Therapy of rat tracheal carcinoma IC-12 in SCID mice: vascular targeting with [213Bi]-MAb TES-23

Development of an intramuscular xenograft model of canine osteosarcoma in mice for evaluation of the effects of radiation therapy

OBJECTIVE

To develop an IM xenograft model of canine osteosarcoma in mice for the purpose of evaluating effects of radiation therapy on tumors.

ANIMALS

27 athymic nude mice.

PROCEDURES

Mice were randomly assigned to 1 of 3 groups of 9 mice each: no treatment (control group), radiation at 10 Gy, or radiation at 15 Gy. Each mouse received 5 x 10(5) highly metastasizing parent osteosarcoma cells injected into the left gastrocnemius muscle. Maximum tumor diameter was determined with a metric circles template to generate a tumor growth curve. Conscious mice were restrained in customized plastic jigs allowing local tumor irradiation. The behavior and development of the tumor xenograft were assessed via evaluations of the interval required for tumor-bearing limbs to reach diameters of 8 and 13 mm, extent of tumor vasculature, histomorphology of tumors, degree of tumor necrosis, and existence of pulmonary metastasis and clinical disease in affected mice.

RESULTS

Tumor-bearing limbs grew to a diameter of 8 mm (0.2-g tumor mass) in a mean +/- SEM interval of 7.0 +/- 0.2 days in all mice. Interval to grow from 8 to 13 mm was significantly prolonged for both radiation therapy groups, compared with that of the control group. Histologic evaluation revealed the induced tumors were highly vascular and had characteristics consistent with those of osteosarcoma. Pulmonary metastasis was not detected, and there was no significant difference in percentage of tumor necrosis between groups.

CONCLUSIONS AND CLINICAL RELEVANCE

A reliable, repeatable, and easily produced IM xenograft model was developed for in vivo assessment of canine osteosarcoma.

213Bi-radioimmunotherapy defeats early-stage disseminated gastric cancer in nude mice

The alpha-emitter 213Bi is characterized by a high relative biological effectiveness. 213Bi-immunoconjugates targeting tumor-specific d9-E-cadherin have been proven to effectively kill tumor cells in a murine peritoneal carcinomatosis model. The aim of the present study was to optimize the efficacy of 213Bi-radioimmunotherapy for disseminated gastric cancer in a mouse model of early- and advanced-stage disease and to evaluate the long-term toxicity of 213Bi-immunoconjugates. For that purpose, nude mice were treated with different activities of 213Bi-d9 monoclonal antibody (MAb) targeting d9-E-cadherin or unspecific 213Bi-d8MAb at days 1 or 8 after inoculation of HSC45-M2 gastric cancer cells expressing mutant d9-E-cadherin. Therapeutic efficacy was evaluated by monitoring survival for up to 300 days. Long-term toxicity was evaluated by the survival of tumor-free mice injected with 213Bi-immunoconjugates, kidney function parameters and histopathological examination of kidneys. We showed that survival was significantly prolonged following treatment of mice with 213Bi-immunoconjugates (0.37-22.2 MBq) at day 1 after tumor cell inoculation (P < 0.002). Therapy with 1.85 MBq of 213Bi-d9MAb was most successful, defeating early-stage disease in 87% of all cases. Treatment at day 8 after tumor cell inoculation was less efficient. Long-term nephrotoxicity could only be observed following application of 22.2 MBq of 213Bi-d9MAb, the highest activity applied in the therapy trials. As treatment with 1.85 MBq 213Bi-d9MAb showed excellent therapeutic efficacy without any signs of acute or chronic toxicity, radioimmunotherapy with the alpha-emitter 213Bi is a promising concept for treatment of early peritoneal carcinomatosis.

