Organ-specific expression of the colon cancer antigen A33, a cell surface target for antibody-based therapy

Diagnostic gastrointestinal markers in primary lung cancer and pulmonary metastases

Histopathological diagnosis of pulmonary tumors is essential for treatment decisions. The distinction between primary lung adenocarcinoma and pulmonary metastasis from the gastrointestinal (GI) tract may be difficult. Therefore, we compared the diagnostic value of several immunohistochemical markers in pulmonary tumors. Tissue microarrays from 629 resected primary lung cancers and 422 resected pulmonary epithelial metastases from various sites (whereof 275 colorectal cancer) were investigated for the immunohistochemical expression of CDH17, GPA33, MUC2, MUC6, SATB2, and SMAD4, for comparison with CDX2, CK20, CK7, and TTF-1. The most sensitive markers for GI origin were GPA33 (positive in 98%, 60%, and 100% of pulmonary metastases from colorectal cancer, pancreatic cancer, and other GI adenocarcinomas, respectively), CDX2 (99/40/100%), and CDH17 (99/0/100%). In comparison, SATB2 and CK20 showed higher specificity, with expression in 5% and 10% of mucinous primary lung adenocarcinomas and both in 0% of TTF-1-negative non-mucinous primary lung adenocarcinomas (25-50% and 5-16%, respectively, for GPA33/CDX2/CDH17). MUC2 was negative in all primary lung cancers, but positive only in less than half of pulmonary metastases from mucinous adenocarcinomas from other organs. Combining six GI markers did not perfectly separate primary lung cancers from pulmonary metastases including subgroups such as mucinous adenocarcinomas or CK7-positive GI tract metastases. This comprehensive comparison suggests that CDH17, GPA33, and SATB2 may be used as equivalent alternatives to CDX2 and CK20. However, no single or combination of markers can categorically distinguish primary lung cancers from metastatic GI tract cancer.

Identification of pyroptosis-related subtypes, development of a prognostic model, and characterization of tumour microenvironment infiltration in gastric cancer

As a new programmed death mode, pyroptosis plays an indispensable role in gastric cancer (GC) and has strong immunotherapy potential, but the specific pathogenic mechanism and antitumor function remain unclear. We comprehensively analysed the overall changes of pyroptosis-related genes (PRGs) at the genomic and epigenetic levels in 886 GC patients. We identified two molecular subtypes by consensus unsupervised clustering analysis. Then, we calculated the risk score and constructed the risk model for predicting prognostic and selected nine PRGs related genes (IL18RAP, CTLA4, SLC2A3, IL1A, KRT7,PEG10, IGFBP2, GPA33, and DES) through LASSO and COX regression analyses in the training cohorts and were verified in the test cohorts. Consequently, a highly accurate nomogram for improving the clinical applicability of the risk score was constructed. Besides, we found that multi-layer PRGs alterations were correlated with patient clinicopathological features, prognosis, immune infiltration and TME characteristics. The low risk group mainly characterized by increased microsatellite hyperinstability, tumour mutational burden and immune infiltration. The group had lower stromal cell content, higher immune cell content and lower tumour purity. Moreover, risk score was positively correlated with T regulatory cells, M1 and M2 macrophages. In addition, the risk score was significantly associated with the cancer stem cell index and chemotherapeutic drug sensitivity. This study revealed the genomic, transcriptional and TME multiomics features of PRGs and deeply explored the potential role of pyroptosis in the TME, clinicopathological features and prognosis in GC. This study provides a new immune strategy and prediction model for clinical treatment and prognosis evaluation.

Endoscopic Applications of Near-Infrared Photoimmunotherapy (NIR-PIT) in Cancers of the Digestive and Respiratory Tracts

Near-infrared photoimmunotherapy (NIR-PIT) is a newly developed and promising therapy that specifically destroys target cells by irradiating antibody-photo-absorber conjugates (APCs) with NIR light. APCs bind to target molecules on the cell surface, and when exposed to NIR light, cause disruption of the cell membrane due to the ligand release reaction and dye aggregation. This leads to rapid cell swelling, blebbing, and rupture, which leads to immunogenic cell death (ICD). ICD activates host antitumor immunity, which assists in killing still viable cancer cells in the treated lesion but is also capable of producing responses in untreated lesions. In September 2020, an APC and laser system were conditionally approved for clinical use in unresectable advanced head and neck cancer in Japan, and are now routine in appropriate patients. However, most tumors have been relatively accessible in the oral cavity or neck. Endoscopes offer the opportunity to deliver light deeper within hollow organs of the body. In recent years, the application of endoscopic therapy as an alternative to surgery for the treatment of cancer has expanded, providing significant benefits to inoperable patients. In this review, we will discuss the potential applications of endoscopic NIR-PIT, especially in thoracic and gastrointestinal cancers.

Radiolabeled Antibodies for Cancer Imaging and Therapy

Simple Summary

Monoclonal antibodies (mAbs) have the ability to specifically target tumor-cell antigens. This unique property has led to their use in the delivery of radioisotopes to tumor sites (scintigraphic imaging and radioimmunotherapy (RIT)). The choice of the radionuclide depends on its unique physical properties and intended use. Using radiolabeled mAbs with imaging techniques provides critical data that are essential for predicting side effects and determining an optimal antibody dose and treatment schedule. While RIT has been successful in the management of hematological malignancies, the treatment of solid tumors remains challenging. Various strategies are being investigated to improve the efficacy of RIT in solid tumors.

