Greater Induction Of Apoptosis Research Articles

Abstract B023: The next-generation farnesyltransferase inhibitor KO-2806 constrains compensatory signaling reactivation to deepen responses to KRASG12D inhibition

Abstract The landmark approval of KRASG12C inhibitors toppled the decades-held notion that KRAS was undruggable, fueling the design and development of small molecules targeting other oncogenic KRAS mutants, including the most prevalent, KRASG12D. MRTX1133 is the first KRASG12D-selective inhibitor to reach the clinic, providing a much-needed therapeutic option for patients with KRASG12D-mutant tumors. Nevertheless, both preclinical MRTX1133 data and early clinical results from KRASG12C inhibitor trials suggest that responses to KRASG12D inhibition will vary widely, at least in part due to incomplete and/or transient inhibition of MAPK and mTOR signaling. We previously demonstrated that farnesyltransferase inhibitors (FTIs) can prevent adaptive resistance to PI3K inhibition by blunting compensatory reactivation of these signaling nodes. We therefore hypothesized that farnesyltransferase inhibition may similarly enhance the antitumor activity of MRTX1133 through synergistic blockade of mitogenic and survival signaling. In this study, we leveraged a panel of in vivo cell line (CDX) and patient-derived xenograft (PDX) models, in parallel with in vitro mechanistic studies, to assess the efficacy of combined KO-2806, a FTI, and MRTX1133, in controlling KRASG12D-mutant tumor growth. KO-2806 is a next-generation FTI with increased potency and improved pharmacokinetic properties relative to earlier FTI candidates and is poised to enter a first-in-human clinical trial. Given that reactivation of phospho-ERK and phospho-S6 is linked to diminished response to MRTX1133, we first probed the impact of KO-2806 on cell signaling in vitro. In KRASG12D mutant cell lines, MRTX1133 transiently inhibited both ERK and mTOR, as evidenced by decreased ERK, p90 RSK, p70 S6K, S6, and 4EBP1 phosphorylation. However, phosphorylation of these proteins rebounded partially within one day and completely by 48 hours post treatment. In contrast, when cells were co-exposed to MRTX1133 and KO-2806, robust inhibition of these pathways was maintained at 48 hours and corresponded with greater induction of apoptosis (PARP and caspase cleavage) and cell cycle arrest (ablation of Rb phosphorylation) compared to MRTX1133. These results are consistent with prior reports suggesting that durable MAPK and mTOR inhibition is required for optimal response to KRAS inhibitors. The mechanistic synergy we observed in vitro provided a strong rationale for evaluating combined MRTX1133 and KO-2806 in vivo. Across a panel of KRASG12D-mutant CDX and PDX solid tumor models, the MRTX1133/KO-2806 doublet led to deeper tumor growth inhibition compared to the single agents while remaining well tolerated in mice. We posit that KO-2806 augments the MAPK-mTOR inhibitory effects of MRTX1133 by blocking compensatory pathway reactivation, resulting in superior antitumor efficacy of the combination without amplifying toxicity. Based upon these results, combined farnesyltransferase and KRASG12D inhibition represents a promising therapeutic strategy for the treatment of KRASG12D0-mutant solid tumors. Citation Format: Alison Smith, Hetika Patel, Stacia Chan, Francis Burrows, Shivani Malik. The next-generation farnesyltransferase inhibitor KO-2806 constrains compensatory signaling reactivation to deepen responses to KRASG12D inhibition [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr B023.

PEGylated G4 dendrimers as a promising nanocarrier for piperlongumine delivery: Synthesis, characterization, and anticancer activity

PAMAM dendrimers are well-known delivery vehicles for various therapeutic agents like synthetic drugs, natural phytoconstituents, and genetic materials. The tunable physicochemical properties and variety of surface interactions make them attractive nano delivery system. However, plain dendrimers particularly higher generation dendrimers are reported to cause dose-dependent toxicities. Therefore, in this study, PEGylated G4 PAMAM dendrimers were synthesized via a click chemistry approach and used for the delivery piperlongumine (PL) for the treatment of colon cancer. PL is an amide alkaloid and potential anticancer agent, but it has poor aqueous solubility. PL was loaded into the dendrimer cavity through both physical loading and electrostatic chemical interactions. The prepared PL-loaded PEGylated G4 PAMAM dendrimers (PL@PEGylated G4) possessed a nanoscale size about 20 nm, monodispersity with a PDI value of 0.098 ± 0.002 and high drug solubility 226 ± 9.4 μg/mL. The drug release profile of PL@PEGylated G4 indicated a sustained release of encapsulated PL. After 24 h, about 43.2 ± 4.2 % and 64.9 ± 4.5 % of PL was released in PBS and SAB, respectively. The PEGylated dendrimers showed good biocompatibility during hemolytic toxicity study. In cytotoxicity studies, PL@PEGylated G4 showed potential cytotoxicity (IC50 = 5.8 μg/mL, p < 0.05) and greater induction of apoptosis in HCT 116 human colon cancer cells in comparison to pure PL, as demonstrated by the MTT and AO/EB assay, respectively. Overall, this biocompatible PEGylated G4 dendrimer-based formulation of PL could be a potential nanomedicine for cancer therapy.

