Anti-prion drugs do not improve survival in novel knock-in models of inherited prion disease.

Prion diseases uniquely manifest in three distinct forms: inherited, sporadic, and infectious. Wild-type prions are responsible for the sporadic and infectious versions, while mutant prions cause inherited variants like fatal familial insomnia (FFI) and familial Creutzfeldt-Jakob disease (fCJD). Although some drugs can prolong prion incubation times up to four-fold in rodent models of infectious prion diseases, no effective treatments for FFI and fCJD have been found. In this study, we evaluated the efficacy of various anti-prion drugs on newly-developed knock-in mouse models for FFI and fCJD. These models express bank vole prion protein (PrP) with the pathogenic D178N and E200K mutations. We applied various drug regimens known to be highly effective against wild-type prions in vivo as well as a brain-penetrant compound that inhibits mutant PrPSc propagation in vitro. None of the regimens tested (Anle138b, IND24, Anle138b + IND24, cellulose ether, and PSCMA) significantly extended disease-free survival or prevented mutant PrPSc accumulation in either knock-in mouse model, despite their ability to induce strain adaptation of mutant prions. Our results show that anti-prion drugs originally developed to treat infectious prion diseases do not necessarily work for inherited prion diseases, and that the recombinant sPMCA is not a reliable platform for identifying compounds that target mutant prions. This work underscores the need to develop therapies and validate screening assays specifically for mutant prions, as well as anti-prion strategies that are not strain-dependent.

Does local fat thickness correlate with post-operative infection in open reduction and internal fixation of acetabulum fractures?

PURPOSE: Obesity is an epidemic which increases risk of many surgical procedures. Previous studies in spine and hip arthroplasty have shown that fat thickness measured on preoperative imaging may be as or more reliable in assessment of risk of post-operative infection and/or wound complications than body mass index (BMI). We hypothesized that, similarly, increased local fat thickness at the surgical site is a predictor of wound complication in acetabulum fracture surgery. METHODS: Patients who underwent open reduction and internal fixation (ORIF) of an acetabulum fracture through a Kocher-Langenbeck (K-L) approach at a single institution from 2013 to 2020 were identified. Pre-operative CT scans were used to measure fat thickness from the skin to the greater trochanter in line with the surgical approach. Post-operative infections and wound complications were recorded and associated with fat thickness and BMI. RESULTS: 238 patients met inclusion criteria. 12 patients had either infection or a wound complication (5.0%). There was no significant association with BMI or preoperative fat thickness on post-operative infection or wound complication (p-value 0.73 and 0.86). CONCLUSIONS: There is no statistically significant association of post-operative infection or wound complications in patients with increased soft tissue thickness or increased BMI. ORIF of acetabulum fractures through a K-L approach can be performed safely in patients with large subcutaneous fat thickness and high BMI with low risk of infection or wound complications.

Anti-prion drugs do not improve survival in knock-in models of inherited prion disease.

Prion diseases uniquely manifest in three distinct forms: inherited, sporadic, and infectious. Wild-type prions are responsible for the sporadic and infectious versions, while mutant prions cause inherited variants like fatal familial insomnia (FFI) and familial Creutzfeldt-Jakob disease (fCJD). Although some drugs can prolong prion incubation times up to four-fold in rodent models of infectious prion diseases, no effective treatments for FFI and fCJD have been found. In this study, we evaluated the efficacy of various anti-prion drugs on newly-developed knock-in mouse models for FFI and fCJD. These models express bank vole prion protein (PrP) with the pathogenic D178N and E200K mutations. We applied various drug regimens known to be highly effective against wild-type prions in vivo as well as a brain-penetrant compound that inhibits mutant PrP Sc propagation in vitro . None of the regimens tested (Anle138b, IND24, Anle138b + IND24, cellulose ether, and PSCMA) significantly extended disease-free survival or prevented mutant PrP Sc accumulation in either knock-in mouse model, despite their ability to induce strain adaptation of mutant prions. Paradoxically, the combination of Anle138b and IND24 appeared to accelerate disease by 16% and 26% in kiBVI E200K and kiBVI D178N mice, respectively, and accelerated the aggregation of mutant PrP molecules in vitro . Our results show that anti-prion drugs originally developed to treat infectious prion diseases do not necessarily work for inherited prion diseases, and that the recombinant sPMCA is not a reliable platform for identifying compounds that target mutant prions. This work underscores the need to develop therapies and validate screening assays specifically for mutant prions.

