The effect of antibody protein dose of anti-renal cell carcinoma monoclonal antibodies in nude mice with renal cell carcinoma xenografts

Novel VHH-Based Tracers with Variable Plasma Half-Lives for Imaging of CAIX-Expressing Hypoxic Tumor Cells

Hypoxic areas are present in the majority of solid tumors, and hypoxia is associated with resistance to therapies and poor outcomes. A transmembrane protein that is upregulated by tumor cells that have adapted to hypoxic conditions is carbonic anhydrase IX (CAIX). Therefore, noninvasive imaging of CAIX could be of prognostic value, and it could steer treatment strategies. The aim of this study was to compare variants of CAIX-binding VHH B9, with and without a C-terminal albumin-binding domain with varying affinity (ABD_low and ABD_high), for SPECT imaging of CAIX expression. The binding affinity and internalization of the various B9-variants were analyzed using SK-RC-52 cells. Biodistribution studies were performed in mice with subcutaneous SCCNij153 human head and neck cancer xenografts. Tracer uptake was determined by ex vivo radioactivity counting and visualized by SPECT/CT imaging. Furthermore, autoradiography images of tumor sections were spatially correlated with CAIX immunohistochemistry. B9-variants demonstrated a similar moderate affinity for CAIX in vitro. Maximal tumor uptake and acceptable tumor-to-blood ratios were found in the SCCNij153 model at 4 h post injection for [¹¹¹In]In-DTPA-B9 (0.51 ± 0.08%ID/g and 8.1 ± 0.85, respectively), 24 h post injection for [¹¹¹In]In-DTPA-B9-ABD_low (2.39 ± 0.44%ID/g and 3.66 ± 0.81, respectively) and at 72 h post injection for [¹¹¹In]In-DTPA-B9-ABD_high (8.7 ± 1.34%ID/g and 2.43 ± 0.15, respectively)_. An excess of unlabeled monoclonal anti-CAIX antibody efficiently inhibited tumor uptake of [¹¹¹In]In-DTPA-B9, while only a partial reduction of [¹¹¹In]In-DTPA-B9-ABD_low and [¹¹¹In]In-DTPA-B9-ABD_high uptake was found. Immunohistochemistry and autoradiography images showed colocalization of all B9-variants with CAIX expression; however, [¹¹¹In]In-DTPA-B9-ABD_low and [¹¹¹In]In-DTPA-B9-ABD_high also accumulated in non-CAIX expressing regions. Tumor uptake of [¹¹¹In]In-DTPA-B9-ABD_low and [¹¹¹In]In-DTPA-B9-ABD_high, but not of [¹¹¹In]In-DTPA-B9, could be visualized with SPECT/CT imaging. In conclusion, [¹¹¹In]In-DTPA-B9 has a high affinity to CAIX and shows specific targeting to CAIX in head and neck cancer xenografts. The addition of ABD prolonged plasma half-life, increased tumor uptake, and enabled SPECT/CT imaging. This uptake was, however, partly CAIX- independent, precluding the ABD-tracers for use in hypoxia quantification in this tumor type.

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.

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.

Targeting carbonic anhydrase IX with small organic ligands

Carbonic anhydrase IX (CAIX) is expressed in many solid tumors in response to hypoxia and plays an important role in tumor acid-base homeostasis under these conditions. It is also constitutively expressed in the majority of renal cell carcinoma. Its functional inhibition with small molecules has recently been shown to retard tumor growth in murine models of cancer, reduce metastasis and tumor stem cell expansion. Additionally, CAIX is a promising antigen for targeted drug delivery approaches. Initially validated with anti-CAIX antibodies, the tumor-homing capacity of high-affinity small-molecule ligands of CAIX has recently been demonstrated. Indeed, conjugates formed of CAIX ligands and potent cytotoxic drugs could eradicate CAIX-expressing solid tumors in mice. These results suggest that CAIX is a promising target for the development of novel therapies for the treatment of solid tumors.