Abstract 1944: Navitoclax enhances the efficacy of copanlisib predominantly through inhibition of BCLxL in PIK3CA mutant colorectal cancer

Abstract Background: Mutations in PIK3CA occur in 18% of colorectal cancers (CRC) and result in constitutive activation of the PI3K pathway. Previous work from our lab has determined that MTORC1/2 inhibition, with copanlisib (cop), a PI3K/MTOR inhibitor, is sufficient to induce a treatment response. We hypothesized that the BCL2 family inhibitor navitoclax (nav), a BCL2/BCLxL inhibitor, would enhance the therapeutic response of cop and increase the induction of apoptosis. Methods: Murine derived cancer organoids (MDCOs) were generated from adenocarcinomas arising in Apc and Pik3ca mutant transgenic mice ((FVB x B6) F1 Apcfl/+ Pik3caH1047R/+). MDCOs were plated and matured for 24 hours. MDCOs were treated for 48 hours. Change in diameter was used to assess response. Additionally, human 2D isogenic cell lines SW48 and SW48PIK3CA-H1047R (SW48PK) were plated and treated for 48 hours. WST-1 proliferation assay was used to determine response. In vivo response was assessed as median relative change (MRC) in tumor volume of SW48 and SW48PK xenografts in immunocompromised Rag2-Il2rg-/- (R2G2) mice. Induction of apoptosis was determined with immunoblotting (IB) for PARP cleavage. Results: MDCOs were treated with cop (200nM) or nav (250nM) alone and in combination. Single agent cop resulted in -16% MRC (p&amp;lt;0.001). Nav alone did not have an effect (+95% p&amp;lt;0.07). Enhanced therapeutic response was seen in the combination therapy compared to cop alone (cop -16% vs combo -100%; p&amp;lt;0.001). In SW48 and SW48PK with cop (1nM or 10nM) or nav (250nM) alone and in combination, a greater response was seen in the combination therapy in both cell lines compared to either single agent alone (p&amp;lt;0.005). SW48 and SW48PK xenograft studies demonstrated significant activity of this combination in vivo. SW48 tumor growth was limited with either cop (10mg/kg), nav (80mg/kg), or the combination compared to control (control +5.0 MRC, cop +3.4, nav +2.6, combo +2.6; control vs combo p&amp;lt;0.01; cop vs combo p=0.29). Enhanced activity of this combination was observed in SW48PK tumors compared to SW48. Growth was significantly more limited with the combination (control +5.0 MRC, cop +3.4, nav +4.5, combo +0.7; control vs combo p&amp;lt;0.01; cop vs combo p=0.06). IB of cleaved PARP showed induction of apoptosis was the highest in the combination therapy in all in vitro models and seen as early as 6 hours post treatment. To identify which BCL2 family member nav was primarily targeting, cop was combined with WEHI539 (BCLxL inhibitor; 250nM) or ABT199 (BCL2 inhibitor; 250nM). BCL2 inhibition did not enhance the efficacy of cop in the MDCOs or isogenic lines. However, BCLxL inhibition did enhance the efficacy of cop in both in vitro models. Conclusion: These data indicate that navitoclax, through BCLxL inhibition, enhances the efficacy of copanlisib with a greater induction of apoptosis in several models of PIK3CA mutant CRC. Citation Format: Rebecca Anna DeStefanis, Alyssa DeZeeuw, Gioia Sha, Autumn Olson, Samantha J. Anderson, Christopher P. Babiarz, Cheri A. Pasch, Linda Clipson, Dustin A. Deming. Navitoclax enhances the efficacy of copanlisib predominantly through inhibition of BCLxL in PIK3CA mutant colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1944.

Abstract 1026: Bi-steric mTORC1-selective inhibitors demonstrate improved potency and efficacy in tumors with mTORC1 hyperactivation

Abstract The PI3K-mTOR pathway is one of the most commonly dysregulated pathways in human tumors. Rapalogs have been used extensively in human clinical trials but exhibit modest clinical benefit for the most part, possibly due to their lack of effect on 4E-BP1, a key target downstream of mTORC1. ATP-competitive mTOR inhibitors can fully inhibit mTORC1 but are poorly tolerated possibly due to their inhibition of mTORC2. A new class of selective mTORC1 inhibitors has been developed and termed ‘bi-steric', which comprise a rapamycin-like core moiety covalently linked to an mTOR active-site inhibitor. RMC-5552 is the first clinical candidate of this class and clinical testing is planned in 2021. RM-001 and RM-006 (also known as RMC-6272) are representative bi-steric tool compounds that exhibit potent and selective (&amp;gt; 10-fold) inhibition of mTORC1 over mTORC2. We report that bi-steric mTORC1-selective inhibitors have greater activity than rapalogs for tumors with mTORC1 hyperactivation secondary to TSC1/2 loss. RM-001 and RM-006 showed more effective growth inhibition in multiple TSC1 or TSC2 mutant tumor cell lines compared to rapamycin. RM-001 and RM-006 caused a more profound growth inhibition in the TSC1 or TSC2 mutant cells than the wild type cells. Two-week low dilution clonogenic assays in TSC1 or TSC2 mutant cells showed clone numbers were significantly reduced by rapamycin, RM-001, and RM-006, whereas in the wild type cells, Rapamycin and RM compounds had less reduction in clone numbers, indicating a differential sensitivity in TSC-null cells. Both RM-001 and RM-006 at ~1 nM showed near complete inhibition of p4E-BP1T37/46, which was not seen with rapamycin treatment, while inhibition of pS6S240/244 levels was similar for rapamycin and RM compounds. Further, the RM compounds had prolonged anti-proliferative activity in TSC-null cells, as shown by washout studies. Rapamycin, MLN0128 and both RM compounds markedly reduced kidney tumor burden in Tsc2+/- A/J mice after four weeks of treatment. Tumor regrowth was assessed two months after treatment cessation, tumor burden was significantly reduced in the RM-006 group as compared to the rapamycin and MLN0128 groups. Finally, TUNEL staining showed RM-006 treatment led to a greater induction of apoptosis in kidney tumor cells relative to rapamycin and MLN0128 after a single dose of each compound in Tsc2+/- A/J mice. This is the first time that clear evidence for cell death after mTORC1 inhibition has been seen in TSC rodent models. In summary, RM-001 and RM-006 demonstrate improved in vitro and in vivo inhibition of mTORC1 in comparison to rapamycin, and induced more cell death in TSC2 null tumors in vivo, indicating the potential of bi-steric mTORC1-selective inhibitors as a novel therapeutic strategy to treat tumors with mTORC1 dysregulation. Citation Format: Heng Du, Yu Chi Yang, Mallika Singh, Heng-jia Liu, David Kwiatkowski. Bi-steric mTORC1-selective inhibitors demonstrate improved potency and efficacy in tumors with mTORC1 hyperactivation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1026.

