Comprehensive clinical and molecular characterization of claudin 18.2 expression in advanced gastric or gastroesophageal junction cancer

BACKGROUND

We conducted comprehensive clinical and molecular characterization of claudin 18.2 expression (CLDN18.2) in advanced gastric or gastroesophageal junction cancer (GC/GEJC).

PATIENTS AND METHODS

Patients with advanced GC/GEJC who received systemic chemotherapy from October 2015 to December 2019 with available tumor specimens were analyzed. We evaluated clinicopathological features of CLDN18.2 expression with four molecular subtypes: mismatch repair deficient, Epstein-Barr virus-positive, human epidermal growth factor receptor 2-positive, and others. In addition, programmed death-ligand 1 (PD-L1) combined positive score (CPS), genomic alterations, and the expression of immune cell markers were assessed. Clinical outcomes of standard first- or second-line chemotherapy and subsequent anti-programmed cell death protein 1 (anti-PD-1) therapy were also investigated according to CLDN18.2 expression.

RESULTS

Among 408 patients, CLDN18.2-positive (moderate-to-strong expression in ≥75%) was identified in 98 patients (24.0%) with almost equal distribution in the four molecular subtypes or CPS subgroups. CLDN18.2-positive was associated with Borrmann type 4, KRAS amplification, low CD16, and high CD68 expression. Overall survival with first-line chemotherapy was not significantly different between CLDN18.2-positive and -negative groups [median 18.4 versus 20.1 months; hazard ratio 1.26 (95% confidence interval 0.89-1.78); P = 0.191] regardless of stratification by PD-L1 CPS ≥5. Progression-free survival and objective response rates of first- and second-line chemotherapy, and anti-PD-1 therapy also showed no significant differences according to CLDN18.2 status.

CONCLUSIONS

CLDN18.2 expression in advanced GC/GEJC was associated with some clinical and molecular features but had no impact on treatment outcomes with chemotherapy or checkpoint inhibition. CLDN18.2-positive also had no impact on overall survival. This information could be useful to interpret the results from currently ongoing clinical trials of CLDN18.2-targeted therapies for advanced GC/GEJC and to consider a treatment strategy for CLDN18.2-positive GC/GEJC.

Impact of the 12-gene recurrence score assay on deciding adjuvant chemotherapy for stage II and IIIA/B colon cancer: the SUNRISE-DI study

BACKGROUND

Recent advances in adjuvant chemotherapy for early colon cancer have widened physicians' recommendations on the regimen and duration (3 or 6 months) of the treatment. We conducted this prospective study to evaluate whether the 12-gene recurrence score (12-RS) assay affected physicians' recommendations on adjuvant treatment selection.

PATIENTS AND METHODS

Patients with stage IIIA/IIIB or stage II colon cancer were enrolled. After the patients discussed adjuvant treatment with their treating physicians, the physicians filled in the questionnaire before assay indicating the treatment recommendation. When the 12-RS assay results were available, the physicians again filled in the questionnaire after assay. The primary endpoint was the rate of change in treatment recommendations from before to after the assay, with a threshold rate of change being 20%. Patients with stage IIIA/B to II were enrolled in a ratio of 2 : 1.

RESULTS

Overall, the treatment recommendations changed in 40% of cases after obtaining 12-RS assay results. Recommendations were changed in 45% (80/178; 95% confidence interval, 37% to 53%; P < 0.001) and 30% (29/97; 95% confidence interval, 21% to 40%; P < 0.001) of patients with stage IIIA/B and II colon cancer, respectively. Patients with stage IIIA/B cancer had significantly more change than those with stage II cancer (P = 0.0148). From before to after the 12-RS assay, the percentage of patients whose physicians reported being confident in their treatment recommendations significantly increased from 54% to 81% in stage IIIA/B (P < 0.001) and from 65% to 83% in stage II (P < 0.001).

CONCLUSION

Our study confirmed the usefulness of the 12-RS assay in aiding the physician-patient decision-making process for tailoring adjuvant chemotherapy for stage IIIA/B colon cancer.

