Human nonunion tissues display differential gene expression in comparison to physiological fracture callus.

The healing of bone fractures can become aberrant and lead to nonunions which in turn have a negative impact on patient health. Understanding why a bone fails to normally heal will enable us to make a positive impact in a patient's life. While we have a wealth of molecular data on rodent models of fracture repair, it is not the same with humans. As such, there is still a lack of information regarding the molecular differences between normal physiological repair and nonunions. This study was designed to address this gap in our molecular knowledge of the human repair process by comparing differentially expressed genes (DEGs) between physiological fracture callus and two different nonunion types, hypertrophic (HNU) and oligotrophic (ONU). RNA sequencing data revealed over ∼18,000 genes in each sample. Using the physiological callus as the control and the nonunion samples as the experimental groups, bioinformatic analyses identified 67 and 81 statistically significant DEGs for HNU and ONU, respectively. Out of the 67 DEGs for the HNU, 34 and 33 were up and down-regulated, respectively. Similarly, out of the 81 DEGs for the ONU, 48 and 33 were up and down-regulated, respectively. Additionally, we also identified common genes between the two nonunion samples; 8 (10.8 %) upregulated and 12 (22.2 %) downregulated. We further identified many biological processes, with several statistically significant ones. Some of these were related to muscle and were common between the two nonunion samples. This study represents the first comprehensive attempt to understand the global molecular events occurring in human nonunion biology. With further research, we can perhaps decipher new molecular pathways involved in aberrant healing of human bone fractures that can be therapeutically targeted.

Surprise positive culture rate in the treatment of presumed aseptic long-bone nonunion: a systematic review with meta-analysis of 2397 patients.

INTRODUCTION: In pre-operatively presumed aseptic nonunions, the definitive diagnosis of infection relies on intraoperative cultures. Our primary objective was to determine (1) the rate of surprise positive intraoperative cultures in presumed aseptic long-bone nonunion (surprise positive culture nonunion), and (2) the rate of surprise positive cultures that represent infection vs. contamination. Secondary objectives were to determine the healing and secondary surgery rates and to identify cultured micro-organisms. MATERIALS AND METHODS: We performed a systematic literature search of PubMed, Embase and Cochrane Libraries from 1980 until December 2021. We included studies reporting on ≥ 10 adult patients with a presumed aseptic long-bone nonunion, treated with a single-stage surgical protocol, of which intraoperative cultures were reported. We performed a meta-analysis for: (1) the rates of surprise positive culture nonunion, surprise infected nonunion, and contaminated culture nonunion, and (2) healing and (3) secondary surgery rates for each culture result. Risk of bias was assessed using the QUADAS-2 tool. RESULTS: 21 studies with 2,397 patients with a presumed aseptic nonunion were included. The rate of surprise positive culture nonunion was 16% (95%CI: 10-22%), of surprise infected nonunion 10% (95%CI: 5-16%), and of contaminated culture nonunion 3% (95%CI: 1-5%). The secondary surgery rate for surprise positive culture nonunion was 22% (95%CI: 9-38%), for surprise infected nonunion 14% (95%CI 6-22%), for contaminated culture nonunion 4% (95%CI: 0-19%), and for negative culture nonunion 6% (95CI: 1-13%). The final healing rate was 98% to 100% for all culture results. Coagulase-negative staphylococci accounted for 59% of cultured micro-organisms. CONCLUSION: These results suggest that surprise positive cultures play a role in the clinical course of a nonunion and that culturing is important in determining the etiology of nonunion, even if the pre-operative suspicion for infection is low. High healing rates can be achieved in presumed aseptic nonunions, regardless of the definitive intraoperative culture result.

Antimicrobial Mechanisms and Preparation of Antibiotic-impregnated Cement-coated Locking Plates in the Treatment of Infected Non-unions.

