Toremifene and its metabolites enhance doxorubicin accumulation in estrogen receptor negative multidrug resistant human breast cancer cells

Repurposing ospemifene for potentiating an antigen-specific immune response

OBJECTIVE

Ospemifene, an estrogen receptor agonist/antagonist approved for the treatment of dyspareunia and vaginal dryness in postmenopausal women, has potential new indications as an immune modulator. The overall objective of the present series of preclinical studies was to evaluate the immunomodulatory activity of ospemifene in combination with a peptide cancer vaccine.

METHODS

Immune regulating effects, mechanism of action and structure activity relationships of ospemifene and related compounds were evaluated by examining expression of T-cell activating cytokines in vitro, and antigen-specific immune response and cytotoxic T-lymphocyte activity in vivo. The effects of ospemifene (OSP) on the immune response to a peptide cancer vaccine (PV) were evaluated after chronic [control (n = 22); OSP 50 mg/kg (n = 16); PV (n = 6); OSP+PV (n = 11)], intermittent [control (n = 10); OSP 10 and 50 mg/kg (n = 11); PV (n = 11); combination treatment (n = 11 each dose)] and pretreatment [control; OSP 100 mg/kg; PV 100 μg; combination treatment (n = 8 all groups)] ospemifene oral dosing schedules in a total of 317 mixed-sex tumor-bearing and nontumor-bearing mice.

RESULTS

The results showed that ospemifene induced expression of the key TH1 cytokines interferon gamma and interleukin-2 in vitro, which may be mediated by stimulating T-cells through phosphoinositide 3-kinase and calmodulin signaling pathways. In combination with an antigen-specific peptide cancer vaccine, ospemifene increased antigen-specific immune response and increased cytotoxic T-lymphocyte activity in tumor-bearing and nontumor-bearing mice. The pretreatment, intermittent, and chronic dosing schedules of ospemifene activate naive T-cells, modulate antigen-induced tolerance and reduce tumor-associated, pro-inflammatory cytokines, respectively.

CONCLUSIONS

Taken together, ospemifene's dose response and schedule-dependent immune modulating activity offers a method of tailoring and augmenting the efficacy of previously failed antigen-specific cancer vaccines for a wide range of malignancies.

Activating adaptive cellular mechanisms of resistance following sublethal cytotoxic chemotherapy: implications for diagnostic microdosing

As Phase 0 studies have proven to be reasonably predictive of therapeutic dose pharmacokinetics, the application of microdosing has expanded into metabolism, drug-drug interactions and now diagnostics. One potentially serious issue with this application of microdosing that has not been previously discussed is the possibility of activating cellular mechanisms of drug resistance. Here, we provide an overview of Phase 0 microdosing and drug resistance, with an emphasis on cisplatin resistance, followed by a discussion of the potential for inducing acquired resistance to platinum-based or other types of chemotherapy in cancer patients participating in Phase 0 diagnostic microdosing studies. A number of alternative approaches to diagnostic microdosing, such as the human tumor cloning assay and the use of peripheral blood mononuclear cells as a surrogate for measuring DNA adducts, are discussed that would avoid exposing cancer patients to low doses of first-line chemotherapy and the possible risk of triggering cellular mechanisms of acquired resistance. Until it has been established that diagnostic microdosing in cancer patients poses no risk of acquired drug resistance, such studies should be approached with caution.

Accelerator mass spectrometry allows for cellular quantification of doxorubicin at femtomolar concentrations

