MCF-7 Xenografts In Nude Mice Research Articles

Abstract P3-03-05: PI3K/PDK1 mediates resistance to CDK4/6 inhibitors through dysregulation of S-phase cyclins/cyclin dependent kinases (CDKs)

Abstract Background: CDK4/6 inhibitors in combination with antiestrogens are approved for the treatment of ER+ advanced breast cancer. However, not all patients benefit from CDK4/6 inhibitors, underscoring the need to develop therapeutic strategies to circumvent de novo and acquired drug resistance. Methods: ER+ breast cancer cells (MCF-7, T47D, HCC1428, and HCC1500) were made resistant to increasing doses to the CDK4/6 inhibitor ribociclib (LEE011; Novartis). LEE011-resistant cells were characterized by 2D/3D growth, cell cycle, and immunoblot analyses. GSK2334470 (PDK1 inhibitor) and dinaciclib (CDK2 inhibitor) were used to modify resistance to ribociclib. PDK1 and pS6 immunohistochemistry (IHC) were performed on primary human tumor explants treated ex vivo with palbociclib. Results: Resistant cell lines (MCF-7/LR, T47D/LR, HCC1428/LR, and HCC1500/LR) exhibited an IC50 at least 20-fold higher than that of their parental cells. They displayed cross-resistance to the CDK4/6 inhibitors palbociclib and abemaciclib. Immunoblot analysis of ribociclib-resistant cells showed increased levels of 3-phosphoinositide dependent protein kinase 1 (PDK1), S227 pRSK2 (target of PDK1), T308 pAKT (target of PDK1), and pS6 (downstream effector of the PDK1 target p70S6K), compared to parental drug sensitive cells. PDK1 is a master kinase that functions downstream of phosphoinositide 3-kinase (PI3K) and is crucial for the activation of AKT and many other AGC kinases including PKC, S6K, SGK, and RSK. Primary tumor explants treated ex vivo with palbociclib for 96 h also exhibited upregulation of PDK1 and pS6 by IHC. Cell cycle analysis revealed that CDK4/6 inhibition failed to induce G1 arrest, a reduction in S phase, and senescence in MCF-7/LR and T47D/LR compared to parental cells. Progression into S phase in the presence of ribociclib suggested upregulation of S-phase cyclins/CDKs. Indeed, the resistant cells exhibited significantly higher levels of pCDK2, cyclin A, cyclin E and S477/T479 pAKT, a CDK2-dependent phosphorylation of AKT required for full kinase activity and limited to the S-phase of the cell cycle. Pharmacological inhibition of PDK1 (with GSK2334470) or CDK2 (with dinaciclib) re-sensitized the ribociclib-resistant cells to CDK4/6 inhibitors. However, ribociclib/GSK2334470 inhibited MCF-7/LR and T47D/LR cell proliferation better than ribociclib/dinaciclib. Further, ribociclib/GSK2334470 but not ribociclib/dinaciclib completely abrogated pRb, pS6, pRSK2, pCDK2, cyclin A, and cyclin E, suggesting the PI3K/PDK1 pathway mediates acquired resistance to CDK4/6 inhibitors through dysregulation of the cell cycle. Consistent with these data, ribociclib/GSK2334470 inhibited growth of established MCF-7 xenografts in nude mice, significantly more potently than each drug alone. Conclusions: These data support a critical role for PI3K/PDK1 in acquired resistance to CDK4/6 inhibitors in ER+ breast cancer cells. Co-targeting of PI3K/PDK1 and CDK4/6 may overcome resistance to CDK4/6 inhibitors and is worthy of further translational and clinical investigation in patients with ER+ breast cancer. Citation Format: Jansen VM, Formisano L, Witkiewicz A, Estrada MV, Sanchez V, Dugger TC, Knudsen ES, Arteaga CL. PI3K/PDK1 mediates resistance to CDK4/6 inhibitors through dysregulation of S-phase cyclins/cyclin dependent kinases (CDKs) [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P3-03-05.