Background: Antibiotic-impregnated cement-coated plates (ACPs) have been used successfully for temporary internal fixation between stages in the two-stage treatment of infected non-unions. We describe our approach of using an ACP in the staged treatment of a methicillin-resistant Staphylococcus aureus (MRSA)-infected distal femoral non-union below a total hip prosthesis. In addition, we present the results of an in vitro experiment to provide an in-depth insight into the capacity of ACPs in (i) treating residual biofilm and (ii) preventing bacterial recolonisation. Materials and methods: In the first stage, we used a titanium LISS plate coated with hand-mixed PALACOS with vancomycin (PAL-V) for temporary internal fixation combined with commercially prepared COPAL with gentamicin and vancomycin (COP-GV) to fill the segmental defect. In the second stage, the non-union was treated with double-plate fixation and bone grafting.A Kirby-Bauer agar disc diffusion assay was performed to determine the antimicrobial activity of both ACPs and a drug-release assay to measure antibiotic release over time. A biofilm killing assay was also carried out to determine if the antibiotic released was able to reduce or eradicate biofilm of the patient's MRSA strain. Results: At one-year follow-up, there was complete bone-bridging across the previous non-union. The patient was pain-free and ambulatory without need for further surgery. Both ACPs with COP-GV and PAL-V exerted an antimicrobial effect against the MRSA strain with peak concentrations of antibiotic released within the first 24 hours. Concentrations released from COP-GV in the first 24 hours in vitro caused a 7.7-fold log reduction of colony-forming units (CFU) in the biofilm. At day 50, both COP-GV and PAL-V still released concentrations of antibiotic above the respective minimal inhibitory concentrations (MIC), likely contributing to the positive clinical outcome. Conclusion: The use of an ACP provides stability and infection control in the clinical scenario of an infected non-union. This is confirmed in vitro where the release of antibiotics from ACPs is characterised by an early burst followed by a prolonged sustained release above the MIC until 50 days. The burst release from COP-GV reduces CFU in the biofilm and prevents early recolonisation through synergistic activity of the released vancomycin and gentamicin. Clinical significance: An antibiotic-impregnated cement-coated plate is a useful addition to the surgeon's armamentarium to provide temporary internal fixation without the disadvantages of external fixation and contribute to infection control in an infected non-union. How to cite this article: Wagner RK, Guarch-Pérez C, van Dam AP, et al. Antimicrobial Mechanisms and Preparation of Antibiotic-impregnated Cement-coated Locking Plates in the Treatment of Infected Non-unions. Strategies Trauma Limb Reconstr 2023;18(2):73-81.

[Non-union]. / Non-union.

A non-union is a fracture that fails to heal within the expected time frame and occurs in approximately 3 to 5% of all fractures. Non-union has a negative impact on mental and physical functioning and quality of life. The causes, clinical presentation and treatment for non-union differ strongly on a case-by-case basis. By presenting three cases we aim to give healthcare providers more insight into the clinical scenario of non-union. In addition, we elaborate on characteristics, etiology, diagnostics and treatment of non-union.

Molecular profiling of osteoprogenitor cells reveals FOS as a master regulator of bone non-union.

Despite the advances in bone fracture treatment, a significant fraction of fracture patients will develop non-union. Most non-unions are treated with surgery since identifying the molecular causes of these defects is exceptionally challenging. In this study, compared with marrow bone, we generated a transcriptional atlas of human osteoprogenitor cells derived from healing callus and non-union fractures. Detailed comparison among the three conditions revealed a substantial similarity of callus and nonunion at the gene expression level. Nevertheless, when assayed functionally, they showed different osteogenic potential. Utilizing longitudinal transcriptional profiling of the osteoprogenitor cells, we identified FOS as a putative master regulator of non-union fractures. We validated FOS activity by profiling a validation cohort of 31 tissue samples. Our work identified new molecular targets for non-union classification and treatment while providing a valuable resource to better understand human bone healing biology.

Blade Plate With Autogenous Bone Grafting to Salvage Peri Ankle Nonunions.

