Illusions of tumour killing using radiolabelled antibodies

Cytoproliferative effect of low dose alpha radiation in human lung cancer cells is associated with connexin 43, caveolin-1, and survivin pathway

PURPOSE

High LET including alpha radiation-based approaches have been proved as a promising mode for cancer therapy owing to their biophysical and radiobiological advantages compared to photon beams. Studies pertaining to effect of α-radiation on cancer cells are limited to cytotoxic high doses.

MATERIALS AND METHODS

In this study, human lung adenocarcinoma (A549) cells were α-irradiated using ²⁴¹Am α-irradiator and effects of low dose of alpha radiation on these cells was studied under in vitro and in vivo conditions.

RESULTS

Clonogenic and other assays showed increased cellular proliferation at lower doses (1.36 and 6.8 cGy) but killing at higher doses (13.6-54.4 cGy). Further studies at low dose of alpha (1.36 cGy) showed increased TGF-β1 in the conditioned medium (CM) at early time point (24 h) but CM replacement did not affect the clonogenic survival. In these cells, increased phosphorylation of connexin 43 was correlated with decrease in gap-junction communication observed by dye transfer co-culture experiment. A decrease in caveolin-1 but increase in survivin expression was observed in low dose α-irradiated cells. An increase in cyclinD1 and decrease in Bcl-2, the target proteins of survivin, was observed in these cells. Low dose α-irradiated cancer cells transplanted in SCID mice showed significantly higher tumor volume, which was accompanied with an increased fraction of mitotic and PCNA/Ki67 positive cells in these tumor tissues.

CONCLUSIONS

Taken together, our results suggest an increase in proliferation and tumor volume at in vitro and in vivo levels, respectively, when A549 cells were irradiated with low dose of α-radiation. These findings may be relevant for a better understanding of radiobiological processes during high LET-based cancer radiotherapy.

Enhanced effects of monoclonal antibody carboplatin immunoconjugates uptake and anti-tumor effects with angiotensin II and tumor necrosis factor

The most important factor influencing the use of monoclonal antibody immunoconjugates for cancer treatment is effectiveness of enhancement for tumor targeting. We call attention to the vasoactive agents angiotensin II (ATII) for selective increase in tumor blood flow and cytokine tumor necrosis factor (TNF) to improve the vascular permeability of the tumor. Tumor localization and biodistribution were investigated by nude mice transplanted human colon adenocarcinoma (LS-180) with radiolabeled carboplatin immunoconjugates. Tumor activity 48 h after administration of ATII and TNF was significantly higher than in the control group. However, nonspecific accumulation in normal organs was not observed. In vivo anti-tumor effects in animals with ATII and TNF was significantly stronger than in those given the same dose drug alone or immunoconjugates alone. These results indicate that ATII and TNF could be useful tools for induction of stronger inhibition of tumor growth without systemic toxicity.

Proposal for translational analysis and development of clinical radiolabeled immunoglobulin therapy

BACKGROUND AND PURPOSE

Radiolabeled immunoglobulin therapy (RIT) can be a selective, effective, low-toxicity outpatient cancer therapy. A consensus on the best approach for the preclinical and clinical development of RIT reagents needs to be developed. We report the M.D. Anderson Cancer Center prior experience in translating RIT from laboratory to clinic for the treatment of Hodgkin's disease and propose a flow diagram for the development of RIT for other malignancies.

MATERIAL AND METHODS

Three different animal models are described: nude mice bearing human tumor xenografts, normal beagle dogs, and normal rhesus monkeys. We produced and purified antibodies and prepared chelate-immunoconjugates reactive with six different human tumor-associated antigens. The Igs used were derived from rabbits, mice, and humans (human-derived RIT reagents being less immunogenic in human patients). Eighty patients with refractory Hodgkin's disease were treated with radiolabeled antiferritin.

RESULTS

We recommend a two-injection scheme using, (1) an indium-111-labeled radioimmunoconjugate for diagnosis, pharmacokinetic studies, and dosimetry, and (2) a yttrium-90-labeled radioimmunoconjugate for therapy. The animal models provide useful data on tumor targeting, radiotoxicology, and undesirable biodistributions. A 70% response rate is obtained in patients with advanced recurrent Hodgkin's disease. More extensive preclinical testing allows for safer and more effective clinical RIT studies.

CONCLUSIONS

We recommend, (1) preclinical optimization of chelation chemistry, Ig size, Ig origin, route of administration, and fractionation, (2) new clinical Phase I-III studies more appropriate for RIT development than the classical Phase I-III studies used for the development of chemotherapeutic agents, and (3) more extensive preclinical testing of RIT reagents.