Comprehensive analyses using next-generation sequencing and immunohistochemistry enable precise treatment in advanced gastric cancer

BACKGROUND

In advanced gastric cancer (AGC), most clinical trials are designed on the basis of protein expression or gene amplification of specific genes. Recently, next-generation sequencing (NGS) allowed us to comprehensively profile the tumor gene status. This study aimed to elucidate the profiling between gene alterations and protein expression in AGC to aid in future clinical trials on AGC.

PATIENTS AND METHODS

Formalin-fixed, paraffin-embedded tumor samples from 121 stage III/IV gastric cancer patients were examined for protein expression of tyrosine kinase receptors (RTKs; ERBB2, EGFR, c-MET, and FGFR2) using immunohistochemistry (IHC). Furthermore, 409 cancer-related genes were sequenced to detect mutations and copy number variations using NGS.

RESULTS

Most ERBB2 overexpression (IHC 3+) cases (80.0%) had ERBB2 amplification and did not have other RTK amplification or oncogene mutations. However, one-fourth of MET overexpression cases (25.0%) had ERBB2 alterations. EGFR and FGFR2 overexpression cases had ERBB2 alterations or other gene alterations such as KRAS or PIK3CA. On the other hand, most of the four RTK amplification cases (88.2%) were mutually exclusive with each amplification. However, RTK amplification did not simply correlate with protein overexpression, whereas cases with RTK high-level amplification had protein overexpression and rarely showed other co-existing gene alterations.

CONCLUSION

AGC involves a complicated arrangement of protein expression and gene alterations. Comprehensive analyses of NGS and IHC will be necessary to design the optimal therapy for treating the appropriate population of patients in future clinical trials.

Effect of the addition of bevacizumab to first-line FOLFOX on efficacy, including response rate, progression-free survival, and overall survival, in patients with metastatic colorectal cancer

588

Background: Bevacizumab (BV) is a recombinant, humanized monoclonal antibody against vascular endothelial growth factor. Used in combination with chemotherapy, BV has been shown to improve survival in both first- and second-line treatment for metastatic colorectal cancer (mCRC). However, it was reported that addition of BV to FOLFOX conferred only little survival benefit (Saltz et al. JCO2008). The aim of this study was to assess the efficacy of addition of BV to FOLFOX in first-line treatment for patients with mCRC.

Methods: Bevacizumab was approved for mCRC in July 2007 in Japan. This study was conducted at a single institution and comprised 217 consecutive patients receiving first-line treatment for mCRC between 2005 and 2009. The primary objective was to compare survival benefit in patients treated with FOLFOX4 (FF) between 2005 and 2007 with that in patients receiving FOLFOX4+BV 5 mg/kg (FF+BV) between 2007 and 2009.

Results: Total number of patients in the FF and FF+BV groups was 132 and 85, respectively. Characteristics of patients were as follows (FF vs. FF+B): median age, 62 yrs (range 28-76 yrs) vs. 60 yrs (range16-74 yrs); ECOG PS0, 98.8% vs. 81.8%; and median follow-up time, 20.8 months vs. 24.4 months. Median progression-free survival (PFS) in the FF and FF+BV groups was 10 months (95% CI, 8.7-11.3) and 17 months (95% CI, 10.2-14.1), while median overall survival (OS) was 21 months (95% CI, 17.9-24.1) and not reached, respectively. Response rate was 46% (95% CI, 37- 54) in FF, and 62% (95% CI, 51-73) in FF+BV. Addition of BV to FOLFOX4 significantly improved PFS (p=0.002) and OS (p<0.001).

Conclusions: The additive effect of BV for first-line FOLFOX was reconfirmed. These data indicate potential survival benefits from the addition of BV to FOLFOX in first-line treatment of mCRC. In addition, PFS may be a sensitive indicator of outcome prior to post-treatment.

No significant financial relationships to disclose.

Use of circulating endothelial cells to predict response to FOLFOX4 plus bevacizumab in metastatic colorectal cancer

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Background: The purpose of this study was to identify CEC threshold proposal for determining response to FOLFOX4 plus bevacizumab in metastatic colorectal cancer (mCRC).

