Synergistic Cell Death Research Articles

Venetoclax Combined with FLAG-IDA Induction and Consolidation in Newly Diagnosed Acute Myeloid Leukemia

Venetoclax Combined with FLAG-IDA Induction and Consolidation in Newly Diagnosed Acute Myeloid Leukemia

CHI3L1 regulates PD-L1 and anti-CHI3L1-PD-1 antibody elicits synergistic antitumor responses.

Evasion of the immune response is a hallmark of cancer, and programmed cell death 1 (PD-1) and PD-1 ligand 1 (PD-L1) are major mediators of this immunosuppression. Chitinase 3-like 1 (CHI3L1) is induced in many cancers, where it portends a poor prognosis and contributes to tumor metastasis and spread. However, the mechanism(s) that CHI3L1 uses in metastasis have not been defined. Here we demonstrate that CHI3L1 regulates the expression of PD-L1, PD-L2, PD-1, LAG3, and TIM3 and plays a critical role in melanoma progression and lymphatic spread. CHI3L1 also contributed to IFN-γ-stimulated macrophage PD-L1 expression, and RIG-like helicase innate immunity suppressed CHI3L1, PD-L1, and melanoma progression. Individual antibodies against CHI3L1 or PD-1 had discrete antitumor effects and additive antitumor responses in metastasis models and T cell-tumor cell cocultures when administered simultaneously. Synergistic cytotoxic tumor cell death was seen in T cell-tumor cell cocultures, and significantly enhanced antitumor responses were seen in in vivo tumor models treated with bispecific antibodies that simultaneously target CHI3L1 and PD-1. CHI3L1 contributes to tumor progression by stimulating the PD-1/PD-L1 axis and other checkpoint molecules. The simultaneous targeting of CHI3L1 and the PD-1/PD-L1 axis with individual and, more powerfully, with bispecific antibodies represents a promising therapy for pulmonary metastasis and progression.

Quinacrine Has Preferential Anticancer Effects on Mesothelioma Cells With Inactivating NF2 Mutations.

Mesothelioma is a rare cancer with disproportionately higher death rates for shipping and mining populations. These patients have few treatment options, which can be partially attributed to limited chemotherapy responses for tumors. We initially hypothesized that quinacrine could be combined with cisplatin or pemetrexed to synergistically eliminate mesothelioma cells. The combination with cisplatin resulted in synergistic cell death and the combination with pemetrexed was not synergistic, although novel artificially-generated pemetrexed-resistant cells were more sensitive to quinacrine. Unexpectedly, we discovered cells with NF2 mutations were very sensitive to quinacrine. This change of quinacrine sensitivity was confirmed by NF2 ectopic expression and knockdown in NF2 mutant and wildtype cell lines, respectively. There are few common mutations in mesothelioma and inactivating NF2 mutations are present in up to 60% of these tumors. We found quinacrine alters the expression of over 3000 genes in NF2-mutated cells that were significantly different than quinacrine-induced changes in NF2 wildtype cells. Changes to NF2/hippo pathway biomarkers were validated at the mRNA and protein levels. Additionally, quinacrine induces a G1 phase cell cycle arrest in NF2-mutated cells versus the S phase arrest in NF2-wildtype cells. This study suggests quinacrine may have repurposing potential for a large subset of mesothelioma patients.

Synergistic melanoma cell death mediated by inhibition of both MCL1 and BCL2 in high-risk tumors driven by NF1/PTEN loss

Melanomas driven by loss of the NF1 tumor suppressor have a high risk of treatment failure and effective therapies have not been developed. Here we show that loss-of-function mutations of nf1 and pten result in aggressive melanomas in zebrafish, representing the first animal model of NF1-mutant melanomas harboring PTEN loss. MEK or PI3K inhibitors show little activity when given alone due to cross-talk between the pathways, and high toxicity when given together. The mTOR inhibitors, sirolimus, everolimus, and temsirolimus, were the most active single agents tested, potently induced tumor-suppressive autophagy, but not apoptosis. Because addition of the BCL2 inhibitor venetoclax resulted in compensatory upregulation of MCL1, we established a three-drug combination composed of sirolimus, venetoclax, and the MCL1 inhibitor S63845. This well-tolerated drug combination potently and synergistically induces apoptosis in both zebrafish and human NF1/PTEN-deficient melanoma cells, providing preclinical evidence justifying an early-stage clinical trial in patients with NF1/PTEN-deficient melanoma.

