Significant Therapeutic Efficacy with Combined Radioimmunotherapy and Cetuximab in Preclinical Models of Colorectal Cancer.

Unlabelled: Despite extensive efforts to improve the clinical management of patients with colorectal cancer, approved treatments for advanced disease offer limited survival benefit. Therefore, the identification of novel treatment strategies is essential. We evaluated the preclinical efficacy of combination radioimmunotherapy, using a humanized (131)I-labeled anti-carcinoembryonic antigen antibody ((131)I-huA5B7), with cetuximab in colorectal cancer (CRC).

Texture analysis of (125)I-A5B7 anti-CEA antibody SPECT differentiates metastatic colorectal cancer model phenotypes and anti-vascular therapy response.

Background: We aimed to test the ability of texture analysis to differentiate the spatial heterogeneity of (125)I-A5B7 anti-carcinoembryonic antigen antibody distribution by nano-single photon emission computed tomography (SPECT) in well-differentiated (SW1222) and poorly differentiated (LS174T) hepatic metastatic colorectal cancer models before and after combretastatin A1 di-phosphate anti-vascular therapy.

Methods: Nano-SPECT imaging was performed following tail vein injection of 20 MBq (125)I-A5B7 in control CD1 nude mice (LS174T, n=3 and SW1222, n=4), and CA1P-treated mice (LS174T, n=3; SW1222, n=4) with liver metastases. Grey-level co-occurrence matrix textural features (uniformity, homogeneity, entropy and contrast) were calculated in up to three liver metastases in 14 mice from control and treatment groups.

A comparative study of PDGFR inhibition with imatinib on radiolabeled antibody targeting and clearance in two pathologically distinct models of colon adenocarcinoma.

The potential of radioimmunotherapy to selectively kill tumour cells is well established. However, optimisation is required with regards to increasing tumour localisation of antibodies. We used the PDGF-receptor inhibitor imatinib mesylate to improve tumour-specific antibody localisation in two models of colorectal adenocarcinoma and correlated antibody localisation with changes to tumour microvasculature.

Immunohistochemical expression of VEGF predicts response to platinum based chemotherapy in patients with epithelial ovarian cancer.

Purpose: For patients with epithelial ovarian cancer (EOC) cytoreduction, with a combination of taxane and platinum, is the standard of care. Despite this, approximately 50% of patients with advanced disease will relapse and moreover 15-20% of cases of EOC are resistant to platinum based chemotherapy. Vascular Endothelial Growth Factor (VEGF), an angiogenic factor, is associated with poor prognosis.

Localization of radiolabeled anti-CEA antibody in subcutaneous and intrahepatic colorectal xenografts: influence of tumor size and location within host organ on antibody uptake.

Introduction: Radioimmunotherapy (RIT) has been shown to be more effective against solid tumor micrometastases, possibly due to an inverse relationship between tumor size and radiolabeled antibody uptake. In this study, the accretion of radiolabeled antibody in intrahepatic micrometastases in an experimental model was investigated using quantitative digital autoradiography, enabling the analysis of antibody uptake in microscopic tumors.

Methods: Mice bearing subcutaneous or intrahepatic metastatic models of LS174T colorectal cancer were injected with radiolabeled anti-carcinoembryonic antigen antibody ([(125)I]A5B7).

Progress and challenges in the automated construction of Markov state models for full protein systems.

Markov state models (MSMs) are a powerful tool for modeling both the thermodynamics and kinetics of molecular systems. In addition, they provide a rigorous means to combine information from multiple sources into a single model and to direct future simulations/experiments to minimize uncertainties in the model. However, constructing MSMs is challenging because doing so requires decomposing the extremely high dimensional and rugged free energy landscape of a molecular system into long-lived states, also called metastable states.

Microdistribution of targeted, fluorescently labeled anti-carcinoembryonic antigen antibody in metastatic colorectal cancer: implications for radioimmunotherapy.

Purpose: Most radioimmunotherapy studies on radiolabeled antibody distribution are based on autoradiographic and radioluminographic data, which provide a lack of detailed information due to low resolution. We used fluorescently labeled anti-carcinoembryonic antigen (CEA) antibody (A5B7) to investigate quantitatively the kinetics and microdistribution of antibody in a clinically relevant orthotopic colorectal cancer model (LS174T) using high-resolution digital microscopy.

Experimental Design: Nude mice bearing LS174T liver orthotopic tumors received a single i.

Predicting response to radioimmunotherapy from the tumor microenvironment of colorectal carcinomas.