Blockage of protease-activated receptor 2 exacerbates inflammation in high-fat environment partly through autophagy inhibition.

Protease-activated receptor 2 (PAR2) regulates inflammatory responses and lipid metabolism. However, its precise role in colitis remains unclear. In this study, we aimed to investigate the function of PAR2 in high-fat diet-fed mice with colitis and its potential role in autophagy. PAR2+/+ and PAR2-/- mice were fed a high-fat diet (HFD) for 7 days before colitis induction with dextran sodium sulfate. Deletion of PAR2 and an HFD significantly exacerbated colitis, as shown by increased mortality, body weight loss, diarrhea or bloody stools, colon length shortening, and mucosal damage. Proinflammatory cytokine levels were elevated in HFD-fed PAR2-/- mice and in cells treated with the PAR2 antagonist GB83, palmitic acid (PA), and a cytokine cocktail (CC). Damaging effects of PAR2 blockage were associated with autophagy regulation by reducing the levels of YAP1, SIRT1, PGC-1α, Atg5, and LC3A/B-I/II. In addition, mitochondrial dysfunction was demonstrated only in cells treated with GB83, PA, and CC. Reduced cell viability and greater induction of apoptosis, as shown by increased levels of cleaved caspase-9, cleaved caspase-3, and cleaved poly(ADP-ribose) polymerase (PARP), were observed in cells treated with GB83, PA, and CC but not in those treated with only PA and CC. Collectively, protective effects of PAR2 were elucidated during inflammation accompanied by a high-fat environment by promoting autophagy and inhibiting apoptosis, suggesting PAR2 as a therapeutic target for inflammatory bowel disease co-occurring with metabolic syndrome.NEW & NOTEWORTHY Deletion of PAR2 with high-fat diet feeding exacerbates colitis in a murine colitis model. Proinflammatory effects of PAR2 blockage in a high-fat environment were associated with an altered balance between autophagy and apoptosis. Increased colonic levels of PAR2 represent as a therapeutic strategy for IBD co-occurring with metabolic syndrome.

Abstract A09: Targeting Hippo-dependent and Hippo-independent regulation of the YAP1 oncoprotein in childhood rhabdomyosarcoma

Abstract Background: Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma of childhood. While outcomes for patients with localized disease have improved, patients with metastatic or recurrent disease continue to do poorly; therefore, new treatments are needed. Previously, we showed that the Src family tyrosine kinase YES1 is upregulated in RMS and necessary for growth, but clinical trials using single-agent dasatinib (Src family kinase inhibitor) have not shown clinical activity in sarcomas. YAP1 (YES-associated protein) is also highly expressed in human RMS tumors, driving cell growth and survival. Thus far, efforts to pharmacologically inhibit YAP1 have been unsuccessful. We hypothesize that a better understanding of the Hippo-dependent and Hippo-independent (through YES1) regulation of YAP1 in RMS may lead to novel therapeutic approaches. Methods: We studied the effect of DNA methyltransferase inhibitors (DNMTi) on cell growth in human RMS cell lines using live cell imaging and analyzed the YES-YAP interaction by proximity ligation assays. We analyzed YES1 and YAP1 signaling with cell fractionation, immunoblots, methylation-specific PCR, qPCR, RNAseq, and genetic loss of function. Results: We demonstrate that DNMTi treatment decreases RMS cell growth and increases apoptosis and differentiation. DNMTi treatment activates canonical Hippo signaling through LATS, shown by a LATS activity biosensor, and increases YAP1 phosphorylation. DNMTi treatment also induces RASSF1 re-expression by promoter demethylation, and the DNMTi-induced growth inhibition can be partially rescued by expression of constitutively active YAPS127A. RNAseq analysis after DNMTi treatment also revealed upregulation of RASSF family members RASSF5 and RASSF6 and downregulation of RASSF4. RASSF4 was previously shown to inhibit MST1 and promote tumorigenesis in the alveolar subtype of RMS. These data suggest the effects of DNMTi treatment are in part due to inhibition of YAP1 in a Hippo-dependent manner. DNMTi treatment also decreases YES1 expression and activation, suggesting DNMTis impact both YES1 and YAP1 activity. Furthermore, YES1 and YAP1 interact in the nucleus of RMS cells and shRNA knockdown of YES1 results in YAP1 cytoplasmic retention and decreased expression of YAP1 target genes, suggesting a role for YES1 in regulating YAP1 cellular localization in a Hippo-independent manner. Lastly, to target both Hippo-dependent and Hippo-independent regulation of YAP1 we combine DNMTi treatment with dasatinib, a YES1 kinase inhibitor. Combination treatment in vitro ablates RMS cell growth and leads to a greater induction of apoptosis than either drug alone. We are currently evaluating this combination strategy in RMS xenografts in mice. Conclusions: Overall, we show that YAP1 is regulated in both Hippo-dependent and Hippo-independent mechanisms in RMS and both mechanisms can be inhibited by a combined treatment of DNMTi and dasatinib, laying the groundwork for future clinical investigations of this novel therapy. Citation Format: Katherine K. Slemmons, Choh Yeung, Josh Baumgart, Amy McCalla, Lee Helman. Targeting Hippo-dependent and Hippo-independent regulation of the YAP1 oncoprotein in childhood rhabdomyosarcoma [abstract]. In: Proceedings of the AACR Special Conference on the Hippo Pathway: Signaling, Cancer, and Beyond; 2019 May 8-11; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2020;18(8_Suppl):Abstract nr A09.

