Fighting Multidrug Resistance with Ruthenium-Cyclopentadienyl Compounds: Unveiling the Mechanism of P-gp Inhibition.

The search for more effective and selective drugs to overcome cancer multidrug resistance is urgent. As such, a new series of ruthenium-cyclopentadienyl ("RuCp") compounds with the general formula [Ru(η5-C5H4R)(4,4'-R'-2,2'-bipy)(PPh3)] were prepared and fully characterized. All compounds were evaluated toward non-small cell lung cancer cells with different degrees of cisplatin sensitivity (A549, NCI-H2228, Calu-3, and NCI-H1975), showing better cytotoxicity than the first-line chemotherapeutic drug cisplatin. Compounds 2 and 3 (R' = -OCH3; R = CHO (2) or CH2OH (3)) further inhibited the activity of P-gp and MRP1 efflux pumps by impairing their catalytic activity. Molecular docking calculations identified the R-site P-gp pocket as the preferred one, which was further validated using site-directed mutagenesis experiments in P-gp. Altogether, our results unveil the first direct evidence of the interaction between P-gp and "RuCp" compounds in the modulation of P-gp activity and establish them as valuable candidates to circumvent cancer MDR.

Autocrine 17-ß-Estradiol/Estrogen Receptor-α Loop Determines the Response to Immune Checkpoint Inhibitors in Non-Small Cell Lung Cancer.

PURPOSE: The response to immune checkpoint inhibitors (ICI) often differs between genders in non-small cell lung cancer (NSCLC), but metanalyses results are controversial, and no clear mechanisms are defined. We aim at clarifying the molecular circuitries explaining the differential gender-related response to anti-PD-1/anti-PD-L1 agents in NSCLC. EXPERIMENTAL DESIGN: We prospectively analyzed a cohort of patients with NSCLC treated with ICI as a first-line approach, and we identified the molecular mechanisms determining the differential efficacy of ICI in 29 NSCLC cell lines of both genders, recapitulating patients' phenotype. We validated new immunotherapy strategies in mice bearing NSCLC patient-derived xenografts and human reconstituted immune system ("immune-PDXs"). RESULTS: In patients, we found that estrogen receptor α (ERα) was a predictive factor of response to pembrolizumab, stronger than gender and PD-L1 levels, and was directly correlated with PD-L1 expression, particularly in female patients. ERα transcriptionally upregulated CD274/PD-L1 gene, more in females than in males. This axis was activated by 17-ß-estradiol, autocrinely produced by intratumor aromatase, and by the EGFR-downstream effectors Akt and ERK1/2 that activated ERα. The efficacy of pembrolizumab in immune-PDXs was significantly improved by the aromatase inhibitor letrozole, which reduced PD-L1 and increased the percentage of antitumor CD8+T-lymphocytes, NK cells, and Vγ9Vδ2 T-lymphocytes, producing durable control and even tumor regression after continuous administration, with maximal benefit in 17-ß-estradiol/ERα highfemale immune-xenografts. CONCLUSIONS: Our work unveils that 17-ß-estradiol/ERα status predicts the response to pembrolizumab in patients with NSCLC. Second, we propose aromatase inhibitors as new gender-tailored immune-adjuvants in NSCLC. See related commentary by Valencia et al., p. 3832.

Mitochondrial ROS drive resistance to chemotherapy and immune-killing in hypoxic non-small cell lung cancer.