Abstract

Radioimmunoconjugates consist of a monoclonal antibody (mAb) linked to a radionuclide. Radioimmunoconjugates as theranostics tools have been in development with success, particularly in hematological malignancies, leading to approval by the US Food and Drug Administration (FDA) for the treatment of non-Hodgkin’s lymphoma. Radioimmunotherapy (RIT) allows for reduced toxicity compared to conventional radiation therapy and enhances the efficacy of mAbs. In addition, using radiolabeled mAbs with imaging methods provides critical information on the pharmacokinetics and pharmacodynamics of therapeutic agents with direct relevance to the optimization of the dose and dosing schedule, real-time antigen quantitation, antigen heterogeneity, and dynamic antigen changes. All of these parameters are critical in predicting treatment responses and identifying patients who are most likely to benefit from treatment. Historically, RITs have been less effective in solid tumors; however, several strategies are being investigated to improve their therapeutic index, including targeting patients with minimal disease burden; using pre-targeting strategies, newer radionuclides, and improved labeling techniques; and using combined modalities and locoregional application. This review provides an overview of the radiolabeled intact antibodies currently in clinical use and those in development.

Antibody-Based Immunotoxins for Colorectal Cancer Therapy

Monoclonal antibodies (mAbs) are included among the treatment options for advanced colorectal cancer (CRC). However, while these mAbs effectively target cancer cells, they may have limited clinical activity. A strategy to improve their therapeutic potential is arming them with a toxic payload. Immunotoxins (ITX) combining the cell-killing ability of a toxin with the specificity of a mAb constitute a promising strategy for CRC therapy. However, several important challenges in optimizing ITX remain, including suboptimal pharmacokinetics and especially the immunogenicity of the toxin moiety. Nonetheless, ongoing research is working to solve these limitations and expand CRC patients' therapeutic armory. In this review, we provide a comprehensive overview of targets and toxins employed in the design of ITX for CRC and highlight a wide selection of ITX tested in CRC patients as well as preclinical candidates.

An integrated magneto-electrochemical device for the rapid profiling of tumour extracellular vesicles from blood plasma

Assays for cancer diagnosis via the analysis of biomarkers on circulating extracellular vesicles (EVs) typically have lengthy sample workups, limited throughput or insufficient sensitivity, or do not use clinically validated biomarkers. Here we report the development and performance of a 96-well assay that integrates the enrichment of EVs by antibody-coated magnetic beads and the electrochemical detection, in less than one hour of total assay time, of EV-bound proteins after enzymatic amplification. By using the assay with a combination of antibodies for clinically relevant tumour biomarkers (EGFR, EpCAM, CD24 and GPA33) of colorectal cancer (CRC), we classified plasma samples from 102 patients with CRC and 40 non-CRC controls with accuracies of more than 96%, prospectively assessed a cohort of 90 patients, for whom the burden of tumour EVs was predictive of five-year disease-free survival, and longitudinally analysed plasma from 11 patients, for whom the EV burden declined after surgery and increased on relapse. Rapid assays for the detection of combinations of tumour biomarkers in plasma EVs may aid cancer detection and patient monitoring.

A novel human monoclonal antibody specific to the A33 glycoprotein recognizes colorectal cancer and inhibits metastasis

Colorectal cancer represents the second most common cause of cancer-related death. The human A33 transmembrane glycoprotein is a validated tumor-associated antigen, expressed in 95% of primary and metastatic colorectal cancers. Using phage display technology, we generated a human monoclonal antibody (termed A2) specific to human A33 and we compared its epitope and performance to those of previously described clinical-stage anti-human A33 antibodies. All antibodies recognized a similar immunodominant epitope, located in the V-domain of A33, as revealed by SPOT analysis. The A2 antibody homogenously stained samples of poorly, moderately, and well differentiated colon adenocarcinomas. All antibodies also exhibited an intense staining of healthy human colon sections. The A2 antibody, reformatted in murine IgG2a format, preferentially localized to A33-transfected CT26 murine colon adenocarcinomas in immunocompetent mice with a homogenous distribution within the tumor mass, while other antibodies exhibited a patchy uptake in neoplastic lesions. A2 efficiently induced killing of A33-expressing cells through antibody-dependent cell-mediated cytotoxicity in vitro and was able to inhibit the growth of A33-positive murine CT26 and C51 lung metastases in vivo. Anti-A33 antibodies may thus represent useful vehicles for the selective delivery of bioactive payloads to colorectal cancer, or may be used in IgG format in a setting of minimal residual disease.

Cancer Nanomedicine Special Issue Review Anticancer Drug Delivery with Nanoparticles: Extracellular Vesicles or Synthetic Nanobeads as Therapeutic Tools for Conventional Treatment or Immunotherapy

Both natural and synthetic nanoparticles have been proposed as drug carriers in cancer treatment, since they can increase drug accumulation in target tissues, optimizing the therapeutic effect. As an example, extracellular vesicles (EV), including exosomes (Exo), can become drug vehicles through endogenous or exogenous loading, amplifying the anticancer effects at the tumor site. In turn, synthetic nanoparticles (NP) can carry therapeutic molecules inside their core, improving solubility and stability, preventing degradation, and controlling their release. In this review, we summarize the recent advances in nanotechnology applied for theranostic use, distinguishing between passive and active targeting of these vehicles. In addition, examples of these models are reported: EV as transporters of conventional anticancer drugs; Exo or NP as carriers of small molecules that induce an anti-tumor immune response. Finally, we focus on two types of nanoparticles used to stimulate an anticancer immune response: Exo carried with A Disintegrin And Metalloprotease-10 inhibitors and NP loaded with aminobisphosphonates. The former would reduce the release of decoy ligands that impair tumor cell recognition, while the latter would activate the peculiar anti-tumor response exerted by γδ T cells, creating a bridge between innate and adaptive immunity.

