Combinatorial Synergy Research Articles

Asynchronous Reciprocal Coupling of Martini 2.2 Coarse-Grained and CHARMM36 All-Atom Simulations in an Automated Multiscale Framework.

The appeal of multiscale modeling approaches is predicated on the promise of combinatorial synergy. However, this promise can only be realized when distinct scales are combined with reciprocal consistency. Here, we consider multiscale molecular dynamics (MD) simulations that combine the accuracy and macromolecular flexibility accessible to fixed-charge all-atom (AA) representations with the sampling speed accessible to reductive, coarse-grained (CG) representations. AA-to-CG conversions are relatively straightforward because deterministic routines with unique outcomes are achievable. Conversely, CG-to-AA conversions have many solutions due to a surge in the number of degrees of freedom. While automated tools for biomolecular CG-to-AA transformation exist, we find that one popular option, called Backward, is prone to stochastic failure and the AA models that it does generate frequently have compromised protein structure and incorrect stereochemistry. Although these shortcomings can likely be circumvented by human intervention in isolated instances, automated multiscale coupling requires reliable and robust scale conversion. Here, we detail an extension to Multiscale Machine-learned Modeling Infrastructure (MuMMI), including an improved CG-to-AA conversion tool called sinceCG. This tool is reliable (∼98% weakly correlated repeat success rate), automatable (no unrecoverable hangs), and yields AA models that generally preserve protein secondary structure and maintain correct stereochemistry. We describe how the MuMMI framework identifies CG system configurations of interest, converts them to AA representations, and simulates them at the AA scale while on-the-fly analyses provide feedback to update CG parameters. Application to systems containing the peripheral membrane protein RAS and proximal components of RAF kinase on complex eight-component lipid bilayers with ∼1.5 million atoms is discussed in the context of MuMMI.

Discovery of Natural Products With Antifungal Potential Through Combinatorial Synergy.

The growing prevalence of antifungal drug resistance coupled with the slow development of new, acceptable drugs and fungicides has raised interest in natural products (NPs) for their therapeutic potential and level of acceptability. However, a number of well-studied NPs are considered promiscuous molecules. In this study, the advantages of drug–drug synergy were exploited for the discovery of pairwise NP combinations with potentiated antifungal activity and, potentially, increased target specificity. A rational approach informed by previously known mechanisms of action of selected NPs did not yield novel antifungal synergies. In contrast, a high-throughput screening approach with yeast revealed 34 potential synergies from 800 combinations of a diverse NP library with four selected NPs of interest (eugenol, EUG; β-escin, ESC; curcumin, CUR; berberine hydrochloride, BER). Dedicated assays validated the most promising synergies, namely, EUG + BER, CUR + sclareol, and BER + pterostilbene (PTE) [fractional inhibitory concentrations (FIC) indices ≤ 0.5 in all cases], reduced to as low as 35 (BER) and 7.9 mg L–1 (PTE). These three combinations synergistically inhibited a range of fungi, including human or crop pathogens Candida albicans, Aspergillus fumigatus, Zymoseptoria tritici, and Botrytis cinerea, with synergy also against azole-resistant isolates and biofilms. Further investigation indicated roles for mitochondrial membrane depolarization and reactive oxygen species (ROS) formation in the synergistic mechanism of EUG + BER action. This study establishes proof-of-principle for utilizing high-throughput screening of pairwise NP interactions as a tool to find novel antifungal synergies. Such NP synergies, with the potential also for improved specificity, may help in the management of fungal pathogens.

Transcriptomics reveals in vivo efficacy of PARP inhibitor combinatorial synergy with platinum-based chemotherapy in human non-small cell lung carcinoma models.

