Tumor retention of 186Re-MAG3, 111In-DTPA and 125I labeled monoclonal antibody G250 in nude mice with renal cell carcinoma xenografts

Imaging using radiolabelled targeted proteins: radioimmunodetection and beyond

The use of radiolabelled antibodies was proposed in 1970s for staging of malignant tumours. Intensive research established chemistry for radiolabelling of proteins and understanding of factors determining biodistribution and targeting properties. The use of radioimmunodetection for staging of cancer was not established as common practice due to approval and widespread use of [¹⁸F]-FDG, which provided a more general diagnostic use than antibodies or their fragments. Expanded application of antibody-based therapeutics renewed the interest in radiolabelled antibodies. RadioimmunoPET emerged as a powerful tool for evaluation of pharmacokinetics of and target engagement by biotherapeutics. In addition to monoclonal antibodies, new radiolabelled engineered proteins have recently appeared, offering high-contrast imaging of expression of therapeutic molecular targets in tumours shortly after injection. This creates preconditions for noninvasive determination of a target expression level and stratification of patients for targeted therapies. Radiolabelled proteins hold great promise to play an important role in development and implementation of personalised targeted treatment of malignant tumours. This article provides an overview of biodistribution and tumour-seeking features of major classes of targeting proteins currently utilized for molecular imaging. Such information might be useful for researchers entering the field of the protein-based radionuclide molecular imaging.

Evaluation of Radiolabeled Girentuximab In Vitro and In Vivo

Girentuximab (cG250) targets carbonic anhydrase IX (CAIX), a protein which is expressed on the surface of most renal cancer cells (RCCs). cG250 labeled with 177Lu has been used in clinical trials for radioimmunotherapy (RIT) of RCCs. In this work, an extensive characterization of the immunoconjugates allowed optimization of the labeling conditions with 177Lu while maintaining immunoreactivity of cG250, which was then investigated in in vitro and in vivo experiments. cG250 was conjugated with S-2-(4-isothiocyanatobenzyl)-1,4,7,10-tetraazacyclododecane tetraacetic acid (DOTA(SCN)) by using incubation times between 30 and 90 min and characterized by mass spectrometry. Immunoconjugates with five to ten DOTA(SCN) molecules per cG250 molecule were obtained. Conjugates with ratios less than six DOTA(SCN)/cG250 had higher in vitro antigen affinity, both pre- and postlabeling with 177Lu. Radiochemical stability increased, in the presence of sodium ascorbate, which prevents radiolysis. The immunoreactivity of the radiolabeled cG250 tested by specific binding to SK-RC-52 cells decreased when the DOTA content per conjugate increased. The in vivo tumor uptake was < 10% ID/g and independent of the total amount of protein in the range between 5 and 100 µg cG250 per animal. Low tumor uptake was found to be due to significant necrotic areas and heterogeneous CAIX expression. In addition, low vascularity indicated relatively poor accessibility of the CAIX target.

Inhibition of carbonic anhydrase IX targets primary tumors, metastases, and cancer stem cells: Three for the price of one

Human carbonic anhydrase (CA) IX is a tumor-associated protein, since it is scarcely present in normal tissues, but highly overexpressed in a large number of solid tumors, where it actively contributes to survival and metastatic spread of tumor cells. Due to these features, the characterization of its biochemical, structural, and functional features for drug design purposes has been extensively carried out, with consequent development of several highly selective small molecule inhibitors and monoclonal antibodies to be used for different purposes. Aim of this review is to provide a comprehensive state-of-the-art of studies performed on this enzyme, regarding structural, functional, and biomedical aspects, as well as the development of molecules with diagnostic and therapeutic applications for cancer treatment. A brief description of additional pharmacologic applications for CA IX inhibition in other diseases, such as arthritis and ischemia, is also provided.