Selective Photokilling of Colorectal Tumors by Near-Infrared Photoimmunotherapy with a GPA33-Targeted Single-Chain Antibody Variable Fragment Conjugate

Antibody-based near-infrared photoimmunotherapy (NIR-PIT) is an attractive strategy for cancer treatment. Tumor cells can be selectively and efficiently killed by the targeted delivery of an antibody-photoabsorber complex followed by exposure to NIR light. Glycoprotein A33 antigen (GPA33) is highly expressed in most human colorectal cancers (CRCs) and is an ideal diagnostic and therapeutic target. We previously produced a single-chain fragment of a variable antibody against GPA33 (A33scFv antibody). Here, we investigate the efficacy of NIR-PIT by combining A33scFv with the NIR photoabsorber IR700 (A33scFv-IR700). In vitro, recombinant A33scFv displayed specific binding and delivery of an NIR dye to GPA33-positive tumor cells. Furthermore, A33scFv-IR700-mediated NIR-PIT was successful in rapidly and specifically killing GPA33-positive colorectal tumor cells. NIR-PIT treatment induced the release of lactate dehydrogenase from tumor cells, followed by cell necrosis, rather than apoptosis, through the promotion of reactive oxygen species accumulation in tumor cells. In mice bearing LS174T tumor grafts, A33scFv selectively accumulated in GPA33-positive tumors. Following only a single injection of the conjugate and subsequent illumination, A33scFv-IR700-mediated NIR-PIT induced a significant increase in therapeutic response in LS174T-tumor mice compared with that in the non-NIR-PIT groups (p < 0.001). Because the GPA33 antigen is specifically expressed in CRC tumors, A33scFv-IR700 might be a promising antibody fragment-photoabsorber conjugate for NIR-PIT of CRC.

Manipulating the In Vivo Behaviour of 68Ga with Tris(Hydroxypyridinone) Chelators: Pretargeting and Blood Clearance

Pretargeting is widely explored in immunoPET as a strategy to reduce radiation exposure of non-target organs and allow the use of short-lived radionuclides that would not otherwise be compatible with the slow pharmacokinetic profiles of antibodies. Here we investigate a pretargeting strategy based on gallium-68 and the chelator THPMe as a high-affinity pair capable of combining in vivo. After confirming the ability of THPMe to bind 68Ga in vivo at low concentrations, the bifunctional THPMe-NCS was conjugated to a humanised huA33 antibody targeting the A33 glycoprotein. Imaging experiments performed in nude mice bearing A33-positive SW1222 colorectal cancer xenografts compared pretargeting (100 μg of THPMe-NCS-huA33, followed after 24 h by 8-10 MBq of 68Ga3+) with both a directly labelled radioimmunoconjugate (89Zr-DFO-NCS-huA33, 88 μg, 7 MBq) and a 68Ga-only negative control (8-10 MBq of 68Ga3+). Imaging was performed 25 h after antibody administration (1 h after 68Ga3+ administration for negative control). No difference between pretargeting and the negative control was observed, suggesting that pretargeting via metal chelation is not feasible using this model. However, significant accumulation of "unchelated" 68Ga3+ in the tumour was found (12.9 %ID/g) even without prior administration of THPMe-NCS-huA33, though tumour-to-background contrast was impaired by residual activity in the blood. Therefore, the 68Ga-only experiment was repeated using THPMe (20 μg, 1 h after 68Ga3+ administration) to clear circulating 68Ga3+, producing a three-fold improvement of the tumour-to-blood activity concentration ratio. Although preliminary, these results highlight the potential of THPMe as a 68Ga clearing agent in imaging applications with gallium citrate.

Novel biomarkers for the diagnosis and prognosis of colorectal cancer

Colorectal cancer (CRC) is among the most common malignancies and remains a major cause of cancer-related death worldwide. Despite recent advances in surgical and multimodal therapies, the overall survival of advanced CRC patients remains very low. Cancer progression, including invasion and metastasis, is a major cause of death among CRC patients. The underlying mechanisms of action resulting in cancer progression are beginning to unravel. The reported molecular and biochemical mechanisms that might contribute to the phenotypic changes in favor of carcinogenesis include apoptosis inhibition, enhanced tumor cell proliferation, increased invasiveness, cell adhesion perturbations, angiogenesis promotion, and immune surveillance inhibition. These events may contribute to the development and progression of cancer. A biomarker is a molecule that can be detected in tissue, blood, or stool samples to allow the identification of pathological conditions such as cancer. Thus, it would be beneficial to identify reliable and practical molecular biomarkers that aid in the diagnostic and therapeutic processes of CRC. Recent research has targeted the development of biomarkers that aid in the early diagnosis and prognostic stratification of CRC. Despite that, the identification of diagnostic, prognostic, and/or predictive biomarkers remains challenging, and previously identified biomarkers might be insufficient to be clinically applicable or offer high patient acceptability. Here, we discuss recent advances in the development of molecular biomarkers for their potential usefulness in early and less-invasive diagnosis, treatment, and follow-up of CRC.