Neoadjuvant sorafenib treatment of clear cell renal cell carcinoma and release of circulating tumor fragments

BACKGROUND

Clear cell renal cell carcinoma (ccRCC) is characterized by high constitutive vascular endothelial growth factor A (VEGF-A) production that induces a specific vascular phenotype. We previously reported that this phenotype may allow shedding of multicellular tumor fragments into the circulation, possibly contributing to the development of metastasis. Disruption of this phenotype through inhibition of VEGF signaling may therefore result in reduced shedding of tumor fragments and improved prognosis. To test this hypothesis, we investigated the effect of neoadjuvant sorafenib treatment on tumor cluster shedding.

PATIENTS AND METHODS

Patients with renal cancer (n = 10, of which 8 have ccRCC) received sorafenib for 4 weeks before tumor nephrectomy. The resection specimens were perfused, and the perfundate was examined for the presence of tumor clusters. Effects of the treatment on the tumor morphology and overall survival were investigated (follow-up of 2 years) and compared with a carefully matched control group.

RESULTS

Neoadjuvant sorafenib treatment induced extensive ischemic tumor necrosis and, as expected, destroyed the characteristic ccRCC vascular phenotype. In contrast to the expectation, vital groups of tumor cells with high proliferation indices were detected in postsurgical renal venous outflow in 75% of the cases. Overall survival of patients receiving neoadjuvant treatment was reduced compared to a control group, matched with regard to prognostic parameters.

CONCLUSIONS

These results suggest that neoadjuvant sorafenib therapy for ccRCC does not prevent shedding of tumor fragments. Although this is a nonrandomized study with a small patient group, our results suggest that neoadjuvant treatment may worsen survival through as yet undefined mechanisms.

Pairwise comparison of 89Zr- and 124I-labeled cG250 based on positron emission tomography imaging and nonlinear immunokinetic modeling: in vivo carbonic anhydrase IX receptor binding and internalization in mouse xenografts of clear-cell renal cell carcinoma

PURPOSE

The PET tracer, (124)I-cG250, directed against carbonic anhydrase IX (CAIX) shows promise for presurgical diagnosis of clear-cell renal cell carcinoma (ccRCC) (Divgi et al. in Lancet Oncol 8:304-310, 2007; Divgi et al. in J Clin Oncol 31:187-194, 2013). The radiometal (89)Zr, however, may offer advantages as a surrogate PET nuclide over (124)I in terms of greater tumor uptake and retention (Rice et al. in Semin Nucl Med 41:265-282, 2011). We have developed a nonlinear immunokinetic model to facilitate a quantitative comparison of absolute uptake and antibody turnover between (124)I-cG250 and (89)Zr-cG250 using a human ccRCC xenograft tumor model in mice. We believe that this unique model better relates quantitative imaging data to the salient biological features of tumor antibody-antigen binding and turnover.

METHODS

We conducted experiments with (89)Zr-cG250 and (124)I-cG250 using a human ccRCC cell line (SK-RC-38) to characterize the binding affinity and internalization kinetics of the two tracers in vitro. Serial PET imaging was performed in mice bearing subcutaneous ccRCC tumors to simultaneously detect and quantify time-dependent tumor uptake in vivo. Using the known specific activities of the two tracers, the equilibrium rates of antibody internalization and turnover in the tumors were derived from the PET images using nonlinear compartmental modeling.

RESULTS

The two tracers demonstrated virtually identical tumor cell binding and internalization but showed markedly different retentions in vitro. Superior PET images were obtained using (89)Zr-cG250, owing to the more prolonged trapping of the radiolabel in the tumor and simultaneous washout from normal tissues. Estimates of cG250/CAIX complex turnover were 1.35 - 5.51 × 10(12) molecules per hour per gram of tumor (20 % of receptors internalized per hour), and the ratio of (124)I/(89)Zr atoms released per unit time by tumor was 17.5.

CONCLUSION

Pairwise evaluation of (89)Zr-cG250 and (124)I-cG250 provided the basis for a nonlinear immunokinetic model which yielded quantitative information about the binding and internalization of radioantibody bound to CAIX on tumor cells in vivo. (89)Zr-cG250 is likely to provide high-quality PET images and may be a useful tool to quantify CAIX/cG250 receptor turnover and cG250-accessible antigen density noninvasively in humans.

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.

