Dasatinib plus Nutlin-3 shows synergistic antileukemic activity in both p53 wild-type and p53 mutated B chronic lymphocytic leukemias by inhibiting the Akt pathway

Integrating bulk RNA-seq and scRNA-seq analyses revealed the function and clinical value of thrombospondins in colon cancer

Background

Acting as mediators in cell-matrix and cell-cell communication, matricellular proteins play a crucial role in cancer progression. Thrombospondins (TSPs), a type of matricellular glycoproteins, are key regulators in cancer biology with multifaceted roles. Although TSPs have been implicated in anti-tumor immunity and epithelial-mesenchymal transition (EMT) in several malignancies, their specific roles to colon cancer remain elusive. Addressing this knowledge gap is essential, as understanding the function of TSPs in colon cancer could identify new therapeutic targets and prognostic markers.

Methods

Analyzing 1981 samples from 10 high-throughput datasets, including six bulk RNA-seq, three scRNA-seq, and one spatial transcriptome dataset, our study investigated the prognostic relevance, risk stratification value, immune heterogeneity, and cellular origin of TSPs, as well as their influence on cancer-associated fibroblasts (CAFs). Utilizing survival analysis, unsupervised clustering, and functional enrichment, along with multiple correlation analyses of the tumor-microenvironment (TME) via Gene Set Variation Analysis (GSVA), spatial localization, Monocle2, and CellPhoneDB, we provided insights into the clinical and cellular implications of TSPs.

Results

First, we observed significant upregulation of THBS2 and COMP in colon cancer, both of which displayed significant prognostic value. Additionally, we detected a significant positive correlation between TSPs and immune cells, as well as marker genes of EMT. Second, based on TSPs expression, patients were divided into two clusters with distinct prognoses: the high TSPs expression group (TSPs-H) was characterized by pronounced immune and stromal cell infiltration, and notably elevated T-cell exhaustion scores. Subsequently, we found that THBS2 and COMP may be associated with the differentiation of CAFs into pan-iCAFs and pan-dCAFs, which are known for their heightened matrix remodeling activities. Moreover, THBS2 enhanced CAFs communication with vascular endothelial cells and monocyte-macrophages. CAFs expressing THBS2 (THBS2+ CAFs) demonstrated higher scores across multiple signaling pathways, including angiogenic, EMT, Hedgehog, Notch, Wnt, and TGF-β, when compared to THBS2- CAFs. These observations suggest that THBS2 may be associated with stronger pro-carcinogenic activity in CAFs.

Conclusions

This study revealed the crucial role of TSPs and the significant correlation between THBS2 and CAFs interactions in colon cancer progression, providing valuable insights for targeting TSPs to mitigate cancer progression.

Microfluidic Fabricated Liposomes for Nutlin-3a Ocular Delivery as Potential Candidate for Proliferative Vitreoretinal Diseases Treatment

Purpose

Proliferative vitreoretinal diseases (PVDs) represent a heterogeneous group of pathologies characterized by the presence of retinal proliferative membranes, in whose development retinal pigment epithelium (RPE) is deeply involved. As the only effective treatment for PVDs at present is surgery, we aimed to investigate the potential therapeutic activity of Nutlin-3a, a small non-genotoxic inhibitor of the MDM2/p53 interaction, on ARPE-19 cell line and on human RPE primary cells, as in vitro models of RPE and, more importantly, to formulate and evaluate Nutlin-3a loaded liposomes designed for ophthalmic administration.

Methods

Liposomes were produced using an innovative approach by a microfluidic device under selection of different conditions. Liposome size distribution was evaluated by photon correlation spectroscopy and centrifugal field flow fractionation, while the liposome structure was studied by transmission electron microscopy and Fourier-transform infrared spectroscopy. The Nutlin-3a entrapment capacity was evaluated by ultrafiltration and HPLC. Nutlin-3a biological effectiveness as a solution or loaded in liposomes was evaluated by viability, proliferation, apoptosis and migration assays and by morphological analysis.

Results

The microfluidic formulative study enabled the selection of liposomes composed of phosphatidylcholine (PC) 5.4 or 8.2 mg/mL and 10% ethanol, characterized by roundish vesicular structures with 150-250 nm mean diameters. Particularly, liposomes based on the lower PC concentration were characterized by higher stability. Nutlin-3a was effectively encapsulated in liposomes and was able to induce a significant reduction of viability and migration in RPE cell models.

Conclusion

Our results lay the basis for a possible use of liposomes for the ocular delivery of Nutlin-3a.

Palmitic Acid Induced a Long-Lasting Lipotoxic Insult in Human Retinal Pigment Epithelial Cells, which Is Partially Counteracted by TRAIL

Hyperglycaemia and increased circulating saturated fatty acids are key metabolic features of type 2 diabetes mellitus (T2DM) that contribute to diabetic retinopathy pathogenesis. Contrarily, tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) has been shown to improve or prevent T2DM. This study aimed at investigating the effect of TRAIL in an in vitro model of human retinal pigment epithelium: the ARPE-19 cell line, treated with palmitic acid (PA) in the presence of high glucose concentration. PA caused a drop in cellular metabolic activity and cell viability as well as an increase in apoptosis rates, which were paralleled by an upregulation of reactive oxygen species (ROS) generation as well as mitochondrial fragmentation. Despite ARPE-19 cells expressing TRAIL-R2 at the cell surface, TRAIL failed to counteract the cytotoxic effects of PA. However, when TRAIL was used alongside PA and then removed or used alone following PA challenge, it partially attenuated PA-induced lipotoxicity. This effect of TRAIL appeared to rely upon the modulation of inflammation and ROS production. Thus, TRAIL exerted a trophic effect on ARPE-19 cells, which became evident only when the lipotoxic insult was removed. Nevertheless, whether recombinant TRAIL might have a therapeutic potential for the treatment of diabetic retinopathy requires further investigation.

