The relationship among tumor architecture, pharmacokinetics, pharmacodynamics, and efficacy of bortezomib in mouse xenograft models

Case report: Preclinical efficacy of NEDD8 and proteasome inhibitors in patient-derived models of signet ring high-grade mucinous colorectal cancer from a Lynch syndrome patient

High-grade mucinous colorectal cancer (HGM CRC) is particularly aggressive, prone to metastasis and treatment resistance, frequently accompanied by "signet ring" cancer cells. A sizeable fraction of HGM CRCs (20-40%) arises in the context of the Lynch Syndrome, an autosomal hereditary syndrome that predisposes to microsatellite instable (MSI) CRC. Development of patient-derived preclinical models for this challenging subtype of colorectal cancer represents an unmet need in oncology. We describe here successful propagation of preclinical models from a case of early-onset, MSI-positive metastatic colorectal cancer in a male Lynch syndrome patient, refractory to standard care (FOLFOX6, FOLFIRI-Panitumumab) and, surprisingly, also to immunotherapy. Surgical material from a debulking operation was implanted in NOD/SCID mice, successfully yielding one patient-derived xenograft (PDX). PDX explants were subsequently used to generate 2D and 3D cell cultures. Histologically, all models resembled the tumor of origin, displaying a high-grade mucinous phenotype with signet ring cells. For preclinical exploration of alternative treatments, in light of recent findings, we considered inhibition of the proteasome by bortezomib and of the related NEDD8 pathway by pevonedistat. Indeed, sensitivity to bortezomib was observed in mucinous adenocarcinoma of the lung, and we previously found that HGM CRC is preferentially sensitive to pevonedistat in models with low or absent expression of cadherin 17 (CDH17), a differentiation marker. We therefore performed IHC on the tumor and models, and observed no CDH17 expression, suggesting sensitivity to pevonedistat. Both bortezomib and pevonedistat showed strong activity on 2D cells at 72 hours and on 3D organoids at 7 days, thus providing valid options for in vivo testing. Accordingly, three PDX cohorts were treated for four weeks, respectively with vehicle, bortezomib and pevonedistat. Both drugs significantly reduced tumor growth, as compared to the vehicle group. Interestingly, while bortezomib was more effective in vitro, pevonedistat was more effective in vivo. Drug efficacy was further substantiated by a reduction of cellularity and of Ki67-positive cells in the treated tumors. These results highlight proteasome and NEDD8 inhibition as potentially effective therapeutic approaches against Lynch syndrome-associated HGM CRC, also when the disease is refractory to all available treatment options.

Quaternary nanoparticles enable sustained release of bortezomib for hepatocellular carcinoma

BACKGROUND AND AIMS

Hepatocellular carcinoma (HCC) represents the third leading cause of cancer-related mortality in the world. Over the past two decades, there has been minimal improvement in therapies as well as clinical outcomes for patients with Barcelona Clinic Liver Cancer (BCLC)-B. These patients are treated with local interventions, including transarterial chemoembolization. Current methodologies only allow sustained intratumoral release measured in hours. Methodologies to allow sustained local release of the drug cargo over days to weeks are acutely needed. We hypothesize that tumor response as well as outcomes of patients with BCLC-B can be improved through utilization of a highly cytotoxic agent delivered with a sustained release platform.

APPROACH AND RESULTS

High-throughput drug screening across 40 HCC patient-derived organoids identified bortezomib (BTZ) as a highly cytotoxic small molecule for HCC. We designed and manufactured sustained release BTZ nanoparticles (BTZ-NP) using a flash nanocomplexation/nanoprecipitation process. We quantified the release profile and tested the anti-tumoral effects in vivo. The BTZ-NP formulation demonstrated a sustained release of BTZ of 30 days. This BTZ-NP formulation was highly effective in controlling tumor size and improved survival in vivo in three animal models of HCC, including when delivered via the hepatic artery, as we envision its delivery in patients. In addition, the BTZ-NP formulation was superior to treatment with doxorubicin-drug eluting beads.

CONCLUSIONS

The BTZ-NP formulation provides a potent and safe treatment of HCC via a localized delivery approach. These results warrant additional preclinical studies to advance this technology to human clinical trials.

The efficacy and mechanism of proteasome inhibitors in solid tumor treatment

BACKGROUND

The ubiquitin-proteasome system (UPS) is critical in cellular protein degradation and widely involved in the regulations of cancer hallmarks. Targeting the UPS pathway has emerged as a promising novel treatment in hematological malignancies and solid tumors.

OBJECTIVE

This review mainly focuses on the preclinical results of proteasome inhibitors in solid tumors.

METHODS

We analyzed the published articles associated with the anticancer results of proteasome inhibitors alone or combination chemotherapy in solid tumors. Important data presented in abstract form were also discussed in this review.

RESULTS/CONCLUSION

Proteasome inhibitors, such as bortezomib and carfilzomib, are highly effective in treating solid tumors. The anticancer efficacy is not limited to affect the proteasomal inhibition-associated signaling pathways but also widely involves the signaling pathways related to cell cycle, apoptosis, and epithelial-mesenchymal transition (EMT). In addition, proteasome inhibitors overcome the conventional chemo-resistance of standard chemotherapeutics by inhibiting signaling pathways, such as NF-κB or PI3K/Akt. Combination chemotherapy of proteasome inhibitors and standard chemotherapeutics are widely investigated in multiple relapsed or chemo-resistant solid tumor types, such as breast cancer and pancreatic cancer. The proteasome inhibitors re-sensitize the standard chemotherapeutic regimens and induce synergistic anticancer effects. The development of novel proteasome inhibitors and delivery systems also improves the proteasome inhibitors' anticancer efficacy in solid tumors. This review summarizes the current preclinical results of proteasome inhibitors in solid tumors and reveals the potential anticancer mechanisms.

Chemical Screen Identifies Diverse and Novel Histone Deacetylase Inhibitors as Repressors of NUT Function: Implications for NUT Carcinoma Pathogenesis and Treatment

NUT carcinoma (NC), characterized most commonly by the BRD4-NUTM1 fusion, is a rare, aggressive variant of squamous carcinoma with no effective treatment. BRD4-NUT drives growth and maintains the poorly differentiated state of NC by activating pro-growth genes such as MYC, through the formation of massive, hyperacetylated, superenhancer-like domains termed megadomains. BRD4-NUT-mediated hyperacetylation of chromatin is facilitated by the chromatin-targeting tandem bromodomains of BRD4, combined with NUT, which recruits the histone acetyltransferase, p300. Here, we developed a high-throughput small-molecule screen to identify inhibitors of transcriptional activation by NUT. In this dCAS9-based GFP-reporter assay, the strongest hits were diverse histone deacetylase (HDAC) inhibitors. Two structurally unrelated HDAC inhibitors, panobinostat and the novel compound, IRBM6, both repressed growth and induced differentiation of NC cells in proportion to their inhibition of NUT transcriptional activity. These two compounds repressed transcription of megadomain-associated oncogenic genes, such as MYC and SOX2, while upregulating pro-differentiation, non-megadomain-associated genes, including JUN, FOS, and key cell-cycle regulators, such as CDKN1A. The transcriptional changes correlate with depletion of BRD4-NUT from megadomains, and redistribution of the p300/CBP-associated chromatin acetylation mark, H3K27ac, away from megadomains toward regular enhancer regions previously populated by H3K27ac. In NC xenograft models, we demonstrated that suppression of tumor growth by panobinostat was comparable with that of bromodomain inhibition, and when combined they improved both survival and growth suppression. IMPLICATIONS: The findings provide mechanistic and preclinical rationale for the use of HDAC inhibitors, alone or combined with other agents, in the treatment of NUT carcinoma.