BACKGROUND: Salvage surgery for a nonunion around the ankle is challenging. Poor bone stock, stiffness, scarring, previous (or persistent) infection, and a compromised soft tissue envelope are common in these patients. We describe 15 cases that underwent blade plate fixation as salvage for a nonunion around the ankle, including patient/nonunion characteristics, Nonunion Scoring System (NUSS), surgical technique, healing rate, complications, and long-term follow-up with 2 patient-reported outcome measures. METHODS: This is a retrospective case series from a level 1 trauma referral center. We included all patients that underwent blade plate fixation for a long-standing nonunion of the distal tibia, talus, or failed subtalar fusion. All patients had autogenous bone grafting, including 14 with posterior iliac crest grafts and 2 with femoral reamer irrigator aspirator grafting. Median follow-up was 24.4 months (interquartile range [IQR], 7.7-40). Main outcome measures were (time to) union, and functional outcomes using the 36-item Short Form Health Survey (SF-36) physical component summary (PCS) and mental component summary (MCS), and the Foot and Ankle Outcome Score (FAOS). RESULTS: We included 15 adults with a median age of 58 years (IQR, 54-62). The median NUSS score at the time of index surgery was 46 (IQR, 34-54). Union was achieved after the index procedure in 11 of 15 patients. Additional surgery was performed in 4 of 15 patients. Union was achieved in all patients at a median of 4.2 months (IQR, 2.9-11). The median score for the PCS was 38 (IQR, 34-48, range 17-58, P = .009), for the MCS 52 (IQR, 45-60, range 33-62, P = .701), and for the FAOS 73 (IQR, 48-83). CONCLUSION: In this series, our use of blade plate fixation with autogenous grafting was an effective method for managing a nonunion around the ankle allowing for alignment correction, stable compression and fixation, union, and fair patient-reported outcome scores. LEVEL OF EVIDENCE: Level IV, therapeutic.

Large segmental defects in midshaft clavicle nonunion treated with autologous tricortical iliac crest bone graft.

Background: To evaluate the use of intercalary iliac crest bone graft in the treatment of clavicle nonunion with a large segmental bone defect (3-6 cm). Methods: This retrospective study evaluated patients with large segmental bone defects (3-6 cm) after clavicle nonunion, treated with open reposition internal fixation and iliac crest bone graft between February 2003 and March 2021. At follow-up the Disabilities of the Arm, Shoulder and Hand (DASH) questionnaire was administered. A literature search was performed to provide an overview of commonly used graft types per defect size. Results: We included five patients treated with open reposition internal fixation and iliac crest bone graft for clavicle nonunion with a median defect size of 3.3 cm (range 3-6 cm). Union was achieved in all five, and all pre-operative symptoms resolved. The median DASH score was 23 out of 100 (IQR 8-24). An extensive literature search revealed that there are no studies describing the use of an used iliac crest graft for defects larger than 3 cm. Instead, a vascularized graft was typically used to treat defects sizes between 2.5 and 8 cm. Discussion: An autologous non-vascularized iliac crest bone graft can be safely used and is reproducible to treat a midshaft clavicle non-union with a bone defect between 3 and 6 cm.

Identification of the miRNAome in human fracture callus and nonunion tissues.

Background: Nonunions remain a challenging post-traumatic complication that often leads to a financial and health burden that affects the patient's quality of life. Despite a wealth of knowledge about fracture repair, especially gene and more recently miRNA expression, much remains unknown about the molecular differences between normal physiological repair (callus tissue) and a nonunion. To probe this lack of knowledge, we embarked on a study that sought to identify and compare the human miRNAome of normal bone to that present in a normal fracture callus and those from two different classic nonunion types, hypertrophic and oligotrophic. Methods: Normal bone and callus tissue samples were harvested during revision surgery from patients with physiological fracture repair and nonunions (hypertrophic and oligotrophic) and analyzed using histology. Also, miRNAs were isolated and screened using microarrays followed by bioinformatic analyses, including, differential expression, pathways and biological processes, as well as elucidation of target genes. Results: Out of 30,424 mature miRNAs (from 203 organisms) screened via microarrays, 635 (∼2.1%) miRNAs were found to be upregulated and 855 (∼2.8%) downregulated in the fracture callus and nonunion tissues as compared to intact bone. As our tissue samples were derived from humans, we focused on the human miRNAs and out of the 4223 human miRNAs, 86 miRNAs (∼2.0%) were upregulated and 51 (∼1.2%) were downregulated. Although there were similarities between the three experimental samples, we also found specific miRNAs that were unique to individual samples. We further identified the predicted target genes from these differentially expressed miRNAs as well as the relevant biological processes, including specific signaling pathways that are activated in all three experimental samples. Conclusion: Collectively, this is the first comprehensive study reporting on the miRNAome of intact bone as compared to fracture callus and nonunion tissues. Further, we identify specific miRNAs involved in normal physiological fracture repair as well as those of nonunions. The translational potential of this article: The data generated from this study further increase our molecular understanding of the roles of miRNAs during normal and aberrant fracture repair and this knowledge can be used in the future in the development of miRNA-based therapeutics for skeletal regeneration.