ImmunoPET imaging of renal cell carcinoma with (124)I- and (89)Zr-labeled anti-CAIX monoclonal antibody cG250 in mice

INTRODUCTION

Monoclonal antibody (mAb) cG250 recognizes carbonic anhydrase IX (CAIX), overexpressed on clear cell renal cell carcinoma (ccRCC). (124)I-cG250 is currently under clinical investigation for the detection of ccRCC. However, the (124)I label is rapidly excreted from the tumor cells after internalization of the radiolabeled mAb. We hypothesized that labeling cG250 with the residualizing positron emitter (89)Zr would lead to higher tumor uptake and more sensitive detection of ccRCC lesions.

MATERIALS AND METHODS

Nude mice with CAIX-expressing ccRCC xenografts (SK-RC-52 or NU-12) were i.v. injected with (89)Zr-cG250 or (124)I-cG250. To determine specificity of (89)Zr-cG250 uptake in ccRCC, one control group was i.v. injected with (89)Zr-MOPC21 (irrelevant mAb). PET images were acquired using a small animal PET camera and the biodistribution of the radiolabeled mAb was determined.

RESULTS

The ccRCC xenografts were clearly visualized after injection of (89)Zr-cG250 and (124)I-cG250. Tumor uptake of (89)Zr-cG250 was significantly higher compared with (124)I-cG250 in the NU-12 tumor model (114.7% ± 25.2% injected dose per gram (%ID/g) vs. 38.2 ± 18.3%ID/g, p=0.029), but in the SK-RC-52 the difference in tumor uptake was not significant (48.7 ± 15.2%ID/g vs. 32.0 ± 22.9%ID/g, p=0.26). SK-RC-52 tumors were not visualized with (89)Zr-MOPC21 (tumor uptake 3.0%ID/g). Intraperitoneal SK-RC-52 lesions as small as 7 mm(3) were visualized with (89)Zr-cG250 PET.

CONCLUSION

ImmunoPET imaging with cG250 visualized s.c. and i.p. ccRCC lesions in murine models. This confirms the potential of cG250 immunoPET in the diagnosis and (re)staging of ccRCC. PET imaging of ccRCC tumors with (89)Zr-cG250 could be more sensitive than (124)I-cG250-PET.

Intracavitary radioimmunotherapy to treat solid tumors

Radioimmunotherapy (RIT) potentially is an attractive treatment for radiosensitive early-stage solid tumors and as an adjuvant to cytoreductive surgery. Topical administration of RIT may improve the efficacy because higher local concentrations are achieved. We reviewed the results of locally applied radiolabeled monoclonal antibodies for the treatment of solid tumors. Intracavitary RIT in patients with ovarian cancer and glioma showed improved targeting after local administration, as compared to the intravenous administration. In addition, various studies showed the feasibility of locally applied RIT in these patients. In studies that included patients with small-volume disease, adjuvant RIT in ovarian cancer and glioma showed to be at least as effective as standard therapy. The information about RIT for peritoneal carcinomatosis of colorectal origin is scarce, while results from preclinical data are promising. RIT may be applied for other, relatively unexplored indications. Studies on the application of radiolabeled antibodies in early urothelial cell cancer have been performed, showing that intracavitary RIT may hold a promise. Moreover, in patients with malignant pleural mesothelioma or malignant pleural effusion, RIT may play a role in the palliative treatment. Intracavitary RIT limits toxicity and improves tumor targeting. RIT is more effective in patients with small-volume disease of solid cancers. RIT may have potential for palliation in patients with malignant pleural mesothelioma or malignant pleural effusion. The future of RIT may, therefore, not only be in the inclusion in contemporary multimodality treatment, but also in the expansion to palliative treatment.

Timing of adjuvant radioimmunotherapy after cytoreductive surgery in experimental peritoneal carcinomatosis of colorectal origin

BACKGROUND

Treatment of patients with peritoneal carcinomatosis (PC) of colorectal cancer (CRC) includes cytoreductive surgery (CS) in combination with (hyperthermic) intraperitoneal chemotherapy (HIPEC), resulting in a limited survival benefit with high morbidity and mortality rates. Radioimmunotherapy (RIT) as adjuvant therapy after CS of CRC has been shown to prolong survival in preclinical studies. However, the optimal setting of RIT remains to be determined.

