Targeting EZH2 in SMARCB1-deficient sarcomas: Advances and opportunities to potentiate the efficacy of EZH2 inhibitors.

Soft tissue sarcomas (STSs) are rare mesechymal malignancies characterized by distintive molecular, histological and clinical features. Many STSs are considered as predominatly epigenetic diseases due to underlying chromatin deregulation. Discovery of deregulated functional antagonism between the chromatin remodeling BRG1/BRM-associated (BAFs) and the histone modifying Polycomb repressor complexes (PRCs) has provided novel actionable targets. In epithelioid sarcoma (ES), extracranial, extrarenal malignant rhabdoid tumors (eMRTs) and synovial sarcoma (SS), the total or partial loss of the BAF core subunit SMARCB1, driven by different alterations, is associated with PRC2 deregulation and dependency on its enzymatic subunit, EZH2. In these SMARCB1-deficient STSs, aberrant EZH2 expression and/or activity emerged as a druggable vulnerability. Although preclinical investigation supported EZH2 targeting as a promising therapeutic option, clinical studies demonstrated a variable response to EZH2 inhibitors. Actually, whereas the clinical benefit recorded in ES patients prompted the FDA approval of the EZH2 inhibitor tazemetostat, the modest and sporadic responses observed in eMRT and SS patients highlighted the need to deepen mechanistic as well as pharmacological investigations to improve drug effectiveness. We summarize the current knowledge of different mechanisms driving SMARCB1 deficiency and EZH2 deregulation in ES, eMRT and SS along with preclinical and clinical studies of EZH2-targeting agents. Possible implication of the PRC2- and enzymatic-independent functions of EZH2 and of its homolog, EZH1, in the response to anti-EZH2 agents will be discussed together with combinatorial strategies under investigation to improve the efficacy of EZH2 targeting in these tumors.

Beyond targeting amplified MDM2 and CDK4 in well differentiated and dedifferentiated liposarcomas: From promise and clinical applications towards identification of progression drivers.

Well differentiated and dedifferentiated liposarcomas (WDLPS and DDLPS) are tumors of the adipose tissue poorly responsive to conventional cytotoxic chemotherapy which currently remains the standard-of-care. The dismal prognosis of the DDLPS subtype indicates an urgent need to identify new therapeutic targets to improve the patient outcome. The amplification of the two driver genes MDM2 and CDK4, shared by WDLPD and DDLPS, has provided the rationale to explore targeting the encoded ubiquitin-protein ligase and cell cycle regulating kinase as a therapeutic approach. Investigation of the genomic landscape of WD/DDLPS and preclinical studies have revealed additional potential targets such as receptor tyrosine kinases, the cell cycle kinase Aurora A, and the nuclear exporter XPO1. While the therapeutic significance of these targets is being investigated in clinical trials, insights into the molecular characteristics associated with dedifferentiation and progression from WDLPS to DDLPS highlighted additional genetic alterations including fusion transcripts generated by chromosomal rearrangements potentially providing new druggable targets (e.g. NTRK, MAP2K6). Recent years have witnessed the increasing use of patient-derived cell and tumor xenograft models which offer valuable tools to accelerate drug repurposing and combination studies. Implementation of integrated "multi-omics" investigations applied to models recapitulating WD/DDLPS genetics, histologic differentiation and biology, will hopefully lead to a better understanding of molecular alterations driving liposarcomagenesis and DDLPS progression, as well as to the identification of new therapies tailored on tumor histology and molecular profile.

Combinatorial strategies to potentiate the efficacy of HDAC inhibitors in fusion-positive sarcomas.

