Bortezomib is cytotoxic to the human growth plate and permanently impairs bone growth in young mice

Lithium rescues cultured rat metatarsals from dexamethasone-induced growth failure

BACKGROUND

Glucocorticoids are commonly used in children with different chronic diseases. Growth failure represents a so far untreatable undesired side-effect. As lithium chloride (LiCl) is known to induce cell renewal in various tissues, we hypothesized that LiCl may prevent glucocorticoid-induced growth failure.

METHODS

We monitored growth of fetal rat metatarsals cultured ex-vivo with dexamethasone and/or LiCl, while molecular mechanisms were explored through RNA sequencing by implementing the differential gene expression and gene set analysis. Quantification of β-catenin in human growth plate cartilage cultured with dexamethasone and/or LiCl was added for verification.

RESULTS

After 14 days of culture, the length of dexamethasone-treated fetal rat metatarsals increased by 1.4 ± 0.2 mm compared to 2.4 ± 0.3 mm in control bones (p < 0.001). The combination of LiCl and dexamethasone led to bone length increase of 1.9 ± 0.3 mm (p < 0.001 vs. dexamethasone alone). By adding lithium, genes for cell cycle and Wnt/β-catenin, Hedgehog and Notch signaling, were upregulated compared to dexamethasone alone group.

CONCLUSIONS

LiCl has the potential to partially rescue from dexamethasone-induced bone growth impairment in an ex vivo model. Transcriptomics identified cell renewal and proliferation as candidates for the underlying mechanisms. Our observations may open up the development of a new treatment strategy for bone growth disorders.

IMPACT

LiCl is capable to prevent glucocorticoid-induced growth failure in rat metatarsals in vitro. The accompanying drug-induced transcriptomic changes suggested cell renewal and proliferation as candidate underlying mechanisms. Wnt/beta-catenin pathway could be one of those novel mechanisms.

The proteasome subunit psmb1 is essential for craniofacial cartilage maturation and morphogenesis

Craniofacial dysmorphisms are among the most common birth defects. Proteasome mutations frequently result in craniofacial dysmorphisms, including lower jaw malformations; however, the underlying mechanisms are unknown. Here, we used a zebrafish proteasome subunit β 1 (psmb1) mutant to define the cellular mechanisms underlying proteasome mutation-induced craniofacial dysmorphisms. psmb1 mutants exhibited a flattened ceratohyal and smaller Meckel's and palatoquadrate cartilages. Ceratohyal flattening was a result of failed chondrocyte convergent extension, accompanied by reduced numbers of chondrocytes in the lower jaw due to defects in chondrocyte differentiation. Morphogenesis of craniofacial muscles and tendons was similarly perturbed. psmb1 mutants lacked the hyohyal muscles, and craniofacial tendons were shortened and disorganized. We additionally identified a critical period for proteasome function in craniofacial development, specifically during chondrocyte and muscle differentiation. psmb1 overexpression in sox10+ cells of mutant embryos rescued both cartilage and tendon phenotypes but induced only a partial rescue of the muscle phenotype, indicating that psmb1 was required in both tissue-autonomous and nonautonomous fashions during craniofacial development. Overall, our work demonstrates that psmb1 is required for craniofacial cartilage, tendon, and muscle differentiation and morphogenesis.

Humanin Treatment Protects Against Venetoclax-Induced Bone Growth Retardation in Ex Vivo Cultured Rat Bones

Context

Recent preclinical studies reported that the BCL-2 inhibitor venetoclax can impair bone growth. A strategy to prevent such a side effect of this promising anticancer drug is highly desired. Earlier in vitro and in vivo studies suggested that the mitochondrial peptide humanin has the potential to prevent drug-induced growth impairment.

Objective

We hypothesized that co-treatment with the humanin analog HNG may prevent venetoclax-induced bone growth impairment.