Mono and bivalent binding of a scFv and covalent diabody to murine laminin-1 using radioiodinated proteins and SPR measurements: effects on tissue retention in vivo

Phage display techniques identified a scFv, 15-9, which binds to murine laminin-1 and accumulated selectively in tumors. In this study, a covalent diabody was constructed by changing the amino acid residues at positions VH44 and VL100 to cysteine residues so that the diabody form could be stabilized via a disulfide bond. The covalent diabody was expressed in Pichia pastoris and purified by affinity chromatography. The binding properties were measured by surface plasmon resonance and solid phase binding of (125)I diabody and scFv. Data from the plasmon resonance method yielded calculated K(D)s of 4.4 x 10(-10) M for the covalent diabody and 9.9 x 10(-8) M for the scFv. K(D)s calculated from solid phase binding of radioiodinated proteins were 1.7-2.1 x 10(-10) M and 2.1-2.4 x 10(-8) M respectively. The rate of dissociation of (125)I scFv from solid phase laminin was independent of laminin concentration; however, the dissociation of the (125)I diabody was dependent both on the concentration of laminin and on the concentration of the diabody. Specifically, high concentrations of laminin yielded very slow rates of diabody dissociation indicating that bivalent attachments had formed. When higher amounts of diabody were used that essentially saturated the laminin sites with univalent binding, the dissociation rate was similar to that for the scFv indicating univalent binding. Biodistribution studies in tumor-bearing SCID mice showed that the covalent diabody improved the ratio of tumor/muscle 2 fold over that obtained with the scFv, although the absolute amount of protein bound to the tumor site was not significantly different for the two forms. The data also showed that retention of the diabody in the tumor and kidney, sites where laminin is present in high concentration, was much longer compared to that of scFv. These data are consistent with the hypothesis that both scFv and diabody forms bind to available laminin in vivo with similar association kinetics, but that in situations of high target concentration, the diabody can bind bivalently and is thus retained at the binding site much longer than the scFv.

Fractionated locoregional low-dose radioimmunotherapy improves survival in a mouse model of diffuse-type gastric cancer using a 213Bi-conjugated monoclonal antibody

PURPOSE

Locoregional radioimmunotherapy of i.p. tumor cell dissemination of diffuse-type gastric cancer using the alpha-emitter 213Bi displayed good therapeutic results after a single application depending on the time interval between tumor cell inoculation and injection of the 213Bi-immunoconjugate. The aim of the present study was to compare single versus double i.p. injection of a tumor-specific antibody (d9MAb) conjugated with low activities of 213Bi in terms of therapeutic efficacy and toxicity.

EXPERIMENTAL DESIGN

Nude mice were inoculated i.p. with 1 x 10(7) human gastric cancer cells (HSC45-M2) expressing tumor-specific mutant d9-E-cadherin (d9-E-cad). After tumor cell inoculation, the mice were injected i.p. with a single injection at day 1 or 8, or double injections at days 1 and 8 or days 8 and 15 with 0.37, 0.74, or 1.48 MBq 213Bi-d9MAb. Therapeutic efficacy was determined by median survival, and toxicity was evaluated by leukocyte and platelet counts. The development of i.p. carcinomatosis was monitored by carcinoembryonic antigen concentrations in the serum of the mice.

RESULTS

The median survival of treated animals increased, depending on the time interval (days) between tumor cell inoculation and therapy, and the injected activity, from 22 days of untreated mice to 48 days (0.37 MBq, 1 day), 84 days (0.37 MBq, 1 and 8 days), 37 days (0.37 MBq, 8 days), 46 days (0.37 MBq, 8 and 15 days), 42 days (0.74 MBq, 8 days), 78 days (0.74 MBq, 8 and 15 days), and 44 days (1.48 MBq, 8 days). The injected activities did not reduce leukocyte and platelet counts. Carcinoembryonic antigen, which was not detectable in the serum of tumor-free mice, increased after tumor cell inoculation and tumor proliferation and decreased after each therapeutic application of 213Bi-d9MAb.

CONCLUSIONS

Double application of only 0.37 MBq of 213Bi-d9MAb at days 1 and 8 after tumor cell inoculation significantly prolonged median survival in nude mice suffering from i.p. tumor cell dissemination compared with a single injection. Even in an advanced stage of the disease, double injection of 0.74 MBq at days 8 and 15 was superior to a single injection of 1.48 MBq at day 8 without any sign of toxicity.

Cyclotron production of Ac-225 for targeted alpha therapy

The feasibility of producing Ac-225 by proton irradiation of Ra-226 in a cyclotron through the reaction Ra-226(p,2n)Ac-225 has been experimentally demonstrated for the first time. Proton energies were varied from 8.8 to 24.8 MeV and cross-sections were determined by radiochemical analysis of reaction yields. Maximum yields were reached at incident proton energies of 16.8 MeV. Radiochemical separation of Ac-225 from the irradiated target yielded a product suitable for targeted alpha therapy of cancer.