Solid tumors have a heterogeneous pathophysiology, which directly affects antibody-targeted therapies. Here, we consider the influence of selected tumor parameters on radioimmunotherapy, by comparing the gross biodistribution, microdistribution, and therapeutic efficacy of either radiolabeled or fluorescently labeled antibodies (A5B7 anti-carcinoembryonic antigen antibody and a nonspecific control) after i.v.

Characterisation and radioimmunotherapy of L19-SIP, an anti-angiogenic antibody against the extra domain B of fibronectin, in colorectal tumour models.

Angiogenesis is a characteristic feature of tumours and other disorders. The human monoclonal antibody L19- SIP targets the extra domain B of fibronectin, a marker of angiogenesis expressed in a range of tumours. The aim of this study was to investigate whole body distribution, tumour localisation and the potential of radioimmunotherapy with the L19-small immunoprotein (SIP) in colorectal tumours.

A phase I study of single administration of antibody-directed enzyme prodrug therapy with the recombinant anti-carcinoembryonic antigen antibody-enzyme fusion protein MFECP1 and a bis-iodo phenol mustard prodrug.

Purpose: Antibody-directed enzyme prodrug therapy is a two-stage treatment whereby a tumor-targeted antibody-enzyme complex localizes in tumor for selective conversion of prodrug. The purpose of this study was to establish optimal variables for single administration of MFECP1, a recombinant antibody-enzyme fusion protein of an anti-carcinoembryonic antigen single-chain Fv antibody and the bacterial enzyme carboxypeptidase G2 followed by a bis-iodo phenol mustard prodrug. MFECP1 is manufactured in mannosylated form to facilitate normal tissue elimination.

Tumour parameters affected by combretastatin A-4 phosphate therapy in a human colorectal xenograft model in nude mice.

Combretastatin A-4 phosphate (CA4-P) is an antivascular agent which inhibits tumour blood flow. The effects of CA4-P were studied at 1 and 24h in colorectal xenografts by the concomitant imaging of multiple physiological parameters (hypoxia, blood vessels and perfusion), selected to demonstrate changes related to vascular shut-down. Untreated tumours were viable, with perfused blood vessels throughout and only small areas of hypoxia.

Immunohistochemical expression of vascular endothelial growth factor and microvessel counting as prognostic indicators in node-negative colorectal cancer.

This manuscript reports a carefully controlled study of patients with Dukes B colorectal cancer (Dukes stage A, n=12 and Dukes stage B, n=44). Immunohistochemistry has been used to demonstrate reactivity for vascular endothelial growth factor (VEGF), and to measure levels of microvessel density (MVD) in order to assess the relationship of tumor angiogenesis with clinical outcome. Immunohistochemistry was performed using antibodies to VEGF and CD34 (for intratumoral vessel identification) and counting was performed at the invasive margin of the tumor.

Sustained tumor regression of human colorectal cancer xenografts using a multifunctional mannosylated fusion protein in antibody-directed enzyme prodrug therapy.

Purpose: Antibody-directed enzyme prodrug therapy (ADEPT) requires highly selective antibody-mediated delivery of enzyme to tumor. MFE-CP, a multifunctional genetic fusion protein of antibody and enzyme, was designed to achieve this by two mechanisms. First by using a high affinity and high specificity single chain Fv antibody directed to carcinoembryonic antigen.

Engineering antibodies for clinical applications in cancer.

The 'magic bullet' concept predicted over a century ago that antibodies would be used to target cancer therapy. Since then initial problems that were related to specificity, purity and immungenicity of antibody-based reagents have slowly been overcome due to developments in technology and increased knowledge. As a result, antibodies are in use for many clinical applications and now comprise the second largest category of medicines in clinical development after vaccines.

Analysis of the regional uptake of radiolabeled deoxyglucose analogs in human tumor xenografts.

Unlabelled: It has been shown in vitro that the cell uptake of (18)F-FDG, a tracer of glucose metabolism, increases under hypoxia. This is consistent with increased glycolytic metabolism. We have previously shown that in ischemic heart ex vivo the rates of uptake of (18)F-FDG and 2-(14)C-deoxy-D-glucose ((14)C-2DG) are both reduced.

The nonuniformity of antibody distribution in the kidney and its influence on dosimetry.

The therapeutic efficacy of radiolabeled antibody fragments can be limited by nephrotoxicity, particularly when the kidney is the major route of extraction from the circulation. Conventional dose estimates in kidney assume uniform dose deposition, but we have shown increased antibody localization in the cortex after glomerular filtration. The purpose of this study was to measure the radioactivity in cortex relative to medulla for a range of antibodies and to assess the validity of the assumption of uniformity of dose deposition in the whole kidney and in the cortex for these antibodies with a range of radionuclides.