Modified use of the proximal humeral internal locking system (PHILOS) plate for distal femoral nonunions.

PURPOSE: Nonunion is a common complication after a distal femoral fracture (DFF). Standard treatment consists of revision plating and/or bone grafting. Single lateral plating for a distal femoral nonunion can be insufficient in case of a persistent medial gap and compromised bone stock. Alternatively, dual plating can be used to treat a distal femoral nonunion, but to date there is no Gold standard. The aim of our study was to report our results after use of a minimally invasively placed proximal humeral internal locking system (Philos) plate as a medial buttress in the treatment of a distal femoral nonunion. METHODS: Fifteen adult patients with a distal femoral nonunion were prospectively entered in a trauma database and retrospectively assessed. All patients underwent a similar operation, which included removal of failed hardware, nonunion debridement, fixation with a lateral plate, and a medial Philos plate combined with bone grafting. Data collected included union rate, time to union, complications and functional outcome. RESULTS: In twelve out of fifteen patients (80%), the fracture united after our index operation. Median time to union was 4.8 months (range 1.6-15). Three patients (20%) needed additional bone grafting surgery. One patient underwent a Judet quadricepsplasty. CONCLUSION: This study suggests that the Philos plate is a safe and effective adjunct as a medial buttress plate for distal femoral nonunions.

Operative treatment of nonunions in the elderly: Clinical and radiographic outcomes in patients at minimum 75 years of age.

BACKGROUND: Limited information exists on nonunion treatment in the elderly. This retrospective study evaluates whether results of operative treatment of nonunion of the humerus or femur in patients aged ≥ 75 years are comparable to those in younger patients. METHODS: We identified patients age ≥ 75 years with a nonunion of humerus or femur treated with open reduction and internal fixation. The Non-Union Scoring System was calculated. Complications, clinical outcome, and radiographic findings were assessed. Primary endpoint was nonunion healing. A literature review compared time to healing of humeral and femoral nonunion in younger populations. RESULTS: We identified 45 patients treated for a nonunion of humerus or femur with > 12 months follow-up. Median age was 79 years (range 75-96). Median time to presentation was 12 months (range 4-127) after injury, median number of prior surgeries was 1 (range 0-4). Union rate was 100%, with median time to union 6 months (range 2-42). Six patients underwent revision for persistent nonunion and healed without further complications. CONCLUSIONS: Using a protocol of debridement, alignment, compression, stable fixation, bone grafting and early motion, patients aged 75 years or older can reliably achieve healing when faced with a nonunion of the humerus or femur. LEVEL OF EVIDENCE: IV.

Treatment of a Recalcitrant Non-union of the Clavicle.