METHODS

PC was induced by intraperitoneal inoculation of CC-531 colon carcinoma cells in Wag/Rij rats. Animals were subjected to exploratory laparotomy (Sham), CS only or CS + RIT at different time points after surgery. RIT consisted of 55 MBq lutetium-177-labelled anti-CC531 antibody MG1 (183 mug). The primary endpoint was survival.

RESULTS

Cytoreductive surgery with or without RIT was well tolerated. Median survival of animals in the Sham and CS group was 29 days and 39 days, respectively (P < 0.04). Compared to CS alone, median survival of rats after adjuvant RIT was 77 days (P < 0.0001), 52 days (P < 0.0001) and 45 days (P < 0.0001) when given directly, 4 and 14 days after surgery, respectively.

CONCLUSION

The efficacy of adjuvant RIT after CS for the treatment of PC of colonic origin decreases when the administration of the radiolabelled MAbs is postponed. This study shows that adjuvant RIT should be given as early as possible after surgery.

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.

Beta-glucan enhanced killing of renal cell carcinoma micrometastases by monoclonal antibody G250 directed complement activation

Metastases from renal cell carcinomas (RCC) are resistant to radiation and chemotherapy but are relatively immunogenic. We have investigated the possibility to eliminate human RCC micrometastases using MAb G250. G250 penetrates human micrometastases completely in a spheroid model and induces complement deposition rapidly on the outmost cell layers. However, complement dependent cytotoxicity (CDC) was barely detected using either (51)chromium release assays or confocal microscopy, due to relatively low expression of the G250 antigen and the effect of membrane bound complement regulatory proteins. Addition of blocking anti-CD59 MAbs enhanced formation of C5b-9 and consequently complement mediated lysis (13%). Complement assisted cellular cytotoxicity (CACC) was not detectable, although the iC3b ligand and CR3 receptor were present on respectively target and effector cells. Addition of soluble beta-glucan induced the killing of MAb and iC3b opsonized spheroids by effector cells (6-21%). Despite a lower affinity for G250 antigen, a bispecific anti-G250*anti-CD55 MAb enhanced cell killing in spheroids comparable to the parental G250 MAb. Our results suggest that complement-activating G250 in combination with anti-mCRP MAbs is able to kill human RCC cells in micrometastasis in vitro. For CACC the presence of CR3-priming beta-glucan seems to be obligatory. In vivo, bi-MAb may be more effective as therapeutic agent due to its increased C5a generating properties.

Quantification of G250 mRNA expression in renal epithelial neoplasms by real-time reverse transcription-PCR of dissected tissue from paraffin sections

AIM

Renal cell carcinoma (RCC) represents the most common malignant tumour in the kidney and is resistant to conventional therapies. G250 is a tumour-associated antigen and is expressed mainly in clear cell RCC. It is a potential therapeutic target as well as a diagnostic marker for RCC. Previous studies relating to G250 protein or G250 mRNA expression in RCC using human tissue have largely been limited to immunohistochemical or conventional RT-PCR approaches that lack reproducibility, are subject to observer bias and are at most semi-quantitative. In this study, we evaluated the feasibility of using real-time RT-PCR in quantifying G250 mRNA expression using tissue dissected from paraffin sections of renal epithelial neoplasms. Using this approach, we performed a preliminary study investigating the relationship between G250 expression and tumor behavior in clear cell RCC.

METHODS

A total of 53 radical nephrectomy specimens with renal epithelial neoplasms (nine oncocytoma, seven chromophobe RCC, four papillary RCC and 33 clear cell RCC) were included in this study. SYBR Green real-time RT-PCR was performed using the ABI PRISM 7700 Sequence Detection System. A TATA box-binding protein (TBP) was used as an endogenous reference gene.

RESULTS

Our study showed that real-time RT-PCR is a reliable approach in quantifying G250 mRNA expression using paraffin sections. Using this methodology, G250 mRNA was detected in all of the clear cell RCCs, but none of the other types of tumours studied or in normal kidney tissue. Our study also suggested that the expression of G250 mRNA might correlate with tumour stage and overall survival.