Abstract 973: The selective polo-like kinase (Plk1) inhibitor onvansertib and the antiandrogen abiraterone synergistically kill cancer cells through disruption of mitosis independently of androgen receptor signaling

Abstract Abiraterone acetate, a widely-used standard of care for metastatic castrate-resistant prostate cancer (mCRPC), both abrogates androgen synthesis and inhibits the androgen receptor (AR). The AR is a central driver of prostate cancer, and abiraterone slows disease progression in the majority of men, however, extended treatment universally results in acquired resistance. We have observed that Plk1 inhibitors (Plk1i), including the clinically active, highly-selective and orally available Plk1i onvansertib, synergize with abiraterone in models of CRPC, providing a potential means to reverse or delay the onset of abiraterone resistance. Plk1 is a serine/threonine kinase that regulates entry into and progression through mitosis. In contrast to abiraterone, the AR-antagonist enzalutamide does not synergistically kill CRPC cells in combination with Plk1i. Moreover, we have found Plk1i-abiraterone synergy in AR-negative cancer cells demonstrating that this synergy is AR independent. A phase 2 clinical trial (NCT03414034) is currently testing combination of onvansertib and abiraterone in mCRPC patients with nascent abiraterone resistance. Preliminary efficacy, as measured by PSA decline or stabilization, was observed in a subset of patients, including those harboring the AR splice variant 7. To identify the mechanisms driving Plk1i-abiraterone synergy, prostate cancer cell lines showing, or not showing, synergy between these drugs (referred to as synergistic or non-synergistic cells, respectively), were treated with vehicle, abiraterone, enzalutamide, or onvansertib prior to RNA sequencing and Gene Set Variation Analysis (GSVA). In synergistic cells, a group of mitosis and mitotic spindle related gene sets were significantly upregulated by both abiraterone and onvansertib. These gene sets were not upregulated in non-synergistic cells, or by enzalutamide, indicating that abiraterone may target mitosis related genes or processes in an AR-independent manner. Live-cell microscopy showed that, while abiraterone does not cause gross mitotic arrest, it does impair mitotic spindle assembly. These mitotic gene sets were also relatively upregulated in untreated synergistic cells, suggesting that synergistic responses reflect baseline differences in molecular pathways. In summary, we have found that abiraterone impacts spindle assembly and sensitizes some cancer cells to Plk1i resulting in synergistic mitotic arrest and spindle assembly checkpoint dependent cell death. Baseline differences in these processes may predict synergy and be predicative of patient responses to the onvansertib + abiraterone combination. This hypothesis is being evaluated in patients currently enrolled in the clinical study of onvansertib + abiraterone. Citation Format: Jesse C. Patterson, Peter J. Croucher, Maya Ridinger, David J. Einstein, Andreas Varkaris, Steven P. Balk, Glenn J. Bubley, Mark G. Erlander, Michael B. Yaffe. The selective polo-like kinase (Plk1) inhibitor onvansertib and the antiandrogen abiraterone synergistically kill cancer cells through disruption of mitosis independently of androgen receptor signaling [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 973.

Abstract 1398: Impact of proteasome inhibitor specificity and efficacy on apoptosis induction by combination with ABT-199

Abstract Metastatic Soft-Tissue Sarcomas (STS) are a rare and highly heterogeneous group of mesenchymal malignancies that carry a poor prognosis. Therapy is hampered by a limited number of effective treatments, and the almost non-existing long-term survival rate illustrates the need of effective targeted treatment. As a potential approach, we investigated combination of the clinically approved BH3-mimetic drug ABT-199 with different proteasome inhibitors (PIs): Bortezomib, Carfilzomib and Ixazomib, each with proven efficacy, e.g., in multiple myeloma. ABT-199 selectively inhibits the anti-apoptotic protein Bcl-2 while Bortezomib (BOZ) and Ixazomib (IXZ) bind reversible to the β1 and β5 subunits of the 20S proteasome and Carfilzomib (CFZ) irreversibly blocks the subunits β2 and β5. We investigated whether the combination of ABT-199 with CFZ or IXZ shows synergistic activity as recently published for BOZ. SW982 sarcoma cells were cultured with PIs alone or in combination with ABT-199. Cell death was detected by flow cytometric analysis of mitochondrial membrane potential (TMRM) and exposure of phosphatidyl serine (Annexin V). To elucidate potential differences due to specificity of PIs, we analyzed expression of BCL-2 family proteins by Western Blot and performed analogue experiments in knock-out (BAXKO, BAKKO, BOKKO) cell lines. In combination, ABT-199&BOZ or ABT-199&CFZ showed comparable synergistic cell death induction in SW982 while ABT-199&IXZ less efficiently induced cell death. Engineered SW982 knock-out cell lines suggests specific relevance of BOK in IXZ induced apoptosis, whereas all tested PIs crucially depend on BAX for apoptosis induction in combination with ABT-199. Also, as shown for ABT-199&BOZ, both CFZ and IXZ, alone and in combination with ABT-199, efficiently induced expression of NOXA. Strikingly, and in line with augmented cell death induction, ABT-199&CFZ resulted in highest expression of NOXA as compared to BOZ and IXZ. ABT-199&PIs synergistically induce apoptotic cell death in SW982 and corresponding knock-out cell lines with CFZ showing exacerbated expression of NOXA. ABT-199&CFZ also induced strongest stabilization of p53, a transcriptional key regulator of NOXA. We suggest that simultaneous inhibition of anti-apoptotic BCL-2 by ABT-199 and the enhanced expression of NOXA double-hit on the BCL-2 and the MCL-1 signaling axis force the cells over the threshold of apoptosis. Enhanced efficacy of CFZ is dually caused by reduced degradation of NOXA and enhanced stabilization of p53, which in turn transactivates expression of NOXA. In conclusion, PI specificity and efficacy modulate apoptosis induction by combination with ABT-199. Future efforts, e.g. knock-out of relevant BH3-only proteins, will elucidate the observed variable efficacy of these and other PIs for prospective translation in clinical applications. Citation Format: Sandra Weller, Benjamin Schaefer, Tobias Beigl, Kathrin Böpple, Walter E. Aulitzky, Hans-Georg Kopp, Frank Essmann. Impact of proteasome inhibitor specificity and efficacy on apoptosis induction by combination with ABT-199 [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 1398.

