Proteasome inhibition induces DNA damage and reorganizes nuclear architecture and protein synthesis machinery in sensory ganglion neurons

Design and synthesis of the first PARP-1 and proteasome dual inhibitors to treat breast cancer

PARP-1 is a crucial factor in repairing DNA single strand damage and maintaining genomic stability. However, the use of PARP-1 inhibitors is limited to combination with chemotherapy or radiotherapy, or as a single agent for indications carrying HRR defects. The ubiquitin-proteasome system processes the majority of cellular proteins and is the principal manner by which cells regulate protein homeostasis. Proteasome inhibitors can cooperate with PARP-1 inhibitors to inhibit DNA homologous recombination repair function. In this study, we designed and synthesized the first dual PARP-1 and proteasome inhibitor based on Olaparib and Ixazomib. Both compounds 42d and 42i exhibited excellent proliferation inhibition and dual-target synergistic effects on cells that were insensitive to PARP-1 inhibitors. Further mechanistic evaluations revealed that 42d and 42i could inhibit homologous recombination repair function by down-regulating the expression of BRCA1 and RAD51. Additionally, 42i induced more significant apoptosis and showed better inhibitory effect on cell proliferation in clonal formation experiments in breast cancer cells than 42d. In summary, our study presented a new class of dual PARP-1/proteasome inhibitors with significant synergistic effects for the treatment of breast cancer.

Lysin (K)-specific demethylase 1 inhibition enhances proteasome inhibitor response and overcomes drug resistance in multiple myeloma

BACKGROUND

Multiple myeloma (MM) is an incurable plasma cell malignancy, accounting for approximately 1% of all cancers. Despite recent advances in the treatment of MM, due to the introduction of proteasome inhibitors (PIs) such as bortezomib (BTZ) and carfilzomib (CFZ), relapses and disease progression remain common. Therefore, a major challenge is the development of novel therapeutic approaches to overcome drug resistance, improve patient outcomes, and broaden PIs applicability to other pathologies.

METHODS

We performed genetic and drug screens to identify new synthetic lethal partners to PIs, and validated candidates in PI-sensitive and -resistant MM cells. We also tested best synthetic lethal interactions in other B-cell malignancies, such as mantle cell, Burkitt's and diffuse large B-cell lymphomas. We evaluated the toxicity of combination treatments in normal peripheral blood mononuclear cells (PBMCs) and bone marrow stromal cells (BMSCs). We confirmed the combo treatment' synergistic effects ex vivo in primary CD138+ cells from MM patients, and in different MM xenograft models. We exploited RNA-sequencing and Reverse-Phase Protein Arrays (RPPA) to investigate the molecular mechanisms of the synergy.

RESULTS

We identified lysine (K)-specific demethylase 1 (LSD1) as a top candidate whose inhibition can synergize with CFZ treatment. LSD1 silencing enhanced CFZ sensitivity in both PI-resistant and -sensitive MM cells, resulting in increased tumor cell death. Several LSD1 inhibitors (SP2509, SP2577, and CC-90011) triggered synergistic cytotoxicity in combination with different PIs in MM and other B-cell neoplasms. CFZ/SP2509 treatment exhibited a favorable cytotoxicity profile toward PBMCs and BMSCs. We confirmed the clinical potential of LSD1-proteasome inhibition in primary CD138+ cells of MM patients, and in MM xenograft models, leading to the inhibition of tumor progression. DNA damage response (DDR) and proliferation machinery were the most affected pathways by CFZ/SP2509 combo treatment, responsible for the anti-tumoral effects.

CONCLUSIONS

The present study preclinically demonstrated that LSD1 inhibition could provide a valuable strategy to enhance PI sensitivity and overcome drug resistance in MM patients and that this combination might be exploited for the treatment of other B-cell malignancies, thus extending the therapeutic impact of the project.

Combinations of ivermectin with proteasome inhibitors induce synergistic lethality in multiple myeloma

Multiple myeloma (MM) is an incurable malignancy of plasma cells. Ivermectin is a US Food and Drug Administration-approved drug for antiparasitic use. Here, we showed that ivermectin exerted anti-MM effects and significantly synergized with proteasome inhibitors in vitro and in vivo. Ivermectin alone exhibited mild anti-MM activity in vitro. Further investigation suggested that ivermectin inhibited proteasome activity in the nucleus by repressing the nuclear import of proteasome subunits, such as PSMB5-7 and PSMA3-4. Therefore, ivermectin treatment caused the accumulation of ubiquitylated proteins and the activation of the UPR pathway in MM cells. Furthermore, ivermectin treatment caused DNA damage and DNA damage response (DDR) signaling pathway activation in MM cells. Ivermectin and bortezomib exhibited synergized anti-MM activity in vitro. The dual-drug treatment resulted in synergistic inhibition of proteasome activity and increased DNA damage. An in vivo study using a human MM cell line xenograft mouse model showed that ivermectin and bortezomib efficiently repressed MM tumor growth in vivo, while the dual-drug treatment was well tolerated by experimental animals. Overall, our results demonstrated that ivermectin alone or cotreated with bortezomib might be promising in MM treatment.