Methods: All patients were enrolled using institutional review board-approved protocols at the Cancer Institute Hospital and provided informed consent. From July 2007 to June 2008, 33 patients treated with FOLFOX4 plus bevacizumab were enrolled in a prospective study. From January 2007 to June 2007, before bevacizumab was approved by the government in Japan, 31 patients treated with FOLFOX4 as a control were enrolled. The study population consisted of patients aged 18 years or older with histologically proven mCRC. Other inclusion criteria were Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1, adequate organ function. CECs of whole blood at the baseline, day 4, 2 weeks after initiation of chemotherapy were isolated and counted using immunomagnetics.

Results: There was no correlation between CEC levels and the outcome in the FOLFOX4. In the FOLFOX4 plus bevacizumab, CEC levels at the baseline were significantly associated with the outcome. Patients with 65 or more CECs at the baseline had shorter median PFS (9.2 months), than the median PFS of fewer than 65 CECs at the baseline (18.9 months) in the FOLFOX4 plus bevacizumab (p = 0.003). Patients with 65 or more CECs at the baseline had shorter median OS (23.3 months), than the median OS of fewer than 65 CEC s at the baseline in the FOLFOX4 plus bevacizumab (p = 0.027). In the univariate analysis, lung metastasis, lymph node metastasis, and CEC levels at the baseline predicted PFS. In the univariate Cox regression analyses, peritoneal metastasis, CEC levels at the baseline were associated with OS. In order to evaluate the independent predictive effect of FOLFOX4 plus bevacizumab, multivariate Cox regression analysis was carried out. CEC levels at the baseline were the strongest predictor.

Conclusions: A threshold of lower than 65 CEC/4mL at the baseline was a significant predictor of the outcome for colorectal cancer patients treated with FOLFOX4 plus bevacizumab.

No significant financial relationships to disclose.

Coagulo-fibrinolytic activity as a predictor of efficacy in bevacizumab-combined chemotherapy in metastatic colorectal cancer patients

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Background: The combination of bevacizumab (BV) and chemotherapy in the first-line and second-line treatment of metastatic colorectal cancer (mCRC) has been shown to improve survival. Bevacizumab is a recombinant, humanized monoclonal antibody against vascular endothelial growth factor. However, the relationship between coagulo-fibrinolytic activity factors and treatment efficacy remains to be clarified. The aim of this study was to determine potential coagulo-fibrinolytic activity markers impacting survival.

Methods: Among 119 consecutive patients included in the study, 85 received first-line FOLFOX4 plus BV 5 mg/kg and 34 received second-line FOLFIRI plus BV 5 mg/kg until progression of disease or unmanageable toxicity occurred. Coagulo-fibrinolytic activity factors, including D-dimer, thrombin antithrombin complex (TAT) and carbohydrate antigen 125 (CA125) encoded by the MUC16 mucin gene were evaluated as candidate predictors of outcome.

Results: In first-line treatment, overall response, median progression-free survival (PFS) and two-year survival rate were 61.9%, 518 days and 67.3%, respectively. In second-line treatment, overall response, median PFS and median overall survival (OS) were 23.5%, 248 days and 651 days, respectively. The outcomes of the univariate analysis were as follows: normal D-dimer and CA125 levels at baseline were associated with better PFS and OS in first-line treatment; normal TAT and CA125 levels at baseline were associated with better PFS and OS in second-line treatment. According to the results of the multivariate analysis, normal D-dimer level was associated with longer PFS in first-line treatment, and only CA125 level at baseline was an independent predictor of both PFS and OS in second-line treatment.

Conclusions: The results suggest that coagulo-fibrinolytic activity factors such as TAT, D-dimer or CA125 may be useful predictors of outcome in mCRC patients receiving BV in combination with chemotherapy.

No significant financial relationships to disclose.

Bone tissue reaction of nano-hydroxyapatite/collagen composite at the early stage of implantation

The purpose of this study was to develop a new biodegradable bone substitute materials consisting of synthesized nano-size hydroxyapatite (nano-HAp) and Type I biodegradable honeycomb collagen sponge (HCS) composites. Bone defects in rabbit mandibles were prepared by a drill, and the composites were implanted into the bone defects. The HCS only and the HCS/calcined hydroxyapatite (HAp) composite were used as comparative materials. The bone tissues reaction at the early stage within 3 weeks after implantaion was investigated histologically. Amounts of new bone formation were determined by NIH-image analysis software using the histological sections. The amounts of the new bone formation were largest in the nano HAp/HCS compared to the comparative materials. Within 2 weeks after implantation, the nano-HAp/HCS composite was more rapidly exchanged by new bone than the comparative materials. From these results it was considered that the nano-HAp/HCS composites can be used as an effective biodegradable bone substitutive material.

