Effect of induced hypertension with angiotensin II infusion on biodistribution of 111in-labeled monoclonal antibody

Current Approaches for Improving Intratumoral Accumulation and Distribution of Nanomedicines

The ability of nanoparticles and macromolecules to passively accumulate in solid tumors and enhance therapeutic effects in comparison with conventional anticancer agents has resulted in the development of various multifunctional nanomedicines including liposomes, polymeric micelles, and magnetic nanoparticles. Further modifications of these nanoparticles have improved their characteristics in terms of tumor selectivity, circulation time in blood, enhanced uptake by cancer cells, and sensitivity to tumor microenvironment. These "smart" systems have enabled highly effective delivery of drugs, genes, shRNA, radioisotopes, and other therapeutic molecules. However, the resulting therapeutically relevant local concentrations of anticancer agents are often insufficient to cause tumor regression and complete elimination. Poor perfusion of inner regions of solid tumors as well as vascular barrier, high interstitial fluid pressure, and dense intercellular matrix are the main intratumoral barriers that impair drug delivery and impede uniform distribution of nanomedicines throughout a tumor. Here we review existing methods and approaches for improving tumoral uptake and distribution of nano-scaled therapeutic particles and macromolecules (i.e. nanomedicines). Briefly, these strategies include tuning physicochemical characteristics of nanomedicines, modulating physiological state of tumors with physical impacts or physiologically active agents, and active delivery of nanomedicines using cellular hitchhiking.

Optimization of radioimmunotherapy of solid tumors: biological impediments and their modulation

In contrast to the overwhelming success of radiolabeled antibodies in treating hematologic malignancies, only modest success has been achieved in the radioimmunotherapy of solid tumors. One of the major limitations in successful application of radioimmunotherapy is the large molecular size of the intact immunoglobulin that results in prolonged serum half-life and poor tumor penetration and uptake. With the advent of antibody engineering, small molecular weight antibody fragments exhibiting improved pharmacokinetics and tumor penetration have been generated. However, their clinical application has been limited by suboptimal tumor uptake and short tumor residence time. There is a greater realization that optimization of the molecular size of the antibodies alone is not sufficient for clinical success of radioimmunotherapy. In addition to their size, radiolabeled antibodies encounter other impediments before reaching their target antigens expressed on the cell surface of solid tumors. Some of the barriers include poor blood flow in large tumors, permeability of vascular endothelium, elevated interstitial fluid pressure of tumor stroma, and heterogeneous antigen expression. Recent research has considerably improved our understanding and appreciation of these forces, and the new wave of optimization strategies involves the use of biological modifiers to modulate the impediments posed by solid tumors. In combination with radiolabeled antibodies, various agents are being used to improve the tumor blood flow, enhance vascular permeability, lower tumor interstitial fluid pressure by modulating stromal cells and extracellular matrix components, up-regulate the expression of target antigens, and improve the penetration and retention of the radiopharmaceuticals. This review outlines ongoing research efforts involving biological modifiers to optimize the uptake and efficacy of radiolabeled antibodies for the treatment of solid tumors.

[Design of radiolabeled antibody fragments for tumor-selective radioactivity localization--brush border enzyme-sensitive bond to decrease renal accumulation of radioactivity]

Nonspecific renal radioactivity localization constitutes a problem in targeted imaging and therapy with radiolabeled antibody fragments. Based on the idea that the renal radioactivity levels should be reduced if radiolabeled compounds excreted in the urine are released from antibody fragments by tubular brush border enzymes, 3'-iodohippuryl N epsilon-maleoyl-L-lysine (HML) was designed as a radioiodination reagent for antibody fragments; the glycyl-lysine sequence in HML is a substrate for a brush border enzyme and m-iodohippuric acid is released by cleavage of the linkage. In normal mice, HML-conjugated Fab demonstrated low renal radioactivity levels from early postinjection times. Directly radioiodinated Fab showed migration of radioactivity from the membrane to the lysosomal fraction of the renal cells from 10 to 30 min postinjection. On the other hand, the majority of the radioactivity was detected only in the membrane fraction after injection of HML-conjugated Fab. In tumor-bearing mice, HML-conjugated Fab showed a marked decrease in renal radioactivity localization without impairing the tumor accumulation. These findings indicate that HML is a useful reagent for reducing the renal radioactivity levels of antibody fragments.