Brain-derived neurotrophic factor: focus on the pathogenesis of multiple myeloma and the development of treatment-induced peripheral neuropathy

For many years, intensive research has been carried out on the in-depth understanding of the pathogenesis of multiple myeloma (MM). Nevertheless, the multifactorial nature of the disease, the development of drug resistance, and the side effects of therapy, make it difficult to effectively treat patients. One of the many factors involved in the pathogenesis of MM is brain-derived neurotrophic factor (BDNF). This factor is widely described as a neuroregenerative and neuroprotective agent, but it also regulates non-neuronal cell functions, such as proliferation, apoptosis, and viability. Therefore, BDNF appears to be a good therapeutic target in MM. On the other hand, its decreased concentration during treatment closely correlates with the development of peripheral neuropathy (PN). BDNF dualism requires a detailed understanding of its action on individual molecular mechanisms. Perhaps the optimization of the BDNF level will contribute to the improvement of MM treatment and the reduction of chemotherapy side effects.

Mechanistic involvement of inflammation in bortezomib induced peripheral neuropathy

AIM

To establish the role of inflammation in bortezomib induced peripheral neuropathy (BIPN).

BACKGROUND

Peripheral neuropathy is the dose-limiting toxicity of bortezomib which can lead to discontinuation of the treatment. There are multiple mechanisms involved in the disposition of BIPN. However, the role of inflammatory mediators is still under investigation. The complete understanding of inflammatory markers in relation to BIPN can lead to the development of effective therapy for prophylaxis and treatment of peripheral neuropathy.

OBJECTIVE

Based on the available data, postulate the role of inflammatory mediators in the development of peripheral neuropathy due to bortezomib.

METHOD

The "Pubmed" and "Google Scholar" were used as the search engines with terms like "peripheral neuropathy", "bortezomib induced peripheral neuropathy" and "inflammation". Original research, case reports and review articles were considered.

RESULTS

Bortezomib use is associated with the development of peripheral neuropathy. This effect is due to the damage to Schwann cells and dorsal root ganglion neurons; mitochondrial damage; increased ion channel susceptibility; and higher infiltration of macrophages in the spinal cord. All these factors collectively increase the secretion of inflammatory mediators and lead to the development of neuropathic pain.

CONCLUSION

Targeting inflammatory mediators may be helpful in the treatment of bortezomib-induced peripheral neuropathy.

The molecular and cellular insight into the toxicology of bortezomib-induced peripheral neuropathy

The proteasome inhibitor bortezomib (BTZ) is a first-line antitumor drug, mainly used for multiple myeloma treatment. However, BTZ shows prominent toxicity in the peripheral nervous system, termed BTZ-induced peripheral neuropathy (BIPN). BIPN is characterized by neuropathic pain, resulting in a dose reduction or even treatment withdrawal. To date, the pathological mechanism of BIPN has not been elucidated. There is still no effective strategy to prevent or treat BIPN. This review summarizes the pathological mechanisms of BIPN, which involves the pathological changes of Schwann cells, neurons, astrocytes and macrophages. A better knowledge of the pathological mechanisms of BIPN would provide new ideas for therapeutic interventions of BIPN patients.

Peripheral Nervous System Involvement in Non-Primary Pediatric Cancer: From Neurotoxicity to Possible Etiologies

Peripheral neuropathy is a well described complication in children with cancer. Oncologists are generally well aware of the toxicity of the main agents, but fear the side effects of new drugs. As chemotherapeutic agents have been correlated with the activation of the immune system such as in Chemotherapy Induced Peripheral Neuropathy (CIPN), an abnormal response can lead to Autoimmune Peripheral Neuropathy (APN). Although less frequent but more severe, Radiation Induced Peripheral Neuropathy may be related to irreversible peripheral nervous system (PNS). Pediatric cancer patients also have a higher risk of entering a Pediatric Intensive Care Unit for complications related to therapy and disease. Injury to peripheral nerves is cumulative, and frequently, the additional stress of a malignancy and its therapy can unmask a subclinical neuropathy. Emerging risk factors for CIPN include treatment factors such as dose, duration and concurrent medication along with patient factors, namely age and inherited susceptibilities. The recent identification of individual genetic variations has advanced the understanding of physiopathological mechanisms and may direct future treatment approaches. More research is needed on pharmacological agents for the prevention or treatment of the condition as well as rehabilitation interventions, in order to allow for the simultaneous delivery of optimal cancer therapy and the mitigation of toxicity associated with pain and functional impairment. The aim of this paper is to review literature data regarding PNS complications in non-primary pediatric cancer.