Background: Plate fixation is the treatment of choice for a midshaft clavicle non-union. Those non-unions that require >1 surgical procedure to heal are termed recalcitrant non-union. Regardless of the number of previously failed procedures, our surgical strategy is aimed at achieving an optimal mechanical and biological environment to facilitate healing. Materials and methods: We performed a retrospective analysis of 14 patients with a recalcitrant clavicle non-union treated with open reduction and plate fixation combined with graft augmentation when indicated. Healing rates after index surgery were analysed. All patients were observed for at least 12 months. Results: All patients healed at a mean time of 193.2 days (range 90-390). Five of the 14 patients had at least one positive surprise culture, for which they received antibiotic treatment. At the latest follow-up, no patient reported pain or discomfort. Mean disability of the arm, shoulder and hand (DASH) score was 16.3 points (range 0-40), indicating only mild residual impairment. A possible link was found between the time between injury and definitive surgery and the time to healing [Pearson correlation 0.527, sig. (two-tailed) 0.000]. Conclusion: This study shows 100% bone healing and good functional outcomes after surgical revision for a recalcitrant clavicle non-union. How to cite this article: Grewal S, Baltes TPA, Wiegerinck E, et al. Treatment of a Recalcitrant Non-union of the Clavicle. Strategies Trauma Limb Reconstr 2022;17(1):1-6.

Prevalence and Hospital Admissions in Patients With Osteogenesis Imperfecta in The Netherlands: A Nationwide Registry Study.

Osteogenesis Imperfecta (OI) is a complex disease caused by genetic alterations in production of collagen type I, and collagen-related proteins. Bone fragility is the most common patient issue, but extraskeletal complications also present an adverse factor in the quality of life and prognosis of patients with OI. However, still little is known about the morbidity and mortality of these patients. The objective of this paper is to determine and describe to what extent OI impacts patients' life in terms of hospitalization and complications describing the incidence and prevalence of the Dutch cohort of OI patients and the characteristics of their hospital admissions. Information regarding OI patients and their hospital admission was extracted from the Statistics Netherlands Database and matched to the OI Genetics Database of Amsterdam UMC. Hospital admission data was available for 674 OI patients. This OI nationwide registry study shows that the life expectancy of OI patients is adversely affected by the disease. The median annual incidence risk of OI between 1992 and 2019 was 6.5 per 100,000 live births. Furthermore, patients with OI had a 2.9 times higher hospitalization rate compared to the general Dutch population. The highest hospitalization rate ratio of 8.4 was reported in the patient group between 0 and 19 years old. OI type and severity had impact on extraskeletal manifestations, which play a key role in the numerous hospital admissions. More awareness about the impact of OI on patients' life is needed to improve and implement prevention and follow-up guidelines.

Two-level fixation with headless compression screws for tibial plateau fractures.

PURPOSE: Reduction and fixation of tibial plateau fractures associated with small, "floating" intra-articular fragments proposes a challenge. We use fully threaded headless compression screws for (interfragmentary) fixation of such fragments before final plate fixation when standard fixation of intra-articular fragments with k-wires or lag screws is deemed insufficient. Our aim is to describe our technique and clinical experience of this two-level fixation. METHODS: Between 2006 and 2021, 29 patients with a comminuted tibial plateau fracture were treated with this two-level fixation in this retrospective case series. Clinical baseline and surgical variables were collected for all patients. Clinical outcome variables were available for 28 patients with a median follow-up of 16.5 months (IQR 5-24). Functional outcomes were measured with the Knee Injury and Osteoarthritis Outcome Score (KOOS) and reported by 22 patients at a median of 5.2 years (IQR 3.5-9.8). RESULTS: Reduction was anatomic or good in 82% of cases, fair in 14%, and a malreduction in 4%. Arthrosis was graded as grade 0 in 25% of cases, 1 in 39%, 2 in 21%, and 3 in 14%. Flexion was 110 degrees (IQR 100-130). Five patients had an extension deficit of 5 to 10 degrees. Median KOOS for symptoms and stiffness was 69 points (IQR 45-78), for pain 71 (IQR 45-88), for ADL 85 (IQR 52-95), for sports 30 (IQR 11-55), and for quality of life 34 (IQR 19-56). CONCLUSION: The use of fully threaded headless compression screws is a simple and helpful addition in the treatment of comminuted tibial plateau fractures.

Supercutaneous locking compression plate in the treatment of infected non-union and open fracture of the leg.

