Continuous versus intermittent extended adjuvant letrozole for breast cancer: final results of randomized phase III SOLE (Study of Letrozole Extension) and SOLE Estrogen Substudy.

BACKGROUND: Late recurrences in postmenopausal women with hormone receptor-positive breast cancers remain an important challenge. Avoidance or delayed development of resistance represents the main objective in extended endocrine therapy (ET). In animal models, resistance was reversed with restoration of circulating estrogen levels during interruption of letrozole treatment. This phase III, randomized, open-label Study of Letrozole Extension (SOLE) studied the effect of extended intermittent letrozole treatment in comparison with continuous letrozole. In parallel, the SOLE estrogen substudy (SOLE-EST) analyzed the levels of estrogen during the interruption of treatment. PATIENTS AND METHODS: SOLE enrolled 4884 postmenopausal women with hormone receptor-positive, lymph node-positive, operable breast cancer between December 2007 and October 2012 and among them, 104 patients were enrolled in SOLE-EST. They must have undergone local treatment and have completed 4-6 years of adjuvant ET. Patients were randomized between continuous letrozole (2.5 mg/day orally for 5 years) and intermittent letrozole treatment (2.5 mg/day for 9 months followed by a 3-month interruption in years 1-4 and then 2.5 mg/day during all of year 5). RESULTS: Intention-to-treat population included 4851 women in SOLE (n = 2425 in the intermittent and n = 2426 in the continuous letrozole groups) and 103 women in SOLE-EST (n = 78 in the intermittent and n = 25 in the continuous letrozole groups). After a median follow-up of 84 months, 7-year disease-free survival (DFS) was 81.4% in the intermittent group and 81.5% in the continuous group (hazard ratio: 1.03, 95% confidence interval: 0.91-1.17). Reported adverse events were similar in both groups. Circulating estrogen recovery was demonstrated within 6 weeks after the stop of letrozole treatment. CONCLUSIONS: Extended adjuvant ET by intermittent administration of letrozole did not improve DFS compared with continuous use, despite the recovery of circulating estrogen levels. The similar DFS coupled with previously reported quality-of-life advantages suggest intermittent extended treatment is a valid option for patients who require or prefer a treatment interruption.

The impact and indications for Oncotype DX on adjuvant treatment recommendations when third-party funding is unavailable.

OBJECTIVES: Industry-supported decision impact studies demonstrate that Oncotype Dx (ODX) changes treatment recommendations (TR) in 24-40% of hormone receptor+/HER2- patients. ODX is not reimbursed by third-party payers in Australia, potentially resulting in more selective use. We sought to evaluate the impact of self-funded ODX on TRs. METHODS: Data collected included demographics, tumor characteristics, indication for ODX and pre- and post-recurrence score (RS) TR. Primary endpoint was frequency of TR change and associations with TR change were sought. RESULTS: Eighteen physicians contributed 382 patients (median age 54). A total of 232 (61%) of tumors were T1 and were grade 1, 2 and 3 in 49 (13%), 252 (66%) and 79 (21%). A total of 257 (67%) were node negative. Assay indications were: confirm need for chemotherapy (CT) (36%), confirm omission of CT (40%) and genuine equipoise (24%). RS was low (≤17) in 55%, intermediate (18-31) in 36% and high (≥32) in 9%. Thirty-eight percent of patients had TR change post-ODX. Sixty-five percent of patients recommended CT pre-ODX changed to hormone therapy alone (HT)-more likely if lower grade and if ER and/or PR > 10%. Fourteen percent of patients with pre-ODX TR for HT added CT-more likely if ER and/or PR ≤10% and if Ki67 > 15% Overall, TR for CT decreased from 47% to 24%. CONCLUSION: Patient-funded ODX changed TRs in 38% of patients, de-escalating 65% from CT to HT and adding CT to 14% of those recommended HT. These changes were greater than an industry-funded study suggesting that physicians can identify situations where the assay may influence decisions.

Development of a conceptual model of cancer caregiver health literacy.

