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The effects of a novel hormonal breast cancer therapy, endoxifen, on the mouse skeleton.

ABSTRACT: Endoxifen has recently been identified as the predominant active metabolite of tamoxifen and is currently being developed as a novel hormonal therapy for the treatment of endocrine sensitive breast cancer. Based on past studies in breast cancer cells and model systems, endoxifen classically functions as an anti-estrogenic compound. Since estrogen and estrogen receptors play critical roles in mediating bone homeostasis, and endoxifen is currently being implemented as a novel breast cancer therapy, we sought to comprehensively characterize the in vivo effects of endoxifen on the mouse skeleton. Two month old ovariectomized C57BL/6 mice were treated with vehicle or 50 mg/kg/day endoxifen hydrochloride via oral gavage for 45 days. Animals were analyzed by dual-energy x-ray absorptiometry, peripheral quantitative computed tomography, micro-computed tomography and histomorphometry. Serum from control and endoxifen treated mice was evaluated for bone resorption and bone formation markers. Gene expression changes were monitored in osteoblasts, osteoclasts and the cortical shells of long bones from endoxifen treated mice and in a human fetal osteoblast cell line. Endoxifen treatment led to significantly higher bone mineral density and bone mineral content throughout the skeleton relative to control animals. Endoxifen treatment also resulted in increased numbers of osteoblasts and osteoclasts per tissue area, which was corroborated by increased serum levels of bone formation and resorption markers. Finally, endoxifen induced the expression of osteoblast, osteoclast and osteocyte marker genes. These studies are the first to examine the in vivo and in vitro impacts of endoxifen on bone and our results demonstrate that endoxifen increases cancellous as well as cortical bone mass in ovariectomized mice, effects that may have implications for postmenopausal breast cancer patients.

SUBMITTER: Gingery A

PROVIDER: S-EPMC4031133 | biostudies-literature | 2014

REPOSITORIES: biostudies-literature

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The effects of a novel hormonal breast cancer therapy, endoxifen, on the mouse skeleton.

Gingery Anne A Subramaniam Malayannan M Pitel Kevin S KS Reese Jordan M JM Cicek Muzaffer M Lindenmaier Laurence B LB Ingle James N JN Goetz Matthew P MP Turner Russell T RT Iwaniec Urszula T UT Spelsberg Thomas C TC Hawse John R JR

PloS one 20140522 5

Endoxifen has recently been identified as the predominant active metabolite of tamoxifen and is currently being developed as a novel hormonal therapy for the treatment of endocrine sensitive breast cancer. Based on past studies in breast cancer cells and model systems, endoxifen classically functions as an anti-estrogenic compound. Since estrogen and estrogen receptors play critical roles in mediating bone homeostasis, and endoxifen is currently being implemented as a novel breast cancer therapy ...[more]

PMID: 24853369

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Project description:As a prodrug, tamoxifen is activated by the P450 enzyme CYP2D6 that is responsible for converting it to the active metabolites, 4-hydroxytamoxifen and endoxifen. Patients with genetic polymorphisms of CYP2D6 may not receive the full benefit of tamoxifen therapy. There is increasing evidence that poor metabolizer patients have lower plasma concentrations of endoxifen and suffer worse disease outcome, although some clinical studies reported no correlation between CYP2D6 polymorphism and tamoxifen therapy outcome. Endoxifen is currently undergoing clinical trials as a potentially improved and more potent SERM (Selective Estrogen Receptor Modulator) for endocrine therapy that is independent of CYP2D6 status in patients. However, direct administration of endoxifen may present the problem of low bioavailability due to its rapid first-pass metabolism via O-glucuronidation. We have designed and synthesized ZB483, a boronic prodrug of endoxifen suitable for oral administration with greatly enhanced bioavailability by increasing the concentration of endoxifen in mouse blood. Our study demonstrated that ZB483 potently inhibited growth of ER+ breast cancer cells in vitro and was efficiently converted to endoxifen in cell culture media by oxidative deboronation. This metabolic conversion is equally efficient in vivo as indicated in the pharmacokinetic study in mice. Moreover, when administered at the same dose, oral ZB483 afforded a 30- to 40-fold higher plasma level of endoxifen in mice than oral administration of endoxifen. The significantly enhanced bioavailability of endoxifen conferred by the boronic prodrug was further validated in an in vivo efficacy study. ZB483 was demonstrated to be more efficacious than endoxifen in inhibiting xenograft tumor growth in mice at equal dosage but more so at lower dosage. Together, these preclinical studies demonstrate that ZB483 is a promising endocrine therapy agent with markedly enhanced bioavailability in systemic circulation and superior efficacy compared to endoxifen.