Prenatal Hyperhomocysteinemia Induces Glial Activation and Alters Neuroinflammatory Marker Expression in Infant Rat Hippocampus

Maternal hyperhomocysteinemia is one of the common complications of pregnancy that causes offspring cognitive deficits during postnatal development. In this study, we investigated the effect of prenatal hyperhomocysteinemia (PHHC) on inflammatory, glial activation, and neuronal cell death markers in the hippocampus of infant rats. Female Wistar rats received L-methionine (0.6 g/kg b.w.) by oral administration during pregnancy. On postnatal days 5 and 20, the offspring’s hippocampus was removed to perform histological and biochemical studies. After PHHC, the offspring exhibited increased brain interleukin-1β and interleukin-6 levels and glial activation, as well as reduced anti-inflammatory interleukin-10 level in the hippocampus. Additionally, the activity of acetylcholinesterase was increased in the hippocampus of the pups. Exposure to PHHC also resulted in the reduced number of neurons and disrupted neuronal ultrastructure. At the same time, no changes in the content and activity of caspase-3 were found in the hippocampus of the pups. In conclusion, our findings support the hypothesis that neuroinflammation and glial activation could be involved in altering the hippocampus cellular composition following PHHC, and these alterations could be associated with cognitive disorders later in life.

Blood molecular biomarkers for chemotherapy-induced peripheral neuropathy: From preclinical models to clinical practice

Chemotherapy-induced peripheral neuropathy (CIPN) has long been recognized as a clinically significant issue in patients treated with antineoplastic drugs. This common long-term toxic side-effect which negatively impacts the outcome of the disease can lead to disability and have detrimental effects on patients' quality of life. Since axonal injury is a prominent feature of CIPN, responsible for several sensory symptoms, including pain, sensory loss and hypersensitivity to mechanical and/or cold stimuli in the hands and feet, neurophysiological assessments remain the gold standard for clinical diagnosis of CIPN. Given the large impact of CIPN on cancer patients, there is increasing emphasis on biomarkers of adverse outcomes in safety assessment and translational research, to prevent permanent neuroaxonal damage. Since the results on reliable blood molecular markers for axonal degeneration are still controversial, here we provide a brief overview of blood molecular biomarkers used for assessing and/or predicting CIPN in preclinical and clinical settings.

Proteomic analysis of human iPSC-derived sensory neurons implicates cell stress and microtubule dynamics dysfunction in bortezomib-induced peripheral neurotoxicity

The neurotoxic effects of the chemotherapeutic agent bortezomib on dorsal root ganglia sensory neurons are well documented, yet the mechanistic underpinnings that govern these cellular processes remain incompletely understood. In this study, system-wide proteomic changes were identified in human induced pluripotent stem cell-derived sensory neurons (iSNs) exposed to a clinically relevant dose of bortezomib. Label-free mass spectrometry facilitated the identification of approximately 2800 iSN proteins that exhibited differential levels in the setting of bortezomib. A significant proportion of these proteins affect the cellular processes of microtubule dynamics, cytoskeletal and cytoplasmic organization, and molecular transport, and pathway analysis revealed an enrichment of proteins in signaling pathways attributable to the unfolded protein response and the integrated stress response. Alterations in microtubule-associated proteins suggest a multifaceted relationship exists between bortezomib-induced proteotoxicity and microtubule cytoskeletal architecture, and MAP2 was prioritized as a topmost influential candidate. We observed a significant reduction in the overall levels of MAP2c in somata without discernable changes in neurites. As MAP2 is known to affect cellular processes including axonogenesis, neurite extension and branching, and neurite morphology, its altered levels are suggestive of a prominent role in bortezomib-induced neurotoxicity.

