Radiotoxicity of 17 alpha-[125I]iodovinyl-11 beta-methoxyestradiol in MCF-7 human breast cancer cells.

Therapeutic strategies for human breast cancer using 125I-labeled steroid hormones are clinically attractive in light of the estrogen dependence of many human breast cancers and the favorable microdosimetry resulting from 125I decay. We determined the uptake specific estrogen receptor binding and radiotoxicity of 17 alpha-[125I]iodovinyl-11 beta-methoxyestradiol (125IVME2) in vitro using cultured MCF-7 human breast carcinoma cells. 125IVME2 rapidly enters MCF-7 cells and reaches a plateau in the presence of competing 10(-7) M 17 beta-estradiol. In the absence of competitor, uptake is substantially greater before reaching a plateau. Efflux of 125IVME2 from cells incubated in the absence of estradiol decreases to levels corresponding to specific binding. Under equilibrium conditions and in the absence of competitor, 125IVME2 binds to both specific and nonspecific sites but, in the presence of excess 17 beta-estradiol, the observed binding is nonspecific. 125IVME2 is cytotoxic to exponentially growing MCF-7 cells and produces a survival curve typical of those observed for [125I]iododeoxyuridine and 16 alpha-[125I]iodoestradiol.

[125I]iodotamoxifen cytotoxicity in cultured human (MCF-7) breast cancer cells.

We evaluated the uptake and radiotoxicity of [125I]iodotamoxifen (125ITAM) in MCF-7 human breast cancer cells in the presence or absence of excess non-radioactive estradiol (E2) or iodotamoxifen (ITAM). Studies in cells under wash-out conditions and in nuclei isolated from previously exposed cells showed that 125ITAM binds estrogen receptor (ER) and antiestrogen binding sites (AEBS) and has the capacity for considerable non-specific binding. The radiotoxicity of 125ITAM was a complex function related to ER content and/or function as well as interactions with ER, AEBS and non-specific binding. Addition of E2 or ITAM abolished ER mediated cell killing. ITAM but not E2 abolished AEBS mediated cytotoxicity. Non-specific binding accounted for considerable cytotoxicity. Although these studies confirm the radiotoxicity of nuclear bound 125I, multiple nuclear binding sites, variability in ER content and function and non-specific binding will all adversely influence ultimate clinical efficacy.

Cytotoxicity of receptor-mediated 16 alpha-[125I]iodoestradiol in cultured MCF-7 human breast cancer cells.

Therapeutic strategies using 125I-labeled steroid hormones are attractive in light of the estrogen dependence of many human breast cancers and the favorable microdosimetry resulting from 125I decay. We determined the uptake, specific estrogen receptor (ER) binding, and cytotoxicity of 16 alpha-[125I]iodoestradiol in cultured MCF-7 human breast cancer cells. The cytotoxicity of receptor-mediated 125I appears to be sufficient in MCF-7 cells to warrant in vivo experimentation. Furthermore, cytotoxicity not specific to ERs is minimal within the dose range necessary for ER saturation and specific cell killing. Competitive toxicity studies using nonradioactive 17 beta-estradiol demonstrate an unequivocal relationship between ER binding and clonogenic viability.

Mouse ovarian tumor cells: an experimental model for progestin-mediated radiotherapy.

Mouse ovarian tumor (MOT) cells have been grown in C3HeB/FeJ mice as an ascites and as a subcutaneous tumor and in cell culture as a suspension. These cells contain saturable, high-affinity, specific progesterone receptors. Estrogen receptors were not detectable in these cells. MOT cells can be used as both an in vivo and an in vitro model for progestin-mediated radiotherapy.

Preliminary observations of malignant melanoma therapy using radiolabeled alpha-methyltyrosine.

A strategy for cancer therapy using astatine-211-labeled alpha-methyltyrosine (211At-AMT) was studied in cultured B16 melanoma cells and compared to the radiotoxicity of iodine-125-labeled iododeoxyuridine (125IUdR), a thymidine analogue. Both 125I and 211At deliver lethal doses of irradiation to melanoma cells when administered as 125IUdR and 211At-AMT. The alpha decay of astatine-211 is more effective however, needing only a fraction of the cellular radioactivity of 125IUdR to effect comparable clonogenic survival. Compared with 125IUdR, 125I-AMT is not cytotoxic because the range of the low energy electrons released does not interact with DNA. Uptake of radiolabeled AMT by melanotic cells is enhanced by theophylline. This preliminary evidence suggests that 211At-labeled melanin precursors may be exquisitely cytotoxic to B16 melanoma cells.