Intratumoral injection of an adriamycin immunoconjugate against human pancreatic cancer xenografts

We have evaluated the effect of an adriamycin conjugate of monoclonal antibody Nd2 (ADM-Nd2) on the growth rate of SW1990 xenografts grown subcutaneously in athymic nude mice. Intravenous or intraperitoneal administration of radiolabeled Nd2 resulted in a maximum tumor accumulation of approximately 45% of the initial dose/g of tumor 3-7 days after administration. However, administration into the tumor produced retention of 1200%ID/g 1 day after, with 50% of this high value remaining even at 7 days after administration. In contrast, intratumoral administration of a non-specific immunoglobulin showed a lower initial retention and rapid loss of label. Both intravenously and intratumorally administered ADM-Nd2 reduced the growth rate of SW1990 xenografts. While a single intravenous administration arrested growth for about two weeks, a single intratumoral injection prevented any increase in tumor size even 45 days after administration. Xenografts treated with ADM-Nd2 showed degenerative changes at the histological level. Neither Nd2 alone nor Adriamycin alone inhibited growth when administered at the same dose as the conjugate.

The curability of tumours of differing size by targeted radiotherapy using 131I or 90Y

A mathematical model has been used to investigate the relationship of curability to tumour size and cell number for spherical tumours treated with targeted 131I or 90Y, assuming uniform uptake of radionuclide throughout the tumour. The analysis shows that, for any given cumulated activity per unit mass of tumour, cure probability is greatest for tumours whose diameter is close to an optimum value which depends on the path length of the emitted beta-particle. Smaller tumours are less curable because of inefficient absorption of radiation energy, and larger tumours are less curable because of greater clonogenic cell number. The lesser curability of very small tumours is a feature of targeted radiotherapy using long-range beta-emitters which does not occur with external beam irradiation. The predicted inefficiency of sterilisation of microscopic tumours poses a problem for targeted radiotherapy which is analogous to "geographic miss" in conventional radiotherapy. The implication is that small micro-metastases could escape sterilisation by radionuclides administered at activity levels sufficient to eradicate larger tumours. It is suggested that single agent targeted radiotherapy should not be used for treatment of disseminated malignancy when multiple tumours of differing size, including micrometastases, may be present. The analysis implies that an advantage might result from the use of a panel of several radionuclides (including short-range emitters) or from combining targeted radiotherapy using long-range beta-emitters with external beam irradiation or some other modality to which microscopic tumours are preferentially vulnerable.

Drug delivery systems--2. Site-specific drug delivery utilizing monoclonal antibodies

Monoclonal antibodies (MAbs) are purified antibodies produced by a single clone of cells. They are engineered to recognize and bind to a single specific antigen. Accordingly, when administered, MAbs home in on a particular circulating protein or on cells that bear the correct antigenic signature on their surfaces. It is the specificity of MAbs that has made them valuable tools for health professions. Following the discovery of Kohler and Milstein regarding the method of somatic cell hybridization, a number of investigators have successfully adopted this technique to obtain T-lymphocyte hybrid cell lines by fusion of activated T (thymus derived) lymphocytes with a T lymphoma cell line leading to an immortalization of a specific differentiated function. The hybrids thus obtained were subsequently shown to produce homogeneous effector molecules with a wide variety of immune functions such as enhancement or suppression of antibody responses, generation of helper T cells, suppressor T cells and cytotoxic T cells. Study of these regulatory molecules has been further shown to provide a greater insight into the genetic, biochemical and molecular mechanisms responsible for cellular development, and the interaction and triggering of various cell types. The successful application of hybridoma technology has now resulted into several advances in the understanding the mechanism and treatment of diseases, especially cancer and development of vaccines, promotion of organ transplantation and therapy against parasites as well. Since monoclonal antibodies could be made in unlimited supply, they have been used in genetic studies such as mRNA and gene isolation, chromosomal isolation of specific genes, immunoglobulin structure, detection of new or rare immunoglobulin gene products, structural studies of enzymes and other proteins and structural and population studies of protein polymorphisms. In some instances, the monoclonal antibodies have been found to replace conventional antisera for studies of chromosome structure and function, gene mapping, embryogenesis, characterization and biosynthesis of developmental and differentiation antigens. These antigens are those that are specific for various cell types and tissues, species specific antigen, antigens involved in chemotaxis, immunogenetics and clinical genetics including genetically inherited disorders, chromosome aberrations and transplantation antigens. Besides these monoclonal antibodies, their complexes have recently been investigated as exquisitely sensitive probes to be guided to target cells or organs. They have been used to deliver cytotoxic drugs to malignant cells or enzymes to specific cell types.(ABSTRACT TRUNCATED AT 400 WORDS)