Fusion positive (FP) sarcomas are characterized by chromosomal rearrangements generating pathognomonic fusion transcripts and oncoproteins. In Ewing's sarcoma family of tumors (ESFTs), FP-rhabdomyosarcomas (FP-RMS) and synovial sarcomas (SS), the most common and aggressive forms of sarcomas in childhood and adolescence, the oncogenic rearrangements involve transcription cofactors causing widespread epigenetic rewiring and aberrant gene expression. Through the cooperation with histone deacetylases (HDACs) in transcription regulatory complexes, the fusion oncoproteins affect histone acetylation and chromatin remodeling. The participation of HDACs in core mechanisms of sarcoma cell transformation has paved the way to the investigation of HDAC inhibitors (HDACis) for therapeutic intervention. Preclinical studies have provided convincing evidence that HDAC activity abrogation can revert malignant cell features driven by FET-ETS, PAX3/7-FOXO1 or SS18-SSX fusion oncogenes in ESFTs, FP-RMS, or SS models, respectively, resulting in in vitro and in vivo growth inhibition. While clinical trials of HDACi monotherapies led to drug approval in some hematologic malignancies, no significant therapeutic benefit has been reported in solid tumors, including sarcomas. HDACi-based combination therapies with targeted or conventional anticancer agents have shown limited efficacy in early studies recruiting sarcoma patients, although partial responses and disease stabilization have been reported. In these trials, sarcomas were represented, however, as unclassified group in most cases. We summarize, here, studies addressing the role of HDACs in FP-sarcoma pathobiology and HDACi-based rational drug combinations. Finally, we discuss the opportunity of exploiting drug inhibitory profile and expression/function of specific HDAC isoenzymes to harness the full therapeutic potential of HDACis in these sarcoma histotypes.

Upregulation of ERK-EGR1-heparanase axis by HDAC inhibitors provides targets for rational therapeutic intervention in synovial sarcoma.

BACKGROUND: Synovial sarcoma (SS) is an aggressive soft tissue tumor with limited therapeutic options in advanced stage. SS18-SSX fusion oncogenes, which are the hallmarks of SS, cause epigenetic rewiring involving histone deacetylases (HDACs). Promising preclinical studies supporting HDAC targeting for SS treatment were not reflected in clinical trials with HDAC inhibitor (HDACi) monotherapies. We investigated pathways implicated in SS cell response to HDACi to identify vulnerabilities exploitable in combination treatments and improve the therapeutic efficacy of HDACi-based regimens. METHODS: Antiproliferative and proapoptotic effects of the HDACi SAHA and FK228 were examined in SS cell lines in parallel with biochemical and molecular analyses to bring out cytoprotective pathways. Treatments combining HDACi with drugs targeting HDACi-activated prosurvival pathways were tested in functional assays in vitro and in a SS orthotopic xenograft model. Molecular mechanisms underlying synergisms were investigated in SS cells through pharmacological and gene silencing approaches and validated by qRT-PCR and Western blotting. RESULTS: SS cell response to HDACi was consistently characterized by activation of a cytoprotective and auto-sustaining axis involving ERKs, EGR1, and the ß-endoglycosidase heparanase, a well recognized pleiotropic player in tumorigenesis and disease progression. HDAC inhibition was shown to upregulate heparanase by inducing expression of the positive regulator EGR1 and by hampering negative regulation by p53 through its acetylation. Interception of HDACi-induced ERK-EGR1-heparanase pathway by cell co-treatment with a MEK inhibitor (trametinib) or a heparanase inhibitor (SST0001/roneparstat) enhanced antiproliferative and pro-apoptotic effects. HDAC and heparanase inhibitors had opposite effects on histone acetylation and nuclear heparanase levels. The combination of SAHA with SST0001 prevented the upregulation of ERK-EGR1-heparanase induced by the HDACi and promoted caspase-dependent cell death. In vivo, the combined treatment with SAHA and SST0001 potentiated the antitumor efficacy against the CME-1 orthotopic SS model as compared to single agent administration. CONCLUSIONS: The present study provides preclinical rationale and mechanistic insights into drug combinatory strategies based on the use of ERK pathway and heparanase inhibitors to improve the efficacy of HDACi-based antitumor therapies in SS. The involvement of classes of agents already clinically available, or under clinical evaluation, indicates the transferability potential of the proposed approaches.