Abstract 1946: Synergistic cell death induction in breast cancer cell lines by combining ABT-199 and cisplatin irrespective of estrogen receptor and p53 expression

Abstract 50 Years after the generation of the most studied human breast cancer cell line, MCF-7, many research results fundamentally changed patient outcomes for the better. The mortality of breast cancer in women has decreased significantly, especially in the last 30 years. But the total number of deaths is rising again in the last ten years. Considering that breast cancer is the most common cancer in women and the second most common cancer overall, with incidences of 24,2% and 11,6%, respectively, total numbers of new cases are in the millions every year. First line drugs for the treatment of breast cancer often target microtubules (e.g. Vinblastine and Paclitaxel) or induce DNA damage (e.g. Carboplatin and Cisplatin (CisPt)). In addition to these classic therapeutic drugs new compounds that specifically target cancer-driving molecular alterations have been developed. Among these is the group of BH3-mimetics. The efficacy of several BH3-mimetics is investigated in numerous clinical trials while the BCL-2 specific inhibitor ABT-199 (Venetoclax) is already approved for clinical application in chronic lymphatic leukemia (CLL), acute myeloid leukemia (AML) and small lymphocytic lymphoma (SLL). BH3-mimetics target the apoptosis machinery by interacting with anti-apoptotic Bcl-2 proteins, mimicking the function of pro-apoptotic BH3-only proteins. In turn, the pro-apoptotic potential of pore-forming BCL-2 effectors BAX, BAK and BOK is released inducing mitochondrial outer membrane permeabilization and cell death. Recently we reported synergistic cell death induction by ABT-199 in combination with the proteasome inhibitor Bortezomib (BOZ) in soft tissue sarcoma (STS) cells. ABT-199 and BOZ induce accumulation of BOK and the BH3-only protein NOXA (Muenchow et al. 2020). Here, we combined ABT-199, CisPt and Nutlin-3 in breast cancer cell lines that differ in expression of the estrogen receptor (ER) and p53 activity. Similar to the results in STS cells synergistic induction of apoptotic cell death was observed by FACS analysis of the mitochondrial membrane potential (TMRM) and exposure of phosphatidyl serine (Annexin-V). Western blot analysis revealed that ABT-199 induced accumulation of NOXA and MCL-1, irrespective of the ER status or p53 mutation. Simultaneous treatment with ABT-199 and CisPt or Nutlin-3 further increased expression of NOXA and MCL-1. Interestingly, qRT-PCR revealed enhanced expression of NOXA and MCL-1 mRNA in ABT-199 treated cells indicating transcriptional regulation. However, transcriptional induction of NOXA was also detected independent of p53 activity. Thus, combined therapeutic approaches using CisPt and ABT-199 should be effective irrespective of ER and p53 expression. Nevertheless, in p53 proficient tumors Nutlins might increase therapeutic efficacy. Citation Format: Benjamin Schaefer, Sandra Weller, Tobias Beigl, Kathrin Boepple, Reiner Hoppe, Klaus Schulze-Osthoff, Hans-Georg Kopp, Walter E. Aulitzky, Frank Essmann. Synergistic cell death induction in breast cancer cell lines by combining ABT-199 and cisplatin irrespective of estrogen receptor and p53 expression [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 1946.

Abstract 1060: Combinatorial therapy of imipridones and histone deacetylase inhibitors in Ewing sarcoma cell lines demonstrates synergistic cell death

Abstract Novel therapies are much needed in treating pediatric sarcomas, such as Ewing sarcoma. In the setting of metastatic Ewing sarcoma, survival expectancy ranges around 10%. A novel class of small molecules, imipridones, target G protein-coupled receptors and mitochondrial protease ClpP. Imipridones inactivate cell proliferation kinases Akt/ERK and induce cell death through the pro-apoptotic tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and its receptor DR5. In pre-clinical and clinical trials, imipridone ONC201 shows increased activity against tumors with mutations in histones, specifically histone H3 at the location of lysine 27 (H3K27). Changes in histone acetylation and the epigenetic effects of imipridones remain under investigation. Most commonly caused by a fusion of the EWS-FLI1 genes, Ewing sarcoma exhibits epigenetic modifications with the EWS-FLI1 protein acting as a transcription factor that causes covalent modifications of histone H3, including acetylation and activation of H3K27. Ewing sarcomas have also shown in vitro response to ERK pathway inhibition, leading to apoptosis and inhibition of metastasis formation. We hypothesized that Ewing sarcoma cell lines, with increased H3K27 acetylation due to EWS-FLI1 acting as an activating transcription factor, would respond to the combination of imipridones with histone deacetylase inhibitors. We performed combinatorial drug treatment on Ewing sarcoma cell lines SK-N-MC and RD-ES with 3 imipridones (ONC201, ONC206, and ONC212) and 3 HDAC inhibitors (vorinostat, entinostat, and panobinostat). Cell viability was measured after drug treatment in vitro. We investigated markers of cell death in established pediatric sarcoma cell lines via protein analysis and flow cytometry analysis. Using protein quantification studies and downstream target analysis on combination drug-treated cells, we investigated the mechanisms of how these two targeted therapies interact synergistically to cause cell death. We show that imipridones inactivate cellular proliferation through the Akt/ERK pathway and induce cell death through the TRAIL pathway, with ONC212 exhibiting the highest cell killing potency. Protein quantification by Western blotting revealed treatment with imipridone ONC201 affected the mitochondrial Clp protease complex by decreasing the chaperone subunit ClpX. Cell viability studies and analysis with Compusyn demonstrate potent synergistic effects causing tumor cell death when imipridones are combined with HDAC inhibitors. Our work presents a novel therapeutic combination for the treatment of Ewing sarcoma. Citation Format: Wen-i Chang, Lanlan Zhou, Attila Seyhan, Varun V. Prabhu, Wafik S. El-Deiry. Combinatorial therapy of imipridones and histone deacetylase inhibitors in Ewing sarcoma cell lines demonstrates synergistic cell death [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 1060.