Methods

Ex vivo studies were performed in fetal rat metatarsal bones and human growth plate samples cultured for 12 and 2 days, respectively, while in vivo studies were performed in young neuroblastoma mice being treated daily for 14 days. The treatment groups included venetoclax, HNG, venetoclax plus HNG, or vehicle. Bone growth was continuously monitored and at the end point, histomorphometric and immunohistochemical analyses were performed in fixed tissues.

Results

Venetoclax suppressed metatarsal bone growth and when combined with HNG, bone growth was rescued and all histological parameters affected by venetoclax monotherapy were normalized. Mechanistic studies showed that HNG downregulated the pro-apoptotic proteins Bax and p53 in cultured metatarsals and human growth plate tissues, respectively. The study in a neuroblastoma mouse model confirmed a growth-suppressive effect of venetoclax treatment. In this short-term in vivo study, no significant bone growth-rescuing effect could be verified when testing HNG at a single dose. We conclude that humanin dose-dependently protects ex vivo cultured metatarsal bones from venetoclax-induced bone growth impairment by restoring the growth plate microstructure.

MiRNAs in renal cell carcinoma

MicroRNAs (miRNAs) are small RNA sequences that act as post-transcriptional regulatory genes to control many cellular processes through pairing bases with a complementary messenger RNA (mRNA). A single miRNA molecule can regulate more than 200 different transcripts and the same mRNA can be regulated by multiple miRNAs. In this review, we highlight the importance of miRNAs and collect the existing evidence on their relationship with kidney cancer.

Radial shockwave treatment promotes chondrogenesis in human growth plate and longitudinal bone growth in rabbits

OBJECTIVE

The process of longitudinal bone growth occurs at the growth plate where the chondrocytes undergo apparent structural and molecular changes to promote growth. Recent reports suggest that radial shockwave treatment (rSWT) stimulates bone length in cultured fetal rat metatarsals. Therefore, we investigated if rSWT has similar growth promoting effects on cultured human growth plate fragments and addressed the same in a preclinical in vivo rabbit model by subjecting their growth plates to rSWT.

METHODS

Short-term effects of high-energy rSWT were evaluated in a unique model of cultured human growth plate cartilage (n = 5) wherein samples exposed to rSWT were assessed for chondrogenic markers at 24 h in comparison to unexposed samples obtained from the same limb. Local in vivo effects were studied in six-week-old rabbits who had their distal femurs exposed to four weekly sessions of rSWT at low- and high-energy levels (n = 4 each). At sacrifice, histomorphometric and immunohistochemistry analyses were performed. For effect on longitudinal growth, proximal tibiae of 22-week-old rabbits (n = 12) were asymmetrically exposed to rSWT; the contralateral side served as untreated controls. At sacrifice, the final bone length was measured.

RESULTS

In the ex vivo model of cultured human growth plate cartilage, rSWT exposure upregulated SOX9 and COL2A1 compared to control. In the immature rabbit model, an increased number of proliferative chondrocytes and column density was seen for both the energy levels. In the adolescent rabbits, an increase in tibial length was observed after the fourth session of high-energy rSWT and until six-weeks after rSWT compared to the untreated limb.

CONCLUSIONS

Our preliminary experimental results suggest that rSWT may serve as a non-invasive treatment and possibly a safe strategy to stimulate longitudinal bone growth. However, further studies are needed to assess the in vivo effects of rSWT in models of disturbed bone growth.

A unique amphiphilic triblock copolymer, nontoxic to human blood and potential supramolecular drug delivery system for dexamethasone