Caregivers play a vital role in caring for people diagnosed with cancer. However, little is understood about caregivers' capacity to find, understand, appraise and use information to improve health outcomes. The study aimed to develop a conceptual model that describes the elements of cancer caregiver health literacy. Six concept mapping workshops were conducted with 13 caregivers, 13 people with cancer and 11 healthcare providers/policymakers. An iterative, mixed methods approach was used to analyse and synthesise workshop data and to generate the conceptual model. Six major themes and 17 subthemes were identified from 279 statements generated by participants during concept mapping workshops. Major themes included: access to information, understanding of information, relationship with healthcare providers, relationship with the care recipient, managing challenges of caregiving and support systems. The study extends conceptualisations of health literacy by identifying factors specific to caregiving within the cancer context. The findings demonstrate that caregiver health literacy is multidimensional, includes a broad range of individual and interpersonal elements, and is influenced by broader healthcare system and community factors. These results provide guidance for the development of: caregiver health literacy measurement tools; strategies for improving health service delivery, and; interventions to improve caregiver health literacy.

Unmet needs and depression among carers of people newly diagnosed with cancer.

AIMS: The aims of this analysis were to examine levels of unmet needs and depression among carers of people newly diagnosed with cancer and to identify groups who may be at higher risk, by examining relationships with demographic characteristics. METHODS: One hundred and fifty dyads of people newly diagnosed with cancer and their carers, aged 18 years and older, were recruited from four Australian hospitals. People with cancer receiving adjuvant cancer treatment with curative intent, were eligible to participate. Carers completed the Supportive Care Needs Survey-Partners & Caregivers (SCNS-P&C45), and both carers and patients completed the Centre of Epidemiologic-Depression Scale (CES-D). RESULTS: Overall, 57% of carers reported at least one, 37% at least three, 31% at least five, and 15% at least 10 unmet needs; the most commonly endorsed unmet needs were in the domains of information and health care service needs. Thirty percent of carers and 36% of patients were at risk of clinical depression. A weak to moderate positive relationship was observed between unmet needs and carer depression (r=0.30, p<0.001). Carer levels of unmet needs were significantly associated with carer age, hospital type, treatment type, cancer type, living situation, relationship status (in both uni- and multi-factor analysis); person with cancer age and carer level of education (in unifactor analysis only); but not with carer gender or patient gender (in both uni- and multi-factor analyses). CONCLUSION: Findings highlight the importance of developing tailored programmes to systematically assist carers who are supporting patients through the early stages of cancer treatment.

Neoadjuvant chemotherapy with sequential anthracycline-docetaxel with gemcitabine for large operable or locally advanced breast cancer: ANZ 0502 (NeoGem).

BACKGROUND: Neoadjuvant chemotherapy has a sound rationale for use in women with large operable breast cancer, and achievement of pathological complete response (pCR) is prognostic. Epirubicin and cyclophosphamide followed by docetaxel is a standard chemotherapy regimen for early breast cancer. In metastatic breast cancer the combination of gemcitabine and a taxane has shown promising results. This phase II study investigated the efficacy and safety of incorporating gemcitabine into neoadjuvant therapy. METHODS: Female patients with operable breast cancer that was clinically T2 (≥3 cm) or T3-4, N0-1, M0 were enrolled to receive 24 weeks of neoadjuvant chemotherapy using epirubicin and cyclophosphamide followed by docetaxel and gemcitabine, plus trastuzumab if HER2-positive. The primary endpoint was the pathological complete response (pCR) rate in the breast in separate HER2-negative and HER2-positive cohorts. Secondary endpoints included pCR in both the breast and axillary lymph nodes, clinical and radiological response rates, disease free survival and safety. RESULTS: 81 patients were enrolled: 63 HER2-negative and 18 HER2-positive. 67 (84%) completed all cycles of chemotherapy, and 78 (96%) proceeded to surgery. pCR was achieved by 12 (20%) patients with HER2-negative, and 9 (53%) with HER2-positive disease. At the first interim analysis, addition of prophylactic G-CSF was recommended due to excess neutropenia. The HER2-negative cohort was closed to accrual because it did not meet the pre-specified target for pCR, and the HER2-positive cohort was closed due to slow accrual. At a median follow-up of 24 months, 12 of 81 (15%) patients had experienced a relapse of their breast cancer. CONCLUSION: Neoadjuvant gemcitabine, when added to docetaxel, after epirubicin and cyclophosphamide, did not reach the pre-specified expectations for pCR rate in HER2-negative tumours. Excess neutropenia was observed, requiring growth factor support. Addition of gemcitabine to docetaxel in this schedule cannot be recommended. Australia and New Zealand Clinical Trials Registry (www.anzctr.org.au) registration number ACTRN12606000191594.