Synthesis and Biological Investigation of Bile Acid-Paclitaxel Hybrids

Chenodeoxycholic acid and ursodeoxycholic acid (CDCA and UDCA, respectively) have been conjugated with paclitaxel (PTX) anticancer drugs through a high-yield condensation reaction. Bile acid-PTX hybrids (BA-PTX) have been investigated for their pro-apoptotic activity towards a selection of cancer cell lines as well as healthy fibroblast cells. Chenodeoxycholic-PTX hybrid (CDC-PTX) displayed cytotoxicity and cytoselectivity similar to PTX, whereas ursodeoxycholic-PTX hybrid (UDC-PTX) displayed some anticancer activity only towards HCT116 colon carcinoma cells. Pacific Blue (PB) conjugated derivatives of CDC-PTX and UDC-PTX (CDC-PTX-PB and UDC-PTX-PB, respectively) were also prepared via a multistep synthesis for evaluating their ability to enter tumor cells. CDC-PTX-PB and UDC-PTX-PB flow cytometry clearly showed that both CDCA and UDCA conjugation to PTX improved its incoming into HCT116 cells, allowing the derivatives to enter the cells up to 99.9%, respect to 35% in the case of PTX. Mean fluorescence intensity analysis of cell populations treated with CDC-PTX-PB and UDC-PTX-PB also suggested that CDC-PTX-PB could have a greater ability to pass the plasmatic membrane than UDC-PTX-PB. Both hybrids showed significant lower toxicity with respect to PTX on the NIH-3T3 cell line.

SATB2 and MDM2 Immunoexpression and Diagnostic Role in Primary Osteosarcomas of the Jaw

Primary osteosarcomas of the jaw (OSJ) are rare, accounting for 6% of all osteosarcomas. This study aims to determine the value of SATB2 and MDM2 immunohistochemistry (IHC) in differentiating OSJ from other jawbone mimickers, such as benign fibro-osseous lesions (BFOLs) of the jaw or Ewing sarcoma of the jaw. Certain subsets of osteosarcoma harbor a supernumerary ring and/or giant marker chromosomes with amplification of the 12q13-15 region, including the murine double-minute type 2 (MDM2) and cyclin-dependent kinase 4 (CDK4) genes. Special AT-rich sequence-binding protein 2 (SATB2) is an immunophenotypic marker for osteoblastic differentiation. Cases of OSJ, BFOLs (ossifying fibroma and fibrous dysplasia) of the jaw, and Ewing sarcoma of the jaw were retrieved from the Departments of Oral Pathology and Oral Medicine, Faculty of Dentistry, Obafemi Awolowo University and Lagos State University College of Medicine, Nigeria. All OSJ retrieved showed histologic features of high-grade osteosarcoma. IHC for SATB2 (clone EP281) and MDM2 (clone IF2), as well as fluorescence in situ hybridization (FISH) for MDM2 amplification, were performed on all cases. SATB2 was expressed in a strong intensity and diffuse staining pattern in all cases (11 OSJ, including a small-cell variant, 7 ossifying fibromas, and 5 fibrous dysplasias) except in Ewing sarcoma, where it was negative in neoplastic cells. MDM2 was expressed in a weak to moderate intensity and scattered focal to limited diffuse staining pattern in 27% (3/11) of cases of OSJ and negative in all BFOLs and the Ewing sarcoma. MDM2 amplification was negative by FISH in interpretable cases. In conclusion, the three cases of high-grade OSJs that expressed MDM2 may have undergone transformation from a low-grade osteosarcoma (LGOS). SATB2 is not a dependable diagnostic marker to differentiate OSJ from BFOLs of the jaw; however, it could serve as a valuable diagnostic marker in differentiating the small-cell variant of OSJ from Ewing sarcoma of the jaw, while MDM2 may be a useful diagnostic marker in differentiating OSJ from BFOLs of the jaw, especially in the case of an LGOS or high-grade transformed osteosarcoma.

The Role of the CREB Protein Family Members and the Related Transcription Factors in Radioresistance Mechanisms

In the framework of space flight, the risk of radiation carcinogenesis is considered a "red" risk due to the high likelihood of occurrence as well as the high potential impact on the quality of life in terms of disease-free survival after space missions. The cyclic AMP response element-binding protein (CREB) is overexpressed both in haematological malignancies and solid tumours and its expression and function are modulated following irradiation. The CREB protein is a transcription factor and member of the CREB/activating transcription factor (ATF) family. As such, it has an essential role in a wide range of cell processes, including cell survival, proliferation, and differentiation. Among the CREB-related nuclear transcription factors, NF-κB and p53 have a relevant role in cell response to ionising radiation. Their expression and function can decide the fate of the cell by choosing between death or survival. The aim of this review was to define the role of the CREB/ATF family members and the related transcription factors in the response to ionising radiation of human haematological malignancies and solid tumours.

Overcoming of Microenvironment Protection on Primary Chronic Lymphocytic Leukemia Cells after Treatment with BTK and MDM2 Pharmacological Inhibitors

In B-chronic lymphocytic leukemia (B-CLL), the interaction between leukemic cells and the microenvironment promotes tumor cell survival. The Bruton’s tyrosine kinase (BTK) inhibitor ibrutinib is one of the first-in-class molecules for the treatment of B-CLL patients; however, the emerging mechanisms of resistance to ibrutinib call for new therapeutic strategies. The purpose of the current study was to investigate the ability of ibrutinib plus the MDM2-inhibitor nutlin-3 to counteract the tumor microenvironment protective effect. We observed that primary B-CLL cells cultivated in microenvironment mimicking conditions were protected from apoptosis by the up-regulation of c-MYC and of p53. In the same setting, combined treatments with ibrutinib plus nutlin-3 led to significantly higher levels of apoptosis compared to the single treatments, counteracting the c-MYC up-regulation. Moreover, the combination induced high p53 levels and a significant dissipation of the mitochondrial membrane potential, together with BAX cleavage in the more active p18 form and phospho-BAD down-regulation, that are key components of the mitochondrial apoptotic pathway, enhancing the apoptosis level. Our findings propose a new therapeutic strategy to overcome the tumor microenvironment protection involved in B-CLL resistance to drugs, with possible clinical implications also for other hematologic and solid tumors for which ibrutinib is considered a therapeutic option.

Helping the Released Guardian: Drug Combinations for Supporting the Anticancer Activity of HDM2 (MDM2) Antagonists

The protein p53, known as the "Guardian of the Genome", plays an important role in maintaining DNA integrity, providing protection against cancer-promoting mutations. Dysfunction of p53 is observed in almost every cancer, with 50% of cases bearing loss-of-function mutations/deletions in the TP53 gene. In the remaining 50% of cases the overexpression of HDM2 (mouse double minute 2, human homolog) protein, which is a natural inhibitor of p53, is the most common way of keeping p53 inactive. Disruption of HDM2-p53 interaction with the use of HDM2 antagonists leads to the release of p53 and expression of its target genes, engaged in the induction of cell cycle arrest, DNA repair, senescence, and apoptosis. The induction of apoptosis, however, is restricted to only a handful of p53wt cells, and, generally, cancer cells treated with HDM2 antagonists are not efficiently eliminated. For this reason, HDM2 antagonists were tested in combinations with multiple other therapeutics in a search for synergy that would enhance the cancer eradication. This manuscript aims at reviewing the recent progress in developing strategies of combined cancer treatment with the use of HDM2 antagonists.