BACKGROUND: Solid tumors subjected to intermittent hypoxia are characterized by resistance to chemotherapy and immune-killing by effector T-lymphocytes, particularly tumor-infiltrating Vγ9Vδ2 T-lymphocytes. The molecular circuitries determining this double resistance are not known. METHODS: We analyzed a panel of 28 human non-small cell lung cancer (NSCLC) lines, using an in vitro system simulating continuous and intermittent hypoxia. Chemosensitivity to cisplatin and docetaxel was evaluated by chemiluminescence, ex vivo Vγ9Vδ2 T-lymphocyte expansion and immune-killing by flow cytometry. Targeted transcriptomics identified efflux transporters and nuclear factors involved in this chemo-immuno-resistance. The molecular mechanism linking Hypoxia-inducible factor-1α (HIF-1α), CCAAT/Enhancer Binding Protein-ß (C/EBP-ß) isoforms LAP and LIP, ABCB1, ABCC1 and ABCA1 transporters were evaluated by immunoblotting, RT-PCR, RNA-IP, ChIP. Oxidative phosphorylation, mitochondrial ATP, ROS, depolarization, O2 consumption were monitored by spectrophotometer and electronic sensors. The role of ROS/HIF-1α/LAP axis was validated in knocked-out or overexpressing cells, and in humanized (Hu-CD34+NSG) mice bearing LAP-overexpressing tumors. The clinical meaning of LAP was assessed in 60 NSCLC patients prospectively enrolled, treated with chemotherapy. RESULTS: By up-regulating ABCB1 and ABCC1, and down-regulating ABCA1, intermittent hypoxia induced a stronger chemo-immuno-resistance than continuous hypoxia in NSCLC cells. Intermittent hypoxia impaired the electron transport chain and reduced O2 consumption, increasing mitochondrial ROS that favor the stabilization of C/EBP-ß mRNA mediated by HIF-1α. HIF-1α/C/EBP-ß mRNA binding increases the splicing of C/EBP-ß toward the production of LAP isoform that transcriptionally induces ABCB1 and ABCC1, promoting the efflux of cisplatin and docetaxel. LAP also decreases ABCA1, limiting the efflux of isopentenyl pyrophosphate, i.e. the endogenous activator of Vγ9Vδ2 T-cells, and reducing the immune-killing. In NSCLC patients subjected to cisplatin-based chemotherapy, C/EBP-ß LAP was abundant in hypoxic tumors and was associated with lower response to treatment and survival. LAP-overexpressing tumors in Hu-CD34+NSG mice recapitulated the patients' chemo-immuno-resistant phenotype. Interestingly, the ROS scavenger mitoquinol chemo-immuno-sensitized immuno-xenografts, by disrupting the ROS/HIF-1α/LAP cascade. CONCLUSIONS: The impairment of mitochondrial metabolism induced by intermittent hypoxia increases the ROS-dependent stabilization of HIF-1α/LAP complex in NSCLC, producing chemo-immuno-resistance. Clinically used mitochondrial ROS scavengers may counteract such double resistance. Moreover, we suggest C/EBP-ß LAP as a new predictive and prognostic factor in NSCLC patients.

Hypoxia as a driver of resistance to immunotherapy.

Hypoxia, a hallmark of solid tumors, determines the selection of invasive and aggressive malignant clones displaying resistance to radiotherapy, conventional chemotherapy or targeted therapy. The recent introduction of immunotherapy, based on immune checkpoint inhibitors (ICPIs) and chimeric antigen receptor (CAR) T-cells, has markedly transformed the prognosis in some tumors but also revealed the existence of intrinsic or acquired drug resistance. In the current review we highlight hypoxia as a culprit of immunotherapy failure. Indeed, multiple metabolic cross talks between tumor and stromal cells determine the prevalence of immunosuppressive populations within the hypoxic tumor microenvironment and confer upon tumor cells resistance to ICPIs and CAR T-cells. Notably, hypoxia-triggered angiogenesis causes immunosuppression, adding another piece to the puzzle of hypoxia-induced immunoresistance. If these factors concurrently contribute to the resistance to immunotherapy, they also unveil an unexpected Achille's heel of hypoxic tumors, providing the basis for innovative combination therapies that may rescue the efficacy of ICPIs and CAR T-cells. Although these treatments reveal both a bright side and a dark side in terms of efficacy and safety in clinical trials, they represent the future solution to enhance the efficacy of immunotherapy against hypoxic and therapy-resistant solid tumors.

Mitochondrial metabolism: Inducer or therapeutic target in tumor immune-resistance?

Mitochondria have been considered for a long time only as the principal source of building blocks and energy upon aerobic conditions. Recently they emerged as key players in cell proliferation, invasion and resistance to therapy. The most aggressive tumors are able to evade the immune-surveillance. Alterations in the mitochondria metabolism either in cancer cells or in host immune system cells are involved in such tumor-induced immune-suppression. This review will focus on the main mitochondrial dysfunctions in tumor and immune cell populations determining immune-resistance, and on the therapies that may target mitochondrial metabolism and restore a powerful anti-tumor immune-activity.

Wnt/IL-1ß/IL-8 autocrine circuitries control chemoresistance in mesothelioma initiating cells by inducing ABCB5.