Tumor-targeted Dual-modality Imaging to Improve Intraoperative Visualization of Clear Cell Renal Cell Carcinoma: A First in Man Study

Intraoperative imaging with antibodies labeled with both a radionuclide for initial guidance and a near-infrared dye for adequate tumor delineation may overcome the main limitation of fluorescence imaging: the limited penetration depth of light in biological tissue. In this study, we demonstrate the feasibility and safety of intraoperative dual-modality imaging with the carbonic anhydrase IX (CAIX)-targeting antibody ¹¹¹In-DOTA-girentuximab-IRDye800CW in clear cell renal cell carcinoma (ccRCC) patients.

Methods: A phase I protein dose escalation study was performed in patients with a primary renal mass who were scheduled for surgery. ¹¹¹In-DOTA-girentuximab-IRDye800CW (5, 10, 30, or 50 mg, n=3 ccRCC patients per dose level) was administered intravenously and after 4 days SPECT/CT imaging was performed. Seven days after antibody injection, surgery was performed with the use of a gamma probe and near-infrared fluorescence camera.

Results: In total, fifteen patients were included (12 ccRCC, 3 CAIX-negative tumors). No study-related serious adverse events were observed. All ccRCC were visualized by SPECT/CT and localized by intraoperative gamma probe detection (mean tumor-to-normal kidney (T:N) ratio 2.5 ± 0.8), while the T:N ratio was 1.0 ± 0.1 in CAIX-negative tumors. ccRCC were hyperfluorescent at all protein doses and fluorescence imaging could be used for intraoperative tumor delineation, assessment of the surgical cavity and detection of (positive) surgical margins. The radiosignal was crucial for tumor localization in case of overlying fat tissue.

Conclusion: This first in man study shows that tumor-targeted dual-modality imaging using ¹¹¹In-DOTA-girentuximab-IRDye800CW is safe and can be used for intraoperative guidance of ccRCC resection.

Successful combination of sunitinib and girentuximab in two renal cell carcinoma animal models: a rationale for combination treatment of patients with advanced RCC

Anti-angiogenic treatment with tyrosine kinase inhibitors (TKI) has lead to an impressive increase in progression-free survival for patients with metastatic RCC (mRCC), but mRCC remains largely incurable. We combined sunitinib, targeting the endothelial cells with Girentuximab (monoclonal antibody cG250, recognizing carbonic anhydrase IX (CAIX) targeting the tumor cells to study the effect of sunitinib on the biodistribution of Girentuximab because combination of modalities targeting tumor vasculature and tumor cells might result in improved effect. Nude mice with human RCC xenografts (NU12, SK-RC-52) were treated orally with 0.8 mg/day sunitinib, or vehicle for 7 to 14 days. Three days before start or cessation of treatment mice were injected i.v. with 0.4 MBq/5 μg (111)In-Girentuximab followed by biodistribution studies. Immunohistochemical analyses were performed to study the tumor vasculature and CAIX expression and to confirm Girentuximab uptake. NU12 appeared to represent a sunitinib sensitive tumor: sunitinib treatment resulted in extensive necrosis and decreased microvessel density (MVD). Accumulation of Girentuximab was significantly decreased when sunitinib treatment preceded the antibody injection but remained unchanged when sunitinib followed Girentuximab injection. Cessation of therapy led to a rapid neovascularization, reminiscent of a tumor flare. SK-RC-52 appeared to represent a sunitinib-resistant tumor: (central) tumor necrosis was minimal and MVD was not affected. Sunitinib treatment resulted in increased Girentuximab uptake, regardless of the sequence of treatment. These data indicate that sunitinib can be combined with Girentuximab. Since these two modalities have different modes of action, this combination might lead to enhanced therapeutic efficacy.

