bluuebunny/crossref_metadata_2025 huggingface dataset:
Abstract 1737: Efficacy of immunotherapy is attenuated with age in triple-negative breast cancer
Authors: McAllister Sandra S. , Sceneay Jaclyn , Laszewski Tyler , DeCristo Molly , Ubellacker Jessalyn , Wilson Kristin , Qin Yuanbo , Hutchinson John
Published: August 2018

Age is associated with increasing immune dysfunction that includes significant changes to both the innate and adaptive immune responses. These age-related changes could present limitations to the application of immunotherapy in breast cancer, as over 50% of patients are over 60 years old at diagnosis. Triple-negative breast cancer (TNBC) is one of the most aggressive subtypes of breast cancer, but remains the only subtype that lacks any type of targeted therapy. Early results from clinical trials of anti-PD-1 therapy in metastatic TNBC patients have shown promise, with approximately 20% of patients demonstrating a partial or complete response. While TNBC incidence is similar in young and old patients, differences in disease progression and outcome with age suggest that treatment needs to be tailored to both age as well as breast cancer subtype. It is not known whether age impacts response to immunotherapy, particularly checkpoint blockade, in breast cancer. Using multiple preclinical models of age-dependent TNBC, we found that aged mice had significantly reduced ability to respond to either anti-PD-L1 or anti-CTLA4. Old mice showed decreased numbers of circulating CD4-positive and CD8-positive T cells, as well as NK cells. Furthermore, PD-1 expression was increased on these populations relative to young mice, suggesting increased immune cell exhaustion with age. The old mice also demonstrated increased central and effector memory T cells, but decreased naive T cells compared to young mice, consistent with reports from clinical studies of aged individuals. These findings suggest decreased ability to respond to neoantigens with age. Importantly, using high-content flow cytometric analyses and RNA-seq, we defined cellular and molecular mechanisms that correlate with response in young mice that are attenuated or lacking in old mice. Many of the differentially expressed genes that defined response to anti-CTLA4 in young mice and resistance to treatment in the old mice were also predictors of response to immunotherapy in cancer patients. Our data suggested novel combination therapies that, when combined with checkpoint blockade, improved responses and survival in old mice with TNBC. Our findings should suggest age-stratified treatments to ensure that TNBC patients see the most benefit possible and prevent overtreatment with futile and harsh chemotherapies.

Citation Format: Sandra S. McAllister, Jaclyn Sceneay, Tyler Laszewski, Molly DeCristo, Jessalyn Ubellacker, Kristin Wilson, Yuanbo Qin, John Hutchinson. Efficacy of immunotherapy is attenuated with age in triple-negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1737.
Abstract 1750: Inducing therapeutic lymphangiogenesis for potentiating cancer immunotherapy in melanoma
Authors: Potin Lambert , Maillat Lea , Briquez Priscilla S. , Hubbell Jeffrey A. , Swartz Melody A.
Published: August 2018

Tumor-associated lymphangiogenesis is well known to promote metastasis and to correlate with poor prognosis in melanoma and other cancers, yet its functional roles in antitumor immunity had remained largely unexplored. In a recent study, we investigated the role of the vascular endothelial growth factor C (VEGF-C)—the main driver of lymphangiogenesis—in regulating antitumor immune response. We showed that in the B16 F10 injectable melanoma model, VEGF-C inhibition prevented T cells from infiltrating the tumor and reduced the efficacy of immunotherapies. Here, we sought to extend this concept to exploit the immunologic benefits of VEGF-C for therapeutic applications. We engineered a VEGF-C variant with an extracellular matrix-binding domain (MB-VEGF-C) allowing retention into the microenvironment after intratumoral injection. MB-VEGF-C induced increased lymphatic vasculature in tumors without reducing tumor growth rate. In an autochthonous melanoma model with reduced immune infiltrates, MB-VEGF-C intratumoral injections promoted the infiltration of cross-presenting DCs, as well as CD8+ and CD4+ T cells. Crucially, in these tumors that are normally unresponsive to immune checkpoint blockade (ICB), we could restore the responsiveness to ICB by delivering MB-VEGF-C together with immune adjuvants. Taken together, our findings suggest that VEGF-C and tumor-associated lymphangiogenesis, albeit promoting metastasis, can also be exploited to promote a T cell-inflamed microenvironment and to subsequently potentiate immunotherapies.

