Abstract: Estrogens induce breast tumor cell proliferation by directly regulating gene expression via the estrogen receptor (ER) transcriptional activity and by affecting growth factor signaling pathways such as mitogen-activated protein kinase (MAPK) and AKT/mammalian target of rapamycin Complex1 (mTORC1) cascades. In this study we demonstrated the preclinical therapeutic efficacy of combining the aromatase inhibitor letrozole with the multi-kinase inhibitor sorafenib in aromatase-expressing breast cancer cell lines. Treatment with letrozole reduced testosterone-driven cell proliferation, by inhibiting the synthesis of estrogens. Sorafenib inhibited cell proliferation in a concentration-dependent manner; this effect was not dependent on sorafenib-mediated inhibition of Raf1, but involved the down-regulation of mTORC1 and its targets p70S6K and 4E-binding protein 1 (4E-BP1). At concentrations of 5-10 muM the growth-inhibitory effect of sorafenib was associated with the induction of apoptosis, as indicated by release of cytochrome c and Apoptosis-Inducing Factor into the cytosol, activation of caspase-9 and caspase-7, and PARP-1 cleavage. Combination of letrozole and sorafenib produced a synergistic inhibition of cell proliferation associated with an enhanced accumulation of cells in the G(0)/G(1) phase of the cell cycle and with a down-regulation of the cell cycle regulatory proteins c-myc, cyclin D1, and phospho-Rb. In addition, longer experiments (12 weeks) demonstrated that sorafenib may be effective in preventing the acquisition of resistance towards letrozole. Together, these results indicate that combination of letrozole and sorafenib might constitute a promising approach to the treatment of hormone-dependent breast cancer.
Abstract: PURPOSE: We have shown previously that tumor infiltration by FOXP3+ regulatory T cells (Treg) is associated with increased relapse and shorter survival of patients with both in situ and invasive breast cancer. Because estrogen regulates Treg numbers in mice and promotes the proliferation of human Tregs, we hypothesized that blocking estrogen receptor-alpha signaling would abrogate Tregs and be associated with response to hormonal therapy and increased survival. EXPERIMENTAL DESIGN: FOXP3+ Tregs were quantified in tumor samples collected at baseline by incisional biopsy and after 6 months at definitive surgery in 83 elderly breast cancer patients (T2-4 N0-1) enrolled in a randomized phase II trial based on 6 months of primary letrozole (2.5 mg/d) or 6 months of letrozole plus oral "metronomic" cyclophosphamide (50 mg/d). RESULTS: Treg number ranged from 0 to 380 (median, 30) before treatment and from 0 to 300 (median, 8) after treatment. There was a significant reduction in Tregs in letrozole and letrozole-cyclophosphamide patients (P < 0.0001 and P < 0.002, respectively) after treatment. Treg number at residual histology was inversely related with response (P < 0.03 and P = 0.50, respectively) and a greater Treg reduction was observed in responding patients (P < 0.03). CONCLUSION: This study suggests that aromatase inhibitors may have an indirect antitumor mechanism of action through reducing Tregs in breast tumors and may be of use in estrogen receptor-alpha-negative tumors in combination with immunotherapy approaches.
Abstract: PURPOSE: We aimed to identify signaling pathways involved in the response and resistance to aromatase inhibitor therapy in patients with breast cancer. PATIENTS AND METHODS: One hundred fourteen women with T2-4 N0-1, estrogen receptor (ER) alpha-positive tumors were randomly assigned to neoadjuvant letrozole or letrozole plus metronomic cyclophosphamide. Twenty-four tumor proteins involved in apoptosis, cell survival, hypoxia, angiogenesis, growth factor, and hormone signaling were assessed by immunohistochemistry in pretreatment samples (eg, caspase 3, phospho- mammalian target of rapamycin, hypoxia-inducible factor 1alpha [HIF-1alpha], vascular endothelial growth factor, mitogen-activated protein kinase [MAPK], phosphorylated epidermal growth factor receptor, phosphorylated ERalpha [pERalpha]). A multivariate generalized linear regression approach was applied using a penalized least-square minimization to perform variable selection and regularization. Ten-fold cross-validation and iterative leave-one-out were employed to validate and test the model, respectively. Tumor size, nodal status, age, tumor grade, histological type, and treatment were included in the analysis. RESULTS: Ninety-one patients (81%) attained a disease response, 48 achieved a complete clinical response (43%) whereas 22 did not respond (19%). Increased pERalpha and decreased p44/42 MAPK were significant factors for complete response to treatment in all leave-one-out iterations. Increased p44/42 MAPK and HIF-1alpha were significant factors for treatment resistance in all leave-one-out iterations. There was no significant interaction between these variables and treatment. CONCLUSION: Activated ERalpha form was an independent factor for sensitivity to chemoendocrine treatment, whereas HIF-1alpha and p44/42 MAPK were independent factors for resistance. Although further confirmatory analyses are needed, these findings have clear potential implications for future strategies in the management of clinical trials with aromatase inhibitors in the breast cancer.
