Trastuzumab Fab Research Articles

Acid-cleavable thiomaleamic acid linker for homogeneous antibody–drug conjugation

In this communication we describe a novel acid-cleavable linker strategy for antibody-drug conjugation. Functional disulfide bridging of the single interchain disulfide bond of a trastuzumab Fab fragment yields a homogeneous antibody-drug conjugate bearing a thiomaleamic acid linker. This linker is stable at physiological pH and temperature, but quantitatively cleaves at lysosomal pH to release the drug payload.

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. 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 24 mer polyethylene glycol (PEG) spacer. bsRICs were derivatized with diethylenetriaminepentaacetic acid for labeling with (111)In. The ability of (111)In-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. 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 (111)In-bsRICs that incorporated a PEG spacer, with the PEG(24) spacer being optimal. The highest uptake of (111)In-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. (111)In-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.

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

To study the effects of backbone composition and charge of biotin-functionalized metal-chelating polymers (Bi-MCPs) for (111)In complexed to streptavidin (SAv)-trastuzumab Fab fragments on tumor and normal tissue localization. Bi-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 (111)In. 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 (111)In-labeled Bi-PAsp(DTPA)(33) or Bi-PGlu(DTPA)(28) complexed to SAv-Fab was evaluated 48h post-injection in athymic mice with subcutaneous SKOV-3 xenografts. SAv-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. (111)In-Bi-PAsp(DTPA)(33) complexed to SAv-Fab accumulated in SKOV-3 tumors; low tumor uptake was found for (111)In-Bi-PGlu(DTPA)(28)-SAv-Fab. Zwitterionic MCPs composed of polyaspartamide with a net neutral charge are most desirable for constructing radioimmunoconjugates.

Block Copolymer Micelles Target Auger Electron Radiotherapy to the Nucleus of HER2-Positive Breast Cancer Cells

Intracellular trafficking of Auger electron emitting radionuclides to perinuclear and nuclear regions of cells is critical to realizing their full therapeutic potential. In the present study, block copolymer micelles (BCMs) were labeled with the Auger electron emitter indium-111 ((111)In) and loaded with the radiosensitizer methotrexate. HER2 specific antibodies (trastuzumab fab) and nuclear localization signal (NLS; CGYGPKKKRKVGG) peptides were conjugated to the surface of the BCMs to direct uptake in HER2 expressing cells and subsequent localization in the cell nucleus. Cell uptake and intracellular distribution of the multifunctional BCMs were evaluated in a panel of breast cancer cell lines with different levels of HER2 expression. Indeed cell uptake was found to be HER2 density dependent, confirming receptor-mediated internalization of the BCMs. Importantly, conjugation of NLS peptides to the surface of BCMs was found to result in a significant increase in nuclear uptake of the radionuclide (111)In. Successful nuclear targeting was shown to improve the antipoliferative effect of the Auger electrons as measured by clonogenic assays. In addition, a significant radiation enhancement effect was observed by concurrent delivery of low-dose MTX and (111)In in all breast cancer cell lines evaluated.

P2-18-06: Conventional Trastuzumab Is an Antagonist of Natural Killer Cells: Making the Case for Fucose-Depleted Trastuzumab.

Abstract The discovery of the HER2 receptor and later the development of trastuzumab (an anti-HER2 antibody) were major advances leading toward the treatment of a significant proportion of human breast cancers. Trastuzumab (Herceptin®) is a humanized monoclonal IgG1 whose discrete antitumor effects are exerted through the 2 main components of the antibody. Trastuzumab's FAB portion binds to the HER2 extracellular domain, interrupting HER2 signaling. The FC portion then engages the activating receptor (FcγRIIIa) on an effector cell, usually a natural killer (NK) cell and instigates a lytic attack via antibody-dependent cellular cytotoxicity (ADCC). The value of trastuzumab in breast cancer therapy is well established, but, there are limitations to the drug's effectiveness. These include: (1) unresponsive tumors with low or equivocal HER2 expression; (2) de novo (primary) resistance to therapy in over 50% of patients with HER2−positive tumors; (3) frequent emergence of secondary resistance often after short exposure periods; (4) competition of plasma IgG proteins with antibodies for binding to the activating FC receptors on NK cells; and (5) the high cost of trastuzumab treatment, raising concerns for the economic sustainability of this form of therapy. Trastuzumab and other therapeutic antibodies share a structural feature that is critical to their effectiveness: a specific oligosaccharide which is covalently linked to the FC region at asparagine 297 (Asn297) in each of the 2 heavy chains. This oligosaccharide, a mannosyl-chitobiose core, is “core-fucosylated” with a single α-L-fucose (fucose) sugar attached via an α(1,6) linkage. In 2002, Shields et al. developed a novel form of trastuzumab which lacked core fucose in the Fc region [J Biol Chem 2002; 277: 26733–40]. When compared to conventional trastuzumab, the fucose-depleted trastuzumab was 43-fold more potent in provoking ADCC against HER2−expressing human breast cancer cells in vitro. Subsequent studies with several monoclonal antibodies have elucidated the role of core fucose in inhibiting ADCC, by reducing the affinity of trastuzumab's Fc portion for the activating FC receptors located on effector cells. The superior ADCC effect of fucose-depleted trastuzumab has now been demonstrated in vivo [Junttila TT et al., Cancer Res 2010; 70: 4481–4489]. We review both in vitro and in vivo evidence from multiple laboratories (working with trastuzumab, rituximab and other therapeutic antibodies) to argue that fucose-depleted trastuzumab offers several potential advantages over conventional trastuzumab. Such advantages in clinical use, we postulate, include (1) treatment of patients with trastuzumab-resistant tumors, (2) treatment of patients with equivocal or low expression of HER2, and (3) decreased cost of treatment. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P2-18-06.