Receptor tyrosine kinases and heparan sulfate proteoglycans: Interplay providing anticancer targeting strategies and new therapeutic opportunities.

The development of pharmacological and biological inhibitors of receptor tyrosine kinases (RTKs) has changed the treatment paradigm of several neoplastic diseases. However, the occurrence of intrinsic and acquired resistance represents a limit to the efficacy of these drugs even in RTK-addicted cancers. The identification of innovative therapeutic approaches and rationale-based drug combinations remains a primary need to improve patients' outcome. Heparan sulfate proteoglycans (HSPGs) at the cell surface and in the extracellular matrix bind to and modulate the biological activity of a great number of heparan sulfate (HS) binding proteins. The participation of HSPGs as accessory molecules in the growth factor-receptor interactions and mechanism of activation of several RTKs provides the basis for developing alternative therapeutic strategies based on targeting HSPGs by antibodies or HS mimetics to interfere with the aberrant oncogenic signaling implicated in the pathobiology of several tumors. Here, we focus on the FGF-FGFR-HSPG and HGF-Met-HSPG axes as paradigmatic examples of the multiple-level interconnections between RTKs and HSPGs influencing cell signaling, gene expression, drug sensitivity, and promoting a permissive microenvironment for tumor growth and progression. In these reciprocal regulations, the HS degrading enzymes heparanase and endosulfatases play key roles contributing to the high structural complexity and heterogeneity of HS chains as well as to the specificity of their interaction with proteins. Actually, heparanase and endosulfatases represent, in turn, promising therapeutic targets. We also report some studies describing the effects of FGFR and Met inhibitors on the expression of genes encoding HSPGs and related enzymes, and discuss about the potential impact of these effects on drug response. Finally, we argue about the need of in-depth investigation of the role of HSPGs and their modifying enzymes in specific tumor pathologies to exploit the opportunity of combination treatments including HS mimetics or HSPG directed antibodies to improve efficacy of RTK inhibitors and overcome drug resistance.

Heparanase: A Potential Therapeutic Target in Sarcomas.

Sarcomas comprise a heterogeneous group of rare malignancies of mesenchymal origin including more than 70 subtypes. They may arise in muscle, bone, cartilage and other connective tissues. Their high histological and genetic heterogeneity makes diagnosis and treatment very challenging. Deregulation of heparanase has been found in several sarcoma subtypes and high expression levels have been correlated with poor prognosis in Ewing's sarcoma and osteosarcoma. Altered expression of specific heparan sulfate proteoglycans and heparan sulfate biosynthetic enzymes has also been observed. Advances in molecular pathogenesis of sarcomas have evidenced the critical role of several heparan sulfate binding growth factors and receptor tyrosine kinases, highly interconnected with the microenvironment, in sustaining tumor growth and progression. Interference with heparanase/heparan sulfate functions represents a potential therapeutic approach in sarcoma. In this chapter, we summarize the current knowledge about the biological significance of heparanase expression and its potential as a therapeutic target in subtypes of both soft tissue and bone sarcomas. Particular emphasis is given to the involvement of heparan sulfate proteoglycans and their synthesizing and modifying enzymes in bone physiology and disorders leading up to the pathobiology of bone sarcomas. The chapter also describes the cooperation between exostin loss-of-function and heparanase upregulation in hereditary Multiple Osteochondroma syndrome as a paradigmatic example of constitutive alteration of the heparanase/heparan sulfate proteoglycan system which may contribute to progression to malignant secondary chondrosarcoma. Preclinical evidence of the role of heparanase as a promising therapeutic target in various sarcoma subtypes is finally resumed.

Overactive IGF1/Insulin Receptors and NRASQ61R Mutation Drive Mechanisms of Resistance to Pazopanib and Define Rational Combination Strategies to Treat Synovial Sarcoma.