INTRODUCTION: Salvage of infected tibia and fibula non-union and severe open fractures is challenging and often requires staged treatment. We describe all cases that underwent supercutaneous plating of the leg as external fixation technique and assessed union rate, time to union, rate of infection clearance, and patient-reported outcome measures. METHODS: This is a retrospective cohort study from a single level 1 trauma center. We included 19 patients that underwent supercutaneous plating-locking compression plate applied as external fixator-of the leg. Indications were: infected non-union of a pilon, cruris, or ankle fracture (n = 13); post-traumatic fistula draining osteomyelitis of the tibia (n = 3); infected mal-reduced subacute cruris fracture (n = 1); acute open pilon fracture (n = 1); and acute open cruris fracture (n = 1). Outcome measures were: union, time to union, infection clearance, the 36-item Short Form (SF-36) physical component summary scale (PCS) and mental component summary scale (MCS), and NRS pain scores. RESULTS: Union was achieved in 88% of the patients after a median of 279 days [interquartile range (IQR) 154-440]. Infection clearance was achieved in 94% of the patients. The PCS (median 51, IQR 46-56, p = 0.903) and MCS (median 57, IQR 50-60, p = 0.241) do not differ from normative population values. NRS Pain score at rest was 0 on average (IQR 0-1), 2 on average when walking (IQR 0-4), and 1 on average when climbing stairs (IQR 0-2). CONCLUSION: Supercutaneous plating is a simple and reliable technical trick to bridge and stabilize a nonunion or fracture site while clearing an infection and have soft-tissues heal before subsequent definitive (internal)fixation and/or cancellous bone grafting. Reasonable union and infection clearance rates are achieved, and good functional outcome can generally be expected. LEVEL OF EVIDENCE: Therapeutic level III.

Failed medial buttress plating of a femoral neck fracture salvaged with a Pauwels osteotomy: Case report and review of literature.

Two young patients with a Pauwels type 3 femoral neck fracture were treated with cannulated screws and the addition of an anteromedial buttress plate on the femoral neck. Both developed a non-union necessitating a salvage procedure. A Pauwels' osteotomy led to uneventful and complete healing in both patients. The purpose of this report is to describe the current literature on anteromedial buttress plating in femoral neck fractures and discusses a reproducible hip preserving salvage option when a non-union develops.

Comparison of an oblique single cut rotation osteotomy with a novel 3D computer-assisted oblique double cut alignment approach.

An oblique double-cut rotation osteotomy (ODCRO) enables correcting a complex bone deformation by aligning, in 3D, the distal, middle and proximal bone segments with a target bone, without intersegmental gaps. We propose virtual preoperative planning of an ODCRO. To minimize a residual translation error, we use an optimization algorithm and optimize towards bone length, alignment in the transverse direction, or a balanced reconstruction. We compare the residual alignment error with an oblique single-cut rotation osteotomy using 15 complex bone deformations. The single-cut approach was not feasible in 5 cases, whereas the ODCRO procedure was feasible in all cases. The residual alignment error was smaller for the ODCRO than for the single-cut approach except for one case. In a subset for length reconstruction, the length error of 7.3-21.3 mm was restored to 0.0 mm in 4 of 5 cases, although at the cost of an increased transverse translation. The proposed method renders planning an ODCRO feasible and helps restoring bone alignment and lengthening better than an oblique single-cut rotation osteotomy. Awareness of the challenges and possibilities in preoperative planning of an ODCRO will be of value for future alignment surgery and for patients.

Wound infection following implant removal of foot, ankle, lower leg or patella; a protocol for a multicenter randomized controlled trial investigating the (cost-)effectiveness of 2 g of prophylactic cefazolin compared to placebo (WIFI-2 trial).