Citation Format: Lambert Potin, Lea Maillat, Priscilla S. Briquez, Jeffrey A. Hubbell, Melody A. Swartz. Inducing therapeutic lymphangiogenesis for potentiating cancer immunotherapy in melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1750.
Abstract 1763: BiTEs vs CAR-Ts: Preclinical targeting of CD133+ brain tumor initiating cells using immunotherapy-based treatment strategies
Authors: Vora Parvez , Adams Jarrett , Singh Mohini , Venugopal Chitra , Tatari Nazanin , Chokshi Chirayu , Qazi Maleeha , Salim Sabra , Mahendram Sujeivan , Bakhshinyan David , London Max , Savage Neil , Subapanditha Minomi , McFarlane Nicole , Pan James , Bramson Jonathan , Sidhu Sachdev , Moffat Jason , Singh Sheila
Published: August 2018

Glioblastoma (GBM) is a uniformly fatal primary brain tumor, characterized by extensive cellular heterogeneity. Numerous studies have implicated CD133+ brain tumor initiating cells (BTICs) as drivers of chemo- and radio-resistance in GBM. We have recently demonstrated that a CD133-driven gene signature is predictive of poor overall survival and targeting CD133+ treatment-refractory cells may be an effective strategy to block GBM recurrence.

Bispecific T-Cell engaging antibodies (BiTEs) and Chimeric antigen receptors (CARs) present promising immunotherapeutic approaches that have not yet been validated for recurrent GBM. Using CellectSeq, a novel methodology that combines the use of phage-displayed synthetic antibody libraries and DNA sequencing, we developed the CD133-specific monoclonal antibody ‘RW03'. We constructed CD133-specific BiTEs that consist of two arms; one recognizes the tumor antigen (CD133) and the second is specific to the CD3 antigen that binds to human GBMs and PBMC-derived T cells, respectively. We observed BiTEs redirecting T cells to kill GBMs, with greater efficiency observed in CD133high GBMs, validating BiTE target specificity. Incubating T-cells with BiTEs and the CD133high GBMs resulted in increased expression of T cell activation markers. In parallel, we derived the single chain variable fragment (scFv) from RW03 we engineered a second-generation CAR T cell. CD133-specific CAR-T cells were cytotoxic to CD133+ GBMs. Co-culturing CD133 CAR-T cells with GBMs triggered T cell activation and proliferation. Treatment of GBM tumor-bearing mice with CD133-specific CAR-T cells yielded extended survival in mice and significant reductions in brain tumor burden.

Furthermore, we uniquely adapted the existing chemoradiotherapy protocol for GBM patients for treatment of immunocompromised mice engrafted with human GBMs. Within this model, we have initiated treatment of recurrent GBM directed against CD133+ BTICs, to allow for a direct prospective comparison of toxicity and efficacy of BiTEs and CAR-T cell strategies.

Citation Format: Parvez Vora, Jarrett Adams, Mohini Singh, Chitra Venugopal, Nazanin Tatari, Chirayu Chokshi, Maleeha Qazi, Sabra Salim, Sujeivan Mahendram, David Bakhshinyan, Max London, Neil Savage, Minomi Subapanditha, Nicole McFarlane, James Pan, Jonathan Bramson, Sachdev Sidhu, Jason Moffat, Sheila Singh. BiTEs vs CAR-Ts: Preclinical targeting of CD133+ brain tumor initiating cells using immunotherapy-based treatment strategies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1763.
Abstract 1767: Synergy between intratumoral immunotoxin and systemic anti-CTLA-4 promotes massive inflammation and leads to complete regression of tumors in mice
Authors: Leshem Yasmin , O'Brien James , Reiter Yoram , Pastan Ira
Published: August 2018

Background: The immunotoxin SS1P consists of an anti-mesothelin Fv attached to Pseudomonas exotoxin A and kills tumor cells by inhibiting protein synthesis. Because of its unique mechanism of cell killing and unlike other anti-cancer drugs, SS1P does not suppress the immune system. Here we determined if SS1P can cooperate with anti-CTLA-4 to induce anti-tumor immunity and cause tumor regression.