Stromal fibroblasts present in breast carcinomas promote tumor growth and angiogenesis through adrenomedullin secretion.

Tumor- or cancer-associated fibroblasts (TAFs or CAFs) are active players in tumorigenesis and exhibit distinct angiogenic and tumorigenic properties. Adrenomedullin (AM), a multifunctional peptide plays an important role in angiogenesis and tumor growth through its receptors calcitonin receptor-like receptor/receptor activity modifying protein-2 and -3 (CLR/RAMP2 and CLR/RAMP3). We show that AM and AM receptors mRNAs are highly expressed in CAFs prepared from invasive breast carcinoma when compared to normal fibroblasts. Immunostaining demonstrates the presence of immunoreactive AM and AM receptors in the CAFs (n = 9). The proliferation of CAFs is decreased by anti-AM antibody (αAM) and anti-AM receptors antibody (αAMR) treatment, suggesting that AM may function as a potent autocrine/paracrine growth factor. Systemic administration of αAMR reduced neovascularization of in vivo Matrigel plugs containing CAFs as demonstrated by reduced numbers of the vessel structures, suggesting that AM is one of the CAFs-derived factors responsible for endothelial cell-like and pericytes recruitment to built a neovascularization. We show that MCF-7 admixed with CAFs generated tumors of greater volume significantly different from the MCF-7 xenografts in nude mice due in part to the induced angiogenesis. αAMR and AM22-52 therapies significantly suppressed the growth of CAFs/MCF-7 tumors. Histological examination of tumors treated with AM22-52 and aAMR showed evidence of disruption of tumor vasculature with depletion of vascular endothelial cells, induced apoptosis and decrease of tumor cell proliferation. Our findings highlight the importance of CAFs-derived AM pathway in growth of breast carcinoma and in neovascularization by supplying and amplifying signals that are essential for pathologic angiogenesis.

CPUY201112, a novel synthetic small-molecule compound and inhibitor of heat shock protein Hsp90, induces p53-mediated apoptosis in MCF-7 cells

Heat-shock protein 90 (Hsp90) is highly expressed in many tumor cells and is associated with the maintenance of malignant phenotypes. Targeting Hsp90 has had therapeutic success in both solid and hematological malignancies, which has inspired more studies to identify new Hsp90 inhibitors with improved clinical efficacy. Using a fragment-based approach and subsequent structural optimization guided by medicinal chemistry principles, we identified the novel compound CPUY201112 as a potent Hsp90 inhibitor. It binds to the ATP-binding pocket of Hsp90 with a kinetic dissociation (Kd) constant of 27 ± 2.3 nM. It also exhibits potent in vitro antiproliferative effects in a range of solid tumor cells. In MCF-7 cells with high Hsp90 expression, CPUY201112 induces the degradation of Hsp90 client proteins including HER-2, Akt, and c-RAF. We prove that treating MCF-7 cells with CPUY201112 results in cell cycle arrest and apoptosis through the wild-type (wt) p53 pathway. CPUY201112 also synergizes with Nutlin-3a to induce cancer cell apoptosis. CPUY201112 significantly inhibited the growth of MCF-7 xenografts in nude mice without apparent body weight loss. These results demonstrate that CPUY201112 is a novel Hsp90 inhibitor with potential use in treating wild-type p53 related cancers.

Abstract 227: Estrogen receptor-α and tumor initiating cells are novel targets of diallyl trisulfide in breast cancer cells