Dual Sphingosine Kinase and Bcl-2 Inhibition Exhibits Synergistic Cell Death in Acute Myeloid Leukemia

Background:Pro-survival Bcl-2 family proteins such as Mcl-1 and Bcl-2 have garnered significant interest as therapeutic targets due to their ability to suppress the apoptotic potential of pro-apoptotic Bax and Bak. In response to cell stress, BH3-only proteins sequester Bcl-2 family members, promoting apoptosis. Small molecule inhibitors such as the Bcl-2 inhibitor Venetoclax have demonstrated poor single agent efficacy in AML. This poor efficacy is a result of AML cells being highly dependent on the pro-survival Bcl-2 family member Mcl-1. Sphingosine kinase 1 (SK1) is a signalling enzyme with established roles in oncogenesis and has recently emerged as a potential therapeutic target in leukaemia. SK1 promotes oncogenic signalling through the production of sphingosine-1-phopshate and subsequent activation of G-protein coupled receptors. In addition, SK1 has been reported to modulate Mcl-1 expression in a number of haematological malignancies including AML. Thus we sought to investigate the efficacy of targeting SK1 to sensitise AML cells to Venetoclax.Results:To determine how SK1 inhibition influences Mcl-1 levels we utilised a short hairpin RNA (shRNA) approach targeting members of the BH3 only protein family (Bid, Bim, Bad, Puma and Noxa). Targeting of Noxa significantly attenuated the cytotoxic effects of the SK1 inhibitor, MP-A08. Immunoprecipitation of Mcl-1 in response to MP-A08 treatment revealed increased association of BH3 only protein, Noxa and ubiquitin-ligase FBW7 suggesting this triggers Mcl-1 degradation in agreeance with previous studies. No interaction was observed between Mcl-1 and Bim further supporting the importance of Noxa in MP-A08 induced Mcl-1 degradation.Canonical pathway analysis of MP-A08 treated cells has previously shown to enrich for genes associated with the unfolded protein response (UPR) (Powell et al. Blood 2017). Western blot analysis recapitulated these findings with activation of the PERK arm, typified by eIF2a phosphorylation and ATF4 upregulation. ATF4 has previously been shown to bind within the Noxa promoter and drive transcription in response to ER stress (Wang et al PNAS 2009). Maintaining global translation with eIF2B agonist, ISRIB blocked Noxa transcription in response to MP-A08 suggesting ATF4 drives Noxa mediated Mcl-1 degradation.Given the Noxa dependent Mcl-1 degradation in response to MP-A08 treatment, we sought to assess the efficacy of combined treatment with the Bcl-2 inhibitor, Venetoclax. Combinational therapies with sub-cytotoxic doses of MP-A08 and Venetoclax induced synergistic cell death in AML cell lines, primary patient AML blasts and leukemic stem and progenitor cells. Synergy could be observed as early as two hours, in agreeance with Noxa upregulation and binding Mcl-1, implicating this as key for synergistic cell death.Conclusions:We have demonstrated SK1 inhibition invokes a pro-apoptotic UPR response via ATF4 driven Noxa upregulation and Mcl-1 degradation. Nullification of the pro-survival function of Mcl-1 by Noxa renders AML cells vulnerable to Bcl-2 targeting strategies such as Venetoclax providing a novel therapeutic angle to enhance patient response to Venetoclax. Current work is underway assessing MP-A08 and Venetoclax using patient-derived xenograft models. DisclosuresNo relevant conflicts of interest to declare.