Methods: A BALB/c breast cancer cell line was transfected with human mesothelin (66C14-M) and implanted in two different locations. SS1P was injected directly into one tumor and anti-CTLA-4 given IP. Twelve days after treatment initiation, the tumors were harvested and evaluated for immune related gene expression by Nanostring Technologies. A portion of each tumor was sent to pathology and stained for CD8.

Results: In mice treated with anti-CTLA-4 and SS1P, complete tumor regressions occurred in 25/30 (86%) SS1P injected tumors and in 16/30 (53%) tumors at the un-injected location. No complete regressions occurred with either drug given separately. This indicates that the combination therapy has a synergistic and systemic anti-tumor effect. Pathological evaluation of injected tumors from combination-treated mice revealed large central abscesses surrounded by a collar of inflammation, containing a mixture of lymphocytes and mononuclear cells. The collar of inflammation was unique to the combination treated mice. Only very small abscesses were observed in tumors from control mice. Immunohistochemistry of tumors from mice treated with SS1P and anti-CTLA-4 showed an increase in CD8+ cells located mainly in the inflammation collar. Analysis of gene expression in tumors from combination-treated mice, compared to PBS-treated tumors, showed that 341/747 (45%) immune transcripts were elevated by 2-fold or more including CD8a, PDL2 and CD56 (8, 15 and 24-fold, respectively). In mice treated with anti-CTLA-4 and PBS, the increase of transcripts was lower: 127/747 (17%) genes. Only 18 out of 747 transcripts (2%) were elevated in the SS1P-treated tumors. This suggests that SS1P by itself does not initiate an inflammatory process. However, SS1P greatly potentiates the inflammatory process initiated by anti-CTLA-4.

Conclusions: Combining local SS1P with anti-CTLA-4 promotes massive inflammation that cures injected and un-injected tumors and provides a strong rational to explore this combination therapy in patients.

Citation Format: Yasmin Leshem, James O'Brien, Yoram Reiter, Ira Pastan. Synergy between intratumoral immunotoxin and systemic anti-CTLA-4 promotes massive inflammation and leads to complete regression of tumors in mice [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1767.
Abstract 1791: Evolutionary dynamics of non-Hodgkin's lymphoma CAR T cell therapy
Authors: Altrock Philipp M. , Kimmel Gregory , Locke Frederick L.
Published: August 2018

Non-Hodgkin Lymphoma (NHL) is the most common hematologic malignancy in the United States with an estimated 72,000 new cases (4.3% of all cancer cases) and 20,000 deaths (3.4% of all cancer deaths) in 2017; the median 5-year survival rate is 71%. Despite a possible cure, with front-line chemotherapy, there exist patients that do not response or relapse and develop refractory disease. These patients have a median overall survival of less than seven months. Chimeric antigen receptor (CAR) T-cell therapy for refractory NHL relies on expansion of engineered T- cells that specifically target tumor cells expressing CD19. Here we combine mathematical modeling with statistical data-analysis based on recent results of clinical studies of CAR T-cell dynamics in individual patients. We use statistical and mathematical modeling to elucidate the key mechanisms that drive evolutionary dynamics of anti-CD19 CAR T-cell therapy. To this end, we integrate patient specific tumor burden profiles, inflammatory cytokine profiles, and CAR T cell population dynamics into our model. We find that the success of therapy may depend on dynamic regulation of inflammatory cytokines in the tumor microenvironment, as well as on specific properties of the heterogeneous CAR T-cell population. Relative abundances of juvenile and effector T cells are key factors that drive the duration of treatment response, and the tumor-killing rate of this CD19-specific immunotherapy. Our modeling framework elucidates disease and treatment specific eco-evolutionary dynamical properties, but can also quantify genetically engineered T-cell population properties related to neurological toxicity and long-term homeostatic mechanisms that determine patient survival.