Abstract Epidemiological studies suggest a protective role for Allium vegetables, such as garlic, against breast and other cancers. Diallyl trisulfide (DATS) is a promising oil-soluble anticancer metabolite generated after cutting or chewing of Allium vegetables. We have shown previously that DATS inhibits viability of human breast cancer cells (MCF-7 and MDA-MB-231) and a cell line derived from spontaneously developed tumor of a mouse mammary tumor virus-neu mouse by causing apoptosis induction. We also found that a non-tumorigenic normal human mammary epithelial cell line (MCF-10A) is resistant to cell death induction by DATS. Studies by others have demonstrated in vivo efficacy of DATS against MCF-7 xenografts in nude mice. The present study builds upon these observations and identifies novel targets of DATS in breast cancer cells. MCF-7 and T47D cells exposed to DATS exhibited downregulation of estrogen receptor-α (ER-α) protein, which peaked between 12 and 24 h post-treatment. Diallyl sulfide and diallyl disulfide analogs were relatively less effective in suppressing protein level of ER-α compared with DATS. The 17β-estradiol (E2)-induced expression of pS2, an ER-α target gene product, was also decreased in the presence of DATS. Downregulation of ER-α protein expression resulting from DATS treatment was accompanied by a decrease in nuclear level of ER-α, suppression of ER-α mRNA, and inhibition of ERE2e1b-luciferase reporter activity. Moreover, apoptotic cell death induced by DATS was partially but statistically significantly attenuated in the presence of E2 in MCF-7 cells as well as by overexpression of ER-α in MDA-MB-231 cells. DATS treatment inhibited breast cancer stem cell (bCSC) population as evidenced by flow cytometric analysis of CD44high/CD24low/epithelial specific antigen positive population, aldehyde dehydrogenase 1 activity, and mammosphere frequency in MCF-7 and SUM159 cells. Inhibition of bCSC by treatment with DATS was associated with downregulation of EZH2 and Kruppel-like factor 4 proteins in both MCF-7 and SUM159 cells. In conclusion, the present study identifies ER-α and bCSC as novel targets of DATS in mammary cancer cells. This study was supported by the grant RO1 CA113363-09 awarded by the National Cancer Institute. Citation Format: Eun-Ryeong Hahm, Su-Hyeong Kim, Shivendra V. Singh. Estrogen receptor-α and tumor initiating cells are novel targets of diallyl trisulfide in breast cancer cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 227. doi:10.1158/1538-7445.AM2014-227

Stat3-coordinated Lin-28–let-7–HMGA2 and miR-200–ZEB1 circuits initiate and maintain oncostatin M-driven epithelial–mesenchymal transition

Inflammation can act as a crucial mediator of epithelial-to-mesenchymal transition (EMT). In this study, we show that oncostatin M (OSM) is expressed in an autocrine/paracrine fashion in invasive breast carcinoma. OSM stimulation promotes spontaneous lung metastasis of MCF-7 xenografts in nude mice. A conspicuous epigenetic transition was induced by OSM stimulation not only in breast cancer cell lines but also in MCF-7 xenografts in nude mice. The expression of miR-200 and let-7 family members in response to OSM stimulation was downregulated in a signal transducer and activator of transcription factor 3 (Stat3)-dependent manner, resulting in comprehensive alterations of the transcription factors and oncoproteins targeted by these microRNAs. Inhibition of Stat3 activation or the ectopic expression of let-7 and miR-200 effectively reversed the mesenchymal phenotype of breast cancer cells. Stat3 promotes the transcription of Lin-28 by directly binding to the Lin-28 promoter, resulting in the repression of let-7 expression and concomitant upregulation of the let-7 target, high-mobility group A protein 2 (HMGA2). Knock down of HMGA2 significantly impairs OSM-driven EMT. Our data indicate that downregulation of let-7 and miR-200 levels initiates and maintains OSM-induced EMT phenotypes, and HMGA2 acts as a master switch of OSM-induced EMT. These findings highlight the importance of Stat3-coordinated Lin-28B-let-7-HMGA2 and miR-200-ZEB1 circuits in the cytokine-mediated phenotypic reprogramming of breast cancer cells.