The Proteasome Inhibitor Ixazomib Inhibits the Formation and Growth of Pulmonary and Abdominal Osteosarcoma Metastases in Mice

Osteosarcoma is the most common form of primary bone cancer. Over 20% of osteosarcoma patients present with pulmonary metastases at diagnosis, and nearly 70% of these patients fail to respond to treatment. Previous work revealed that human and canine osteosarcoma cell lines are extremely sensitive to the therapeutic proteasome inhibitor bortezomib in vitro. However, bortezomib has proven disappointingly ineffective against solid tumors including sarcomas in animal experiments and clinical trials. Poor tumor penetration has been speculated to account for the inconsistency between in vitro and in vivo responses of solid tumors to bortezomib. Here we show that the second-generation proteasome inhibitor ixazomib, which reportedly has enhanced solid tumor penetration compared to bortezomib, is toxic to human and canine osteosarcoma cells in vitro. We used experimental osteosarcoma metastasis models to compare the efficacies of ixazomib and bortezomib against primary tumors and metastases derived from luciferase-expressing KRIB or 143B human osteosarcoma cell lines in athymic mice. Neither proteasome inhibitor reduced the growth of primary intramuscular KRIB tumors, however both drugs inhibited the growth of established pulmonary metastases created via intravenous inoculation with KRIB cells, which were significantly better vascularized than the primary tumors. Only ixazomib slowed metastases from KRIB primary tumors and inhibited the growth of 143B pulmonary and abdominal metastases, significantly enhancing the survival of mice intravenously injected with 143B cells. Taken together, these results suggest ixazomib exerts better single agent activity against osteosarcoma metastases than bortezomib. These data provide hope that incorporation of ixazomib, or other proteasome inhibitors that penetrate efficiently into solid tumors, into current regimens may improve outcomes for patients diagnosed with metastatic osteosarcoma.

BET Inhibitors Synergize with Carfilzomib to Induce Cell Death in Cancer Cells via Impairing Nrf1 Transcriptional Activity and Exacerbating the Unfolded Protein Response

Currently, proteasome inhibitors bortezomib, carfilzomib, and ixazomib are successfully used in clinics to treat multiple myeloma. However, these agents show limited efficacy against solid tumors. Identification of drugs that can potentiate the action of proteasome inhibitors could help expand the use of this therapeutic modality to solid tumors. Here, we found that bromodomain extra-terminal (BET) family protein inhibitors such as JQ1, I-BET762, and I-BET151 synergize with carfilzomib in multiple solid tumor cell lines. Mechanistically, BET inhibitors attenuated the ability of the transcription factor Nrf1 to induce proteasome genes in response to proteasome inhibition, thus, impeding the bounce-back response of proteasome activity, a critical pathway by which cells cope with proteotoxic stress. Moreover, we found that treatment with BET inhibitors or depletion of Nrf1 exacerbated the unfolded protein response (UPR), signaling that was initiated by proteasome inhibition. Taken together, our work provides a mechanistic explanation behind the synergy between proteasome and BET inhibitors in cancer cell lines and could prompt future preclinical and clinical studies aimed at further investigating this combination.

Carrier-Enhanced Anticancer Efficacy of Sunitinib-Loaded Green Tea-Based Micellar Nanocomplex beyond Tumor-Targeted Delivery

Although a few nanomedicines have been approved for clinical use in cancer treatment, that recognizes improved patient safety through targeted delivery, their improved efficacy over conventional drugs has remained marginal. One of the typical drawbacks of nanocarriers for cancer therapy is a low drug-loading capacity that leads to insufficient efficacy and requires an increase in dosage and/or frequency of administration, which in turn increases carrier toxicity. In contrast, elevating drug-loading would cause the risk of nanocarrier instability, resulting in low efficacy and off-target toxicity. This intractable drug-to-carrier ratio has imposed constraints on the design and development of nanocarriers. However, if the nanocarrier has intrinsic therapeutic effects, the efficacy would be synergistically augmented with less concern for the drug-to-carrier ratio. Sunitinib-loaded micellar nanocomplex (SU-MNC) was formed using poly(ethylene glycol)-conjugated epigallocatechin-3-O-gallate (PEG-EGCG) as such a carrier. SU-MNC specifically inhibited the vascular endothelial growth factor-induced proliferation of endothelial cells, exhibiting minimal cytotoxicity to normal renal cells. SU-MNC showed enhanced anticancer effects and less toxicity than SU administered orally/intravenously on human renal cell carcinoma-xenografted mice, demonstrating more efficient effects on anti-angiogenesis, apoptosis induction, and proliferation inhibition against tumors. In comparison, a conventional nanocarrier, SU-loaded polymeric micelle (SU-PM) comprised of PEG-b-poly(lactic acid) (PEG-PLA) copolymer, only reduced toxicity with no elevated efficacy, despite comparable drug-loading and tumor-targeting efficiency to SU-MNC. Improved efficacy of SU-MNC was ascribed to the carrier-drug synergies with the high-performance carrier of PEG-EGCG besides tumor-targeted delivery.

Expanding therapeutic utility of carfilzomib for breast cancer therapy by novel albumin-coated nanocrystal formulation

Carfilzomib (CFZ) is the second-in-class proteasome inhibitor with much improved efficacy and safety profiles over bortezomib in multiple myeloma patients. In expanding the utility of CFZ to solid cancer therapy, the poor aqueous solubility and in vivo instability of CFZ are considered major drawbacks. We investigated whether a nanocrystal (NC) formulation can address these issues and enhance anticancer efficacy of CFZ against breast cancer. The surface of NC was coated with albumin in order to enhance the formulation stability and drug delivery to tumors via interactions with albumin-binding proteins located in and near cancer cells. The novel albumin-coated NC formulation of CFZ (CFZ-alb NC) displayed improved metabolic stability and enhanced cellular interactions, uptake and cytotoxic effects in breast cancer cells in vitro. Consistently, CFZ-alb NC showed greater anticancer efficacy in a murine 4T1 orthotopic breast cancer model than the currently used cyclodextrin-based formulation. Overall, our results demonstrate the potential of CFZ-alb NC as a viable formulation for breast cancer therapy.

Clogging the Ubiquitin-Proteasome Machinery with Marine Natural Products: Last Decade Update

The ubiquitin-proteasome pathway (UPP) is the central protein degradation system in eukaryotic cells, playing a key role in homeostasis maintenance, through proteolysis of regulatory and misfolded (potentially harmful) proteins. As cancer cells produce proteins inducing cell proliferation and inhibiting cell death pathways, UPP inhibition has been exploited as an anticancer strategy to shift the balance between protein synthesis and degradation towards cell death. Over the last few years, marine invertebrates and microorganisms have shown to be an unexhaustive factory of secondary metabolites targeting the UPP. These chemically intriguing compounds can inspire clinical development of novel antitumor drugs to cope with the incessant outbreak of side effects and resistance mechanisms induced by currently approved proteasome inhibitors (e.g., bortezomib). In this review, we report about (a) the role of the UPP in anticancer therapy, (b) chemical and biological properties of UPP inhibitors from marine sources discovered in the last decade, (c) high-throughput screening techniques for mining natural UPP inhibitors in organic extracts. Moreover, we will tell about the fascinating story of salinosporamide A, the first marine natural product to access clinical trials as a proteasome inhibitor for cancer treatment.

