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Hormonal modulation of plasminogen activator: an approach to prediction of human breast tumor responsiveness
Abstract:
We have determined that the primary reason for the frequently encountered poor survival of human scirrhous breast carcinomas in short-term (4 days) organ culture is mechanical injury to the tumor tissue during explant preparation. It was possible to minimize this injury by preparing 0.5-mm-thick slices using very sharp blades. This resulted in much improved preservation of tissue structure and function, as assessed by histology, DNA content, and enzyme synthesis and secretion. With the exception of insulin, which was always present in the culture medium, exogenous hormones, including estrogen, or serum did not further improve explant preservation. In rodent mammary tumors, growth in vivo and production of the serine protease plasminogen activator (PA) in organ culture are coordinately regulated by hormones, suggesting that PA may be a valuable indicator of tumor hormone responsiveness. We have now tested the effect of estrogen and other hormones on PA secretion in organ cultures of primary human breast carcinomas. We found that: modulation of PA by 17-beta-estradiol (10-8) M) occurred only in carcinomas which were positive for both estrogen and progesterone receptors; of 21 such tumors, 11 (52%) were responsive. Plasminogen activator was not modulated by estradiol in any of the 22 tumors which were negative for one or both receptors; hydrocortisone (10(-7) M) effectively inhibited, and 3,5,3'-L-triiodothyronine (10(-8) M) and adenylate cyclase activators effectively stimulated PA in most breast tumors, regardless of their estrogen and progesterone receptor status. Prolactin (5 micrograms/ml) had no effect when tested alone; urokinase-type PA was found to be the principal PA produced by human breast tumors. Changes in its rate of synthesis and secretion and not in the content of PA inhibitors appeared to be the prevailing mechanism of enzyme regulation by hormones. In summary, short-term organ culture coupled with the use of PA as an index of response appears to be a promising approach to the study of hormone sensitivity of primary human breast carcinomas.
Insights
Minimizing mechanical injury during organ culture preparation improves human breast carcinoma survival. Plasminogen activator (PA) secretion in culture indicates tumor hormone sensitivity, aiding research into breast cancer treatment.
Area of Science:
- Oncology
- Biochemistry
- Cell Biology
Background:
- Poor survival of human scirrhous breast carcinomas in short-term organ culture is often due to mechanical injury during preparation.
- Organ culture is a valuable tool for studying tumor biology and hormone responsiveness.
- Plasminogen activator (PA) is a hormone-regulated enzyme in rodent mammary tumors, suggesting its potential as a biomarker in human breast cancer.
Purpose of the Study:
- To optimize organ culture techniques for human breast carcinomas.
- To investigate the hormonal regulation of plasminogen activator (PA) secretion in primary human breast carcinomas.
- To assess the utility of PA as an indicator of hormone sensitivity in breast cancer.
Main Methods:
- Developed a technique using sharp blades to prepare 0.5-mm-thick tumor slices, minimizing mechanical injury.
- Cultured human breast carcinoma explants for short-term (4 days) in a medium with insulin.
- Measured tissue structure, DNA content, enzyme synthesis/secretion, and specifically plasminogen activator (PA) secretion in response to various hormones (estradiol, hydrocortisone, triiodothyronine, prolactin).
Main Results:
- Minimized mechanical injury significantly improved the preservation of tissue structure and function in organ cultures.
- 17-beta-estradiol modulated PA secretion only in tumors positive for both estrogen and progesterone receptors (11 out of 21).
- Hydrocortisone inhibited PA, while triiodothyronine and adenylate cyclase activators stimulated PA in most tumors, irrespective of receptor status. Prolactin had no effect.
- Urokinase-type PA was the primary form produced, with regulation occurring via synthesis/secretion changes, not inhibitor content.
Conclusions:
- Optimized organ culture methods enhance the viability and function of human breast carcinoma explants.
- PA secretion in organ culture serves as a reliable indicator of hormone sensitivity in human breast carcinomas.
- This approach holds promise for studying hormone sensitivity and developing targeted therapies for breast cancer.