Accelerator mass spectrometry (AMS) is a highly sensitive analytical methodology used to quantify the content of radioisotopes, such as (14)C, in a sample. The primary goals of this work were to demonstrate the utility of AMS in determining total cellular [(14)C]anthracycline concentrations following administration of doxorubicin (DOX) and to develop a sensitive assay that is superior to high performance liquid chromatography (HPLC) for the quantification of [(14)C]anthracycline at the tumor level. In order to validate the sensitivity of AMS versus HPLC with fluorescence detection, we performed three studies comparing the cellular accumulation of DOX: one in vitro cell line study, and two in vivo xenograft mouse studies. Using AMS, we quantified cellular [(14)C]anthracycline content up to 4 h following in vitro exposure at concentrations ranging from 0.2 pg/ml (345 fM) to 2 microg/ml (3.45 microM) [(14)C]DOX. The results of this study show that, compared to standard fluorescence-based HPLC, the AMS method was over five orders of magnitude more sensitive. Two in vivo studies compared the sensitivity of AMS to HPLC using a nude mouse xenograft model in which breast cancer cells were implanted subcutaneously. After sufficiently large tumors formed, [(14)C]DOX was administered intravenously at two dose levels. Additionally, we tested the AMS method in a nude mouse xenograft model of multidrug resistance (MDR) in which each mouse was implanted with both wild type and MDR+ cells on opposite flanks. The results of the second and third studies showed that [(14)C]anthracycline concentrations were significantly higher in the wild type tumors compared to the MDR+ tumors, consistent with the MDR model. Although this method does not discriminate between parent drug and metabolites, the extreme sensitivity of AMS should facilitate similar studies in humans to establish target site drug delivery and to potentially determine the optimal treatment dose and regimen.

Paclitaxel after doxorubicin plus cyclophosphamide as adjuvant chemotherapy for node-positive breast cancer: results from NSABP B-28

PURPOSE

The primary aim of National Surgical Adjuvant Breast and Bowel Project (NSABP) B-28 was to determine whether four cycles of adjuvant paclitaxel (PTX) after four cycles of adjuvant doxorubicin/cyclophosphamide (AC) will prolong disease-free survival (DFS) and overall survival (OS) compared with four cycles of AC alone in patients with resected operable breast cancer and histologically positive axillary nodes.

PATIENTS AND METHODS

Between August 1995 and May 1998, 3,060 patients were randomly assigned (AC, 1,529; AC followed by PTX [AC --> PTX], 1,531). Patients > or = 50 years and those younger than 50 years with estrogen receptor (ER) or progesterone receptor (PR) -positive tumors also received tamoxifen for 5 years, starting with the first dose of AC. Postlumpectomy radiotherapy was mandated. Postmastectomy or regional radiotherapy was prohibited. Median follow-up is 64.6 months.

RESULTS

The addition of PTX to AC significantly reduced the hazard for DFS event by 17% (relative risk [RR], 0.83; 95% CI, 0.72 to 0.95; P = .006). Five-year DFS was 76% +/- 2% for patients randomly assigned to AC --> PTX compared with 72% +/- 2% for those randomly assigned to AC. Improvement in OS was small and not statistically significant (RR, 0.93; 95% CI, 0.78 to 1.12; P = .46). Five-year OS was 85% +/- 2% for both groups. Subset analysis of the effect of paclitaxel according to hormone receptors or tamoxifen administration did not reveal statistically significant interaction (for DFS, P = .30 and P = .44, respectively). Toxicity with the AC --> PTX regimen was acceptable for the adjuvant setting.

CONCLUSION

The addition of PTX to AC resulted in significant improvement in DFS but no significant improvement in OS with acceptable toxicity. No significant interaction between treatment effect and receptor status or tamoxifen administration was observed.

The evolving role of specific estrogen receptor modulators (SERMs)

Estrogens are the most effective therapy for women with postmenopausal problems. However, relatively few women use estrogen and then often for a limited time because of the fear of its carcinogenic effects on the uterus and breast; in addition, estrogen is not advised for women who have had breast cancer. Selective estrogen receptor modulators (SERMs) are agents with antagonist action on the uterus and breast and agonist action on the bones, cardiovascular system, and brain. Unlike estrogens, however, existing SERMs do not help alleviate the vasomotor and urogenital problems associated with menopause. A comprehensive review of the literature published from January 1995 to June 1999 was conducted. Reports were identified using Medline and Cancer Lit. The effect of menopausal problems on the health of women and the socioeconomic effects of menopause are discussed. All currently available and investigational SERMs are reviewed and discussed, including their mechanism of action, metabolism, dose scheduling, antitumor activity, and potential role in maintaining the health of menopausal women and in preventing breast cancer.