The journey of metformin from glycaemic control to mTOR inhibition and the suppression of tumour growth

Our knowledge of the effect of metformin on human health is increasing. In addition to its ability to improve the control of hyperglycaemia, metformin has been shown to reduce the burden o,f ageing via effects on damaged DNA and the process of apoptosis. Studies have shown that metformin may reduce the risk of cardiovascular disease through influences on body weight, blood pressure, cholesterol levels and the progression of atherosclerosis. Studies also suggest that metformin may be beneficial for neuro-psychiatric disorders, cognitive impairment and in reducing the risk of dementia, erectile dysfunction and Duchenne muscular dystrophy. In vivo and in vitro studies have shown that metformin has anti-cancer properties, and population studies have suggested that metformin may reduce the risk of cancer or improve cancer prognosis. It is thought that it exerts its anti-cancer effect through the inhibition of the mammalian target of rapamycin (mTOR) signalling pathway. Because of its effect on the mTOR pathway, there may be a role for metformin in slowing or reversing growth of life-threatening hamartomas in tuberous sclerosis complex.

Non-invasive imaging of disrupted protein homeostasis induced by proteasome inhibitor treatment using chemical exchange saturation transfer MRI

Proteasome inhibitors (PIs) are now standard of care for several cancers, and noninvasive biomarkers of treatment response are critically required for early patient stratification and treatment personalization. The present study evaluated whether chemical exchange (CEST) magnetic resonance imaging (MRI) can provide measurements that can be used as the noninvasive biomarkers of proteasome inhibition, alongside diffusion MRI and relaxometry. The sensitivity of human colorectal carcinoma cells to the PI Ixazomib was assessed via in vitro and in vivo dose-response experiments. Acute in vivo response to Ixazomib was assessed at three dosing concentrations, using CEST MRI (amide, amine, hydroxyl signals), diffusion MRI (ADC) and relaxometry (T1, T2). These responses were further evaluated with the known histological markers for Ixazomib and Bradford assay ex vivo. The CEST signal from amides and amines increased in proportion to Ixazomib dose in colorectal cancer xenografts. The cell lines differed in their sensitivity to Ixazomib, which was reflected in the MRI measurements. A mild stimulation in tumor growth was observed at low Ixazomib doses. Our results identify CEST MRI as a promising method for safely and noninvasively monitoring disrupted tumor protein homeostasis induced by proteasome inhibitor treatment, and for stratifying sensitivity between tumor types.

Next-generation proteasome inhibitors for cancer therapy

Over 2 decades ago, the proteasome was considered a risky or even untenable therapeutic target. Today, proteasome inhibitors are a mainstay in the treatment of multiple myeloma (MM) and have sales in excess of 3 billion US dollars annually. More importantly, the availability of proteasome inhibitors has greatly improved the survival and quality of life for patients with MM. Despite the remarkable success of proteasome inhibitor therapies to date, the potential for improvement remains, and the development and optimal use of proteasome inhibitors as anticancer agents continues to be an active area of research. In this review, we briefly discuss the features and limitations of the 3 proteasome inhibitor drugs currently used in the clinic and provide an update on current efforts to develop next-generation proteasome inhibitors with the potential to overcome the limitations of existing proteasome inhibitor drugs.

Pre-clinical evaluation of proteasome inhibitors for canine and human osteosarcoma

Osteosarcoma, a common malignancy in large dog breeds, typically metastasises from long bones to lungs and is usually fatal within 1 to 2 years of diagnosis. Better therapies are needed for canine patients and their human counterparts, a third of whom die within 5 years of diagnosis. We compared the in vitro sensitivity of canine osteosarcoma cells derived from 4 tumours to the currently used chemotherapy drugs doxorubicin and carboplatin, and 4 new anti-cancer drugs. Agents targeting histone deacetylases or PARP were ineffective. Two of the 4 cell lines were somewhat sensitive to the BH3-mimetic navitoclax. The proteasome inhibitor bortezomib potently induced caspase-dependent apoptosis, at concentrations substantially lower than levels detected in the bones and lungs of treated rodents. Co-treatment with bortezomib and either doxorubicin or carboplatin was more toxic to canine osteosarcoma cells than each agent alone. Newer proteasome inhibitors carfilzomib, ixazomib, oprozomib and delanzomib manifested similar activities to bortezomib. Human osteosarcoma cells were as sensitive to bortezomib as the canine cells, but slightly less sensitive to the newer drugs. Human osteoblasts were less sensitive to proteasome inhibition than osteosarcoma cells, but physiologically relevant concentrations were toxic. Such toxicity, if replicated in vivo, may impair bone growth and strength in adolescent human osteosarcoma patients, but may be tolerated by canine patients, which are usually diagnosed later in life. Proteasome inhibitors such as bortezomib may be useful for treating canine osteosarcoma, and ultimately may improve outcomes for human patients if their osteoblasts survive exposure in vivo, or if osteoblast toxicity can be managed.

Positioning of proteasome inhibitors in therapy of solid malignancies

Targeting of the protein degradation pathway, in particular, the ubiquitin-proteasome system, has emerged as an attractive novel cancer chemotherapeutic modality. Although proteasome inhibitors have been most successfully applied in the treatment of hematological malignancies, they also received continuing interest for the treatment of solid tumors. In this review, we summarize the current positioning of proteasome inhibitors in the treatment of common solid malignancies (e.g., lung, colon, pancreas, breast, and head and neck cancer), addressing topics of their mechanism(s) of action, predictive factors and molecular mechanisms of resistance.

ER stress in temozolomide-treated glioblastomas interferes with DNA repair and induces apoptosis

Glioblastoma multiforme (GBM) is a deadly grade IV brain tumor. Radiation in combination with temozolomide (TMZ), the current chemotherapeutic for GBMs, only provides 12–14 months survival post diagnosis. Because GBMs are dependent on both activation of the DNA damage pathway and the endoplasmic reticulum (ER) stress response, we asked if a novel ER stress inducing agent, JLK1486, increases the efficacy of TMZ.

We found that the combination of TMZ+JLK1486 resulted in decreased proliferation in a panel of adherent GBM cells lines and reduced secondary sphere formation in non-adherent and primary lines. Decreased proliferation correlated with increased cell death due to apoptosis. We found prolonged ER stress in TMZ+JLK1486 treated cells that resulted in sustained activation of the unfolded protein response (UPR) through increased levels of BiP, ATF4, and CHOP. In addition, TMZ+JLK1486 treatment caused decreased RAD51 levels, impairing DNA damage repair. Furthermore, we found delayed time to tumor doubling in TMZ+JLK1486 treated mice.

Our data shows that the addition of JLK1486 to TMZ increases the efficaciousness of the treatment by decreasing proliferation and inducing cell death. We propose increased cell death is due to two factors. One, prolonged ER stress driving the expression of the pro-apoptotic transcription factor CHOP, and, second, unresolved DNA double strand breaks, due to decreased RAD51 levels. The combination of TMZ+JLK1486 is a potential novel therapeutic combination and suggests an inverse relationship between unresolved ER stress and the DNA damage response pathway.

Prediction of Tumor-to-Plasma Ratios of Basic Compounds in Subcutaneous Xenograft Mouse Models

BACKGROUND

Predicting target site drug concentrations is of key importance for rank ordering compounds before proceeding to chronic pharmacodynamic models. We propose generic tumor-specific correlation-based regression equations to predict tumor-to-plasma ratios (tumor-Kps) in slow- and fast-growing xenograft mouse models.

METHODS

Disposition of 14 basic small molecules was investigated extensively in mouse plasma, tissues and tumors after a single oral dose administration. Linear correlation was assessed and compared between tumor-Kp and normal tissue-to-plasma ratio (tissue-Kps) separately for each tumor xenograft. The developed regression equations were validated by leave-one-out cross-validation (LOOCV) method.