Phospholipid cofactor solubilization inhibits formation of native prions.

Cofactor molecules are required to generate infectious mammalian prions in vitro. Mouse and hamster prions appear to have different cofactor preferences: Whereas both mouse and hamster prions can use phosphatidylethanolamine (PE) as a prion cofactor, only hamster prions can also use single-stranded RNA as an alternative cofactor. Here, we investigated the effect of detergent solubilization on rodent prion formation in vitro. We discovered that detergents that can solubilize PE (n-octylglucoside, n-octylgalactoside, and CHAPS) inhibit mouse prion formation in serial protein misfolding cyclic amplification (sPMCA) reactions using bank vole brain homogenate substrate, whereas detergents that are unable to solubilize PE (Triton X-100 and IPEGAL) have no effect. For all three PE-solubilizing detergents, inhibition of RML mouse prion formation was only observed above the critical micellar concentration (CMC). Two other mouse prion strains, Me7 and 301C, were also inhibited by the three PE-solubilizing detergents but not by Triton X-100 or IPEGAL. In contrast, none of the detergents inhibited hamster prion formation in parallel sPMCA reactions using the same bank vole brain homogenate substrate. In reconstituted sPMCA reactions using purified substrates, n-octylglucoside inhibited hamster prion formation when immunopurified bank vole PrPC substrate was supplemented with brain phospholipid but not with RNA. Interestingly, phospholipid cofactor solubilization had no effect in sPMCA reactions using bacterially expressed recombinant PrP substrate, indicating that the inhibitory effect of solubilization requires PrPC post-translational modifications. Overall, these in vitro results show that the ability of PE to facilitate the formation of native but not recombinant prions requires phospholipid bilayer integrity, suggesting that membrane structure may play an important role in prion formation in vivo.

Conformational diversity in purified prions produced in vitro.

Prion diseases are caused by misfolding of either wild-type or mutant forms of the prion protein (PrP) into self-propagating, pathogenic conformers, collectively termed PrPSc. Both wild-type and mutant PrPSc molecules exhibit conformational diversity in vivo, but purified prions generated by the serial protein misfolding cyclic amplification (sPMCA) technique do not display this same diversity in vitro. This discrepancy has left a gap in our understanding of how conformational diversity arises at the molecular level in both types of prions. Here, we use continuous shaking instead of sPMCA to generate conformationally diverse purified prions in vitro. Using this approach, we show for the first time that wild type prions initially seeded by different native strains can propagate as metastable PrPSc conformers with distinguishable strain properties in purified reactions containing a single active cofactor. Propagation of these metastable PrPSc conformers requires appropriate shaking conditions, and changes in these conditions cause all the different PrPSc conformers to converge irreversibly into the same single conformer as that produced in sPMCA reactions. We also use continuous shaking to show that two mutant PrP molecules with different pathogenic point mutations (D177N and E199K) adopt distinguishable PrPSc conformations in reactions containing pure protein substrate without cofactors. Unlike wild-type prions, the conformations of mutant prions appear to be dictated by substrate sequence rather than seed conformation. Overall, our studies using purified substrates in shaking reactions show that wild-type and mutant prions use fundamentally different mechanisms to generate conformational diversity at the molecular level.

Delayed Repair of a Lesser Tuberosity Avulsion Fracture in an Adolescent 3 Years After Initial Injury.

This case study examines an adolescent athlete who had an avulsion fracture of the lesser tuberosity of the humerus. This is a relatively rare injury, although a collection of case studies have identified an increase in this type of injury in the past 15 years. Uniquely, the patient experienced a delay in appropriate diagnosis for approximately 3 years from the time of his initial injury. This is one of the most significant delays in diagnosis and treatment in the current body of literature regarding lesser tuberosity fractures. The authors include a detailed series of imaging studies, including preoperative plain radiographs, preoperative computed tomography, intraoperative arthroscopic images, and postoperative plain radiographs. In addition, a thorough description of the patient's surgery is presented. The degree of scarring to the axillary nerve present in this patient required conversion to a full open reduction. The authors' aim is that this case can be used as a reference for future surgical decision making, particularly in pediatric patients whose injuries are highly chronic or who are actively involved in athletic physical training programs. [Orthopedics. 2023;46(3):e189-e192.].

Identification of a homology-independent linchpin domain controlling mouse and bank vole prion protein conversion.