The Immunomodulatory Drugs, through Loss of Ikaros and Aiolos, Derepress CD38 and Functionally Synergise with Daratumumab

The transcription factors Ikaros (IKZF1) and Aiolos (IKZF3) have recently been found to be targeted for destruction by the immunomodulatory drugs (IMiDs). However, the role of Ikaros and Aiolos and why their loss leads to multiple myeloma (MM) cell death remains unclear. We have used CRISPR-Cas9 genome editing to delete IKZF1 and IKZF3 in human MM cell lines to gain further insight into their downstream gene regulatory networks.Consistent with the action of the IMiDs, loss of either of these genes resulted in both a G1/S cell cycle arrest and induction of apoptosis. This was not dependent on the subsequent reduction of the IRF4-MYC “axis”, as neither IRF4 or MYC were consistently downregulated across all cell lines examined (despite cell death occurring) and overexpression of either factor failed to rescue for Ikaros loss. This led us to further investigate the transcriptional changes resulting from deletion of Ikaros, Aiolos or treatment with the IMiD lenalidomide using RNA-sequencing.Supporting their central role in the action of the IMiDs, significant overlap was seen on loss of Ikaros, Aiolos, or lenalidomide treatment; with loss of Ikaros/Aiolos accounting for approximately 75% of differential gene expression following lenalidomide.Importantly both Ikaros and Aiolos were found to repress the expression of interferon stimulated genes (ISGs) and their loss led to the activation of an interferon-like response, possibly contributing to cell death. In keeping with this, treatment with lenalidomide and low dose IFNb resulted in synergistic cell death. Furthermore, CD38 appeared to be both an ISG and repressed target of Ikaros/Aiolos through their interaction with the nucleosome remodelling and deacetylase complex, and its expression is increased at both mRNA and protein level on their loss. Given recent clinical studies have shown improved outcomes with combination treatment with lenalidomide and the anti-CD38 monoclonal antibody daratumumab, we wondered whether this represented a MM cell intrinsic mechanism explaining this synergy. Consistent with this hypothesis, loss of Ikaros, or treatment with lenalidomide or IFNb led to increased daratumumab induced NK cell mediated antibody-dependent cellular cytotoxicity.These results give further insight into the mechanism of action of the IMiDs, and provide mechanistic rationale for combination with anti-CD38 monoclonal antibodies. DisclosuresFedele:Celgene: Other: Travel grant to attend ASH. Low:Merck: Honoraria.

Inhibition of FLT3-ITD and Melk By Small Molecule Inhibitor OTS167 in FLT3 mutant Acute Myeloid Leukemia (AML)

Background and Rationale: Maternal embryonic leucine zipper kinase (MELK) is a Ser/Thr protein kinase that is aberrantly expressed in many tumor types and demonstrated to be important in formation and maintenance of cancer stem cells. We have previously reported that MELK is also aberrantly expressed in AML cell lines and primary patient leukemia cells and is associated with a poor prognosis (Alachkar et. al., Oncotarget, 2014). MELK knockdown resulted in leukemia cell growth inhibition and apoptosis. Based on these preclinical insights, a small molecule inhibitor of MELK kinase activity, OTS167, (OncoTherapy Sciences, Tokyo, Japan) has been developed and is being tested in an early phase clinical trial in advanced myeloid malignancies at the University of Chicago (IRB#15-1373). Here, we report the activity of MELK signaling blockade in AML with FLT3 mutations, which are associated with drug resistance and poor clinical outcomes, and demonstrate synergy with known FLT3 kinase inhibitors.Methods: Both MELK and FLT3-ITD activity were targeted by treating the human AML cell lines MV4:11, MOLM-13, KOCL-48 and KG-1 which aberrantly express MELK as well as a FLT3-ITD, FLT3-TKD or FLT3-WT with the small molecule MELK inhibitor OTS167 alone or in combination with FLT3 kinase inhibitors Crenolanib or Gilteritinib.Results: OTS167 induced cell death of FLT3 mutant cell lines in a dose dependent manner and with IC50 similar to known FLT3 kinase inhibitors (OTS167 IC50 1.8-18.2nM; Crenolanib IC50 2.31-13.8nM; Gilteritinib IC50 4.9-36.3nM). Using isobologram analysis, OTS167 in combination with either Gilteritinib or Crenolanib induced synergistic cell death in FLT3 mutant leukemia cells at 48hrs (Figure 1A), but not in FLT3-WT leukemia cells. We found that OTS167 alone had the effect of inhibiting auto-phosphorylation of FLT3-ITD, as well as inhibiting MELK activity resulting in downregulation of MELK protein expression. Treatment of cells with 50nM OTS167 resulted in loss of FLT3-ITD (Y591) phosphorylation within 1hr, and total FLT3-ITD protein expression within 24 hours (Figure 1B). Loss of FLT3-ITD protein expression occurred in the presence of FLT3 mRNA and was not due to decreased stability of the protein, as treatment with OTS167 in the presence of cycloheximide did not decrease FLT3-ITD lifespan. Notably, the loss of FLT3-ITD protein expression observed with OTS167 treatment was not observed with the same concentration of FLT3 inhibitors Crenolanib or Gilteritinib. In vitro kinase assays using recombinant FLT3-ITD confirmed that OTS167 could act directly to inhibit FLT3-ITD kinase activity at an IC50 of 4.9nM, compared to a reported MELK IC50 of 0.11-1.1nM (Chung, et. al., Oncotarget, 2012). In MV4:11 cells, the constitutive activation of the MAPK, PI3K, and STAT5 signaling pathways by FLT3-ITD is inhibited by 50nM OTS167, similar to inhibition by 50nM FLT3 inhibitors Crenolanib and Gilteritinib (Figure 1C).In addition, treatment with either OTS167 or FLT3 inhibitor resulted in loss of MYC mRNA and protein expression at 3hr, suggesting that more effective downregulation of MYC expression by the combination may increase the susceptibility of FLT3 mutant AML to apoptosis. The inhibition of FLT3-ITD activation and expression after OTS167 treatment was not observed when MELK protein activity was downregulated using siRNA, suggesting the inhibitor may simultaneously target two independent signaling pathways active in cellular transformation. These results indicate that OTS167 may have a dual specificity in FLT3 mutant AML through targeting both aberrant MELK and FLT3 activity.Conclusion: In summary, the MELK inhibitor, OTS167, may be an attractive therapeutic agent for FLT3 mutant AML, with dual targeting resulting in decreased levels of FLT3-ITD protein and kinase activity. These data provide a rationale for testing dual MELK and FLT3 kinase inhibitors in patients with FLT3 mutant AML. [Display omitted] DisclosuresOdenike:CTI/Baxalta: Membership on an entity's Board of Directors or advisory committees; Jazz: Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Incyte: Membership on an entity's Board of Directors or advisory committees; AbbVie: Honoraria. Stock:Seattle Genetics: Consultancy, Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy; Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees.