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.

Abstract 4553: Novel bispecific 111In-labeled immunoconjugates (bsICs) for imaging HER2/HER3 heterodimerization in breast cancer

Abstract Objective: Our objective was to construct novel bsICs capable of binding HER2 and HER3 labeled with 111In for imaging HER2-HER3 heterodimerization in breast cancer (BC) possibly through higher avidity for dimeric vs. monomeric complexes. Methods: bsICs were composed of trastuzumab Fab recognizing HER2 linked to a 7.5 kDa HER3-binding peptide of heregulin-β1 (pHRG). Fab were produced by digestion of trastuzumab IgG with papain. Fab were modified with Sulfosuccinimidyl-4-(N-maleimidomethyl)cyclohexane-1-carboxylate (sulfo-SMCC) or related analogues with polyethyleneglycol (PEG) spacers (SM-PEG12-NHS and SM-PEG24-NHS) to introduce maleimide groups for cross-linking to pHRG thiolated with Traut's reagent. bsICs were derivatized with diethylenetriaminepentaacetic acid (DTPA) for labeling with 111In. The ability to independently bind HER2 or HER3 was determined in competition assays using 111In-bsICs on cells expressing HER2, HER3 or both receptors competed with a 25-fold excess of Fab, pHRG or combined ligands. Results: Conjugation of Fab to pHRG was confirmed by SDS-PAGE, Western blot and size-exclusion HPLC. bsICs were labeled with 111In to a radiochemical purity of 98.9 ± 0.2% (specific activity 375 ± 14 MBq/mg). Insertion of a PEG spacer between Fab and pHRG was required for displacement of binding of 111In-bsICs to HER3 but not HER2. For 111In-bsICs with the longest spacer (PEG24), the binding to SKBR-3 cells (HER2+/HER3+) was reduced to 32.7 ± 0.7%, 85.9 ± 1.0% or 30.4 ± 1.6%, respectively by Fab, pHRG or both ligands. The binding to SKOV-3 cells (HER2+/HER3-) was reduced to 16.7 ± 0.8%, 88.8 ± 5.3% or 13.4 ± 0.1% by Fab, pHRG or both ligands. The binding to MDA-MB-468 cells (HER2-/HER3+) was reduced to 98.5 ± 1.5%, 68.8 ± 0.3% or 64.8 ± 4.5% by Fab, pHRG or both ligands. Less efficient competition for HER3 was observed for the PEG12 spacer and no competition for 111In-bsICs without a spacer. Conclusion: 111In-bsICs composed of trastuzumab Fab and pHRG bound specifically to HER2 and HER3 when an appropriate length PEG spacer was inserted between these two binding moieies. These 111In-bsICs may be useful for imaging HER2-HER3 heterodimerization in BC. Supported by the Ontario Institute of Cancer Research (1 mm Challenge) and the Canadian Breast Cancer Foundation (Ontario Branch). Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4553.