Malignant pleural mesothelioma (MPM) is a tumor with high chemoresistance and poor prognosis. MPM-initiating cells (ICs) are known to be drug resistant, but it is unknown if and how stemness-related pathways determine chemoresistance. Moreover, there are no predictive markers of IC-associated chemoresistance. Aim of this work is to clarify if and by which mechanisms the chemoresistant phenotype of MPM IC was due to specific stemness-related pathways. We generated MPM IC from primary MPM samples and compared the gene expression and chemo-sensitivity profile of IC and differentiated/adherent cells (AC) of the same patient. Compared to AC, IC had upregulated the drug efflux transporter ABCB5 that determined resistance to cisplatin and pemetrexed. ABCB5-knocked-out (KO) IC clones were resensitized to the drugs in vitro and in patient-derived xenografts. ABCB5 was transcriptionally activated by the Wnt/GSK3ß/ß-catenin/c-myc axis that also increased IL-8 and IL-1ß production. IL-8 and IL-1ß-KO IC clones reduced the c-myc-driven transcription of ABCB5 and reacquired chemosensitivity. ABCB5-KO clones had lower IL-8 and IL-1ß secretion, and c-myc transcriptional activity, suggesting that either Wnt/GSK3ß/ß-catenin and IL-8/IL-1ß signaling drive c-myc-mediated transcription of ABCB5. ABCB5 correlated with lower time-to-progression and overall survival in MPM patients treated with cisplatin and pemetrexed. Our work identified multiple autocrine loops linking stemness pathways and resistance to cisplatin and pemetrexed in MPM IC. ABCB5 may represent a new target to chemosensitize MPM IC and a potential biomarker to predict the response to the first-line chemotherapy in MPM patients.

Potential Diagnostic and Prognostic Role of Microenvironment in Malignant Pleural Mesothelioma.

INTRODUCTION: A comprehensive analysis of the immune cell infiltrate collected from pleural fluid and from biopsy specimens of malignant pleural mesothelioma (MPM) may contribute to understanding the immune-evasion mechanisms related to tumor progression, aiding in differential diagnosis and potential prognostic stratification. Until now such approach has not routinely been verified. METHODS: We enrolled 275 patients with an initial clinical diagnosis of pleural effusion. Specimens of pleural fluids and pleural biopsy samples used for the pathologic diagnosis and the immune phenotype analyses were blindly investigated by multiparametric flow cytometry. The results were analyzed using the Kruskal-Wallis test. The Kaplan-Meier and log-rank tests were used to correlate immune phenotype data with patients' outcome. RESULTS: The cutoffs of intratumor T-regulatory (>1.1%) cells, M2-macrophages (>36%), granulocytic and monocytic myeloid-derived suppressor cells (MDSC; >5.1% and 4.2%, respectively), CD4 molecule-positive (CD4+) programmed death 1-positive (PD-1+) (>5.2%) and CD8+PD-1+ (6.4%) cells, CD4+ lymphocyte activating 3-positive (LAG-3+) (>2.8% ) and CD8+LAG-3+ (>2.8%) cells, CD4+ T cell immunoglobulin and mucin domain 3-positive (TIM-3+) (>2.5%), and CD8+TIM-3+ (>2.6%) cells discriminated MPM from pleuritis with 100% sensitivity and 89% specificity. The presence of intratumor MDSC contributed to the anergy of tumor-infiltrating lymphocytes. The immune phenotype of pleural fluid cells had no prognostic significance. By contrast, the intratumor T-regulatory and MDSC levels significantly correlated with progression-free and overall survival, the PD-1+/LAG-3+/TIM-3+ CD4+ tumor-infiltrating lymphocytes correlated with overall survival. CONCLUSIONS: A clear immune signature of pleural fluids and tissues of MPM patients may contribute to better predict patients' outcome.

ERK is a Pivotal Player of Chemo-Immune-Resistance in Cancer.

The extracellular signal-related kinases (ERKs) act as pleiotropic molecules in tumors, where they activate pro-survival pathways leading to cell proliferation and migration, as well as modulate apoptosis, differentiation, and senescence. Given its central role as sensor of extracellular signals, ERK transduction system is widely exploited by cancer cells subjected to environmental stresses, such as chemotherapy and anti-tumor activity of the host immune system. Aggressive tumors have a tremendous ability to adapt and survive in stressing and unfavorable conditions. The simultaneous resistance to chemotherapy and immune system responses is common, and ERK signaling plays a key role in both types of resistance. In this review, we dissect the main ERK-dependent mechanisms and feedback circuitries that simultaneously determine chemoresistance and immune-resistance/immune-escape in cancer cells. We discuss the pros and cons of targeting ERK signaling to induce chemo-immune-sensitization in refractory tumors.