Inhibitors of poly(ADP)-ribose polymerase (PARP) exploit defective DNA repair pathways existing in several forms of cancer, such as those with BRCA mutations, and have proven clinical efficacy as chemosensitizers. However, platinum-based chemopotentiation by PARP inhibitors (PARPi), particularly for non-small cell lung cancer (NSCLC), has only been confirmed in a few preclinical models and the molecular mechanisms that drive PARPi combinatorial synergy with chemotherapeutics remains poorly defined. To better understand these mechanisms, we characterized cisplatin and veliparib efficacy in A549 and Calu6 NSCLC in vivo tumor xenograft models and observed combinatorial synergy in the Calu6 model. Transcriptome-wide analysis of xenografts revealed several differentially expressed genes (DEGs) between untreated and cisplatin + veliparib-treated groups, which were unique from genes identified in either of the single-agent treatment arms. Particularly at 10- and 21-days post-treatment, these DEGs were enriched within pathways involved in DNA damage repair, cell cycle regulation, and senescence. Furthermore, TGF-β- and integrin-related pathways were enriched in the combination treatment arm, while pathways involved in cholesterol metabolism were identified at earlier time points in both the combination and cisplatin-only groups. These data advance the biological underpinnings of PARPi combined with platinum-based chemotherapy and provides additional insight into the diverse sensitivity of NSCLC models.

MA16.03 CRISPR Screen Reveals XPO1 as a Therapeutic Target Strongly Sensitizing to First and Second Line Therapy in Small Cell Lung Cancer

Small cell lung cancer (SCLC) is an exceptionally aggressive disease comprising 13% of all lung cancer cases. With limited treatment options that typically result in transient responses, SCLC is responsible for approximately 250,000 deaths globally per year. The recent addition of immunotherapy to first-line platinum-based doublet chemotherapy appears to benefit only a small subset of patients, resulting in a 2-month increase in median overall survival. Major hurdles to improving SCLC treatment include development of rapid chemoresistance and ineffective second line therapies. The identification of more durably effective therapeutic strategies is a major unmet clinical need. We performed an in vitro CRISPR screen in seven SCLC cell lines, including commercially available and short term-cultured cell lines derived from patient-derived-xenografts (PDXs), representing all major SCLC subtypes. We used an in-house druggable genome library including targets for which active inhibitors, either FDA-approved or in clinical development, are available. The screen was performed with two conditions per cell line, untreated and cisplatin-treated, to identify targets whose disruption would specifically sensitize to cisplatin. Candidate targets of interest were validated genetically with independent sgRNAs in Cas9-expressing in vitro and in vivo models (pSpCTRE-PDXs) and pharmacologically, with in vitro synergy assays and PDX treatments. Signaling pathways were studied by western blot, and toxicity studies were performed in vivo, to assess the safety of the agents at pharmacologically effective doses. We performed immunohistochemistry (IHC) to assess expression of candidate targets in SCLC tissue microarrays (TMAs). Our CRISPR screen approach revealed XPO1 (Exportin 1) as a candidate that may contribute to cisplatin resistance across all SCLC subtypes. Combination of Exportin 1 inhibitors with cisplatin demonstrated synergy in vitro, and use of cisplatin with the Exportin 1 inhibitor selinexor showed combinatorial efficacy in vivo in chemonäive SCLC PDXs representing all SCLC subtypes. This efficacy was associated with increased DNA damage and apoptosis. The combination was well tolerated in mice at the drug concentrations tested. Exportin 1 inhibition also exhibited combinatorial synergy with irinotecan, a standard agent use for recurrent SCLC, and combination of selinexor with irinotecan demonstrated substantial efficacy in SCLC PDXs derived from chemorelapsed tumors including models for all SCLC subtypes, again with manageable toxicity profiles. We found SCLC to have the highest XPO1 mRNA expression among a diverse array of tumor histologies. High XPO1 expression was confirmed at the protein level in a SCLC tissue microarray, independent of SCLC subtype. Exportin 1 is highly expressed in SCLC tumors, independent of their subtype, and its inhibition enhances sensitivity to the chemotherapeutic drugs used in first line and second line treatment of SCLC tumors. Our results provide preclinical rationale for the combination of selinexor with cisplatin or with irinotecan as first or second line treatment, respectively, of SCLC.

Combinations of peptides synergistically activate the regenerative capacity of skin cells in vitro.