Abstract 2097: LIN9 regulation of NEK2 underlies taxol resistance in triple-negative breast cancer

Abstract Currently, there are no targeted strategies to combat triple negative breast cancer, resulting in poor patient survival. This disease initially responds well to cytotoxic chemotherapies such as paclitaxel, yet resistance and metastatic recurrence are common. Taxanes cause defects in centrosome function and chromosome segregation leading to cell death. While greatly effective, they are also associated with high toxicity. Thus discovering new therapeutic targets that provide a selective vulnerability for TNBC should yield novel approaches for improving patient outcomes. We discovered that LIN9, a transcriptional regulator of mitosis, is overexpressed in 66% of TNBC and is associated with poor survival. We now report that both LIN9 mRNA and protein expression are upregulated in paclitaxel-resistant versus sensitive cells and directly correlates with paclitaxel IC50 values across eight breast cancer cell lines. In MDA-MB-231 and MDA-MB-468 cell lines, LIN9 silencing results in multi- and micronucleation, and supernumerary centrosomes. Moreover, LIN9 silencing increases sensitivity to paclitaxel in TNBC cells with intrinsic (BT549) or acquired (MDA-MB-231 and -468) resistance. We previously reported that Bromodomain and ExtraTerminal protein inhibitors (BETi) treatment reduces LIN9 expression, and thus determined if BETi could reverse paclitaxel resistance. Treatment with the BETi, JQ1, in conjunction with paclitaxel caused a greater induction of apoptosis, abnormal centrosomes, multi- and micronucleation compared to either drug alone. To identify the mechanism(s) by which suppression of LIN9 reverses paclitaxel resistance, we compared the transcriptomes of MDA-MB-231 and HCC70 TNBC cells transiently transfected with non-targeting or LIN9-targeted siRNAs. The resulting gene list was then filtered to include only genes whose expression correlates with LIN9 in breast cancer, are bound to LIN9 in a published ChIP-Seq dataset, and are associated with breast cancer survival. Using this approach, we identified NIMA-related Kinase 2 (NEK2), a serine/threonine kinase required for centrosome separation during mitosis, as a potential mediator of LIN9-associated paclitaxel resistance. NEK2 is overexpressed in 47% of basal breast cancers and is associated with poor patient outcomes. Additionally, NEK2 is upregulated in paclitaxel-resistant cells and LIN9 silencing decreases expression of NEK2. Importantly, silencing NEK2 expression also restores sensitivity to paclitaxel in resistant cells. Together, these data indicate that increased LIN9 expression in TNBC promotes paclitaxel resistance by upregulating NEK2 and that loss of LIN9 or NEK2 contributes to centrosome dysfunction, potentiating paclitaxel sensitivity. They also indicate that suppressing LIN9 expression using agents such as BET inhibitors may be a viable therapeutic approach for improving paclitaxel efficacy in TNBC patients. Citation Format: Melyssa S. Shively, Ruth A. Keri. LIN9 regulation of NEK2 underlies taxol resistance in triple-negative breast cancer [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 2097.

Prexasertib, a cell cycle checkpoint kinases 1 and 2 inhibitor, increases in vitro toxicity of PARP inhibition by preventing Rad51 foci formation in BRCA wild type high-grade serous ovarian cancer.

PARP inhibitors (PARPi) have been effective in high-grade serous ovarian cancer (HGSOC), although clinical activity is limited against BRCA wild type HGSOC. The nearly universal loss of normal p53 regulation in HGSOCs causes dysfunction in the G1/S checkpoint, making tumor cells reliant on Chk1-mediated G2/M cell cycle arrest for DNA repair. Therefore, Chk1 is a reasonable target for a combination strategy with PARPi in treating BRCA wild type HGSOC. Here we investigated the combination of prexasertib mesylate monohydrate (LY2606368), a Chk1 and Chk2 inhibitor, and a PARP inhibitor, olaparib, in HGSOC cell lines (OVCAR3, OV90, PEO1 and PEO4) using clinically attainable concentrations. Our findings showed combination treatment synergistically decreased cell viability in all cell lines and induced greater DNA damage and apoptosis than the control and/or monotherapies (p<0.05). Treatment with olaparib in BRCA wild type HGSOC cells caused formation of Rad51 foci, whereas the combination treatment with prexasertib inhibited transnuclear localization of Rad51, a key protein in homologous recombination repair. Overall, our data provide evidence that prexasertib and olaparib combination resulted in synergistic cytotoxic effects against BRCA wild type HGSOC cells through reduced Rad51 foci formation and greater induction of apoptosis. This may be a novel therapeutic strategy for HGSOC.

