The hypoxia-selective cytotoxin NLCQ-1 (NSC 709257) controls metastatic disease when used as an adjuvant to radiotherapy.

BACKGROUND: Metastases cause most cancer-related deaths. We investigated the use of hypoxia-selective cytotoxins as adjuvants to radiotherapy in the control of metastatic tumour growth. METHODS: The NLCQ-1, RB6145 and tirapazamine were assessed against the spontaneously metastasising KHT model. Subcutaneous KHT tumours (250 mm(3)) were irradiated with 25 Gy (single fraction) to control primary growth. Equitoxic drug treatments (NLCQ-1 (10 mg kg(-1)) once daily; RB6145 (75 mg kg(-1)) and tirapazamine (13 mg kg(-1)) twice daily) were administered 3-6 days post-radiotherapy when hypoxic cells were evident in lung micrometastases. Mice were culled when 50% of controls exhibited detrimental signs of lung metastases. RESULTS: In total, 95% of control mice presented with lung disease. This was significantly reduced by NLCQ-1 (33%; P=0.0002) and RB6145 (60%; P=0.02). Semi-quantitative grading of lung disease revealed a significant improvement with all treatments, with NLCQ-1 proving most efficacious (median grades: control, 4; NLCQ, 0 (P<0.0001); RB6145, 1 (P<0.001), tirapazamine, 3 (P=0.007)). Positron emission tomography (PET) was evaluated as a non-invasive means of assessing metastatic development. Primary and metastatic KHT tumours showed robust uptake of [(18)F]fluorodeoxyglucose ([(18)F]FDG). Metastatic burden discernable by [(18)F]FDG PET correlated well with macroscopic and histological lung analysis. CONCLUSION: The hypoxia-selective cytotoxin NLCQ-1 controls metastatic disease and may be a successful adjuvant to radiotherapy in the clinical setting.

Bipiperidyl mustard, a new obesifying agent in the mouse.

Bipiperidyl mustard, after conversion to its bis-cyclic immonium ion forme, has been found to cause rapid and extensive lipid deposition in mice given single doses of the drug. The obe sity appears to result from an alkylation reaction; the responses of the treated ani mals to food restriction and realimenta tion resemble those observed in gold thioglucose-treated mice; also in anal ogy to gold thioglucose, the bipiperidyl mustard effects can be counteracted by sulfhydryl compounds. These observa tions are suggestive of a similarity of mode of action between the alkylating agent and gold thioglucose, a conclusion which is supported by preliminary find ings of ventromedial lesions in the hypo thalamus of the bipiperidyl mustard treated mice.

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.

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.

Interstitial hypertension in carcinoma of uterine cervix in patients: possible correlation with tumor oxygenation and radiation response.

Elevated tumor interstitial fluid pressure (IFP) is believed to be responsible, at least in part, for the poor penetration and heterogeneous distribution of blood-borne therapeutic agents and nutrients in solid tumors. Using the wick-in-needle technique, IFP was measured in human patients with squamous cell carcinoma of the uterine cervix at the initial and final stages of fractionated external beam radiotherapy. Mean IFP values ranged from 10 to 26 mm Hg with an overall mean of 15.7 +/- 5.7 (SD) mm Hg in stage IIB and IIIB tumors (n = 12) and from 0 to 3 mm Hg in normal cervix (n = 3). IFP decreased in some patients with therapy while in others it increased. The changes in IFP values agree well with the clinical response to radiotherapy (n = 7, P less than 0.05). Oxygen tension, measured in selected tumors (n = 3) with polarographic oxygen microelectrodes, inversely correlated with IFP. These results show for the first time that the IFP in human cervical carcinomas is elevated, and that it can be lowered in some tumors using fractionated radiation therapy. These findings also suggest that IFP values may provide an indication of tumor oxygenation and that IFP modifications could be prognostic indicators of radiation response.

Effect of radiation on interstitial fluid pressure and oxygenation in a human tumor xenograft.