1HN, 13C, and 15N backbone resonance assignments of the SET/TAF-1β/I2PP2A oncoprotein (residues 23-225).

SET (TAF-1β/I2PP2A) is a ubiquitously expressed, multifunctional protein that plays a role in regulating diverse cellular processes, including cell cycle progression, migration, apoptosis, transcription, and DNA repair. SET expression is ubiquitous across all cell types. However, it is overexpressed or post-translationally modified in several solid tumors and blood cancers, where expression levels are correlated with worsening clinical outcomes.SET exerts its oncogenic effects primarily through the formation of antagonistic protein complexes with the tumor suppressor, protein phosphatase 2A (PP2A), and the well-known metastasis suppressor, nm23-H1. PP2A inhibition is often observed as a secondary driver of tumorigenesis and metastasis in human cancers. Preclinical studies have shown that the pharmacological reactivation of PP2A combined with potent inhibitors of the primary driver oncogene produces synergistic cell death and decreased drug resistance.Therefore, the development of novel inhibitors of the SET-PP2A interaction presents an attractive approach to reactivation of PP2A, and thereby, tumor suppression. NMR provides a unique platform to investigate protein targets in their natively folded state to identify protein and small-molecule ligands and report on the protein internal dynamics.The backbone 1HN, 13C, and 15N NMR resonance assignments were completed for the 204 amino acid nucleosome assembly protein-1 (NAP-1) domain of the human SET oncoprotein (residues 23-225).These assignments provide a vital first step toward the development of novel PP2A reactivators via SET-selective inhibition.

A phase Ib trial of ERK inhibition with ulixertinib combined with palbociclib in patients (Pts) with advanced solid tumors.

3103 Background: Activating KRAS mutations are the most frequently detected aberrant oncogenes in pancreatic adenocarcinoma. Combination strategies to target the downstream RAF-MEK-ERK effector pathway are a rational approach. Preclinical data with ERK and CDK4/6 inhibition in both pancreatic cancer cell lines and xenografts demonstrates synergistic cell death and tumor growth suppression. Ulixertinib (BVD-523) is an oral small molecule inhibitor of ERK1/2. This phase 1b study evaluated the safety, pharmacokinetics, and early clinical efficacy of ulixertinib when combined with the oral CDK4/6 inhibitor palbociclib in pts with advanced solid tumors. Methods: Using a 3+3 design, pts received ulixertinib at a starting dose of 300mg (range 300-600mg) twice daily continuously with palbociclib at a starting dose of 75mg (range 75-125mg) on D1-21 out of a 28 day cycle. The primary objective was to establish the maximum tolerated dose (MTD) of the combination. Secondary objectives included characterizing safety and estimating progression free survival (PFS). Dose limiting toxicities (DLTs) were evaluated during the first cycle of treatment. Adverse events were graded by CTCAE v4.03. Response was evaluated after 2 cycles (8 weeks) by RECIST 1.1 criteria. Results: 26 pts were enrolled (13 colorectal, 9 pancreas, 2 melanoma, 1 cholangiocarcinoma, 1 GIST); 16 were evaluable for response. The MTD of the combination was ulixertinib 450mg BID and palbociclib 125mg daily. DLTs included grade 3 fatigue, grade 3 acute kidney injury and grade 3 hyponatremia (Table). Due to toxicity in cohort 3, the protocol was amended to include two additional cohorts (2A and 2B) with a reduced dose of ulixertinib and increasing doses of palbociclib. The most common treatment-related adverse events (TRAEs) (all grades) were fatigue (70%), rash (62%) and nausea (54%). The most common laboratory TRAEs were decreased lymphocyte count (77%), decreased WBC count (73%) and anemia (65%). Grade 3 TRAEs were decreased WBC count, decreased lymphocyte count, anemia and fatigue. No grade 4/5 TRAEs were reported. Three pts demonstrated stable disease (SD). For this heavily pre-treated pt population, PFS was 2.05 months (95% CI 1.87, not determined). PK analysis for ulixertinib and palbociclib was linear and consistent with previously reported data; no drug-drug interactions were observed. Conclusions: The MTD of this phase Ib study of advanced solid tumor pts was ulixertinib 450mg BID combined with palbociclib 125 mg daily. At this dosing, 2 pts demonstrated SD, one with pancreatic cancer and one with cholangiocarcinoma. An expansion cohort of metastatic pancreatic cancer pts is ongoing. Clinical trial information: NCT03454035. [Table: see text]