Preventive approach to allergic reaction to oxaliplatin

14569

Background: Allergic reaction to oxaliplatin is a chronic adverse event in the treatment of cancer. Patients with colorectal cancer were given FOLFOX4, using preventive approaches composed of two steps. Methods: Step I included 40 mg famotidine, 8 mg dexamethasone from the first cycle and 50 mg of diphenhydramine after cycle 4. In step II, for the patients who had a reaction but not a severe one in step I, a 20 mg dose of dexamethasone and four-hour oxaliplatin infusion were administered. Results: Forty-eight patients (15.1%) presented with allergic reaction, divided into group A receiving step I except diphenhydramine and B undergoing all of step I. Significant delay on occurrence was observed in group B. Thirty patients underwent step II. Prevention success (well-prevented) was defined as no reaction in two or more treatments. Allergic reaction appeared again in eleven patients (not well-prevented, 36.7%), but most well-prevented patients got four months longer treatment time with no reaction than not well-prevented patients. Conclusions: In our preventive approach, administration of H-1RA was effective in delaying the occurrence of allergic reaction to oxaliplatin, and increased dose of dexamethasone 20 mg and prolongation of oxaliplatin infusion from 2 to 4 hours was succeeded in continuing the FOLFOX4.

No significant financial relationships to disclose.

Growth factor-loaded scaffolds for bone engineering

The objective of the study presented here was to investigate the bone inductive properties as well as release kinetics of rhTGF-beta1- and rhBMP-2-loaded Ti-fiber mesh and CaP cement scaffolds. Therefore, Ti-fiber mesh and porous CaP cement scaffolds were provided with these growth factors and inserted in subcutaneous and cranial implant locations in rats and rabbits. In vitro, a rapid release of rhTGF-beta1 was observed during the first 2 h of the Ti-fiber mesh scaffolds. During this time, more than 50% of the total dose of rhTGF-beta1 was released. Following this initial peak, a decline in the level of rhTGF-beta1 occurred. After 1 week, the entire theoretical initial dose was observed to have been released. This in contrast to the rhTGF-beta1 and rhBMP-2 release of the porous CaP cement scaffolds. Here, no substantial initial burst release was observed. The scaffolds showed an initial release of about 1% after 1 day, followed by an additional marginal release after 1 week. Histological analysis revealed excellent osteoconductive properties of non-loaded Ca-P material. Inside non-loaded Ti-mesh fiber scaffolds, also bone ingrowth occurred. Quantification of the bone ingrowth showed that bone formation was increased significantly in all scaffold materials by administration of rhTGF-beta1 and rhBMP-2. Consequently, we conclude that the release kinetics of growth factors from porous CaP cement differs from other scaffold materials, like metals and polymers. Nevertheless, orthotopic bone formation in a rabbit cranial defect model was stimulated in rhTGF-beta1- and rhBMP-2-loaded CaP cement and Ti-fiber mesh scaffolds compared with non-loaded implants.

Laser-perforated membranous biomaterials induced pore size-dependent bone induction when used as a new BMP carrier

Previously we found that laser perforation of a collagen membrane (35 microm thickness, Koken Co., Tokyo) produced an effective bone morphogenetic protein (BMP) carrier, if the created pore sizes were larger than 0.5 mm. In this study we applied the same technique to create pores of 0.2 and 1.0 mm in a thicker (1.2 mm thickness) porous biodegradable membrane made of polylactic acid and an epsilon-caprolactone copolymer (PLA-CL) to obtain an effective membranous BMP carrier with higher mechanical strength. Pieces of PLA-CL (0.5 x 1.0 x 0.12 cm) combined with rhBMP-2 (5 microg) were implanted subcutaneously into rats and processed for analyses at 1-3 weeks. The laser-perforated PLA-CL membranes equipped with 1.0 mm pores induced mineralization beginning from the margins of the pores judging from the X-ray patterns, but bone formation seemed to proceed irregularly inside the pores. In the perforated PLA-CL membrane with 1.0-mm pores bone formation did not significantly increase compared with the nonperforated one. This was due to the fact that the PLA-CL membrane was already a porous structure (85% porosity). In contrast with laser-perforated PLA-CL 0.2 mm pores, bone was induced on the collagen fibers and fiber bundles inside the pores. The different patterns of bone formation between the PLA-CL membranes with 1.0 and 0.2 mm pores seemed to be related to the active formation of perpendicular collagen fibers through the 0.2 mm pores.