Carbonic anhydrase expression in kidney and renal cancer: implications for diagnosis and treatment

Four different carbonic anhydrases are expressed in the human nephron, the functional unit of the kidney. These are specifically expressed in different nephron segments, emphasizing the critical role carbonic anhydrases play in maintaining the homeostasis of this crucial organ.Whereas the localization of carbonic anhydrases in the kidney has been long established, interest in carbonic anhydrases has increased dramatically for renal cancer, in particular for the clear cell variant of renal cell carcinoma (ccRCC) because carbonic anhydrase IX is specifically expressed in ccRCC. Therefore carbonic anhydrase IX is being studied as potential diagnostic and therapeutic target, despite carbonic anhydrase IX expression in non-renal tissues.

Application of monoclonal antibody G250 recognizing carbonic anhydrase IX in renal cell carcinoma

Monoclonal antibody G250 (mAbG250) recognizes a determinant on carbonic anhydrase IX (CAIX). CAIX is expressed by virtually all renal cell carcinomas of the clear cell type (ccRCC), but expression in normal tissues is restricted. The homogeneous CAIX expression in ccRCC and excellent targeting capability of mAbG250 in animal models led to the initiation of the clinical evaluation of mAbG250 in (metastatic) RCC (mRCC) patients. Clinical studies confirmed the outstanding targeting ability of mAbG250 and cG250 PET imaging, as diagnostic modality holds great promise for the future, both in detecting localized and advanced disease. Confirmation of the results obtained in the non-randomized clinical trials with unmodified cG250 is needed to substantiate the value of cG250 treatment in mRCC. cG250-Based radio immuno-therapy (RIT) holds promise for treatment of patients with small-volume disease, and adjuvant treatment with unmodified cG250 may be of value in selected cases. In the upcoming years, ongoing clinical trials should provide evidence for these assumptions. Lastly, whether cG250-based RIT can be combined with tyrosine kinase inhibitors, which constitutes the current standard treatment for mRCC, needs to be established.

Radiolabeled antibodies in renal cell carcinoma

Renal cell carcinoma (RCC) is a radio- and chemotherapy resistant tumor, which has a very high morbidity and mortality when metastasized. The current treatment options demonstrate limited efficacy and severe side-effects. Therefore, there is a need for new therapeutic strategies for RCC. As for other malignancies, monoclonal antibodies (mAbs) targeting tumor-associated antigens have been developed for RCC. One of these, mAb G250, targets the MN/CAIX/G250 antigen, which is ubiquitously expressed in clear cell RCC (ccRCC). ccRCC is the most common form of RCC with a prevalence of 80%. Expression of G250 in normal tissue is restricted to the gastrointestinal mucosa and related structures, thereby making it a suitable candidate for targeting ccRCC. In several clinical studies the efficient accumulation of mAb G250 in ccRCC has been demonstrated, resulting in high contrast images. G250-imaging could prove to be a valuable tool in diagnosing metastases in patients with a G250-antigen positive primary tumor and/or in the differential diagnosis of suspect kidney lesions. Furthermore, the therapeutic efficacy of radiolabeled G250 has been investigated in a series of studies. Thus far, most efforts have been devoted to G250 labeled with high doses of ¹³¹I. Other radionuclides which may enhance the therapeutic index of this radiolabeled mAb are currently under investigation. In our institution, an activity dose escalation study is currently ongoing to investigate the therapeutic potential of ¹⁷⁷Lu-labeled G250 in metastatic ccRCC patients. In this review, the current status of the diagnostic and therapeutic properties of radiolabeled antibodies in RCC is described.

Scintigraphic imaging of P-glycoprotein expression with a radiolabelled antibody

PURPOSE

P-glycoprotein (P-gp) is a membrane efflux pump protein that is involved in multidrug resistance (MDR). Tumour cells with high P-gp expression show poor response to cancer treatment with several chemotherapeutics. In vivo targeting and visualisation of P-gp expression would allow MDR to be evaluated non-invasively prior to treatment. The aim of this study was to investigate the feasibility of visualising P-gp expression in tumours using a monoclonal anti-P-gp antibody, 15D3.