Project description:Endocrine therapy agents (the selective estrogen receptor (ER) modulators such as tamoxifen or the selective ER down-regulators such as ICI 182,780) are key treatment regimens for hormone receptor-positive breast cancers. While these drugs are very effective in controlling ER-positive breast cancer, many tumors that initially respond well to treatment often acquire drug resistance, which is a major clinical problem. In clinical practice, hormonal therapy agents are commonly used in combination or sequence with radiation therapy. Tamoxifen treatment and radiotherapy improve both local tumor control and patient survival. However, tamoxifen treatment may render cancer cells less responsive to radiation therapy. Only a handful of data exist on the effects of radiation on cells resistant to hormonal therapy agents. These scarce data show that cells that were resistant to tamoxifen were also resistant to radiation. Yet, the existence and mechanisms of cross-resistance to endocrine therapy and radiation therapy need to be established. Here, we for the first time examined and compared radiation responses of MCF-7 breast adenocarcinoma cells (MCF-7/S0.5) and two antiestrogen resistant cell lines derived from MCF-7/S0.5: the tamoxifen resistant MCF-7/TAMR-1 and ICI 182,780 resistant MCF-7/182R-6 cell lines. Specifically, we analyzed the radiation-induced changes in the expression of genes involved in DNA damage, apoptosis, and cell cycle regulation. We found that the tamoxifen-resistant cell line in contrast to the parental and ICI 182,780-resistant cell lines displayed a significantly less radiation-induced decrease in the expression of genes involved in DNA repair. Furthermore, we show that MCF-7/TAMR-1 and MCF-7/182R-6 cells were less susceptible to radiation-induced apoptosis as compared to the parental line. These data indicate that tamoxifen-resistant breast cancer cells have a reduced sensitivity to radiation treatment. The current study may therefore serve as a roadmap to the future analysis of the mechanisms of cross-resistance between hormonal therapy and radiation.

Project description:OBJECTIVE:High-deductible health plans (HDHPs) have become the predominant commercial health insurance arrangement in the US. HDHPs require substantial out-of-pocket (OOP) costs for most services but often exempt medications from high cost sharing. We examined effects of HDHPs on OOP costs and utilization of adjuvant hormonal therapy (AHT), which are fundamental care for patients with breast cancer. METHODS:This controlled quasi-experimental study used claims data (2003-2012) from a large national health insurer. We included 986 women with incident early-stage breast cancer, age 25-64 years, insured by employers that mandated a transition from low-deductible (??$500/year) to high-deductible (??$1000/year) coverage, and 3479 propensity score-matched controls whose employers offered only low-deductible plans. We examined AHT utilization and OOP costs per person-year before and after the HDHP switch. RESULTS:At baseline, the OOP costs for AHT were $40.41 and $36.55 per person-year among the HDHP and control groups. After the HDHP switch, the OOP costs for AHT were $91.76 and $72.98 per person-year among the HDHP and control groups, respectively. AHT OOP costs increased among HDHP members relative to controls but the change was not significant (relative change 13.72% [95% CI -?9.25, 36.70%]). AHT use among HDHP members did not change compared to controls (relative change of 2.73% [95% CI -?14.01, 19.48%]); the change in aromatase inhibitor use was -?11.94% (95% CI -?32.76, 8.88%) and the change in tamoxifen use was 20.65% (95% CI -?8.01, 49.32%). CONCLUSION:We did not detect significant changes in AHT use after the HDHP switch. Findings might be related to modest increases in overall AHT OOP costs, the availability of low-cost generic tamoxifen, and patient awareness that AHT can prolong life and health. Minimizing OOP cost increases for essential medications might represent a feasible approach for maintaining medication adherence among HDHP members with incident breast cancer.

Dataset Information

The effects of a novel hormonal breast cancer therapy, endoxifen, on the mouse skeleton.

Publications

The effects of a novel hormonal breast cancer therapy, endoxifen, on the mouse skeleton.

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