Estrogen-induced factors of breast cancer cells partially replace estrogen to promote tumor growth.

The hormone 17 beta-estradiol acts through its receptor system to induce MCF-7 human breast cancer cells to form tumors in athymic mice. In vitro studies have identified the production of estrogen-induced growth factors from MCF-7 cells that may have a role in growth control. These induced growth factors were sufficient to stimulate MCF-7 tumor growth in ovariectomized athymic mice, thus partially replacing estradiol. Growth factors may act as estrogen-induced "second messengers" in estrogen-responsive growth of human breast cancer.

Characterization of estrogen responsive transforming activity in human breast cancer cell lines.

We have characterized the production of transforming growth factor (TGF) activities by five human breast cancer cell lines in culture. The presence of TGF-alpha and -beta activity in medium conditioned by these cells was detected by induction of anchorage-independent colony formation of normal rat kidney cells in soft agar and by epidermal growth factor and TGF-beta receptor competition studies. In MCF-7, an estrogen-receptor positive cell line which requires estrogen for tumorigenesis in vivo, 17 beta-estradiol induced a 2-5-fold increase in a TGF-alpha-like activity (apparent molecular weight, 68,000 and 30,000 by column chromatography). An estrogen induction of lower magnitude (1.5-2.5-fold) was also seen in two other estrogen responsive cell lines, ZR-75-B and T47D. TGF-beta was not induced by 17 beta-estradiol in any of the three cell lines and was decreased by up to 50% of control in the MCF-7 and T47D cell lines. TGF-beta was not detectable by radioreceptor assay in the ZR-75-B cell line. Two hormone-independent and highly tumorigenic cell lines were studied. The MDA-MB-231 cell line produced large amounts of both TGF-alpha-like (Mr 30,000) and TGF-beta activities. In the HS578T cell line, little TGF-alpha was detectable, while large amounts of TGF-beta were produced. No simple correlations between the tumorigenicity of the cell lines in nude mice and production of either TGF activity could be demonstrated.

[125I]17-alpha-iodovinyl 11-beta-methoxyestradiol interaction in vivo with estrogen receptors in hormone-independent MCF-7 human breast cancer transfected with the v-rasH oncogene.

[125I]17-alpha-Iodovinyl 11-beta-methoxyestradiol [( 125I]MIVE2) has been evaluated as a potential radiotracer for the diagnostic imaging of estrogen receptor (ER)-positive human breast cancer. In vivo distribution experiments with athymic ovariectomized nude mice bearing human breast tumors revealed an apparent correlation between uptake of 125I-labeled compound and estrogen receptor concentration in the tumors. At 4 h after i.v. injection of [125I]MIVE2, HS578T (ER negative), ZR75-B (intermediate ER), and MCF-7ras (high ER) tumors accumulated 0.320 +/- 0.186, 0.679 +/- 0.467, and 2.6163 +/- 1.0121% injected dose/g, respectively. With coinjection of unlabeled 17-beta-estradiol, levels of radioactivity in MCF-7ras tumors were decreased to 0.4859 +/- 0.1424% injected dose/g, indicating a receptor-mediated process. Peak activity of radioligand in MCF-7ras tumors and uteri was observed at 2 h and was retained for the 8-h time course. Blood and nontarget tissue, such as muscle, revealed a rapid clearance of 125I-labeled compound by 8 h. Eight hours after injection, uterus and tumor-to-blood ratios were calculated to be 225 and 21, respectively. Also, MCF-7ras tumors were shown to accumulate 6.5-fold more radioactivity than muscle. These data suggest that [125I]MIVE2 has the capability of interacting specifically and with high affinity with estrogen receptors in human breast tumors in nude mice and may possibly be used for imaging receptor-positive tumors in breast cancer patients with very low serum estrogen levels. Selective uptake of compound in MCF-7ras tumors emphasizes the usefulness of an estrogen receptor-positive tumor model which has a unique ability to grow in a host system without circulating estrogens.

Binding characteristics and biological activity of 17 alpha-[125I]iodovinyl-11 beta-methoxyestradiol, an estrogen receptor-binding radiopharmaceutical, in human breast cancer cells (MCF-7).

17 alpha-[125I]Iodovinyl-11 beta-methoxyestradiol ([125I]MIVE2), a gamma-emitting analogue of estradiol, previously shown to bind to rat uterine estradiol receptor, was studied to determine the binding characteristics and biological activity in human breast cancer cells. In vitro determination of receptor binding by dextran-coated charcoal assays indicates that [125I]-MIVE2 binds specifically and with a high affinity to cytosolic estrogen receptors in the human breast cancer cell line, MCF-7. [3H]Estradiol binds to the receptor with approximately four times the affinity of [125I]-MIVE2 (Kd = 2.55 X 10(-9) M for [125I]MIVE2; Kd = 6.4 X 10(-10) M for [3H]estradiol). Unlabeled MIVE2 produces estrogenic effects similar to those of estradiol such as progesterone receptor induction and increases in thymidine incorporation in MCF-7 cells in culture. Cytosolic progesterone receptor levels were elevated 2.8-fold over control levels by 6 X 10(-9) M MIVE2. Stimulation of thymidine incorporation (approximately 300% above control levels) was observed after exposure to 1 X 10(-9) M MIVE2. Preliminary data show receptor-mediated uptake by the uterus in biodistribution studies in athymic nude mice given injections of [125I] MIVE2 (32-34 microCi). At 4 h, uterus:blood ratios are 20.5 and target tissue:nontarget tissue ratios are 12.9. In light of the fact that this compound can be prepared with a high specific activity, [125I]MIVE2 may have potential as a radiotracer for imaging estrogen receptor-positive breast tumors or metastatic lesions in human breast cancer patients.