METHODS

Nude BALB/c mice with subcutaneously growing human uterine sarcoma cell tumours with either high (MES-SA/Dx5 1977) or low (MES-SA 1976) P-gp expression were used. When tumours were 0.2-0.4 g, mice received (131)I-15D3 or (111)In-DTPA-15D3 monoclonal anti-P-gp antibody intravenously. Images were acquired up to 3 days p.i. and radioactivity concentration in various tissues was determined after euthanisation of the animals.

RESULTS

The images demonstrated that radioactivity accumulated to a higher concentration in high P-gp expressing tumours than in the low P-gp expressing MES-SA 1976 tumour. Furthermore, visualisation of the P-gp expressing tumours was superior with (111)In-DTPA-15D3 than with (131)I-15D3. After injection of (111)In-DTPA-15D3, the high P-gp expressing MES-SA/Dx5 1977 tumours were clearly visualised at 3 days p.i. The biodistribution data indicated that radioactivity concentration in the high P-gp expressing tumours was higher than in the tumours with low P-gp expression (20.78+/-1.42 %ID/g for MES-SA/Dx5 1977 tumours and 8.39+/-3.78 %ID/g for MES-SA 1976 tumours for (111)In-DTPA-15D3).

CONCLUSION

The (111)In-labelled monoclonal anti-P-gp antibody clearly visualised P-gp expression in a human uterine sarcoma tumour in nude mice.

G250: A carbonic anhydrase IX monoclonal antibody

G250 or carbonic anhydrase IX (CA IX) is a membrane-associated carbonic anhydrase (CA) thought to play a role in the regulation of cell proliferation in response to hypoxic conditions and may be involved in oncogenesis and tumor progression. G250 refers to a monoclonal antibody (mAb) that was raised by immunization of mice with human renal cell carcinoma (RCC) homogenates. The RCC-associated transmembrane protein designated G250 has since proven to be identical to tumor-associated protein MN or CA IX. Previous studies using a mAb against CA IX have shown that CA IX is induced constitutively in certain tumor types, but is absent in most normal tissues with the exception of epithelial cells of the gastric mucosa. Furthermore, previous immunobiochemical studies of malignant and benign renal tissues revealed that CA IX was also highly expressed in RCC. Studies on tumor-bearing kidneys demonstrate selective uptake of mAb CA IX in antigen-positive cells versus antigen-negative cells. Furthermore, extraordinarily high uptake and the requirement of a low protein dose to obtain tumor saturation with respect to tumor targeting occur with mAb CA IX. These studies formed the basis of numerous clinical trials aimed at mAb-guided therapy in patients with metastatic RCC.

Experimental radioimmunotherapy of small peritoneal metastases of colorectal origin

Radioimmunotherapy using radiolabeled monoclonal antibodies (MoAbs) directed against tumor-associated antigens might be an effective treatment modality for small volume disease. Our aim was to optimize an experimental model of radioimmunotherapy for small peritoneal metastases of colorectal origin using the anti-CEA MoAb MN-14. In nude mice with intraperitoneal (i.p.) LS174T tumors, a protein dose-escalation study was carried out to determine the maximal dose of radioiodinated MN-14 to be used in radioimmunotherapy. The biodistribution of radioiodinated MN-14 was determined after intravenous (i.v.) and i.p. administration. Finally, the therapeutic efficacy of escalating activity doses of (131)I-labeled MN-14 (62.5-500 microCi) was assessed and compared to that of unlabeled MN-14 or 500 microCi of (131)I-labeled irrelevant control antibody. At protein doses higher than 25 microg, uptake in tumor was reduced, presumably due to saturation of tumor antigen. During the first 24 hours i.p. administration led to higher tumor uptake and higher tumor:blood ratios than i.v. administration. Median survival of the control groups was 38 days (unlabeled MN-14) and 52 days ((131)I-labeled nonspecific antibody). Median survival of the groups treated with increasing activity doses of (131)I-labeled MN-14 was 42 days (62.5 microCi), 49 days (125 microCi), 63 days (250 microCi) and 101 days (500 microCi), respectively (p < 0.0001 compared to unlabeled MN-14). The present study shows that the anti-CEA-antibody MN-14 preferentially accumulates in i.p. LS174T tumor xenografts after both i.p. and i.v. administration. Intraperitoneal radioimmunotherapy using (131)I-labeled MN-14 delays significantly the outgrowth of peritoneal LS174T metastases, even at relatively low activity doses.

