Multidrug resistance in breast cancer--is the jury in yet?

Phase II study of tariquidar, a selective P-glycoprotein inhibitor, in patients with chemotherapy-resistant, advanced breast carcinoma

BACKGROUND

The primary objective of this study was to determine whether addition of the selective P-glycoprotein (P-gp) inhibitor tariquidar (XR9576) to chemotherapy could induce an objective tumor response in patients who previously were resistant to the same agents. The secondary objectives were to evaluate P-gp expression by immunohistochemistry (IHC), to determine functional activity of the P-gp transporter before and after administration of tariquidar with serial technetium-99m ((99m)Tc)-sestamibi scans, and to correlate those parameters with clinical response.

METHODS

Seventeen women with Stage III-IV breast carcinoma were included in the study who progressed (n = 13 women) or had stable disease (n = 4 women) on doxorubicin-containing or taxane-containing chemotherapy regimens. During the study, the same chemotherapy was continued without dose modifications, but tariquidar (150 mg intravenously) was added to the treatment regimen.

RESULTS

Thirty-six percent of patients had P-gp-positive tumors by IHC, and 5 patients (29%) experienced increases > or = 10% in sestamibi uptake (median increase, 40%; range, 10-63%) after the administration of tariquidar. There was one partial response in a patient who had the greatest increase in sestamibi uptake and who also showed inducible P-gp expression. There was one patient who experienced severe doxorubicin/docetaxel-related toxicity after tariquidar was added to her chemotherapy regimen.

CONCLUSIONS

Tariquidar showed limited clinical activity to restore sensitivity to anthracycline or taxane chemotherapy. Functional imaging of the tumor with (99m)Tc-sestamibi scans before and after administration of multidrug-resistance inhibitor may be useful to identify the small subset of patients who could benefit from multidrug-resistance modulation in future trials.

Activation of the MDR1 upstream promoter in breast carcinoma as a surrogate for metastatic invasion

PURPOSE

Activation of the MDR1 upstream promoter (USP) has been described previously in four lymphoblastic leukemia patients, where it is the major MDR1 promoter associated with P-glycoprotein overexpression. We asked whether MDR1 USP-derived transcripts were also present in breast carcinoma and assessed their potential as a biomarker.

EXPERIMENTAL DESIGN

We developed a sensitive method for detecting transcripts derived from the MDR1 USP and used it to identify MDR1 USP-derived transcripts in cell model systems, in 61 breast carcinoma biopsies of the primary tumor, and in isolated malignant epithelial cells both from the primary tumor and from the associated invaded lymph nodes.

RESULTS

The MDR1 USP was not active in several independent leukemic and breast cancer cell lines or nucleated peripheral blood cells (n = 9). However, transcripts derived from the MDR1 USP were detected in some drug-resistant cell lines and a high proportion of primary breast tumors (71.6%; n = 61), whereas they were present at low frequency in normal breast tissue (10%; n = 10). Activation of MDR1 USP was not due to chromosomal amplifications or rearrangements at the MDR1 locus. Transcription from the MDR1 USP correlated with metastatic node invasion [N = 0-3 versus N > 3 (N = number of lymph nodes invaded); Fisher's exact test, P = 0.011] and was detected in malignant epithelial cells from the primary tumor and those that metastasized to the lymph nodes.

CONCLUSIONS

MDR1 USP activation is a surrogate marker for breast carcinoma progression and can be used as a marker to study breast cancer susceptibility.

