Deborah A. Scollard

Associations between the uptake of 111In-DTPA-trastuzumab, HER2 density and response to trastuzumab (Herceptin) in athymic mice bearing subcutaneous human tumour xenografts

PurposeThe purpose of the study was to investigate the associations between uptake of 111In-DTPA-trastuzumab, tumour HER2 density and response to trastuzumab (Herceptin) of human breast cancer (BC) xenografts in athymic mice.Materials and methodsThe tumour uptake of 111In-DTPA-trastuzumab in athymic mice bearing BC xenografts with increasing HER2 density (0 to 3+) was evaluated. Specific uptake ratios were established in biodistribution (SUR) and imaging studies (ROI-SUR) using 111In-labeled mouse IgG (111In-DTPA-mIgG). Further corrections were made for circulating radioactivity using tumour-to-blood ratios defined as a localization index (LI) and region-of-interest localization index (ROI-LI), respectively. Mice were treated with trastuzumab (Herceptin). A tumour growth inhibition index (TGI) was calculated and relative TGIs calculated by dividing the TGI of control by that of trastuzumab-treated mice.ResultsStrong, nonlinear associations with HER2 density were obtained if the uptake of 111In-DTPA-trastuzumab was corrected for nonspecific IgG localization (i.e., SUR; r2u2009=u20090.99) and circulating radioactivity (i.e., LI; r2u2009=u20090.87), but without these corrections, the association between HER2 density and tumour uptake was poor (r2u2009=u20090.22). There was a strong association between ROI-SUR and ROI-LI values and HER2 expression (r2u2009=u20090.90 and r2u2009=u20090.95, respectively. All tumours were imaged. Relative TGI values were associated with increasing uncorrected tumour uptake of 111In-DTPA-trastuzumab but not always with HER2 density (i.e., MCF-HER2-18 cells with trastuzumab-resistance).ConclusionHER2 expression (0 to 3+) can be differentiated using 111In-DTPA-trastuzumab, but requires correction of tumour uptake for nonspecific IgG localization and circulating radioactivity. The uncorrected uptake of 111In-DTPA-trastuzumab was associated with tumour response to trastuzumab.

Small-Animal SPECT/CT of HER2 and HER3 Expression in Tumor Xenografts in Athymic Mice Using Trastuzumab Fab–Heregulin Bispecific Radioimmunoconjugates

Heterodimerization of human epidermal growth factor receptor 2 (HER2) with HER3 initiates aberrant downstream growth-signaling pathways in tumors. Our objective was to construct bispecific radioimmunoconjugates (bsRICs) that recognize HER2 and HER3 and evaluate their ability to image tumors in athymic mice that express one or both receptors using small-animal SPECT/CT. Methods: bsRICs were constructed by reacting the maleimide-derivatized trastuzumab Fab fragments that bind HER2 with a thiolated form of the HER3-binding peptide of heregulin-β1 (HRG) with or without a 12- or 24mer polyethylene glycol (PEG) spacer. bsRICs were derivatized with diethylenetriaminepentaacetic acid for labeling with 111In. The ability of 111In-bsRICs to bind HER2 or HER3 was determined in competition assays with unlabeled Fab or HRG on cells expressing one or both receptors. Tumor and normal-tissue uptake were examined in CD1 athymic mice bearing subcutaneous tumor xenografts that expressed HER2, HER3, or both receptors, with or without the preadministration of unlabeled Fab or HRG to determine the specificity of uptake. Results: Conjugation of Fab to HRG was confirmed by sodium dodecyl sulphate polyacrylamide gel electrophoresis–Western blot and size-exclusion high-performance liquid chromatography. Improved HER2 and HER3 binding and greater displacement of binding by competitors was found for 111In-bsRICs that incorporated a PEG spacer, with the PEG24 spacer being optimal. The highest uptake of 111In-bsRICs (7.8% ± 2.1% injected dose per gram [%ID/g]) in BT-474 human breast cancer xenografts (HER2-positive/HER3-positive) occurred at 48 h after injection. The preadministration of trastuzumab Fab decreased uptake in SK-OV-3 (HER2-positive/HER3-negative) human ovarian cancer xenografts from 7.0 ± 1.2 to 2.6 ± 1.5 %ID/g (P < 0.001). The preadministration of an excess of HRG decreased uptake in MDA-MB-468 (HER2-negative/HER3-positive) human breast cancer xenografts from 4.4 ± 0.9 to 2.6 ± 0.5 %ID/g (P < 0.05). All tumors were imaged by small-animal SPECT/CT. Conclusion: 111In-bsRICs composed of trastuzumab Fab and HRG exhibited specific binding in vitro to tumor cells displaying HER2 or HER3 and were taken up specifically in vivo in tumors expressing one or both receptors, permitting tumor visualization by small-animal SPECT/CT. These agents could be useful for imaging heterodimerized HER2 and HER3 receptors because their bivalent properties may result in preferential binding to the heterodimerized forms. The approach may also be extended to constructing bsRICs for visualizing other peptide growth factor receptors.