CONCLUSION

Among common renal epithelial neoplasms, G250 is a specific marker for clear cell RCC. Quantification of G250 mRNA expression by real-time RT-PCR using paraffin sections is a feasible approach for future clinical studies in evaluating the prognostic and predictive value of G250 in clear cell RCC.

Interferons Can Upregulate the Expression of the Tumor Associated Antigen G250-MN/CA IX, a Potential Target for (Radio)Immunotherapy of Renal Cell Carcinoma

BACKGROUND

Interleukin-2 (IL-2) and interferon-alpha (IFN-alpha) can induce therapeutic responses in a minority (5-25%) of patients with metastatic renal cell carcinoma (RCC). G250-MN/CA IX, a tumor-associated antigen expressed on the majority of clear cell RCCs, is a potential (radio)immunotherapeutic target for G250-antibody based (radio)immunotherapy. We investigated the effect of the biological response modifiers (BRMs) IL-2, IFN-alpha, and IFN-gamma on the expression of the G250 antigen on RCC cells.

METHODS

In vitro, the expression of the G250 antigen was measured by flow cytometry (FCM) after culturing RCC cells in the presence of various concentrations of the BRMs. Additionally, the number of G250 epitopes per cell was determined quantitatively by Scatchard analysis.

RESULTS

Upregulation of G250 expression was observed on RCC cells cultured in the presence of IFN-alpha or IFN-gamma, whereas the addition of IL-2 had no effect. For both IFNs a clear dose-response relation between G250 antigen expression and IFN dose was observed, with IFN-gamma being the more potent agent. G250 expression could be upregulated four-fold. Interestingly, the effect of combining IFN-alpha and IFN-gamma revealed a more pronounced upregulation of G250 expression than either one of the IFNs alone.

CONCLUSIONS

On the basis of in vitro experiments, G250 expression can be upregulated by IFN-alpha and IFN-gamma. In vivo studies are warranted to investigate whether due to IFN treatment increased G250 expression occurs, and whether increased G250 expression can enhance the therapeutic efficacy of G250-antibody based (radio)immunotherapy.

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.

A review of the intravenous administration of radiolabeled immunoglobulin G to cancer patients. High or low protein dose?

This retrospective analysis of preclinical and clinical radiolabeled immunoglobulin studies focuses on three well-known observations: (1) IV tumor reactive IgG provides higher response rates in patients with hematological malignancies than in patients with solid tumors. (2) Patients with CD20 positive B cell lymphoma require a high IV IgG protein dose for effective tumor targeting. (3) Most patients experience high uptake of IV administered radiolabeled IgG in normal liver. This review supports the following new hypotheses: (1) The blood-tumor barrier in most solid tumors is higher than in most hematological malignancies. (2) The blood-tumor barrier in CD20 positive B cell lymphomas is lowered by the IV administration of high doses [> 100 mg] of anti-CD20 IgG, presumably due to IgG induced intra-tumoral production of vaso-active biological response modifiers. (3) The blood-tumor barrier is low in Hodgkin's disease, presumably due to the continuous and innate production of biological response modifiers in tissues containing Hodgkin's disease. (4) The uptake of tumor reactive IgG in the normal liver is controlled by the Fc portion of the IgG. The radioimmunoconjugate is not catabolized in the liver. This appears to indicate that the F(c) portion of the IgG binds to the MHC class I like, F(c)gammaRn receptors in liver endothelium and hepatocytes and not to F(c)gamma RI, RII or RIII receptors The new hypotheses require verification and can be instrumental in the design of new more effective clinical RIT studies.