ObjectiveTo explore synergistic effects related to skin regeneration, peptides with distinct biological mechanisms of action were evaluated in combination with different skin cell lines in the presence or absence of niacinamide (Nam). Furthermore, the synergistic responses of peptide combinations on global gene expression were compared with the changes that occur with fractional laser resurfacing treatment, a gold standard approach for skin rejuvenation, to further define optimal peptide combinations.MethodsMicroarray profiling was used to characterize the biological responses of peptide combinations (+/− Nam) relative to the individual components in epidermal keratinocyte and dermal fibroblast cell lines. Cellular functional assays were utilized to confirm the synergistic effects of peptide combinations. Bioinformatics approaches were used to link the synergistic effects of peptide combinations on gene expression to the transcriptomics of the skin rejuvenation response from fractional laser treatment.ResultsMicroarray analysis of skin cells treated with peptide combinations revealed synergistic changes in gene expression compared with individual peptide controls. Bioinformatic analysis of synergy genes in keratinocytes revealed the activation of NRF2‐mediated oxidative stress responses by a combination of Ac‐PPYL, Pal‐KTTKS and Nam. Additional analysis revealed direct downstream transcriptional targets of NRF2/ARE exhibiting synergistic regulation by this combination of materials, which was corroborated by a cellular reporter assay. NRF2‐mediated oxidative stress response pathways were also found to be activated in the transcriptomics of the early skin rejuvenation response to fractional laser treatment, suggesting the importance of this biology in the early stages of tissue repair. Additionally, the second combination of peptides (pal‐KT and Ac‐PPYL) was found to synergistically restore cellular ATP levels that had been depleted due to the presence of ROS, indicating an additional mechanism, whereby peptide synergies may accelerate skin repair.ConclusionThrough combinatorial synergy studies, we have identified additional in vitro skin repair mechanisms beyond the previously described functions of individual peptides and correlated these to the transcriptomics of the skin rejuvenation response of fractional laser treatment. These findings suggest that specific peptides can act together, via complementary and synergistic mechanisms, to holistically enhance the regenerative capacity of in vitro skin cells.

Photosensitizer-stabilized self-assembling nanoparticles potentiate chemo/photodynamic efficacy of patient-derived melanoma

Development of injectable nanoparticles for delivery of active anticancer compounds often requires complicated schemes that involve tedious synthetic protocols and nanoformulations. In particular, clinical translation of synergistic nanoparticles that can facilitate multimodal therapies remains a considerable challenge. Herein, we describe a self-assembling, small-molecule nanosystem with unique properties, including near-infrared (NIR) light-responsive drug activation, size transformability, combinatorial synergy, and substantially reduced toxicity. Ligation of anticancer cabazitaxel (CTX) drugs via a reactive oxygen species-activatable thioketal linkage generates a dimeric TKdC prodrug, and subsequent coassembly with a photosensitizer, chlorin e6 (Ce6), forms colloidal-stable nanoassemblies (termed psTKdC NAs). Upon NIR laser irradiation, psTKdC NAs are transformed into smaller size particles and facilitate production of pharmacologically active CTX. Importantly, reactive oxygen species yielded by coassembled Ce6 can synergize with chemotherapy to achieve potent combinatorial effects. In a preclinical orthotopic model of an aggressive, human melanoma patient-derived xenograft (PDX), we show that administration of psTKdC NAs followed by laser irradiation produced durable tumor regression, with the tumors being completely eradicated in three of six PDXs. Furthermore, low systemic toxicity of this smart, photo-activatable nanotherapy was observed in animals. The new self-deliverable combinatorial system addresses essential requirements for high efficacy, safety, and translational capacity and deserves further investigation.

Abstract 6396: Sarcoma treatment using HSP90 inhibitors in combinatorial synergy with doxorubicin