Design, Biological Evaluation, and Molecular Modeling of Tetrahydroisoquinoline Derivatives: Discovery of A Potent P-Glycoprotein Ligand Overcoming Multidrug Resistance in Cancer Stem Cells.

P-Glycoprotein is a well-known membrane transporter responsible for the efflux of an ample spectrum of anticancer drugs. Its relevance in the management of cancer chemotherapy is increased in view of its high expression in cancer stem cells, a population of cancer cells with strong tumor-promoting ability. In the present study, a series of compounds were synthesized through structure modulation of [4'-(6,7-dimethoxy-3,4-dihydro-1 H-isoquinolin-2-ylmethyl)biphenyl-4-ol] (MC70), modifying the phenolic group of the lead compound. Among them, compound 5b emerged for its activity against the transporter (EC50 = 15 nM) and was capable of restoring doxorubicin antiproliferative activity at nontoxic concentration. Its behavior was rationalized through a molecular modeling study consisting of a well-tempered metadynamics simulation, which allowed one to identify the most favorable binding pose, and of a subsequent molecular dynamics run, which indicated a peculiar effect of the compound on the motion pattern of the transporter.

Increasing intratumor C/EBP-ß LIP and nitric oxide levels overcome resistance to doxorubicin in triple negative breast cancer.

BACKGROUND: Triple negative breast cancer (TNBC) easily develops resistance to the first-line drug doxorubicin, because of the high levels of the drug efflux transporter P-glycoprotein (Pgp) and the activation of pro-survival pathways dependent on endoplasmic reticulum (ER). Interfering with these mechanisms may overcome the resistance to doxorubicin, a still unmet need in TNBC. METHODS: We analyzed a panel of human and murine breast cancer cells for their resistance to doxorubicin, Pgp expression, lysosome and proteasome activity, nitrite production, ER-dependent cell death and immunogenic cell death parameters. We evaluated the efficacy of genetic (C/EBP-ß LIP induction) and pharmacological strategies (lysosome and proteasome inhibitors), in restoring the ER-dependent and immunogenic-dependent cell death induced by doxorubicin, in vitro and in syngeneic mice bearing chemoresistant TNBC. The results were analyzed by one-way analysis of variance test. RESULTS: We found that TNBC cells characterized by high levels of Pgp and resistance to doxorubicin, had low induction of the ER-dependent pro-apoptotic factor C/EBP-ß LIP upon doxorubicin treatment and high activities of lysosome and proteasome that constitutively destroyed LIP. The combination of chloroquine and bortezomib restored doxorubicin sensitivity by activating multiple and interconnected mechanisms. First, chloroquine and bortezomib prevented C/EBP-ß LIP degradation and activated LIP-dependent CHOP/TRB3/caspase 3 axis in response to doxorubicin. Second, C/EBP-ß LIP down-regulated Pgp and up-regulated calreticulin that triggered the dendritic cell (DC)-mediated phagocytosis of tumor cell, followed by the activation of anti-tumor CD8+T-lymphocytes upon doxorubicin treatment. Third, chloroquine and bortezomib increased the endogenous production of nitric oxide that further induced C/EBP-ß LIP and inhibited Pgp activity, enhancing doxorubicin's cytotoxicity. In orthotopic models of resistant TNBC, intratumor C/EBP-ß LIP induction - achieved by a specific expression vector or by chloroquine and bortezomib - effectively reduced tumor growth and Pgp expression, increased intra-tumor apoptosis and anti-tumor immune-infiltrate, rescuing the efficacy of doxorubicin. CONCLUSIONS: We suggest that preventing C/EBP-ß LIP degradation by lysosome and proteasome inhibitors triggers multiple virtuous circuitries that restore ER-dependent apoptosis, down-regulate Pgp and re-activate the DC/CD8+T-lymphocytes response against TNBC. Lysosome and proteasome inhibitors associated with doxorubicin may overcome the resistance to the drug in TNBC.

Carbonic Anhydrase XII Inhibitors Overcome P-Glycoprotein-Mediated Resistance to Temozolomide in Glioblastoma.