Tumor uptake of radioiodinated anti-human pulmonary surfactant-associated protein monoclonal antibody PE10 in nude mice bearing human pulmonary adenocarcinoma in combination with an unlabeled preload

This study assessed the potential use of radioimmunoscintigraphy of pulmonary alveolar Type II cells tumor with the radiolabeled anti-human surfactant-associated protein (SP) monoclonal antibody (MAb) PE 10 in combination with preloads of unlabeled MAb. The in vitro binding of iodine-125 ((125)I)-labeled MAb PE 10 (1 microg), which had a specific radioactivity of 400 MBq/mg, on human pulmonary papillary adenocarcinoma NCI-H441 cells that produced SP was investigated. In NCI-H441 tumor-bearing nude mice, the tumor uptake of (125)I-MAb PE 10 (5 microg) was examined in combination with preloads of unlabeled MAb PE 10 (0, 5, 10, and 50 microg). An isotype-matched unassociated murine MAb was used as a control both in vitro and in vivo. (125)I-MAb PE 10 showed specific cell binding compared with (125)I-control MAb. Tumor uptake of (125)I-MAb PE 10 in vivo reached a peak of 4.97+/-0.33% injected dose per gram (%ID/g) at 48 h postinjection. Preloads of 5 and 10 microg unlabeled MAb PE 10 significantly enhanced tumor uptake at 48 h postinjection ( 5.94+/-0.29% ID/g and 5.72+/-0.29% ID/g, respectively), whereas preload of 50 microg unlabeled MAb PE 10 significantly decreased tumor uptake ( 2.75+/-0.32% ID/g) at 48 h. Preload of 5 microg unlabeled MAb PE 10 significantly increased the tumor-to-blood radioactivity ratio at 48 h ( 2.39+/-0.16). Preloads of unlabeled control MAb did not cause any significant change in tumor uptake. Immunohistochemistry showed the intracellular and pericellular patterns of SP expression in tumor cells. In conclusion, radioimmunoscintigraphy with MAb PE 10 labeled with a gamma-emitting radioiodine such as (123)I might be a useful means of targeting pulmonary alveolar Type II tumor cells in combination with preloading with an optimal dose of the unlabeled MAb.

Kidney cancer

In the USA, the incidence of kidney cancer has increased 43% since 1973. The risk of the disorder is higher in men than in women and increases with age. The von Hippel-Lindau tumour-suppressor gene is inactivated in over 75% of sporadic cases. Metastatic disease is present in 20-30% of patients at diagnosis. Early-stage kidney cancer is treated with a radical nephrectomy, but under certain circumstances a partial nephrectomy may be done. Tumour thrombus into the vena cava or right atrium requires thoracotomy and hypothermic circulatory arrest for successful removal of the tumour, but should not be done if extensive nodal or frank metastatic disease is present. Interleukin-2 is the systemic therapy of choice for metastatic disease at present, with long-term relapse-free survival of 5-8%. Several treatments including anti-angiogenesis drugs, cyclin-dependent kinase inhibitors, and differentiating agents are being actively investigated. Fluorouracil has a 10-15% response rate, and surgical excision of isolated metastases should always be considered. Therapy for metastatic renal cancer remains inadequate, but recent developments in basic and clinical research suggest future improvement.

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

In radioimmunotherapy of solid tumors substantial gain might be achieved by carefully selecting the radionuclide and the linker connecting it to the antibody. In contrast to 131I, radiometals such as 90Y and 111In may be retained in the tumor cell after internalization of the antibody, thereby enhancing the radiation dose to the tumor. The physical properties of 186Re with 1.08 MeV beta-emission (71%) and 137 keV gamma-emission (10%) seem ideal for radioimmunotherapy. In this study we investigated in nude mice with s.c. renal cell carcinoma xenografts the biodistribution and the retention in the tumor of 186Re-MAG3 labeled monoclonal antibody (mAb) G250 as compared to 111In-DTPA-G250, to 125I-G250 and to 131I-MN14 (non-specific control mAb). Radiolabeled antibody preparations were i.v. injected. Seventy two hours p.i. the biodistribution of the radiolabel was determined. Blood levels of all mAb G250 preparations were remarkably low (mean: 2.38, 1.40 and 1.43% ID/g for 125I, 111In and 186Re respectively) whereas blood levels of mAb MN14 were significantly higher (mean: 12.3% ID/g), indicating tumor processing of mAb G250. Retention of 111In in the tumor was significantly higher than of 186Re and 125I whereas retention in the tumor of 186Re and 125I did not differ significantly.

CONCLUSION

In contrast to other radiometals such as 111In and 90Y, 186Re is not retained in the tumor cell. Therefore 186Re has no additional advantage for radioimmunotherapy with respect to retention in the tumor.