Pazopanib is approved for treatment of advanced soft tissue sarcomas, but primary and secondary drug resistance limits its clinical utility. We investigated the molecular mechanisms mediating pazopanib resistance in human synovial sarcoma (SS) models. We found reduced cell sensitivity to pazopanib associated with inefficient inhibition of the two critical signaling nodes, AKT and ERKs, despite strong inhibition of the main drug target, PDGFRα. In the CME-1 cell line, overactivation of IGF1 and Insulin receptors (IGF1R/InsR) sustained AKT activation and pazopanib resistance, which was overcome by a combination treatment with the double IGF1R/InsR inhibitor BMS754807. In the highly pazopanib resistant MoJo cell line, NRASQ61R mutation sustained constitutive ERK activation. Transfection of the NRAS mutant in the pazopanib sensitive SYO-1 cell line increased the drug IC50. MoJo cells treatment with pazopanib in combination with the MEK inhibitor trametinib restored ERK inhibition, synergistically inhibited cell growth, and induced apoptosis. The combination significantly enhanced the antitumor efficacy against MoJo orthotopic xenograft abrogating growth in 38% of mice. These findings identified two different mechanisms of intrinsic pazopanib resistance in SS cells, supporting molecular/immunohistochemical profiling of tumor specimens as a valuable approach to selecting patients who may benefit from rational drug combinations.

Heparan Sulfate Mimetics in Cancer Therapy: The Challenge to Define Structural Determinants and the Relevance of Targets for Optimal Activity.

Beyond anticoagulation, the therapeutic potential of heparin derivatives and heparan sulfate (HS) mimetics (functionally defined HS mimetics) in oncology is related to their ability to bind and modulate the function of a vast array of HS-binding proteins with pivotal roles in cancer growth and progression. The definition of structural/functional determinants and the introduction of chemical modifications enabled heparin derivatives to be identified with greatly reduced or absent anticoagulant activity, but conserved/enhanced anticancer activity. These studies paved the way for the disclosure of structural requirements for the inhibitory effects of HS mimetics on heparanase, selectins, and growth factor receptor signaling, as well as for the limitation of side effects. Actually, HS mimetics affect the tumor biological behavior via a multi-target mechanism of action based on their effects on tumor cells and various components of the tumor microenvironment. Emerging evidence indicates that immunomodulation can participate in the antitumor activity of these agents. Significant ability to enhance the antitumor effects of combination treatments with standard therapies was shown in several tumor models. While the first HS mimetics are undergoing early clinical evaluation, an improved understanding of the molecular contexts favoring the antitumor action in certain malignancies or subgroups is needed to fully exploit their potential.

Supersulfated low-molecular weight heparin synergizes with IGF1R/IR inhibitor to suppress synovial sarcoma growth and metastases.

Synovial sarcoma (SS) is an aggressive tumor with propensity for lung metastases which significantly impact patients' prognosis. New therapeutic approaches are needed to improve treatment outcome. Targeting the heparanase/heparan sulfate proteoglycan system by heparin derivatives which act as heparanase inhibitors/heparan sulfate mimetics is emerging as a therapeutic approach that can sensitize the tumor response to chemotherapy. We investigated the therapeutic potential of a supersulfated low molecular weight heparin (ssLMWH) in preclinical models of SS. ssLMWH showed a potent anti-heparanase activity, dose-dependently inhibited SS colony growth and cell invasion, and downregulated the activation of receptor tyrosine kinases including IGF1R and IR. The combination of ssLMWH and the IGF1R/IR inhibitor BMS754807 synergistically inhibited proliferation of cells exhibiting IGF1R hyperactivation, also abrogating cell motility and promoting apoptosis in association with PI3K/AKT pathway inhibition. The drug combination strongly enhanced the antitumor effect against the CME-1 model, as compared to single agent treatment, abrogating orthotopic tumor growth and significantly repressing spontaneous lung metastatic dissemination in treated mice. These findings provide a strong preclinical rationale for developing drug regimens combining heparanase inhibitors/HS mimetics with IGF1R antagonists for treatment of metastatic SS.