Abstract Synovial sarcoma, a rare muscle cancer, has few targeted therapies, and is most commonly treated using doxorubicin (DOX). Even as a primary treatment agent, successful treatment and remission rates are low, and the significant cardiotoxicity of DOX limits dosage options. Synovial sarcoma, and other sarcomas, have a high expression of HSP90, a protein that acts as a chaperone molecule to stabilize and help fold other proteins within the cellular matrix. Under high stress situations, HSP90 is upregulated and acts to stabilize other more thermally labile proteins, including many oncogenes. Using FDA approved drug panels, it was determined that HSP90 is a suitable target for treatment. We look to use a novel HSP90 inhibitor (HS10) compound, to target the high expression of HSP90 within synovial sarcoma and osteosarcoma in combination with the chemotherapy standard DOX to determine if a synergistic effect is observed. This synergistic effect would allow for an overall decreased dose to induce effective cancer cell targeting, reducing overall systemic toxicity within patients. Our results indicate such synergism does occur between DOX and HS10, at a dosage of 5-25 nM DOX and 1000 nM HS10, reducing cell survival to 37-68%, dependent on cell line. DOX dosage alone reduced cell survival to 74% in the most effective case, with no reduction in the least effective case, at a dose of 100 nM. This dose is four times stronger than the highest DOX synergistic dose. It can be concluded, then, that synergistic combination does exist between DOX and HS10, and dosage of DOX can be reduced with more effective targeting for synovial and osteosarcoma cell lines. Protein expression was evaluated using immunoblotting to isolate protein fractions within the cytoplasm and cell membrane, showing high expression within the cytoplasm. Isolated blood plasma from mice with and without tumors was analyzed through ELISA, showing elevated HSP90 presence in mice with tumors (236.4±190pg) vs mice without tumors (6.5±3.5pg). This confirmation of elevated HSP90 expression within sarcoma patients suggests targeting using HS10 to induce synergy to be a viable approach for advanced sarcoma treatment. Citation Format: Matt Kirkham, Sarah Luelling, Kaniz Fatema, Jared Barrott. Sarcoma treatment using HSP90 inhibitors in combinatorial synergy with doxorubicin [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6396.

Abstract CT232: Phase I combination study of the CHK1 inhibitor prexasertib (LY2606368) and olaparib in patients with high-grade serous ovarian cancer and other advanced solid tumors

Abstract Background: Checkpoint kinase 1 (CHK1) plays a central role in replication fork stabilization and homologous recombination repair (HRR) through modulation of cell cycle checkpoints and phosphorylation of HRR proteins. BRCA-deficient cancers frequently upregulate CHK1 for protection of stalled replication forks. Prexasertib is an ATP-competitive inhibitor of CHK1. Addition of prexasertib to olaparib, an oral PARP inhibitor, may allow for combinatorial synergy and sensitization to PARP inhibition among tumors with de novo or acquired resistance. Methods: We conducted an open-label phase 1 study following a 3+3 design. Patients (pts) received a 7-day lead-in of olaparib alone (C0), followed by 28-day cycles with prexasertib administered on days 1 and 15 and olaparib on days 1-5 and 15-19 with starting dose of prexasertib at 80mg/m2 and olaparib at 200mg. The MTD was defined as the highest dose level at which less than 1/3rd of at least 6 pts experienced a DLT during C0+C1. Pharmacokinetic blood samples were obtained at C0, C1, and C2. Pts enrolled to the expansion phase of the study underwent tumor biopsies during C0 and on C1D16 after the combination for pharmacodynamic assessment of target effects on HRR. Patient-derived organoid cultures with functional assays for HRR proficiency and replication fork stability were conducted in parallel as an exploratory objective. Results: Twenty-one pts have been treated, 19 in the dose escalation phase. Three of 6 pts experienced DLTs at the starting dose and included Gr 3 neutropenia and Gr 3 febrile neutropenia. Lower doses for both agents were evaluated; the MTD is prexasertib at 70mg/m2 IV on days 1 and 15 in combination with olaparib at 100 mg PO BID D1-5 and 15-19. No DLTs were observed at this dose level. Drug-related adverse events occurring in ≥ 50% of pts included leukopenia, neutropenia, thrombocytopenia, anemia, and nausea. Three pts with BRCA1-mutant high-grade serous ovarian cancer (HGSOC) achieved PRs, two of whom had progressed on a prior PARP inhibitor. Tumor biopsies from pts in the expansion cohort demonstrated decreased RAD51 foci after prexasertib exposure. Pre-prexasertib patient-derived organoid cultures were successfully established and subjected to a DNA fiber assay to assess replication fork stability. The organoid derived from tumor from a non-responding patient had stable replication forks, whereas the organoid from a responding patient demonstrated baseline fork instability. Conclusion: Prexasertib in combination with an abbreviated course of olaparib has preliminary clinical activity in patients with BRCA-mutant HGSOC who have previously progressed on a PARP inhibitor. A functional assay for HRR in tumor biopsies indicates that prexasertib can compromise RAD51 focus formation, consistent with the role of CHK1 in RAD51 phosphorylation and filament formation. Preliminary data in patient-derived organoid cultures parallels that of clinical responses and confirms previously published data suggesting replication fork instability contributes to response to prexasertib. An expansion cohort in the BRCA-mutant, PARP inhibitor-resistant HGSOC population is being enrolled to further assess efficacy of the combination and to obtain additional pharmacodynamic determinants of response and resistance. Citation Format: Khanh T. Do, Sarah J. Hill, Bose Kochupurakkal, Jeffrey G. Supko, Courtney Gannon, Adrienne Anderson, Alona Muzikansky, Andrew Wolanski, Jennifer Hedglin, Kalindi Parmar, Jean-Bernard Lazaro, Joyce Liu, Susana Campos, Ursula A. Matulonis, Alan D. D'Andrea, Geoffrey I. Shapiro. Phase I combination study of the CHK1 inhibitor prexasertib (LY2606368) and olaparib in patients with high-grade serous ovarian cancer and other advanced solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr CT232.