Citation Format: Philipp M. Altrock, Gregory Kimmel, Frederick L. Locke. Evolutionary dynamics of non-Hodgkin's lymphoma CAR T cell therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1791.
Abstract 1808: The anti-estrogen endoxifen altered bone morphology and reduced muscle function in mice
Authors: Wright Laura , Mohammad Khalid , Guise Theresa
Published: August 2018

Endoxifen, the predominant CYP2D6 metabolite of the selective estrogen receptor modulator (SERM) tamoxifen, is currently being developed as a novel anti-estrogen therapy for the treatment of estrogen receptor (ER)+ breast cancer. Genetic polymorphism of CYP2D6 is a predictor of response to tamoxifen in patients, implicating endoxifen as one of the most active and relevant tamoxifen metabolites. Breast cancer patients treated with adjuvant endocrine therapies including aromatase inhibitors (AIs) and SERMs often report unmanageable musculoskeletal toxicities that can result in treatment discontinuation. While ER binding affinity and anti-tumor effects have been established in preclinical models, the effects of endoxifen on the musculoskeletal system are not fully known. Twenty-week female C57BL/6 mice underwent sham surgery or ovariectomy (OVX) and were treated daily with vehicle, the AI letrozole, or the SERM endoxifen. Body composition was assessed prospectively by DXA. Bone indices and marrow adipose tissue volume were measured by μCT and muscle contractility of the extensor digitorum longus (EDL) was measured ex vivo. After eight weeks, trabecular bone volume fraction (BV/TV) decreased by 50% in OVX-vehicle and OVX-letrozole mice, whereas BV/TV increased threefold in endoxifen mice relative to sham-vehicle. Despite the presence of significantly more trabecular bone following endoxifen treatment, cortical bone analyses revealed impaired periosteal and endosteal expansion of bone, resulting in reduced polar moment of inertia, which is a measure of resistance to fracture. Uterine weight increased significantly in endoxifen-treated mice relative to all OVX groups, similar to what is observed with tamoxifen treatment. Peripheral body fat, bone marrow adipose tissue, and circulating leptin were reduced by endoxifen, suggesting that the drug may elicit positive systemic metabolic effects. At the termination of the study, muscle-specific force was reduced in OVX-endoxifen mice relative to sham-vehicle, OVX-vehicle, and OVX-AI mice, despite no change in muscle mass. While endoxifen shows promise as a potent anti-estrogen therapy for the treatment of ER+ breast cancer, it may be important to monitor patients for endometrial proliferation, morphological changes in bone that increase fracture risk, and for musculoskeletal side effects that could reduce drug compliance.

Citation Format: Laura Wright, Khalid Mohammad, Theresa Guise. The anti-estrogen endoxifen altered bone morphology and reduced muscle function in mice [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1808.
Abstract 1810: Stapled peptide inhibitors of mutant estrogen receptor/coactivator interactions
Authors: Speltz Thomas E. , Danes Jeanne M. , Fanning Sean W. , Mayne Christopher G. , Tajkhorshid Emad , Greene Geoffrey L. , Frasor Jonna M. , Moore Terry W.
Published: August 2018

A current limitation in treating estrogen receptor-positive breast cancer is the development of resistance to endocrine therapy. Among the many possible mechanisms of resistance, mutations in the estrogen receptor ligand binding domain have been recently shown to be a contributing factor. Specifically, estrogen receptor mutations Y537S and D538G have been reported to contribute to resistance by decreasing the efficacy of the clinically used drug tamoxifen. A standing hypothesis in estrogen receptor pharmacology is that coactivator binding inhibitors can be used in place of traditional endocrine therapy to block cellular proliferation mediated by estrogen receptor. To validate the coactivator binding inhibitor hypothesis within a cellular context, we have prepared cell-permeable stapled peptides to function as inhibitors of the estrogen receptor/steroid receptor coactivator interaction in both wild-type and mutant estrogen receptors. Guided by x-ray crystallography, we have applied molecular dynamics and structure-based rational design to develop stapled peptides with high affinity for the estrogen receptor. In targeting the wild-type receptor, we have found that stapled peptides mimicking steroid receptor coactivators have even higher affinity against mutant receptors Y537S and D538G. In addition to inhibiting the estrogen receptor/coactivator interaction in biochemical assays, we find inhibition of estrogen receptor function within multiple breast cancer cell lines. The stapled peptides reported in this research support the coactivator binding inhibitor hypothesis and shed light on estrogen receptor coactivator interactions in cells expressing both wild-type and mutant receptors.

