Search

To elucidate the possible roles of proto-oncogenes and growth factors in estrogen-regulated cell proliferation of human breast and gynecologic cancers, we have determined the gene expressions of c-myc, transforming growth factor-alpha and beta 1 (TGF-alpha, beta 1) and epidermal growth factor receptor (EGFR) in a number of these cancer cell lines by using an intron-Differential (ID) RNA/PCR method, which differentially identifies the amplified cDNA from PCR products of genomic DNA contaminants. With this method, we demonstrated the expression of these genes, except EGFR, in an estrogen-dependent breast cancer cell line (CAMA-1). Our results show that TGF-alpha/EGF does not function as an autocrine factor in this cell line. Accordingly, it is unlikely that the TGF-alpha/EGFR system participates as a mediator in the estrogen-induced cell proliferation of CAMA-1 cells. The ID RNA/PCR method is a rapid, sensitive and specific technique for mRNA phenotyping and will have great clinical utility.

In order to test the in vivo effect of prolactin on estrogen receptor (ER) binding capacity in tumors induced by 7,12 dimethylbenz(a)anthrancene (DMBA-tumor), growth of the tumors from changes in prolactin and estrogen levels was compared retrospectively with cytoplasmic ER levels. It was demonstrated that some tumors required prolactin, some needed prolactin-estrogen during their growth period anda small number were not influenced by hormonal milieu. ER was present in hormonally dependent tumors but was low or absent in hormonaly-independent tumors. Deletion of hormones by endocrine ablation in the host rat resulted in tumor regression loss of ER. Replenishment of ER and subsequent tumor growth were accomplished by injection of prolactin or prolactin-estrogen in endocrine ablated rats but were not achieved in rats bearing tumors exposed to prolactin-nafoxidine. Our results demonstrate that both estrogen and prolactin were essential for growth of hormonally dependent DMBA-tumors. Tumor growth was also prevented when cytoplasmic ER was not replenished , indicating that ER may be an indispensable prerequisite for growth. Prolactin, independently of or cooperatively with estrogen, stimulated ER binding capacity. These results support the hypothesis that there may exist a prolactin regulatory mechanism of estrogen action at the tumor site. The interactions of estrogen and prolactin in situ in modulating hormonal receptor binding capacities may contribute to the overall stimulatory effect of these two hormones on DMBA-tumors.

The presence of ER in DMBA-tumors was demonstrated by the use of dextran-charcoal assay, sephadex chromatography, sucrose gradient sedimentation, and organ culture techniques. It was found that tumors have binding sites ranging from 10-13 to 10-15 moles/mg protein, and a dissociation constant of ER 10-9 to 10-10 M. In experiments with tumor explants, prolactin-insulin significantly stimulated ER binding capacity, as compared with control without prolactin. This stimulation was tissue-specific and inhibited by progesterone. Insulin had a synergistic effect on prolactin stimulation of ER. Our results presents a plausible explanation for tumor responses to these hormones in vivo. This interaction of prolactin, estrogen, and progesterone may be a common phenomenon for all estrogen-responsive tissues.

Hormonal influences on dimethylbenz(a)anthracene-induced tumor growth were investigated in detail by endocrine ablation and replacement of hormones. The majority of tumors regressed following ablation and most of them were reactivated by subsequent administrations of estrogen (0.1 to 5 mug) or prolactin (2 mg). Increasing numbers of tumors, however, were not stimulated by prolactin when administration was delayed, and a basal level of estradiol (0.01 mug) in addition to prolactin was required for reactivation of tumors. Nafoxidine hydrochloride, a competitor of estrogen at the receptor sites, arrested growth of a large portion of dimethylbenz(a)anthracene-induced tumors in intact animals but failed to retard growth of prolactin-stimulated tumors. On withdrawal of prolactin-nafoxidine, rapid regression of tumor occurred and readministration of prolactin failed to activate most of the tumors for as long as 28 days. Our results give good supporting evidence that estrogen plays a primary role in tumor growth. The interactions of prolactin and estrogen at tumor sites are necessary for regulatory events related to tumor growth.

The ability of L-dopa to arrest pain can be used to predict objective response of skeletal disease to endocrine ablation or additive therapy. In the present study, 43 patients with painful skeletal metastases were evaluated for the relief of pain by L-dopa, given 250 mg to 500 mg orally every 4 hours for 4 days. Sixteen of the 25 responders to L-dopa had objective response to either previous or later hormonal therapy while all the 18 non-responders did not benefit from endocrine ablation. The results of L-dopa responses also correlated well to the presence of absence of cytoplasmic ER in tumor. These results demonstrate that both tests (L-dopa and ER) are reliable indicators, one complimenting the other, in prognosticating response to endocrine therapy and should be used prior to hormone treatment. Alternative therapy should be considered for patients who are non-responders to the L-dopa test and/or whose tumors contain negligible ER. The long term therapeutic value of L-Dopa, however, is limited.