Functionally significant, novel GATA4 variants are frequently associated with Tetralogy of Fallot.

Transcription factor GATA4 is known to play crucial role during heart development, regulating expression of several other key cardiogenic factors. Various GATA4 mutations are reported in familial as well as sporadic cases of congenital heart defects (CHDs). To estimate the prevalence and pathogenic potential of GATA4 variants in our CHD cohort, we have screened 285 CHD cases along with 200 controls by Sanger sequencing and identified 9 genetic variants (c.23C>A; p.Ala8Asp, c.25G>A; p.Ala9Thr, c.223G>T; p.Ala75Ser, c.383A>T; p.Glu128Val, c.397A>T; p.Ser133Cys, c.682T>A; p.Trp228Arg, c.1064C>G; p.Thr355Ser, c.1073G>C; p.Ser358Thr, and c.1220C>A; p.Pro407Gln) in 22 unrelated CHD probands (frequency:7.72%). Five of these are novel and located in the N-terminal transactivation domain (TAD) and first zinc finger domain. Majority C-terminal domain variants are polymorphic. Two of the TAD variants p.Glu128Val, p.Ser133Cys, and a first zinc finger variant p.Trp228Arg, impair combinatorial synergy of NKX2-5, SRF, and TBX5, suggesting potential role of these domains in GATA4 interactions with these factors. Decreased DNA-binding affinity with EMSA also supports this observation. Homology modeling and tertiary structure comparison show conformational changes in these variants. Interestingly, GATA4 variants are more frequently associated with ToF (45%; P=0.0046) and PS (22.7%; P<0.0001) in spite of abundance of septal defects in our study cohort.

RhoB upregulation leads to either apoptosis or cytostasis through differential target selection.

Anaplastic thyroid carcinoma is a highly aggressive undifferentiated carcinoma with a mortality rate near 100% due to an assortment of genomic abnormalities which impede the success of therapeutic options. Our laboratory has previously identified that RhoB upregulation serves as a novel molecular therapeutic target and agents upregulating RhoB combined with paclitaxel lead to antitumor synergy. Knowing that histone deacetylase 1 (HDAC1) transcriptionally suppresses RhoB, we sought to extend our findings to other HDACs and to identify the HDAC inhibitor (HDACi) that optimally synergize with paclitaxel. Here we identify HDAC6 as a newly discovered RhoB repressor. By using isoform selective HDAC inhibitors (HDACi) and shRNAs, we show that RhoB has divergent downstream signaling partners, which are dependent on the HDAC isoform that is inhibited. When RhoB upregulates only p21 (cyclin kinase inhibitor) using a class I HDACi (romidepsin), cells undergo cytostasis. When RhoB upregulates BIMEL using class II/(I) HDACi (belinostat or vorinostat), apoptosis occurs. Combinatorial synergy with paclitaxel is dependent upon RhoB and BIMEL while upregulation of RhoB and only p21 blocks synergy. This bifurcated regulation of the cell cycle by RhoB is novel and silencing either p21 or BIMEL turns the previously silenced pathway on, leading to phenotypic reversal. This study intimates that the combination of belinostat/vorinostat with paclitaxel may prove to be an effective therapeutic strategy via the novel observation that class II/(I) HDACi antagonize HDAC6-mediated suppression of RhoB and subsequent BIMEL, thereby promoting antitumor synergy. These overall observations may provide a mechanistic understanding of optimal therapeutic response.