Synergy between vascular targeting agents and antibody-directed therapy.

Purpose: Tumor heterogeneity necessitates the use of combined therapies. We have shown that combining antibody-directed therapy with antivascular agents converts a subcurative to a curative treatment. The purpose of this study was to investigate, by radioluminographic and microscopic techniques, the regional effects of the two complementary therapies.

Spatial accuracy of 3D reconstructed radioluminographs of serial tissue sections and resultant absorbed dose estimates.

Many agents using tumour-associated characteristics are deposited heterogeneously within tumour tissue. Consequently, tumour heterogeneity should be addressed when obtaining information on tumour biology or relating absorbed radiation dose to biological effect. We present a technique that enables radioluminographs of serial tumour sections to be reconstructed using automated computerized techniques, resulting in a three-dimensional map of the dose-rate distribution of a radiolabelled antibody.

Antibody and radionuclide characteristics and the enhancement of the effectiveness of radioimmunotherapy by selective dose delivery to radiosensitive areas of tumour.

Purpose: Estimating the absorbed dose to tumour relative to normal tissues has often been used in the assessment of the therapeutic efficacy of radiolabelled antibodies for radioimmunotherapy. Typically, the calculations assume a uniform dose deposition and response throughout the tumour. However, the heterogeneity of the dose delivery and response within tumours can lead to a radiobiological effect inconsistent with dose estimates.

A model-based approach for the optimization of radioimmunotherapy through antibody design and radionuclide selection.

Background: The effectiveness of radioimmunotherapy (RIT) is known to depend on at least six factors: total absorbed dose and pattern of delivery, radiosensitivity, rate of repair of sublethal damage, ongoing proliferation during treatment, tumor heterogeneity, and tumor size. The purpose of this study was to develop a mathematic model that would relate the absorbed dose and its pattern of delivery to tumor response by incorporating information on each factor. This model was used to optimize therapeutic efficacy in mice by matching the antibody and radionuclide characteristics while ensuring recoverable marrow toxicity.

Optimizing radioimmunotherapy by matching dose distribution with tumor structure using 3D reconstructions of serial images.

The biological effect of radioimmunotherapy (RIT) is most commonly assessed in terms of the absorbed radiation dose. In tumor, conventional dosimetry methods assume a uniform radionuclide and calculate a mean dose throughout the tumor. However, the vasculature of solid tumors tends to be highly irregular and the systemic delivery of antibodies is therefore heterogeneous.

In-vitro uptake of radioactive lipiodol I-131 and I-125 by hepatoblastoma: implications for targeted radiotherapy.

Lipiodol, a stable iodine addition product of fatty ethyl esters derived from poppyseed oil, has been used as a vehicle for targeted cytotoxic or radiotherapeutic treatment in adults with unresectable hepatocellular carcinoma and in a few children with advanced hepatoblastoma (HB). Prolonged retention of lipiodol by the cancer cells might enable more effective targeted therapy to advanced, multifocal, or metastatic HB. To investigate the uptake and cytotoxic efficacy of beta and Auger electron-emitting radioconjugates on HB cells, monolayers of HB (C3a, Hep Tow1) and normal human hepatocyte cell lines were exposed to lipiodol131 (L131), lipiodol125 (L125), or a cocktail of both isotopes.

A mouse model for calculating the absorbed beta-particle dose from (131)I- and (90)Y-labeled immunoconjugates, including a method for dealing with heterogeneity in kidney and tumor.

Flynn, A. A., Green, A.

Eradication of colorectal xenografts by combined radioimmunotherapy and combretastatin a-4 3-O-phosphate.

Solid tumors have a heterogeneous pathophysiology, which has a major impact on therapy. Using SW1222 colorectal xenografts grown in nude mice, we have shown that antibody-targeted radioimmunotherapy (RIT) effectively treated the well-perfused tumor rim, producing regressions for approximately 35 days, but was less effective at the more hypoxic center. By 72 h after RIT, the number of apoptotic cells rose from an overall value of 1% in untreated tumors to 35% at the tumor periphery and 10% at the center.

Relationship between tumour morphology, antigen and antibody distribution measured by fusion of digital phosphor and photographic images.

Antibody-directed cancer therapy has achieved encouraging responses despite poor localisation in tumour. This discrepancy may be attributed to heterogeneity of antibody delivery within tumours: preferential localisation in the better perfused and more radio- and chemosensitive areas provides a therapeutic advantage. Antibody distribution depends upon the interactions of many complex mechanisms.