Biodistribution of 131I-, 186Re-, 177Lu-, and 88Y-Labeled hLL2 (Epratuzumab) in Nude Mice with CD22-Positive Lymphoma

Radioimmunotherapy (RIT) is a new and effective treatment modality in patients with non-Hodgkin's lymphoma. The monoclonal antibody (mAb) hLL2 (epratuzumab), a humanized mAb directed against the CD22 antigen, and which internalizes, can be labeled with various radionuclides. The biodistribution of hLL2 labeled with (131)I, (186)Re, (177)Lu, and (88)Y was studied in nude mice with subcutaneous human lymphoma xenografts in order to determine the most suitable of these four radionuclides for RIT with hLL2.

METHODS

Human Ramos lymphoma xenografts were transplanted in cyclophosphamide-pretreated athymic BALB/c mice. Four groups of mice were injected intravenously with (131)I-, (186)Re-, (88)Y-, or (177)Lu-labeled hLL2, respectively. To determine the nonspecific tumor uptake, two groups of mice received (88)Y-labeled or (131)I-labeled control antibody, cG250. The biodistribution of the radiolabel was determined 1, 3, and 7 days postinjection (p.i.).

RESULTS

Radiolabeled hLL2 had a higher tumor uptake than the nonspecific mAb at all time-points, irrespective of the radiolabel used. Tumor accretion of (88)Y- and (177)Lu-hLL2 was higher than tumor uptake of (131)I- and (186)Re-hLL2. Activity in the bone, represented by the femur without bone marrow, was higher for (177)Lu- and (88)Y-hLL2 than for (131)I- and (186)Re-hLL2 on day 7 p.i.

CONCLUSION

The use of the residualizing radiolabels (88)Y and (177)Lu in combination with a mAb directed against an internalizing antigen resulted in higher uptake and better retention of the radiolabel in the tumor.

Long-Lived Positron Emitters Zirconium-89 and Iodine-124 for Scouting of Therapeutic Radioimmunoconjugates with PET

Antibody-PET imaging might be of value for the selection of radioimmunotherapy (RIT) candidates to confirm tumor targeting and to estimate radiation doses to tumor and normal tissues. One of the requirements to be set for such a scouting procedure is that the biodistributions of the diagnostic and therapeutic radioimmunoconjugates should be similar. In the present study we evaluated the potential of the positron emitters zirconium-89 ((89)Zr) and iodine-124 ((124)I) for this approach, as these radionuclides have a relatively long half-life that matches with the kinetics of MAbs in vivo (t(1/2) 3.27 and 4.18 days, respectively). After radiolabeling of the head and neck squamous cell carcinoma (HNSCC)-selective chimeric antibody (cMAb) U36, the biodistribution of two diagnostic (cMAb U36-N-sucDf-(89)Zr and cMAb U36-(124)I) and three therapeutic radioimmunoconjugates (cMAb U36-p-SCN-Bz-DOTA-(88)Y-with (88)Y being substitute for (90)Y, cMAb U36-(131)I, and cMAb U36-MAG3-(186)Re) was assessed in mice with HNSCC-xenografts, at 24, 48, and 72 hours after injection. Two patterns of biodistribution were observed, one pattern matching for (89)Zr- and (88)Y-labeled cMAb U36 and one pattern matching for (124)I-, (131)I-, and (186)Re-cMAb U36. The most remarkable differences between both patterns were observed for uptake in tumor and liver. Tumor uptake levels were 23.2 +/- 0.5 and 24.1 +/- 0.7%ID/g for the (89)Zr- and (88)Y-cMAb U36 and 16.0 +/- 0.8, 15.7 +/- 0.79 and 17.1 +/- 1.6%ID/g for (124)I-, (131)I-, and (186)Re-cMAb U36-conjugates, respectively, at 72 hours after injection. For liver these values were 6.9 +/- 0.8 ((89)Zr), 6.2 +/- 0.8 ((88)Y), 1.7 +/- 0.1 ((124)I), 1.6 +/- 0.1 ((131)I), and 2.3 +/- 0.1 ((186)Re), respectively. These preliminary data justify the further development of antibody-PET with (89)Zr-labeled MAbs for scouting of therapeutic doses of (90)Y-labeled MAbs. In such approach (124)I-labeled MAbs are most suitable for scouting of (131)I- and (186)Re-labeled MAbs.