Non-Hematologic Toxicity of Bortezomib in Multiple Myeloma: The Neuromuscular and Cardiovascular Adverse Effects

Simple Summary

Multiple myeloma (MM) is a still uncurable tumor of mainly elderly patients originating from the terminally differentiated B cells. Introduction to the treatment of MM patients of a new class of drugs called proteasome inhibitors (bortezomib followed by carfilzomib and ixazomib) significantly improved disease control. Proteasome inhibitors interfere with the major mechanism of protein degradation in a cell leading to the severe imbalance in the protein turnover that is deadly to MM cells. Currently, these drugs are the mainstream of MM therapy but are also associated with an increased rate of the injuries to multiple organs and tissues. In this review, we summarize the current knowledge on the molecular mechanisms of the first-in-class proteasome inhibitor bortezomib-induced disturbances in the function of peripheral nerves and cardiac and skeletal muscle.

Abstract

The overall approach to the treatment of multiple myeloma (MM) has undergone several changes during the past decade. and proteasome inhibitors (PIs) including bortezomib, carfilzomib, and ixazomib have considerably improved the outcomes in affected patients. The first-in-class selective PI bortezomib has been initially approved for the refractory forms of the disease but has now become, in combination with other drugs, the backbone of the frontline therapy for newly diagnosed MM patients, as well as in the maintenance therapy and relapsed/refractory setting. Despite being among the most widely used and highly effective agents for MM, bortezomib can induce adverse events that potentially lead to early discontinuation of the therapy with negative effects on the quality of life and outcome of the patients. Although peripheral neuropathy and myelosuppression have been recognized as the most relevant bortezomib-related adverse effects, cardiac and skeletal muscle toxicities are relatively common in MM treated patients, but they have received much less attention. Here we review the neuromuscular and cardiovascular side effects of bortezomib. focusing on the molecular mechanisms underlying its toxicity. We also discuss our preliminary data on the effects of bortezomib on skeletal muscle tissue in mice receiving the drug.

Nusinersen ameliorates motor function and prevents motoneuron Cajal body disassembly and abnormal poly(A) RNA distribution in a SMA mouse model

Spinal muscular atrophy (SMA) is a devastating autosomal recessive neuromuscular disease characterized by degeneration of spinal cord alpha motor neurons (αMNs). SMA is caused by the homozygous deletion or mutation of the survival motor neuron 1 (SMN1) gene, resulting in reduced expression of SMN protein, which leads to αMN degeneration and muscle atrophy. The majority of transcripts of a second gene (SMN2) generate an alternative spliced isoform that lacks exon 7 and produces a truncated nonfunctional form of SMN. A major function of SMN is the biogenesis of spliceosomal snRNPs, which are essential components of the pre-mRNA splicing machinery, the spliceosome. In recent years, new potential therapies have been developed to increase SMN levels, including treatment with antisense oligonucleotides (ASOs). The ASO-nusinersen (Spinraza) promotes the inclusion of exon 7 in SMN2 transcripts and notably enhances the production of full-length SMN in mouse models of SMA. In this work, we used the intracerebroventricular injection of nusinersen in the SMN∆7 mouse model of SMA to evaluate the effects of this ASO on the behavior of Cajal bodies (CBs), nuclear structures involved in spliceosomal snRNP biogenesis, and the cellular distribution of polyadenylated mRNAs in αMNs. The administration of nusinersen at postnatal day (P) 1 normalized SMN expression in the spinal cord but not in skeletal muscle, rescued the growth curve and improved motor behavior at P12 (late symptomatic stage). Importantly, this ASO recovered the number of canonical CBs in MNs, significantly reduced the abnormal accumulation of polyadenylated RNAs in nuclear granules, and normalized the expression of the pre-mRNAs encoding chondrolectin and choline acetyltransferase, two key factors for αMN homeostasis. We propose that the splicing modulatory function of nusinersen in SMA αMN is mediated by the rescue of CB biogenesis, resulting in enhanced polyadenylated pre-mRNA transcription and splicing and nuclear export of mature mRNAs for translation. Our results support that the selective restoration of SMN expression in the spinal cord has a beneficial impact not only on αMNs but also on skeletal myofibers. However, the rescue of SMN expression in muscle appears to be necessary for the complete recovery of motor function.

