Induction of mitotic cell death by overriding G2/M checkpoint in endometrial cancer cells with non-functional p53

OBJECTIVE

Endometrial tumors with non-functional p53, such as serous uterine endometrial carcinomas, are aggressive malignancies with a poor outcome, yet they have an Achilles' heel: due to loss of p53 function, these tumors may be sensitive to treatments which abrogate the G2/M checkpoint. Our objective was to exploit this weakness to induce mitotic cell death using two strategies: (1) EGFR inhibitor gefitinib combined with paclitaxel to arrest cells at mitosis, or (2) BI2536, an inhibitor of polo-like kinase 1 (PLK1), to block PLK1 activity.

METHODS

We examined the impact of combining gefitinib and paclitaxel or PLK1 inhibitor on expression of G2/M checkpoint controllers, cell viability, and cell cycle progression in endometrial cancer cells with mutant p53.

RESULTS

In cells lacking normal p53 activity, each treatment activated CDC25C and inactivated Wee1, which in turn activated cdc2 and sent cells rapidly through the G2/M checkpoint and into mitosis. Live cell imaging demonstrated irreversible mitotic arrest and eventual cell death. Combinatorial therapy with paclitaxel and gefitinib was highly synergistic and resulted in a 10-fold reduction in the IC50 for paclitaxel, from 14nM as a single agent to 1.3nM in the presence of gefitinib. However, BI2536 alone at low concentrations (5nM) was the most effective treatment and resulted in massive mitotic cell death. In a xenograft mouse model with p53-deficient cells, low dose BI2536 significantly inhibited tumor growth.

CONCLUSIONS

These findings reveal induction of mitotic cell death as a therapeutic strategy for endometrial tumors lacking functional p53.

USA hCG reference service, 10-year report

INTRODUCTION

The USA hCG Reference Service has been dealing with cases of persistent low levels of hCG and gestational trophoblastic diseases for 10years. Here we present the complete experience.

METHODS

Total hCG in serum and urine was measured using the Siemen's Immulite 1000 assay. Hyperglycosylated hCG, nicked hCG, free ss-subunit and ss-core fragment were measured using microtiterplate assays with antibodies B152, B151, FBT11 and B210, respectively.

RESULTS

The USA hCG Reference Service has identified 83 cases of false-positive hCG, 71 cases of aggressive gestational trophoblastic disease (GTD), 52 cases of minimally invasive GTD, 168 cases of quiescent GTD and 22 cases of placenta site trophoblastic tumor (PSTT). In addition, 103 cases of pituitary hCG have been identified, 60 cases of nontrophoblastic tumor, 4 cases of inherited hCG and 2 cases of Munchausen's syndrome. This is 565 cases total. Multiple new methods are described and tested for diagnosing all of these disorders.

CONCLUSIONS

The USA hCG Reference Service experience shows new methods for detecting multiple hCG-related disorders and recommends new approaches for detecting these hCG-related disorders.

Abstract 1795: The Combination of Paclitaxel and Gefitinib Inhibits Endometrial Cancer Cells by Inducing Mitotic Catastrophe: Proof of Principle for Dual Therapy in Endometrial Cancer

Serous uterine endometrial cancer is a lethal disease for which new therapeutic regimens are urgently needed. Combinations of chemotherapeutic agents and small molecule growth factor inhibitors have demonstrated activity in cancers from other sites. Our objective was to determine whether such a combination could be active in serous endometrial cancer cells. The effects of the EGFR inhibitor gefitinib (ZD1839, Iressa) alone, paclitaxel alone, and the combination of both agents on the cell cycle and on cell proliferation were studied using Hec50co cells, a validated model for type II serous endometrial cancer with absent p53. First, we established the IC50 for paclitaxel alone (14 nM) compared to that of paclitaxel and gefitinib in combination (1.3 nM). This 10-fold reduction in the IC50 with dual therapy yielded a combination index of 0.25, strongly suggesting that the paclitaxel and gefitinib combination resulted in synergistic growth inhibition. Sixty-seven percent of the cells treated with paclitaxel and gefitinib arrested in the G2/M phase. This arrest of the cell cycle at G2/M with combination therapy was significantly greater than with single agent treatment alone (p < 0.001) and was associated with inhibition of p38 phosphorylation and the induction of CDC25C phosphatase and Cyclin B1. When induced, these factors abrogate the G2/M checkpoint and result in rapid, premature progression to M phase; this mechanism is particularly active in the setting of absent p53. With rapid progression into M, the cells were highly sensitive to paclitaxel and were killed by the mechanism of mitotic catastrophe. Similar findings were observed in the same cells treated with the combination of paclitaxel and a specific inhibitor of p38, SB203580. Our study suggests that inhibition of EGFR or downstream p38 pathway can abrogate the mitotic stress checkpoint induced by cytotoxic agents targeting microtubules such as paclitaxel. These findings suggest a new therapeutic strategy for the treatment of serous endometrial carcinoma worthy of clinical confirmation.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1795.