Elevated interstitial fluid pressure (IFP) is a pathophysiological characteristic of most human and experimental tumors and may be responsible, in part, for the poor distribution of blood-borne therapeutic agents and low blood flow rate in tumors. Recent data in cervical carcinomas in patients suggest that fractionated radiation can lower tumor IFP and increase oxygen partial pressure (pO (2)) in some patients. The goals of this study were to find the minimum dose of radiation required to modulate IFP and pO(2) and to determine the time course of IFP changes due to radiation in a preclinical model. Xenografts of the LS174T human colon adenocarcinoma were grown in the right flank of nude (BALB/c) mice. IFP and pO(2) were measured before and 24 h after graded doses of irradiation. The mean +/- SD initial IFP in untreated tumors was 12.9 +/- 0.5 mm Hg (n=109), and the range was 3.0 to 40.3 mm Hg. The mean +/- SD and median initial pO(2) were 20.2 +/- 2.4 and 11.9 mm Hg, respectively (n=37). IFP and pO(2) were independent of tumor size. Fractionated radiation lowered IFP by 2.5 mm Hg when the total dose was 10 or 15 Gy (P<0.05), but IFP did not change in the controls or the 5-Gy radiation group (P>0.05). Irradiation increased the proportion of tumors at higher oxygen tensions when compared to control tumors. The IFP and tumor volumes were followed for up to 10 days after a single dose of 10, 20, or 30 Gy of irradiation. IFP decreased for all treatment groups. The decrease was most significant for the group receiving 30 Gy. On day five following irradiation, the IFP had decreased by 35%. The changes in IFP and pO(2) occurred before any macroscopic changes in tumor volume could be observed. The radiation-induced decrease in IFP could be, in part, responsible for the increased uptake of monoclonal antibodies following single or fractionated radiation that has been reported in the literature.

Interaction of strong DNA-intercalating bioreductive compounds with topoisomerases I and II.

Nitro(imidazole/triazole)-linked acridines (NLAs) have been previously developed in our laboratory as DNA-intercalating bioreductive drugs. Such compounds demonstrate toxicity through the formation of bulky monoadducts with cellular macromolecules upon activation and reductive metabolism under hypoxic conditions. However, NLAs also demonstrate considerable aerobic toxicity. Based on the ability of NLAs to bind strongly to DNA through intercalation, we investigated whether their relatively high aerobic cytotoxicity and their relatively low hypoxic selectivity in vitro are associated with topoisomerases I and II (Topo I and II) inhibition. DNA Topo I or II-mediated activity studies have been performed using supercoiled or kinetoplast DNA plasmids. Calf thymus or human Topo I and human Topo II purified enzymes were used. All NLA derivatives strongly inhibited relaxation of supercoiled DNA catalyzed by either Topo I or II, in a concentration-dependent manner, without stabilization of a cleavable complex. Aerobic toxicity correlated well with the inhibition of Topo II-mediated decatenation of kinetoplast DNA, whereas the intracellular concentrations of NLAs were 27-152-fold greater than those needed for 50% inhibition of Topo-II mediated decatenation of DNA. These results suggest that topoisomerase inhibition accounts for NLAs aerobic toxicity.

A variant estrogen receptor messenger ribonucleic acid is associated with reduced levels of estrogen binding in human mammary tumors.

An analysis of the human estrogen receptor (ER) mRNA was performed on 71 human breast tumors using an RNase protection assay. Complementary DNA clones to the human estrogen receptor (lambda R8 and lambda R3) were used to generate small antisense 32P-labeled RNA molecules that were hybridized to the tumor RNA. We determined the relative amounts of ER mRNA in each tumor by measuring the amount of RNases A and T1 resistant hybrids. Moreover, because RNase A has the ability to cleave single-base mismatches within RNA/RNA duplexes, we were able to use the assay to screen for possible mutations or deletions in the ER mRNA. A significant correlation was found between the ER mRNA levels and the estrogen binding concentrations determined by a dextran-coated charcoal assay (r = 0.68; P less than 0.0001; n = 58). We also identified a subpopulation of tumors in which a mismatch in the ER mRNA was detected. This message modification, in the B region of the message, significantly correlated with low levels of estrogen binding. This result suggests that the observed B variant might lead to the production of receptors with altered properties.

Enhancement of pulmonary metastasis formation and gamma-glutamyltranspeptidase activity in B16 melanoma induced by differentiation in vitro.

B16 melanoma sublines (B16-F10-BL6 and B16-F1) exhibited elevated adenosine 3',5'-cyclic monophosphate (cAMP) levels when cultured in Dulbecco's modified Eagle's medium (DMEM) in comparison to cells in RPMI-1640 medium. In parallel, cells cultured in DMEM had increased tyrosinase activity, melanization and dendrite formation, all markers of melanoma differentiation. Also, the proliferative rates of both cell lines were decreased by 80-85% when cultured in DMEM relative to cells maintained in RPMI-1640 medium. In these studies, elevated levels of the melanin precursors tyrosine (Tyr) and phenylalanine (Phe) found in DMEM were shown not to be solely responsible for the phenotypic changes observed with DMEM. Both BL6 and B16-F1 cell lines formed more experimental pulmonary tumor metastasis in syngeneic C57BL/6 mice when maintained in DMEM vs RPMI-1640 medium. Analysis of metastasis formation in nude mice with normal and depleted natural killer (NK) cell activity revealed that the enhanced lung colonizing capacity of the BL6 cells maintained in DMEM was independent of the function of T-cell or NK-cell-mediated immunity. A close association between metastatic ability of tested lines and the expression of the membrane-associated enzyme gamma-glutamyltranspeptidase (gamma-GTPase, EC 2.3.2.2) was observed. The highly metastatic BL6 cell line had 20-fold higher levels of gamma-GTPase activity than the weakly metastatic B16-F1 cell line. Both cell lines, when grown in DMEM, had elevated gamma-GTPase activity that paralleled augmentation of metastatic ability. The dramatic changes in lung-colonizing capacity of the variant B16 melanoma cells maintained in DMEM in contrast to those grown in RPMI-1640 medium may serve as a useful model in understanding certain steps involved in triggering cell differentiation as well as metastasis development.