Maternal Hyperhomocysteinemia Induces Neuroinflammation and Neuronal Death in the Rat Offspring Cortex

Maternal hyperhomocysteinemia is one of the common complications of pregnancy that causes offspring cognitive deficits during postnatal development. In the present work, we evaluated the effect of prenatal hyperhomocysteinemia on structural and ultrastructural organization, neuronal and glial cell number, apoptosis (caspase-3 content and activity), inflammatory markers (tumor necrosis factor-α, interleukin-6, and interleukin-1β), and p38 mitogen-activated protein kinase (p38 MAPK) phosphorylation in the offspring brain cortex in early ontogenesis. Wistar female rats received methionine (0.6 g/kg body weight) by oral administration during pregnancy. Histological and biochemical analyses of 5- and 20-day-old pups' cortical tissue were performed. Lysosome accumulation and other neurodegenerative changes in neurons of animals with impaired embryonic development were investigated by electron microscopy. Neuronal staining (anti-NeuN) revealed a reduction in neuronal number, accompanied by increasing of caspase-3 active form protein level and activity. Maternal hyperhomocysteinemia also elevated the number of astroglial and microglial cells and increased expression of interleukin-1β and p38 MAPK phosphorylation, which indicates the development of neuroinflammatory processes.

Proteasome inhibitors trigger mutations via activation of caspases and CAD, but mutagenesis provoked by the HDAC inhibitors vorinostat and romidepsin is caspase/CAD-independent

Genotoxic anti-cancer therapies such as chemotherapy and radiotherapy can contribute to an increase in second malignancies in cancer survivors due to their oncogenic effects on non-cancerous cells. Inhibition of histone deacetylase (HDAC) proteins or the proteasome differ from chemotherapy in that they eliminate cancer cells by regulating gene expression or cellular protein equilibrium, respectively. As members of these drug classes have been approved for clinical use in recent times, we investigated whether these two drug classes exhibit similar mutagenic capabilities as chemotherapy. The HDAC inhibitors vorinostat/SAHA and romidepsin/FK288 were found to induce DNA damage, and mis-repair of this damage manifested into mutations in clonogenically viable surviving cells. DNA damage and mutations were also detected in cells treated with the proteasome inhibitor bortezomib. Exposure to both drug classes stimulated caspase activation consistent with apoptotic cell death. Inhibition of caspases protected cells from bortezomib-induced acute (but not clonogenic) death and mutagenesis, implying caspases were required for the mutagenic action of bortezomib. This was also observed for second generation proteasome inhibitors. Cells deficient in caspase-activated DNase (CAD) also failed to acquire DNA damage or mutations following treatment with bortezomib. Surprisingly, vorinostat and romidepsin maintained an equivalent level of killing and mutagenic ability regardless of caspase or CAD activity. Our findings indicate that both drug classes harbour mutagenic potential in vitro. If recapitulated in vivo, the mutagenicity of these agents may influence the treatment of cancer patients who are more susceptible to oncogenic mutations due to dysfunctional DNA repair pathways.

Persistent accumulation of unrepaired DNA damage in rat cortical neurons: nuclear organization and ChIP-seq analysis of damaged DNA

Neurons are highly vulnerable to DNA damage induced by genotoxic agents such as topoisomerase activity, oxidative stress, ionizing radiation (IR) and chemotherapeutic drugs. To avert the detrimental effects of DNA lesions in genome stability, transcription and apoptosis, neurons activate robust DNA repair mechanisms. However, defective DNA repair with accumulation of unrepaired DNA are at the basis of brain ageing and several neurodegenerative diseases. Understanding the mechanisms by which neurons tolerate DNA damage accumulation as well as defining the genomic regions that are more vulnerable to DNA damage or refractory to DNA repair and therefore constitute potential targets in neurodegenerative diseases are essential issues in the field. In this work we investigated the nuclear topography and organization together with the genome-wide distribution of unrepaired DNA in rat cortical neurons 15 days upon IR. About 5% of non-irradiated and 55% of irradiated cells accumulate unrepaired DNA within persistent DNA damage foci (PDDF) of chromatin. These PDDF are featured by persistent activation of DNA damage/repair signaling, lack of transcription and localization in repressive nuclear microenvironments. Interestingly, the chromatin insulator CTCF is concentrated at the PDDF boundaries, likely contributing to isolate unrepaired DNA from intact transcriptionally active chromatin. By confining damaged DNA, PDDF would help preserving genomic integrity and preventing the production of aberrant proteins encoded by damaged genes.

ChIP-seq analysis of genome-wide γH2AX distribution revealed a number of genomic regions enriched in γH2AX signal in IR-treated cortical neurons. Some of these regions are in close proximity to genes encoding essential proteins for neuronal functions and human neurodegenerative disorders such as epm2a (Lafora disease), serpini1 (familial encephalopathy with neuroserpin inclusion bodies) and il1rpl1 (mental retardation, X-linked 21). Persistent γH2AX signal close to those regions suggests that nearby genes could be either more vulnerable to DNA damage or more refractory to DNA repair.