Carrier dependent cell differentiation of bone morphogenetic protein-2 induced osteogenesis and chondrogenesis during the early implantation stage in rats

To evaluate the osteoinductive effects of recombinant human bone morphogenetic protein (rhBMP)-2 during the early stages of rat ectopic bone formation, we prepared two distinct carriers. Two carriers, insoluble bone matrix (IBM) and fibrous glass membrane (FGM) were combined with rhBMP-2 and implanted into the backs of rats to evaluate the osteoinductive effects of the two rhBMP-2 carrier systems. Insoluble bone matrix particle size was 320 to 620 microm. Fibrous glass membrane was constructed from unwoven glass fibers 1 microm in diameter. Alkaline phosphatase (ALP) activity and type II collagen were detected in IBM/rhBMP-2 at 5 days postimplantation. Calcium (Ca) was also detected in IBM/rhBMP-2 at 7 and 9 days postimplantation. In contrast, ALP and type II collagen were detected in FGM/rhBMP-2 at 7 days. Calcium was undetected, indicating that the bone formation in IBM/rhBMP-2 proceeded faster than in FGM/rhBMP-2 during the early stage of BMP-induced osteogenesis. In addition, mRNA expression level of KDR, a receptor for vascular endothelial growth factor, was also increased in IBM/rhBMP-2. To investigate the in vivo release profile of rhBMP-2, iodine 125 ((125)I)-labeled BMP-2-incorporating IBM and FGM implants were inserted into the back subcutis of mice. More than 60% of the rhBMP-2 was released from the IBM/rhBMP-2 carrier within 1 day after implantation, whereas 50% of the rhBMP-2 was released from the FGM/rhBMP-2 10 days postimplantation. These results indicated that osteo- and chondrogenesis depends highly upon the geometry of the carrier and the in situ retention of rhBMP-2 during the early stage of rhBMP-2 induced bone formation.

In vitro effect of platelet-derived growth factor-BB on collagen synthesis and proliferation of human periodontal ligament cells

OBJECTIVES

Platelet-derived growth factor (PDGF)-BB is a polypeptide growth factor which has been shown to stimulate periodontal regeneration. In this study, we investigated the time- and dose-dependent effect of PDGF-BB on the proliferation and collagen synthesis of human periodontal ligament (PDL) cells.

MATERIALS AND METHODS

For the proliferation assay, PDL cells were cultured in 0.01-10 ng ml(-1) of PDGF-BB for 12 or 24 h, and cell numbers were counted. For the collagen synthesis assay, PDL cells were cultured in 0.1-10 ng ml(-1) of PDGF-BB for 1 to 24 h. The ratio of collagen content in total protein was evaluated, and the gene expression of type I collagen was assessed quantitatively by Northern blotting analysis.

RESULT AND CONCLUSIONS

PDGF-BB stimulated the proliferation of PDL cells in a time- and dose-dependent manner with the maximum effect at 10 ng ml(-1). PDGF-BB induced the collagen synthesis of PDL cells with the maximum effect for 24-h treatment, and 1 ng ml(-1) of PDGF-BB. PDGF-BB exhibits an inverse dose-dependent effect on proliferation and collagen synthesis by PDL cells. These findings suggest that PDGF-BB is one of the important regulators of the maintenance of the extracellular matrix in PDL, and may play an important role in the regeneration of PDL.