Monoclonal antibody-based therapy for renal cell carcinoma

Monoclonal antibody G250 treatment may have a role in the management of metastatic RCC; however, particular subgroups who are more prone to benefit from this treatment must be delineated. High-risk patients may benefit from adjuvant treatment with this nontoxic treatment modality. Large cohort studies are needed to investigate this possibility.

Tumor targeting properties of monoclonal antibodies with different affinity for target antigen CD44V6 in nude mice bearing head-and-neck cancer xenografts

The CD44 protein family consists of isoforms with tissue-specific expression, which are encoded by standard exons and up to 9 alternatively spliced variant exons (v2-v10) of the same gene. The murine MAbs U36 and BIWA-1, directed against overlapping epitopes within the v6 region of CD44, have previously been shown to efficiently target HNSCC. We herein report on the construction of 1 chimeric (BIWA-2) and 2 humanized (BIWA-4 and BIWA-8) derivatives of BIWA-1. Together with U36 and BIWA-1, these new antibodies were evaluated for affinity to the antigen in vitro as well as for biodistribution and efficacy in RIT using nude mice bearing the HNSCC xenograft line HNX-OE. As determined by surface plasmon resonance, the MAbs bound to CD44v6 with an up to 46-fold difference in affinity (K(d) ranging from 1.1 x 10(-8) to 2.4 x 10(-10) M) with the following ranking: mMAb U36 < hMAb BIWA-4 < hMAb BIWA-8 < mMAb BIWA-1 approximately cMAb BIWA-2. To evaluate their in vivo tumor-targeting properties, 2 MAbs with identical murine or human isotype were labeled with either (131)I or (125)I and administered simultaneously (50 microg/10 microCi each) as pairs showing a stepwise decrease in the difference in affinity: U36 vs. BIWA-1 (35.0-fold difference), BIWA-4 vs. BIWA-2 (14.0-fold) and BIWA-4 vs. BIWA-8 (4.0-fold). Biodistribution was assessed at 1, 2, 3 or 4 and 7 days after injection. Remarkably, for all 3 MAb pairs tested, the lower-affinity MAb showed a higher degree and specificity of tumor localization. The difference in tumor localization was more pronounced when the difference in affinity was larger. For example, 3 days after injection, the lower-affinity mMAb U36 showed a 50% higher tumor uptake than the higher-affinity mMAb BIWA-1, while blood levels and uptake in organs were similar. After labeling with (186)Re (300 or 400 microCi), the same MAb pairs showed RIT efficacy consistent with the biodistribution data: (186)Re-U36 was more effective than (186)Re-BIWA-1, (186)Re-BIWA-4 was slightly more effective than (186)Re-BIWA-2 and (186)Re-BIWA-4 and (186)Re-BIWA-8 demonstrated similar efficacy. Based on these data, we conclude that antibodies with markedly lower affinity to a given target antigen (e.g., U36, BIWA-4) may show superior tumor targeting in comparison with higher-affinity versions of these antibodies.