The drug delivery system (DDS) often causes toxicity, triggering undesired cellular injuries. Thus, developing supramolecules used as DDS with tunable self-assembly and nontoxic behavior is highly desired. To address this, we aimed to develop a tunable amphiphilic ABA-type triblock copolymer that is nontoxic to human blood cells but also capable of self-assembling, binding and releasing the clinically used drug dexamethasone. We synthesized an ABA-type amphiphilic triblock copolymer (P2L) by incorporating tetra(aniline) TANI as a hydrophobic and redox active segment along with monomethoxy end-capped polyethylene glycol (mPEG2k; Mw = 2000 g mol-1) as biocompatible, flexible and hydrophilic part. Cell cytotoxicity was measured in whole human blood in vitro and lung cancer cells. Polymer-drug interactions were investigated by UV-Vis spectroscopy and computational analysis. Our synthesized copolymer P2L exhibited tuned self-assembly behavior with and without external stimuli and showed no toxicity in human blood samples. Computational analysis showed that P2L can encapsulate the clinically used drug dexamethasone and that drug uptake or release can also be triggered under oxidation or low pH conditions. In conclusion, copolymer P2L is nontoxic to human blood cells with the potential to carry and release anticancer/anti-inflammatory drug dexamethasone. These findings may open up further investigations into implantable drug delivery systems/devices with precise drug administration and controlled release at specific locations.

Methylation and expression levels of microRNA-23b/-24-1/-27b, microRNA-30c-1/-30e, microRNA-301a and let-7g are dysregulated in clear cell renal cell carcinoma

BACKGROUND

Renal cell carcinoma is the most common form of kidney cancer in adults. DNA methylation of regulatory sequences at the genomic level and interaction between microRNAs and the messenger RNAs of target genes at the posttranscriptional level contribute to the dynamic regulation of gene activity. Aberrations in these mechanisms can result in impaired functioning of cell signaling pathways, such as that observed in malignant tumors. We hypothesized that microRNA genes methylation may be associated with renal cancer in patients.

METHODS AND RESULTS

We examined methylation levels of 22 microRNA genes in tumor and normal kidney tissue of 30 patients with TNM Stage III clear cell renal cell carcinoma using a pathway-specific real-time polymerase chain reaction array (EpiTect Methyl II PCR Arrays, Qiagen). MicroRNA expression analysis by quantitative polymerase chain reaction was also performed. Significant differences in methylation levels were found in two genes and in two clusters of microRNA genes. MicroRNA-23b/-24-1/-27b, microRNA -30c-1/-30e and let-7 g was hypermetylated in clear cell renal cell carcinoma tissue, microRNA -301a was hypomethylated in tumor compared with the adjacent normal tissues. Expression of microRNA-301a, microRNA-23b in the clear cell renal cell carcinoma tissues was significantly overexpressed when compared with the adjacent normal tissues and let-7 g was significantly downregulated in tumor.

CONCLUSIONS

Our results may indicate the contribution of microRNA-301a, microRNA-23b and let-7 g in the pathogenesis of renal cancer, but further studies are needed to determine the functional significance of the detected changes.

Activity of immunoproteasome inhibitor ONX-0914 in acute lymphoblastic leukemia expressing MLL-AF4 fusion protein

Proteasome inhibitors bortezomib and carfilzomib are approved for the treatment of multiple myeloma and mantle cell lymphoma and have demonstrated clinical efficacy for the treatment of acute lymphoblastic leukemia (ALL). The t(4;11)(q21;q23) chromosomal translocation that leads to the expression of MLL-AF4 fusion protein and confers a poor prognosis, is the major cause of infant ALL. This translocation sensitizes tumor cells to proteasome inhibitors, but toxicities of bortezomib and carfilzomib may limit their use in pediatric patients. Many of these toxicities are caused by on-target inhibition of proteasomes in non-lymphoid tissues (e.g., heart muscle, gut, testicles). We found that MLL-AF4 cells express high levels of lymphoid tissue-specific immunoproteasomes and are sensitive to pharmacologically relevant concentrations of specific immunoproteasome inhibitor ONX-0914, even in the presence of stromal cells. Inhibition of multiple active sites of the immunoproteasomes was required to achieve cytotoxicity against ALL. ONX-0914, an inhibitor of LMP7 (ß5i) and LMP2 (ß1i) sites of the immunoproteasome, and LU-102, inhibitor of proteasome ß2 sites, exhibited synergistic cytotoxicity. Treatment with ONX-0914 significantly delayed the growth of orthotopic ALL xenograft tumors in mice. T-cell ALL lines were also sensitive to pharmacologically relevant concentrations of ONX-0914. This study provides a strong rationale for testing clinical stage immunoproteasome inhibitors KZ-616 and M3258 in ALL.