Enhanced oral bioavailability and anti‐tumour effect of paclitaxel by 20(s)‐ginsenoside Rg3in vivo

The purpose of this study was to investigate the effect of paclitaxel in combination with 20(s)-ginsenoside Rg3 on its anti-tumour effect in nude mice. In the Caco-2 transport assay, the apparent permeability from the apical side to the basal side (P(app)) (A-B) and P(app) (B-A) of paclitaxel were measured when co-incubated with different concentrations of 20(s)-ginsenoside Rg3. The results indicated that the penetration of paclitaxel through the Caco-2 monolayer from the apical side to the basal side was facilitated by 20(s)-ginsenoside Rg3 in a concentration-dependent manner. Meanwhile, 20(s)-ginsenoside Rg3 inhibited P-glycoprotein (P-gp), and the maximum inhibition was achieved at 80 µM (p < 0.05). The pharmacokinetic parameters of paclitaxel after oral co-administration of paclitaxel (40 mg/kg) with various doses of 20(s)-ginsenoside Rg3 in rats were investigated by an in vivo pharmacokinetic experiment. The results showed that the AUC of paclitaxel co-administered with 20(s)-ginsenoside Rg3 was significantly higher (p < 0.001 at 10 mg/kg) compared with the control. The relative bioavailability (RB) % of paclitaxel with 20(s)-ginsenoside Rg3 was 3.4-fold (10 mg/kg) higher than that of the control. The effect of paclitaxel orally co-administered with 20(s)-ginsenoside Rg3 against human tumour MCF-7 xenografts in nude mice was also evaluated. Paclitaxel (20 mg/kg) co-administered with 20(s)-ginsenoside Rg3 (10 mg/kg) exhibited an effective anti-tumour activity with the relative tumor growth rate (T/C) values of 39.36% (p <0.05). The results showed that 20(s)-ginsenoside Rg3 enhanced the oral bioavailability of paclitaxel in rats and improved the anti-tumour activity in nude mice, indicating that oral co-administration of paclitaxel with 20(s)-ginsenoside Rg3 could provide an effective strategy in addition to the established i.v. route.

Annonacin induces cell cycle-dependent growth arrest and apoptosis in estrogen receptor-α-related pathways in MCF-7 cells

Ethnopharmacological relevanceTamoxifen resistance is common in estrogen receptor-α (ERα)-positive breast cancers. Pawpaw and soursop are anticancer annonaceous plants in complementary medicine. Thus, we studied the effects of annonacin, an annonaceous acetogenin, in breast cancer cells. Materials and MethodsCell growth and ERα-related pathways were studied. The effects of annonacin were tested in MCF-7 xenografts in nude mice. ResultsIn ERα-positive MCF-7 cells, annonacin (half-effective dose ED50=0.31μM) and 4-hydroxytamoxifen (ED50=1.13μM) decreased cell survival whereas annonacin (0.5-1μM) increased cell death at 48h. Annonacin and 4-hydroxytamoxifen were additive in inhibiting cell survival. Annonacin (0.1μM) induced G0/G1 growth arrest while increasing p21WAF1 and p27kip1 and decreasing cyclin D1 protein expression. Annonacin (0.1μM) decreased cyclin D1 protein expression more than 4-hydroxytamoxifen (1μM). Annonacin (0.1μM) increased apoptosis while decreasing Bcl-2 protein expression. The combination of annonacin (0.1μM) and 4-hydroxytamoxifen (1μM) decreased Bcl-2 protein expression and ERα transcriptional activity more than annonacin (0.1μM) did alone. Annonacin, but not 4-hydroxytamoxifen, decreased ERα protein expression. Moreover, annonacin decreased phosphorylation of ERK1/2, JNK and STAT3. In nude mice, annonacin decreased MCF-7 xenograft tumor size at 7–22 days. Moreover, annonacin decreased ERα, cyclin D1 and Bcl-2 protein expression in the xenograft at 22 days. ConclusionsAnnonacin induced growth arrest and apoptosis in ERα-related pathways in MCF-7 cells. Annonacin and 4-hydroxytamoxifen were additive in inhibiting cell survival and ERα transcriptional activity. Moreover, annonacin attenuated MCF-7 xenograft tumor growth while inhibiting ERα, cyclin D1 and Bcl-2 protein expressions in nude mice.