YB-1 modulates the drug resistance of glioma cells by activation of MDM2/p53 pathway

Background

Y-box-binding protein-1 (YB-1) is aberrantly expressed in a variety of cancers. However, the biological functional role of YB-1 in glioma is not yet clear.

Methods

The expression of MDM2 and YB-1 was analyzed by real time PCR. Overexpression and knockdown of YB-1 in glioma cells were created by transfection of pcDNA-YB-1 and siRNA against YB-1, respectively. Cell viability was performed by CCK8 assay.

Results

Our findings showed that glioma tissues had higher expressions of YB-1 than that in cancer-free tissues in 54 glioma patients, which were also positively correlated with Murine MDM2 expression. Overexpression of YB-1 or MDM2 renders a drug resistance feature in glioma cell exposed to temozolomide (TMZ), by directly targeting p53. Genetic or chemical inhibition of MDM2 significantly blocked YB-1-modulated response of glioma cells to TMZ. Moreover, inhibition of YB-1 or MDM2 reduced glioma cells metastasis and mortality in mice.

Conclusion

YB-1 facilitates the resistance of glioma cells to TMZ by direct activation of MDM2/p53 signaling and represents a promising molecular target for glioma treatment.

Ibrutinib synergizes with MDM-2 inhibitors in promoting cytotoxicity in B chronic lymphocytic leukemia

OBJECTIVE

The aim of this study was to investigate the anti-leukemic activity of the Bruton tyrosine kinase inhibitor Ibrutinib in combination with the small molecule MDM-2 inhibitor Nutlin-3 in preclinical models.

METHODS

The potential efficacy of the Ibrutinib/Nutlin-3 combination was evaluated in vitro in a panel of B leukemic cell lines (EHEB, JVM-2, JVM-3, MEC-1, MEC-2) and in primary B-chronic lymphocytic leukemia (B-CLL) patient samples, by assessing cell viability, cell cycle profile, apoptosis and intracellular pathway modulations. Validation of the combination therapy was assessed in a B leukemic xenograft mouse model.

RESULTS

Ibrutinib exhibited variable anti-leukemic activity in vitro and the combination with Nutlin-3 synergistically enhanced the induction of apoptosis independently from the p53 status. Indeed, the Ibrutinib/Nutlin-3 combination was effective in promoting cytotoxicity also in primary B-CLL samples carrying 17p13 deletion and/or TP53 mutations, already in therapy with Ibrutinib. Molecular analyses performed on both B-leukemic cell lines as well as on primary B-CLL samples, while confirming the switch-off of the MAPK and PI3K pro-survival pathways by Ibrutinib, indicated that the synergism of action with Nutlin-3 was independent by p53 pathway and was accompanied by the activation of the DNA damage cascade signaling through the phosphorylation of the histone protein H2A.X. This observation was confirmed also in the JVM-2 B leukemic xenograft mouse model.

CONCLUSIONS

Taken together, our data emphasize that the Ibrutinib/Nutlin-3 combination merits to be further evaluated as a therapeutic option for B-CLL.

Oridonin synergizes with Nutlin-3 in osteosarcoma cells by modulating the levels of multiple Bcl-2 family proteins

The small-molecule inhibitors of p53-murine double minute 2 interaction, such as Nutlin-3, are effective against cancers bearing wild-type p53. However, murine double minute 2 inhibitors often are unable to completely eliminate solid tumor cells. To address this issue, we investigated the anticancer effects of Nutlin-3 in combination with Oridonin in osteosarcoma cells. We found that Oridonin at sub-toxic concentrations synergistically enhanced Nutlin-3-mediated cell viability inhibition in wild-type p53 U2OS and SJSA-1, but not in p53-mutant MNNG/HOS and in null-p53 Saos-2 osteosarcoma cell lines. Importantly, in the presence of Oridonin, Nutlin-3 could completely abolish cell viability in the wild-type p53 osteosarcoma cell lines. Western blotting analysis showed that Oridonin treatment rapidly and distinctly increased the levels of all three forms of Bim and also markedly reduced the levels of Bcl-2 and Bcl-xl in osteosarcoma cells. Western blotting analysis further showed that Oridonin considerably enhanced Nutlin-3-triggered activation of caspases-9 and -3 and poly(ADP-ribose) polymerase cleavage. Flow cytometry assay showed that Oridonin significantly enhanced Nutlin-3-mediated apoptosis in wild-type p53 osteosarcoma cells. Overall, our results suggest that the combined treatment of Nutlin-3 plus Oridonin may offer a novel therapeutic strategy for osteosarcoma.

MDM2/X inhibitors under clinical evaluation: perspectives for the management of hematological malignancies and pediatric cancer

The two murine double minute (MDM) family members MDM2 and MDMX are at the center of an intense clinical assessment as molecular target for the management of cancer. Indeed, the two proteins act as regulators of P53, a well-known key controller of the cell cycle regulation and cell proliferation that, when altered, plays a direct role on cancer development and progression. Several evidence demonstrated that functional aberrations of P53 in tumors are in most cases the consequence of alterations on the MDM2 and MDMX regulatory proteins, in particular in patients with hematological malignancies where TP53 shows a relatively low frequency of mutation while MDM2 and MDMX are frequently found amplified/overexpressed. The pharmacological targeting of these two P53-regulators in order to restore or increase P53 expression and activity represents therefore a strategy for cancer therapy. From the discovery of the Nutlins in 2004, several compounds have been developed and reported with the ability of targeting the P53-MDM2/X axis by inhibiting MDM2 and/or MDMX. From natural compounds up to small molecules and stapled peptides, these MDM2/X pharmacological inhibitors have been extensively studied, revealing different biological features and different rate of efficacy when tested in in vitro and in vivo experimental tumor models. The data/evidence coming from the preclinical experimentation have allowed the identification of the most promising molecules and the setting of clinical studies for their evaluation as monotherapy or in therapeutic combination with conventional chemotherapy or with innovative therapeutic protocols in different tumor settings. Preliminary results have been recently published reporting data about safety, tolerability, potential side effects, and efficacy of such therapeutic approaches. In this light, the aim of this review is to give an updated overview about the state of the art of the clinical evaluation of MDM2/X inhibitor compounds with a special attention to hematological malignancies and to the potential for the management of pediatric cancers.