NLCQ-1, a novel hypoxic cytotoxin: potentiation of melphalan, cisDDP and cyclophosphamide in vivo.

PURPOSE: To investigate in vivo interactions between the recently developed bioreductive agent 4-[3-(2-nitroimidazolyl)-propylamino]-7-chloroquinoline hydrochloride (NLCQ-1) and the chemotherapeutic agents melphalan (L-PAM), cis-platin (cisDDP) and cyclophosphamide (CPM). METHODS AND MATERIALS: EMT6 and FSaIIC tumor cells were inoculated (subcutaneously) into the leg(s) of female Balb/c and male C3H mice, respectively. Treatment was initiated at 10 mm (EMT6) and 5 mm (FSaIIC) mean tumor diameter. The in vivo-in vitro and tumor regrowth assays were used, respectively, as endpoints. Bone marrow toxicity studies were also performed when the in vivo-in vitro assay was used. Drugs were given by i.p. injection. Tumors were excised 18-h after chemotherapeutic drug administration (Balb/c mice) or measured daily until three times their original size (C3H mice). The optimum administration schedule for potentiation between NLCQ-1 and each chemotherapeutic drug, as well as dose modification factors (DMF) at the optimum time, were determined with the in vivo-in vitro assay. When the tumor regrowth assay was used, each chemotherapeutic agent was given either as a single dose or as a split dose over two consecutive days at the optimum administration time after a 10 mg/kg NLCQ-1 i.p. injection. RESULTS: NLCQ-1 (at 0.33 times MTD), strongly potentiated the antitumor effect of L-PAM, cisDDP and CPM without concurrent enhancement in bone marrow toxicity. Potentiation was strictly schedule dependent and the optimum effect (1.5 to 2 logs killing beyond additivity) was observed when NLCQ-1 was given 60-, 45-, and 110-min before L-PAM, cisDDP, and CPM, respectively. The DMF values at 30% survival were 2.5, 1.9, and 3.8 for L-PAM, cisDDP, and CPM, respectively. DMF values for bone marrow toxicity at 50% survival were ca. 1 for all chemotherapeutic drugs. Pretreatment with NLCQ-1 resulted in 4-12 days extra delay in the regrowth of FSaIIC tumors. CONCLUSIONS: These results support the clinical investigation of NLCQ-1 as a chemosensitizer.

Dosimetric consequences of 10B(n, alpha)7Li reaction occurring at the cellular membrane.

PURPOSE: Microdosimetric expectations of Boron contents are extracted from a CRAY-Monte Carlo simulation of the nuclear reaction 10B(n, alpha)7Li as it occurs on a boronated membrane of a model cell and as the reaction fragments (alpha and Li) traverse into the cellular nucleus. METHODS AND MATERIALS: The present microdosimetry calculation is based upon the assumption that the therapeutic advantage of boron neutron capture therapy (BNCT), while depending upon the RBE and LET of the reaction particles, is equally dependent on the boron carrier preferential localization to tumor tissue, and the boron selectivity to cancerous cells and its specificity within subcellular compartments. In particular, boron fixes to cell membrane as it ought to, using monoclonal antibodies. The present Monte Carlo simulation computes stochastic expectations of alpha/Li energy depositions to the nucleus in a uniformly boronated membrane shell of a spherical cell. Differential energy gain was deduced from the stochastic energy depositions in events of neutron reactions with membrane boron compared against those with natural elements (O, H, N) in the cell. RESULTS: Microdosimetry data are presented in terms of specific energy (keV/micron3) and lineal energy (keV/micron) functions of the nucleus-to-cell volume ratios (NCVR). When folded with the geometric boron content and accounting for background reaction energies, the distributions yield effective energy gain to the cell nucleus per neutron capture event. Boron amount required to yield these energy gains are found to be of the order of picograms of boron per gram of cell mass. CONCLUSION: The boron content as inferred by the present Monte Carlo microdosimetry compares well with that deliverable by present pharmacokinetic means, but are orders of magnitude (mu-grams) less than those deduced previously from anthropomorphic macrodosimetry.