The cytotoxicity of decays of tritium and iodine-125 incorporated in DNA of mammalian cells. Implications for the low-LET dosimetry of incorporated nuclides.

To quantify the toxicity of low-LET radiation from incorporated radionuclides, we have determined the toxicity of decays of [3H]dThd pulse-incorporated into CHO cells in early S phase, with the cells frozen for decay accumulation at 30, 120 or 360 min after the pulse. D37 values of 1500, 2000 and 2100 decays were found by colony formation assay, corresponding to average nuclear doses of 4.6 and 2.7 Gy at the 30- and 360-min times. As D37 for external irradiation (60Co, 2.2 Gy/min) under these conditions is approximately 18 Gy, these results confirm the inadequacy of the dosimetry used for external irradiation to predict the biological effects of the low-LET radiation from incorporated radionuclides. We also determined the toxicity of 125IdU administered as above, and have confirmed the previously reported finding that D37 falls dramatically from 165 decays at 30 min to 40 decays at 360 min. Using the data for tritium to estimate the effect of the dose of 125I low-LET radiation, we conclude that even at 30 min, most of the toxicity of the 125I decays is due to the high-LET portion of the 125I electron spectrum, not the low-LET portion as reported previously.

Characterization and hormonal regulation of casein kinase II activity in heterotransplanted human breast tumors in nude mice.

Cytosolic casein kinase type II activity has been identified in MCF-7 and MDA-MB-231 human breast cancer cells heterotransplanted into athymic nude mice. Sephacryl S-300 chromatography of MCF-7 and MDA-MB-231 tumor cytosols revealed a major peak of casein kinase activity with an estimated molecular weight of 150,000. This peak was further characterized and optimal conditions for breast tumor casein kinase activity were established. Polylysine (10 micrograms) acted as a potent stimulator with casein as the phosphate acceptor protein. This enzyme used both ATP and GTP as phosphate donors and the Km for GTP was 10 microM. The rate of phosphorylation with increasing concentrations of [gamma-32p]GTP revealed typical Michaelis-Menten kinetics and Vmax was approached at a concentration of 30 microM GTP. MgCl2 stimulated enzyme activity at concentrations between 10-20 mM. Quercetin, a bioflavonoid, inhibited casein kinase type II activity in a dose dependent manner. MCF-7 (hormone-dependent) human breast cancer cells (2-3 X 10(6)) were inoculated into the mammary fat pads of nude mice, supplemented with a 0.5 mg estradiol pellet. To determine the influence of various regulatory agents on casein kinase activity in vivo, tumor-bearing mice were treated for five days with estradiol, progesterone, dexamethasone or tamoxifen. Casein kinase type II was partially purified by gel filtration on a Sephacryl S-300 column and assayed in the presence of polylysine and casein. Dexamethasone treatment significantly decreased casein kinase II activity in MCF-7 tumors, which are receptor-positive for estrogen, androgen and glucocorticoid receptors.

Heterotransplantation of human Burkitt's lymphoma cell lines in athymic nude mice: tumor-host relationships.

We have explored the factors which influence tumorigenicity of Burkitt's lymphoma (BL) cell lines in athymic nude mice. Four cell lines, Namalwa, CA46, JD38, and ST486 revealed tumor incidence of 63.5, 69.0, 45.5 and 10.0%, respectively, in nude mice, but there was no correlation between tumor incidence and growth rate in vivo. Thus, growth rate and tumorigenicity are dependent upon different biochemical pathways. Evidence of tumor cell heterogeneity was demonstrated in the CA46 parent cell line. Five subclones derived from CA46 revealed varying degrees of tumor incidence (but very similar growth rates) that were consistently less than the parent CA46 line. Line 5, for example, produced 5.7-fold less tumors than the parent line. None of the BL cell lines or clones produced any metastatic lesions in liver, lung, brain, bone marrow or spleen in athymic nude mice. Northern blot analysis of c-myc mRNA levels in different BL cell lines revealed a possible relationship between percent tumor takes (but not growth rates) and the level of c-myc oncogene expression. However, no correlation was observed between c-myc mRNA levels and tumor incidence or growth rates among the CA46 clones. There was no correlation between the ability of the cell lines and the subclones to either secrete growth factors or to respond to growth factors secreted by Epstein-Barr virus-induced lymphoblastoid cells or lipopolysaccharide-activated monocytes, and their growth rates or percent tumor takes in mice. Comparison of tumor incidence and growth rates in irradiated and unirradiated mice showed that host factors influenced the growth of BL in nude mice.(ABSTRACT TRUNCATED AT 250 WORDS)

Tumour-specific inhibition of lymphoma growth by an antisense oligodeoxynucleotide.

In a high proportion of Burkitt lymphomas, transcription of the c-myc gene is initiated from a cryptic promoter in the first intron, creating abnormal messenger RNA molecules in which intron sequences, normally spliced out of the nascent transcripts, persist. An antisense oligodeoxynucleotide directed against these intron sequences greatly inhibited the proliferation of Burkitt lymphoma cell lines containing the abnormal transcripts (ST486 and JD38), but not that of cell lines containing normal c-myc transcripts (KK124). Flow cytometry showed a pronounced reduction in intracellular c-myc protein levels in cell lines containing aberrant myc transcripts, but no change in other cellular proteins. Control oligonucleotide did not inhibit c-myc protein expression or growth. These experiments provide evidence that antisense oligonucleotides targeted against tumour-specific, aberrant RNA species could be effective in controlling the proliferation of tumour cells without affecting normal cells.