Abstract: The ubiquitin-proteasome system plays a key regulatory role in cellular homeostasis. The inhibition of the 26S proteasome by Bortezomib leads to the accumulation of misfolded proteins, resulting in endoplasmic reticulum stress followed by a coordinated cellular response called unfolded protein response (UPR). Endoplasmic reticulum stress is also a potent inducer of macroautophagy. Bortezomib is a selective and potent inhibitor of the 26S proteasome and is approved for the treatment of multiple myeloma. Clinical trials with Bortezomib have shown promising results for some types of cancers, but not for some others, including those of the breast. In this study, we show that Bortezomib induces the UPR and autophagy in MCF7 breast cancer cells. Surprisingly, Bortezomib did not induce phosphorylation of PERK, a key initial step of the UPR. We show that induction of autophagy by Bortezomib is dependent on the proteasomal stabilisation of ATF4 and up-regulation of LC3B by ATF4. We show that ATF4 and LC3B play a critical role in activating autophagy and protecting cells from Bortezomib-induced cell death. Our experiments also reveal that HDAC6 knockdown results in decreased LC3B protein and reduced autophagy. Our work shows that the induction of autophagy through ATF4 may be an important resistance mechanism to Bortezomib treatment in breast cancer, and targeting autophagy may represent a novel approach to sensitize breast cancers to Bortezomib.
Abstract: The epidermal growth factor receptor (EGFR) is a validated target for therapy in non-small cell lung cancer (NSCLC). Most patients, however, either do not benefit or develop resistance to specific inhibitors of the EGFR tyrosine kinase activity, such as gefitinib or erlotinib. The mammalian target of rapamycin (mTOR) is a key intracellular kinase integrating proliferation and survival pathways and has been associated with resistance to EGFR tyrosine kinase inhibitors. In this study, we assessed the effects of combining the mTOR inhibitor everolimus (RAD001) with gefitinib on a panel of NSCLC cell lines characterized by gefitinib resistance and able to maintain S6K phosphorylation after gefitinib treatment. Everolimus plus gefitinib induced a significant decrease in the activation of MAPK and mTOR signaling pathways downstream of EGFR and resulted in a growth-inhibitory effect rather than in an enhancement of cell death. A synergistic effect was observed in those cell lines characterized by high proliferative index and low doubling time. These data suggest that treatment with everolimus and gefitinib might be of value in the treatment of selected NSCLC patients that exhibit high tumor proliferative activity.
Abstract: PURPOSE: The phosphatidylinositol 3'-kinase (PI3K)/AKT/molecular target of rapamycin (mTOR) pathway is involved in the development of tumor resistance to endocrine therapy in breast cancer cell lines and represents an attractive target for pharmacologic intervention. However, the effects of endocrine therapy with aromatase inhibitors on in vivo expression of this signaling cascade, and its relation to tumor response and patient outcome, is unknown. EXPERIMENTAL DESIGN: PI3K, phospho-AKT (pAKT) and phospho-mTOR were assessed by immunohistochemistry on tumor specimens collected at baseline and after 6 months of treatment in 113 elderly breast cancer patients consecutively enrolled in a randomized phase II trial of primary letrozole therapy and letrozole associated with metronomic cyclophosphamide. RESULTS: Basal expression of the pathway was not significantly correlated with response or patient outcome. Both letrozole alone and letrozole with cyclophosphamide resulted in a significant reduction of PI3K expression (P = 0.02 and P < 0.005, respectively) and phospho-mTOR expression (P = 0.0001 and P = 0.0001, respectively). pAKT showed no change in the letrozole arm, whereas it was significantly decreased in the letrozole plus cyclophosphamide arm (P < 0.005). pAKT expression reduction was associated with a greater response rate (P = 0.05) and greater reduction in Ki67 expression (P = 0.05). Phospho-mTOR expression reduction was associated with a significantly longer disease-free survival in a multivariate analysis (P = 0.02). CONCLUSIONS: Letrozole inhibits key molecules in the PI3K pathway that are important targets of new drugs being developed to overcome resistance. Changes in these molecules may have prognostic significance. These results should be taken into account when planning prospective trials testing up-front aromatase inhibitor with drugs targeting the PI3K/AKT/mTOR signaling pathway.