Resveratrol Reduces COMPopathy in Mice Through Activation of Autophagy

Misfolding mutations in cartilage oligomeric matrix protein (COMP) cause it to be retained within the endoplasmic reticulum (ER) of chondrocytes, stimulating a multitude of damaging cellular responses including ER stress, inflammation, and oxidative stress, which ultimately culminates in the death of growth plate chondrocytes and pseudoachondroplasia (PSACH). Previously, we demonstrated that an antioxidant, resveratrol, substantially reduces the intracellular accumulation of mutant-COMP, dampens cellular stress, and lowers the level of growth plate chondrocyte death. In addition, we showed that resveratrol reduces mammalian target of rapamycin complex 1 (mTORC1) signaling, suggesting a potential mechanism. In this work, we investigate the role of autophagy in treatment of COMPopathies. In cultured chondrocytes expressing wild-type COMP or mutant-COMP, resveratrol significantly increased the number of Microtubule-associated protein 1A/1B-light chain 3 (LC3) vesicles, directly demonstrating that resveratrol-stimulated autophagy is an important component of the resveratrol-driven mechanism responsible for the degradation of mutant-COMP. Moreover, pharmacological inhibitors of autophagy suppressed degradation of mutant-COMP in our established mouse model of PSACH. In contrast, blockage of the proteasome did not substantially alter resveratrol clearance of mutant-COMP from growth plate chondrocytes. Mechanistically, resveratrol increased SIRT1 and PP2A expression and reduced MID1 expression and activation of phosphorylated protein kinase B (pAKT) and mTORC1 signaling in growth plate chondrocytes, allowing clearance of mutant-COMP by autophagy. Importantly, we show that optimal reduction in growth plate pathology, including decreased mutant-COMP retention, decreased mTORC1 signaling, and restoration of chondrocyte proliferation was attained when treatment was initiated between birth to 1 week of age in MT-COMP mice, translating to birth to approximately 2 years of age in children with PSACH. These results clearly demonstrate that resveratrol stimulates clearance of mutant-COMP by an autophagy-centric mechanism. © 2020 The Authors. JBMR Plus published by Wiley Periodicals LLC. on behalf of American Society for Bone and Mineral Research.

Timing of proteasome inhibition as a pharmacologic strategy for prevention of muscle contractures in neonatal brachial plexus injury

Neonatal brachial plexus injury (NBPI) causes disabling and incurable contractures, or limb stiffness, which result from proteasome-mediated protein degradation impairing the longitudinal growth of neonatally denervated muscles. We recently showed in a mouse model that the 20S proteasome inhibitor, bortezomib, prevents contractures after NBPI. Given that contractures uniquely follow neonatal denervation, the current study tests the hypothesis that proteasome inhibition during a finite window of neonatal development can prevent long-term contracture development. Following neonatal forelimb denervation in P5 mice, we first outlined the minimum period for proteasome inhibition to prevent contractures 4 weeks post-NBPI by treating mice with saline or bortezomib for varying durations between P8 and P32. We then compared the ability of varying durations of longer-term proteasome inhibition to prevent contractures at 8 and 12 weeks post-NBPI. Our findings revealed that proteasome inhibition can be delayed 3-4 days after denervation but is required throughout skeletal growth to prevent contractures long term. Furthermore, proteasome inhibition becomes less effective in preventing contractures beyond the neonatal period. These therapeutic effects are primarily associated with bortezomib-induced attenuation of 20S proteasome β1 subunit activity. Our collective results, therefore, demonstrate that temporary neonatal proteasome inhibition is not a viable strategy for preventing contractures long term. Instead, neonatal denervation causes a permanent longitudinal growth deficiency that must be continuously ameliorated during skeletal growth. Additional mechanisms must be explored to minimize the necessary period of proteasome inhibition and reduce the risk of toxicity from long-term treatment.