Development and Characterization of a Genetic Mouse Model of KRAS Mutated Colorectal Cancer

Patients with KRAS mutated colorectal cancer (CRC) represent a cohort with unmet medical needs, with limited options of FDA-approved therapies. Representing 40-45% of all CRC patients, they are considered ineligible to receive anti-EGFR monoclonal antibodies that have added a significant therapeutic benefit for KRAS wild type CRC patients. Although several mouse models of CRC have been developed during the past decade, one genetically resembling the KRAS mutated CRC is yet to be established. In this study C57 BL/6 mice with truncated adenomatous polyposis coli (APC) floxed allele was crossed with heterozygous KRAS floxed outbred mice to generate an APCf/f KRAS+/f mouse colony. In another set of breeding, APC floxed mice were crossed with CDX2-Cre-ERT2 mice and selected for APCf/f CDX2-Cre-ERT2 after the second round of inbreeding. The final model of the disease was generated by the cross of the two parental colonies and viable APC f/f KRAS +/f CDX2-Cre-ERT2 (KPC: APC) were genotyped and characterized. The model animals were tamoxifen (TAM) induced to generate tumors. Micro-positron emission tomography (PET) scan was used to detect and measure tumor volume and standard uptake value (SUV). Hematoxylin and eosin (H&E) staining was performed to establish neoplasm and immunohistochemistry (IHC) was performed to determine histological similarities with human FFPE biopsies. The MSI/microsatellite stable (MSS) status was determined. Finally, the tumors were extensively characterized at the molecular level to establish similarities with human CRC tumors. The model KPC: APC animals are conditional mutants that developed colonic tumors upon induction with tamoxifen in a dose-dependent manner. The tumors were confirmed to be malignant within four weeks of induction by H&E staining and higher radioactive [18F] fluoro-2-deoxyglucose (FDG) uptake (SUV) in micro-PET scan. Furthermore, the tumors histologically and molecularly resembled human colorectal carcinoma. Post tumor generation, the KPC: APC animals died of cachexia and rectal bleeding. Implications: This model is an excellent preclinical platform to molecularly characterize the KRAS mutated colorectal tumors and discern appropriate therapeutic strategies to improve disease management and overall survival.

Development of a Tetravalent Anti-GPA33/Anti-CD3 Bispecific Antibody for Colorectal Cancers

Despite progress in the treatment of colorectal cancer, curing metastatic colorectal cancer remains a major unmet medical need worldwide. Here, we describe a T-cell-engaging bispecific antibody (T-BsAb) to redirect polyclonal cytotoxic T cells to eradicate colorectal cancer. A33, a murine antibody specific for GPA33, was humanized to huA33 and reformatted to huA33-BsAb, based on a novel IgG(L)-scFv platform by linking the anti-CD3 huOKT3 scFv to the carboxyl end of the light chain. This T-BsAb was stably expressed in CHO cells and purified as a stable monomer by HPLC, retaining immunoreactivity by FACS through 30 days of incubation at 37°C. In vitro, it induced activation and expansion of unstimulated T cells and elicited potent T-cell-dependent cell-mediated cytotoxicity against colon and gastric cancer cells in an antigen-specific manner. In vivo, huA33-BsAb inhibited the colon and gastric cancer xenografts, in both subcutaneous and intraperitoneal tumor models. More importantly, both microsatellite instable and microsatellite stable colorectal cancer were effectively eliminated by huA33-BsAb. These preclinical results provide further support for the use of IgG(L)-scFv platform to build BsAb, and especially one targeting GPA33 for colorectal cancer. These preclinical results also support further development of huA33-BsAb as a potential immunotherapeutic. Mol Cancer Ther; 17(10); 2164-75. ©2018 AACR.

Targeted Radionuclide Therapy of Human Tumors

Targeted radionuclide therapy is one of the most intensively developing directions of nuclear medicine. Unlike conventional external beam therapy, the targeted radionuclide therapy causes less collateral damage to normal tissues and allows targeted drug delivery to a clinically diagnosed neoplastic malformations, as well as metastasized cells and cellular clusters, thus providing systemic therapy of cancer. The methods of targeted radionuclide therapy are based on the use of molecular carriers of radionuclides with high affinity to antigens on the surface of tumor cells. The potential of targeted radionuclide therapy has markedly grown nowadays due to the expanded knowledge base in cancer biology, bioengineering, and radiochemistry. In this review, progress in the radionuclide therapy of hematological malignancies and approaches for treatment of solid tumors is addressed.

Theranostic pretargeted radioimmunotherapy of colorectal cancer xenografts in mice using picomolar affinity ⁸⁶Y- or ¹⁷⁷Lu-DOTA-Bn binding scFv C825/GPA33 IgG bispecific immunoconjugates

PURPOSE

GPA33 is a colorectal cancer (CRC) antigen with unique retention properties after huA33-mediated tumor targeting. We tested a pretargeted radioimmunotherapy (PRIT) approach for CRC using a tetravalent bispecific antibody with dual specificity for GPA33 tumor antigen and DOTA-Bn-(radiolanthanide metal) complex.

METHODS

PRIT was optimized in vivo by titrating sequential intravenous doses of huA33-C825, the dextran-based clearing agent, and the C825 haptens (177)Lu-or (86)Y-DOTA-Bn in mice bearing the SW1222 subcutaneous (s.c.) CRC xenograft model.

RESULTS

Using optimized PRIT, therapeutic indices (TIs) for tumor radiation-absorbed dose of 73 (tumor/blood) and 12 (tumor/kidney) were achieved. Estimated absorbed doses (cGy/MBq) to tumor, blood, liver, spleen, and kidney for single-cycle PRIT were 65.8, 0.9 (TI 73), 6.3 (TI 10), 6.6 (TI 10), and 5.3 (TI 12), respectively. Two cycles of PRIT (66.6 or 111 MBq (177)Lu-DOTA-Bn) were safe and effective, with a complete response of established s.c. tumors (100 - 700 mm(3)) in nine of nine mice, with two mice alive without recurrence at >140 days. Tumor log kill in this model was estimated to be 2.1 - 3.0 based on time to 500-mm(3) tumor recurrence. In addition, PRIT dosimetry/diagnosis was performed by PET imaging of the positron-emitting DOTA hapten (86)Y-DOTA-Bn.