RESULT

Both slow- and fast-growing tumor-Kps showed good correlation (r ² ≥ 0.7) with majority of the normal tissue-Kps. Substantial difference was observed in the slopes of developed equations between two xenografts, which was in line with observed difference in tumor distribution. The linear correlations between tumor-Kp and skin- or spleen-Kp were within the acceptable statistical criteria (LOOCV) across xenografts and the class of compounds evaluated. Since > 70% of tumor-Kps from the test data sets were predicted within a factor of twofold for both slow- and fast-growing xenograft mouse models, the results validate the applicability of the developed equations across xenografts.

CONCLUSION

Tumor-specific correlation-based regression equations were developed and their applicability was adequately validated across xenografts. These equations could be successfully translated to predict tumor concentrations in order to preclude experimental tumor-Kp determination.

Heterogeneous drug penetrance of veliparib and carboplatin measured in triple negative breast tumors

BACKGROUND

Poly(ADP-ribose) polymerase inhibitors (PARPi), coupled to a DNA damaging agent is a promising approach to treating triple negative breast cancer (TNBC). However, not all patients respond; we hypothesize that non-response in some patients may be due to insufficient drug penetration. As a first step to testing this hypothesis, we quantified and visualized veliparib and carboplatin penetration in mouse xenograft TNBCs and patient blood samples.

METHODS

MDA-MB-231, HCC70 or MDA-MB-436 human TNBC cells were implanted in 41 beige SCID mice. Low dose (20 mg/kg) or high dose (60 mg/kg) veliparib was given three times daily for three days, with carboplatin (60 mg/kg) administered twice. In addition, blood samples were analyzed from 19 patients from a phase 1 study of carboplatin + PARPi talazoparib. Veliparib and carboplatin was quantified using liquid chromatography-mass spectrometry (LC-MS). Veliparib tissue penetration was visualized using matrix-assisted laser desorption/ionization mass spectrometric imaging (MALDI-MSI) and platinum adducts (covalent nuclear DNA-binding) were quantified using inductively coupled plasma-mass spectrometry (ICP-MS). Pharmacokinetic modeling and Pearson's correlation were used to explore associations between concentrations in plasma, tumor cells and peripheral blood mononuclear cells (PBMCs).

RESULTS

Veliparib penetration in xenograft tumors was highly heterogeneous between and within tumors. Only 35% (CI 95% 26-44%), 74% (40-97%) and 46% (9-37%) of veliparib observed in plasma penetrated into MDA-MB-231, HCC70 and MDA-MB-436 cell-based xenografts, respectively. Within tumors, penetration heterogeneity was larger with the 60 mg/kg compared to the 20 mg/kg dose (RSD 155% versus 255%, P = 0.001). These tumor concentrations were predicted similar to clinical dosing levels, but predicted tumor concentrations were below half maximal concentration values as threshold of response. Xenograft veliparib concentrations correlated positively with platinum adduct formation (R 2 = 0.657), but no PARPi-platinum interaction was observed in patients' PBMCs. Platinum adduct formation was significantly higher in five gBRCA carriers (ratio of platinum in DNA in PBMCs/plasma 0.64% (IQR 0.60-1.16%) compared to nine non-carriers (ratio 0.29% (IQR 0.21-0.66%, P < 0.0001).

CONCLUSIONS

PARPi/platinum tumor penetration can be measured by MALDI-MSI and ICP-MS in PBMCs and fresh frozen, OCT embedded core needle biopsies. Large variability in platinum adduct formation and spatial heterogeneity in veliparib distribution may lead to insufficient drug exposure in select cell populations.

Intratumoral delivery of bortezomib: impact on survival in an intracranial glioma tumor model

OBJECTIVE Glioblastoma (GBM) is the most prevalent and the most aggressive of primary brain tumors. There is currently no effective treatment for this tumor. The proteasome inhibitor bortezomib is effective for a variety of tumors, but not for GBM. The authors' goal was to demonstrate that bortezomib can be effective in the orthotopic GBM murine model if the appropriate method of drug delivery is used. In this study the Alzet mini-osmotic pump was used to bring the drug directly to the tumor in the brain, circumventing the blood-brain barrier; thus making bortezomib an effective treatment for GBM. METHODS The 2 human glioma cell lines, U87 and U251, were labeled with luciferase and used in the subcutaneous and intracranial in vivo tumor models. Glioma cells were implanted subcutaneously into the right flank, or intracranially into the frontal cortex of athymic nude mice. Mice bearing intracranial glioma tumors were implanted with an Alzet mini-osmotic pump containing different doses of bortezomib. The Alzet pumps were introduced directly into the tumor bed in the brain. Survival was documented for mice with intracranial tumors. RESULTS Glioma cells were sensitive to bortezomib at nanomolar quantities in vitro. In the subcutaneous in vivo xenograft tumor model, bortezomib given intravenously was effective in reducing tumor progression. However, in the intracranial glioma model, bortezomib given systemically did not affect survival. By sharp contrast, animals treated with bortezomib intracranially at the tumor site exhibited significantly increased survival. CONCLUSIONS Bypassing the blood-brain barrier by using the osmotic pump resulted in an increase in the efficacy of bortezomib for the treatment of intracranial tumors. Thus, the intratumoral administration of bortezomib into the cranial cavity is an effective approach for glioma therapy.

Bortezomib alters sour taste sensitivity in mice

Chemotherapy-induced taste disorder is one of the critical issues in cancer therapy. Bortezomib, a proteasome inhibitor, is a key agent in multiple myeloma therapy, but it induces a taste disorder. In this study, we investigated the characteristics of bortezomib-induced taste disorder and the underlying mechanism in mice. Among the five basic tastes, the sour taste sensitivity of mice was significantly increased by bortezomib administration. In bortezomib-administered mice, protein expression of PKD2L1 was increased. The increased sour taste sensitivity induced by bortezomib returned to the control level on cessation of its administration. These results suggest that an increase in protein expression of PKD2L1 enhances the sour taste sensitivity in bortezomib-administered mice, and this alteration is reversed on cessation of its administration.

Visualizing the antivascular effect of bortezomib on the hypoxic tumor microenvironment

Bortezomib, a novel proteasome inhibitor, has been approved for treating multiple myeloma and mantle cell lymphoma and studied pre-clinically and clinically for solid tumors. Preferential cytotoxicity of bortezomib was found toward hypoxic tumor cells and endothelial cells in vitro. The purpose of this study is to investigate the role of a pretreatment hypoxic tumor microenvironment on the effects of bortezomib in vitro and ex vivo, and explore the feasibility of dynamic contrast enhanced magnetic resonance imaging (DCE MRI) to noninvasively evaluate the biological effects of bortezomib. It was shown in vitro by Western blot, flow cytometry, and ELISA that bortezomib accumulated HIF-1α in non-functional forms and blocks its hypoxia response in human colorectal cancer cell lines. Ex vivo experiments were performed with fluorescent immunohistochemical staining techniques using multiple endogenous and exogenous markers to identify hypoxia (pimonidazole, HRE-TKeGFP), blood flow/permeability (Hoechst 33342), micro-vessels (CD31 and SMA), apoptosis (cleaved caspase 3) and hypoxia response (CA9). After bortezomib administration, overall apoptosis index was significantly increased and blood perfusion was dramatically decreased in tumor xenografts. More importantly, apoptosis signals were found preferentially located in moderate and severe pretreatment hypoxic regions in both tumor and endothelial cells. Meanwhile, DCE MRI examinations showed that the tumor blood flow and permeability decreased significantly after bortezomib administration. The present study revealed that bortezomib reduces tumor hypoxia response and blood perfusion, thus, presenting antivascular properties. It will be important to determine the hypoxic/perfusion status pre- and during treatment at further translational studies.