Cellular bases of the RNA metabolism dysfunction in motor neurons of a murine model of spinal muscular atrophy: Role of Cajal bodies and the nucleolus

Spinal muscular atrophy (SMA) is caused by a homozygous deletion or mutation in the survival motor neuron 1 (SMN1) gene that leads to reduced levels of SMN protein resulting in degeneration of motor neurons (MNs). The best known functions of SMN is the biogenesis of spliceosomal snRNPs. Linked to this function, Cajal bodies (CBs) are involved in the assembly of spliceosomal (snRNPs) and nucleolar (snoRNPs) ribonucleoproteins required for pre-mRNA and pre-rRNA processing. Recent studies support that the interaction between CBs and nucleoli, which are especially prominent in neurons, is essential for the nucleolar rRNA homeostasis. We use the SMN∆7 murine model of type I SMA to investigate the cellular basis of the dysfunction of RNA metabolism in MNs. SMN deficiency in postnatal MNs produces a depletion of functional CBs and relocalization of coilin, which is a scaffold protein of CBs, in snRNP-free perinucleolar caps or within the nucleolus. Disruption of CBs is the earliest nuclear sign of MN degeneration. We demonstrate that depletion of CBs, with loss of CB-nucleolus interactions, induces a progressive nucleolar dysfunction in ribosome biogenesis. It includes reorganization and loss of nucleolar transcription units, segregation of dense fibrillar and granular components, retention of SUMO-conjugated proteins in intranucleolar bodies and a reactive, compensatory, up-regulation of mature 18S rRNA and genes encoding key nucleolar proteins, such as upstream binding factor, fibrillarin, nucleolin and nucleophosmin. We propose that CB depletion and nucleolar alterations are essential components of the dysfunction of RNA metabolism in SMA.

Chemotherapy-induced peripheral neuropathy: A current review

Chemotherapy-induced peripheral neuropathy (CIPN) is a common dose-limiting side effect experienced by patients receiving treatment for cancer. Approximately 30 to 40% of patients treated with neurotoxic chemotherapy will develop CIPN, and there is considerable variability in its severity between patients. It is often sensory-predominant with pain and can lead to long-term morbidity in survivors. The prevalence and burden of CIPN late effects will likely increase as cancer survival rates continue to improve. In this review, we discuss the approach to peripheral neuropathy in patients with cancer and address the clinical phenotypes and pathomechanisms of specific neurotoxic chemotherapeutic agents. Ann Neurol 2017;81:772-781.

15th Annual Meeting of the Safety Pharmacology Society: Focus on traditional sensory systems

INTRODUCTION

This report summarizes and comments key talks on the five traditional senses (ear, vestibular system, vision, taste, olfaction, and touch) which were delivered during the 2015 Annual Meeting of the Safety Pharmacology (SP) Society.

AREAS COVERED

The functional observational battery (FOB) can detect major candidate drug liabilities only on ear, touch and vision. Anatomy, physiology, pharmacology, and pathology notions on each sensory system introduce speaker talks. Techniques for evaluating drug effects on hearing functions are reviewed. Nonclinical approaches to assess vestibular toxicity leading to balance deficits are presented. Retinal explants studied with multielectrode arrays allow the identification of drug liability sites on the retina. Routinely performed Safety Pharmacology assays are not powered to address candidate drug-induced disturbances on taste and smell. This weakness needs correction since unintended pharmacological impairment of these sensorial functions may have serious health consequences. Neuropathy produced by chemotherapeutic agents may cause multiple sensorial perception distortions.

CONCLUSIONS

Safety Pharmacology studies should ensure the safety of any candidate drug on the five sensorial systems.

Bortezomib-mediated down-regulation of telomerase and disruption of telomere homeostasis contributes to apoptosis of malignant cells