The role of carbonic anhydrase XII (CAXII) in the chemoresistance of glioblastoma is unexplored. We found CAXII and P-glycoprotein (Pgp) coexpressed in neurospheres derived from 3 of 3 patients with different genetic backgrounds and low response to temozolomide (time to recurrence: 6-9 months). CAXII was necessary for the Pgp efflux of temozolomide and second-line chemotherapeutic drugs, determining chemoresistance in neurospheres. Psammaplin C, a potent inhibitor of CAXII, resensitized primary neurospheres to temozolomide by reducing temozolomide efflux via Pgp. This effect was independent of other known temozolomide resistance factors present in the patients. The overall survival in orthotopic patient-derived xenografts of temozolomide-resistant neurospheres, codosed with Psammaplin C and temozolomide, was significantly increased over temozolomide-treated (P < 0.05) and untreated animals (P < 0.02), without detectable signs of systemic toxicity. We propose that a CAXII inhibitor in combination with temozolomide may provide a new and effective approach to reverse chemoresistance in glioblastoma stem cells. This novel mechanism of action, via the interaction of CAXII and Pgp, ultimately blocks the efflux function of Pgp to improve glioblastoma patient outcomes.

Loss of C/EBP-ß LIP drives cisplatin resistance in malignant pleural mesothelioma.

OBJECTIVES: Cisplatin-based chemotherapy is moderately active in malignant pleural mesothelioma (MPM) due to intrinsic drug resistance and to low immunogenicity of MPM cells. CAAT/enhancer binding protein (C/EBP)-ß LIP is a pro-apoptotic and chemosensitizing transcription factor activated in response to endoplasmic reticulum (ER) stress. MATERIALS AND METHODS: We investigated if LIP levels can predict the clinical response to cisplatin and survival of MPM patients receiving cisplatin-based chemotherapy. We studied the LIP-dependent mechanisms determining cisplatin-resistance and we identified pharmacological approaches targeting LIP, able to restore cisplatin sensitiveness, in patient-derived MPM cells and animal models. Results were analyzed by a one-way analysis of variance test. RESULTS: We found that LIP was degraded by constitutive ubiquitination in primary MPM cells derived from patients poorly responsive to cisplatin. LIP ubiquitination was directly correlated with cisplatin chemosensitivity and was associated with patients' survival after chemotherapy. Overexpression of LIP restored cisplatin's pro-apoptotic effect by activating CHOP/TRB3/caspase 3 axis and up-regulating calreticulin, that triggered MPM cell phagocytosis by dendritic cells and expanded autologous anti-tumor CD8+CD107+T-cytotoxic lymphocytes. Proteasome inhibitor carfilzomib and lysosome inhibitor chloroquine prevented LIP degradation. The triple combination of carfilzomib, chloroquine and cisplatin increased ER stress-triggered apoptosis and immunogenic cell death in patients' samples, and reduced tumor growth in cisplatin-resistant MPM preclinical models. CONCLUSION: The loss of LIP mediates cisplatin resistance, rendering LIP a possible predictor of cisplatin response in MPM patients. The association of proteasome and lysosome inhibitors reverses cisplatin resistance by restoring LIP levels and may represent a new adjuvant strategy in MPM treatment.

Folate-targeted liposomal nitrooxy-doxorubicin: An effective tool against P-glycoprotein-positive and folate receptor-positive tumors.

Drug efflux transporters, in particular P-glycoprotein (Pgp), limit the success of chemotherapy. We previously found that synthetic doxorubicin conjugated with nitric oxide (NO)-releasing group overcomes resistance by inducing a NO-mediated inhibition of Pgp. Here we produced the first liposomal formulations of this nitrooxy-doxorubicin decorated with folic acid (FA), termed LNDF, in order to improve their active targeting against Pgp-expressing tumors. Folate was inserted onto liposomes surface using two different methods and the formulations were compared with respect to their technological features and in vitro behavior. By analyzing human and murine breast cancer cells with different expression of FA receptor (FAR) and Pgp, we demonstrated that LNDF are internalized in a FAR-dependent manner and achieve maximal anti-tumor efficacy against FAR-positive/Pgp-positive cells. Upon uptake of LNDF, nitrooxy-doxorubicin was delivered within nucleus, where it induced cell cycle arrest and DNA damages, and mitochondria, where it impaired the mitochondrial energy metabolism and triggered mitochondria-dependent apoptosis. LNDF reduced the growth of FAR-positive/Pgp-positive tumors and prevented tumor formation in mice, whereas doxorubicin and Caelyx® failed. LNDF cardiotoxicity was comparable to Caelyx®. The sensitivity to LNDF was maintained in tumors exposed to repeated cycles of the drug and in cells derived from the exposed tumors, excluding the onset of secondary resistance. By combining an innovative multitarget cargo drug, conceived to achieve high efficacy against Pgp-expressing cells, and appropriate strategies of liposome formulation and decoration, we produced a therapeutic tool that may represent a significant advancement in the treatment of FAR-positive/Pgp-positive tumors.

