Review of recent trials of chemotherapy for advanced breast cancer: studies excluding taxanes

Investigating the discernible and distinct effects of platinum-based chemotherapy regimens for metastatic triple-negative breast cancer on time to progression

Platinum-based chemotherapy regimens are frequently used in patients with triple-negative breast cancer (TNBC). The aim of the current study was to assess whether or not platinum-based chemotherapy is associated with an increased time to progression when compared with non-platinum-based regimens in TNBC and non-TNBC. A retrospective analysis was conducted within a cohort of patients with metastatic breast cancer who received platinum-based chemotherapy at a single institution. Data were collected for up to three lines of treatment for metastatic disease. Time to progression was determined for platinum-based chemotherapy and non-platinum-based regimens for each line of treatment. Adjusted hazard ratios (HRs), together with 95% confidence intervals (CIs) were estimated comparing the time to progression associated with the use of platinum-based chemotherapy versus non-platinum-based regimens. A total of 159 patients were included in the analysis, with 58 diagnosed with TNBC. Among the patients with TNBC, compared with non-platinum-based chemotherapy, no correlation was identified between platinum-based chemotherapy and an improved time to progression [first line: HR, 0.97 (95% CI, 0.40-2.35); second line: HR, 0.91 (95% CI, 0.42-2.01); and third line: HR, 2.83 (95% CI, 0.73-11.03)]. By contrast, patients with non-TNBC appeared to improve with non-platinum-based chemotherapy [first line: HR, 2.57 (95% CI, 1.11-5.99); second line: HR, 1.91 (95% CI, 1.00-3.63); and third line: HR, 1.08 (95% CI, 0.53-2.18)]. Although the present study was limited by the sample size and its observational nature, the results indicated that platinum-based chemotherapy does not offer a discernible or distinct advantage compared with standard regimens in patients with TNBC, and is perhaps less efficacious in patients with non-TNBC.

O6-(4-bromothenyl)guanine reverses temozolomide resistance in human breast tumour MCF-7 cells and xenografts

Tumour resistance to chemotherapy involving methylating agents such as DTIC (dacarbazine) and temozolomide is linked to expression of the DNA repair protein O(6)-alkylguanine-DNA alkyltransferase (MGMT). There is considerable interest in improving the efficacy of such O(6)-alkylating chemotherapy by the prior inactivation of MGMT. We have examined the effect of the modified guanine base, O(6)-(4-bromothenyl)guanine (PaTrin-2, Patrin, Lomeguatrib) on MGMT activity and cell or xenograft tumour growth inhibition by temozolomide in the human breast carcinosarcoma cell line, MCF-7. PaTrin-2 effectively inactivated MGMT in MCF-7 cells (IC(50) approximately 6 nM) and in xenografts there was complete inactivation of MGMT within 2 h of dosing (20 mg kg(-1) i.p.) and only slight recovery by 24 h. MGMT inactivation in a range of murine host tissues varied between complete and approximately 60%, with extensive recovery by 24 h. PaTrin-2 (10 microM) substantially increased the growth inhibitory effects of temozolomide in MCF-7 cells (D(60)=10 microM with PaTrin-2 vs 400 microM without). In MCF-7 xenografts, neither temozolomide (100 mg kg(-1) day(-1) for 5 days) nor PaTrin-2 (20 mg kg(-1) day(-1) for 5 days) had any significant effect on tumour growth. In contrast, the PaTrin-2-temozolomide combination produced a substantial tumour growth delay: median tumour quintupling time was increase by 22 days (P<0.005) without any significant increase in toxicity as assessed from animal weight. A PaTrin-2-temozolomide combination may therefore be beneficial in the treatment of human breast cancers.

Heterogeneity of O6-alkylguanine DNA-alkyltransferase expression in human breast tumours

An important determinant of cellular resistance to chemotherapeutic O6-alkylating agents, which comprise methylating and chloroethylating agents, is the ability of cells to repair alkylation damage at the O6-position of guanine in DNA. This is achieved by a specific DNA repair enzyme O6-alkylguanine DNA-alkyltransferase. In this study O6-alkylguanine DNA-alkyltransferase expression was measured in human breast tumours using both biochemical and immunohistochemical techniques. O6-alkylguanine DNA-alkyltransferase activity was then compared with known clinical prognostic indices to assess the potential role of O6-alkylguanine DNA-alkyltransferase in predicting the behaviour of this common malignancy. The application of both biochemical and immunohistochemical techniques was feasible and practical. Most breast tumours expressed high levels of O6-alkylguanine DNA-alkyltransferase. Immunohistochemical analysis showed marked variation in expression not only between individuals but also within individual tumours, and in the same patient, between metastases and between primary tumour and metastatic site. O6-alkylguanine DNA-alkyltransferase activity in tissue extracts significantly correlated not only with immunohistochemical staining intensity determined by subjective quantitation, but also with measures of protein levels using a computerised image analysis system including mean grey (P<0.001), percentage of cells positive for O6-alkylguanine DNA-alkyltransferase (P<0.001), and integrated optical density (P<0.001). O6-alkylguanine DNA-alkyltransferase expression did not correlate with any of the established clinical prognostic indicators for current treatment regimens. However, immunohistochemical offers a rapid and convenient method for assessing potential utility of O6-alkylating agents or O6-alkylguanine DNA-alkyltransferase inactivating agents in future studies of breast cancer treatment.

Pharmacokinetic interactions of paclitaxel, docetaxel and their vehicles with doxorubicin

BACKGROUND

The combination of doxorubicin (Dx) with paclitaxel or docetaxel is clinically effective but there are concerns regarding the higher incidence of cardiotoxicity of the combination compared with Dx alone. The mechanism of the increased toxicity is still unclear.

PURPOSE

To assess whether there is a pharmacokinetic interaction between paclitaxel, docetaxel or their vehicles and Dx in mice.

MATERIALS AND METHODS

CDF1 male mice were treated with Dx either alone (10 mg/kg i.v.) or in combination with paclitaxel (25 mg/kg) or docetaxel (25 mg/kg) or their vehicles, i.e., cremophor-ethanol-glucose (cremophor) or polysorbate80-ethanol-glucose (polysorbate). Four mice were killed 4, 8 or 24 hours after Dx in each experimental group and Dx was assayed in serum and in heart, liver, kidney and spleen by HPLC.

RESULTS

Four hours after treatment the concentrations of Dx in heart, liver and kidney were much higher in mice concomitantly treated with paclitaxel, docetaxel (dissolved in either cremophor or polysorbate) and cremophor. At subsequent times the differences were modest and only reached statistical significance in a few cases. Dx metabolites were modified by concomitant treatment with taxanes or their vehicles. In particular, the levels of Dx aglycone in liver and kidney were significantly lower in mice treated with the combination than in mice given Dx alone.

CONCLUSIONS

Paclitaxel, docetaxel and cremophor when given together with Dx modify its distribution and metabolism, increasing Dx levels in many tissues including the heart. This might have some bearing on the toxicity of regimens in which Dx is combined with taxanes.