Aromatase inhibitors associated with knee subchondral bone expansion without cartilage loss.

BACKGROUND: The profound estrogen depletion caused by aromatase inhibitors (AIs) is associated with musculoskeletal symptoms, but the underlying pathophysiology remains unclear. OBJECTIVE: To assess the effects of AI therapy on structural changes in knee cartilage and subchondral bone over 2 years in postmenopausal women. Setting and participants Thirty women with breast cancer, mean age 58.5 (standard deviation ± 5.6) years and 62 healthy controls, mean age 56.5 (standard deviation ± 4.6) years. MAIN OUTCOME MEASURES: Annualized changes in tibial cartilage volume and subchondral bone area, and worsening of tibiofemoral cartilage defects from paired knee magnetic resonance imaging 2 years apart were compared between the two groups. RESULTS: The AI-treated women had significantly greater expansion of the tibial plateau than the control group. The mean annualized differences, after adjusting for age, body mass index and baseline bone area, were 22.1 mm(2) (95% confidence interval (CI) 7.6-36.6, p = 0.003) for the medial tibial plateau and 19.1 mm(2) (95% CI 9.6-28.5, p < 0.001) for the lateral tibial plateau. The annual change in tibial cartilage volume and the worsening of cartilage defects did not differ between women taking AI therapy and controls. CONCLUSIONS: AI therapy is associated with knee subchondral bone expansion knee with no effect on knee cartilage in postmenopausal women without pre-existing joint symptoms. This suggests the effect of severe estrogen depletion on knee is on bone, with the tibial bone expansion most likely a response to mechanical load in the setting of bone loss. Whether this then results in an increased risk of knee osteoarthritis will need to be determined.

Cardiac safety of adjuvant pegylated liposomal doxorubicin with concurrent trastuzumab: a randomized phase II trial.

BACKGROUND: The cardiac safety of trastuzumab concurrent with pegylated liposomal doxorubicin (PLD) in an adjuvant breast cancer treatment regimen is unknown. PATIENTS AND METHODS: Women with resected node-positive or intermediate-risk node-negative HER2 overexpressing breast cancer and baseline left ventricular ejection fraction (LVEF)≥55% were randomized (1:2) to doxorubicin 60 mg/m2 (A)+cyclophosphamide 600 mg/m2 (C) every 21 days (q21d) for four cycles or PLD 35 mg/m2+C q21d+trastuzumab 2 mg/kg weekly (H) for 12 weeks. Both groups then received paclitaxel (Taxol, T) 80 mg/m2 with H for 12 weeks followed by H to complete 1 year. The primary end point was cardiac event rate or inability to administer 1 year of trastuzumab. RESULTS: Of 181 randomized patients, 179 underwent cardiac analysis. The incidence of cardiac toxicity or inability to administer trastuzumab due to cardiotoxicity was 18.6% [n=11; 95% confidence interval (CI) 9.7% to 30.9%] with A+C→T+H and 4.2% (n=5; 95% CI 1.4% to 9.5%) with PLD+C+H→T+H (P=0.0036). All events, except one, were asymptomatic systolic dysfunction or mildly symptomatic heart failure. Mean absolute LVEF reduction at cycle 8 was greater with doxorubicin (5.6% versus 2.1%; P=0.0014). CONCLUSION: PLD+C+H→T+H is feasible and results in lower early cardiotoxicity rates compared with A+C→T+H.