Organoastatine chemistry. Astatination via electrophilic destannylation.

Substantial interest is currently focused on the alpha-emitting radiohalogen 211At, principally because of its potential use in the radiation therapy of cancer. Knowledge of organoastatine chemistry is incomplete and existing methods for its incorporation restrict the range of compounds which may be labeled. Aryl and vinyl Sn(IV) compounds are notably susceptible to substitution of tin by a variety of electrophiles. We have investigated the reaction of aryltrialkylstannanes with astatine and report here the first examples of astatodestannylation. Formation of aryl astatides proceeds rapidly, cleanly and under mild conditions. The data further elucidate aspects of astatine reactivity and suggest a general route to synthesize astatinated compounds.

The oil-microcentrifuge assay: a rapid and sensitive method for analyzing specific [3H]estradiol binding in cultured cells.

We have developed an oil- microcentrifuge assay system for analyzing the binding of [3H]estradiol in metabolically active MCF-7 and MDA human breast cancer cells. Complete separation of 2 X 10(6) cells from radioactive media can be achieved within 5 s of centrifugation at 12,000 rpm. The [3H]estradiol binding sites in MCF-7 cells are filled within 20 min of radioligand exposure. Using this assay, our MCF-7 cells contain approximately 15,000 high affinity and saturable binding sites. Binding is inhibited by estradiol and tamoxifen but not progesterone. There is no specific binding of [3H]estradiol in MDA cells. This assay is a rapid, sensitive and reproducible method for investigating hormone-receptor binding and ligand specificity in cultured cells; results compare favorably with those obtained by more complex and lengthy techniques.

211At radiocolloid therapy: further observations and comparison with radiocolloids of 32P, 165Dy, and 90Y.

We compared the therapeutic efficacy of alpha and beta emitting radiocolloids for the treatment of experimental malignant ascites. 211At is an almost pure alpha-emitter. As 211At-tellurium colloid, the dose survival curve is linear and extrapolates through the origin in a manner similar to other high linear energy transfer radiations. Doses of 25 microCi were curative. Less than curative doses showed a graded prolongation of median survival. In cured mice, long term histological changes were seen in thyroid tissue. Acute changes were seen in the gastrointestinal tract as early as 2 hr after radiocolloid administration; these changes reached a plateau at 6 hr and were essentially gone 36 hr later. By comparison, radiocolloids of the beta emitters 32P, 165Dy and 90Y were not curative, but relatively large doses did substantially prolong median survival. The doses for maximal effect were 150 microCi 32P-chromic phosphate, 8000 microCi ++165Dy-ferric hydroxide macroaggregates and 200 microCi 90Y-citrate. The most compelling reason for the increased therapeutic efficacy of 211At-tellurium colloid is the direct and densely ionizing character of the emitted alpha radiations.

Estrogen receptor-mediated cytotoxicity using iodine-125.

Auger effects from 125I decay are singularly damaging if localized in DNA as the thymidine analogue 125I-iododeoxyuridine (125IUdR). Recent experience with steroid sex hormones extends these observations by demonstrating cytotoxicity in sites other than the DNA backbone. We have compared the cytotoxicity in human MCF-7 breast cancer cells of 125IUdR, 125I-iodotamoxifen, a nonsteroidal antiestrogen that is translocated from the cytoplasm to the nucleus of receptor containing cells, and 125I-iodoantipyrine, a biological indicator of the body water space. Cytotoxicity is critically dependent upon subcellular localization.

Astatine-211--tellurium radiocolloid cures experimental malignant ascites.

An investigation of the efficacy of astatine-211--tellurium colloid for the treatment of experimental malignant ascites in mice reveals that this alpha-emitting radiocolloid can be curative without causing undue toxicity to normal tissue. By comparison, negatron-emitting phosphorus-32 as colloidal chromic phosphate had no antineoplastic activity. The most compelling explanation for this striking difference is the dense ionization and short range of action associated with alpha-emission. These results have important implications for the development and use of alpha-emitters as radiocolloid therapy for the treatment of human tumors.