Proteasome Addiction Defined in Ewing Sarcoma Is Effectively Targeted by a Novel Class of 19S Proteasome Inhibitors

Ewing sarcoma is a primitive round cell sarcoma with a peak incidence in adolescence that is driven by a chimeric oncogene created from the fusion of the EWSR1 gene with a member of the ETS family of genes. Patients with metastatic and recurrent disease have dismal outcomes and need better therapeutic options. We screened a library of 309,989 chemical compounds for growth inhibition of Ewing sarcoma cells to provide the basis for the development of novel therapies and to discover vulnerable pathways that might broaden our understanding of the pathobiology of this aggressive sarcoma. This screening campaign identified a class of benzyl-4-piperidone compounds that selectively inhibit the growth of Ewing sarcoma cell lines by inducing apoptosis. These agents disrupt 19S proteasome function through inhibition of the deubiquitinating enzymes USP14 and UCHL5. Functional genomic data from a genome-wide shRNA screen in Ewing sarcoma cells also identified the proteasome as a node of vulnerability in Ewing sarcoma cells, providing orthologous confirmation of the chemical screen findings. Furthermore, shRNA-mediated silencing of USP14 or UCHL5 in Ewing sarcoma cells produced significant growth inhibition. Finally, treatment of a xenograft mouse model of Ewing sarcoma with VLX1570, a benzyl-4-piperidone compound derivative currently in clinical trials for relapsed multiple myeloma, significantly inhibited in vivo tumor growth. Overall, our results offer a preclinical proof of concept for the use of 19S proteasome inhibitors as a novel therapeutic strategy for Ewing sarcoma. Cancer Res; 76(15); 4525-34. ©2016 AACR.

A phase II trial of tamoxifen and bortezomib in patients with recurrent malignant gliomas

NF-kB inhibition by bortezomib enhances tamoxifen-induced apoptosis in preclinical glioma models. We conducted a single institution, phase II trial to evaluate efficacy and safety of high dose tamoxifen with bortezomib in adults with recurrent malignant gliomas. The primary endpoint was radiographic response. Concurrent enzyme inducing anticonvulsants and grade ≥2 peripheral neuropathy were exclusion criteria. Patients received tamoxifen (120 mg PO twice daily) and bortezomib (1.3 mg/m2 IV on days 3, 6, 10, 13, 24, 27, 31, and 34) per 6-week cycles. We enrolled 42 patients with anaplastic gliomas (AGs, n = 12) and glioblastomas (GBMs, n = 30), 32 males and 10 females. Median age was 38 years (range 22-65) and 48 years (range 19-68) for AGs and GBMs, respectively. median karnofsky performance status was 90% (range 70-100) for AGs and 80% (range 60-100) for GBMs. Median prior therapies was 3, ranging 1-7. Grade ≥3 toxicities included lymphopenia (4/42), hypophosphatemia (3/42), thromobocytopenia (2/42), and 1/42 with hyponatremia, headache, dyspnea, or DVT. One patient withdrew consent, two were removed for toxicity, and all others discontinued for progression. Among 40 patients evaluable for response, only one achieved stable disease for 3 months; all others progressed rapidly. For AGs and GBMs respectively, median progression-free survival was 5.9 and 5.7 weeks and median overall survival was 25.6 and 14.7 weeks. The study was closed due to poor accrual and therapeutic futility. Combination tamoxifen and bortezomib has no activity in recurrent malignant gliomas. Poor penetration across blood brain barrier of bortezomib likely limited efficacy.

Proteasome inhibitors with pyrazole scaffolds from structure-based virtual screening

We performed a virtual screen of ∼340 000 small molecules against the active site of proteasomes followed by in vitro assays and subsequent optimization, yielding a proteasome inhibitor with pyrazole scaffold. The pyrazole-scaffold compound displayed excellent metabolic stability and was highly effective in suppressing solid tumor growth in vivo. Furthermore, the effectiveness of this compound was not negatively impacted by resistance to bortezomib or carfilzomib.

Linking the activity of bortezomib in multiple myeloma and autoimmune diseases

Since their introduction to the clinic 10 years ago, proteasome inhibitors have become the cornerstone of anti-multiple myeloma therapy. Despite significant progress in understanding the consequences of proteasome inhibition, the unique activity of bortezomib is still unclear. Disappointing results from clinical trials with bortezomib in other malignancies raise the question of what makes multiple myeloma so sensitive to proteasome inhibition. Successful administration of bortezomib in various immunological disorders that exhibit high antibody production suggests that the balance between protein synthesis and degradation is a key determinant of sensitivity to proteasome inhibition because a high rate of protein production is a shared characteristic in plasma and myeloma cells. Initial or acquired resistance to bortezomib remains a major obstacle in the clinic as in vitro data from cell lines suggest a key role for the β5 subunit mutation in resistance; however the mutation was not found in patient samples. Recent studies indicate the importance of selecting for a subpopulation of cells that produce lower amounts of paraprotein during bortezomib therapy.

Magnetic fluid hyperthermia enhances cytotoxicity of bortezomib in sensitive and resistant cancer cell lines

The proteasome inhibitor bortezomib (BZ) has shown promising results in some types of cancer, but in others it has had minimal activity. Recent studies have reported enhanced efficacy of BZ when combined with hyperthermia. However, the use of magnetic nanoparticles to induce hyperthermia in combination with BZ has not been reported. This novel hyperthermia modality has shown better potentiation of chemotherapeutics over other types of hyperthermia. We hypothesized that inducing hyperthermia via magnetic nanoparticles (MFH) would enhance the cytotoxicity of BZ in BZ-sensitive and BZ-resistant cancer cells more effectively than hyperthermia using a hot water bath (HWH). Studies were conducted using BZ in combination with MFH in two BZ-sensitive cell lines (MDA-MB-468, Caco-2), and one BZ-resistant cell line (A2780) at two different conditions, ie, 43°C for 30 minutes and 45°C for 30 minutes. These experiments were compared with combined application of HWH and BZ. The results indicate enhanced potentiation between hyperthermic treatment and BZ. MFH combined with BZ induced cytotoxicity in sensitive and resistant cell lines to a greater extent than HWH under the same treatment conditions. The observation that MFH sensitizes BZ-resistant cell lines makes this approach a potentially effective anticancer therapy platform.

A preclinical assay for chemosensitivity in multiple myeloma

Accurate preclinical predictions of the clinical efficacy of experimental cancer drugs are highly desired but often haphazard. Such predictions might be improved by incorporating elements of the tumor microenvironment in preclinical models by providing a more physiological setting. In generating improved xenograft models, it is generally accepted that the use of primary tumors from patients are preferable to clonal tumor cell lines. Here we describe an interdisciplinary platform to study drug response in multiple myeloma, an incurable cancer of the bone marrow. This platform uses microfluidic technology to minimize the number of cells per experiment, while incorporating three-dimensional extracellular matrix and mesenchymal cells derived from the tumor microenvironment. We used sequential imaging and a novel digital imaging analysis algorithm to quantify changes in cell viability. Computational models were used to convert experimental data into dose-exposure-response "surfaces," which offered predictive utility. Using this platform, we predicted chemosensitivity to bortezomib and melphalan, two clinical multiple myeloma treatments, in three multiple myeloma cell lines and seven patient-derived primary multiple myeloma cell populations. We also demonstrated how this system could be used to investigate environment-mediated drug resistance and drug combinations that target it. This interdisciplinary preclinical assay is capable of generating quantitative data that can be used in computational models of clinical response, demonstrating its utility as a tool to contribute to personalized oncology.