Effects of stealth liposomal daunorubicin plus tamoxifen on the breast cancer and cancer stem cells

The cancer stem cells play an important role in the invasion, metastasis and relapse of cancers as they are resistant to regular chemotherapy. In the present study, stealth liposomal daunorubicin plus tamoxifen was developed for eradicating breast cancer cells together with cancer stem cells. Inhibitory effects were performed on the bulk human breast cancer cells (MCF-7), the sorted MCF-7 cancer stem-like cells (side population, SP), and the sorted MCF-7 cancer cells (NSP), respectively. Antitumor activity and TUNEL analysis were evaluated on the MCF-7 xenografts in nude mice. The encapsulation efficiencies of daunorubicin and tamoxifen were 95% and 90%, respectively. The mean particle size of the stealth liposomes was about 100 nm. Breast cancer stem cells were identified by the specific markers CD44+/CD24-, and isolated from bulk MCF-7 cells. When applying stealth liposomal daunorubicin plus tamoxifen, the inhibitory effects on both the breast cancer cells and the cancer stem cells were significantly increased in vitro, respectively. In the MCF-7 xenografts in mice, stealth liposomal daunorubicin plus tamoxifen showed the most favorable antitumor activity due to the passive targeting the tumor tissue and the synergistic effects in eliminating breast cancer cells and cancer stem cells. Stealth liposomal daunorubicin plus tamoxifen could have the potentials in eliminating both breast cancer cells and cancer stem cells.

A potential target associated with both cancer and cancer stem cells: A combination therapy for eradication of breast cancer using vinorelbine stealthy liposomes plus parthenolide stealthy liposomes

The cancer stem cells play a critical role in both initiation and relapse of the cancers as they are resistant to the most of cytotoxic agents and able to proliferate indefinitely. Vinorelbine stealthy liposomes and parthenolide stealthy liposomes were developed for providing beneficial pharmacological properties and to eradicate cancer stem cells and non-stem cancer cells together by a combination therapy. Cytotoxicity and cancer stem-like cells (side population, SP) identification were performed on human breast cancer cell lines MCF-7 and MDA-MB-231. SP cells were further sorted from MCF-7 cells and characterized. Inhibitory effect was evaluated on the sorted SP and non-SP cells. Antitumor activity was evaluated on MCF-7 xenografts in nude mice. SP cells were identified with a higher percentage in MCF-7 cells (3.8%) and lower in MDA-MB-231 cells (0.6%). Both vinorelbine and parthenolide inhibited the proliferation in MCF-7 and MDA-MB-231 cells. As compared to non-SP cells, inhibitory effect of vinorelbine in the SP cells was lower while a robust inhibitory effect was observed when applying vinorelbine in combination with parthenolide. In the MCF-7 xenografts, stealthy liposomal vinorelbine plus stealthy liposomal parthenolide produced a full inhibitory effect. This combination therapy may provide a potential strategy for eradication of breast cancer by targeting cancer together with cancer stem cells.

Newly identified biologically active and proteolysis-resistant VEGF-A isoform VEGF111 is induced by genotoxic agents

Ultraviolet B and genotoxic drugs induce the expression of a vascular endothelial growth factor A (VEGF-A) splice variant (VEGF111) encoded by exons 1–4 and 8 in many cultured cells. Although not detected in a series of normal human and mouse tissue, VEGF111 expression is induced in MCF-7 xenografts in nude mice upon treatment by camptothecin. The skipping of exons that contain proteolytic cleavage sites and extracellular matrix–binding domains makes VEGF111 diffusible and resistant to proteolysis. Recombinant VEGF111 activates VEGF receptor 2 (VEGF-R2) and extracellularly regulated kinase 1/2 in human umbilical vascular endothelial cells and porcine aortic endothelial cells expressing VEGF-R2. The mitogenic and chemotactic activity and VEGF111's ability to promote vascular network formation during embyonic stem cell differentiation are similar to those of VEGF121 and 165. Tumors in nude mice formed by HEK293 cells expressing VEGF111 develop a more widespread network of numerous small vessels in the peritumoral tissue than those expressing other isoforms. Its potent angiogenic activity and remarkable resistance to proteolysis makes VEGF111 a potential adverse factor during chemotherapy but a beneficial therapeutic tool for ischemic diseases.

