Thomas W. Grunt

Involvement of nuclear steroid/thyroid/retinoid receptors and of protein kinases in the regulation of growth and of c-erbB and retinoic acid receptor expression in MCF-7 breast cancer cells

Nuclear steroid/thyroid/retinoid receptors and c‐erbB membrane receptor tyrosine kinases control epithelial growth and differentiation. Retinoid receptors can dimerize with the vitamin D receptor, the glucocorticoid receptor or the thyroid receptor. Furthermore, multiple c‐erbB receptor dimers have been identified. It has been shown that some of these receptor pathways communicate with each other via cross‐connected regulatory networks. Molecular interactions between retinoid receptors or estrogen receptors (ER) and c‐erbB‐2, and between ER and retinoic acid receptor(RAR)‐α have been reported. Here, we demonstrate the effects of steroids/thyroids/retinoids and of activators of protein kinase A (forskolin, Forsk) and C (12‐O‐tetradecanoylphorbol‐13‐acetate, TPA), on growth and expression of c‐erbB and RARs in MCF‐7 breast cancer cells, which contain high levels of RAR‐α and ‐γ, and which express significant amounts of c‐erbB‐2 and ‐3. All trans‐retinoic acid (tRA), the anti‐estrogen ICI 182 780 (ICI), Forsk and TPA reduced, whereas triiodothyronine and 17β‐estradiol (E2) stimulated cell growth. Flow cytometry revealed that tRA and E2 reduced c‐erbB‐2 and ‐3, whereas tamoxifen, Forsk and TPA up‐regulatedc‐erbB‐2. c‐erbB‐3 was co‐regulated with c‐erbB‐2. Northern analysis demonstrated that RAR‐α was down‐regulated by dexamethasone, ICI, and TPA, whereas vitamin D3 and E2 up‐regulated RAR‐α. RAR‐γ expression was less responsive to such treatment, being reduced only by ICI and Forsk. These data indicate that nuclear receptor and protein kinase signaling communicate with each other and control the expression of RARs and c‐erbB receptors. Efficient growth control requires the coordinated interplay of both receptor systems.

Expression of c-erbB-41HER4 Is Regulated in T47D Breast Carcinoma Cells by Retinoids and Vitamin D31

Abstract Nuclear steroidlretinoid and membrane c-erbB receptor tyrosine kinase signaling control proliferation and differentiation of mammary epithelial cells. Recently, we reported that retinoic acids are efficient repressors of c-erbB-2 and -3, but not of c-erbB-1 gene expression. Here we demonstrate that retinoic acidmediated growth inhibition is accompanied with reduced expression of c-erbB-4EIER4 in T47D breast cancer cells as determined by FACS, Western, and RTPCR. All-trans and 9-cis retinoic acid reduce c-erbB-4 expression to 30%-60% of control, depending on the concentration. Dexamethasone (Dex) is inactive on T47D cell growth and on c-erbB-4 expression. Vitamin D3 (D3), in contrast, acts as a strong inducer, elevating c-erbB-4 expression up to 360% at the protein level and more than twofold at the mRNA, but does not significantly affect cell growth. We conclude that retinoic acids are efficient growth inhibitors and repressors of c-erbB-4 gene expression. Dex is unable to influence cell growth and c-erbB-4, whereas D3 represents a highly efficient inducer of c-erbB-4 expression without affecting cell proliferation.

Octreotide combined with goserelin in the therapy of advanced pancreatic cancer-results of a pilot study and review of the literature

The two hormone analogues octreotide and goserelin have been shown to decelerate growth of human pancreatic cancer in vitro and in vivo. The objective of this pilot study was to investigate the efficacy and toxicity of the combination of these two agents in patients with advanced pancreatic cancer. Octreotide was injected subcutaneously in dosages increasing weekly, starting with 50 μg twice daily, until the level of maintenance therapy of 500 μg three times a day was reached. In addition, 3.8 mg goserelin acetate was administered subcutaneously at monthly intervals. A median of 7 cycles (range 1–27 cycles) were applied; 13 out of 14 patients entered into the study were evaluable for response and all 14 were evaluated for toxicity. In one patient with initially non-resectable pancreatic cancer, systemic therapy yielded a partial remission lasting 9 months. The degree of tumour regression then allowed a consecutive macroscopic radical tumour resection followed by an additional 6 months of no evidence of disease while the same drug combination was continued. In an additional 9 patients, no change of disease was observed, in some cases for a remarkably long time (up to 27 months). Nevertheless, the objective response rate of 7% (95% confidence interval 0±21%) was low. In 5 patients a clear improvement in their performance status was seen soon after the start of therapy; 3 patients showed progression of the disease at first evaluation or earlier and 1 patient was not evaluable at the time of study assessment. According to the product-limit method of Kaplan and Meier, the time to progression was 3.0±1.8 months [median±asymptotic standard error (ASE)] and overall survival was 6.0±1.5 months (median±ASE). Toxicity was rare and only of mild to moderate degree. Overall, the regimen under investigation did not meet the criteria for sufficient antitumoural effectiveness. Nevertheless, this study reinforces the concept that pancreatic cancer is principally responsive to endocrine therapy and therefore the further investigation of hormonal manipulation seems worth while in the future.

Tyrosine kinase signaling pathways control the expression of retinoic acid receptor-α in SK-BR-3 breast cancer cells

Breast carcinomas are frequently characterized by hyperactivated c-erbB receptor tyrosine kinase signaling. Combination of anti-proliferative retinoids with growth-inhibitory c-erbB-specific agents might induce therapeutic benefit. We demonstrate close interactions between the c-erbB and the retinoic acid receptor system in SK-BR-3 breast cancer cells. Epidermal growth factor and heregulin-beta1 activate c-erbB receptors and dose- and time-dependently up-regulate retinoic acid receptor-alpha (RAR-alpha) mRNA. Similar effects have been found for the growth-inhibitory c-erbB-2 receptor tyrosine kinase-activating antibody 4D5 and the tyrosine phosphatase inhibitor orthovanadate. In contrast, the tyrosine kinase-inhibitor herbimycin A reduces tyrosine-specific protein phosphorylation and down-regulates RAR-alpha. Our data demonstrate that the expression of RAR-alpha, which represents a key mediator of the anti-proliferative effects of retinoids in breast cancer cells, is regulated by modulators of tyrosine kinase signaling. The levels of RAR-beta and -gamma mRNAs, however, are not affected by such agents.

In vitro and in vivo evaluation of the combination of cisplatin and its analogue carboplatin for platinum dose intensification in ovarian carcinoma

Background. Cisplatin and its analogue carboplatin have been shown to cause dose‐dependent growth inhibition throughout a wide dose range in the ovarian cancer cell lines OVCAR‐3, 2780, HTB‐77, and CRL‐1572 tested. Cisplatin was 30 times more effective than carboplatin. The combination of both substances led to a less‐than‐synergistic effect, as was revealed by an isobologram in the OVCAR‐3 cell line. Because of the different toxicity pattern, cisplatin and carboplatin theoretically are ideal candidates for combination chemotherapy in platinum‐sensitive tumors.