CONCLUSION

We have developed anti-GPA33 PRIT as a triple-step theranostic strategy for preclinical detection, dosimetry, and safe targeted radiotherapy of established human colorectal mouse xenografts.

Correlations between ASCC3 Gene Polymorphisms and Chronic Hepatitis B in a Chinese Han Population

We have previously identified 8 SNPs in Han Chinese HBV carriers that are associated with disease progression. Although not well studied, genetic factors may also play a significant role in developing chronic HBV disease after exposure. We extend the effect of these eight SNPs on persistent HBV infection in this study. A total of 875 unrelated Han Chinese, 493 chronic hepatitis B subjects (CHB) and 382 HBV clearance individuals (Clear), were recruited from Hubei Province from September 2007 to March 2010. SNPs were verified by using TaqMan 7900HT Sequence Detection System. By using multiple logistic regression analysis, each of the 8 SNP associations was tested using 3 different genetic models (Dominant, Recessive and Additive model), in 4 types of analyses (full sample, men, women, age stratified). A Bonferroni correction was used to account for multiple statistical tests for each SNP association (P<0.05/8 = 0.0063). A significant correlation was observed at SNP rs10485138 located in ASCC3 gene in female patients (OR, 0.445; 95% CI, 0.253–0.784; P = 0.005). Females bearing C allele infected by HBV had an increased susceptibility to CHB compared with those T allele carriers. Our results indicated that SNP rs10485138 located in ASCC3 gene was associated with persistent HBV infection in Han Chinese.

CF750-A33scFv-Fc-Based Optical Imaging of Subcutaneous and Orthotopic Xenografts of GPA33-Positive Colorectal Cancer in Mice

Antibody-based imaging agents are attractive as adjuvant diagnostic tools for solid tumors. GPA33 is highly expressed in most human colorectal cancers and has been verified as a diagnostic and therapeutic target. Here, we built an A33scFv-Fc antibody against GPA33 by fusing A33scFv to the Fc fragment of human IgG1 antibodies. The A33scFv-Fc specifically binds GPA33-positive colorectal cancer cells and tumor tissues. After the intravenous injection of mice bearing subcutaneous GPA33-positive LS174T tumor grafts with near-infrared fluorescence probe CF750-labeled A33scFv-Fc (CF750-A33scFv-Fc), high contrast images of the tumor grafts could be kinetically documented within 24 h using an optical imaging system. However, GPA33-negative SMMC7721 tumor grafts could not be visualized by injecting the same amount of CF750-A33scFv-Fc. Moreover, in subcutaneous LS174T tumor-bearing mice, tissue scanning revealed that the CF750-A33scFv-Fc accumulated in the tumor grafts, other than the kidney and liver. In mice with orthotopic tumor transplantations, excrescent LS174T tumor tissues in the colon were successfully removed under guidance by CF750-A33scFv-Fc-based optical imaging. These results indicate that CF750-A33scFv-Fc can target GPA33, suggesting the potential of CF750-A33scFv-Fc as an imaging agent for the diagnosis of colorectal cancer.

Glycoprotein A33 deficiency: a new mouse model of impaired intestinal epithelial barrier function and inflammatory disease

The cells of the intestinal epithelium provide a selectively permeable barrier between the external environment and internal tissues. The integrity of this barrier is maintained by tight junctions, specialised cell-cell contacts that permit the absorption of water and nutrients while excluding microbes, toxins and dietary antigens. Impairment of intestinal barrier function contributes to multiple gastrointestinal disorders, including food hypersensitivity, inflammatory bowel disease (IBD) and colitis-associated cancer (CAC). Glycoprotein A33 (GPA33) is an intestinal epithelium-specific cell surface marker and member of the CTX group of transmembrane proteins. Roles in cell-cell adhesion have been demonstrated for multiple CTX family members, suggesting a similar function for GPA33 within the gastrointestinal tract. To test a potential requirement for GPA33 in intestinal barrier function, we generated Gpa33^−/− mice and subjected them to experimental regimens designed to produce food hypersensitivity, colitis and CAC. Gpa33^−/− mice exhibited impaired intestinal barrier function. This was shown by elevated steady-state immunosurveillance in the colonic mucosa and leakiness to oral TRITC-labelled dextran after short-term exposure to dextran sodium sulphate (DSS) to injure the intestinal epithelium. Gpa33^−/− mice also exhibited rapid onset and reduced resolution of DSS-induced colitis, and a striking increase in the number of colitis-associated tumours produced by treatment with the colon-specific mutagen azoxymethane (AOM) followed by two cycles of DSS. In contrast, Gpa33^−/− mice treated with AOM alone showed no increase in sporadic tumour formation, indicating that their increased tumour susceptibility is dependent on inflammatory stimuli. Finally, Gpa33^−/− mice displayed hypersensitivity to food allergens, a common co-morbidity in humans with IBD. We propose that Gpa33^−/− mice provide a valuable model to study the mechanisms linking intestinal permeability and multiple inflammatory pathologies. Moreover, this model could facilitate preclinical studies aimed at identifying drugs that restore barrier function.

Highlighted Article: We show that GPA33, an intestine-specific cell surface protein, plays a role in the maintenance of intestinal barrier function and the prevention of intestinal pathologies such as food hypersensitivity, inflammatory bowel disease and colitis-associated cancer.