Management of breast cancer with nanoparticle albumin-bound (nab)-paclitaxel combination regimens: a clinical review.

BACKGROUND: Monotherapy with nanoparticle albumin-bound (nab)-paclitaxel has demonstrated improved efficacy and safety compared with solvent-based paclitaxel and docetaxel. DESIGN: A comprehensive review of all reported studies of nab-paclitaxel combinations with other agents in all breast cancer settings was undertaken. RESULTS: Most studies reviewed are small, phase II and non-comparative. Combinations studied included nab-paclitaxel plus trastuzumab and/or bevacizumab (with or without additional cytotoxic agents), gemcitabine, capecitabine, carboplatin, or lapatinib. The majority of metastatic and neoadjuvant studies demonstrated satisfactory efficacy and safety for nab-paclitaxel combinations, although conclusions regarding comparison with solvent-based taxane (SBT) regimens are not possible. The two adjuvant studies confirmed the safety of nab-paclitaxel combinations in this setting. CONCLUSIONS: Although results of this review indicate that nab-paclitaxel may be an appropriate substitute for SBTs in combination regimens, additional research is required to confirm the place and cost effectiveness of these combinations before nab-paclitaxel could be recommended routinely in all settings.

Molecular interactions between breast cancer cells and the bone microenvironment drive skeletal metastases.

Breast cancer cells preferentially spread to bone. Bone metastases are currently incurable and therefore better treatments need to be developed. Metastasis is an inefficient, multi-step process. Specific aspects of both breast cancer cells and the bone microenvironment contribute to the development of bone metastases. Breast cancers express chemokine receptors, integrins, cadherins, and bone-resorbing and bone-forming factors that contribute to the successful and preferential spread of tumor to bone. Bone is rich in growth factors and cell types that make it a hospitable environment for breast cancer growth. Once breast cancer cells enter the bone, a highly complex vicious cycle develops, in which breast cancer cells secrete factors that act on bone cells and other cells within the bone (stem cells, T cells, platelets, adipocytes, fibroblasts, and endothelial cells), causing them to secrete factors that act on adjacent cancer cells. The steps in the metastatic cascade and the vicious cycle within bone offer unique targets for adjuvant treatments to treat and cure bone metastases.

Tumor-bone cellular interactions in skeletal metastases.

Human tumor cells inoculated into the arterial circulation of immunocompromised mice can reliably cause bone metastases, reproducing many of the clinical features seen in patients. Animal models permit the identification of tumor-produced factors, which act on bone cells, and of bone-derived factors. Local interactions stimulated by these factors drive a vicious cycle between tumor and bone that perpetuates skeletal metastases. Bone metastases can be osteolytic, osteoblastic, or mixed. Parathyroid hormone-related protein, PTHrP, is a common osteolytic factor, while vascular endothelial growth factor and interleukins 8 and 11 also contribute. Osteoblastic metastases can be caused by tumor-secreted endothelin-1, ET-1. Other potential osteoblastic factors include bone morphogenetic proteins, platelet-derived growth factor, connective tissue growth factor, stanniocalcin, N-terminal fragments of PTHrP, and adrenomedullin. Osteoblasts are the main regulators of osteoclasts, and stimulation of osteoblast proliferation can increase osteoclast formation and activity. Thus, combined expression of osteoblastic and osteolytic factors can lead to mixed metastases or to increased osteolysis. Prostate-specific antigen is a protease, which can cleave PTHrP and thus change the balance of osteolytic versus osteoblastic responses to metastatic tumor cells. Bone itself stimulates tumor by releasing insulin-like growth factors and transforming growth factor-beta. Secreted factors transmit the interactions between tumor and bone. They provide novel targets for therapeutic interactions to break the vicious cycle of bone metastases. Clinically approved bisphosphonate anti-resorptive drugs reduce the release of active factors stored in bone, and PTHrP-neutralizing antibody, inhibitors of the RANK ligand pathway, and ET-1 receptor antagonist are in clinical trials. These adjuvant therapies act on bone cells, rather than the tumor cells. Recent gene array experiments identify additional factors, which may in the future prove to be clinically important targets.