Metformin combined with sodium dichloroacetate promotes B leukemic cell death by suppressing anti-apoptotic protein Mcl-1

Metformin and the mitochondrial targeting dichloroacetate (DCA) have recently received attention due to their ability to inhibit anaerobic glycolysis, which renders most cancer cells resistant to apoptosis induction. We observed that Metformin alone exhibited a dose-dependent anti-leukemic activity in both B leukemic cell lines and primary B-chronic lymphocytic leukemia (B-CLL) patients' cells and its anti-leukemic activity was enhanced when used in combination with DCA. In order to overcome the problems of poor bioavailability and cellular uptake, which limit DCA efficacy, we have designed and synthetized cocrystals consisting of Metformin and DCA (Met-DCA) at different stoichiometric ratios. Of note, the MetH(2)(++)•2DCA(-) cocrystal exhibited enhanced in vitro anti-leukemic activity, with respect to the treatment with the mix consisting of Metformin plus DCA. In particular, the treatment with the cocrystal MetH(2)(++)•2DCA(-) induced a synergistic apoptotic cell death coupled to a marked down-modulation of the anti-apoptotic Mcl-1 protein. Taken together, our data emphasize that innovative compounds based on Metformin-DCA combination merit to be further evaluated as chemotherapeutic agents for the treatment of B-CLL.

The anti-leukemic activity of sodium dichloroacetate in p53mutated/null cells is mediated by a p53-independent ILF3/p21 pathway

B-chronic lymphocytic leukemia (B-CLL) patients harboring p53 mutations are invariably refractory to therapies based on purine analogues and have limited treatment options and poor survival. Having recently demonstrated that the mitochondria-targeting small molecule sodium dichloroacetate (DCA) exhibits anti-leukemic activity in p53^wild-type B-CLL cells, the aim of this study was to evaluate the effect of DCA in p53^mutated B-CLL cells and in p53^mutated/null leukemic cell lines. DCA exhibited comparable cytotoxicity in p53^wild-type and p53^mutated B-CLL patient cell cultures, as well as in p53^mutated B leukemic cell lines (MAVER, MEC-1, MEC-2). At the molecular level, DCA promoted the transcriptional induction of p21 in all leukemic cell types investigated, including p53^null HL-60. By using a proteomic approach, we demonstrated that DCA up-regulated the ILF3 transcription factor, which is a known regulator of p21 expression. The role of the ILF3/p21 axis in mediating the DCA anti-leukemic activity was underscored by knocking-down experiments. Indeed, transfection with ILF3 and p21 siRNAs significantly decreased both the DCA-induced p21 expression and the DCA-mediated cytotoxicity. Taken together, our results emphasize that DCA is a small molecule that merits further evaluation as a therapeutic agent also for p53^mutated leukemic cells, by acting through the induction of a p53-independent pathway.

Dasatinib-related Follicular Hyperplasia: An Underrecognized Entity With Characteristic Morphology

Dasatinib, a second-generation tyrosine kinase inhibitor with activity against BCR-ABL1 and other Src family tyrosine kinases, is approved as a first-line treatment option for Philadelphia chromosome-positive chronic myelogenous leukemia (CML) in the chronic phase. Recently, lymphadenopathy with morphologic features of reactive follicular hyperplasia was described in a cohort of patients with CML on long-term dasatinib therapy. However, the complete morphologic and immunophenotypic features of this previously underappreciated adverse effect have not been fully described. Herein, we report 3 cases of unexplained lymphadenopathy resulting in multiple diagnostic procedures in patients with CML and a history of long-term dasatinib therapy. Morphologic examination demonstrated preserved nodal architecture showing hybrid features of progressive transformation of germinal centers and Castleman-type changes in a background of florid follicular hyperplasia. Large germinal centers were disrupted by complex infolding of IgD+ mantle zones arranged as cuffs surrounding perforating capillaries. Other abnormalities variably present included decreased CD20 expression among polytypic B cells and increased Epstein-Barr virus reactivity in scattered paracortical cells and/or individual germinal centers. B-cell clonality studies showed no predominant clonal rearrangements. Consideration of dasatinib-related lymphadenopathy may pre-empt unnecessary repeat diagnostic procedures in patients with CML or other dasatinib-susceptible malignancies and persistent lymphadenopathy.

The p53 transcriptional pathway is preserved in ATMmutated and NOTCH1mutated chronic lymphocytic leukemias

By using next generation sequencing, we have analyzed 108 B chronic lymphocytic leukemia (B-CLL) patients. Among genes involved in the TP53 pathway, we found frequent mutations in ATM (n=18), TP53 (n=10) and NOTCH1 (n=10) genes, rare mutations of NOTCH2 (n=2) and CDKN1A/p21 (n=1) and no mutations in BAX, MDM2, TNFRSF10A and TNFRSF10B genes. The in vitro treatment of primary B-CLL cells with the activator of p53 Nutlin-3 induced the transcription of p53 target genes, without significant differences between the B-CLL without mutations and those harboring either ATM or NOTCH1 mutations. On the other hand, the subgroup of TP53^mutated B-CLL exhibited a significantly lower induction of the p53 target genes in response to Nutlin-3 as compared to the other B-CLL samples. However, among the TP53^mutated B-CLL, those showing mutations in the high hot spot region of the DNA binding domain [273-280 aa] maintained a significantly higher p53-dependent transcriptional activity as compared to the other TP53^mutated B-CLL samples. Since the ability to elicit a p53-dependent transcriptional activity in vitro has a positive prognostic significance, our data suggest that ATM^mutated, NOTCH1^mutated and surprisingly, also a subset of TP53^mutated B-CLL patients might benefit from therapeutic combinations including small molecule activator of the p53 pathway.

Sodium dichloroacetate exhibits anti-leukemic activity in B-chronic lymphocytic leukemia (B-CLL) and synergizes with the p53 activator Nutlin-3

The anti-leukemic activity of the mitochondria-targeting small molecule sodium dichloroacetate (DCA), used alone and in association with the small molecule inhibitor of the p53/MDM2 interaction Nutlin-3, was analyzed in primary B-chronic lymphocytic leukemia (B-CLL) samples (n=22), normal peripheral blood cells (n=10) and in p53wild-type EHEB, JVM-2, JVM-3 B lymphoblastoid cell lines. DCA exhibited a dose-dependent anti-leukemic activity in both primary B-CLL and B leukemic cell lines with a functional p53 status and showed a synergistic cytotoxic activity when used in combination with Nutlin-3. At the molecular level, DCA positively regulated p53 activity, as documented by post-transcriptional modifications of p53 protein and synergized with Nutlin-3 in increasing the expression of the p53-target genes MDM2, PUMA, TIGAR and in particular p21. The potential role of p21 in mediating the DCA+Nutlin-3 anti-leukemic activity was underscored in knocking-down experiments. Indeed, transfection of leukemic cells with p21 siRNAs significantly decreased the DCA+Nutlin-3-induced cytotoxicity. Taken together, our data emphasize that DCA is a molecule that merits to be further evaluated as a chemotherapeutic agent for B-CLL, likely in combination with other therapeutic compounds.