Radioimmunotherapy: a specific treatment protocol for cancer by cytotoxic radioisotopes conjugated to antibodies

Radioimmunotherapy (RIT) represents a selective internal radiation therapy, that is, the use of radionuclides conjugated to tumor-directed monoclonal antibodies (including those fragments) or peptides. In a clinical field, two successful examples of this treatment protocol are currently extended by ⁹⁰Y-ibritumomab tiuxetan (Zevalin) and ¹³¹I-tositumomab (Bexxar), both of which are anti-CD20 monoclonal antibodies coupled to cytotoxic radioisotopes and are approved for the treatment of non-Hodgkin lymphoma patients. In addition, some beneficial observations are obtained in preclinical studies targeting solid tumors. To date, in order to reduce the unnecessary exposure and to enhance the therapeutic efficacy, various biological, chemical, and treatment procedural improvements have been investigated in RIT. This review outlines the fundamentals of RIT and current knowledge of the preclinical/clinical trials for cancer treatment.

Quantitative intratumoural microdistribution and kinetics of (131)I-huA33 antibody in patients with colorectal carcinoma

BACKGROUND

The ability of recombinant antibodies to adequately penetrate into tumours is a key factor in achieving therapeutic effect; however, the behaviour of antibodies at a cellular level in tumours is poorly understood. The purpose of this study was to investigate those factors that influence the macroscopic and microscopic intratumoural distribution of an IgG1-humanized antibody, huA33, in colorectal tumours.

METHODS

Twelve patients were infused with radiolabelled huA33 at 7 days prior to elective surgery for colorectal carcinoma. Macroscopic huA33 uptake was determined by both gamma well counter and autoradiography measurements of the resected tumour specimens. Microscopic uptake was then quantitated at a cellular level and compared to vascular penetrance. The impact of variation in tumour antigen (GPA33) expression, tumour size, specimen type (primary vs metastatic), presence of macroscopic necrosis, and tumour vasculature on huA33 uptake were examined.

RESULTS

The I-huA33 uptake in whole tumour sections was (mean ± SD) 5.13 ± 2.71 × 10(-3)% injected dose per gram (ID/g). GPA33 was expressed in all viable tumour cells, and huA33 uptake was excellent regardless of tumour size and specimen type. In tumours with macroscopically evident central necrosis (n = 5), huA33 uptake in tumour necrotic centres was lower than in viable peripheries (0.606 ± 0.493 vs 2.98 ± 2.17 × 10(-3)%ID, p = 0.06). However, when corrected for low cell viability in necrotic centres, uptake of huA33 at the cellular level was highly comparable to that in the more viable tumour periphery (7.10 ± 5.10 × 10(-9) vs 3.82 ± 3.67 × 10(-9)%ID/cell, p = 0.4). In the five patients who exhibited macroscopic necrosis in their tumours, huA33 showed excellent tissue penetration, with a maximum penetration distance of 26 μm in peripheral tumour regions and 118 μm in central regions. No correlation was observed between (131)I-huA33 uptake in tumour on a cellular basis and tumour vascularity.

CONCLUSIONS

In patients with colorectal carcinoma, monoclonal antibody huA33 effectively targets viable tumour cells in all cellular milieus examined, including effective penetration into necrotic tumour centres, a novel and therapeutically important finding.

Phase 1/2 study of KRN330, a fully human anti-A33 monoclonal antibody, plus irinotecan as second-line treatment for patients with metastatic colorectal cancer

KRN330 is a recombinant, fully-human monoclonal antibody directed against A33, a surface differentiation antigen that is uniformly expressed in 95 % of colorectal cancers. A previous Phase 1 study of single-agent KRN330 identified a maximum tolerated dose (MTD) of 3 mg/kg q2w and preliminary evidence of clinical activity among patients with advanced and metastatic colorectal cancer (mCRC). This Phase 1/2 trial sought to assess the safety and activity of second-line KRN330 plus irinotecan in patients with mCRC. Patients with mCRC who showed disease progression after FOLFOX/CapOx received intravenous doses of KRN330 (0.5 or 1.0 mg/kg qw or q2w) plus irinotecan (180 mg/m(2)) in a standard 3 + 3 dose escalation. The MTD of KRN330 with irinotecan in 19 patients was 0.5 mg/kg qw in the Phase 1 study with gastrointestinal effects and neutropenia being the predominant dose-limiting toxicities. In the Phase 2 study, the most frequent treatment-related Grade ≥3 toxicities in 44 patients were fatigue (15.9 %), neutropenia (13.6 %), leukopenia (6.8 %), diarrhea (4.5 %), and dehydration (4.5 %). Objective response rate (ORR) was 4.5 % and disease control rate was 45.5 % for the intent-to-treat population. Median progression-free survival was 87 days (95 % CI, 43-136 days). The prespecified ORR of KRN330 plus irinotecan was not met. Further investigation of KRN330 plus other agents may be warranted.

Bone marrow dosimetry using 124I-PET

Bone marrow is usually dose-limiting for radioimmunotherapy. In this study, we directly estimated red marrow activity concentration and the self-dose component of absorbed radiation dose to red marrow based on PET/CT of 2 different (124)I-labeled antibodies (cG250 and huA33) and compared the results with plasma activity concentration and plasma-based dose estimates.

METHODS

Two groups of patients injected with (124)I-labeled monoclonal antibodies (11 patients with renal cancer receiving (124)I-cG250 and 5 patients with colorectal cancer receiving (124)I- huA33) were imaged by PET or PET/CT on 2 or 3 occasions after infusion. Regions of interest were drawn over several lumbar vertebrae, and red marrow activity concentration was quantified. Plasma activity concentration was also quantified using multiple patient blood samples. The red marrow-to-plasma activity concentration ratio (RMPR) was calculated at the times of imaging. The self-dose component of the absorbed radiation dose to the red marrow was estimated from the images, from the plasma measurements, and using a combination of both sets of measurements.