Histological characterization of the early stages of bone morphogenetic protein-induced osteogenesis

On the basis of currently available knowledge, we hypothesize that the initial bone formation, as induced by bone morphogenetic protein (BMP), is influenced by the chemical composition and three-dimensional spatial configuration of the used carrier material. Therefore, in the current study, the osteoinductive properties of porous titanium (Ti) fiber mesh with a calcium phosphate (Ca-P) coating (Ti-CaP), insoluble bone matrix (IBM), fibrous glass membrane (FGM), and porous particles of hydroxy apatite (PPHAP) loaded with rhBMP-2 were compared in a rat ectopic assay model at short implantation periods. Twelve Ti-CaP, 12 IBM, 12 FGM, and 12 PPHAP implants, loaded with rhBMP-2, were subcutaneously placed in 16 Wistar King rats. The rats were sacrificed at 3, 5, 7, and 9 days post-operative, and the implants were retrieved. Histological analysis demonstrated that IBM and Ti-CaP had induced ectopic cartilage and bone formation by 5 and 7 days, respectively. However, in PPHAP, bone formation and cartilage formation were seen together at 7 days. At 9 days, in Ti-CaP, IBM, and PPHAP, cartilage was seen together with trabecular bone. At 9 days, in FGM, only cartilage was observed. Quantitative rating of the tissue response, using a scoring system, demonstrated that the observed differences were statistically significant (Wilcoxon rank sum test, p < 0.05). We conclude that IBM, CaP-coated Ti mesh, FGM, and PPHAP provided with rhBMP-2 can indeed induce ectopic bone formation with a cartilaginous phase in a rat model at short implantation periods. Considering the different chemical composition and three-dimensional spatial configuration of the carrier materials used, these findings even suggest that endochondral ossification is present in rhBMP-2-induced osteogenesis, even though the amount of cartilage may differ.

Bone induction in subcutaneous tissue in rats by a newly developed DNA-coated atelocollagen and bone morphogenetic protein

A unique biomaterial, a mixture of DNA and collagen (DNA/collagen), was developed and its efficacy as a carrier matrix for bone morphogenetic protein (BMP) was evaluated histologically. The material was prepared as a composite of DNA from salmon milt and pepsin-digested type I collagen (atelocollagen) from bovine dermis. Phase-contrast and fluorescence microscopy showed atelocollagen fibres with DNA coating. The dose-response and time-course of bone induction by BMP in DNA/collagen (5 x 10 x 1 mm) in the subcutaneous tissue was investigated in 20 male Wistar rats. The BMP/DNA/collagen induced new bone in a dose-dependent manner (0, 25, 50 or 100 micrograms of BMP). Histological examination in the time-course study showed that the BMP (100 micrograms)/DNA/collagen induced bone formation, while the DNA/collagen alone resulted in the accumulation of fibroblasts. These results indicate that the DNA/collagen is effective as a carrier matrix for BMP. It provides a cell anchorage for differentiation of osteoblasts and is absorbed as bone matures.

Immunohistochemical localization of amelogenin in human odontogenic tumors, using a polyclonal antibody against bovine amelogenin

In the present study, we investigated the localization of amelogenin in odontogenic tumors, using an anti-amelogenin polyclonal antibody. In order to make the antibody, antisera against an amelogenin fraction obtained from the enamel matrix of unerupted bovine tooth was raised in rabbits. By Western blot analysis, a main band of 25 kDa and six minor bands (6.8, 12, 18, 20, 23, and 27 kDa) were detected under nonreducing conditions. Immunoreactivity for the amelogenin was observed in ameloblasts and in the immature enamel matrix of 4-day-old rats. In odontogenic tumors, positive reactions for amelogenin were localized in limited areas in adenomatoid odontogenic tumor, calcifying odontogenic cyst, primary intraosseous carcinoma and odontoma. The strongest immunoreactions were shown in enamel matrices in odontomas. Small mineralized foci in epithelial nests showed positive reactions, and a few reactions were observed in epithelium adjacent to the mineralized foci. In calcifying odontogenic cysts, some ghost cells in the lining epithelium were strongly stained. The results indicate that the present antibody for amelogenin is useful for the determination of odontogenic tumors, especially in those in which small mineralized foci are present in the epithelial nests.