Cyclophosphamide, adriamycin, 5-fluorouracil and high-dose toremifene for patients with advanced/recurrent breast cancer. The Japan Toremifene Cooperative Study Group

BACKGROUND

Multi-combination chemotherapy consisting of anthracyclines has been effective but has not invariably prolonged the survival period in advanced/recurrent breast cancer. The possibility has been discussed that chemoendocrine therapy combined with endocrine agents is more effective.

METHODS

In order to evaluate the toxicity and efficacy of a new endocrine therapy for advanced/recurrent breast cancer, we ran a pilot study during the period from July 1994 to July 1996.

RESULTS

Twenty-two patients with advanced/recurrent breast cancer were treated with chemoendocrine therapy consisting of cyclophosphamide (100 mg/body) p.o. daily for 14 days, with adriamycin (40 mg/m2) i.v. and 5-fluorouracil (500 mg/body) i.v. on day 1 (repeated every 3 weeks for 9 weeks) (CAF therapy), and high-dose toremifene (120 mg/body) p.o. daily. Of 20 evaluable patients, two showed complete response (10%), eight partial response (40%), six no change (30%) and four progressive disease (20%). The overall response rate was 50%, and the median duration of response was 69.5 days (28-133+ days). The major toxicities were drug-induced alopecia, gastrointestinal toxicity and hematological toxicity, but these were clinically well tolerated. No serious cardiac, liver or renal symptom was seen.

CONCLUSIONS

Based on these results, we consider the addition of high-dose toremifene to the CAF therapy to be useful in the treatment of advanced and recurrent breast cancer.

Toremifene. A review of its pharmacological properties and clinical efficacy in the management of advanced breast cancer

The triphenylethylene antiestrogen toremifene is a chlorinated derivative of the antiestrogen tamoxifen, an agent which has been widely and successfully used in the treatment of breast cancer. Clinical trials investigating the efficacy of toremifene as first-line endocrine therapy in postmenopausal women with advanced breast cancer (estrogen receptor status positive or unknown) have shown this drug to have similar antitumour activity to that of tamoxifen. In multicentre comparative trials, objective responses (complete and partial) occurred in 20 to 29% of patients treated with toremifene (60 to 240 mg/day) and in 19 to 37.5% of tamoxifen (20 or 40 mg/day) recipients. The duration of response, time to disease progression and median overall survival time were generally similar in both treatment groups. Toremifene is well tolerated. Most drug-related adverse effects are mild or moderate in severity and rarely necessitate discontinuation of therapy. The tolerability profile of toremifene is similar to that reported for tamoxifen, the most common adverse effects being hot flushes, sweating, nausea and/or vomiting, dizziness, oedema, and vaginal discharge and/or bleeding. Thus, toremifene provides an equally effective and well tolerated alternative to tamoxifen for the first-line endocrine therapy of postmenopausal advanced breast cancer. Preclinical studies showing toremifene to have a lower carcinogenic potential than tamoxifen indicate that toremifene may be a preferable agent for long term treatment regimens; however, these findings require confirmation in the clinical setting.

Toremifene, a novel antiestrogen, can overcome hsp27-induced drug resistance in human breast cancer cells

Human breast cancer cell lines derived from MDA-MB-231 were constructed to express hsp27 constitutively. The elevated presence of this protein resulted in an enhanced ability to survive a heat shock and exposure to doxorubicin, a chemotherapeutic agent. Hsp27 expression was unable to protect cells from doxorubicin if they were cultured in the presence of toremifene. Flow cytometry analysis indicated that wells exposed to both toremifene and doxorubicin accumulate at G2 + M. Protective effects of hsp27 were overcome by addition of an estrogen antagonist at clinically nontoxic levels. Addition of toremifene to chemotherapeutic regimes may enhance the sensitivity of breast cancer cells to doxorubicin.