A comparison of 111In- or 64Cu-DOTA-trastuzumab Fab fragments for imaging subcutaneous HER2-positive tumor xenografts in athymic mice using microSPECT/CT or microPET/CT

BackgroundOur objective was to compare 111In- or 64Cu-DOTA-trastuzumab Fab fragments for imaging small or large s.c. tumor xenografts in athymic mice that display a wide range of human epidermal growth factor receptor-2 (HER2) expression using microSPECT/CT or microPET/CT.MethodsTrastuzumab Fab were labeled with 111In or 64Cu by conjugation to 1,4,7,10-tetraazacyclododecane N, N, N, N-tetraacetic acid (DOTA). The purity of 111In- and 64Cu-DOTA-trastuzumab Fab was measured by SDS-PAGE and HPLC. HER2 binding affinity was determined in saturation radioligand binding assays using SKBR-3 cells (1.3 × 106 HER2/cell). MicroSPECT/CT and microPET/CT were performed in athymic mice bearing s.c. BT-20 and MDA-MB-231 xenografts with low (0.5 to 1.6 × 105 receptors/cell), MDA-MB-361 tumors with intermediate (5.1 × 105 receptors/cell) or SKOV-3 xenografts with high HER2 expression (1.2 × 106 receptors/cell) at 24 h p.i. of 70 MBq (10 μg) of 111In-DOTA-trastuzumab Fab or 22 MBq (10 μg) of 64Cu-DOTA-trastuzumab Fab or irrelevant 111In- or 64Cu-DOTA-rituximab Fab. Tumor and normal tissue uptake were quantified in biodistribution studies.Results111In- and 64Cu-DOTA-trastuzumab were > 98% radiochemically pure and bound HER2 with high affinity (Kd = 20.4 ± 2.5 nM and 40.8 ± 3.5 nM, respectively). MDA-MB-361 and SKOV-3 tumors were most clearly imaged using 111In- and 64Cu-DOTA-trastuzumab Fab. Significantly higher tumor/blood (T/B) ratios were found for 111In-DOTA-trastuzumab Fab than 111In-DOTA-rituximab Fab for BT-20, MDA-MB-231 and MDA-MB-361 xenografts, and there was a direct association between T/B ratios and HER2 expression. In contrast, tumor uptake of 64Cu-DOTA-trastuzumab Fab was significantly higher than 64Cu-DOTA-rituximab Fab in MDA-MB-361 tumors but no direct association with HER2 expression was found. Both 111In- and 64Cu-DOTA-trastuzumab Fab imaged small (5 to 10 mm) or larger (10 to 15 mm) MDA-MB-361 tumors. Higher blood, liver, and spleen radioactivity were observed for 64Cu-DOTA-trastuzumab Fab than 111In-DOTA-trastuzumab Fab.ConclusionsWe conclude that 111In-DOTA-trastuzumab Fab was more specific than 64Cu-DOTA-trastuzumab Fab for imaging HER2-positive tumors, especially those with low receptor density. This was due to higher levels of circulating radioactivity for 64Cu-DOTA-trastuzumab Fab which disrupted the relationship between HER2 density and T/B ratios. Use of alternative chelators that more stably bind 64Cu may improve the association between T/B ratios and HER2 density for 64Cu-labeled trastuzumab Fab.