Prions are unorthodox pathogens that cause fatal neurodegenerative diseases in humans and other mammals. Prion propagation occurs through the self-templating of the pathogenic conformer PrPSc, onto the cell-expressed conformer, PrPC. Here we study the conversion of PrPC to PrPSc using a recombinant mouse PrPSc conformer (mouse protein-only recPrPSc) as a unique tool that can convert bank vole but not mouse PrPC substrates in vitro. Thus, its templating ability is not dependent on sequence homology with the substrate. In the present study, we used chimeric bank vole/mouse PrPC substrates to systematically determine the domain that allows for conversion by Mo protein-only recPrPSc. Our results show that that either the presence of the bank vole amino acid residues E227 and S230 or the absence of the second N-linked glycan are sufficient to allow PrPC substrates to be converted by Mo protein-only recPrPSc and several native infectious prion strains. We propose that residues 227 and 230 and the second glycan are part of a C-terminal domain that acts as a linchpin for bank vole and mouse prion conversion.

Cofactor and glycosylation preferences for in vitro prion conversion are predominantly determined by strain conformation.

Prion diseases are caused by the misfolding of a host-encoded glycoprotein, PrPC, into a pathogenic conformer, PrPSc. Infectious prions can exist as different strains, composed of unique conformations of PrPSc that generate strain-specific biological traits, including distinctive patterns of PrPSc accumulation throughout the brain. Prion strains from different animal species display different cofactor and PrPC glycoform preferences to propagate efficiently in vitro, but it is unknown whether these molecular preferences are specified by the amino acid sequence of PrPC substrate or by the conformation of PrPSc seed. To distinguish between these two possibilities, we used bank vole PrPC to propagate both hamster or mouse prions (which have distinct cofactor and glycosylation preferences) with a single, common substrate. We performed reconstituted sPMCA reactions using either (1) phospholipid or RNA cofactor molecules, or (2) di- or un-glycosylated bank vole PrPC substrate. We found that prion strains from either species are capable of propagating efficiently using bank vole PrPC substrates when reactions contained the same PrPC glycoform or cofactor molecule preferred by the PrPSc seed in its host species. Thus, we conclude that it is the conformation of the input PrPSc seed, not the amino acid sequence of the PrPC substrate, that primarily determines species-specific cofactor and glycosylation preferences. These results support the hypothesis that strain-specific patterns of prion neurotropism are generated by selection of differentially distributed cofactors molecules and/or PrPC glycoforms during prion replication.

Full restoration of specific infectivity and strain properties from pure mammalian prion protein.

The protein-only hypothesis predicts that infectious mammalian prions are composed solely of PrPSc, a misfolded conformer of the normal prion protein, PrPC. However, protein-only PrPSc preparations lack significant levels of prion infectivity, leading to the alternative hypothesis that cofactor molecules are required to form infectious prions. Here, we show that prions with parental strain properties and full specific infectivity can be restored from protein-only PrPSc in vitro. The restoration reaction is rapid, potent, and requires bank vole PrPC substrate, post-translational modifications, and cofactor molecules. To our knowledge, this represents the first report in which the essential properties of an infectious mammalian prion have been restored from pure PrP without adaptation. These findings provide evidence for a unified hypothesis of prion infectivity in which the global structure of protein-only PrPSc accurately stores latent infectious and strain information, but cofactor molecules control a reversible switch that unmasks biological infectivity.

A Structural and Functional Comparison Between Infectious and Non-Infectious Autocatalytic Recombinant PrP Conformers.

Infectious prions contain a self-propagating, misfolded conformer of the prion protein termed PrPSc. A critical prediction of the protein-only hypothesis is that autocatalytic PrPSc molecules should be infectious. However, some autocatalytic recombinant PrPSc molecules have low or undetectable levels of specific infectivity in bioassays, and the essential determinants of recombinant prion infectivity remain obscure. To identify structural and functional features specifically associated with infectivity, we compared the properties of two autocatalytic recombinant PrP conformers derived from the same original template, which differ by >105-fold in specific infectivity for wild-type mice. Structurally, hydrogen/deuterium exchange mass spectrometry (DXMS) studies revealed that solvent accessibility profiles of infectious and non-infectious autocatalytic recombinant PrP conformers are remarkably similar throughout their protease-resistant cores, except for two domains encompassing residues 91-115 and 144-163. Raman spectroscopy and immunoprecipitation studies confirm that these domains adopt distinct conformations within infectious versus non-infectious autocatalytic recombinant PrP conformers. Functionally, in vitro prion propagation experiments show that the non-infectious conformer is unable to seed mouse PrPC substrates containing a glycosylphosphatidylinositol (GPI) anchor, including native PrPC. Taken together, these results indicate that having a conformation that can be specifically adopted by post-translationally modified PrPC molecules is an essential determinant of biological infectivity for recombinant prions, and suggest that this ability is associated with discrete features of PrPSc structure.