MDM2 antagonists synergize broadly and robustly with compounds targeting fundamental oncogenic signaling pathways

While MDM2 inhibitors hold great promise as cancer therapeutics, drug resistance will likely limit their efficacy as single agents. To identify drug combinations that might circumvent resistance, we screened for agents that could synergize with MDM2 inhibition in the suppression of cell viability. We observed broad and robust synergy when combining MDM2 antagonists with either MEK or PI3K inhibitors. Synergy was not limited to cell lines harboring MAPK or PI3K pathway mutations, nor did it depend on which node of the PI3K axis was targeted. MDM2 inhibitors also synergized strongly with BH3 mimetics, BCR-ABL antagonists, and HDAC inhibitors. MDM2 inhibitor-mediated synergy with agents targeting these mechanisms was much more prevalent than previously appreciated, implying that clinical translation of these combinations could have far-reaching implications for public health. These findings highlight the importance of combinatorial drug targeting and provide a framework for the rational design of MDM2 inhibitor clinical trials.

Intranasal administration of recombinant TRAIL down-regulates CXCL-1/KC in an ovalbumin-induced airway inflammation murine model

Ovalbumin (OVA)-sensitized BALB/c mice were i.n. instilled with recombinant TNF-related apoptosis inducing ligand (TRAIL) 24 hours before OVA challenge. The total number of leukocytes and the levels of the chemokine CXCL-1/KC significantly increased in the bronchoalveolar lavage (BAL) fluids of allergic animals with respect to control littermates, but not in the BAL of mice i.n. pretreated with recombinant TRAIL before OVA challenge. In particular, TRAIL pretreatment significantly reduced the BAL percentage of both eosinophils and neutrophils. On the other hand, when TRAIL was administrated simultaneously to OVA challenge its effect on BAL infiltration was attenuated. Overall, the results show that the i.n. pretreatment with TRAIL down-modulated allergic airway inflammation.

p53 Family and Cellular Stress Responses in Cancer

p53 is an important tumor suppressor gene, which is stimulated by cellular stress like ionizing radiation, hypoxia, carcinogens, and oxidative stress. Upon activation, p53 leads to cell-cycle arrest and promotes DNA repair or induces apoptosis via several pathways. p63 and p73 are structural homologs of p53 that can act similarly to the protein and also hold functions distinct from p53. Today more than 40 different isoforms of the p53 family members are known. They result from transcription via different promoters and alternative splicing. Some isoforms have carcinogenic properties and mediate resistance to chemotherapy. Therefore, expression patterns of the p53 family genes can offer prognostic information in several malignant tumors. Furthermore, the p53 family constitutes a potential target for cancer therapy. Small molecules (e.g., Nutlins, RITA, PRIMA-1, and MIRA-1 among others) have been objects of intense research interest in recent years. They restore pro-apoptotic wild-type p53 function and were shown to break chemotherapeutic resistance. Due to p53 family interactions small molecules also influence p63 and p73 activity. Thus, the members of the p53 family are key players in the cellular stress response in cancer and are expected to grow in importance as therapeutic targets.

The MEC1 and MEC2 lines represent two CLL subclones in different stages of progression towards prolymphocytic leukemia

The EBV carrying lines MEC1 and MEC2 were established earlier from explants of blood derived cells of a chronic lymphocytic leukemia (CLL) patient at different stages of progression to prolymphocytoid transformation (PLL). This pair of lines is unique in several respects. Their common clonal origin was proven by the rearrangement of the immunoglobulin genes. The cells were driven to proliferation in vitro by the same indigenous EBV strain. They are phenotypically different and represent subsequent subclones emerging in the CLL population. Furthermore they reflect the clinical progression of the disease. We emphasize that the support for the expression of the EBV encoded growth program is an important differentiation marker of the CLL cells of origin that was shared by the two subclones. It can be surmised that proliferation of EBV carrying cells in vitro, but not in vivo, reflects the efficient surveillance that functions even in the severe leukemic condition. The MEC1 line arose before the aggressive clinical stage from an EBV carrying cell within the subclone that was in the early prolymphocytic transformation stage while the MEC2 line originated one year later, from the subsequent subclone with overt PLL characteristics. At this time the disease was disseminated and the blood lymphocyte count was considerably elevated. The EBV induced proliferation of the MEC cells belonging to the subclones with markers of PLL agrees with earlier reports in which cells of PLL disease were infected in vitro and immortalized to LCL. They prove also that the expression of EBV encoded set of proteins can be determined at the event of infection. This pair of lines is particularly important as they provide in vitro cells that represent the subclonal evolution of the CLL disease. Furthermore, the phenotype of the MEC1 cells shares several characteristics of ex vivo CLL cells.

Mitochondrial dysregulation and protection in cisplatin nephrotoxicity

Nephrotoxicity is a major side effect of cisplatin in chemotherapy. Pathologically, cisplatin nephrotoxicity is characterized by cell injury and death in renal tubules. The research in the past decade has gained significant understanding of the cellular and molecular mechanisms of tubular cell death, revealing a central role of mitochondrial dysregulation. The pathological changes in mitochondria in cisplatin nephrotoxicity are mainly triggered by DNA damage response, pro-apoptotic protein attack, disruption of mitochondrial dynamics, and oxidative stress. As such, inhibitory strategies targeting these cytotoxic events may provide renal protection. Nonetheless, ideal approaches for renoprotection should not only protect kidneys but also enhance the anticancer efficacy of cisplatin in chemotherapy.

Nutlin-3 overcomes arsenic trioxide resistance and tumor metastasis mediated by mutant p53 in Hepatocellular Carcinoma

Background

Arsenic trioxide has been demonstrated as an effective anti-cancer drug against leukemia and solid tumors both in vitro and in vivo. However, recent phase II trials demonstrated that single agent arsenic trioxide was poorly effective against hepatocellular carcinoma (HCC), which might be due to drug resistance.

Methods

Mutation detection of p53 gene in arsenic trioxide resistant HCC cell lines was performed. The therapeutic effects of arsenic trioxide and Nutlin-3 on HCC were evaluated both in vitro and in vivo. A series of experiments including MTT, apoptosis assays, co-Immunoprecipitation, siRNA transfection, lentiviral infection, cell migration, invasion, and epithelial-mesenchy-mal transition (EMT) assays were performed to investigate the underlying mechanisms.