Fluoride Inhibits Longitudinal Bone Growth by Acting Directly at the Growth Plate in Cultured Neonatal Rat Metatarsal Bones

Excessive intake of fluoride inhibits bone growth in both humans and animals. It is unknown whether fluoride acts directly on the growth plate to inhibit longitudinal bone growth, and its mechanism of action has not been elucidated. In this study, we used an organ culture system and SW1353 cells to evaluate the effects of fluoride on endochondral ossification. Neonatal rat metatarsal bones were dissected and cultured with or without fluoride for 7 days. The total length and width of the metatarsal rudiments and the length of the calcification zone were measured. Chondrocyte proliferation, differentiation, and apoptosis were analyzed by immunohistochemistry and TUNEL assay in sectioned bones. The apoptosis was detected by flow cytometry, and the expression of apoptosis-related proteins Bax, Bcl-2, and Caspase-3 were detected by western blotting in SW1353 cells. Linear measurements demonstrated that fluoride induced a biphasic effect on longitudinal bone growth in organ culture, with a significant growth inhibition at a high concentration (10^-4 M) and a stimulatory action at low concentration (10^-6 M) of fluoride. Histomorphometrical analysis of growth plate from fluoride-exposed metatarsal rudiments showed a significant reduction in the height of the proliferative and hypertrophic chondrocyte zones. Analysis of the Col2α1 and Col10α1 expression by immunohistochemistry revealed fluoride-suppressed metatarsal growth plate chondrocyte proliferation and differentiation. In addition, fluoride increased the number of apoptotic chondrocytes in the metatarsal growth plate. Western blotting showed an up-regulated expression of Caspase-3 and Bax and down-regulated expression of anti-apoptotic protein Bcl-2 after treatment with 5 × 10^-4 M fluoride in SW1353 cells. Our findings indicated that fluoride inhibited longitudinal bone growth by acting directly at the growth plate in cultured neonatal rat metatarsal bones. Such growth inhibition was mediated by suppressing proliferation and differentiation, increasing apoptosis of resting chondrocytes and causing premature cell senescence in the growth plate.

Radial shock waves prevent growth retardation caused by the clinically used drug vismodegib in ex vivo cultured bones

In childhood medulloblastoma patients, the hedgehog antagonist vismodegib is an effective anti-cancer treatment but unfortunately induces irreversible growth arrests and growth impairment limiting its use in skeletally immature patients. We hypothesized that radial shock wave treatment (rSWT) may protect drug-induced growth impairment owing to its osteogenic effects. Fetal rat metatarsal bones were exposed to vismodegib (day 0–5; 100 nM) and/or rSWT (single session); other bones from day 1 were continuously exposed to a Gli1 antagonist (GANT61; 10 µM) and/or rSWT (single session). Control bones were untreated. The bone length was measured at intervals; histomorphometric analysis and immunostaining for PCNA, Gli1, and Ihh were performed on the sectioned bones. Bones treated with vismodegib showed impaired bone growth, reduced height of the resting-proliferative zone and reduced hypertrophic cell size compared to control. In vismodegib treated bones, a single session of rSWT partially rescued bone growth, increased the growth velocity, hypertrophic cell size, and restored growth plate morphology. Bones exposed to GANT61 showed impaired bone growth and disorganized growth plate while when combined with rSWT these effects were partially prevented. Locally applied rSWT had a chondroprotective effect in rat metatarsal bones and suggest a novel strategy to prevent growth impairment caused by vismodegib.

Switching to Bortezomib may Improve Recovery From Severe Vincristine Neuropathy in Pediatric Acute Lymphoblastic Leukemia

PURPOSE

The purpose of this study was to evaluate the impact of switching patients being treated for acute lymphoblastic leukemia (ALL) from vincristine to bortezomib.