Inhibition of HSP90 sensitizes a novel Raf/ERK dual inhibitor CY-9d in triple-negative breast cancer cells.

Raf and extracellular signal-regulated kinases (ERK) are both important therapeutic targets in the mitogen-activated protein kinase (MAPK) pathway, and play crucial roles in the apoptosis resistance of breast cancer cells. In the present study, cytotoxic and apoptosis-inducing activities of the Raf/ERK dual inhibitor CY-9d were found to be restricted in triple negative breast cancer (TNBC) cells compared with ER/PR-positive cells. Based on the analysis of differentially expressed proteins using a quantitative proteomic iTRAQ method and bioinformatics analysis, HSP90 was found to identify as a potential mediator between Raf and ERK in TNBC cells. Western blotting and RNA interference suggested that down-regulated IQGAP1 can attenuate the routine Raf/MEK/ERK cascade and recruit HSP90 as a bypass pathway. Simultaneous treatment with the HSP90 inhibitor and CY-9d at sub-therapeutic doses was found to produce synergistic therapeutic and apoptosis-inducing effects in TNBC cells. Moreover, CY-9d was also found to suppress breast cancer growth, inhibit the activation of Raf/ERK, and induce mitochondrial apoptosis in vivo without remarkable toxicity. These results support the combination of HSP90 and Raf/ERK inhibitors as a potential target therapeutic strategy with enhanced tumor growth suppression, downstream pathway blockade, and greater induction of apoptosis.

Anticancer effects of phytocannabinoids used with chemotherapy in leukaemia cells can be improved by altering the sequence of their administration.

Phytocannabinoids possess anticancer activity when used alone, and a number have also been shown to combine favourably with each other invitro in leukaemia cells to generate improved activity. We have investigated the effect of pairing cannabinoids and assessed their anticancer activity in cell line models. Those most effective were then used with the common anti-leukaemia drugs cytarabine and vincristine, and the effects of this combination therapy on cell death studied invitro. Results show a number of cannabinoids could be paired together to generate an effect superior to that achieved if the components were used individually. For example, in HL60 cells, the IC50 values at 48h for cannabidiol (CBD) and tetrahydrocannabinol (THC) when used alone were 8 and 13µM, respectively; however, if used together, it was 4µM. Median-effect analysis confirmed the benefit of using cannabinoids in pairs, with calculated combination indices being <1 in a number of cases. The most efficacious cannabinoid-pairs subsequently synergised further when combined with the chemotherapy agents, and were also able to sensitise leukaemia cells to their cytotoxic effects. The sequence of administration of these drugs was important though; using cannabinoids after chemotherapy resulted in greater induction of apoptosis, whilst this was the opposite when the schedule of administration was reversed. Our results suggest that when certain cannabinoids are paired together, the resulting product can be combined synergistically with common anti-leukaemia drugs allowing the dose of the cytotoxic agents to be dramatically reduced yet still remain efficacious. Nevertheless, the sequence of drug administration is crucial to the success of these triple combinations and should be considered when planning such treatments.

A Novel Combination of Withaferin A and Sulforaphane Inhibits Epigenetic Machinery, Cellular Viability and Induces Apoptosis of Breast Cancer Cells.

With cancer often classified as a disease that has an important epigenetic component, natural compounds that have the ability to regulate the epigenome become ideal candidates for study. Humans have a complex diet, which illustrates the need to elucidate the mechanisms of interaction between these bioactive compounds in combination. The natural compounds withaferin A (WA), from the Indian winter cherry, and sulforaphane (SFN), from cruciferous vegetables, have numerous anti-cancer effects and some report their ability to regulate epigenetic processes. Our study is the first to investigate the combinatorial effects of low physiologically achievable concentrations of WA and SFN on breast cancer cell proliferation, histone deacetylase1 (HDAC1) and DNA methyltransferases (DNMTs). No adverse effects were observed on control cells at optimal concentrations. There was synergistic inhibition of cellular viability in MCF-7 cells and a greater induction of apoptosis with the combinatorial approach than with either compound administered alone in both MDA-MB-231 and MCF-7 cells. HDAC expression was down-regulated at multiple levels. Lastly, we determined the combined effects of these bioactive compounds on the pro-apoptotic BAX and anti-apoptotic BCL-2 and found decreases in BCL-2 and increases in BAX. Taken together, our findings demonstrate the ability of low concentrations of combinatorial WA and SFN to promote cancer cell death and regulate key epigenetic modifiers in human breast cancer cells.

Nestin expression involves invasiveness of esophageal carcinoma and its downregulation enhances paclitaxel sensitivity to esophageal carcinoma cell apoptosis.