Influence of formulation variables on the biodistribution of multifunctional block copolymer micelles.

The physico-chemical characteristics and composition of block copolymer micelles (BCMs) may influence the pharmacokinetics and consequently, the desired delivery characteristics. In this study the influence of formulation variables such as size, density of targeting ligand [i.e. epidermal growth factor (hEGF)] and the bifunctional chelator (BFC) used for labelling the BCMs with (111)In, on the pharmacokinetics and biodistribution in mice were evaluated. BCMs were prepared from Me-PEG(x)-b-PCL(y) (x=2.5 k, y=1.2 k for 15 nm BCMs and x=5 k, y=5 k for 60 nm BCMs) with (targeted, 1 or 5 mol% hEGF) or without (non-targeted) hEGF-PEG(x)-b-PCL(y). To investigate the effect of the BFC on the pharmacokinetics, the BCMs were labelled with (111)In using p-SCN-Bn-DOTA (Bn-DOTA-PEG(x)-b-PCL(y)), H(2)N-DOTA (DOTA-PEG(x)-b-PCL(y)), DTPA anhydride (DTPA-PEG(x)-b-PCL(y)) or p-SCN-Bn-DTPA (Bn-DTPA-PEG(x)-b-PCL(y)). The resulting 15 nm or 60 nm non-targeted or targeted (1 or 5 mol% hEGF) were injected via a tail vein to mice bearing MDA-MB-468 human breast cancer xenograft that overexpress EGFR, followed by pharmacokinetics and biodistribution studies. Pharmacokinetic parameters were determined by fitting the blood concentration vs time data using a two compartment model with i.v. bolus input. Pharmacokinetic parameters were found to depend on BCM size, the BFC used as well as the density of hEGF on the surface of the BCMs. BCMs labelled with p-SCN-Bn-DTPA ((111)In-Bn-BCMs) showed improved pharmacokinetics (i.e. extended circulation lifetime) and tumor uptake compared to those labelled with DOTA-PEG(x)-b-PCL(y), p-SCN-Bn-DOTA or DTPA dianhydride. Formulations with a high density of hEGF (5 mol% hEGF) had short circulation half-lives. BCMs labelled with (111)In via p-SCN-Bn-DTPA showed highest accumulation in the liver and spleen and slower whole body elimination. Smaller sized BCMs were rapidly cleared from the circulation. Increasing the density of hEGF on the surface did not improve tumor uptake due to faster clearance from the circulation. To achieve improved pharmacokinetics and in turn effective exploitation of the EPR effect, p-SCN-Bn-DTPA emerged as the optimal BFC for radiolabelling BCMs while a lower density of hEGF gave more favourable organ distribution.

A kit to prepare 111In-DTPA-trastuzumab (Herceptin) Fab fragments injection under GMP conditions for imaging or radioimmunoguided surgery of HER2-positive breast cancer