BACKGROUND: Elective implant removal (IR) after fracture fixation is one of the most common procedures within (orthopedic) trauma surgery. The rate of surgical site infections (SSIs) in this procedure is quite high, especially below the level of the knee. Antibiotic prophylaxis is not routinely prescribed, even though it has proved to lower SSI rates in other (orthopedic) trauma surgical procedures. The primary objective is to study the effectiveness of a single intravenous dose of 2 g of cefazolin on SSIs after IR following fixation of foot, ankle and/or lower leg fractures. METHODS: This is a multicenter, double-blind placebo controlled trial with a superiority design, including adult patients undergoing elective implant removal after fixation of a fracture of foot, ankle, lower leg or patella. Exclusion criteria are: an active infection, current antibiotic treatment, or a medical condition contraindicating prophylaxis with cefazolin including allergy. Patients are randomized to receive a single preoperative intravenous dose of either 2 g of cefazolin or a placebo (NaCl). The primary analysis will be an intention-to-treat comparison of the proportion of patients with a SSI at 90 days after IR in both groups. DISCUSSION: If 2 g of prophylactic cefazolin proves to be both effective and cost-effective in preventing SSI, this would have implications for current guidelines. Combined with the high infection rate of IR which previous studies have shown, it would be sufficiently substantiated for guidelines to suggest protocolled use of prophylactic antibiotics in IR of foot, ankle, lower leg or patella. Trial registration Nederlands Trial Register (NTR): NL8284, registered on 9th of January 2020, https://www.trialregister.nl/trial/8284.

Corrigendum: Dual-mTOR Inhibitor Rapalink-1 Reduces Prostate Cancer Patient-Derived Xenograft Growth and Alters Tumor Heterogeneity.

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Collaboration Around Rare Bone Diseases Leads to the Unique Organizational Incentive of the Amsterdam Bone Center.

In the field of rare bone diseases in particular, a broad care team of specialists embedded in multidisciplinary clinical and research environment is essential to generate new therapeutic solutions and approaches to care. Collaboration among clinical and research departments within a University Medical Center is often difficult to establish, and may be hindered by competition and non-equivalent cooperation inherent in a hierarchical structure. Here we describe the "collaborative organizational model" of the Amsterdam Bone Center (ABC), which emerged from and benefited the rare bone disease team. This team is often confronted with pathologically complex and under-investigated diseases. We describe the benefits of this model that still guarantees the autonomy of each team member, but combines and focuses our collective expertise on a clear shared goal, enabling us to capture synergistic and innovative opportunities for the patient, while avoiding self-interest and possible harmful competition.

Dual-mTOR Inhibitor Rapalink-1 Reduces Prostate Cancer Patient-Derived Xenograft Growth and Alters Tumor Heterogeneity.

Bone metastasis is the leading cause of prostate cancer (PCa) mortality, frequently marking the progression to castration-resistant PCa. Dysregulation of the androgen receptor pathway is a common feature of castration-resistant PCa, frequently appearing in association with mTOR pathway deregulations. Advanced PCa is also characterized by increased tumor heterogeneity and cancer stem cell (CSC) frequency. CSC-targeted therapy is currently being explored in advanced PCa, with the aim of reducing cancer clonal divergence and preventing disease progression. In this study, we compared the molecular pathways enriched in a set of bone metastasis from breast and prostate cancer from snap-frozen tissue. To further model PCa drug resistance mechanisms, we used two patient-derived xenografts (PDX) models of bone-metastatic PCa, BM18, and LAPC9. We developed in vitro organoids assay and ex vivo tumor slice drug assays to investigate the effects of mTOR- and CSC-targeting compounds. We found that both PDXs could be effectively targeted by treatment with the bivalent mTORC1/2 inhibitor Rapalink-1. Exposure of LAPC9 to Rapalink-1 but not to the CSC-targeting drug disulfiram blocked mTORC1/2 signaling, diminished expression of metabolic enzymes involved in glutamine and lipid metabolism and reduced the fraction of CD44+ and ALDEFluorhigh cells, in vitro. Mice treated with Rapalink-1 showed a significantly delayed tumor growth compared to control and cells recovered from the tumors of treated animals showed a marked decrease of CD44 expression. Taken together these results highlight the increased dependence of advanced PCa on the mTOR pathway, supporting the development of a targeted approach for advanced, bone metastatic PCa.