Requirements for mutant and wild-type prion protein misfolding in vitro.

Misfolding of the prion protein (PrP) plays a central role in the pathogenesis of infectious, sporadic, and inherited prion diseases. Here we use a chemically defined prion propagation system to study misfolding of the pathogenic PrP mutant D177N in vitro. This mutation causes PrP to misfold spontaneously in the absence of cofactor molecules in a process dependent on time, temperature, pH, and intermittent sonication. Spontaneously misfolded mutant PrP is able to template its unique conformation onto wild-type PrP substrate in a process that requires a phospholipid activity distinct from that required for the propagation of infectious prions. Similar results were obtained with a second pathogenic PrP mutant, E199K, but not with the polymorphic substitution M128V. Moreover, wild-type PrP inhibits mutant PrP misfolding in a dose-dependent manner, and cofactor molecules can antagonize this effect. These studies suggest that interactions between mutant PrP, wild-type PrP, and other cellular factors may control the rate of PrP misfolding in inherited prion diseases.

Purification and characterisation of a ß-1,4-xylanase from Remersonia thermophila CBS 540.69 and its application in bread making.

This work reports the first investigation of Remersonia thermophila hemicellulosic hydrolytic enzyme production, with subsequent purification of an extracellular endo-ß-1,4-xylanase (RtXyl) and its application in bread making. The research describes RtXyl purification from sorghum-induced submerged liquid cultures of this moderately thermophilic, aerobic, ascomycete fungus. The purified enzyme is a single subunit protein with a molecular mass of 42 kDa and exhibits glycosyl hydrolase family-10-like activity over a broad pH and temperature range. Optimal activity was measured at pH 6.0 and 65 °C respectively, which is suitable for bread making applications. Substrate specificity studies revealed that RtXyl is purely xylanolytic with no side-activities against other plant polysaccharides. The RtXyl catalytic efficiency (K cat/K m) was highest with oats spelt xylan (810.90 mg mL(-1) s(-1)), wheat arabinoxylan (809.52 mg mL(-1) s(-1)) and beechwood xylan (417.40 mg mL(-1) s(-1)) with less efficiency towards insoluble oats spelt xylan (236.40 mg mL(-1) s(-1)). Hydrolysis products analysed by thin layer chromatography yielded a range of xylosaccharides, predominantly xylotriose and xylobiose. RtXyl application in a basic wheat bread recipe at low dosages (0.297 XU/g) showed its suitability to increase loaf volume by 8.0 % compared with the control bread. RtXyl increased loaf softness by 19.6 % while reducing bread staling by 20.4 % up to 4 days of storage.

Prion nucleation site unmasked by transient interaction with phospholipid cofactor.

Infectious mammalian prions can be formed de novo from purified recombinant prion protein (PrP) substrate through a pathway that requires the sequential addition of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol (POPG) and RNA cofactor molecules. Recent studies show that the initial interaction between PrP and POPG causes widespread and persistent conformational changes to form an insoluble intermediate species, termed PrP(Int1). Here, we characterize the mechanism and functional consequences of the interaction between POPG and PrP. Negative-stain electron microscopy of PrP(Int1) revealed the presence of amorphous aggregates. Pull-down and photoaffinity label experiments indicate that POPG induces the formation of a PrP(C) polybasic-domain-binding neoepitope within PrP(Int1). The ongoing presence of POPG is not required to maintain PrP(Int1) structure, as indicated by the absence of stoichiometric levels of POPG in solid-state NMR measurements of PrP(Int1). Together, these results show that a transient interaction with POPG cofactor unmasks a PrP(C) binding site, leading to PrP(Int1) aggregation.

Sustainable production of biologically active molecules of marine based origin.