INTRODUCTIONnThe human epidermal growth factor receptor-2 (HER2) gene is amplified in 25% of invasive breast cancers, and receptor overexpression has been noted in up to 60% of early stages of the disease [ductal carcinoma in situ (DCIS)]. Preclinical studies have revealed high tumor/blood ratios (>27:1) for (111)In-labeled Fab fragments of the HER2 monoclonal antibody, trastuzumab (Herceptin) ((111)In-DTPA-trastuzumab Fab) at 72 h pi in athymic mice bearing subcutaneous human breast cancer xenografts. Our aim in this study was to formulate a kit for preparation of (111)In-DTPA-trastuzumab Fab injection under good manufacturing practice (GMP) conditions suitable for human administration in a Phase I clinical trial of imaging and radioimmunoguided surgery (RIGS) of HER2-positive breast cancer.nnnMETHODSnFab fragments were produced by digestion of trastuzumab IgG (Herceptin) with immobilized papain for 20 h at 37°C. Fab fragments were purified by ultrafiltration, then reacted with a 10-fold molar excess of diethylenetriaminepentaacetic acid (DTPA) dianhydride. DTPA-Fab fragments were purified, then sterilized by filtration into unit dose glass vials (kits). Kits were tested against specifications for volume (0.9-1.1 ml), protein concentration (0.45-0.55 mg/ml), pH (5.5-6.5), DTPA substitution (0.5-4.0 mol DTPA/mol Fab), appearance (clear, colorless and particle free), labeling efficiency (≥ 85%), and sterility and apyrogenicity (USP XXXII). Immunoreactivity of (111)In-DTPA-trastuzumab Fab towards HER2 was measured by saturation radioligand binding assays using SKBR-3 human breast cancer cells (specifications: K(a) = 0.6-9.6 × 10(7) L/mol; B(max) = 0.6-10.4 × 10(6) sites/cell). (111)In-DTPA-trastuzumab Fab injection was prepared by adding 80-100 MBq of (111)InCl(3) to a single kit vial and incubating for 30 min at room temperature. (111)In-DTPA-trastuzumab Fab was assayed for the amount of radioactivity and tested for pH, radiochemical purity (RCP), appearance and sterility.nnnRESULTSnPure and homogeneous Fab fragments were produced. Eleven lots of kits met established quality specifications. The labeling efficiency with (111)In was 90.6 ± 2.2%. (111)In-DTPA-trastuzumab Fab bound specifically to HER2 on SKBR-3 cells (K(a) = 4.8 ± 2.5 × 10(7) L/mol and B(max) = 1.6 ± 0.8 × 10(6) sites/cell). Thirteen lots of (111)In-DTPA-trastuzumab injection met all established specifications. Kits were stable for 90 days and (111)In-DTPA-trastuzumab Fab injection was stable for 24 h stored at 4 °C.nnnCONCLUSIONSnA kit was formulated under GMP conditions for the preparation of (111)In-DTPA-trastuzumab Fab injection suitable for human administration. The kits were approved by Health Canada.

MicroSPECT/CT imaging of co-expressed HER2 and EGFR on subcutaneous human tumor xenografts in athymic mice using 111In-labeled bispecific radioimmunoconjugates

Epidermal growth factor receptors (EGFR) form heterodimers with HER2 in breast cancer, and increased EGFR expression has been found in HER2-positive tumors resistant to trastuzumab (Herceptin). Our objective was to synthesize bispecific radioimmunoconjugates (bsRICs) that recognize HER2 and EGFR and evaluate their ability to image tumors in athymic mice that express one or both receptors by microSPECT/CT. Bispecific radioimmunoconjugates were constructed by conjugating maleimide-derivatized trastuzumab Fab fragments that bind HER2 to a thiolated form of EGF with an intervening 24 mer polyethylene glycol (PEG24) spacer. Bispecific radioimmunoconjugates were derivatized with diethylenetriaminepentaacetic acid for labeling with 111In. The ability of 111In-bsRICs to bind HER2 or EGFR was determined in competition assays using cells expressing one or both receptors. Tumor and normal tissue uptake were examined in CD1 athymic mice bearing subcutaneous tumor xenografts that expressed HER2, EGFR, or both receptors, with or without pre-administration of Fab or EGF to determine specificity. HER2 and EGFR binding and displacement of binding by competitors were found for 111In-bsICs. The highest uptake of 111In-bsRICs [7.3xa0±xa03.5xa0%ID/g] in 231-H2N human breast cancer xenografts (HER2+/EGFR+) occurred at 48xa0h post-injection. Pre-administration of trastuzumab Fab decreased uptake in SK-OV-3 (HER2+/EGFR−) human ovarian cancer xenografts from 7.1xa0±xa01.2 to 2.4xa0±xa01.5xa0%ID/g. Pre-administration of excess EGF decreased uptake in MDA-MB-231 (HER2−/EGFR+) human breast cancer xenografts from 5.9xa0±xa00.5 to 2.0xa0±xa00.1xa0%ID/g. All tumors were imaged by microSPECT/CT. We conclude that 111In-bsRICs composed of trastuzumab Fab and EGF exhibited specific binding in vitro to tumor cells displaying HER2 or EGFR, and were taken up specifically in vivo in tumors expressing one or both receptors, permitting tumor visualization by microSPECT/CT. These agents may ultimately be useful for imaging heterodimerized HER2-EGFR complexes since their bivalent properties permit more avid binding to these complexes.