A Novel Small Molecule STAT Inhibitor, BP-4-018, Demonstrates Significant Anti-Tumour Activity and Synergism With Bortezomib In Pre-Clinical In Vivo Models Of Multiple Myeloma

Despite significant advances in the treatment of Multiple Myeloma (MM), it remains incurable and thus, novel therapeutic strategies are critically needed. Prior work has demonstrated that the transcription factor STAT3 is aberrantly activated in a number of human tumors and drives hallmark oncogenic processes such as proliferation, survival, angiogenesis and drug resistance. As such, this master regulator of malignant processes has become the focus of therapeutic targeting in human tumors that harbor constitutive STAT3 activation, including MM. In the present studies, we characterize a newly developed small molecule, BP-4-018. The inhibitory mechanism of BP-4-018 is based on its ability to function as a phosphotyrosine mimetic, and thus bind the STAT3 SH2 domain to inhibit STAT3 phosphorylation (pSTAT3), STAT3 dimerization and DNA binding. Based on the 3D crystal structure of STAT3, SH2 docking simulations and fluorescence polarization assays, BP-4-018 demonstrates high affinity binding to the SH2 domain of STAT3. Using a panel of molecularly heterogeneous human myeloma cell lines (HMCLs), BP-4-018 demonstrated potent and broad anti-tumor activity in MTT assays, with IC50 values in the low μM range (1.91 μM - 6.48 μM). These anti-MM effects are mediated through the induction of the apoptosis as evidence by Annexin V+ staining, PARP cleavage and activation of caspases 3 and 9. Using patient derived bone marrow (BM) cells, BP-4-018 was shown to retain its anti-MM activity against HMCLs cultured in the presence of a BM stroma, induce apoptosis in primary MM tumor cells, and importantly, displayed little to no toxicity against non-malignant BM cells. Using cell-based assays, we show that BP-4-018 inhibits basal and cytokine-induced pSTAT3, as well as STAT3 transcriptional activity in HMCLs that stably express a STAT3-driven luciferase reporter construct. Consistent with these effects, western blot analyses of BP-4-018-treated cells reveal decreased expression of STAT3 target genes including c-Myc, Mcl-1 and Bcl-xL. Interestingly, BP-4-018 did not demonstrate preferential inhibition of cytokine induced STAT3 phosphorylation over that of STATs 1 or 5 suggesting that this compound may in fact be a pan-STAT inhibitor. BP-4-018 does not however inhibit the phosphorylation of other proteins whose regulation is SH2-dependent including AKT, ERK, SRC and LYN. In vitro combinatorial studies revealed that BP-4-018 is synergistic in combination with dexamethasone (CI=0.62), melphalan (CI=0.94), lenalidomide (CI=0.82) and is highly synergistic with bortezomib (BTZ) (CI=0.37). To examine the potential mechanisms of combinatorial synergy with BTZ, we evaluated the effects of BTZ on STAT3 signaling in HMCLs. BTZ treatment alone augmented STAT3 transcriptional activity and led to the accumulation of Mcl-1 protein, which was reversed when cells were co-treated with BP-4-018. Furthermore, HMCLs expressing a dominant negative STAT3 mutant display increased sensitivity to BTZ. Collectively these data suggest that the combinatorial synergism with BTZ is at least in part related to BP-4-018-mediated inhibition of STAT3. Finally, we used a novel STAT3-driven luciferase xenograft model of MM to show that BP-4-018 (15 mg/kg/day, PO) reduces STAT3-driven luciferase activity in vivo, significantly delays tumor growth as a single agent, and in combination with BTZ, induces marked and in some animals complete tumor regression. Neither BP-4-018 alone or in combination elicited significant toxicities as assessed by weight loss, and more extensive pharmacodynamic, pharmacokinetic and toxicology studies of BP-4-018 are currently underway. Taken together, our results highlight the promising therapeutic potential of BP-4-018 and support the continued development of targeted therapies for MM with a focus on aberrant STAT signaling. Disclosures: No relevant conflicts of interest to declare.