The marine environment offers both economic and scientific potential which are relatively untapped from a biotechnological point of view. These environments whilst harsh are ironically fragile and dependent on a harmonious life form balance. Exploitation of natural resources by exhaustive wild harvesting has obvious negative environmental consequences. From a European industry perspective marine organisms are a largely underutilised resource. This is not due to lack of interest but due to a lack of choice the industry faces for cost competitive, sustainable and environmentally conscientious product alternatives. Knowledge of the biotechnological potential of marine organisms together with the development of sustainable systems for their cultivation, processing and utilisation are essential. In 2010, the European Commission recognised this need and funded a collaborative RTD/SME project under the Framework 7-Knowledge Based Bio-Economy (KBBE) Theme 2 Programme 'Sustainable culture of marine microorganisms, algae and/or invertebrates for high value added products'. The scope of that project entitled 'Sustainable Production of Biologically Active Molecules of Marine Based Origin' (BAMMBO) is outlined. Although the Union is a global leader in many technologies, it faces increasing competition from traditional rivals and emerging economies alike and must therefore improve its innovation performance. For this reason innovation is placed at the heart of a European Horizon 2020 Strategy wherein the challenge is to connect economic performance to eco performance. This article provides a synopsis of the research activities of the BAMMBO project as they fit within the wider scope of sustainable environmentally conscientious marine resource exploitation for high-value biomolecules.

Cofactor molecules maintain infectious conformation and restrict strain properties in purified prions.

Prions containing misfolded prion protein (PrP(Sc)) can be formed with cofactor molecules using the technique of serial protein misfolding cyclic amplification. However, it remains unknown whether cofactors materially participate in maintaining prion conformation and infectious properties. Here we show that withdrawal of cofactor molecules during serial propagation of purified recombinant prions caused adaptation of PrP(Sc) structure accompanied by a reduction in specific infectivity of >10(5)-fold, to undetectable levels, despite the ability of adapted "protein-only" PrP(Sc) molecules to self-propagate in vitro. We also report that changing only the cofactor component of a minimal reaction substrate mixture during serial propagation induced major changes in the strain properties of an infectious recombinant prion. Moreover, propagation with only one functional cofactor (phosphatidylethanolamine) induced the conversion of three distinct strains into a single strain with unique infectious properties and PrP(Sc) structure. Taken together, these results indicate that cofactor molecules can regulate the defining features of mammalian prions: PrP(Sc) conformation, infectivity, and strain properties. These findings suggest that cofactor molecules likely are integral components of infectious prions.

Isolation of phosphatidylethanolamine as a solitary cofactor for prion formation in the absence of nucleic acids.

Infectious prions containing the pathogenic conformer of the mammalian prion protein (PrP(Sc)) can be produced de novo from a mixture of the normal conformer (PrP(C)) with RNA and lipid molecules. Recent reconstitution studies indicate that nucleic acids are not required for the propagation of mouse prions in vitro, suggesting the existence of an alternative prion propagation cofactor in brain tissue. However, the identity and functional properties of this unique cofactor are unknown. Here, we show by purification and reconstitution that the molecule responsible for the nuclease-resistant cofactor activity in brain is endogenous phosphatidylethanolamine (PE). Synthetic PE alone facilitates conversion of purified recombinant (rec)PrP substrate into infectious recPrP(Sc) molecules. Other phospholipids, including phosphatidylcholine, phosphatidylserine, phosphatidylinositol, and phosphatidylglycerol, were unable to facilitate recPrP(Sc) formation in the absence of RNA. PE facilitated the propagation of PrP(Sc) molecules derived from all four different animal species tested including mouse, suggesting that unlike RNA, PE is a promiscuous cofactor for PrP(Sc) formation in vitro. Phospholipase treatment abolished the ability of brain homogenate to reconstitute the propagation of both mouse and hamster PrP(Sc) molecules. Our results identify a single endogenous cofactor able to facilitate the formation of prions from multiple species in the absence of nucleic acids or other polyanions.

Non-reducing alkaline solubilization and rapid on-column refolding of recombinant prion protein.

Mature prion protein (PrP) is a 208-residue polypeptide that contains a single disulfide bond. We report an alternative method to purify recombinant mouse PrP produced in Escherichia coli. Bacterial inclusion bodies were solubilized in a buffer containing 2 M urea at pH 12.5. The solubilized protein was rapidly purified on a nickel affinity column without a chaotrope gradient, followed by ion-exchange chromatography. The yield and purity of PrP produced by this alternative approach was similar to that obtained using a conventional solubilization and on-column refolding protocol. Recombinant PrP produced using the non-reducing purification protocol is properly folded, as determined by circular dichroism, and a competent substrate for amyloid fibril formation, as determined by Thoflavin-T dye binding assays. In summary, this report describes a rapid method for producing properly folded recombinant PrP without reducing agents or a chaotrope gradient.