Noninvasive Molecular Imaging of MYC mRNA Expression in Human Breast Cancer Xenografts with a [99mTc]Peptide−Peptide Nucleic Acid−Peptide Chimera

Human estrogen receptor-positive breast cancer cells typically display elevated levels of Myc protein due to overexpression of MYC mRNA, and elevated insulin-like growth factor 1 receptor (IGF1R) due to overexpression of IGF1R mRNA. We hypothesized that scintigraphic detection of MYC peptide nucleic acid (PNA) probes with an IGF1 peptide loop on the C-terminus, and a [99mTc]chelator peptide on the N-terminus, could measure levels of MYC mRNA noninvasively in human IGF1R-overexpressing MCF7 breast cancer xenografts in nude mice. We prepared the chelator-MYC PNA-IGF1 peptide, as well as a 4-nt mismatch PNA control, by solid-phase synthesis. We imaged MCF7 xenografts scintigraphically and measured the distribution of [99mTc]probes by scintillation counting of dissected tissues. MCF7 xenografts in nude mice were visualized at 4 and 24 h after tail vein administration of the [99mTc]PNA probe specific for MYC mRNA, but not with the mismatch control. The [99mTc]probes distributed normally to the kidneys, livers, tumors, and other tissues. Molecular imaging of oncogene mRNAs in solid tumors with radiolabel-PNA-peptide chimeras might provide additional genetic characterization of preinvasive and invasive breast cancers.

Tyrosine kinase inhibitors. 18. 6-Substituted 4-anilinoquinazolines and 4-anilinopyrido[3,4-d]pyrimidines as soluble, irreversible inhibitors of the epidermal growth factor receptor.

4-Anilinoquinazoline- and 4-anilinopyrido[3,4-d]pyrimidine-6-acrylamides are potent pan-erbB tyrosine kinase inactivators, and one example (CI-1033) is in clinical trial. A series of analogues with a variety of Michael acceptor units at the 6-position were prepared to define the structural requirements for irreversible inhibition. A particular goal was to determine whether additional functions to increase solubility could be appended to the Michael acceptor. Substituted acrylamides were prepared by direct acylation of the corresponding 6-amines with the requisite acid or acid chloride. Vinylsulfonamide derivatives were obtained by acylation of the amines with chloroethylsulfonyl chloride followed by base-promoted elimination. Vinylsulfone and vinylsulfine derivatives were prepared by oxidation and base elimination of a hydroxyethylthio intermediate. The compounds were evaluated for their inhibition of phosphorylation of the isolated EGFR enzyme and for inhibition of EGF-stimulated autophosphorylation of EGFR in A431 cells and of heregulin-stimulated autophosphorylation of erbB2 in MDA-MB 453 cells. Substitution at the nitrogen of the acrylamide was tolerated only with a methyl group; larger substituents were dystherapeutic, and no substitution at all was tolerated at the acrylamide alpha-carbon. In contrast, while electron-donating groups at the acrylamide beta-carbon were not useful, even quite large electron-withdrawing groups (which increase its electrophilicity) were tolerated. A series of derivatives with solubility-enhancing substituents linked to the acrylamide beta-carbon via amides were potent irreversible inhibitors of isolated EGFR (IC50s = 0.4-1.1 nM), with weakly basic morpholine and imidazole derivatives being the best. Vinylsulfonamides were also potent and irreversible inhibitors, but vinylsulfones and vinylsulfines were reversible and only poorly active. Two compounds were evaluated against A431, H125, and MCF-7 xenografts in nude mice but were inferior in these assays to the clinical trial compound CI-1033.

Apoptotic regression of MCF-7 xenografts in nude mice treated with the vitamin D3 analog, EB1089.