A Mechanism for Synergy with Combined mTOR and PI3 Kinase Inhibitors

Dysregulation of the mammalian target of rapamycin (mTOR) signaling has been found in many human cancers, particularly those with loss of the tumor suppressor PTEN. However, mTORC1 inhibitors such as temsirolimus have only modest activity when used alone and may induce acquired resistance by activating upstream mTORC2 and Akt. Other tumors that do not depend upon PI3K/Akt/mTOR signaling for survival are primarily resistant. This study tested the hypothesis that the limited clinical efficacy of temsirolimus is due to a compensatory increase in survival signaling pathways downstream of Akt as well as an incomplete block of 4E-BP1-controlled proliferative processes downstream of mTOR. We explored the addition of a PI3K inhibitor to temsirolimus and identified the mechanism of combinatorial synergy. Proliferation assays revealed that BEZ235 (dual PI3K/mTOR inhibitor) or ZSTK474 (pan PI3K inhibitor) combined with temsirolimus synergistically inhibited cell growth compared to cells treated with any of the agents alone. Co-treatment resulted in G0/G1 cell cycle arrest and up-regulation of p27. Cell death occurred through massive autophagy and subsequent apoptosis. While molecular profiling revealed that, in most cases, sensitivity to temsirolimus alone was most marked in cells with high basal phospho-Akt resulting from PTEN inactivation, combining a PI3K inhibitor with temsirolimus prevented compensatory Akt phosphorylation and synergistically enhanced cell death regardless of PTEN status. Another molecular correlate of synergy was the finding that temsirolimus treatment alone blocks downstream S6 kinase signaling, but not 4E-BP1. Adding BEZ235 completely abrogated 4E-BP1 phosphorylation. We conclude that the addition of a PI3K inhibitor overcomes cellular resistance to mTORC1 inhibitors regardless of PTEN status, and thus substantially expands the molecular phenotype of tumors likely to respond.

Interleukin-24 overcomes temozolomide resistance and enhances cell death by down-regulation of O6-methylguanine-DNA methyltransferase in human melanoma cells

Melanoma is the most malignant of skin cancers, highly resistant to chemotherapy and radiotherapy. Temozolomide, a promising new derivative of dacarbazine, is currently being tested for treatment of metastatic melanoma. Resistance to alkylating agents such as temozolomide correlates with increased expression of DNA repair protein O6-methylguanine-DNA methyltransferase (MGMT). Interleukin-24 (IL-24; mda-7) is a tumor suppressor cytokine that selectively inhibits tumor cell growth by inducing apoptosis and cell cycle arrest in melanoma cell lines and solid tumors. This tumor-selective activity has been observed in multiple preclinical animal models and in clinical trials. In this study, we analyzed the ability of Ad-IL-24 and its protein product, IL-24, to overcome temozolomide resistance in human melanoma cells. We have shown that Ad-IL-24 via exogenous IL-24 protein induces combinatorial synergy of temozolomide-induced cell killing in temozolomide-resistant melanoma cells by inhibition of MGMT. Neutralizing antibodies against IL-24 or its receptors significantly blocked the apoptotic activity of IL-24 + MGMT treatment. We show that accumulation of functional p53 is essential for IL-24-induced down-regulation of MGMT. Using either MGMT small interfering RNA, p53 small interfering RNA, or a p53 dominant-negative mutant to block MGMT protein expression resulted in increased sensitization to temozolomide. However, MGMT blockade in combination with IL-24 + temozolomide resulted in loss of combinatorial synergy, indicating that MGMT expression is required for the reversal of temozolomide resistance in melanoma cells. This study shows that IL-24 can play a significant role in overcoming temozolomide resistance and that the clinical efficacy of temozolomide may be improved by using a biochemotherapy combination with IL-24.

Combinatorial synergy induced by adenoviral-mediated mda-7 and Herceptin in Her-2+ breast cancer cells