Seeding specificity and ultrastructural characteristics of infectious recombinant prions.

Infectious mouse prions can be produced from a mixture of bacterially expressed recombinant prion protein (recPrP), palmitoyloleoylphosphatidylglycerol (POPG), and RNA [Wang, F.; et al. (2010) Science 327, 1132]. In contrast, amyloid fibers produced from pure recPrP without POPG or RNA (recPrP fibers) fail to infect wild type mice [Colby, D.W.; et al. (2010) PLoS Pathog. 387, e1000736]. We compared the seeding specificity and ultrastructural features of infectious recombinant prions (recPrP(Sc)) with those of recPrP fibers. Our results indicate that PrP fibers are not able to induce the formation of PrP(Sc) molecules from wild type mouse brain homogenate substrate in serial protein misfolding cyclic amplification (sPMCA) reactions. Conversely, recPrP(Sc) molecules did not accelerate the formation of amyloid in vitro, under conditions that produce recPrP fibers spontaneously. Ultrastructurally, recombinant prions appear to be small spherical aggregates rather than elongated fibers, as determined by atomic force and electron microscopy. Taken together, our results show that recPrP(Sc) molecules and PrP fibers have different ultrastructural features and seeding specificities, suggesting that prion infectivity may be propagated by a specific and unique assembly pathway facilitated by cofactors.

Cancellous bone adaptation to tibial compression is not sex dependent in growing mice.

Mechanical loading can be used to increase bone mass and thus attenuate pathological bone loss. Because the skeleton's adaptive response to loading is most robust before adulthood, elucidating sex-specific responses during growth may help maximize peak bone mass. This study investigated the effect of sex on the response to controlled, in vivo mechanical loading in growing mice. Ten-week-old male and female C57Bl/6 mice underwent noninvasive compression of the left tibia. Peak loads of -11.5 N were applied, corresponding to +1,200 microepsilon at the tibial midshaft in both sexes. Cancellous bone mass, architecture, and dynamic formation in the proximal metaphysis were compared between loaded and control limbs via micro-computed tomography and histomorphometry. The strain environment of the proximal metaphysis during loading was characterized using finite element analysis. Both sexes responded to tibial compression through increased bone mass and altered architecture. Cancellous bone mass and tissue density were enhanced in loaded limbs relative to control limbs in both sexes through trabecular thickening and reduced separation. Changes in mass were due to increased cellular activity in loaded limbs compared with control limbs. Adaptation to loading increased the proportion of load transferred by the cancellous bone in the proximal metaphysis. For all cancellous measures, the response to tibial compression did not differ between male and female mice. When similar strains are engendered in males and females, the adaptive response in cancellous bone to mechanical loading does not depend on sex.

A phase II trial of docetaxel and carboplatin as first-line chemotherapy for metastatic breast cancer: NCCTG study N9932.

OBJECTIVE: A phase II multi-institutional clinical trial conducted to evaluate the efficacy and tolerability of docetaxel and carboplatin as first-line therapy for women with metastatic breast cancer. METHODS: Patients had histologically confirmed metastatic breast cancer with at least one measurable lesion. Prior adjuvant chemotherapy was permitted, provided that at least 12 months had elapsed between any prior taxane and platinum therapy. Patients received docetaxel 75 mg/m(2) with carboplatin AUC 6 mg/ml.min every 21 days until disease progression or prohibitive toxicity. RESULTS: All 53 patients enrolled were evaluable for response and toxicity. Median number of cycles delivered was 6. Overall response rate was 60%, with 3 complete responses (6%) and 29 partial responses (54%). Median time to disease progression was 9.6 months. Median survival time was 20.4 months. Myelosuppression was the predominant toxicity, with grade 3 or 4 neutropenia occurring in 94% of patients and 15% of patients experiencing febrile neutropenia. The overall incidence (grades 1-3) of neurosensory toxicity was 57% and neuromotor toxicity was 25%, respectively, with grade 3 toxicity occurring in 4% of patients each. CONCLUSIONS: The combination of docetaxel and carboplatin is highly active in metastatic breast cancer. Prophylactic growth factor support is recommended in any further evaluation of this combination in the treatment of patients with breast cancer.