Results

The acquisition of p53 mutation contributed to arsenic trioxide resistance and enhanced metastatic potential of HCC cells. Mutant p53 (Mutp53) silence could re-sensitize HCC resistant cells to arsenic trioxide and inhibit the metastatic activities, while mutp53 overexpression showed the opposite effects. Neither arsenic trioxide nor Nutlin-3 could exhibit obvious effects against arsenic trioxide resistant HCC cells, while combination of them showed significant effects. Nutlin-3 can not only increase the intracellular arsenicals through inhibition of p-gp but also promote the p73 activation and mutp53 degradation mediated by arsenic trioxide. In vivo experiments indicated that Nutlin-3 can potentiate the antitumor activities of arsenic trioxide in an orthotopic hepatic tumor model and inhibit the metastasis to lung.

Conclusions

Acquisitions of p53 mutations contributed to the resistance of HCC to arsenic trioxide. Nutlin-3 could overcome arsenic trioxide resistance and inhibit tumor metastasis through p73 activation and promoting mutant p53 degradation mediated by arsenic trioxide.

Drugging the p53 pathway: understanding the route to clinical efficacy

The tumour suppressor p53 is the most frequently mutated gene in human cancer, with more than half of all human tumours carrying mutations in this particular gene. Intense efforts to develop drugs that could activate or restore the p53 pathway have now reached clinical trials. The first clinical results with inhibitors of MDM2, a negative regulator of p53, have shown efficacy but hint at on-target toxicities. Here, we describe the current state of the development of p53 pathway modulators and new pathway targets that have emerged. The challenge of targeting protein-protein interactions and a fragile mutant transcription factor has stimulated many exciting new approaches to drug discovery.

In vitro endothelial cell proliferation assay reveals distinct levels of proangiogenic cytokines characterizing sera of healthy subjects and of patients with heart failure

Although myocardial angiogenesis is thought to play an important role in heart failure (HF), the involvement of circulating proinflammatory and proangiogenic cytokines in the pathogenesis and/or prognosis of HF has not been deeply investigated. By using a highly standardized proliferation assay with human endothelial cells, we first demonstrated that sera from older (mean age 52 ± 7.6 years; n = 46) healthy donors promoted endothelial cell proliferation to a significantly higher extent compared to sera obtained from younger healthy donors (mean age 29 ± 8.6 years; n = 20). The promotion of endothelial cell proliferation was accompanied by high serum levels of several proangiogenic cytokines. When we assessed endothelial cell proliferation in response to HF patients' sera, we observed that a subset of sera (n = 11) promoted cell proliferation to a significantly lesser extent compared to the majority of sera (n = 18). Also, in this case, the difference between the patient groups in the ability to induce endothelial cell proliferation correlated to significant (P < 0.05) differences in serum proangiogenic cytokine levels. Unexpectedly, HF patients associated to the highest endothelial proliferation index showed the worst prognosis as evaluated in terms of subsequent cardiovascular events in the follow-up, suggesting that high levels of circulating proangiogenic cytokines might be related to a worse prognosis.

Targeting p53-MDM2-MDMX loop for cancer therapy

The tumor suppressor p53 plays a central role in anti-tumorigenesis and cancer therapy. It has been described as "the guardian of the genome", because it is essential for conserving genomic stability by preventing mutation, and its mutation and inactivation are highly related to all human cancers. Two important p53 regulators, MDM2 and MDMX, inactivate p53 by directly inhibiting its transcriptional activity and mediating its ubiquitination in a feedback fashion, as their genes are also the transcriptional targets of p53. On account of the importance of the p53-MDM2-MDMX loop in the initiation and development of wild type p53-containing tumors, intensive studies over the past decade have been aiming to identify small molecules or peptides that could specifically target individual protein molecules of this pathway for developing better anti-cancer therapeutics. In this chapter, we review the approaches for screening and discovering efficient and selective MDM2 inhibitors with emphasis on the most advanced synthetic small molecules that interfere with the p53-MDM2 interaction and are currently on Phase I clinical trials. Other therapeutically useful strategies targeting this loop, which potentially improve the prospects of cancer therapy and prevention, will also be discussed briefly.

Dasatinib in combination with fludarabine in patients with refractory chronic lymphocytic leukemia: a multicenter phase 2 study

Resistance to chemotherapy-induced apoptosis in CLL is associated with overexpression of antiapoptotic proteins induced by signals from the microenvironment. In vitro, dasatinib effectively inhibits expression of anti-apoptotic regulators and restores fludarabine sensitivity in activated CLL. The aim of this study was to evaluate efficacy of one cycle of dasatinib monotherapy (100mg/day, days 1-28) followed by combination of dasatinib with fludarabine (40mg/m²/day, days 1-3 every 28 day) for a total of 6 cycles in fludarabine-refractory CLL. The primary endpoint was overall response rate according to the IWCLL'08 criteria. 20 patients were enrolled: 18 completed at least one cycle of treatment of which 67% finished at least 2 cycles of combination treatment. 3 of these 18 patients reached a formal PR (16.7%). Majority of patients obtained some reduction in lymph node (LN) size. Most frequent toxicity was related to myelosuppression. NF-κB RNA expression levels of circulating CLL cells decreased whereas the levels of pro-apoptotic NOXA increased during treatment. In conclusion, dasatinib/fludarabine combination has modest clinical efficacy in fludarabine-refractory patients.

New potential therapeutic approach for the treatment of B-Cell malignancies using chlorambucil/hydroxychloroquine-loaded anti-CD20 nanoparticles

Current B-cell disorder treatments take advantage of dose-intensive chemotherapy regimens and immunotherapy via use of monoclonal antibodies. Unfortunately, they may lead to insufficient tumor distribution of therapeutic agents, and often cause adverse effects on patients. In this contribution, we propose a novel therapeutic approach in which relatively high doses of Hydroxychloroquine and Chlorambucil were loaded into biodegradable nanoparticles coated with an anti-CD20 antibody. We demonstrate their ability to effectively target and internalize in tumor B-cells. Moreover, these nanoparticles were able to kill not only p53 mutated/deleted lymphoma cell lines expressing a low amount of CD20, but also circulating primary cells purified from chronic lymphocitic leukemia patients. Their safety was demonstrated in healthy mice, and their therapeutic effects in a new model of Burkitt's lymphoma. The latter serves as a prototype of an aggressive lympho-proliferative disease. In vitro and in vivo data showed the ability of anti-CD20 nanoparticles loaded with Hydroxychloroquine and Chlorambucil to increase tumor cell killing in comparison to free cytotoxic agents or Rituximab. These results shed light on the potential of anti-CD20 nanoparticles carrying Hydroxychloroquine and Chlorambucil for controlling a disseminated model of aggressive lymphoma, and lend credence to the idea of adopting this therapeutic approach for the treatment of B-cell disorders.