Axl molecular targeting counteracts aggressiveness but not platinum-resistance of ovarian carcinoma cells.

Ovarian carcinoma, the most common gynaecological cancer, is characterized by high lethality mainly due to late diagnosis and treatment failure. The efficacy of platinum drug-based therapy in the disease is limited by the occurrence of drug resistance, a phenomenon often associated with increased metastatic potential. Because the Tyr-kinase receptor Axl can be deregulated in ovarian carcinoma and plays a pro-metastatic/anti-apoptotic role, the aim of this study was to examine if Axl inhibition modulates drug resistance and aggressive features of ovarian carcinoma cells, using various pairs of cisplatin-sensitive and -resistant cell lines. We found that mRNA and protein levels of Axl were increased in the platinum-resistant IGROV-1/Pt1 and IGROV-1/OHP cell lines compared to the parental IGROV-1 cells. IGROV-1/Pt1 cells displayed increased migratory and invasive capabilities. When Axl was silenced, these cells exhibited reduced growth and invasive/migratory capabilities compared to control siRNA-transfected cells, associated with decreased p38 and STAT3 phosphorylation. In keeping with this evidence, pharmacological inhibition of p38 and STAT3 decreased IGROV-1/Pt1 invasive capability. Molecular inhibition of Axl did not sensitize IGROV-1/Pt1 cells to cisplatin, but enhanced ErbB3 activation in IGROV-1/Pt1 cells and suppressed the clonogenic capability of various ovarian carcinoma cell lines. The combination of cisplatin and AZD8931, a small molecule which inhibits ErbB3, produced a synergistic effect in IGROV-1/Pt1 cells. Thus, Axl targeting per se reduces invasive capability of drug-resistant cells, but sensitization to cisplatin requires the concomitant inhibition of additional survival pathways.

Targeting Heparan Sulfate Proteoglycans and their Modifying Enzymes to Enhance Anticancer Chemotherapy Efficacy and Overcome Drug Resistance.

Targeting heparan sulfate proteoglycans (HSPGs) and enzymes involved in heparan sulfate (HS) chain editing is emerging as a new anticancer strategy. The involvement of HSPGs in tumor cell signaling, inflammation, angiogenesis and metastasis indicates that agents able to inhibit aberrant HSPG functions can potentially act as multitarget drugs affecting both tumor cell growth and the supportive boost provided by the microenvironment. Moreover, accumulating evidence supports that an altered expression or function of HSPGs, or of the complex enzyme system regulating their activities, can also depress the tumor response to anticancer treatments in several tumor types. Thereby, targeting HSPGs or HSPG modifying enzymes appears an appealing approach to enhance chemotherapy efficacy. A great deal of effort from academia and industry has led to the development of agents mimicking HS, and/or inhibiting HSPG modifying enzymes. Inhibitors of Sulf-2, an endosulfatase that edits the HS sulfation pattern, and inhibitors of heparanase, the endoglycosidase that produces functional HS fragments, appear particularly promising. In fact, a Sulf-2 inhibitor (OKN-007), and two heparanase inhibitors/HS mimics (roneparstat, PG545) are currently under early clinical investigation. In this review, we summarized preclinical studies in experimental tumor models of the main chemical classes of Sulf-2 and heparanase inhibitors. We described examples of different mechanisms through which heparanase and HSPGs, often in cooperation, may impact tumor sensitivity to various antitumor agents. Finally, we reported a few preclinical studies showing increased antitumor efficacy obtained with the use of candidate clinical HS mimics in combination regimens.

The heparanase/heparan sulfate proteoglycan axis: A potential new therapeutic target in sarcomas.

