zr]Zr-DFO*-T-DM1 and [⁸⁹Zr]Zr-DFO-T-DM1 in a HER2-overexpressing tumor xenograft mouse model. Our results indicate that [⁸⁹Zr]Zr-DFO*-T-DM1 provides superior imaging properties due to the greater stability of the [⁸⁹Zr]Zr-DFO* than [⁸⁹Zr]Zr-DFO complex.

Targeting HER2 in Nuclear Medicine for Imaging and Therapy

Since its discovery, the human epidermal growth factor 2 (HER2) has been extensively studied. Presently, there are 2 standard diagnostic techniques to assess HER2 status in biopsies: immunohistochemistry and fluorescence in situ hybridization. While these techniques have played an important role in the treatment of patients with HER2-positive cancer, they both require invasive biopsies for analysis. Moreover, the expression of HER2 is heterogeneous in breast cancer and can change over the course of the disease. Thus, the degree of HER2 expression in the small sample size of biopsied tumors at the time of analysis may not represent the overall status of HER2 expression in the whole tumor and in between tumor foci in the metastatic setting as the disease progresses. Unlike biopsy, molecular imaging using probes against HER2 allows for a noninvasive, whole-body assessment of HER2 status in real time. This technique could potentially select patients who may benefit from HER2-directed therapy and offer alternative treatments to those who may not benefit. Several antibodies and small molecules against HER2 have been labeled with different radioisotopes for nuclear imaging and/or therapy. This review presents the most recent advances in HER2 targeting in nuclear medicine focusing on preclinical and clinical studies.

Development and preclinical studies of 64Cu-NOTA-pertuzumab F(ab')2 for imaging changes in tumor HER2 expression associated with response to trastuzumab by PET/CT

We previously reported that microSPECT/CT imaging with ¹¹¹In-labeled pertuzumab detected decreased HER2 expression in human breast cancer (BC) xenografts in athymic mice associated with response to treatment with trastuzumab (Herceptin). Our aim was to extend these results to PET/CT by constructing F(ab')₂ of pertuzumab modified with NOTA chelators for complexing ⁶⁴Cu. The effect of the administered mass (5-200 µg) of ⁶⁴Cu-NOTA-pertuzumab F(ab')₂ was studied in NOD/SCID mice engrafted with HER2-positive SK-OV-3 human ovarian cancer xenografts. Biodistribution studies were performed in non-tumor bearing Balb/c mice to predict radiation doses to normal organs in humans. Serial PET/CT imaging was conducted on mice engrafted with HER2-positive and trastuzumab-sensitive BT-474 or trastuzumab-insensitive SK-OV-3 xenografted mice treated with weekly doses of trastuzumab. There were no significant effects of the administered mass of ⁶⁴Cu-NOTA-pertuzumab F(ab')₂ on tumor or normal tissue uptake. The predicted total body dose in humans was 0.015 mSv/MBq, a 3.3-fold reduction compared to ¹¹¹In-labeled pertuzumab. MicroPET/CT images revealed specific tumor uptake of ⁶⁴Cu-NOTA-pertuzumab F(ab')₂ at 24 or 48 h post-injection in mice with SK-OV-3 tumors. Image analysis of mice treated with trastuzumab showed 2-fold reduced uptake of ⁶⁴Cu-NOTA-pertuzumab F(ab')₂ in BT-474 tumors after 1 week of trastuzumab normalized to baseline, and 1.9-fold increased uptake in SK-OV-3 tumors after 3 weeks of trastuzumab, consistent with tumor response and resistance, respectively. We conclude that PET/CT imaging with ⁶⁴Cu-NOTA-pertuzumab F(ab')₂ detected changes in HER2 expression in response to trastuzumab while delivering a lower total body radiation dose compared to ¹¹¹In-labeled pertuzumab.

Measuring HER2-Receptor Expression In Metastatic Breast Cancer Using [68Ga]ABY-025 Affibody PET/CT

Purpose: Positron Emission Tomography (PET) imaging of HER2 expression could potentially be used to select patients for HER2-targed therapy, predict response based on uptake and be used for monitoring. In this phase I/II study the HER2-binding Affibody molecule ABY-025 was labeled with ⁶⁸Ga-gallium ([⁶⁸Ga]ABY-025) for PET to study effect of peptide mass, test-retest variability and correlation of quantified uptake in tumors to histopathology.

Experimental design: Sixteen women with known metastatic breast cancer and on-going treatment were included and underwent FDG PET/CT to identify viable metastases. After iv injection of 212±46 MBq [⁶⁸Ga]ABY-025 whole-body PET was performed at 1, 2 and 4 h. In the first 10 patients (6 with HER2-positive and 4 with HER2-negative primary tumors), [⁶⁸Ga]ABY-025 PET/CT with two different doses of injected peptide was performed one week apart. In the last six patients (5 HER2-positive and 1 HER2-negative primary tumors), repeated [⁶⁸Ga]ABY-025 PET were performed one week apart as a test-retest of uptake in individual lesions. Biopsies from 16 metastases in 12 patients were collected for verification of HER2 expression by immunohistochemistry and in-situ hybridization.

Results: Imaging 4h after injection with high peptide content discriminated HER2-positive metastases best (p<0.01). PET SUV correlated with biopsy HER2-scores (r=0.91, p<0.001). Uptake was five times higher in HER2-positive than in HER2-negative lesions with no overlap (p=0.005). The test-retest intra-class correlation was r=0.996. [⁶⁸Ga]ABY-025 PET correctly identified conversion and mixed expression of HER2 and targeted treatment was changed in 3 of the 16 patients.

Conclusion: [⁶⁸Ga]ABY-025 PET accurately quantifies whole-body HER2-receptor status in metastatic breast cancer.

Advancing novel molecular imaging agents from preclinical studies to first-in-humans phase I clinical trials in academia--a roadmap for overcoming perceived barriers

There is a critical need to advance promising novel molecular imaging (MI) agents for cancer from preclinical studies to first-in-humans Phase I clinical trials in order to realize their full potential for cancer detection and for predicting or monitoring response to targeted ("personalized") cancer therapies. Steps to clinical translation include radiopharmaceutical formulation, preclinical pharmacology and toxicology studies, clinical trial design and human ethics approval, and regulatory agency submission. In this Topical Review, we provide a "roadmap" to advancing one class of novel MI agents to Phase I trials in academia and illustrate the processes that we have successfully applied for (111)In-labeled pertuzumab, a MI probe for monitoring response of HER2-positive breast cancer to treatment with trastuzumab (Herceptin). We hope that our experience will encourage other academic radiopharmaceutical scientists to embrace this challenge.