1,25-Dihydroxyvitamin D3 [1,25-(OH)2D3] and its synthetic analog EB1089 induce characteristic morphological features of apoptosis in MCF-7 cells in vitro that coincide with up-regulation of clusterin and cathepsin B, proteins associated with apoptosis in the mammary gland, and with down-regulation of Bcl-2, an antiapoptotic protein. To determine whether vitamin D3 compounds could mediate apoptosis of breast tumors in vivo, we treated nude mice carrying established MCF-7 xenografts with the low calcemic vitamin D3 analog EB1089 via daily injection or sustained release pellets for up to 5 weeks. The volume of tumors from mice treated with 45 pmol/day EB1089 was 4-fold lower than that of tumors from vehicle-treated control mice after 5 weeks. The reduced growth of tumors from EB1089-treated mice was associated with characteristic apoptotic morphology and a marked reduction in the proportion of epithelial cells to stroma. After 5 weeks of treatment with EB1089, MCF-7 tumors exhibited a 6-fold increase in DNA fragmentation (as measured by in situ end labeling) relative to that in control tumors. The enhanced rate of apoptosis in tumors from EB1089-treated mice was coupled to a 2-fold reduction in proliferation (as measured by expression of proliferating cell nuclear antigen) compared with that in tumors from control mice. The antitumor effects of EB1089 were evident at doses that had minimal effects on serum calcium and body weight. EB1089 treatment did not alter the growth of xenografts derived from a vitamin D3-resistant variant of MCF-7 cells (MCF-7(D3Res) cells), which display resistance to EB1089 in vitro, indicating that resistance to EB1089 is maintained in vivo. Tumors derived from both MCF-7 and MCF-7(D3Res) cells underwent apoptotic regression upon estradiol withdrawal, indicating comparable estrogen dependence of tumors with differential sensitivity to vitamin D3 compounds. These are the first studies to demonstrate apoptotic morphology and regression of human breast tumors in response to treatment with a vitamin D3 analog in vivo and support the concept that vitamin D3 compounds can effectively target human breast cancer.

Apoptotic Regression of MCF-7 Xenografts in Nude Mice Treated with the Vitamin D3 Analog, EB1089

Apoptotic Regression of MCF-7 Xenografts in Nude Mice Treated with the Vitamin D3 Analog, EB1089

Human recombinant interferon-?SER and tamoxifen: growth suppressive effects for the human breast carcinoma MCF-7 grown in the athymic mouse

Tamoxifen is the endocrine treatment of choice for breast cancer. However, resistance to therapy and patient relapse inevitably occurs. In future treatment schedules, interferons could be administered with tamoxifen, in an attempt to prevent disease recurrence. Human recombinant interferon-beta SER (rIFN-beta SER) inhibited the growth in vitro of the estrogen receptor (ER) positive breast cancer cell line MCF-7 and the ER negative breast cancer cell line MDA-MB-231. This inhibitory effect was achieved at doses of 50 U/ml and above. The growth of MCF-7 tumors in estradiol-stimulated athymic mice was greatly inhibited by high dose rIFN-beta SER treatment (10(6)U/day). In spite of the impressive antitumor effects upon MCF-7 tumors, rIFN-beta SER had no effect upon ER levels within the tumors at either the RNA or protein level, as measured by Northern blotting and ER-EIA respectively. High dose rIFN-beta SER (10(6)U/day) did result in some inhibition in the growth in vivo of the tamoxifen-stimulated MCF-7 variant MCF-7 TAM, although not to the same extent as was observed with the estradiol-stimulated MCF-7 tumors. rIFN-beta SER was also administered to animals bearing MCF-7 tumors and treated with estradiol and tamoxifen. In the animals undergoing high dose therapy (10(6)U/day), tumor growth was completely suppressed. Furthermore, tumor growth continued to be suppressed in those animals in which the rIFN-beta SER therapy was halted and the tamoxifen capsule removed. No tumors were observed in spite of the environment of estradiol stimulation. Thus, the combination of interferon and tamoxifen was totally growth suppressive for MCF-7 xenografts in nude mice.