The proteasome inhibitor bortezomib inhibits the growth of canine malignant melanoma cells in vitro and in vivo

Canine malignant melanomas are highly aggressive and fatal neoplasms. In the present report, 21 drugs that target specific signalling pathways were screened for their growth inhibitory activity on three canine malignant melanoma cell lines. The proteasome inhibitor bortezomib inhibited the growth of these cell lines. The growth inhibitory properties of bortezomib were then examined using nine canine malignant melanoma cell lines. Bortezomib demonstrated potent growth inhibitory activity in all cell lines with calculated IC50 values of 3.5-5.6 nM. Because suppression of the NF-κB pathway by preventing proteasomic degradation of I κB is an important mechanism of the anti-tumour activity of bortezomib, the activation status of and the effect of bortezomib on the NF-κB pathway were examined using a canine malignant melanoma cell line, CMM-1. The NF-κB pathway was constitutively activated in CMM-1 cells and bortezomib efficiently suppressed this activated pathway. Using a CMM-1 xenograft mouse model, bortezomib also significantly inhibited tumour growth via suppression of tumour cell proliferation. Collectively, these findings suggest that bortezomib has growth inhibitory activity against canine malignant melanomas potentially through suppression of the constitutively activated NF-κB pathway. Targeted therapy using bortezomib could therefore be beneficial in the management of canine malignant melanomas.

From bench to bedside: lessons learned in translating preclinical studies in cancer drug development

The development of targeted agents in oncology has rapidly expanded over the past 2 decades and has led to clinically significant improvements in the treatment of numerous cancers. Unfortunately, not all success at the bench in preclinical experiments has translated to success at the bedside. As preclinical studies shift toward defining proof of mechanism, patient selection, and rational drug combinations, it is critical to understand the lessons learned from prior translational studies to gain an understanding of prior drug development successes and failures. By learning from prior drug development, future translational studies will provide more clinically relevant data, and the underlying hope is that the clinical success rate will improve and the treatment of patients with ineffective targeted therapy will be limited.

Proteasome inhibitors block DNA repair and radiosensitize non-small cell lung cancer

Despite optimal radiation therapy (RT), chemotherapy and/or surgery, a majority of patients with locally advanced non-small cell lung cancer (NSCLC) fail treatment. To identify novel gene targets for improved tumor control, we performed whole genome RNAi screens to identify knockdowns that most reproducibly increase NSCLC cytotoxicity. These screens identified several proteasome subunits among top hits, including the topmost hit PSMA1, a component of the core 20 S proteasome. Radiation and proteasome inhibition showed synergistic effects. Proteasome inhibition resulted in an 80–90% decrease in homologous recombination (HR), a 50% decrease in expression of NF-κB-inducible HR genes BRCA1 and FANCD2, and a reduction of BRCA1, FANCD2 and RAD51 ionizing radiation-induced foci. IκBα RNAi knockdown rescued NSCLC radioresistance. Irradiation of mice with NCI-H460 xenografts after inducible PSMA1 shRNA knockdown markedly increased murine survival compared to either treatment alone. Proteasome inhibition is a promising strategy for NSCLC radiosensitization via inhibition of NF-κB-mediated expression of Fanconi Anemia/HR DNA repair genes.

A phase I/II study of carfilzomib 2-10-min infusion in patients with advanced solid tumors

PURPOSE

Tolerability, pharmacokinetics (PK), pharmacodynamics, and antitumor activity of carfilzomib, a selective proteasome inhibitor, administered twice weekly by 2-10-min intravenous (IV) infusion on days 1, 2, 8, 9, 15, and 16 in 28-day cycles, were assessed in patients with advanced solid tumors in this phase I/II study.

METHODS

Adult patients with solid tumors progressing after ≥1 prior therapies were enrolled. The dose was 20 mg/m(2) in week 1 of cycle 1 and 20, 27, or 36 mg/m(2) thereafter. The maximum tolerated dose or protocol-defined maximum planned dose (MPD) identified during dose escalation was administered to an expansion cohort and to patients with small cell lung, non-small cell lung, ovarian, and renal cancer in phase II tumor-specific cohorts.

RESULTS

Fourteen patients received carfilzomib during dose escalation. The single dose-limiting toxicity at 20/36 mg/m(2) was grade 3 fatigue, establishing the MPD as the expansion and phase II dose. Sixty-five additional patients received carfilzomib at the MPD. Adverse events included fatigue, nausea, anorexia, and dyspnea. Carfilzomib PK was dose proportional with a half-life <1 h. All doses resulted in at least 80 % proteasome inhibition in blood. Partial responses occurred in two patients in phase I, with 21.5 % stable disease after four cycles in evaluable patients in the expansion and phase II cohorts.

CONCLUSION

Carfilzomib 20/36 mg/m(2) was well tolerated when administered twice weekly by 2-10-min IV infusion. At this dose and infusion rate, carfilzomib inhibited the proteasome in blood but demonstrated limited antitumor activity in patients with advanced solid tumors.

Targeting the ubiquitin+proteasome system in solid tumors

The ubiquitin+proteasome system (UPS) is a highly complex network that maintains protein homeostasis and cell viability through the selective turnover of targeted substrates. The proteasome serves as the catalytic core of the UPS to recognize and execute the coordinated and efficient removal of ubiquitinated proteins. Pharmacologic inhibitors that exploit the pivotal role of the proteasome in cellular metabolism promote tumor cytotoxicity and have yielded durable clinical responses that dramatically improve patient survival. Success of the proteasome inhibitor (PI) bortezomib in the treatment of the hematologic malignancy multiple myeloma (MM) has emerged as the standard-of-care and catapulted the UPS into a position of prominence as a model system in cancer biology and drug development. However, expansion of PIs in the treatment of the more complex solid tumors has been less successful. While clinical evaluation of second-generation PIs progresses, other potential sites of therapeutic intervention within the UPS continue to emerge, such as the non-proteolytic activities associated with the proteasome and the rapidly expanding number of Ub-binding proteins. Molecular-genetic approaches to further unravel the complexity of the UPS will advance its utilization as a platform for the development of novel, mechanism-based anticancer strategies.

Applied techniques for mining natural proteasome inhibitors

In eukaryotic cells, the ubiquitin-proteasome-system (UPS) is responsible for the non-lysosomal degradation of proteins and plays a pivotal role in such vital processes as protein homeostasis, antigen processing or cell proliferation. Therefore, it is an attractive drug target with various applications in cancer and immunosuppressive therapies. Being an evolutionary well conserved pathway, many pathogenic bacteria have developed small molecules, which modulate the activity of their hosts' UPS components. Such natural products are, due to their stepwise optimization over the millennia, highly potent in terms of their binding mechanisms, their bioavailability and selectivity. Generally, this makes bioactive natural products an ideal starting point for the development of novel drugs. Since four out of the ten best seller drugs are natural product derivatives, research in this field is still of unfathomable value for the pharmaceutical industry. The currently most prominent example for the successful exploitation of a natural compound in the UPS field is carfilzomib (Kyprolis®), which represents the second FDA approved drug targeting the proteasome after the admission of the blockbuster bortezomib (Velcade®) in 2003. On the other hand side of the spectrum, ONX 0914, which is derived from the same natural product as carfilzomib, has been shown to selectively inhibit the immune response related branch of the pathway. To date, there exists a huge potential of UPS inhibitors with regard to many diseases. Both approved drugs against the proteasome show severe side effects, adaptive resistances and limited applicability, thus the development of novel compounds with enhanced properties is a main objective of active research. In this review, we describe the techniques, which can be utilized for the discovery of novel natural inhibitors, which in particular block the 20S proteasomal activity. In addition, we will illustrate the successful implementation of a recently published methodology with the example of a highly potent but so far unexploited group of proteasome inhibitors, the syrbactins, and their biological functions. This article is part of a Special Issue entitled: Ubiquitin-Proteasome System. Guest Editors: Thomas Sommer and Dieter H. Wolf.