Inherited human chorionic gonadotropin

OBJECTIVE

To investigate 405 cases of persistent low concentrations of human chorionic gonadotropin (hCG).

STUDY DESIGN

The USA hCG Reference Service measured total regular hCG, follicle stimulating hormone and luteinizing hormone (LH) with the Siemens (New York, New York) Immulite 1000 assay. Hyperglycosylated hCG, nicked hCG, C-terminal peptide total hCG, intact regular hCG, free beta-subunit and beta-core fragment were measured in manual microtiter plate assays.

RESULTS

Four cases of inherited hCG were identified, with similar hCG production recorded in first degree relatives. All cases produced primarily the regular hCG dimer. In 1 case hCG was detected only in the urine sample.

CONCLUSION

Inherited hCG is disclosed as a source of persistent low concentrations ofhCG. It was assumed that this regular hCG is produced by the pituitary gland, either as excess pituitary production beyond that which occurs alongside the LH peak in every menstrual cycle or as a genetic disorder.

Regulation of signaling phosphoproteins by epidermal growth factor and Iressa (ZD1839) in human endometrial cancer cells that model type I and II tumors

To understand how type I and II endometrial tumors uniquely respond to tyrosine kinase inhibitor treatments, we evaluated the signaling pathways of epidermal growth factor (EGF) receptor (EGFR) under the effects of EGF and Iressa (ZD1839, gefitinib) using Ishikawa H and Hec50co cells that model type I and II endometrial carcinomas, respectively. The cells were assayed for the expression of EGFR and both cell lines express an average of 100,000 EGFR per cell; however, Ishikawa H cells express higher levels of HER-2/neu compared with Hec50co cells (1.38 x 10(5) compared with 2.04 x 10(4), respectively). Using the Kinetworks multi-immunoblotting approach, which profiles 31 signaling phosphoproteins, the most striking result was that Hec50co cells show a higher number of basal phosphorylated sites compared with Ishikawa H cells. Furthermore, we identified targets of Iressa treatment in both cell lines. Iressa, at a dose of 1 micromol/L, blocked the autophosphorylation of EGFR in Ishikawa H and Hec50co cells with some distinctive effects on downstream effectors. Nevertheless, in both cell lines, EGF stimulated and Iressa blocked the major EGFR target mitogen-activated protein kinases extracellular signal-regulated kinase 1 and 2 equally. The high basal phosphorylation of numerous signaling molecules in Hec50co cells that were not inhibited by Iressa indicates that other growth factor pathways are active in addition to EGFR. We conclude that endometrial cancer cells that model type I and II carcinomas have the capacity to respond to EGFR inhibition as a therapeutic strategy; however, the response of the more aggressive type II tumors may be limited by the constitutive activation of other signaling pathways.

A therapeutic model for advanced endometrial cancer: systemic progestin in combination with local adenoviral-mediated progesterone receptor expression

Cancer of the uterine endometrium is a frequent gynecologic malignant disease for which few therapeutic options are available for advanced disease. Progesterone is the normal female hormone that limits growth and proliferation of endometrial cancers; however, progesterone receptors are frequently down-regulated, leading to treatment failures. The current studies explored the effectiveness of adenoviral-mediated progesterone receptor gene transduction in combination with progestin therapy in mouse xenograft models. Pretreatment of cells with progesterone receptor-encoding adenovirus and progestin inhibited the development of s.c. tumors in athymic mice. In the i.p. xenograft model, replacement of both isoforms of progesterone receptor, PRA and PRB, in combination with progestin treatment resulted in a significant 2.6-fold increase in overall survival time compared with control animals. These studies indicate that when progesterone receptor levels are maintained, progestin therapy is effective in limiting tumor growth. Future therapeutic regimens targeted at enhancing progesterone receptor expression have the potential to improve outcomes in women with endometrial cancer.

A therapeutic model for advanced endometrial cancer: Systemic progestin in combination with local adenoviral-mediated progesterone receptor expression

Cancer of the uterine endometrium is a frequent gynecologic malignant disease for which few therapeutic options are available for advanced disease. Progesterone is the normal female hormone that limits growth and proliferation of endometrial cancers; however, progesterone receptors are frequently down-regulated, leading to treatment failures. The current studies explored the effectiveness of adenoviral-mediated progesterone receptor gene transduction in combination with progestin therapy in mouse xenograft models. Pretreatment of cells with progesterone receptor–encoding adenovirus and progestin inhibited the development of s.c. tumors in athymic mice. In the i.p. xenograft model, replacement of both isoforms of progesterone receptor, PRA and PRB, in combination with progestin treatment resulted in a significant 2.6-fold increase in overall survival time compared with control animals. These studies indicate that when progesterone receptor levels are maintained, progestin therapy is effective in limiting tumor growth. Future therapeutic regimens targeted at enhancing progesterone receptor expression have the potential to improve outcomes in women with endometrial cancer.