Heparanase, the only known mammalian endoglycosidase degrading heparan sulfate (HS) chains of HS proteoglycans (HSPG), is a highly versatile protein affecting multiple events in tumor cells and their microenvironment. In several malignancies, deregulation of the heparanase/HSPG system has been implicated in tumor progression, hence representing a valuable therapeutic target. Currently, multiple agents interfering with the heparanase/HSPG axis are under clinical investigation. Sarcomas are characterized by a high biomolecular complexity and multiple levels of interconnection with microenvironment sustaining their growth and progression. The clinical management of advanced diseases remains a challenge. In several sarcoma subtypes, high levels of heparanase expression have been correlated with poor prognosis associated factors. On the other hand, expression of cell surface-associated HSPGs (i.e. glypicans and syndecans) has been found altered in specific sarcoma subtypes. Recent studies provided the preclinical proof-of-principle of the role of the heparanase/HSPG axis as therapeutic target in various sarcoma subtypes. Although currently there are no clinical trials evaluating agents targeting heparanase and/or HSPGs in sarcomas, we here provide arguments for this strategy as potentially able to implement the therapeutic options for sarcoma patients.

Antitumor efficacy of the heparan sulfate mimic roneparstat (SST0001) against sarcoma models involves multi-target inhibition of receptor tyrosine kinases.

The heparan sulfate (HS) mimic/heparanase inhibitor roneparstat (SST0001) shows antitumor activity in preclinical sarcoma models. We hypothesized that this 100% N-acetylated and glycol-split heparin could interfere with the functions of several receptor tyrosine kinases (RTK) coexpressed in sarcomas and activated by heparin-binding growth factors. Using a phospho-proteomic approach, we investigated the drug effects on RTK activation in human cell lines representative of different sarcoma subtypes. Inhibition of FGF, IGF, ERBB and PDGF receptors by the drug was biochemically and functionally validated. Roneparstat counteracted the autocrine loop induced by the COL1A1/PDGFB fusion oncogene, expressed in a human dermatofibrosarcoma protuberans primary culture and in NIH3T3COL1A1/PDGFB transfectants, inhibiting cell anchorage-independent growth and invasion. In addition, roneparstat inhibited the activation of cell surface PDGFR and PDGFR-associated FAK, likely contributing to the reversion of NIH3T3COL1A1/PDGFB cell transformed and pro-invasive phenotype. Biochemical and histological/immunohistochemical ex vivo analyses confirmed a reduced activation of ERBB4, EGFR, INSR, IGF1R, associated with apoptosis induction and angiogenesis inhibition in a drug-treated Ewing's sarcoma family tumor xenograft. The combination of roneparstat with irinotecan significantly improved the antitumor effect against A204 rhabdoid xenografts resulting in a high rate of complete responses and cures. These findings reveal that roneparstat exerts a multi-target inhibition of RTKs relevant in the pathobiology of different sarcoma subtypes. These effects, likely cooperating with heparanase inhibition, contribute to the antitumor efficacy of the drug. The study supports heparanase/HS axis targeting as a valuable approach in combination therapies of different sarcoma subtypes providing a preclinical rationale for clinical investigation.

Synthetic sulfoglycolipids targeting the serine-threonine protein kinase Akt.

The serine-threonine protein kinase Akt, also known as protein kinase B, is a key component of the phosphoinositide 3-kinase (PI3K)-Akt-mTOR axis. Deregulated activation of this pathway is frequent in human tumors and Akt-dependent signaling appears to be critical in cell survival. PI3K activation generates 3-phosphorylated phosphatidylinositols that bind Akt pleckstrin homology (PH) domain. The blockage of Akt PH domain/phosphoinositides interaction represents a promising approach to interfere with the oncogenic potential of over-activated Akt. In the present study, phosphatidyl inositol mimics based on a ß-glucoside scaffold have been synthesized as Akt inhibitors. The compounds possessed one or two lipophilic moieties of different length at the anomeric position of glucose, and an acidic or basic group at C-6. Docking studies, ELISA Akt inhibition assays, and cellular assays on different cell models highlighted 1-O-octadecanoyl-2-O-ß-d-sulfoquinovopyranosyl-sn-glycerol as the best Akt inhibitor among the synthesized compounds, which could be considered as a lead for further optimization in the design of Akt inhibitors.