Mitochondrial dysfunction induced by callyspongiolide promotes autophagy-dependent cell death

Callyspongiolide is a marine macrolide known to induce caspase-independent cancer cell death. While its toxic effects have been known, the mechanism leading to cell death is yet to be identified. We report that Callyspongiolide R form at C-21 (cally2R) causes mitochondrial dysfunction by inhibiting mitochondrial complex I or II, leading to a disruption of mitochondrial membrane potential and a deprivation of cellular energy. Subsequently, we observed, using electron microscopy, a drastic formation of autophagosome and mitophagy. Supporting these data, LC3, an autophagosome marker, was shown to co-localize with LAMP2, a lysosomal protein, showing autolysosome formation. RNA sequencing results indicated the induction of hypoxia and blocking of EGF-dependent pathways, which could be caused by induction of autophagy. Furthermore, mTOR and AKT pathways preventing autophagy were repressed while AMPK was upregulated, supporting autophagosome progress. Finally, the combination of cally2R with known anti-cancer drugs, such as gefitinib, sorafenib, and rapamycin, led to synergistic cell death, implicating potential therapeutic applications of callyspongiolide for future treatments.

Synergistic Effects of TW-37 and ABT-263 on Renal Cell Carcinoma Cells.

BackgroundRenal cell carcinoma (RCC) is a common urological system malignancy lack of effective therapeutic options. Upregulation of the Bcl-2 proteins was correlated with poor prognosis of RCC, suggesting that BH-3 mimetics may be a promising treatment option. ABT-263 is a BH3 mimetic that possesses anti-tumor effects. TW-37 is another inhibitor of Bcl-2 family protein with potential anti-tumor activities. However, since their effect as single agent is limited, combination treatment represents a strategy to improve the efficiency. We studied the ABT-263 in combination with TW-37 and analyzed the molecular mechanisms of action in RCC cells.MethodsMTT and colony formation assays were used to measure the proliferation of RCC cells. Transwell assay was used to assay the migration and invasion of RCC cells. Cell cycle distribution and apoptosis were measured using the flow cytometry and apoptotic nucleosome assay, respectively. Western blotting was performed to measure the change of proteins. The anti-tumor effects of ABT-263, TW-37 and their combination were also evaluated in vivo.ResultsCotreatment of TW-37 and ABT-263 synergistically repressed the proliferation of RCC cells. TW-37 and ABT-263 also synergistically inhibited the migration and invasion of RCC cells It was also showed that TW-37 and ABT-263 synergistically induced cell cycle arrest at the G2/M phase. Furthermore, increased apoptosis was observed after exposure to TW-37 and ABT-263. Mechanism investigation showed that TW-37 and ABT-263 synergistically induced apoptosis via the mitochondrial pathway and relied on the activation of Bax and caspases. Furthermore, ERK signaling pathway activation was detected after treated with TW-37 and ABT-263. Finally, TW-37 and ABT-263 also synergistically repressed the growth of RCC cells in xenograft mice.ConclusionIn summary, our data demonstrated that combined treatment with TW-37 and ABT-263 exhibited synergistic RCC cell death and this combination may be applied as an effective therapeutic strategy against RCC.

Metabolic compensation activates pro-survival mTORC1 signaling upon 3-phosphoglycerate dehydrogenase inhibition in osteosarcoma

SUMMARYOsteosarcoma is the most common pediatric and adult primary malignant bone cancer. Curative regimens target the folate pathway, downstream of serine metabolism, with high-dose methotrexate. Here, the rate-limiting enzyme in the biosynthesis of serine from glucose, 3-phosphoglycerate dehydrogenase (PHGDH), is examined, and an inverse correlation between PHGDH expression and relapse-free and overall survival in osteosarcoma patients is found. PHGDH inhibition in osteosarcoma cell lines attenuated cellular proliferation without causing cell death, prompting a robust metabolic analysis to characterize pro-survival compensation. Using metabolomic and lipidomic profiling, cellular response to PHGDH inhibition is identified as accumulation of unsaturated lipids, branched chain amino acids, and methionine cycle intermediates, leading to activation of pro-survival mammalian target of rapamycin complex 1 (mTORC1) signaling. Increased mTORC1 activation sensitizes cells to mTORC1 pathway inhibition, resulting in significant, synergistic cell death in vitro and in vivo. Identifying a therapeutic combination for PHGDH-high cancers offers preclinical justification for a dual metabolism-based combination therapy for osteosarcoma.