PERK induces resistance to cell death elicited by endoplasmic reticulum stress and chemotherapy.

BACKGROUND: Nutrient deprivation, hypoxia, radiotherapy and chemotherapy induce endoplasmic reticulum (ER) stress, which activates the so-called unfolded protein response (UPR). Extensive and acute ER stress directs the UPR towards activation of death-triggering pathways. Cancer cells are selected to resist mild and prolonged ER stress by activating pro-survival UPR. We recently found that drug-resistant tumor cells are simultaneously resistant to ER stress-triggered cell death. It is not known if cancer cells adapted to ER stressing conditions acquire a chemoresistant phenotype. METHODS: To investigate this issue, we generated human cancer cells clones with acquired resistance to ER stress from ER stress-sensitive and chemosensitive cells. RESULTS: ER stress-resistant cells were cross-resistant to multiple chemotherapeutic drugs: such multidrug resistance (MDR) was due to the overexpression of the plasma-membrane transporter MDR related protein 1 (MRP1). Gene profiling analysis unveiled that cells with acquired resistance to ER stress and chemotherapy share higher expression of the UPR sensor protein kinase RNA-like endoplasmic reticulum kinase (PERK), which mediated the erythroid-derived 2-like 2 (Nrf2)-driven transcription of MRP1. Disrupting PERK/Nrf2 axis reversed at the same time resistance to ER stress and chemotherapy. The inducible silencing of PERK reduced tumor growth and restored chemosensitivity in resistant tumor xenografts. CONCLUSIONS: Our work demonstrates for the first time that the adaptation to ER stress in cancer cells produces a MDR phenotype. The PERK/Nrf2/MRP1 axis is responsible for the resistance to ER stress and chemotherapy, and may represent a good therapeutic target in aggressive and resistant tumors.

P-glycoprotein-mediated chemoresistance is reversed by carbonic anhydrase XII inhibitors.

Carbonic anhydrase XII (CAXII) is a membrane enzyme that maintains pH homeostasis and sustains optimum P-glycoprotein (Pgp) efflux activity in cancer cells. Here, we investigated a panel of eight CAXII inhibitors (compounds 1-8), for their potential to reverse Pgp mediated tumor cell chemoresistance. Inhibitors (5 nM) were screened in human and murine cancer cells (colon, lung, breast, bone) with different expression levels of CAXII and Pgp. We identified three CAXII inhibitors (compounds 1, 2 and 4) that significantly (≥ 2 fold) increased the intracellular retention of the Pgp-substrate and chemotherapeutic doxorubicin, and restored its cytotoxic activity. The inhibitors lowered intracellular pH to indirectly impair Pgp activity. Ca12-knockout assays confirmed that the chemosensitizing property of the compounds was dependent on active CAXII. Furthermore, in a preclinical model of drug-resistant breast tumors compound 1 (1900 ng/kg) restored the efficacy of doxorubicin to the same extent as the direct Pgp inhibitor tariquidar. The expression of carbonic anhydrase IX had no effect on the intracellular doxorubicin accumulation. Our work provides strong evidence that CAXII inhibitors are effective chemosensitizer agents in CAXII-positive and Pgp-positive cancer cells. The use of CAXII inhibitors may represent a turning point in combinatorial chemotherapeutic schemes to treat multidrug-resistant tumors.

Mitochondria-Targeted Doxorubicin: A New Therapeutic Strategy against Doxorubicin-Resistant Osteosarcoma.