Targeting of RET oncogene by naphthalene diimide-mediated gene promoter G-quadruplex stabilization exerts anti-tumor activity in oncogene-addicted human medullary thyroid cancer.

Medullary thyroid cancer (MTC) relies on the aberrant activation of RET proto-oncogene. Though targeted approaches (i.e., tyrosine kinase inhibitors) are available, the absence of complete responses and the onset of resistance mechanisms indicate the need for novel therapeutic interventions. Due to their role in regulation of gene expression, G-quadruplexes (G4) represent attractive targets amenable to be recognized or stabilized by small molecules. Here, we report that exposure of MTC cells to a tri-substituted naphthalene diimide (NDI) resulted in a significant antiproliferative activity paralleled by inhibition of RET expression. Biophysical analysis and gene reporter assays showed that impairment of RET expression was consequent to the NDI-mediated stabilization of the G4 forming within the gene promoter. We also showed for the first time that systemic administration of the NDI in mice xenotransplanted with MTC cells resulted in a remarkable inhibition of tumor growth in vivo. Overall, our findings indicate that NDI-dependent RET G4 stabilization represents a suitable approach to control RET transcription and delineate the rationale for the development of G4 stabilizing-based treatments for MTC as well as for other tumors in which RET may have functional and therapeutic implications.

Role of the Receptor Tyrosine Kinase Axl and its Targeting in Cancer Cells.

Aberrant expression and activation of receptor tyrosine kinases (RTK) is a frequent feature of tumor cells that may underlie tumor aggressiveness. Among RTK, Axl, a member of the Tyro3-Axl-Mer family, represents a potential therapeutic target in different tumor types given its over-expression which leads to activation of oncogenic signaling promoting cell proliferation and survival, as well as migration and invasion. Axl can promote aggressiveness of various cell types through PI3K/Akt and/or MAPK/ERK, and its expression can be transcriptionally regulated by multiple factors. Deregulated Axl expression and activation have been shown to be implicated in reduced sensitivity of tumor cells to target-specific and conventional antitumor agents, but the precise mechanism underlying these phenomena are still poorly understood. Several small molecules acting as Axl inhibitors have been reported, and some of them are undergoing clinical investigation. In this review, we describe Axl biological functions, its expression in cancer and in drug-resistant tumor cells and the development of inhibitors tailored to this receptor tyrosine kinase.

New mechanisms for old drugs: Insights into DNA-unrelated effects of platinum compounds and drug resistance determinants.

Platinum drugs have been widely used for the treatment of several solid tumors. Although DNA has been recognized as the primary cellular target for these agents, there are unresolved issues concerning their effects and the molecular mechanisms underlying the antitumor efficacy. These cytotoxic agents interact with sub-cellular compartments other than the nucleus. Here, we review how such emerging phenomena contribute to the pharmacologic activity as well as to drug resistance phenotypes. DNA-unrelated effects of platinum drugs involve alterations at the plasma membrane and in endo-lysosomal compartments. A direct interaction with the mitochondria also appears to be implicated in drug-induced cell death. Moreover, the pioneering work of a few groups has shown that platinum drugs can act on the tumor microenvironment as well, and potentiate antitumor activity of the immune system. These poorly understood aspects of platinum drug activity sites may be harnessed to enhance their antitumor efficacy. A complete understanding of DNA-unrelated effects of platinum compounds might reveal new aspects of drug resistance allowing the implementation of the antitumor therapeutic efficacy of platinum compound-based regimens and minimization of their toxic side effects.