Proper design of silica nanoparticles combines high brightness, lack of cytotoxicity and efficient cell endocytosis

Silica-based luminescent nanoparticles (SiNPs) show promising prospects in nanomedicine in light of their chemical properties and versatility. In this study, we have characterized silica core-PEG shell SiNPs derivatized with PEG moieties (NP-PEG), with external amino- (NP-PEG-amino) or carboxy-groups (NP-PEG-carbo), both in cell cultures as well as in animal models. By using different techniques, we could demonstrate that these SiNPs were safe and did not exhibit appreciable cytotoxicity in different relevant cell models, of normal or cancer cell types, growing either in suspension (JVM-2 leukemic cell line and primary normal peripheral blood mononuclear cells) or in adherence (human hepatocarcinoma Huh7 and umbilical vein endothelial cells). Moreover, by multiparametric flow cytometry, we could demonstrate that the highest efficiency of cell uptake and entry was observed with NP-PEG-amino, with a stable persistence of the fluorescence signal associated with SiNPs in the loaded cell populations both in vitro and in vivo settings suggesting this as an innovative method for cell traceability and detection in whole organisms. Finally, experiments performed with the endocytosis inhibitor Genistein clearly suggested the involvement of a caveolae-mediated pathway in SiNP endocytosis. Overall, these data support the safe use of these SiNPs for diagnostic and therapeutic applications.

Src kinases in chondrosarcoma chemoresistance and migration: dasatinib sensitises to doxorubicin in TP53 mutant cells

BACKGROUND

Chondrosarcomas are malignant cartilage-forming tumours of bone. Because of their resistance to conventional chemotherapy and radiotherapy, currently no treatment strategies exist for unresectable and metastatic chondrosarcoma. Previously, PI3K/AKT/GSK3β and Src kinase pathways were shown to be activated in chondrosarcoma cell lines. Our aim was to investigate the role of these kinases in chemoresistance and migration in chondrosarcoma in relation to TP53 mutation status.

METHODS

We used five conventional and three dedifferentiated chondrosarcoma cell lines and investigated the effect of PI3K/AKT/GSK3β pathway inhibition (enzastaurin) and Src pathway inhibition (dasatinib) in chemoresistance using WST assay and live cell imaging with AnnexinV staining. Immunohistochemistry on tissue microarrays (TMAs) containing 157 cartilaginous tumours was performed for Src family members. Migration assays were performed with the RTCA xCelligence System.

RESULTS

Src inhibition was found to overcome chemoresistance, to induce apoptosis and to inhibit migration. Cell lines with TP53 mutations responded better to combination therapy than wild-type cell lines (P=0.002). Tissue microarray immunohistochemistry confirmed active Src (pSrc) signalling, with Fyn being most abundantly expressed (76.1%).

CONCLUSION

These results strongly indicate Src family kinases, in particular Fyn, as a potential target for the treatment of inoperable and metastatic chondrosarcomas, and to sensitise for doxorubicin especially in the presence of TP53 mutations.

Targeting p53 by small molecules in hematological malignancies

p53 is a powerful tumor suppressor and is an attractive cancer therapeutic target. A breakthrough in cancer research came from the discovery of the drugs which are capable of reactivating p53 function. Most anti-cancer agents, from traditional chemo- and radiation therapies to more recently developed non-peptide small molecules exert their effects by enhancing the anti-proliferative activities of p53. Small molecules such as nutlin, RITA, and PRIMA-1 that can activate p53 have shown their anti-tumor effects in different types of hematological malignancies. Importantly, nutlin and PRIMA-1 have successfully reached the stage of phase I/II clinical trials in at least one type of hematological cancer. Thus, the pharmacological activation of p53 by these small molecules has a major clinical impact on prognostic use and targeted drug design. In the current review, we present the recent achievements in p53 research using small molecules in hematological malignancies. Anticancer activity of different classes of compounds targeting the p53 signaling pathway and their mechanism of action are discussed. In addition, we discuss how p53 tumor suppressor protein holds promise as a drug target for recent and future novel therapies in these diseases.

Targeting the LYN/HS1 signaling axis in chronic lymphocytic leukemia

HS1 protein activation is differentially regulated by LYN kinase in CLL subsets. Dasatinib targets cytoskeletal activity, BCR signaling and survival of a sizable portion of patients with activated LYN/HS1.

Role of ubiquitin ligases and the proteasome in oncogenesis: novel targets for anticancer therapies

The ubiquitin proteasome system (UPS) regulates the ubiquitination, and thus degradation and turnover, of many proteins vital to cellular regulation and function. The UPS comprises a sequential series of enzymatic processes using four key enzyme families: E1 (ubiquitin-activating enzymes), E2 (ubiquitin-carrier proteins), E3 (ubiquitin-protein ligases), and E4 (ubiquitin chain assembly factors). Because the UPS is a crucial regulator of the cell cycle, and abnormal cell-cycle control can lead to oncogenesis, aberrancies within the UPS pathway can result in a malignant cellular phenotype and thus has become an attractive target for novel anticancer agents. This article will provide an overall review of the mechanics of the UPS, describe aberrancies leading to cancer, and give an overview of current drug therapies selectively targeting the UPS.

Integrin α5β1 plays a critical role in resistance to temozolomide by interfering with the p53 pathway in high-grade glioma

Integrins play a role in the resistance of advanced cancers to radiotherapy and chemotherapy. In this study, we show that high expression of the α5 integrin subunit compromises temozolomide-induced tumor suppressor p53 activity in human glioblastoma cells. We found that depletion of the α5 integrin subunit increased p53 activity and temozolomide sensitivity. However, when cells were treated with the p53 activator nutlin-3a, the protective effect of α5 integrin on p53 activation and cell survival was lost. In a functional p53 background, nutlin-3a downregulated the α5 integrin subunit, thereby increasing the cytotoxic effect of temozolomide. Clinically, α5β1 integrin expression was associated with a more aggressive phenotype in brain tumors, and high α5 integrin gene expression was associated with decreased survival of patients with high-grade glioma. Taken together, our findings indicate that negative cross-talk between α5β1 integrin and p53 supports glioma resistance to temozolomide, providing preclinical proof-of-concept that α5β1 integrin represents a therapeutic target for high-grade brain tumors. Direct activation of p53 may remain a therapeutic option in the subset of patients with high-grade gliomas that express both functional p53 and a high level of α5β1 integrin.