Neoadjuvant Chemotherapy of Breast Cancer

The use of neoadjuvant chemotherapy in the treatment of breast cancer has been evolving during the past two decades. Fisher's group accomplished the scientific rationale in mouse models in the 1970s. The Milan group was the first to use neoadjuvant therapy in locally advanced breast cancer and also determined that adjuvant sequential doxorubicin with cyclophosphamide/methotrexate/fluorouracil (CMF) offered improved survival when compared to alternating CMF with doxorubicin. Other groups (M. D. Anderson and NSABP) have evaluated similar doxorubicin-based neoadjuvant therapies in locally advanced breast cancer (LABC) and in early disease. These studies have shown an increase in breast-conserving therapy (BCT) and an increase in pathologic complete response (pCR) when neoadjuvant therapy was used. Due to anthracycline resistance, taxanes were added to the doxorubicin-based neoadjuvant chemotherapy regimen with an increase in BCT and pCR than when an anthracycline regimen was used alone. Overall survival has yet to be determined when comparing an anthracycline-based regimen to the same regimen with the addition of a sequential taxane. Therefore, a combined treatment of an anthracycline/cyclophosphamide/taxane regimen is the recommended neoadjuvant chemotherapy for patients with breast cancer.

Inhibition of P-glycoprotein function by XR9576 in a solid tumour model can restore anticancer drug efficacy

Resistance to cancer chemotherapy involves both altered drug activity at the designated target and modified intra-tumour pharmacokinetic properties (e.g. uptake, metabolism). The membrane transporter P-glycoprotein (P-gp) plays a major role in pharmacokinetic resistance by preventing sufficient intracellular accumulation of several anticancer agents. Whilst inhibiting P-gp has great potential to restore chemotherapeutic effectiveness in blood-borne cancers, the situation in solid tumours is less clear. Therefore, the degree of resistance tumours pose to the cytotoxicity of vinblastine and doxorubicin was characterised using the multicellular tumour spheroid model. Tumour spheroids were generated from either drug-sensitive MCF7(WT) breast cancer cells or a resistant P-gp-expressing variant (NCI/ADR(Res)). Drug-induced cytotoxicity in tumour spheroids was measured using an outgrowth assay and compared with that observed in monolayer cultures. As anticipated, the 3-D organisation of MCF7(WT) in tumour spheroids was associated with a reduction in the potency of doxorubicin and vinblastine-i.e. the inherent multicellular resistance phenomenon. In contrast, tumour spheroids from NCI/ADR(Res) cells did not display multicellular resistance. However their constitutive expression of P-gp reduced the potency of both anticancer drugs. Moreover, the highly potent P-gp inhibitor, the anthranilic acid derivative, XR9576, was able to restore the cytotoxic efficacy of both drugs in tumour spheroids comprising NCI/ADR(Res) cells. The results suggest that inhibition of P-gp in solid tumours is achievable and that generation of potent inhibitors will provide a significant benefit towards restoration of chemotherapy in solid tissues.

Neoadjuvant docetaxel in locally advanced breast cancer

Neoadjuvant chemotherapy produces substantial increases in clinical response rates and rates of breast conserving therapy. Pathologic response rate, though generally low, is an important outcome as it is presumably associated with eradication of micrometastatic disease and may likely result in improved outcomes. Anthracyclines have long been considered the most efficacious chemotherapy agents for neoadjuvant therapy of early breast cancer. Unfortunately, not all patients respond to neoadjuvant anthracycline-based chemotherapy. In an effort to improve primary tumor response, docetaxel, an active agent in breast cancer, has been evaluated in the neoadjuvant setting. Several randomized trials, including the NSABP B-27, GEPAR-duo, and the Aberdeen trial, evaluating docetaxel in sequence with a doxorubicin-based neoadjuvant regimen have been reported, with encouraging findings. We designed the Aberdeen trial with two primary aims: (1) to evaluate primary docetaxel in patients that initially fail a neoadjuvant anthracycline-based polychemotherapy regimen, and (2) to compare a docetaxel-based neoadjuvant regimen with a standard anthracycline-based regimen in patients who do respond to the first four cycles of the anthracycline-based regimen. Eligible patients (n = 162) had previously untreated large (> or = 3 cm) or locally advanced (T3, T4, T x N2) breast cancer. All received four cycles of CVAP, after which clinical response was assessed. Responding patients were then randomized to four additional cycles of CVAP or to docetaxel 100 mg/m2 every 3 weeks for four cycles. Patients failing to respond to CVAP received the docetaxel regimen. After the first four cycles of CVAP, the overall response rate (ORR) was 67%. Ultimately, responses were higher in the group randomized to docetaxel compared with those continuing CVAP (cCR: 94% vs. 66%; p = 0.001; pCR 34% vs. 16%; p = 0.04). The addition of docetaxel improved overall survival and disease-free survival for patients responding to four cycles of CVAP as compared with those receiving eight cycles of CVAP. Relative dose intensity was higher and the incidence of severe leukopenia was lower in the group randomized to docetaxel. These data and data from the NSABP B-27 and GEPAR-duo trials strongly support a combined anthracycline/docetaxel regimen in the neoadjuvant setting.