High dose toremifene for estrogen and progesterone receptor negative metastatic breast cancer: a phase II trial of the Cancer and Leukemia Group B (CALGB)

In pre-clinical and limited clinical studies, high doses ( > or = 200 mg/day) of the triphenylethylene derivative toremifene showed activity in estrogen receptor (ER) negative and ER-unknown metastatic breast cancer after progression on tamoxifen, and a mechanism of action independent of hormone receptor binding was speculated. The CALGB conducted a Phase II trial (CALGB 8945) to test the efficacy of high dose toremifene in a population of patients who had hormone receptor-negative, metastatic breast cancer with limited prior chemotherapy exposure, good performance status, and measurable disease. Twenty eligible patients received toremifene at a dose of 400 mg/day orally for 8 weeks. Toxicity was minimal. Nausea was reported by 20% of the patients, lightheadedness by 20%, weight loss by 20%, and hot flashes by 15%. There was no grade 3-4 toxicity. No objective responses were observed, and 5 of 6 patients with stable disease at 8 weeks developed progressive disease at 11 to 33 weeks. High dose toremifene (400 mg/day) is well-tolerated but imparts no detectable activity in hormone receptor-negative, metastatic breast cancer.

Comparative study of intracellular calcium and adenosine 3',5'-cyclic monophosphate levels in human breast carcinoma cells sensitive or resistant to Adriamycin: contribution to reversion of chemoresistance

Multidrug resistance (MDR) corresponds to the cross-over resistance of tumour cells to structurally unrelated cytotoxic chemotherapeutic drugs. One of the mechanisms causing this resistance is the enhanced expression of a transmembrane drug efflux pump P-glycoprotein (P-170). Reversal of P-glycoprotein-associated MDR has received much attention in recent years. In experimental cell lines, P-170 and the glutathione redox cycle seem to contribute to this phenomenon; P-170 may be inactivated by calcium and calmodulin antagonists and the glutathione redox cycle altered by buthionine sulphoximine (BSO). Treatment of human MCF-7 breast cancer cells with chemosensitizers (CS), such as verapamil, trifluoperazine or BSO, for 72 hr resulted in an enhanced sensitization of cells to Adriamycin, trifluoperazine being the most potent compound in the reversion of chemoresistance. In these Adriamycin sensitive or resistant cells, treated or not by the CS, the possible role of calcium and cyclic adenosine monophosphate (cAMP) in mediating the reversion of chemoresistance to Adriamycin was investigated. It was found that intracellular calcium was approximately 2-fold higher in resistant than in sensitive cells, the opposite was true for cAMP. Modifications in calcium and cAMP levels were observed in MCF-7 resistant cells after treatment with verapamil and BSO; trifluoperazine had no effect on these two parameters. These results seemed to rule out any implication of calcium and cAMP levels in the contribution of these three chemosensitizers in the mechanisms of reversion of chemoresistance to Adriamycin.

Flow cytometry: potential utility in monitoring drug effects in breast cancer

Flow cytometric analysis of DNA ploidy and S-phase fraction are well recognized prognostic indicators in breast cancer. The present paper deals with the widening of the applications of flow cytometry to monitoring the effectiveness of antiestrogen therapy, detecting clonal selection and emergence of drug resistance, and monitoring chemosensitizing properties of drugs. Antiestrogen activity can be studied by DNA flow cytometry to address clinical research problems such as patient-specific pharmacokinetics, dosing compliance, and acquired antiestrogen resistance. Patient plasma specimens containing various concentrations of triphenylethylenes can be monitored for drug-induced effects using cell cycle measurements and correlated to in vivo drug levels. DNA flow cytometry has also been instrumental in the study of the effects of prolonged low-dose (0.5 microM for > 100 days) tamoxifen treatment on human estrogen receptor negative MDA-MB-231 cells, where it was shown that tamoxifen may significantly alter cell cycle kinetics and tumorigenicity of these cells, selecting a new, more aggressive, and rapidly growing clone. Lastly, it has been shown that the chemosensitizing properties of another triphenylethylene antiestrogen, toremifene, on estrogen receptor negative, multidrug resistant MDA-MB-231-A1 human breast cancer cells can be studied using flow cytometric analysis. Toremifene (and its metabolites N-desmethyltoremifene and toremifene IV) are able to "resensitize" MDA-MB-231-A1 cells to vinblastine and doxorubicin, as reflected in a marked shift of cells to G2/M phase of the cell cycle. Flow cytometry is a widely available technique that might be applied clinically to monitor, at the cellular level, drug effects on tumors, including the modulators of drug resistance.