Dasatinib synergizes with both cytotoxic and signal transduction inhibitors in heterogeneous breast cancer cell lines--lessons for design of combination targeted therapy

Molecularly targeted therapies have emerged as the leading theme in cancer therapeutics. Multi-cytotoxic drug regimens have been highly successful, yet many studies in targeted therapeutics have centered on a single agent. We investigated whether the Src/Abl kinase inhibitor dasatinib displays synergy with other agents in molecularly heterogeneous breast cancer cell lines. MCF-7, SKBR-3, and MDA-MB-231 display different signaling and gene signatures profiles due to expression of the estrogen receptor, ErbB2, or neither. Cell proliferation was measured following treatment with dasatinib±cytotoxic (paclitaxel, ixabepilone) or molecularly targeted agents (tamoxifen, rapamycin, sorafenib, pan PI3K inhibitor LY294002, and MEK/ERK inhibitor U0126). Dose-responses for single or combination drugs were calculated and analyzed by the Chou-Talalay method. The drugs with the greatest level of synergy with dasatinib were rapamycin, ixabepilone, and sorafenib, for the MDA-MB-231, MCF-7, and SK-BR-3 cell lines respectively. However, dasatinib synergized with both cytotoxic and molecularly targeted agents in all three molecularly heterogeneous breast cancer cell lines. These results suggest that effectiveness of rationally designed therapies may not entirely rest on precise identification of gene signatures or molecular profiling. Since a systems analysis that reveals emergent properties cannot be easily performed for each cancer case, multi-drug regimens in the near future will still involve empirical design.

The coexistence of chronic lymphocytic leukemia and myeloproliperative neoplasms: a retrospective multicentric GIMEMA experience

Although the coexistence of chronic lymphocytic leukemia (CLL) and myeloproliferative neoplasms (MPN) has been sporadically reported in the literature, no systematic studies on this disease association are available. We retrospectively analyzed 46 patients affected by CLL/MPN referred by 15 Italian GIMEMA centers. The aim of this retrospective multicenter study was to define the following: clinico-biological characteristics, possible familiarity, clinical course of both diseases, and influence of MPN chemotherapy on the course of CLL. Among 46 patients, 30 patients were males, 16 patients were females; median age was 71 years. Only one case had familiar CLL. Myeloproliferative disorders consisted of essential thrombocytemia in 18 cases, polycythemia vera in 10 cases, chronic myeloid leukemia in 9 cases, primary myelofibrosis in 6 cases, and MPN/myelodysplastic syndrome in 3 cases. The lymphoproliferative disorder was diagnosed as monoclonal B-cell lymphocytosis in 8 patients and as Binet Stage A CLL in 38 patients. After a median follow-up of 49 months, 9 patients experienced progressive CLL and only 6 patients required treatment after a median of 57.5 months. The biological profile confirmed a subset of low-risk CLL. Twenty patients received chemotherapy for MPN without influence on the course of CLL: lymphocyte counts remained unchanged after 3, 6, and 12 months of treatment. This series is the largest so far reported in literature. The diagnosis of concomitant CLL/MPN is a rare event and lymphoproliferative disorders present a clinical indolent course with a low-risk biological profile. MPN therapy does not interfere with the prognosis of patients with CLL.

Treatment of chronic lymphocytic leukemia requires targeting of the protective lymph node environment with novel therapeutic approaches

Chronic lymphocytic leukemia (CLL) remains associated with low complete response rates and high relapse rates. This is in part due to poor understanding of CLL biology and thus inadequate targeting of therapy. For years CLL has been proposed as bi-compartmental: the quiescent tumor in the periphery and the proliferating cells within specific microenvironments. Historically the bone marrow was considered the major tissue of the CLL microenvironment. However, many recent innovative studies have categorically shown that peripheral CLL cells are derived from the lymph nodes (LN). Proliferation here is largely driven by helper T cells via CD40-CD40L engagement. Critically, in vitro studies have shown that such engagement additionally protects LN CLLs from apoptosis. Agents inducing apoptosis in non-CD40 engaged CLL cells are frequently ineffective against those continually engaged with CD40L. This emphasizes that, in order to improve responses and prevent relapse, novel therapies must be assessed against CD40L engaged CLL cells to show effective targeting against the LN. This review discusses the evidence supporting the superior involvement of the LN in CLL, how CD40L engaged CLL studies should be conducted, and the novel therapies studied in vitro and in vivo that have been proposed to be effective in this setting.

Blockade of Hsp90 by 17AAG antagonizes MDMX and synergizes with Nutlin to induce p53-mediated apoptosis in solid tumors

Strategies to induce p53 activation in wtp53-retaining tumors carry high potential in cancer therapy. Nutlin, a potent highly selective MDM2 inhibitor, induces non-genotoxic p53 activation. Although Nutlin shows promise in promoting cell death in hematopoietic malignancies, a major roadblock is that most solid cancers do not undergo apoptosis but merely reversible growth arrest. p53 inhibition by unopposed MDMX is one major cause for apoptosis resistance to Nutlin. The Hsp90 chaperone is ubiquitously activated in cancer cells and supports oncogenic survival pathways, many of which antagonize p53. The Hsp90 inhibitor 17-allylamino-17-demethoxygeldanamycin (17AAG) is known to induce p53-dependent apoptosis. We show here that in multiple difficult-to-kill solid tumor cells 17AAG modulates several critical components that synergize with Nutlin-activated p53 signaling to convert Nutlin's transient cytostatic response into a cytotoxic killing response in vitro and in xenografts. Combined with Nutlin, 17AAG destabilizes MDMX, reduces MDM2, induces PUMA and inhibits oncogenic survival pathways, such as PI3K/AKT, which counteract p53 signaling at multiple levels. Mechanistically, 17AAG interferes with the repressive MDMX-p53 axis by inducing robust MDMX degradation, thereby markedly increasing p53 transcription compared with Nutlin alone. To our knowledge Nutlin+17AAG represents the first effective pharmacologic knockdown of MDMX. Our study identifies 17AAG as a promising synthetic lethal partner for a more efficient Nutlin-based therapy.

Pharmacologic activation of p53 by small-molecule MDM2 antagonists

Restoring p53 activity by inhibiting the interaction between p53 and MDM2 represents an attractive approach for cancer therapy. To this end, a number of small-molecule p53-MDM2 binding inhibitors have been developed during the past several years. Nutlin-3 is a potent and selective small-molecule MDM2 antagonist that has shown considerable promise in pre-clinical studies. This review will highlight recent advances in the development of small-molecule MDM2 antagonists as potential cancer therapeutics, with special emphasis on Nutlin-3.