Abstract: The variability of serum osteoprotegerin (OPG) and soluble RANKL (sRANKL) along the 24-h cycle was assessed in 20 healthy women. No rhythmic variations of serum OPG, sRANKL or sRANKL/OPG ratio were detected as a group phenomenon. Timing of sampling is unlikely to influence the results of measurements of circulating OPG and sRANKL. INTRODUCTION: Physiological bone turnover shows diurnal variations. The aim of the study was to assess variability of OPG and sRANKL serum levels along the 24-h cycle. METHODS: Blood was collected from 20 healthy women (median age 31 years, range 25-65 years) at 4-h intervals between 08:00 and 24:00 and at 2-h intervals between 24:00 and 08:00. Serum albumin, cortisol, osteocalcin (OC), C-terminal telopeptide of type I collagen (CTX), OPG and total sRANKL were measured. Temporal variations were assessed by the COSINOR model. RESULTS: Circadian rhythms of cortisol and albumin documented a normal synchronization within the circadian structure. Serum OC and CTX showed rhythmic variations, peaking at night-time. Rhythmic variations of serum OPG, sRANKL and sRANKL/OPG ratio were not detected as a group phenomenon. On an individual basis, rhythmic changes were detected in ten patients for OPG and eight patients for sRANKL, with very small amplitudes and heterogeneous acrophases. CONCLUSIONS: The absence of consistent rhythmic variations of circulating OPG and sRANKL levels may reflect the absence of rhythmic variations of their expression in the bone microenvironment. Were this the case, the nocturnal rise of bone resorption should be accounted for by different, not RANKL/OPG-mediated factors. Since circulating OPG and sRANKL may derive from sources other than bone, rhythmicity could be masked by non-rhythmic or non-synchronized rhythmic expression in these sources. Timing of sampling is unlikely to influence the results of measurements of circulating OPG and sRANKL.
Abstract: Persistent circadian rhythm of bone turnover in bone metastatic breast cancer suggests greater skeletal retention of bisphosphonates if administered in the night. We assessed differential effects of night vs morning administration of zoledronic acid (ZA) on bone turnover. Forty-four breast cancer patients with bone metastases were randomised to receive intravenous ZA (4 mg) at 1100 or 2300 hours every 28 days for four times. Urinary concentration N-telopeptide of type-I collagen (NTX) and deoxypyridinolines, and serum C-telopeptide of type-I collagen (CTX), bone alkaline phosphatase (ALP), osteocalcin and Parathyroid hormone (PTH) was measured in the morning at baseline and after 4, 7, 14, 28, 56 and 84 days. Urinary ZA concentration was also measured. Zoledronic acid caused significant decreases of NTX and CTX (P<0.001), without any difference in percent changes between night and morning arms. Bone ALP and osteocalcin were also significantly affected by ZA (P=0.001), without any difference between arms. Parathyroid hormone significantly increased in both the arms; PTH increase was lower in the night arm (P=0.001). From the second administration onwards, urinary ZA level was significantly higher in the night arm (P<0.01). Administration of ZA at two opposite phases of the circadian cycle causes similar changes of bone-turnover marker levels, but has differential effects on the level of serum PTH.
Abstract: There are several advantages of administering primary systemic therapy (PST) instead of adjuvant therapy in the management of early breast cancer patients: (a) PST allows for a quantifiable evaluation of the sensitivity or resistance of any treated case and (b) the response assessment offers the opportunity to "cross over" to a different regimen for an individual patient, leading to more flexible, "tailored" therapies. Indeed, these advantages are tenable if one assumes that the primary tumor response serves as a surrogate marker of the efficacy of PST in terms of survival. Unfortunately, this has not yet been validated. The data that are actually available show that both clinical complete response (cCR) and pathological (p)CR have prognostic significance. pCR after chemotherapy has a greater prognostic impact than cCR; however, it is frequently observed in a subset of tumors-such as those that are estrogen receptor negative, are human epidermal growth factor receptor positive, and have elevated proliferative activity-but occurs rarely in their human epidermal growth factor receptor-2/neu counterparts. cCR is more sensitive than pCR, but its assessment presents many hindrances. cCR after chemotherapy can predict early on which tumors are destined to undergo pCR, suggesting a role for this endpoint guiding further treatment decisions early on. The pCR rate in small randomized PST studies comparing chemotherapy with chemotherapy plus trastuzumab was able to predict the difference in survival observed in large, randomized adjuvant trials with a similar study design. Conversely pCR cannot predict the outcome benefit of patients undergoing different hormonal therapies. In conclusion, pCR may be a reliable surrogate endpoint for PST efficacy in a subset of patients undergoing chemotherapy.
Abstract: The central importance of tumour neovascularization has been emphasized by clinical trials using antiangiogenic therapy in breast cancer. This review gives a background to breast tumour neovascularization in in situ and invasive breast cancer, outlines the mechanisms by which this is achieved and discusses the influence of the microenvironment, focusing on hypoxia. The regulation of angiogenesis and the antivascular agents that are used in an antiangiogenic dosing schedule, both novel and conventional, are also summarized.