The crystal structure of human phosphoglucose isomerase at 1.6 A resolution: implications for catalytic mechanism, cytokine activity and haemolytic anaemia.

Phosphoglucose isomerase (PGI) is a multifunctional protein, which, inside the cell, functions as a housekeeping enzyme of glycolysis and gluconeogenesis and, outside the cell, exerts wholly unrelated cytokine properties. We have determined the structure of human PGI to a resolution of 1.6 A using X-ray crystallography. The structure is highly similar to other PGIs, especially the architecture of the active site. Fortuitous binding of a sulphate molecule from the crystallisation solution has facilitated an accurate description of the substrate phosphate-binding site. Comparison with both native and inhibitor-bound rabbit PGI structures shows that two loops move closer to the active site upon binding inhibitor. Interestingly, the human structure most closely resembles the inhibitor-bound structure, suggesting that binding of the phosphate moiety of the substrate may trigger this conformational change. We suggest a new mechanism for catalysis that uses Glu357 as the base catalyst for the isomerase reaction rather than His388 as proposed previously. The human PGI structure has also provided a detailed framework with which to map mutations associated with non-spherocytic haemolytic anaemia.

Reproductive tissue renin gene expression in preeclampsia.

OBJECTIVE: Using an analogy with renin gene overexpression, low-renin hypertension animal models, we wished to test the hypothesis that renin gene expression is increased in decidua basalis in human gestation with preeclampsia. METHODS: Human placentas were obtained immediately after delivery from 11 control (C) and 11 preeclamptics (PE). Tissue samples were microdissected and renin gene expression in decidua basalis (DB), chorionic villi (CV), and decidua vera (DV) was measured using dot-blot hybridization. RESULTS: Overall renin gene expression is highest in decidua basalis (mean +/- SEM, 2.66 +/- 0.69 densitometry area units) compared to chorionic villi (mean +/- SEM, 1.85 +/- 0.5) or compared to decidua vera (mean +/- SEM, 1.63 +/- 0.9) (both t-tests p = 0.001 two-tailed and analysis of variance p = 0.0001). Renin gene expression in DB and in CV was similar in both preeclamptic and normal pregnancies (DB mean +/- SEM C 2.79 +/- 0.96 versus PE 2.54 +/- 1.04, and CV mean +/- SEM C 2.11 +/- 0.91 versus PE, 1.59 +/- 0. 44). Renin gene expression in DV was approximately threefold higher in tissues from preeclamptics compared to control (mean +/- SEM PE 2. 44 +/- 1.76 versus C 0.82 +/- 0.42). Using the median value of 0.5 units for DV as cutoff, the preeclamptics displayed higher renin gene expression (chi square p = 0.033, two tailed). CONCLUSION: Our data suggest that renin gene expression is increased in preeclampsia in decidua vera. This may explain previously reported increased renin secretion in uterine circulation in preeclampsia.

Transcriptional activation of cathepsin D gene expression by growth factors.

Insulin-like growth factor-I (IGF-I), transforming growth factor alpha (TGFalpha) and epidermal growth factor (EGF) induced cathepsin D gene expression and reporter gene activity in MCF-7 human breast cancer cells transiently transfected with a construct (pCD1) containing a -2576 to -124 cathepsin D gene promoter insert. In contrast, IGF-I, but not TGFalpha or EGF, induced reporter gene activity in cells cotransfected with wild-type estrogen receptor (ER) expression plasmid and a construct (pCD2) containing estrogen-responsive downstream elements from -208 to -101. Promoter deletion and mutational analysis experiments identified four GC-rich sites and an imperfect palindromic estrogen responsive element required for IGF-I activation of the ER (ligand-independent). Subsequent studies with the mitogen-activated protein kinase (MAPK) inhibitor, PD98059, and a serine(118(-ER mutant confirmed the role of the MAPK pathway for IGF-I activation of the ER in MCF-7 cells. Thus, growth factor activation of ER can mediate transactivation vs ER/Sp1 binding to GC-rich sites and represents a novel pathway for ligand-independent ER action. The divergent pathways for IGF-I and TGFalpha/EGF activation of the ER observed in MCF-7 cells contrast with previous data indicating that pathways for growth factor activation of the ER are dependent on the gene and/or gene promoter and on cell context.