Bortezomib inhibits the ubiquitin/proteasome pathway to achieve its anti-cancer effect and its well characterized activity is the NF-κB inhibition through which the anti-apoptotic bcl-2 expression is down-regulated and apoptosis is subsequently induced. However, the downstream molecular targets of bortezomib are still incompletely defined. Because telomere stabilization via activation of telomerase, induction of telomerase reverse transcriptase (hTERT) and appropriate expression of shelterin proteins is essential to cancer development and progression, we investigated the effect of bortezomib on telomere homeostasis/function in malignant cells. The bortezomib treatment of leukemic (HEL) and gastric cancer cells (BGC-823) led to significant inhibition of hTERT and telomerase expression, widespread dysregulation of shelterin protein expression, and telomere shortening, thereby triggering telomere dysfunction and DNA damage. hTERT over-expression attenuated bortezomib-induced telomere shortening, abnormal shelterin expression and telomere dysfunction. Importantly, bortezomib-mediated apoptosis of malignant cells was partially prevented by hTERT over-expression. Mechanistically, hTERT first robustly enhances bcl2 expression and maintains significantly high residual levels of bcl2 even in bortezomib-treated HEL cells. Second, hTERT protects against bortezomib-induced DNA damage. Our findings collectively reveal a profound impact of bortezomib on telomere homeostasis/function. Down-regulation of hTERT expression and telomere dysfunction induced by bortezomib both contribute to its cancer cell killing actions. It is evident from the present study that hTERT can confer resistance of malignant cells to bortezomib-based target cancer therapy, which may have important clinical implications.

Inhibition of the neuronal NFκB pathway attenuates bortezomib-induced neuropathy in a mouse model

Bortezomib is a proteasome inhibitor with a remarkable antitumor activity, used in the clinic as first line treatment for multiple myeloma. One hallmark of bortezomib mechanism of action in neoplastic cells is the inhibition of nuclear factor kappa B (NFκB), a transcription factor involved in cell survival and proliferation. Bortezomib-induced peripheral neuropathy is a dose-limiting toxicity that often requires adjustment of treatment and affects patient's prognosis and quality of life. Since disruption of NFκB pathway can also affect neuronal survival, we assessed the role of NFκB in bortezomib-induced neuropathy by using a transgenic mouse that selectively provides blockage of the NFκB pathway in neurons. Interestingly, we observed that animals with impaired NFκB activation developed significantly less severe neuropathy than wild type animals, with particular preservation of large myelinated fibers, thus suggesting that neuronal NFκB activation plays a positive role in bortezomib induced neuropathy and that bortezomib treatment might induce neuropathy by inhibiting NFκΒ in non-neuronal cell types or by targeting other signaling pathways. Therefore, inhibition of NFκB might be a promising strategy for the cotreatment of cancer and neuropathy.

Neuronal accumulation of unrepaired DNA in a novel specific chromatin domain: structural, molecular and transcriptional characterization

There is growing evidence that defective DNA repair in neurons with accumulation of DNA lesions and loss of genome integrity underlies aging and many neurodegenerative disorders. An important challenge is to understand how neurons can tolerate the accumulation of persistent DNA lesions without triggering the apoptotic pathway. Here we study the impact of the accumulation of unrepaired DNA on the chromatin architecture, kinetics of the DNA damage response and transcriptional activity in rat sensory ganglion neurons exposed to 1-to-3 doses of ionizing radiation (IR). In particular, we have characterized the structural, molecular and transcriptional compartmentalization of unrepaired DNA in persistent DNA damaged foci (PDDF). IR induced the formation of numerous transient foci, which repaired DNA within the 24 h post-IR, and a 1-to-3 PDDF. The latter concentrate DNA damage signaling and repair factors, including γH2AX, pATM, WRAP53 and 53BP1. The number and size of PDDF was dependent on the doses of IR administered. The proportion of neurons carrying PDDF decreased over time of post-IR, indicating that a slow DNA repair occurs in some foci. The fine structure of PDDF consisted of a loose network of unfolded 30 nm chromatin fiber intermediates, which may provide a structural scaffold accessible for DNA repair factors. Furthermore, the transcription assay demonstrated that PDDF are transcriptionally silent, although transcription occurred in flanking euchromatin. Therefore, the expression of γH2AX can be used as a reliable marker of gene silencing in DNA damaged neurons. Moreover, PDDF were located in repressive nuclear environments, preferentially in the perinucleolar domain where they were frequently associated with Cajal bodies or heterochromatin clumps forming a structural triad. We propose that the sequestration of unrepaired DNA in discrete PDDF and the transcriptional silencing can be essential to preserve genome stability and prevent the synthesis of aberrant mRNA and protein products encoded by damaged genes.