Paclitaxel has been generally used to treat primary and metastatic esophageal carcinoma. It has been shown that nestin is highly expressed in esophageal carcinoma and that there is a strong association of nestin expression with poor prognosis in esophageal carcinoma patients. In this study, using immunohistochemistry, in situ hybridization and Western blotting we demonstrated that nestin was overexpressed in the invasive esophageal carcinoma. To further elucidate whether nestin inhibition could enhance paclitaxel sensitivity to esophageal carcinoma cells, we applied nestin siRNA in esophageal squamous cell carcinoma Eca-109 cells. Flow cytometry and TUNEL staining both showed that combination of paclitaxel treatment and nestin knockdown resulted in greater induction of apoptosis of esophageal carcinoma cells as compared with the cells transfected with control siRNA (also treated with paclitaxel). This study indicates that nestin knockdown enhances chemotherapeutic sensitivity of paclitaxel to esophageal carcinoma, and suggests that silencing of nestin could be a valuble therapeutic approach for enhancing drug sensitivity and thereby improving the treatment outcome of esophageal carcinoma patients.

Apoptosis is augmented in high-grade serous ovarian cancer by the combined inhibition of Bcl-2/Bcl-xL and PARP.

The aim of our study was to evaluate possible synergistic cytotoxic effects of the combination treatment with the BH3-mimetic ABT-263 and the PARP inhibitor BMN 673 in high-grade serous ovarian cancer (HGSOC) cells using clinically achievable concentrations of each drug. In vitro cytotoxic effects of ABT-263 and BMN 673 were assessed by XTT assay in three HGSOC cell lines: OVCAR3, OVCAR8, and OV90 cells. Combination index values and synergy/antagonism volumes were used to determine synergy. The drug effects on DNA damage accumulation, cell cycle progression, apoptosis induction, and expression levels of Bcl-2 family proteins were examined to dissect molecular mechanisms. The combination treatment synergistically decreased cell viability in a concentration- and time-dependent manner in all cell lines; combination index values were <0.9 and synergy/antagonism volumes were >100 after 72 h of treatment. Clinically achievable concentrations of ABT-263 2 µM and BMN 673 25 nM were used to investigate mechanisms. No increase in γ-H2AX foci formation was observed with addition of ABT-263 to BMN 673 treatment. The combination treatment increased the sub-G1 and Annexin V-positive cell populations after 48 h compared with the control and each monotherapy. It also induced greater caspase-3/7 activity and PARP cleavage. ABT-263 alone and in combination with BMN 673 induced expression levels of Bim, a pro-apoptotic protein. In conclusion, the ABT-263 and BMN 673 combination resulted in synergistic cytotoxic effects against HGSOC cells through greater induction of apoptosis. This may be a novel therapeutic strategy for HGSOC.

Adenovirus-mediated FKHRL1/TM sensitizes melanoma cells to apoptosis induced by temozolomide.

Melanoma exhibits variable resistance to the alkylating agent temozolomide (TMZ). We evaluated the potential of adenovirus expressing forkhead human transcription factor like 1 triple mutant (Ad-FKHRL1/TM) to sensitize melanoma cells to TMZ. Four melanoma cell lines were treated with Ad-FKHRL1/TM and TMZ, alone or in combination. Apoptosis was assessed by activation and inhibition of caspase pathway, nuclei fragmentation, and annexin V staining. The potential therapeutic efficacy of Ad-FKHRL1/TM with TMZ was also assessed in a mouse melanoma xenograft model. Combination therapy of Ad-FKHRL1/TM and TMZ resulted in greater cell killing (<20% cell viability) compared with single therapy and controls (p<0.05). Combination indices of Ad-FKHRL1/TM and TMZ therapy indicated significant (p<0.05) synergistic killing effect. Greater apoptosis induction was found in cells treated with Ad-FKHRL1/TM and TMZ than with Ad-FKHRL1/TM or TMZ-treated cells alone. Treatment with TMZ enhanced adenovirus transgene expression in a cell type-dependent manner. In an in vivo model, combination therapy of Ad-FKHRL1/TM with TMZ results in greater tumor growth reduction in comparison with single treatments. We suggest that Ad-FKHRL1/TM is a promising vector to sensitize melanoma cells to TMZ, and that a combination of both approaches would be effective in the clinical setting.

Adenovirus-mediated FKHRL1/TM sensitizes melanoma cells to apoptosis induced by temozolomide.

Melanoma exhibits variable resistance to the alkylating agent temozolomide (TMZ). We evaluated the potential of adenovirus expressing forkhead human transcription factor like 1 triple mutant (Ad-FKHRL1/TM) to sensitize melanoma cells to TMZ. Four melanoma cell lines were treated with Ad-FKHRL1/TM and TMZ, alone or in combination. Apoptosis was assessed by activation and inhibition of caspase pathway, nuclei fragmentation, and annexin V staining. The potential therapeutic efficacy of Ad-FKHRL1/TM with TMZ was also assessed in a mouse melanoma xenograft model. Combination therapy of Ad-FKHRL1/TM and TMZ resulted in greater cell killing (<20% cell viability) compared to single therapy and controls (p<0.05). Combination indices of Ad-FKHRL1/TM and TMZ therapy indicated significant (p<0.05) synergistic killing effect. Greater apoptosis induction was found in cells treated with Ad-FKHRL1/TM and TMZ than Ad-FKHRL1/TM or TMZ-treated cells alone. Treatment with temozolomide enhanced adenovirus transgene expression in a cell type-dependent manner. In an in vivo model, combination therapy of Ad-FKHRL1/TM with TMZ results in greater tumor growth reduction in comparison with single treatments. We suggest that Ad-FKHRL1/TM is a promising vector to sensitize melanoma cells to TMZ, and that a combination of both approaches would be effective in the clinical setting.