Doxorubicin is one of the leading drugs for osteosarcoma standard chemotherapy. A total of 40% to 45% of high-grade osteosarcoma patients are unresponsive, or only partially responsive, to doxorubicin (Dox), due to the overexpression of the drug efflux transporter ABCB1/P-glycoprotein (Pgp). The aim of this work is to improve Dox-based regimens in resistant osteosarcomas. We used a chemically modified mitochondria-targeted Dox (mtDox) against Pgp-overexpressing osteosarcomas with increased resistance to Dox. Unlike Dox, mtDox accumulated at significant levels intracellularly, exerted cytotoxic activity, and induced necrotic and immunogenic cell death in Dox-resistant/Pgp-overexpressing cells, fully reproducing the activities exerted by anthracyclines in drug-sensitive tumors. mtDox reduced tumor growth and cell proliferation, increased apoptosis, primed tumor cells for recognition by the host immune system, and was less cardiotoxic than Dox in preclinical models of drug-resistant osteosarcoma. The increase in Dox resistance was paralleled by a progressive upregulation of mitochondrial metabolism. By widely modulating the expression of mitochondria-related genes, mtDox decreased mitochondrial biogenesis, the import of proteins and metabolites within mitochondria, mitochondrial metabolism, and the synthesis of ATP. These events were paralleled by increased reactive oxygen species production, mitochondrial depolarization, and mitochondria-dependent apoptosis in resistant osteosarcoma cells, where Dox was completely ineffective. We propose mtDox as a new effective agent with a safer toxicity profile compared with Dox that may be effective for the treatment of Dox-resistant/Pgp-positive osteosarcoma patients, who strongly need alternative and innovative treatment strategies. Mol Cancer Ther; 15(11); 2640-52. ©2016 AACR.

The cross-talk between canonical and non-canonical Wnt-dependent pathways regulates P-glycoprotein expression in human blood-brain barrier cells.

In this work, we investigate if and how transducers of the 'canonical' Wnt pathway, i.e., Wnt/glycogen synthase kinase 3 (GSK3)/ß-catenin, and transducers of the 'non-canonical' Wnt pathway, i.e., Wnt/RhoA/RhoA kinase (RhoAK), cooperate to control the expression of P-glycoprotein (Pgp) in blood-brain barrier (BBB) cells. By analyzing human primary brain microvascular endothelial cells constitutively activated for RhoA, silenced for RhoA or treated with the RhoAK inhibitor Y27632, we found that RhoAK phosphorylated and activated the protein tyrosine phosphatase 1B (PTP1B), which dephosphorylated tyrosine 216 of GSK3, decreasing the GSK3-mediated inhibition of ß-catenin. By contrast, the inhibition of RhoA/RhoAK axis prevented the activation of PTP1B, enhanced the GSK3-induced phosphorylation and ubiquitination of ß-catenin, and reduced the ß-catenin-driven transcription of Pgp. The RhoAK inhibition increased the delivery of Pgp substrates like doxorubicin across the BBB and improved the doxorubicin efficacy against glioblastoma cells co-cultured under a BBB monolayer. Our data demonstrate that in human BBB cells the expression of Pgp is controlled by a cross-talk between canonical and non-canonical Wnt pathways. The disruption of this cross-talk, e.g., by inhibiting RhoAK, downregulates Pgp and increases the delivery of Pgp substrates across the BBB.

Temozolomide down-regulates P-glycoprotein in human blood-brain barrier cells by disrupting Wnt3 signaling.

Low delivery of many anticancer drugs across the blood-brain barrier (BBB) is a limitation to the success of chemotherapy in glioblastoma. This is because of the high levels of ATP-binding cassette transporters like P-glycoprotein (Pgp/ABCB1), which effluxes drugs back to the bloodstream. Temozolomide is one of the few agents able to cross the BBB; its effects on BBB cells permeability and Pgp activity are not known. We found that temozolomide, at therapeutic concentration, increased the transport of Pgp substrates across human brain microvascular endothelial cells and decreased the expression of Pgp. By methylating the promoter of Wnt3 gene, temozolomide lowers the endogenous synthesis of Wnt3 in BBB cells, disrupts the Wnt3/glycogen synthase kinase 3/ß-catenin signaling, and reduces the binding of ß-catenin on the promoter of mdr1 gene, which encodes for Pgp. In co-culture models of BBB cells and human glioblastoma cells, pre-treatment with temozolomide increases the delivery, cytotoxicity, and antiproliferative effects of doxorubicin, vinblastine, and topotecan, three substrates of Pgp that are usually poorly delivered across BBB. Our work suggests that temozolomide increases the BBB permeability of drugs that are normally effluxed by Pgp back to the bloodstream. These findings may pave the way to new combinatorial chemotherapy schemes in glioblastoma.