RESULTS

RMPR was observed to increase with time for both groups of patients. Mean (±SD) time-dependent RMPR (RMPR(t)) for the cG250 group increased from 0.13 ± 0.06 immediately after infusion to 0.23 ± 0.09 at approximately 6 d after infusion. For the huA33 group, mean RMPR(t) was 0.10 ± 0.04 immediately after infusion, 0.13 ± 0.05 approximately 2 d after infusion, and 0.20 ± 0.09 approximately 7 d after infusion. Plasma-based estimates of red marrow self-dose tended to be greater than image-based values by, on average, 11% and 47% for cG250 and huA33, respectively, but by as much as -73% to 62% for individual patients. The hybrid method combining RMPR(t) and plasma activity concentration provided a closer match to the image-based dose estimates (average discrepancies, -2% and 18% for cG250 and huA33, respectively).

CONCLUSION

These results suggest that the assumption of time-independent proportionality between red marrow and plasma activity concentration may be too simplistic. Individualized imaged-based dosimetry is probably required for the optimal therapeutic delivery of radiolabeled antibodies, which does not compromise red marrow and may allow, for some patients, a substantial increase in administered activity and thus tumor dose.

124I-huA33 antibody uptake is driven by A33 antigen concentration in tissues from colorectal cancer patients imaged by immuno-PET

The primary aim of this analysis was to examine the quantitative features of antibody-antigen interactions in tumors and normal tissue after parenteral administration of antitumor antibodies to human patients.

METHODS

Humanized anti-A33 antibody (10 mg) labeled with the positron-emitting radionuclide (124)I ((124)I-huA33) was injected intravenously in 15 patients with colorectal cancer. Clinical PET/CT was performed approximately 1 wk later, followed by a detailed assay of surgically removed tissue specimens including radioactivity counting, autoradiography, immunohistochemistry, and antigen density determination.

RESULTS

PET/CT showed high levels of antibody targeting in tumors and normal bowel. In tissue specimens, the spatial distribution of (124)I-huA33 conformed to that of A33 antigen, and there was a linear relationship between the amount of bound antibody and antigen concentration. Antibody uptake was high in 1- to 2-mm regions of antigen-positive tumor cells (mean, ~0.05 percentage injected dose per gram) and in antigen-positive normal colonic mucosa (mean, ~0.03 percentage injected dose per gram). The estimated binding site occupancy for tumor and normal colon was 20%-50%.

CONCLUSION

The in vivo biodistribution of (124)I-huA33 in human patients 1 wk after antibody administration was determined by A33 antigen expression. Our data imply that the optimal strategy for A33-based radioimmunotherapy of colon cancer will consist of a multistep treatment using a radionuclide with short-range (α- or β-particle) emissions.

KLF4-dependent, PPARgamma-induced expression of GPA33 in colon cancer cell lines

The glycoprotein A33 (GPA33) is a colon cancer antigen. Phase I trials with 131I and 125I monoclonal antibody A33 in colon carcinoma patients showed excellent localization to colorectal cancer and some evidence of tumor response. Using DNA microarrays, we have identified the GPA33 gene as a target of PPARgamma in HT29-Cl.16E colon cancer cells. Treatment of HT29-Cl.16E, Caco2, SW1116 and LS174T colon cancer cells with the PPARgamma agonist GW7845 induced a 2- to 6-fold increase in GPA33 mRNA as determined by real-time PCR. This induction was also found in HT29-Cl.16E cells treated with rosiglitazone and ciglitazone and was prevented by cotreatment with the PPARgamma antagonist GW9662, indicating that this regulation was PPARgamma dependent. No canonical PPAR responsive element was found in the GPA33 promoter. We therefore analyzed the expression of transcription factors involved in GPA33 expression. CDXl, CDX2 and KLF5 expression was not modified by PPARgamma activation. By contrast, a significant increase in KLF4 was seen, both at mRNA and protein levels. Furthermore, chromatin immunoprecipitation studies demonstrated that an increased amount of KLF4 protein was bound to the GPA33 promoter in cells treated with rosiglitazone. Finally, downregulation of KLF4 expression by siRNA reduced rosiglitazone-induced GPA33 expression. This indicates that PPARgamma activation induces KLF4 expression, which in turn increases GPA33 expression. We also demonstrate that PPARgamma activation leads to increased (p21WAF1/Cip1 and keratin 19) or decreased (cyclin D1) expression of known KLF4 targets, suggesting that KLF4 is a nodal player in a network of PPARgamma-regulated genes.

Proteomics analysis of A33 immunoaffinity-purified exosomes released from the human colon tumor cell line LIM1215 reveals a tissue-specific protein signature

Exosomes are 40-100-nm-diameter nanovesicles of endocytic origin that are released from diverse cell types. To better understand the biological role of exosomes and to avoid confounding data arising from proteinaceous contaminants, it is important to work with highly purified material. Here, we describe an immunoaffinity capture method using the colon epithelial cell-specific A33 antibody to purify colorectal cancer cell (LIM1215)-derived exosomes. LC-MS/MS revealed 394 unique exosomal proteins of which 112 proteins (28%) contained signal peptides and a significant enrichment of proteins containing coiled coil, RAS, and MIRO domains. A comparative protein profiling analysis of LIM1215-, murine mast cell-, and human urine-derived exosomes revealed a subset of proteins common to all exosomes such as endosomal sorting complex required for transport (ESCRT) proteins, tetraspanins, signaling, trafficking, and cytoskeletal proteins. A conspicuous finding of this comparative analysis was the presence of host cell-specific (LIM1215 exosome) proteins such as A33, cadherin-17, carcinoembryonic antigen, epithelial cell surface antigen (EpCAM), proliferating cell nuclear antigen, epidermal growth factor receptor, mucin 13, misshapen-like kinase 1, keratin 18, mitogen-activated protein kinase 4, claudins (1, 3, and 7), centrosomal protein 55 kDa, and ephrin-B1 and -B2. Furthermore, we report the presence of the enzyme phospholipid scramblase implicated in transbilayer lipid distribution membrane remodeling. The LIM1215-specific exosomal proteins identified in this study may provide insights into colon cancer biology and potential diagnostic biomarkers.