Rabbit phosphoglucose isomerase/neuroleukin/autocrine motility factor: cloning via interspecies identity.

Phosphoglucose isomerase is the first committed enzyme of glycolysis. The protein also has a variety of biological activities on mammalian cells. The molecular basis of these extracellular functions is unclear, and the high resolution three-dimensional structure of a mammalian enzyme has not been described. We report here the cDNA and protein sequence for phosphoglucose isomerase from rabbit muscle. The sequence was obtained directly by PCR without the need to screen clones from a cDNA library and encoded active enzyme when expressed in bacterial cells. The 558 amino acid rabbit coding sequence is the same length as and highly similar (92% residue identity) to the sequences from human and pig and less so (88%) to the mouse enzyme. Non-conservative amino acid changes between the four mammalian sequences are concentrated in the first 35 and last five residues. The rabbit protein has an additional Cys residue and amino acid changes at five positions otherwise invariant in the mammalian enzymes.

Molecular mechanisms of tumor-bone interactions in osteolytic metastases.

In patients with advanced disease, several cancer types frequently metastasize to the skeleton, where they cause bone destruction. Osteolytic metastases are incurable and cause pain, hypercalcemia, fracture, and nerve compression syndromes. It was proposed over a century ago that certain cancers, such as that of the breast, preferentially metastasize to the favorable microenvironment provided by bone. Bone matrix is a rich store of immobilized growth factors that are released during bone resorption. Histological analysis of osteolytic bone metastases indicates that the bone destruction is mediated by the osteoclast rather than directly by the tumor cells. These observations suggest a vicious cycle driving the formation of osteolytic metastases: tumor cells secrete factors stimulating osteoclasts through adjacent bone marrow stromal cells; osteoclastic resorption in turn releases growth factors from the bone matrix; finally, locally released growth factors activate the tumor cells. This vicious cycle model has now been confirmed at the molecular level. In particular, transforming growth factor beta (TGF3beta) is abundant in bone matrix and released as a consequence of osteoclastic bone resorption. Bone-derived TGFbeta plays an integral role in promoting the development and progression of osteolytic bone metastases by inducing tumor production of parathyroid hormone-related protein (PTHrP), a known stimulator of osteoclastic bone resorption. In breast cancer cells TGFbeta appears to stimulate PTHrP secretion by a posttranscriptional mechanism through both Smad and p38 mitogen activated protein (MAP) kinase signaling pathways. Osteolytic metastases can be suppressed in vivo by inhibition of bone resorption, blockade of TGFbeta signaling in tumor cells, and by neutralization of PTHrP. Other factors released from bone matrix may also act on tumor cells in bone, which in turn may produce other factors that stimulate bone resorption, following the vicious cycle paradigm established for TGFbeta and PTHrP. An understanding at the molecular level of the mechanisms of osteolytic metastasis will result in more effective therapies for this devastating complication of cancer.

NH2-terminal sequence truncation decreases the stability of bovine rhodanese, minimally perturbs its crystal structure, and enhances interaction with GroEL under native conditions.