Abstract 4891: Radiation enhances the efficacy of Bcl-2 and Bcl-XL inhibition in small cell lung cancer: A new concept of using radiation for targeted therapy through contextual oncogene addiction

Abstract Purpose: Radiotherapy has a critical role in the treatment of small cell lung cancer (SCLC). Effectiveness of radiation in SCLC remains limited as resistance results from defects in apoptosis. Experimental Design: We investigated whether using a new Bcl-2/Bcl-XL inhibitor, S44563, can enhance radiosensitivity of SCLC cells in vitro and in vivo. We also explored the mechanisms of the potential interaction. Results: In vitro studies confirmed that S44563 induce apoptosis in SCLC cells by inducing hallmarks of apoptosis (cleaved caspase-3, sub-G1 fraction induction and induction of the mitochondrial caspase activation pathway). S44563 markedly enhanced sensitivity of H146 and H69 cells to radiation in clonogenic assay. In vitro experiments demonstrated a greater induction of apoptosis (sub-G1 fraction and cleaved caspase-3) with the combination as well as in vivo caspase-3 immunostaining. This positive interaction between S44563 and radiation was greater when S44563 was given during and after the completion of the radiation, which was explained by the radiation-induced over expression of anti-apoptotic proteins (Bcl-2 and Bcl-XL). in vitro studies based on gene expression and immunoblotting indicated that radiation activates NF-κB pathways which results in anti-apoptotic expression. In addition, S44563 combined with cisplatin-based chemo-radiation showed a dramatic tumor growth delay and increased overall survival in mouse xenograft models.Conclusion: This study underlines the critical role of sequence administration of targeted therapies with conventional therapies such as radiation and chemotherapy. SCLC cells which survive to IR highly rely on the induction of anti apoptotic proteins for their survival therefore yielding to the concept of “contextual oncogene addiction” to the Bcl-2/Bcl-XL pathway. These results suggest that radioresistance results in part from resistance to apoptosis in SCLC mediated by up regulation of Bcl-2/Bcl-XL. The inhibition of Bcl-2 and Bcl-XL leads to the induction of radiation-induced apoptosis and enhances radiation therapy both in vitro and in SCLC xenograft models. Our data suggest that targeting radiation induced survival pathways may constitute an efficient strategy to potentiate IR. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4891. doi:1538-7445.AM2012-4891

Abstract 5406: ErbB inhibitory protein [EBIP], a modified ectodomain of EGFR, synergizes with dasatinib to inhibit growth of breast cancer cells

Abstract It is becoming increasingly evident that many solid tumors including breast cancer show increased activation of several growth factor receptors, specifically EGFR and its family members (EGFRs) as well as c-Src, a non-receptor tyrosine kinase that promote proliferation, inhibit apoptosis and induce metastasis. We hypothesize that inhibition of c-Src and EGFRs will be an effective therapeutic strategy for breast cancer. To test our hypothesis we used dasatinib (BMS-354825; Bristol-Myers Squibb), a newly developed highly potent, ATP-competitive Src and Abl kinase inhibitor and ErbB Inhibitory Protein (EBIP) that we generated and found to be an effective pan-ErbB inhibitor. EBIP is composed of 1-448 amino acids of the ectodomain of human EGFR (hEGFR), and the 30 amino acid epitope (known as “U” region) of rat EGFR-Related Protein (ERRP) fused at the carboxy-terminal end. Four different breast cancer cell lines (MDA-MB-468, SKBr-3, MDA-MB-453 and MDA-MB-231) expressing different levels of EGFR and/or its family members were used. Indeed, the combination of dasatinib and EBIP was more effective in inhibiting growth of these breast cancer cell lines than either agent alone. To evaluate further the efficacy of combination therapy we chose MDA-MB-468 cells, which represent triple negative breast cancer. Triple negative breast cancer is characterized by absence of expression of hormone receptors (estrogen receptor; ER and progesterone receptor; PR) and no amplification of HER2. This kind of cancer comprising 15% of all breast cancers, is more frequent among African-American and BRCA1-mutation carriers and is associated with aggressive histology and poor prognosis. In EGFR overexpressing MDA-MB-468 cells, the combination therapy caused a greater induction of apoptosis by activating caspases −9 and 8 and attenuating EGFR and c-Src signaling. The combination therapy was greatly effective in inhibiting aggressive behavior of MDA-MB-468 as evidenced by (a) decreased extracellular invasion (b) colony formation and (c) tubule formation by endothelial cells. Furthermore, the combination therapy was highly effective in inhibiting the growth of xenografts of MDA-MB-468 cells in SCID mice, which could be attributed to inhibition of proliferation and induction of apoptosis, accompanied by decreased activation of EGFR and c-Src. In conclusion, our data suggest that combination treatment of dasatinib and EBIP that target EGFRs and Src could be a highly effective therapeutic strategy for breast cancer, with particular reference to triple negative breast cancer. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5406.