PATIENTS AND METHODS

A total of 20 patients with ALL were switched from vincristine to bortezomib (1.3 mg/m/dose) because of worsening neuropathy despite physical therapy interventions (n=18) or at increased risk of neuropathy (n=2). Relapse rates were compared with 56 vincristine-only patients matched by prognostic factors. Maintenance blood counts in bortezomib patients were compared with cooperative group data using vincristine during maintenance. In addition, 6 evaluable patients were assessed for neuropathy using the pediatric-modified total neuropathy score. Neuropathy scores were collected during treatment with vincristine and after switching to bortezomib.

RESULTS

After a median follow-up of 3.5 years the relapse rate in patients switched to bortezomib was nonsignificantly different than those remaining on vincristine. Patients on monthly bortezomib had statistically significantly lower platelet counts that did not require transfusions or dose adjustment. Total neuropathy for all 6 cases decreased significantly when switched to bortezomib from vincristine (P=0.015), with motor neuropathy declines in 5 of 6 subjects.

CONCLUSIONS

Bortezomib substitution for vincristine in ALL treatment is a potential strategy to mitigate severe vincristine neuropathy. These findings should be confirmed in a randomized clinical trial to further assess benefits and risks of this approach.

Profound activity of the anti-cancer drug bortezomib against Echinococcus multilocularis metacestodes identifies the proteasome as a novel drug target for cestodes

A library of 426 FDA-approved drugs was screened for in vitro activity against E. multilocularis metacestodes employing the phosphoglucose isomerase (PGI) assay. Initial screening at 20 µM revealed that 7 drugs induced considerable metacestode damage, and further dose-response studies revealed that bortezomib (BTZ), a proteasome inhibitor developed for the chemotherapy of myeloma, displayed high anti-metacestodal activity with an EC₅₀ of 0.6 µM. BTZ treatment of E. multilocularis metacestodes led to an accumulation of ubiquinated proteins and unequivocally parasite death. In-gel zymography assays using E. multilocularis extracts demonstrated BTZ-mediated inhibition of protease activity in a band of approximately 23 kDa, the same size at which the proteasome subunit beta 5 of E. multilocularis could be detected by Western blot. Balb/c mice experimentally infected with E. multilocularis metacestodes were used to assess BTZ treatment, starting at 6 weeks post-infection by intraperitoneal injection of BTZ. This treatment led to reduced parasite weight, but to a degree that was not statistically significant, and it induced adverse effects such as diarrhea and neurological symptoms. In conclusion, the proteasome was identified as a drug target in E. multilocularis metacestodes that can be efficiently inhibited by BTZ in vitro. However, translation of these findings into in vivo efficacy requires further adjustments of treatment regimens using BTZ, or possibly other proteasome inhibitors.

Tapeworms (cestodes) are a class of important human pathogens, causing very severe diseases in man such as alveolar echinococcosis (Echinococcus multilocularis), cystic echinococcosis (E. granulosus) and neurocysticercosis (Taenia solium). Current treatments are mainly based on benzimidazoles that show some limited activity against cestode larvae, but often do not kill them. These compounds have to be taken for extended periods of time, and can cause adverse side-effects. Cestode infections cause neglected diseases and the pharmaceutical industry is generally not interested in investments for developing novel bioactive compounds. In this study we focus on a panel of FDA-approved drugs and assessed them in E. multilocularis, which causes the most deadly of all helminth infections. One compound, the anti-cancer drug bortezomib, exhibits considerable in vitro activity against E. multilocularis metacestodes, and we provide evidence that it acts on the proteasome. In experimentally infected mice bortezomib activity was lower than the currently used albendazole and induced adverse effects. Bortezomib is therefore not a useful drug for treatment of Echinococcus larvae, but our results demonstrate that in future studies the cestode proteasome should gain more attention as a drug target.