Impairment of the ubiquitin-proteasome pathway by methyl N-(6-phenylsulfanyl-1H-benzimidazol-2-yl)carbamate leads to a potent cytotoxic effect in tumor cells: a novel antiproliferative agent with a potential therapeutic implication

In recent years, there has been a great deal of interest in proteasome inhibitors as a novel class of anticancer drugs. We report that fenbendazole (FZ) (methyl N-(6-phenylsulfanyl-1H-benzimidazol-2-yl)carbamate) exhibits a potent growth-inhibitory activity against cancer cell lines but not normal cells. We show here, using fluorogenic substrates, that FZ treatment leads to the inhibition of proteasomal activity in the cells. Succinyl-Leu-Leu-Val-Tyr-methylcoumarinamide (MCA), benzyloxycarbonyl-Leu-Leu-Glu-7-amido-4-MCA, and t-butoxycarbonyl-Gln-Ala-Arg-7-amido-4-MCA fluorescent derivatives were used to assess chymotrypsin-like, post-glutamyl peptidyl-hydrolyzing, and trypsin-like protease activities, respectively. Non-small cell lung cancer cells transiently transfected with an expression plasmid encoding pd1EGFP and treated with FZ showed an accumulation of the green fluorescent protein in the cells due to an increase in its half-life. A number of apoptosis regulatory proteins that are normally degraded by the ubiquitin-proteasome pathway like cyclins, p53, and IκBα were found to be accumulated in FZ-treated cells. In addition, FZ induced distinct ER stress-associated genes like GRP78, GADD153, ATF3, IRE1α, and NOXA in these cells. Thus, treatment of human NSCLC cells with fenbendazole induced endoplasmic reticulum stress, reactive oxygen species production, decreased mitochondrial membrane potential, and cytochrome c release that eventually led to cancer cell death. This is the first report to demonstrate the inhibition of proteasome function and induction of endoplasmic reticulum stress/reactive oxygen species-dependent apoptosis in human lung cancer cell lines by fenbendazole, which may represent a new class of anticancer agents showing selective toxicity against cancer cells.

Glucocorticoid and proteasome inhibitor impact on the leukemic lymphoblast: multiple, diverse signals converging on a few key downstream regulators

Twenty years ago a proteasome inhibitor was suggested as therapy for glucocorticoid-resistant multiple myeloma, a disease that involves terminally differentiated B cells. Since then, research has proven that it has utility on a number of tumors resistant to chemotherapy. Hematologic malignancy, however, often involves lesser differentiated cells, which have a high potential to modulate their intrinsic machinery and thereby activate alternative rescue pathways. A corresponding multiplicity of therapies is not always practical. One approach to conditions with heterogeneous physiology is to identify key biochemical mediators, thereby reducing the number of treatment targets. Results from several ongoing studies indicate convergence of genomically diverse signal pathways to a limited number of key downstream regulators of apoptosis. Convergence of pathways can be exploited to address the problem of genetic heterogeneity in acute leukemia: this would mean treating multiple molecular aberrations with fewer drugs and enhanced therapeutic benefit.

Therapeutic trial of metformin and bortezomib in a mouse model of tuberous sclerosis complex (TSC)

Tuberous sclerosis complex (TSC) is a human genetic disorder in which loss of either TSC1 or TSC2 leads to development of hamartoma lesions, which can progress and be life-threatening or fatal. The TSC1/TSC2 protein complex regulates the state of activation of mTORC1. Tsc2^+/− mice develop renal cystadenoma lesions which grow progressively. Both bortezomib and metformin have been proposed as potential therapeutics in TSC. We examined the potential benefit of 1 month treatment with bortezomib, and 4 month treatment with metformin in Tsc2^+/− mice. Results were compared to vehicle treatment and treatment with the mTORC1 inhibitor rapamycin for 1 month. We used a quantitative tumor volume measurement on stained paraffin sections to assess the effect of these drugs. The median tumor volume per kidney was decreased by 99% in mice treated with rapamycin (p = 0.0004). In contrast, the median tumor volume per kidney was not significantly reduced for either the bortezomib cohort or the metformin cohort. Biochemical studies confirmed that bortezomib and metformin had their expected pharmacodynamic effects. We conclude that neither bortezomib nor metformin has significant benefit in this native Tsc2^+/− mouse model, which suggests limited benefit of these compounds in the treatment of TSC hamartomas and related lesions.

How to improve exposure of tumor cells to drugs: promoter drugs increase tumor uptake and penetration of effector drugs

Solid tumors are characterized by an abnormal architecture and composition that limit the uptake and distribution of antitumor drugs. Over the last two decades, drugs have been identified that improve the tumor uptake and distribution of drugs that have direct antitumor effects. We propose to refer to these drugs as promoter drugs, and as effector drugs to drugs that have direct antitumor effects. Some promoter drugs have received regulatory approval, while others are in active clinical development. This review gives an overview of promoter drugs, by classifying them according to their mechanism of action: promoter drugs that modulate tumor blood flow, modify the barrier function of tumor vessels, induce tumor cell killing, and overcome stromal barriers. Eventually, we discuss those that we feel are the main conclusions to be drawn from promoter drug research that has been performed so far, and suggest areas of future investigation to improve the efficacy of promoter drugs in cancer therapy.

Reductionism and complexity in nanoparticle-vectored drug targeting

This paper briefly discusses reductionism as a process for dissecting the complexities of drug targeting mediated by nanoparticulate carriers. While reductionism has been said to have been a drawback to enhanced appreciation and understanding of complex biological systems, it is concluded here that the dissection of the individual stages of the procession from injection to final destination in specific targets in a living complex organism is essential. It should allow a decrease in the empiricism from laudable and inventive efforts to achieve high levels of drug delivery to specific diseased targets such as tumours. At the stage of development of the field there have perhaps been fewer than desirable detailed experimental or theoretical investigations of these individual stages. However, there are frequently analogies in the literature from which to draw at least tentative conclusions about the physics, physical chemistry and biology which underpin the processes involved.

Targeting the proteasome as a promising therapeutic strategy in thyroid cancer

BACKGROUND AND OBJECTIVES

Targeting the ubiquitin-proteasome system by using proteasome inhibitors represents a novel approach for cancer therapy. Anaplastic thyroid cancer (ATC), a subtype of thyroid cancer (TC), fails to respond to conventional TC treatment. Here we investigated the effects of bortezomib on TC in vitro. Further, the study aimed to evaluate its potential for TC treatment in vivo.

METHODS

Three anaplastic (Hth74, C643, Kat4), one follicular (FTC133), and one papillary (TPC1) TC cell lines were used. Antiproliferative, proapoptotic, and transcriptional effects of bortezomib treatment were analyzed in vitro and growth inhibition of ATC xenografts in vivo. Tumor samples were analyzed by Ki67, CD31, caspase-3, and NF-κB immunohistochemistry.

RESULTS

In vitro, bortezomib inhibited proliferation of TC cells (IC(50) 4-10 nM), increased caspase-3 activity and induced cell cycle arrest. NF-κB activity was affected differently. In vivo, bortezomib treatment was effective in reducing tumor volume (up to 74%), accompanied by reduced proliferation (Ki67) and 57% reduced tumor vascularity.