Neoadjuvant chemotherapy in breast cancer: significantly enhanced response with docetaxel

PURPOSE

To compare the efficacy of neoadjuvant (NA) docetaxel (DOC) with anthracycline-based therapy and determine the efficacy of NA DOC in patients with breast cancer initially failing to respond to anthracycline-based NA chemotherapy (CT).

PATIENTS AND METHODS

Patients with large or locally advanced breast cancer received four pulses of cyclophosphamide 1,000 mg/m(2), doxorubicin 50 mg/m(2), vincristine 1.5 mg/m(2), and prednisolone 40 mg (4 x CVAP) for 5 days. Clinical tumor response was assessed. Those who responded (complete response [CR] or partial response [PR]) were randomized to receive further 4 x CVAP or 4 x DOC (100 mg/m(2)). All nonresponders received 4 x DOC.

RESULTS

One hundred sixty-two patients were enrolled; 145 patients completed eight cycles of NA CT. One hundred two patients (66%) achieved a clinical response (PR or CR) after 4 x CVAP. After randomization, 50 patients received 4 x CVAP and 47 patients received 4 x DOC. In patients who received eight cycles of CT, the clinical CR (cCR) and clinical PR (cPR) (94% v 66%) and pathologic CR (pCR) (34% v 16%) response rates were higher (P =.001 and P =.04) in those who received further DOC. Intention-to-treat analysis demonstrated cCR and cPR (85% v 64%; P =.03) and pCR (31% v 15%; P =.06). Axillary lymph node examination revealed residual tumor in 33% of patients who received 8 x CVAP and 38% of patients who received further DOC. In patients who failed to respond to the initial CVAP, 4 x DOC resulted in a cCR and cPR rate of 55% and a pCR rate of 2%. Forty-four percent of these patients had residual tumor within axillary lymph nodes.

CONCLUSION

NA DOC resulted in substantial improvement in responses to DOC.

Y-box factor YB-1 predicts drug resistance and patient outcome in breast cancer independent of clinically relevant tumor biologic factors HER2, uPA and PAI-1

Intrinsic or acquired resistance to chemotherapy is responsible for failure of current treatment regimens in breast cancer patients. The Y-box protein YB-1 regulates expression of the P-glycoprotein gene mdr1, which plays a major role in the development of a multidrug-resistant tumor phenotype. In human breast cancer, overexpression and nuclear localization of YB-1 is associated with upregulation of P-glycoprotein. In our pilot study, we analyzed the clinical relevance of YB-1 expression in breast cancer (n = 83) after a median follow-up of 61 months and compared it with tumor-biologic factors already used for clinical risk-group discrimination, i.e., HER2, urokinase-type plasminogen activator (uPA) and plasminogen activator inhibitor type 1 (PAI-1). High YB-1 expression in tumor tissue and surrounding benign breast epithelial cells was significantly associated with poor patient outcome. In patients who received postoperative chemotherapy, the 5-year relapse rate was 66% in patients with high YB-1 expression. In contrast, in patients with low YB-1 expressions, no relapse has been observed so far. YB-1 expression thus indicates clinical drug resistance in breast cancer. Moreover, YB-1 correlates with breast cancer aggressiveness: in patients not treated with postoperative chemotherapy, those with low YB-1 expression are still free of disease, whereas the 5-year relapse rate in those with high YB-1 was 30%. There was no significant correlation between YB-1 expression and either HER2 expression or uPA and PAI-1 levels. Risk-group assessment achieved by YB-1 differed significantly from that by HER2 or uPA/PAI-1. In conclusion, YB-1 demonstrated prognostic and predictive significance in breast cancer by identifying high-risk patients in both the presence and absence of postoperative chemotherapy, independent of tumor-biologic factors currently available for clinical decision making.