Engineering antibodies to enhance efector functions

2551 Background: Despite great progress, the clinical success of therapeutic anti-tumor antibodies against proven targets is still partial. Bringing immune effector functions to bear on target cells is a primary method of antibody mediated tumor cell killing. Published analyses of clinical outcomes in cohorts of patients treated with anti-tumor antibodies show that, all else being equal, patients with higher Fc:Fc-gamma-Receptor IIIa interactions have a survival advantage over patients with weaker receptor binding. Xencor has engineered the Fc to improve Fc-gamma-R binding. Importantly this approach can be used to improve the effector potency of any antibody regardless of the receptor phenotype of the patient. This translates to enhanced specific target cell killing in vitro and in vivo. Methods: Variants of human IgG1 at the constant region Fc:Fc-gamma-receptor interface were made and tested for their ability to interact with various Fc-gamma-receptors, especially Fc-gamma-receptor IIIa. These were further analyzed for potency and efficacy using in vitro ADCC assays. The data presented here compare the variant and wild type human IgG1 Fc grafted onto an anti-CD20 (Rituxan, rituxumab) or anti-Her2 (Herceptin, trastuzumab) Fab. Finally, some were tested for in vivo activity against CD20 bearing cells in a primate B-cell depletion model. Results: Hundreds of high activity variants have been developed and characterized with respect to binding against a panel of Fc-gamma-receptors (including R IIIa), C1q and FcRn. Shown are the results for a case study that has been advanced to the primate B-cell depletion model. Conclusions: XmAb antibodies improve effector functions. The improvement may be conferred on any antibody by grafting the engineered Fc to a desired Fab. In vivo efficacy and available clinical evidence suggests the XmAb technology will impart substantial clinical benefit when used with therapeutic anti-tumor antibodies. Author Disclosure Employment or Leadership Consultant or Advisory Role Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration Xencor Xencor

Imaging of HER2/neu expression in BT-474 human breast cancer xenografts in athymic mice using [99mTc]-HYNIC-trastuzumab (Herceptin) Fab fragments

To evaluate the ability of trastuzumab (Herceptin) Fab, labelled with (99m)Tc through introduced hydrazinenicotinamide (HYNIC) functionalities, to image HER2/neu-overexpressing human breast cancer xenografts in athymic mice. Fab fragments were produced by immobilized papain digestion of trastuzumab immunoglobulin G (IgG), followed by purification by ultrafiltration. The immunoreactivity of trastuzumab Fab was evaluated by receptor-binding assays against HER2/neu-positive SK-BR-3 human breast cancer cells. Trastuzumab Fab fragments were labelled with (99m)Tc following modification with HYNIC N-hydroxysuccinimide ester. Biodistribution and tumour imaging studies were performed in athymic mice bearing subcutaneous HER2/neu-overexpressing BT-474 human breast cancer xenografts following intravenous injection of 1.1 or 25 MBq of [(99m)Tc]-trastuzumab Fab (30 microg), respectively. The specificity of tumour uptake was assessed by comparison with that of [(99m)Tc]-labelled irrelevant anti-CD33 HuM195 Fab. Trastuzumab Fab was pure and exhibited preserved immunoreactivity towards SK-BR-3 cells (K(d) = 1.6 x 10(-8) M). Modification with HYNIC diminished its receptor-binding affinity fourfold. [(99m)Tc]-trastuzumab Fab localized avidly and specifically in BT-474 xenografts, achieving a tumour uptake of 10.7% of the injected dose (ID) per gram and a tumour to blood (T/B) ratio of 3 : 1 at 24 h. The tumour uptake and T/B ratio for [(99m)Tc]-trastuzumab Fab were significantly higher than those for control [(99m)Tc]-HuM195 Fab (2.6% ID x g(-1) and 0.9 : 1, respectively; P<0.05). Tumours were imaged as early as 2 h post-injection of [(99m)Tc]-trastuzumab Fab, but were more clearly visualized at 6 and 24 h post-injection. [(99m)Tc]-HYNIC-trastuzumab Fab localized specifically in HER2/neu-overexpressing human breast cancer xenografts in athymic mice, allowing imaging of the tumours within the useful lifetime of the radionuclide.

Imaging of HER2/neu-positive BT-474 human breast cancer xenografts in athymic mice using 111In-trastuzumab (Herceptin) Fab fragments

Trastuzumab (Herceptin) Fab were prepared by digestion of intact IgG with immobilized papain, derivatized with diethylenetriaminepentaacetic acid (DTPA) and radiolabeled with 111In. The dissociation constant ( K d) for binding of Fab to HER2/neu-positive SK-BR-3 human breast cancer cells was two- to threefold higher than for intact IgG (14–36 vs. 8–14 nM). The binding affinity was not significantly decreased after DTPA derivatization ( K d=47 nM). 111In-trastuzumab Fab localized specifically in HER2/neu-positive BT-474 human breast cancer xenografts in athymic mice with tumor uptake of 7.8±0.7% injected dose (ID)/g and tumor/blood ratio of 25.2±1.6 at 72 h postinjection compared with 2.7±0.7% ID/g and 7.0±0.9 for 111In-HuM195 anti-CD33 Fab (significantly different, P<.001). Small (3–5 mm in diameter) BT-474 tumors were imaged with 111In-trastuzumab Fab as early as 24 h postinjection.