A33 antigen displays persistent surface expression

The A33 antigen is a cell surface glycoprotein of the small intestine and colonic epithelium with homology to tight junction-associated proteins of the immunoglobulin superfamily, including CAR and JAM. Its restricted tissue localization and high level of expression have led to its use as a target in colon cancer immunotherapy. Although the antigen is also present in normal intestine, radiolabeled antibodies against A33 are selectively retained by tumors in the gut as well as in metastatic lesions for as long as 6 weeks. Accordingly, we have studied the trafficking and kinetic properties of the antigen to determine its promise in two-step, pretargeted therapies. The localization, mobility, and persistence of the antigen were investigated, and this work has demonstrated that the antigen is both highly immobile and extremely persistent-retaining its surface localization for a turnover halflife of greater than 2 days. In order to explain these unusual properties, we explored the possibility that A33 is a component of the tight junction. The simple property of surface persistence, described here, may contribute to the prolonged retention of the clinically administered antibodies, and their uncommon ability to penetrate solid tumors.

A phase I trial of humanized monoclonal antibody A33 in patients with colorectal carcinoma: biodistribution, pharmacokinetics, and quantitative tumor uptake

PURPOSE

To determine the in vivo characteristics of huA33, a CDR-grafted humanized antibody against the A33 antigen, we have conducted an open-label, dose escalation, biopsy-based phase I trial of huA33 in patients with colorectal carcinoma.

EXPERIMENTAL DESIGN

Patients with colorectal carcinoma were infused with [131I]huA33 (400 MBq: 10 mCi) and [125I]huA33 (40 MBq: 1 mCi) 1 week before surgery. There were four huA33 dose levels (0.25, 1.0, 5.0, and 10 mg/m2). Adverse events, pharmacokinetics, biodistribution, tumor biopsies, and immune responses to huA33 were evaluated.

RESULTS

There were 12 patients entered into the trial (6 males and 6 females; age range, 39-66 years). No dose-limiting toxicity was observed. The biodistribution of huA33 showed excellent uptake of [131I]huA33 in metastatic colorectal carcinoma. Pharmacokinetic analysis showed no significant difference in terminal half-life (T1/2beta) between dose levels (mean +/- SD, 86.92 +/- 22.12 hours). Modeling of colon uptake of huA33 showed a T1/2 of elimination of 32.4 +/- 8.1 hours. Quantitative tumor uptake ranged from 2.1 x 10(-3) to 11.1 x 10(-3) %ID/g, and tumor/normal tissue and tumor/serum ratios reached as high as 16.3:1 and 4.5:1, respectively. Biosensor analysis detected low-level human anti-human antibody responses in four patients following huA33 infusion.

CONCLUSIONS

huA33 shows selective and rapid localization to colorectal carcinoma in vivo and penetrates to the center of large necrotic tumors, and colon elimination half-life of huA33 is equivalent to basal colonocyte turnover. The excellent targeting characteristics of this humanized antibody indicate potential for the targeted therapy of metastatic colorectal cancer in future trials.

A33scFv-cytosine deaminase: a recombinant protein construct for antibody-directed enzyme-prodrug therapy

A recombinant fusion protein of colon carcinoma binding A33 single chain antibody with cytosine deaminase displayed specific antigen binding and enzyme activity in surface plasmon resonance and is catalytic activity assay. In vitro, it selectively increased the toxicity of 5-FC to A33 antigen-positive cells by 300-fold, demonstrating the potency of this ADEPT strategy.

The human A33 antigen is a transmembrane glycoprotein and a novel member of the immunoglobulin superfamily

The mAb A33 detects a membrane antigen that is expressed in normal human colonic and small bowel epithelium and > 95% of human colon cancers. It is absent from most other human tissues and tumor types. The murine A33 mAb has been shown to target colon cancer in clinical trials, and the therapeutic potential of a humanized antibody is currently being evaluated. Using detergent extracts of the human colon carcinoma cell lines LIM1215 and SW1222, in which the antigen is highly expressed, the molecule was purified, yielding a 43-kDa protein. The N-terminal sequence was determined and further internal peptide sequence obtained following enzymatic cleavage. Degenerate primers were used in PCRs to produce a probe to screen a LIM1215 cDNA library, yielding clones that enabled us to deduce the complete amino acid sequence of the A33 antigen and express the protein. The available data bases have been searched and reveal no overall sequence similarities with known proteins. Based on a hydrophilicity plot, the A33 protein has three distinct structural domains: an extracellular region of 213 amino acids (which, by sequence alignment of conserved residues, contains two putative immunoglobulin-like domains), a single hydrophobic transmembrane domain, and a highly polar intracellular tail containing four consecutive cysteine residues. These data indicate that the A33 antigen is a novel cell surface receptor or cell adhesion molecule in the immunoglobulin superfamily.