Quality assurance for gamma knife stereotactic radiosurgery.

PURPOSE: This quality assurance program is designed for stereotactic radiosurgical units, gamma knife, to check and maintain the unit to preclude accidents and comply with current regulations. MATERIALS AND METHODS: Over 58 stereotactic radiosurgical units using 201 focused 60Co beams have been installed in the last 7 years and are in use at hospitals throughout the world, with at least 11 additional units being prepared to come on-line in the next year. This system has been in use at the University of Pittsburgh Medical Center (UPMC) for 7 years. A comprehensive quality assurance program has been developed. It includes the physics and dosimetry parameters and safety checks required by regulatory agencies. The program, based on over 7 years of experience in measurements, and used during the treatment of over 1500 patients, is separated into three aspects, namely physics, dosimetry, and safety. The UPMC program hopefully will indicate out-of-tolerance problems. Some quality assurance items are checked on a daily basis prior to patient treatment, while other aspects are checked on a weekly, monthly, and/or annual basis. A complete list of items with their respective time tables and tolerances is provided. RESULTS: Although experience shows very small margins of error, larger values were chosen to account for variations in equipment and techniques. CONCLUSIONS: Items included in this quality assurance program should indicate and/or preclude problems encountered in the use of this unit.

Physics of gamma knife approach on convergent beams in stereotactic radiosurgery.

The Presbyterian-University Hospital of Pittsburgh installed the first clinically designated Leksell gamma knife in the U.S. in August 1987. Gamma knife radiosurgery involves stereotactic target localization with the Leksell frame and subsequent closed-skull single-treatment session irradiation of a lesion with multiple highly focused gamma ray beams produced from 60Co sources. The hemispherical array of sources, the large number of small-diameter beams, and the steep dose gradients surrounding a targeted lesion make physical characterization of the radiation field complex. This paper describes the physical features and the operation of the gamma knife as well as the calibration procedures of the very small, well-collimated beams. The results of studies using in-phantom ion chamber, diode, film, and lithium fluoride thermoluminescent dosimetry were all in close agreement. Both single-beam and multiple-beam dose profiles were measured and reported for the interchangeable helmets, which have 4-, 8-, 14-, and 18-mm-diameter collimators. We also describe the dose calculation and treatment planning algorithm in the treatment planning system. Measurements of the accuracy of mechanical and radiation alignment are also performed and discussed.

Clinical use of a wing field with transmission block for the treatment of the pelvis including the inguinal node.

Treatment planning of photon and electron beams to include the pelvis and the groin poses a technical difficulty of positioning beams, and a dosimetric problem of abutting fields at the groin. We have analyzed a simpler AP/PA method using a central transmission block. The posterior portal is smaller and opposes only the pelvic portion of the anterior portal under the transmission block, while the anterior extended portion (hence the wing) is unattenuated to treat the inguinal region. By calculating the attenuation thickness according to the patient's separation and the beam quality, the dose distribution is tailored to yield the proper dose to the pelvic mid-plane and the inguinal nodes while minimizing the dose to the femora. Measured dose distribution (6MV) using film dosimetry in a tissue-equivalent phantom indicates that a 30% hot spot is created by the posterior portal diverging into the wings of the anterior field. Therefore, the pelvic attenuator is tapered at its lateral edges, thereby significantly reduced the dose inhomogeneity (5%) at the groin. Clinical methods are outlined for the verification of the patient portal films against possible mismatch in beam divergence.

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.

Lymphoscintigraphy in gynecologic malignancies.

Lymphoscintigraphy is an easily performed noninvasive procedure that offers the potential to detect small numbers of ascitic tumor cells and early diaphragmatic tumor involvement. Moreover, it can be used to delineate and define abnormalities in lymph nodes that are not routinely visualized by bipedal contrast lymphangiography, ultrasound or computed tomography. Lymphoscintigraphy is recommended as an important investigative and adjunctive procedure in diagnosing gynecologic malignancies; there does not appear to be sufficient sensitivity and specificity to justify its routine clinical use.

Effects of tyrosinase activity on the cytotoxicity of 4-S-cysteaminylphenol and N-acetyl-4-S-cysteaminylphenol in melanoma cells.