Crizotinib Prodrug Micelles Co-Delivered Doxorubicin Synergistic Immunogenic Cell Death Induction for Chemo-Immunotherapy on Breast Cancer

Crizotinib Prodrug Micelles Co-Delivered Doxorubicin Synergistic Immunogenic Cell Death Induction for Chemo-Immunotherapy on Breast Cancer

A thiol‐bound drug reservoir enhances APR‐246‐induced mutant p53 tumor cell death

The tumor suppressor gene TP53 is the most frequently mutated gene in cancer. The compound APR‐246 (PRIMA‐1Met/Eprenetapopt) is converted to methylene quinuclidinone (MQ) that targets mutant p53 protein and perturbs cellular antioxidant balance. APR‐246 is currently tested in a phase III clinical trial in myelodysplastic syndrome (MDS). By in vitro, ex vivo, and in vivo models, we show that combined treatment with APR‐246 and inhibitors of efflux pump MRP1/ABCC1 results in synergistic tumor cell death, which is more pronounced in TP53 mutant cells. This is associated with altered cellular thiol status and increased intracellular glutathione‐conjugated MQ (GS‐MQ). Due to the reversibility of MQ conjugation, GS‐MQ forms an intracellular drug reservoir that increases availability of MQ for targeting mutant p53. Our study shows that redox homeostasis is a critical determinant of the response to mutant p53‐targeted cancer therapy.

Melphalan and Exportin 1 Inhibitors Exert Synergistic Antitumor Effects in Preclinical Models of Human Multiple Myeloma.

High-dose chemotherapy with melphalan followed by autologous transplantation is a first-line treatment for multiple myeloma. Here, we present preclinical evidence that this treatment may be significantly improved by the addition of exportin 1 inhibitors (XPO1i). The XPO1i selinexor, eltanexor, and KOS-2464 sensitized human multiple myeloma cells to melphalan. Human 8226 and U266 multiple myeloma cell lines and melphalan-resistant cell lines (8226-LR5 and U266-LR6) were highly sensitized to melphalan by XPO1i. Multiple myeloma cells from newly diagnosed and relapsed/refractory multiple myeloma patients were also sensitized by XPO1i to melphalan. In NOD/SCIDγ mice challenged with either parental 8226 or U266 multiple myeloma and melphalan-resistant multiple myeloma tumors, XPO1i/melphalan combination treatments demonstrated stronger synergistic antitumor effects than single-agent melphalan with minimal toxicity. Synergistic cell death resulted from increased XPO1i/melphalan-induced DNA damage in a dose-dependent manner and decreased DNA repair. In addition, repair of melphalan-induced DNA damage was inhibited by selinexor, which decreased melphalan-induced monoubiquitination of FANCD2 in multiple myeloma cells. Knockdown of FANCD2 was found to replicate the effect of selinexor when used with melphalan, increasing DNA damage (γH2AX) by inhibiting DNA repair. Thus, combination therapies that include selinexor or eltanexor with melphalan may have the potential to improve treatment outcomes of multiple myeloma in melphalan-resistant and newly diagnosed patients. The combination of selinexor and melphalan is currently being investigated in the context of high-dose chemotherapy and autologous transplant (NCT02780609). SIGNIFICANCE: Inhibition of exportin 1 with selinexor synergistically sensitizes human multiple myeloma to melphalan by inhibiting Fanconi anemia pathway-mediated DNA repair.

Abstract PO-035: Overcoming adaptive resistance to mutant KRAS and MEK inhibitors by co-targeting mTORC1/2 in pancreatic cancer

Abstract Activating KRAS mutations are found in over 90% of pancreatic ductal adenocarcinomas (PDAC), yet KRAS has remained a difficult target to inhibit pharmacologically. While mutant KRAS-specific inhibitors have recently been developed, there is increasing awareness that adaptive resistance to these inhibitors limits their efficacy as single agents. Here, we demonstrate, using several human and mouse models of PDAC, rapid acquisition of tumor resistance in response to genetic or pharmacologic targeting of KRAS or MEK, associated with increased phosphorylation of Akt and Rictor, in an ILK-dependent manner. While pharmacologic inhibition ofmTORC1/2 results in a compensatory increase in ERK phosphorylation, combinatorial treatment of PDAC cells with either KRAS or MEK inhibitors together with mTORC1/2 inhibitors results in synergistic cytotoxicity and cell death reflected by sustained inhibition of p-ERK and p-Rictor/p-Akt, and of downstream regulators of protein synthesis and cell survival. Importantly, relative to single agents alone, this combination leads to significant inhibition of tumor growth in vivo, including durable tumor regressions and increased survival. We have identified a highly effective combinatorial treatment strategy, using clinically viable inhibitors, which can be applied to PDAC tumors with different KRAS mutations. Citation Format: Wells Brown, Paul McDonald, Shoukat Dedhar. Overcoming adaptive resistance to mutant KRAS and MEK inhibitors by co-targeting mTORC1/2 in pancreatic cancer [abstract]. In: Proceedings of the AACR Virtual Special Conference on Pancreatic Cancer; 2020 Sep 29-30. Philadelphia (PA): AACR; Cancer Res 2020;80(22 Suppl):Abstract nr PO-035.