A novel immunoscintigraphy technique using metabolizable linker with angiotensin II treatment

Immunoscintigraphy is a tumour imaging technique that can have specificity, but high background radioactivity makes it difficult to obtain tumour imaging soon after the injection of radioconjugate. The aim of this study is to see whether clear tumour images can be obtained soon after injection of a radiolabelled reagent using a new linker with antibody fragments (Fab), in conditions of induced hypertension in mice. Fab fragments of a murine monoclonal antibody against human osteosarcoma were labelled with radioiodinated 3′-iodohippuryl N-ɛ-maleoyl-L-lysine (HML) and were injected intravenously to tumour-bearing mice. Angiotensin II was administered for 4 h before and for 1 h after the injection of radiolabelled Fab. Kidney uptake of ¹²⁵I-labelled-HML-Fab was much lower than that of ¹²⁵I-labelled-Fab radioiodinated by the chloramine-T method, and the radioactivity of tumour was increased approximately two-fold by angiotensin II treatment at 3 h after injection, indicating high tumour-to-normal tissue ratios. A clear tumour image was obtained with ¹³¹I-labelled-HML-Fab at 3 h post-injection. The use of HML as a radiolabelling reagent, combined with angiotensin II treatment, efficiently improved tumour targeting and enabled the imaging of tumours. These results suggest the feasibility of PET scan using antibody fragment labelled with ¹⁸F-fluorine substitute for radioiodine. © 1999 Cancer Research Campaign

Rhenium-186-mercaptoacetyltriglycine-labeled monoclonal antibody for radioimmunotherapy: in vitro assessment, in vivo kinetics and dosimetry in tumor-bearing nude mice

Stability and immunoreactivity of 186Re-labeled monoclonal antibody were examined, and its in vivo kinetics was investigated in tumor-bearing Balb/c nu/nu female mice to assess the feasibility of using it in radioimmunotherapy (RIT). A murine IgG1, A7, against a 45 kD glycoprotein in human colon cancer was radiolabeled with 186Re by using a chelating method with a mercaptoacetyltriglycine (MAG3). 186Re-MAG3 complex was conjugated to A7 after esterification of 186Re-MAG3 with tetrafluorophenol (TFP). The efficiency of 186Re-MAG3-TFP production and the labeling efficiency of A7 were 51-59% and 57-60%, respectively. Immunoreactivity of purified 186Re-MAG3-A7 was 68.2% at infinite antigen excess. In 0.9% NaCl at 4 degrees C, the radioactivity (12.7 MBq/mg, 3.55 MBq/ml) dissociated with time from 186Re-MAG3-A7 as a small molecular weight moiety because of autoradiolysis. The addition of ascorbic acid, 5 mg/ml, as a radioprotectant or storage at -80 degrees C could effectively prevent the radiolysis of 186Re-MAG3-A7 for 7 days. Immunoreactivity of 186Re-MAG3-A7, 6.70 MBq/mg (6.66 MBq/ml), stored in the presence of ascorbic acid was well retained up to 8 days after the preparation. In colon cancer xenografted mice, 31.0% of the injected dose/g of 186Re-MAG3-A7 had accumulated in the tumors at 24 h postinjection. Estimated radiation dose to tumors was 14.9 cGy/37 kBq up to 8 days postinjection which was 12-fold greater than the whole-body radiation dose. These in vivo characteristics were superior to those of A7 labeled with radioiodine, affording greater therapeutic ratios than 131I-A7. Because of the better image quality of 186Re-MAG3-A7 as well as more favorable dosimetry, 186Re-MAG3-A7 would be a better choice for RIT of colon cancer than 131I-A7. These results indicated the feasibility of RIT with 186Re-MAG3-A7, though the prevention of radiolysis of the labeled antibody should be considered.

Short-period-induced hypertension could improve tumor-to-nontumor ratios of radiolabeled monoclonal antibody

This study was undertaken to find optimum period of hypertensive treatment for the improvement of tumor targeting of 111In-labeled monoclonal antibody. Angiotensin II was infused into tumor-bearing mice at an infusion rate of 2.0 micrograms/kg/min determined by the dose-finding study. The infusion was continued for up to 72 h, and biodistribution of 111In-DTPA-A7, a murine IgG1, was observed 72 h postinjection. Tumor-to-nontumor ratios were best improved with the infusion for 0.5-3 h. However, with the longer infusion, the effect deteriorated by the increase of nontumor uptakes, and body-weight loss became remarkable. It could be concluded that hypertensive treatment for a short period could be safely performed to benefit targeting of radiolabeled monoclonal antibody.