In vivo studies of the anti-tumor effects of a human prolactin antagonist, hPRL-G129R.

Previously we demonstrated that a mutated human prolactin (hPRL) with a single amino acid substitution at position 129 (hPRL-G129R) was able to inhibit human breast cancer cell proliferation via the induction of apoptosis. In this study, we report the in vivo anti-tumor effects of hPRL-G129R in nude mice bearing human breast cancer xenografts (T-47D and MCF-7). In an effort to prolong the half-life of the proteins, hPRL or hPRL-G129R were formulated with either growth factor reduced Matrigel or into slow-releasing pellets (custom made 5 mg/5 day release). Initially, nude mice inoculated (s.c.) with T-47D human breast cancer cells were treated with either hPRL or hPRL-G129R formulated with Matrigel. At the end of the 7-week study, it was found that hPRL significantly stimulated the in vivo growth of T-47D xenografts (mean tumor volume, 202 +/- 62 mm(3) as compared to 124 +/- 31 mm(3) in control mice), whereas hPRL-G129R inhibited the tumor growth (mean tumor volume, 79+/-32 mm3). The inhibitory effects of hPRL-G129R were further confirmed in a second experiment using nude mice bearing MCF-7 human breast cancer xenografts and treated with slow-releasing pellets containing hPRL-G129R. Based on these results, we believe that hPRL-G129R can be used to improve the outcome of human breast cancer treatment in the near future.

Quantification of prolactin receptor mRNA in multiple human tissues and cancer cell lines by real time RT-PCR.

Human prolactin (hPRL) has been reported to be involved in breast and prostate cancer development. The hPRL receptor (hPRLR) is expressed in a wide variety of tissues in at least three isoforms. In this study, a one-step real time reverse transcription PCR technique was used to determine relative expression levels of hPRLR mRNA in eleven human breast cancer cell lines, HeLa cells, three prostate cancer cell lines and nine normal human tissues. The housekeeping gene beta-actin was used for internal normalization. We demonstrate that hPRLR mRNA is up-regulated in six of the eleven breast cancer cell lines tested when compared with normal breast tissue. Of the cancer cell lines tested, we found that T-47D cells have the highest level of hPRLR mRNA, followed by MDA-MB-134, BT-483, BT-474, MCF-7 and MDA-MB-453 cells. In two breast cancer cell lines (MDA-MB-468 and BT-549), the hPRLR levels were found to be comparable to that of normal breast tissue. Three breast cancer cell lines (MDA-MB-436, MDA-MB-157 and MDA-MB-231) expressed hPRLR mRNA at levels lower than that of normal tissue. In contrast, in all three commonly used prostate cancer cell lines (LNCaP, PC-3 and DU 145), the levels of hPRLR mRNA were found to be down-regulated relative to that of normal prostate tissue. Of nine normal human tissues tested, we found that the uterus and the breast have the highest levels of hPRLR mRNA, followed by the kidney, the liver, the prostate and the ovary. The levels of hPRLR mRNA were the lowest among the trachea, the brain and the lung.