The combination of raloxifene and epigallocatechin gallate suppresses growth and induces apoptosis in MDA-MB-231 cells

Previous studies have demonstrated that raloxifene induces apoptosis in a variety of cancer cell lines. We aimed to determine if this effect was enhanced by combining raloxifene with epigallocatechin gallate (EGCG). Results demonstrated that EGCG (25 µM) and raloxifene (1–5 µM) produced enhanced cytotoxicity toward MDA-MB-231 breast cancer cells compared to either drug alone following 7 days of treatment. The combination of 5 µM raloxifene and EGCG was the most effective as it decreased cell number by 96% of control, and time-course studies demonstrated that significant cytotoxicity began 36 h after treatment. Potential mechanisms for this effect were then investigated. Flow cytometry experiments demonstrated that apoptosis was significantly increased following 12 h of combination treatment compared to all other treatment groups. A maximal increase in the proportion of cells in the G 1-phase of the cell cycle (116% of control) occurred following 24 h of combination treatment, 12 h after the significant increase in apoptosis, and thus was not considered to be a viable mechanism for the enhancement of apoptosis. While raloxifene was a competitive inhibitor of microsomal UDP-glucuronosyltransferase activity ( K i of 24 µM), it did not decrease the metabolism of EGCG as the rate of disappearance of EGCG from the media was the same for cells treated with either EGCG or EGCG + raloxifene. Finally, the combination treatment reduced the phosphorylation of EGFR and AKT proteins by 21.2 ± 3.3% and 31.5 ± 1.7% from control, respectively. In conclusion, the synergistic cytotoxicity elicited by the combination of EGCG and raloxifene results from an earlier and greater induction of apoptosis. This is likely to be a result of reduced phosphorylation of EGFR and AKT signaling proteins.

Cyclophosphamide-Induced Apoptosis in COV434 Human Granulosa Cells Involves Oxidative Stress and Glutathione Depletion

The anticancer drug cyclophosphamide induces granulosa cell apoptosis and is detoxified by glutathione (GSH) conjugation. We previously showed that both cyclophosphamide treatment and GSH depletion induced granulosa cell apoptosis in rats, but the role of GSH in apoptosis in human ovarian cells has not been studied. Using the COV434 human granulosa cell line, we tested the hypotheses that (1) GSH depletion or treatment with 4-hydroperoxycyclophosphamide (4HC), a preactivated form of cyclophosphamide, induces apoptosis, (2) GSH depletion potentiates 4HC-induced apoptosis, and (3) 4HC-induced apoptosis is mediated by GSH depletion and oxidative stress. Cells were treated with buthionine sulfoximine (BSO), a specific inhibitor of GSH synthesis, with or without follicle stimulating hormone (FSH) or serum. A significant increase in the number of apoptotic cells, assessed by terminal deoxynucleotidyl transferase-mediated deoxy-uridine triphosphate nick-end labeling (TUNEL) and Hoechst 33342 staining, occurred with BSO treatment. Treatment with 4HC dose-dependently induced apoptosis by TUNEL, Hoechst staining, and caspase 3 activation. Treatment with 4HC caused an increase in reactive oxygen species generation, measured by dichlorofluorescein fluorescence, oxidative DNA damage, measured by 8-hydroxyguanosine immunostaining, and an oxidation of the redox potential for the oxidized glutathione/reduced glutathione couple. Total intracellular GSH declined after 4HC treatment, preceding the onset of cell death. Treatment with antioxidants inhibited 4HC-induced apoptosis. Combined treatment with BSO and 4HC caused greater induction of apoptosis than either treatment alone. These findings are consistent with roles for oxidative stress and GSH depletion in mediating the induction of apoptosis in COV434 cells by cyclophosphamide.

Sequential combination of flavopiridol and docetaxel reduces the levels of X-linked inhibitor of apoptosis and AKT proteins and stimulates apoptosis in human LNCaP prostate cancer cells

Clinical trials have shown that chemotherapy with docetaxel combined with prednisone can improve survival of patients with androgen-independent prostate cancer. It is likely that the combination of docetaxel with other novel chemotherapeutic agents would also improve the survival of androgen-independent prostate cancer patients. We investigated whether the combination of docetaxel and flavopiridol, a broad cyclin-dependent kinase inhibitor, can increase apoptotic cell death in prostate cancer cells. Treatment of DU 145 prostate cancer cells with 500 nmol/L flavopiridol and 10 nmol/L docetaxel inhibited apoptosis probably because of their opposing effects on cyclin B1-dependent kinase activity. In contrast, when LNCaP prostate cancer cells were treated with flavopiridol for 24 hours followed by docetaxel for another 24 hours (FD), there was a maximal induction of apoptosis. However, there was greater induction of apoptosis in DU 145 cells when docetaxel was followed by flavopiridol or docetaxel. These findings indicate a heterogeneous response depending on the type of prostate cancer cell. Substantial decreases in X-linked inhibitor of apoptosis (XIAP) protein but not survivin, both being members of the IAP family, were required for FD enhanced apoptosis in LNCaP cells. Androgen ablation in androgen-independent LNCaP cells increased activated AKT and chemoresistance to apoptosis after treatment with FD. The proteasome inhibitor MG-132 blocked FD-mediated reduction of XIAP and AKT and antagonized apoptosis, suggesting that the activation of the proteasome pathway is one of the mechanisms involved. Overall, our data suggest that the docetaxel and flavopiridol combination requires a maximal effect on cyclin B1-dependent kinase activity and a reduction of XIAP and AKT prosurvival proteins for augmentation of apoptosis in LNCaP cells.