Comparisons of [18F]-1-deoxy-1-fluoro-scyllo-inositol with [18F]-FDG for PET imaging of inflammation, breast and brain cancer xenografts in athymic mice.

INTRODUCTIONnThe aim of the study was to evaluate the uptake of [(18)F]-1-deoxy-1-fluoro-scyllo-inositol ([(18)F]-scyllo-inositol) in human breast cancer (BC) and glioma xenografts, as well as in inflammatory tissue, in immunocompromised mice. Studies of [(18)F]-2-fluoro-2-deoxy-d-glucose ([(18)F]-FDG) under the same conditions were also performed.nnnMETHODSnRadiosynthesis of [(18)F]-scyllo-inositol was automated using a commercial synthesis module. Tumour, inflammation and normal tissue uptakes were evaluated by biodistribution studies and positron emission tomography (PET) imaging using [(18)F]-scyllo-inositol and [(18)F]-FDG in mice bearing subcutaneous MDA-MB-231, MCF-7 and MDA-MB-361 human BC xenografts, intracranial U-87 MG glioma xenografts and turpentine-induced inflammation.nnnRESULTSnThe radiosynthesis of [(18)F]-scyllo-inositol was automated with good radiochemical yields (24.6%±3.3%, uncorrected for decay, 65±2 min, n=5) and high specific activities (≥195 GBq/μmol at end of synthesis). Uptake of [(18)F]-scyllo-inositol was greatest in MDA-MB-231 BC tumours and was comparable to that of [(18)F]-FDG (4.6±0.5 vs. 5.5±2.1 %ID/g, respectively; P=.40), but was marginally lower in MDA-MB-361 and MCF-7 xenografts. Uptake of [(18)F]-scyllo-inositol in inflammation was lower than [(18)F]-FDG. While uptake of [(18)F]-scyllo-inositol in intracranial U-87 MG xenografts was significantly lower than [(18)F]-FDG, the tumour-to-brain ratio was significantly higher (10.6±2.5 vs. 2.1±0.6; P=.001).nnnCONCLUSIONSnConsistent with biodistribution studies, uptake of [(18)F]-scyllo-inositol was successfully visualized by PET imaging in human BC and glioma xenografts, with lower accumulation in inflammatory tissue than [(18)F]-FDG. The tumour-to-brain ratio of [(18)F]-scyllo-inositol was also significantly higher than that of [(18)F]-FDG for visualizing intracranial glioma xenografts in NOD SCID mice, giving a better contrast.

The Effect of Metal-Chelating Polymers (MCPs) for 111In Complexed via the Streptavidin-Biotin System to Trastuzumab Fab Fragments on Tumor and Normal Tissue Distribution in Mice