Targeting chemosensitizing doses of toremifene based on protein binding

Toremifene is currently being evaluated as a chemosensitizing agent in doxorubicin-resistant patients. Although concentrations of > 2 microM reverse resistance in vitro, target concentrations required to reverse multidrug resistance (MDR) in vivo may be highly influenced by variables such as protein binding in serum. We examined the effects of high serum concentrations on the cellular accumulation of toremifene in an MDR MDA-MB-A-1 human breast-cancer cell line. We then examined the cellular accumulation of doxorubicin at various toremifene concentrations in 5% - 100% serum. We also measured the concentrations of toremifene and its major metabolites in plasma specimens obtained from two patients receiving 360 mg/day for 5 days in a phase I study. Our results show that (1) high serum concentrations decrease toremifene accumulation, (2) toremifene concentrations of < or = 2.5 microM enhance doxorubicin accumulation, and (3) patients achieve plasma toremifene concentrations of 10-15 microM following doses of 360 mg/day x 5 days. Our findings suggest that in vivo toremifene concentrations well above those used to reverse resistance in vitro are required to overcome the effect of high serum-protein binding.

Pharmacologic circumvention of multidrug resistance

The ability of malignant cells to develop resistance to chemotherapeutic drugs is a major obstacle to the successful treatment of clinical tumors. The phenomenon multidrug resistance (MDR) in cancer cells results in cross-resistance to a broad range of structurally diverse antineoplastic agents, due to outward efflux of cytotoxic substrates by the mdr1 gene product, P-glycoprotein (P-gp). Numerous pharmacologic agents have been identified which inhibit the efflux pump and modulate MDR. The biochemical, cellular and clinical pharmacology of agents used to circumvent MDR is analyzed in terms of their mechanism of action and potential clinical utility. MDR antagonists, termed chemosensitizers, may be grouped into several classes, and include calcium channel blockers, calmodulin antagonists, anthracycline and Vinca alkaloid analogs, cyclosporines, dipyridamole, and other hydrophobic, cationic compounds. Structural features important for chemosensitizer activity have been identified, and a model for the interaction of these drugs with P-gp is proposed. Other possible cellular targets for the reversal of MDR are also discussed, such as protein kinase C. Strategies for the clinical modulation of MDR and trials combining chemosensitizers with chemotherapeutic drugs in humans are reviewed. Several novel approaches for the modulation of MDR are examined.

Monitoring the chemosensitizing effects of toremifene with flow cytometry in estrogen receptor negative multidrug resistant human breast cancer cells

The clinical study of compounds that modulate multidrug resistance in cancer cells has been hindered by both the toxicities of these agents and the inability to monitor their effectiveness at a cellular level. The non-steroidal triphenylethylene toremifene is well tolerated clinically and can sensitize multidrug resistant cells to the effects of doxorubicin in vitro. The chemosensitizing properties of toremifene in estrogen receptor negative, multidrug resistant MDA-A1 human breast cancer cells were studied using flow cytometric analysis. Cell cycle kinetics of MDA-A1 cells were not significantly affected by treatment with either toremifene or doxorubicin alone, as the majority of cells remained in G0/G1. However, preincubation with toremifene for 70 hours followed by treatment with doxorubicin caused a marked shift of cells to G2, as cells appeared to be blocked in that phase of the cell cycle. This result was nearly identical to the effect of doxorubicin alone on doxorubicin-sensitive MDA-MB-231 breast cancer cells and can be interpreted as a "resensitization" by toremifene of MDA-A1 cells to doxorubicin. This chemosensitizing effect of toremifene was accompanied by an enhanced accumulation of doxorubicin in MDA-A1 cells (+110% after 70 hours pre-incubation with toremifene), and by a depression in protein kinase C activity in MDA-A1 cells that was maximal following 70 hours incubation with toremifene. Flow cytometry is a widely available technique that might be applied clinically to monitor at the cellular level the chemosensitizing effects of toremifene and other modulators of multidrug resistance.