Trials, tribulations, and trends in tumor modeling in mice

Selection of mouse models of cancer is often based simply on availability of a mouse strain and a known compatible tumor. Frequently this results in use of tumor models long on history but short on homology and quality control. Other factors including genetics, sex, immunological status, method and site of tumor implantation, technical competence, biological activity of the tumor, protocol sequence and timing, and selection of endpoints interact to produce outcomes in tumor models. Common reliance on survival and tumor burden data in a single mouse model often skews expectations towards high remission and cure rates; a finding seldom duplicated in clinical trials. Inherent limitations of tumor models coupled with the advent of new therapeutic targets reinforce need for careful attention to design, conduct, and stringent selection of in vivo and ex vivo endpoints. Preclinical efficacy testing for anti-tumor therapies should progress through a series of models of increasing sophistication that includes incorporation of genetically engineered animals, and orthotopic and combination therapy models. Pharmacology and safety testing in tumor-bearing animals may also help to improve predictive value of these models for clinical efficacy. Trends in bioinformatics, genetic refinements, and specialized imaging techniques are helping to maintain mice as the most scientifically and economically powerful model of malignant neoplasms.

Vascular targeting agents as cancer therapeutics

Vascular targeting agents (VTAs) for the treatment of cancer are designed to cause a rapid and selective shutdown of the blood vessels of tumors. Unlike antiangiogenic drugs that inhibit the formation of new vessels, VTAs occlude the pre-existing blood vessels of tumors to cause tumor cell death from ischemia and extensive hemorrhagic necrosis. Tumor selectivity is conferred by differences in the pathophysiology of tumor versus normal tissue vessels (e.g., increased proliferation and fragility, and up-regulated proteins). VTAs can kill indirectly the tumor cells that are resistant to conventional antiproliferative cancer therapies, i.e., cells in areas distant from blood vessels where drug penetration is poor, and hypoxia can lead to radiation and drug resistance. VTAs are expected to show the greatest therapeutic benefit as part of combined modality regimens. Preclinical studies have shown VTA-induced enhancement of the effects of conventional chemotherapeutic agents, radiation, hyperthermia, radioimmunotherapy, and antiangiogenic agents. There are broadly two types of VTAs, small molecules and ligand-based, which are grouped together, because they both cause acute vascular shutdown in tumors leading to massive necrosis. The small molecules include the microtubulin destabilizing drugs, combretastatin A-4 disodium phosphate, ZD6126, AVE8062, and Oxi 4503, and the flavonoid, DMXAA. Ligand-based VTAs use antibodies, peptides, or growth factors that bind selectively to tumor versus normal vessels to target tumors with agents that occlude blood vessels. The ligand-based VTAs include fusion proteins (e.g., vascular endothelial growth factor linked to the plant toxin gelonin), immunotoxins (e.g., monoclonal antibodies to endoglin conjugated to ricin A), antibodies linked to cytokines, liposomally encapsulated drugs, and gene therapy approaches. Combretastatin A-4 disodium phosphate, ZD6126, AVE8062, and DMXAA are undergoing clinical evaluation. Phase I monotherapy studies have shown that the agents are tolerated with some demonstration of single agent efficacy. Because efficacy is expected when the agents are used with conventional chemotherapeutic drugs or radiation, the results of Phase II combination studies are eagerly awaited.

[DDS and Me]

With the success of the human genome project, the focus of life science research has shifted to the functional and structural analyses of proteins, such as proteomics and structural genomics. These analyses of proteins including newly identified proteins are expected to contribute to the identification of therapeutically applicable proteins for various diseases. Thus, pharmaco-proteomic-based drug discovery and development for protein therapies, including gene therapy, cell therapy, and vaccine therapy, is attracting current attention. However, there is clinical difficulty in using almost all bioactive proteins, because of their very low stability and pleiotropic actions in vivo. To promote pharmaco-proteomic-based drug discovery and development, we have attempted to develop drug delivery systems (DDSs), such as the protein-drug innovation system and the optimal cell therapeutic system. In this review, we introduce our original DDSs.