Strategies for systemic radiotherapy of micrometastases using antibody-targeted 131I

A simple analysis is developed to evaluate the likely effectiveness of treatment of micrometastases by antibody-targeted 131I. Account is taken of the low levels of tumour uptake of antibody-conjugated 131I presently achievable and of the "energy wastage" in targeting microscopic tumours with a radionuclide whose disintegration energy is widely dissipated. The analysis shows that only modest doses can be delivered to micrometastases when total body dose is restricted to levels which allow recovery of bone marrow. Much higher doses could be delivered to micrometastases when bone marrow rescue is used. A rationale is presented for targeted systemic radiotherapy used in combination with external beam total body irradiation (TBI) and bone marrow rescue. This has some practical advantages. The effect of the targeted component is to impose a biological non-uniformity on the total body dose distribution with regions of high tumour cell density receiving higher doses. Where targeting results in high doses to particular normal organs (e.g. liver, kidney) the total dose to these organs could be kept within tolerable limits by appropriate shielding of the external beam radiation component of the treatment. Greater levels of tumour cell kill should be achievable by the combination regime without any increase in normal tissue damage over that inflicted by conventional TBI. The predicted superiority of the combination regime is especially marked for tumours just below the threshold for detectability (e.g. approximately 1 mm-1 cm diameter). This approach has the advantage that targeted radiotherapy provides only a proportion of the total body dose, most of which is given by a familiar technique. The proportion of dose given by the targeted component could be increased as experience is gained. The predicted superiority of the combination strategy should be experimentally testable using laboratory animals. Clinical applications should be cautiously approached, with due regard to the limitations of the theoretical analysis.

Human monoclonal antibodies and monoclonal antibody multispecificity

The majority of human anti-tumour monoclonal antibodies (Mabs) isolated to date have been disappointing. Firstly, they react or cross react with intracellular cytoskeletal proteins or nuclear antigens and therefore are of limited value as blood borne agents. They are also generally of the IgM isotype and show relatively low intrinsic affinity for the primary epitope. Secondly, such Mabs can be generated from normal, non tumour bearing subjects at a frequency comparable to their production from tumour patients. This latter observation is true also for common autoantigens such as DNA and IgG since Mabs to these can also be generated from normal subjects in addition to autoimmune individuals. This article rationalises these observations in the context of the requirement for clinical use for human Mabs. It discusses the evidence that there is a potentially useful B cell response to be immortalised, and examines the consequences of the newly recognised phenomenon of monoclonal antibody multispecificity both on the methodology of their generation and on their subsequent use as imaging and therapeutic tools.

Human leukemia cell binding and killing by anti-CD5 radioimmunotoxins

We have synthesized a reagent for antibody directed cell targeting composed of the monoclonal antibody (MoAb) T101 linked to the potent toxin ricin. The immunotoxin (IT) was subsequently radiolabeled by a cyclic anhydride procedure with 90Yttrium (90Y) to construct a radioimmunotoxin (RIT) that may have potential for cancer therapy. We evaluated the reagent for selectivity in binding and protein synthesis inhibition (PSI) assays. The RIT selectively bound antigen positive leukemia T-cell lines, with minimal binding to antigen negative control lines. The IT inhibited 87% or greater protein synthesis activity at 1 microgram/ml and exhibited an IC50 (the dose inhibiting 50% activity) of 0.18 +/- 0.08 microgram/ml in the presence of lactose. RIT and nonlabeled IT showed comparable degrees of PSI at 1 microgram/ml and 10 micrograms/ml, suggesting that labeling had little overall effect on the activity of the immunoconjugate. However, indirect evidence showed that the galactose binding site of ricin was inhibited 10-fold by its exposure to 90Y. Control RIT were minimally inhibitory. IT labeled with 131Iodine (131I) by an iodine monochloride technique also retained its capability to selectively inhibit protein synthesis. When RIT were tested for potency in a clonogenic assay against human leukemia T-cell lines, they inhibited 3.61 logs of tumor cell growth at 10 micrograms/ml. This did not represent an improvement over the log elimination with radiolabeled antibody alone, which showed 4.19 log elimination of tumor cells. Our observation that the 90Y-labeled RIT and labeled antibody can selectively eliminate about four logs of tumor cells in an in vitro clonogenic assay is unique. The ability of RIT to kill several logs of tumor cells in vitro renders RIT interesting anti-tumor reagents.