Dynamic Behavior of the RNA Polymerase II and the Ubiquitin Proteasome System During the Neuronal DNA Damage Response to Ionizing Radiation

Neurons are highly vulnerable to genotoxic agents. To restore genome integrity upon DNA lesions, neurons trigger a DNA damage response (DDR) that requires chromatin modifications and transcriptional silencing at DNA damage sites. To study the reorganization of the active RNA polymerase II (Pol II), which transcribes all mRNA-encoding genes, and the participation of the ubiquitin-proteasome system (UPS) in the neuronal DDR, we have used rat sensory ganglion neurons exposed to X-rays (4 Gy) ionizing radiation (IR). In control neurons, Pol II appears concentrated in numerous chromatin microfoci identified as transcription factories by the incorporation of 5'-fluorouridine into nascent RNA. Upon IR treatment, numerous IR-induced foci (IRIF), which were immunoreactive for γH2AX and 53BP1, were observed as early as 30 min post-IR; their number progressively reduced at 3 h, 1 day, and 3 days post-IR. The formation of IRIF was associated with a decrease in Pol II levels by both immunofluorescence and Western blotting. Treatment with the proteasome inhibitor bortezomib strongly increased Pol II levels in both control and irradiated neurons, suggesting that proteasome plays a proteolytic role by clearing stalled Pol II complexes at DNA damage sites, as a prelude to DNA repair. Neuronal IRIF recruited ubiquitylated proteins, including ubiquitylated histone H2A (Ub-H2A), and the catalytic proteasome 20S. Ub-H2A has been associated with transcriptional silencing at DNA damage sites. On the other hand, the participation of UPS in neuronal DDR may be essential for the ubiquitylation of Pol II and other proteasome substrates of the DNA repair machinery and their subsequent proteasome-mediated degradation.

An Overview of Bortezomib-Induced Neurotoxicity

The boronic acid dipeptide bortezomib, able to induce tumor cell death by degradation of key proteins, is the first proteasome inhibitor drug to enter clinical practice. It is employed as first-line treatment in relapsed or resistant multiple myeloma (MM) patients. However, bortezomib often induces a dose-limiting toxicity in the form of painful sensory neuropathy, which can mainly be reduced by subcutaneous administration or dose modification. In this review we focus on the current understanding of the pathophysiological mechanisms of bortezomib-induced neuropathy to allow further studies in animal models and humans, including analysis of clinical and pharmacogenetic aspects, to optimize the treatment regimens.

Targeting DNA repair pathways for cancer treatment: what's new?

Disruptions in DNA repair pathways predispose cells to accumulating DNA damage. A growing body of evidence indicates that tumors accumulate progressively more mutations in DNA repair proteins as cancers progress. DNA repair mechanisms greatly affect the response to cytotoxic treatments, so understanding those mechanisms and finding ways to turn dysregulated repair processes against themselves to induce tumor death is the goal of all DNA repair inhibition efforts. Inhibition may be direct or indirect. This burgeoning field of research is replete with promise and challenge, as more intricacies of each repair pathway are discovered. In an era of increasing concern about healthcare costs, use of DNA repair inhibitors can prove to be highly effective stewardship of R&D resources and patient expenses.

Compensatory Motor Neuron Response to Chromatolysis in the Murine hSOD1(G93A) Model of Amyotrophic Lateral Sclerosis

We investigated neuronal self-defense mechanisms in a murine model of amyotrophic lateral sclerosis (ALS), the transgenic hSOD1(G93A), during both the asymptomatic and symptomatic stages. This is an experimental model of endoplasmic reticulum (ER) stress with severe chromatolysis. As a compensatory response to translation inhibition, chromatolytic neurons tended to reorganize the protein synthesis machinery at the perinuclear region, preferentially at nuclear infolding domains enriched in nuclear pores. This organization could facilitate nucleo-cytoplasmic traffic of RNAs and proteins at translation sites. By electron microscopy analysis, we observed that the active euchromatin pattern and the reticulated nucleolar configuration of control motor neurons were preserved in ALS chromatolytic neurons. Moreover the 5'-fluorouridine (5'-FU) transcription assay, at the ultrastructural level, revealed high incorporation of the RNA precursor 5'-FU into nascent RNA. Immunogold particles of 5'-FU incorporation were distributed throughout the euchromatin and on the dense fibrillar component of the nucleolus in both control and ALS motor neurons. The high rate of rRNA transcription in ALS motor neurons could maintain ribosome biogenesis under conditions of severe dysfunction of proteostasis. Collectively, the perinuclear reorganization of protein synthesis machinery, the predominant euchromatin architecture, and the active nucleolar transcription could represent compensatory mechanisms in ALS motor neurons in response to the disturbance of ER proteostasis. In this scenario, epigenetic activation of chromatin and nucleolar transcription could have important therapeutic implications for neuroprotection in ALS and other neurodegenerative diseases. Although histone deacetylase inhibitors are currently used as therapeutic agents, we raise the untapped potential of the nucleolar transcription of ribosomal genes as an exciting new target for the therapy of some neurodegenerative diseases.