Enhancement of mdr1 gene expression in normal tissue adjacent to advanced breast cancer

In the present study, mdr1 gene expression was investigated by a sensitive reverse transcriptase-PCR assay in advanced breast cancer and in corresponding adjacent normal tissues obtained before and after treatment with primary chemotherapy. Comparatively to normal tissues, a significant induction of mdr1 expression was observed in untreated tumors (p = 0.0222). Similarly, a significant induction of mdr1 expression was revealed when treated samples were compared to untreated counterparts (p = 0.0222), but no differences were detected between tumor and normal samples (p = 0.3199). Noteworthy, a significant induction of mdr1 gene expression occurred in treated normal samples comparatively to untreated ones (p = 0.0037), and this induction was even more important in normal than in tumoral tissue (p = 0.0627). However, neither the basal expression nor the induction of mdr1 were correlated with subsequent response to chemotherapy or with survival. Thus, in agreement with previous reports, our data show that chemotherapy induce mdr1 gene expression in breast cancer cells, but they also indicate that a similar phenomenon occurs in adjacent normal tissues. Therefore, our results strongly suggest that mdr1 gene overexpression is not a characteristic of breast malignant cells, but rather constitutes a general phenomenon occurring both in normal and tumor cells which could explain at least in part the absence of relationship between mdr1 expression and the clinical outcome of breast cancer patients.

Phase II trial of dexverapamil and epirubicin in patients with non-responsive metastatic breast cancer

Agents capable of reversing P-glycoprotein-associated multidrug resistance have usually failed to enhance chemotherapy activity in patients with solid tumours. Based on its toxicity profile and experimental potency, dexverapamil, the R-enantiomer of verapamil, is considered to be promising for clinical use as a chemosensitizer. The purpose of this early phase II trial was to evaluate the effects of dexverapamil on epirubicin toxicity, activity and pharmacokinetics in patients with metastatic breast cancer. A two-stage design was applied. Patients first received epirubicin alone at 120 mg m(-2) i.v. over 15 min, repeated every 21 days. Patients with refractory disease continued to receive epirubicin at the same dose and schedule but supplemented with oral dexverapamil 300 mg every 6 h x 13 doses. The Gehan design was applied to the dexverapamil/epirubicin cohort of patients. Thirty-nine patients were entered on study, 25 proceeded to receive epirubicin plus dexverapamil. Dexverapamil did not increase epirubicin toxicity. The dose intensity of epirubicin was similar when used alone or with dexverapamil. In nine intrapatient comparisons, the area under the plasma concentration-time curve (AUC) of epirubicin was significantly reduced by dexverapamil (mean 2968 vs 1901 microg ml[-1] h[-1], P= 0.02). The mean trough plasma levels of dexverapamil and its major metabolite nor-dexverapamil were 1.2 and 1.5 microM respectively. The addition of dexverapamil to epirubicin induced partial responses in 4 of 23 patients evaluable for tumour response (17%, CI 5-39%, s.e.P 0.079). The remissions lasted 3, 8, 11 and 11+ months. These data suggest that the concept of enhancing chemotherapy activity by adding chemosensitizers may function not only in haematological malignancies but also in selected solid tumours. An increase in the AUC and toxicity of cytotoxic agents does not seem to be a prerequisite for chemosensitizers to enhance anti-tumour activity.