CONCLUSION

Proteasome inhibition is effective in reducing cell growth and inducing apoptosis of ATC in vitro and inhibiting tumor growth and vascularity in vivo. However, the impact on nuclear transcription remains controversial. Clinical evaluation of bortezomib treatment in ATC is warranted.

An integrated in vitro and in vivo high-throughput screen identifies treatment leads for ependymoma

Using a mouse model of ependymoma-a chemoresistant brain tumor-we combined multicell high-throughput screening (HTS), kinome-wide binding assays, and in vivo efficacy studies, to identify potential treatments with predicted toxicity against neural stem cells (NSC). We identified kinases within the insulin signaling pathway and centrosome cycle as regulators of ependymoma cell proliferation, and their corresponding inhibitors as potential therapies. FDA approved drugs not currently used to treat ependymoma were also identified that posses selective toxicity against ependymoma cells relative to normal NSCs both in vitro and in vivo, e.g., 5-fluorouracil. Our comprehensive approach advances understanding of the biology and treatment of ependymoma including the discovery of several treatment leads for immediate clinical translation.

Differential, type I interferon-mediated autophagic trafficking of hepatitis C virus proteins in mouse liver

BACKGROUND & AIMS

The hepatitis C virus (HCV) serine protease NS3/4A can cleave mitochondria-associated antiviral signaling protein (MAVS) and block retinoic acid-inducible gene I-mediated interferon (IFN) responses. Although this mechanism is thought to have an important role in HCV-mediated innate immunosuppression, its significance in viral persistence is not clear.

METHODS

We generated transgenic mice that express the HCV NS3/4A proteins specifically in the liver and challenged the animals with a recombinant vesicular stomatitis virus, a synthetic HCV genome, IFN alfa, or IFN beta. We evaluated the effects of HCV serine protease on the innate immune responses and their interactions.

RESULTS

Expression of HCV NS3/4A resulted in cleavage of intrahepatic MAVS; challenge of transgenic mice with vesicular stomatitis virus or a synthetic HCV genome induced strong, type I IFN-mediated responses that were not significantly lower than those of control mice. Different challenge agents induced production of different ratios of IFN alfa and beta, resulting in different autophagic responses and vesicular trafficking patterns of endoplasmic reticulum- and mitochondria-associated viral proteins. IFN beta promoted degradation of the viral proteins by the autolysosome. Variant isoforms of MAVS were associated with distinct, type I IFN-mediated autophagic responses; these responses have a role in trafficking of viral components to endosomal compartments that contain Toll-like receptor-3.

CONCLUSIONS

IFN beta mediates a distinct autophagic mechanism of antiviral host defense. MAVS has an important role in type I IFN-induced autophagic trafficking of viral proteins.

A volumetric method for quantifying atherosclerosis in mice by using microCT: comparison to en face

Precise quantification of atherosclerotic plaque in preclinical models of atherosclerosis requires the volumetric assessment of the lesion(s) while maintaining in situ architecture. Here we use micro-computed tomography (microCT) to detect ex vivo aortic plaque established in three dyslipidemic mouse models of atherosclerosis. All three models lack the low-density lipoprotein receptor (Ldlr^−/−), each differing in plaque severity, allowing the evaluation of different plaque volumes using microCT technology. From clearly identified lesions in the thoracic aorta from each model, we were able to determine plaque volume (0.04–3.1 mm³), intimal surface area (0.5–30 mm²), and maximum plaque (intimal-medial) thickness (0.1–0.7 mm). Further, quantification of aortic volume allowed calculation of vessel occlusion by the plaque. To validate microCT for future preclinical studies, we compared microCT data to intimal surface area (by using en face methodology). Both plaque surface area and plaque volume were in excellent correlation between microCT assessment and en face surface area (r² = 0.99, p<0.0001 and r² = 0.95, p<0.0001, respectively). MicroCT also identified internal characteristics of the lipid core and fibrous cap, which were confirmed pathologically as Stary type III-V lesions. These data validate the use of microCT technology to provide a more exact empirical measure of ex vivo plaque volume throughout the entire intact aorta in situ for the quantification of atherosclerosis in preclinical models.

Preclinical evaluation of the antitumor activity of bortezomib in combination with vitamin C or with epigallocatechin gallate, a component of green tea

Purpose

To investigate whether clinically relevant levels of epigallocatechin gallate (EGCG, a component of green tea) or vitamin C (ascorbic acid) could antagonize bortezomib antitumor activity in CWR22 human prostate xenograft tumors.

Methods

The pharmacokinetics (PK) of EGCG and ascorbic acid were determined in immunocompromised mice and compared with concentrations measured in human PK studies of dietary supplements. Antitumor activity of bortezomib in combination with EGCG or ascorbic acid was determined using several dosing regimens to evaluate different target plasma concentrations of EGCG and ascorbic acid.

Results

Bortezomib dosed twice-weekly at 0.8 mg/kg IV demonstrated tumor growth inhibition (TGI) of 53.9–58.9%. However, when combined with EGCG such that the plasma concentrations of EGCG were >200 μM at the time of bortezomib dosing, all antitumor activity was abrogated (TGI = −17.7%). A lower concentration of EGCG (11–16 μM), which is severalfold higher than measured clinically in humans taking EGCG supplements (0.6–3 μM), was not antagonistic to bortezomib (TGI 63.5%). Pharmacodynamic studies of proteasome inhibition reflected these findings. Ascorbic acid (40 and 500 mg/kg PO daily) was evaluated under a similar study design and did not antagonize bortezomib antitumor activity (TGI 57.2 and 72.2%).

Conclusions

No antagonism of bortezomib is seen in preclinical in vivo experiments, where EGCG or ascorbic acid plasma concentrations are commensurate with dietary or supplemental intake. The data suggest that patients receiving bortezomib treatment do not need to avoid normal dietary consumption of green tea, vitamin C-containing foods, or EGCG or vitamin C dietary supplements.

Electronic supplementary material

The online version of this article (doi:10.1007/s00280-011-1591-2) contains supplementary material, which is available to authorized users.

Proteasome functional insufficiency activates the calcineurin-NFAT pathway in cardiomyocytes and promotes maladaptive remodelling of stressed mouse hearts

AIMS

Proteasome functional insufficiency (PFI) may play an important role in the progression of congestive heart failure but the underlying molecular mechanism is poorly understood. Calcineurin and nuclear factor of activated T-cells (NFAT) are degraded by the proteasome, and the calcineurin-NFAT pathway mediates cardiac remodelling. The present study examined the hypothesis that PFI activates the calcineurin-NFAT pathway and promotes maladaptive remodelling of the heart.

METHODS AND RESULTS

Using a reporter gene assay, we found that pharmacological inhibition of 20S proteasomes stimulated NFAT transactivation in both mouse hearts and cultured adult mouse cardiomyocytes. Proteasome inhibition stimulated NFAT nuclear translocation in a calcineurin-dependent manner and led to a maladaptive cell shape change in cultured neonatal rat ventricular myocytes. Proteasome inhibition facilitated left ventricular dilatation and functional decompensation and increased fatality in mice with aortic constriction while causing cardiac hypertrophy in the sham surgery group. It was further revealed that both calcineurin protein levels and NFAT transactivation were markedly increased in the mouse hearts with desmin-related cardiomyopathy and severe PFI. Expression of an aggregation-prone mutant desmin also directly increased calcineurin protein levels in cultured cardiomyocytes.

CONCLUSIONS

The calcineurin-NFAT pathway in the heart can be activated by proteasome inhibition and is activated in the heart of a mouse model of desmin-related cardiomyopathy that is characterized by severe PFI. The interplay between PFI and the calcineurin-NFAT pathway may contribute to the pathological remodelling of cardiomyocytes characteristic of congestive heart failure.