ABSTRACTPurposeTo study the effects of backbone composition and charge of biotin-functionalized metal-chelating polymers (Bi-MCPs) for 111In complexed to streptavidin (SAv)-trastuzumab Fab fragments on tumor and normal tissue localization.MethodsBi-MCPs were synthesized with a polyacrylamide [Bi-PAm(DTPA)40], polyaspartamide [Bi-PAsp(DTPA)33] or polyglutamide [Bi-PGlu(DTPA)28] backbone and harboured diethylenetriaminepentaacetic acid (DTPA) chelators for 111In. Bi-PAm(DTPA)40 had a net negative charge; Bi-PAsp(DTPA)33 and Bi-PGlu(DTPA)28 were zwitterionic with a net neutral charge. Binding to HER2+ SKOV-3 human ovarian carcinoma cells was determined. Tissue uptake was studied in Balb/c mice by MicroSPECT/CT imaging and biodistribution studies. Tumor and normal tissue uptake of 111In-labeled Bi-PAsp(DTPA)33 or Bi-PGlu(DTPA)28 complexed to SAv-Fab was evaluated 48xa0h post-injection in athymic mice with subcutaneous SKOV-3 xenografts.ResultsSAv-Fab complexed to MCPs bound specifically to SKOV-3 cells; but specific binding was decreased 2-fold. Liver uptake was 5–13 fold higher for Bi-PAm(DTPA)40 than Bi-PAsp(DTPA)33 and Bi-PGlu(DTPA)28 but was reduced by decreasing negative charges by saturation with indium. 111In-Bi-PAsp(DTPA)33 complexed to SAv-Fab accumulated in SKOV-3 tumors; low tumor uptake was found for 111In-Bi-PGlu(DTPA)28-SAv-Fab.ConclusionsZwitterionic MCPs composed of polyaspartamide with a net neutral charge are most desirable for constructing radioimmunoconjugates.

Phase I trial of intraoperative detection of tumor margins in patients with HER2-positive carcinoma of the breast following administration of 111In-DTPA-trastuzumab Fab fragments

INTRODUCTIONnOur aim was to conduct a Phase I clinical trial to determine the feasibility of intraoperative detection of tumor margins in HER2 positive breast carcinoma using a hand-held γ-probe following administration of (111)In-DTPA-trastuzumab Fab fragments. Accurate delineation of tumor margins is important for preventing local recurrence.nnnMETHODSnSix patients with HER2-positive in situ or invasive ductal carcinoma were administered 74MBq (0.5mg) of (111)In-DTPA-trastuzumab Fab fragments and counts in the tumor, surgical cavity wall and en face margins were measured intraoperatively at 72h post-injection using the Navigator or C-Trak γ-probes. Margins were evaluated histologically. Quantitative whole body planar imaging was performed to estimate radiation absorbed doses using OLINDA/EXM software. SPECT imaging of the thorax was performed to evaluate tumor uptake. The pharmacokinetics of elimination from the blood and plasma were determined over 72h.nnnRESULTSnThere were no acute adverse reactions from (111)In-DTPA-trastuzumab Fab fragments and no changes in hematological or biochemical indices were found over a 3month period. (111)In-DTPA-trastuzumab Fab fragments exhibited a biphasic elimination from the blood and plasma with t1/2α=11.9h and 7.5h, respectively, and t1/2β=26.6 and 20.7h, respectively. The radiopharmaceutical accumulated in the liver, spleen and kidneys. SPECT imaging did not reveal tumor in any patient. The mean effective dose was 0.146mSv/MBq (10.8mSv for 74MBq). Counts in excised tumors were low but were higher than in margins. Margins in two patients harboured tumor but this was not correlated with counts obtained using the γ-probes. Surgical cavity counts were high and likely due to detection of γ-photons outside the surgical field.nnnCONCLUSIONnWe conclude that it was not feasible, at least at the administered amount of radioactivity used in this study, to reliably detect the margins of disease in patients with in situ or invasive ductal carcinoma intraoperatively using a hand-held γ-probe and (111)In-DTPA-trastuzumab Fab fragments due to low uptake in the tumor and involved margins.

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

We previously reported that 111In-labeled pertuzumab imaged trastuzumab (Herceptin)-mediated changes in HER2 expression preclinically in breast cancer tumors. To advance 111In-labeled pertuzumab to a Phase I/II clinical trial, a kit was designed for preparing this agent in a form suitable for human administration. Unit-dose kits containing pertuzumab modified with 2-(4-isothiocyanatobenzyl)-diethylenetriaminepentaacetic acid (BzDTPA) were prepared that labeled to high efficiency (>90%) with 111In and met specifications for pharmaceutical quality. The kits were stable for 4 months and the final radiopharmaceutical was stable for 24h. Imaging studies demonstrated high and specific uptake in HER2-positive tumors in mice using this clinical kit formulation.