The rationale for melanoma specific antitumor agents containing phenolic amines is based in part upon the ability of the enzyme tyrosinase to oxidize these prodrugs to toxic intermediates. Two phenolic amine compounds, N-acetyl-4-S-cysteaminylphenol (N-Ac-4-S-CAP) and 4-S-cysteaminylphenol (4-S-CAP), demonstrated growth inhibitory activity with a variety of melanoma cell lines and were essentially non-toxic to non-melanoma cell lines. Theophylline, an inhibitor of cyclic nucleotide phosphodiesterase, increased in situ tyrosinase activity and enhanced the antimelanoma effects of 4-S-CAP and N-Ac-4-S-CAP in pigmented melanoma cell lines. Phenylthiourea, a specific inhibitor of tyrosinase activity, partially blocked the growth inhibitory activity of N-Ac-4-S-CAP in human pigmented melanoma cells. Buthionine sulfoximine, an inhibitor of the synthesis of the cellular antioxidant glutathione, potentiated the growth inhibitory activity of N-Ac-4-S-CAP in pigmented melanoma cells.

Salvage radiotherapy for local failures of lumpectomy and breast irradiation.

BACKGROUND AND PURPOSE: In-breast tumor recurrence (IBTR) following lumpectomy and breast irradiation is usually managed by mastectomy. For women who refused mastectomy at the time of an IBTR, a repeat course of radiotherapy following repeat lumpectomy was offered. MATERIALS AND METHODS: Sixteen women with an IBTR following lumpectomy, axillary node dissection and breast irradiation were treated with repeat lumpectomy and radiotherapy to the operative area. Fifteen patients received 5000 cGy/25 fractions. One patient discontinued radiotherapy for non-medical reasons after having received only 3200 cGy/16 fractions. The interval from completion of the initial course of radiotherapy to documentation of IBTR varied from 10-130 months (median 31 months). RESULTS: Four patients (20%) have had further local failure. Ten of sixteen patients (62.5%) are alive and free or disease at 42-119 months from completion of the repeat course of radiotherapy. Of these latter patients, one had another in-breast tumor recurrence treated by excision alone and another had an in-breast tumor recurrence in the contra lateral breast post-lumpectomy and irradiation. Four patients died with distant metastasis, one is currently alive with contralateral breast cancer and distant metastasis, and one is alive with an extensive recurrence in the re-irradiated breast. Two of the patients with distant metastasis had abnormal bone scans at the time they received the repeat course of radiotherapy. There have been no severe late sequelae from the repeat course of radiotherapy. CONCLUSIONS: For selected patients, a repeat course of radiotherapy for an IBTR following lumpectomy and radiotherapy is well tolerated and may provide long-term local control.

Mechanism(s) regulating inhibition of thymidylate synthase and growth by gamma-L-glutaminyl-4-hydroxy-3-iodobenzene, a novel melanin precursor, in melanogenic melanoma cells.

A proposed mechanism for the melanoma specific activity of phenolic amines is based upon the ability of the enzyme tyrosinase to oxidize these prodrugs to toxic intermediates. In this study, we synthesized an iodinated analog of gamma-L-glutaminyl-4-hydroxybenzene (GHB) with increased antimelanoma activity in both human and murine melanoma cell lines. GHB and gamma-L-glutaminyl-4-hydroxy-3-iodobenzene (I-GHB) were shown to be substrates for both mammalian and mushroom tyrosinase. Glutathione, a cellular antioxidant, inhibited tyrosinase mediated formation of gamma-L-glutaminyl-3,4-benzoquinone (GBQ) from GHB, inhibited melanin production, and blocked the inhibition of the enzyme thymidylate synthase by oxidized GHB. Buthionine sulfoximine (BSO) depletion of cellular glutathione enhanced the growth inhibitory activity and the inhibition of in situ thymidylate synthase by phenolic amines in melanoma cells. GHB and I-GHB were shown to be approximately 5- and 10-fold more cytotoxic, respectively, in highly metastatic B16-BL6 cells than in weakly metastatic B16-F1 cells with approximately equal tyrosinase activity. B16-BL6 cells had approximately 20-fold higher gamma-glutamyltranspeptidase (gamma-GTPase) activity than B16-F1 cells which suggested the possible involvement of this enzyme in the activation of the cytotoxicity of the phenolic amines. 4-Aminophenol, a product of gamma-GTPase reaction with GHB, was a substrate for tyrosinase and a potent inhibitor of in situ thymidylate synthase activity in melanogenic cells. In pigmented melanoma cells containing the enzyme tyrosinase, the quinone mediated mechanism of phenolic amine cytotoxicity may be uniquely important and the cellular antioxidant glutathione essential in the detoxification of these quinone-generated intermediates.

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.