Ectopic bone formation in titanium mesh loaded with bone morphogenetic protein and coated with calcium phosphate

The osteoinductive properties of porous titanium fiber mesh, with or without a calcium phosphate coating and loaded with recombinant human bone morphogenic protein-2 (rhBMP-2) or rhBMP-2 and native bovine BMP (S-300) were investigated in a rat ectopic assay model. A total of 112 calcium phosphate-coated and 112 noncoated porous titanium implants, either loaded with rhBMP-2 and S-300 or loaded with rhBMP-2 alone, were subcutaneously placed in 56 Wistar-King rats. The rats were killed 5, 10, 20, and 40 days postoperatively, and the implants were retrieved. Histologic analysis demonstrated that all growth factor and carrier combinations induced ectopic cartilage and bone formation at 5 and 10 days, respectively. At 20 days, bone formation increased and was characterized by trabecular bone and bone marrow-like tissue. At 40 days, more lamellar bone and hemopoietic bone marrow-like tissue were present. At both times, more bone had been formed in calcium phosphate-coated implants than in noncoated samples. Further, in rhBMP-2 and S-300-loaded specimens, bone formation was higher than in rhBMP-2 only-loaded specimens. In rhBMP-2 only-loaded specimens, bone formation was mainly localized inside the mesh material, whereas in specimens loaded with both rhBMP-2 and S-300, the bone was localized inside and surrounding the titanium mesh. The histological findings were confirmed by calcium content and alkaline phosphatase activity measurements. In addition, all specimens showed osteocalcin expression as early as 5 days postoperatively. Our results show that the combination of titanium mesh with BMPs can induce ectopic bone formation and that this bone formation seems to be similar to "enchondral" ossification. In addition, a thin calcium phosphate coating can have a beneficial effect on the bone-inducing properties of a scaffold material. Finally, rhBMP-2 and native BMP act synergistically in ectopic bone induction.

Geometry of carriers controlling phenotypic expression in BMP-induced osteogenesis and chondrogenesis

BACKGROUND

The effect of the geometry of extracellular matrices on bone morphogenetic protein (BMP)-induced osteogenesis has not been systematically studied. Geometry is crucially important for the scaffold in bone and joint tissue engineering. The purpose of this study was to elucidate principles of geometry of matrices in designing new scaffolds and matrices for use in reconstruction of bone and joints.

METHODS

More than ten biomaterials with different geometries, including a unique device of honeycomb-shaped hydroxyapatite, were combined with BMPs of recombinant (rhBMP-2) or natural bovine origin (S300 BMP cocktail) and implanted subcutaneously into 4-week-old Wistar-King rats. The implanted pellets were removed at 1-4 weeks and analyzed for bone and cartilage formation by histological and biochemical methods.

RESULTS

BMP-induced bone and cartilage induction was highly dependent on the geometric properties of the carrier. Some carriers such as porous particles or blocks of hydroxyapatite induced osteogenesis directly, without detectable chondrogenesis, whereas other carriers such as fibrous glass membrane induced cartilage exclusively. Still other carriers induced mostly cartilage followed by bone formation. Solid particles of hydroxyapatite and fibrous glass membrane with too tight a meshwork did not induce bone or cartilage. The optimal pore size for bone-forming efficacy in porous blocks of hydroxyapatite was a diameter of 300-400 microm. In straight tunnel structures with various diameters in honeycomb-shaped hydroxyapatite, tunnels with smaller diameters (90-120 microm) induced cartilage followed by bone formation, whereas those with larger diameters (350 microm) induced bone formation directly within the tunnels.

CONCLUSIONS

BMP carriers were classified into three types: bone-inducing, cartilage-inducing, and cartilage-bone-inducing. From the analysis of causative factors inducing osteogenesis and chondrogenesis in the BMP system, we concluded that the geometry of the carrier is crucially important and vasculature-inducing geometry should be considered in designing effective scaffolds for bone formation. We propose a classification of geometry of the artificial extracellular matrices that is useful for designing a scaffold for tissue engineering of bone and related tissues.

CLINICAL RELEVANCE

Conventional requisites of the BMP carriers for clinical use have mainly concerned the affinities of carriers with cells and biomolecules and their mechanical strength. The vasculature-inducing geometry of carriers adds a new criterion in designing systems for effective bone and joint reconstruction. The geometries of porous structures-their sizes, continuity, and straightness as verified by hydroxyapatite in this study-will be applicable for other biomaterials for clinical reconstruction therapy.