The NH2-terminal sequence of rhodanese influences many of its properties, ranging from mitochondrial import to folding. Rhodanese truncated by >9 residues is degraded in Escherichia coli. Mutant enzymes with lesser truncations are recoverable and active, but they show altered active site reactivities (Trevino, R. J., Tsalkova, T., Dramer, G., Hardesty, B., Chirgwin, J. M., and Horowitz, P. M. (1998) J. Biol. Chem. 273, 27841-27847), suggesting that the NH2-terminal sequence stabilizes the overall structure. We tested aspects of the conformations of these shortened species. Intrinsic and probe fluorescence showed that truncation decreased stability and increased hydrophobic exposure, while near UV CD suggested altered tertiary structure. Under native conditions, truncated rhodanese bound to GroEL and was released and reactivated by adding ATP and GroES, suggesting equilibrium between native and non-native conformers. Furthermore, GroEL assisted folding of denatured mutants to the same extent as wild type, although at a reduced rate. X-ray crystallography showed that Delta1-7 crystallized isomorphously with wild type in polyethyleneglycol, and the structure was highly conserved. Thus, the missing NH2-terminal residues that contribute to global stability of the native structure in solution do not significantly alter contacts at the atomic level of the crystallized protein. The two-domain structure of rhodanese was not significantly altered by drastically different crystallization conditions or crystal packing suggesting rigidity of the native rhodanese domains and the stabilization of the interdomain interactions by the crystal environment. The results support a model in which loss of interactions near the rhodanese NH2 terminus does not distort the folded native structure but does facilitate the transition in solution to a molten globule state, which among other things, can interact with molecular chaperones.

Properties of soluble fusions between mammalian aspartic proteinases and bacterial maltose-binding protein.

The mammalian aspartic proteinases procathepsin D and pepsinogen form insoluble inclusion bodies when expressed in bacteria. They become soluble but nonnative when synthesized as fusions to the carboxy terminus of E. coli maltose-binding protein (MBP). Since these nonnative states of the two aspartic proteinases showed no tendency to form insoluble aggregates, their biophysical properties were analyzed. The MBP portions were properly folded as shown by binding to amylose, but the aspartic proteinase moieties failed to bind pepstatin and lacked enzymatic activity, indicating that they were not correctly folded. When treated with proteinase K, only the MBP portion of the fusions was resistant to proteolysis. The fusion between MBP and cathepsin D had increased hydrophobic surface exposure compared to the two unfused partners, as determined by bis-ANS binding. Ultracentrifugal sedimentation analysis of MBP-procathepsin D and MBP-pepsinogen revealed species with very large and heterogeneous sedimentation values. Refolding of the fusions from 8 M urea generated proteins no larger than dimers. Refolded MBP-pepsinogen was proteolytically active, while only a few percent of renatured MBP-procathepsin D was obtained. The results suggest that MBP-aspartic proteinase fusions can provide a source of soluble but nonnative folding states of the mammalian polypeptides in the absence of aggregation.

TGF-beta signaling blockade inhibits PTHrP secretion by breast cancer cells and bone metastases development.

Breast cancer frequently metastasizes to the skeleton, and the associated bone destruction is mediated by the osteoclast. Growth factors, including transforming growth factor-beta (TGF-beta), released from bone matrix by the action of osteoclasts, may foster metastatic growth. Because TGF-beta inhibits growth of epithelial cells, and carcinoma cells are often defective in TGF-beta responses, any role of TGF-beta in metastasis is likely to be mediated by effects on the surrounding normal tissue. However, we present evidence that TGF-beta promotes breast cancer metastasis by acting directly on the tumor cells. Expression of a dominant-negative mutant (TbetaRIIDeltacyt) of the TGF-beta type II receptor rendered the human breast cancer cell line MDA-MB-231 unresponsive to TGF-beta. In a murine model of bone metastases, expression of TbetaRIIDeltacyt by MDA-MB-231 resulted in less bone destruction, less tumor with fewer associated osteoclasts, and prolonged survival compared with controls. Reversal of the dominant-negative signaling blockade by expression of a constitutively active TGF-beta type I receptor in the breast cancer cells increased tumor production of parathyroid hormone-related protein (PTHrP), enhanced osteolytic bone metastasis, and decreased survival. Transfection of MDA-MB-231 cells that expressed the dominant-negative TbetaRIIDeltacyt with the cDNA for PTHrP resulted in constitutive tumor PTHrP production and accelerated bone metastases. These data demonstrate an important role for TGF-beta in the development of breast cancer metastasis to bone, via the TGF-beta receptor-mediated signaling pathway in tumor cells, and suggest that the bone destruction is mediated by PTHrP.