The melanoma differentiation-associated gene-7 (mda-7) is a member of the interleukin-10 cytokine family and a novel tumor suppressor gene. Adenoviral-mediated mda-7 (Ad-mda7) gene transfer has tumor-specific growth inhibitory and proapoptotic effects in a broad spectrum of cancer cells. In breast cancer cells, adenoviral-induced mda-7 expression triggers antiproliferative effects by downregulation of survival signals, such as Bcl-2 and Akt. The anti-human epidermal growth factor receptor-2 (Her-2) monoclonal antibody, Trastuzumab (Herceptin), increases the sensitivity of Her-2/neu-overexpressing breast cancer cells to chemotherapeutic agents and radiotherapy. In this study, we evaluate the effects of treatment with Ad-mda7 and Herceptin combination therapy in a panel of Her-2/neu-overexpressing cell lines, and in established tumors in nude mice. Compared to individual treatments, the combination of Ad-mda7 and Herceptin elicits supra-additive antitumor activity in Her-2/neu-overexpressing tumor cell lines: increased cell death, cell cycle block and apoptosis. The Ad-mda7 and Herceptin interaction was shown to be synergistic by isobologram analysis. Ad-mda7 does not alter cell surface Her-2/neu levels, but the combination of Ad-mda7+Herceptin results in increased expression of cell surface E-cadherin with concomitant translocation of beta-catenin from the nucleus to the cell membrane. In vivo, the combination of Ad-mda7 and Herceptin showed significantly increased antitumor activity (P<0.003) against Her-2/neu-overexpressing tumors. These data suggest that the combination of Ad-mda7 with Herceptin may be a novel therapy for breast cancer patients whose tumors overexpress Her-2/neu. The observed synergistic effect may improve treatment options for otherwise poorly responsive, Her-2-positive, breast cancer patients.

Celastrols as Inducers of the Heat Shock Response and Cytoprotection

Alterations in protein folding and the regulation of conformational states have become increasingly important to the functionality of key molecules in signaling, cell growth, and cell death. Molecular chaperones, because of their properties in protein quality control, afford conformational flexibility to proteins and serve to integrate stress-signaling events that influence aging and a range of diseases including cancer, cystic fibrosis, amyloidoses, and neurodegenerative diseases. We describe here characteristics of celastrol, a quinone methide triterpene and an active component from Chinese herbal medicine identified in a screen of bioactive small molecules that activates the human heat shock response. From a structure/function examination, the celastrol structure is remarkably specific and activates heat shock transcription factor 1 (HSF1) with kinetics similar to those of heat stress, as determined by the induction of HSF1 DNA binding, hyperphosphorylation of HSF1, and expression of chaperone genes. Celastrol can activate heat shock gene transcription synergistically with other stresses and exhibits cytoprotection against subsequent exposures to other forms of lethal cell stress. These results suggest that celastrols exhibit promise as a new class of pharmacologically active regulators of the heat shock response.

Suppression of cell proliferation and gene expression by combinatorial synergy of EGCG, resveratrol and γ-tocotrienol in estrogen receptor-positive MCF-7 breast cancer cells

Numerous dietary phytochemicals have shown anti-breast carcinogenic activities when tested in vitro; however, in most cases, the demonstrated efficacy of individual phytochemicals requires doses not readily achievable in vivo. Therefore, whether diets might exert translational promises and benefits in clinical settings and prevention of breast cancer remain unclear. Since cancer cells are endowed with complex, redundant, converging and diverging pathways spanning both the genetic and metabolic networks that are not merely replicates of those in normal cells, it is of interest to test whether a multicomponent approach involving lower, physiologically relevant doses of natural dietary agents may be developed as a chemopreventive strategy for breast cancer. Herein, we investigated, using the estrogen receptor-positive MCF-7 breast cancer cells as a model, whether the combination of epigallocatechin gallate (EGCG), resveratrol and gamma-tocotrienol at suboptimal doses elicits synergism in suppressing cell proliferation, modulating gene expression, and increasing antioxidant activity, as compared to each of the three phytochemicals added alone. The results showed that there was a approximately 33, 50 and 58% inhibition of cell proliferation by > or =50 microM EGCG, > or =25 microM resveratrol and > or =10 microM gamma-tocotrienol, respectively, added as a single agent. When a suboptimal dose (10 microM) of each phytochemical was used, a significant additive effect in suppression of cell proliferation was observed with the combination of resveratrol and gamma-tocotrienol whereas the three phytochemicals added together did not produce more pronounced inhibition of cell proliferation. A significant additive effect in reducing cyclin D1 and bcl-2 expression was found when gamma-tocotrienol was added with either EGCG or resveratrol. Functional synergism among the three phytochemicals was only observed in the induction of quinone reductase NQO1. These results suggest that diet-based protection against breast cancer may partly derive from synergy amongst dietary phytochemicals directed against specific molecular targets in responsive breast cancer cells, and provide support for the feasibility of the development of a diet-based combinatorial approach in the prevention and treatment of breast cancer.