Bortezomib treatment causes long-term testicular dysfunction in young male mice

Background

With increased long-term survivors of childhood cancer patients, therapy-associated infertility has become one of the most common late side-effects and significantly affects their life-quality. Therefore, evaluation of anti-cancer agents on male reproduction and infertility prevention are urgently demanding. The proteasome inhibitor bortezomib has been launched in clinical trials for childhood cancers, however, its potential side effects on reproduction have so far been neither investigated experimentally nor reported in treated children. Thus the present study is designed to explore the impact of bortezomib on male reproductive function and to gain insights into how bortezomib exerts its adverse effects on man gonad, thereby providing pediatric oncologists relevant information.

Methods

35 day-old male mice were treated with one 11-day cycle of bortezomib and then sacrificed 2 days, 45 days, or 6 months later. A mating study was performed in the group followed for 6 months, and their pups were analyzed on postnatal day 50. Serum follicle-stimulating hormone (FSH) and testicular testosterone levels were measured. Testicular morphology was evaluated by light- and electron microscopy, and the underlying mechanisms and pathways of testis damage were investigated.

Results

Testicular damage was visible already 2 days after stopping bortezomib and increased in severity by day 45. Then 80% of seminiferous tubules exhibited hypospermatogenesis with arrest at the levels of spermatogonia, spermatocytes and round spermatids. Germ cells were specifically targeted by bortezomib as evidenced by increased apoptosis mediated through activation of p53 and caspases. Even six months after the bortezomib treatment, testis weight, sperm concentration and seminiferous tubule length remained at a decreased level, indicating that spermatogenesis and tubular outgrowth could not fully recover. Combined with persistently increased serum levels of FSH in these mice, our results demonstrate that bortezomib can have long-term effects on testicular function, although fertility of bortezomib-exposed males remained and their offspring looked healthy.

Conclusion

Bortezomib treatment causes long-term gonadal dysfunction in male mice. Careful monitoring of gonadal function in male childhood cancer patients treated with bortezomib is thus strongly recommended.

Protective role of humanin on bortezomib-induced bone growth impairment in anticancer treatment

BACKGROUND

Bortezomib is a proteasome inhibitor currently studied in clinical trials of childhood cancers. So far, no side effects on bone growth have been reported in treated children. However, bortezomib was recently found to induce apoptosis in growth plate chondrocytes and impair linear bone growth in treated mice. We hypothesize that [Gly(14)]-humanin (HNG), a 24-amino acid synthetic antiapoptotic peptide, can prevent bortezomib-induced bone growth impairment.

METHODS

Mice with human neuroblastoma or medulloblastoma tumor xenografts (9-13 animals/group) received one 2-week cycle (2 injections/week) of bortezomib (0.8 mg/kg or 1.0mg/kg), or HNG (1 µg/mouse), or the combination of HNG/bortezomib, or vehicle. Cultures of human growth plate cartilage, chondrogenic- and cancer cell lines, and immunohistochemistry for detection of proapoptotic proteins were also used. Statistical significance was evaluated by two-sided Mann-Whitney U test or by parametric or nonparametric analysis of variance.

RESULTS

Bortezomib efficiently blocked the proteasome and induced pronounced impairment of linear bone growth from day 0 to day 13 (0.09 mm/day, 95% confidence interval [CI] = 0.07 to 0.11 mm/day; vs 0.19 mm/day, 95% CI = 0.15 to 0.23 mm/day in vehicle; P < .001), an effect significantly prevented by the addition of HNG (0.15 mm growth/day, 95% CI = 0.14 to 0.16 mm/day; P < .001 vs bortezomib only; P = 0.03 vs vehicle). Bortezomib was highly toxic when added to cultures of human growth plate cartilage, with markedly increased apoptosis compared with control (P < .001). However, when combining with HNG, bortezomib-induced apoptosis was entirely prevented, as was Bax and PARP activation. Bortezomib delayed tumor growth, and HNG did not interfere with the anticancer effect when studied in human tumor xenografts or cell lines.

CONCLUSIONS

HNG prevents bortezomib-induced bone growth impairment without interfering with bortezomib's desired anticancer effects.