Citation Format: Thomas E. Speltz, Jeanne M. Danes, Sean W. Fanning, Christopher G. Mayne, Emad Tajkhorshid, Geoffrey L. Greene, Jonna M. Frasor, Terry W. Moore. Stapled peptide inhibitors of mutant estrogen receptor/coactivator interactions [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1810.
Abstract 1813: The role of androgen receptor variant AR-V9 in prostate cancer
Authors: Ho Yeung , Etten Jamie L. Van , Henzler Christine , Li Yingming , Yang Rendong , Tseng Elizabeth , Hon Ting , Clark Tyson , Dehm Scott M.
Published: August 2018

The expression of androgen receptor (AR) variants is a frequent, yet poorly-understood mechanism of clinical resistance to AR-targeted therapy for castration-resistant prostate cancer (CRPC). Among the multiple AR variants expressed in CRPC, AR-V7 is considered the most clinically-relevant AR variant due to broad expression in CRPC, correlations of AR-V7 expression with clinical resistance, and growth inhibition when AR-V7 is knocked down in CRPC models. Therefore, efforts are under way to develop strategies for monitoring and inhibiting AR-V7 in castration-resistant prostate cancer (CRPC). The aim of this study was to understand whether other AR variants are co-expressed with AR-V7 and promote resistance to AR-targeted therapies. To test this, we utilized RNA-seq to characterize AR expression in CRPC models. RNA-seq revealed the frequent coexpression of AR-V9 and AR-V7 in multiple CRPC models and metastases. Furthermore, long-read single-molecule real-time (SMRT) sequencing of AR isoforms revealed that AR-V7 and AR-V9 shared a common 3'terminal cryptic exon. To test this, we knocked down AR-V7 in prostate cancer cell lines and confirmed that AR-V9 mRNA and protein expression were also impacted. In reporter assays with AR-responsive promoters, AR-V9 functioned as a constitutive activator of androgen/AR signaling. Similarly, infection of AR-V9 lentiviral construct in LNCaP cells induced androgen-independent cell proliferation. In conclusion, these data implicate co-expression of AR-V9 with AR-V7 as an important component of constitutive AR signaling and therapeutic resistance in CRPC.

Citation Format: Yeung Ho, Jamie L. Van Etten, Christine Henzler, Yingming Li, Rendong Yang, Elizabeth Tseng, Ting Hon, Tyson Clark, Scott M. Dehm. The role of androgen receptor variant AR-V9 in prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1813.
Abstract 1817: Establishment and characterization of non-small cell lung cancer cell line variants selected for resistance to osimertinib
Authors: Ferguson Peter J. , Vincent Mark D. , Koropatnick James
Published: August 2018

Many non-small cell lung cancers (NSCLC) are oncogenically driven by mutant epidermal growth factor receptor (EGFR). EGFR tyrosine kinase inhibitors (TKIs) are commonly used as a first-line treatment against such tumors, but NSCLC tumors often recur with a mutant EGFR (often with a T790M mutation in exon 20) that confers resistance to these drugs [Ther Adv Respir Dis 10(6): 549-565, 2016]. Third generation EGFR TKIs (e.g., osimertinib) have been designed that are highly active aganst both T790M EGFR and the original non-T790M-mutated, oncogenic EGFR. Clinical resistance to third generation TKIs has been observed, but model systems in which to study the mechanisms of resistance are few. The human NSCLC cell line H1975, derived from an EGFR-TKI-resistant tumor, contains EGFR mutations T790M and L858R (exon 21). To explore mechanisms mediating resistance to third generation TKIs, we selected variants of the H1975 cell line for resistance to osimertinib to create models in which mechanisms of resistance can be characterized and tested for potential methods to overcome that resistance. Cells were exposed continuously to a single concentration of osimertinib, in some cases with the inclusion of verapamil to avoid possible selection of multidrug resistant cells. After 4 weeks, with weekly changes of drug-medium, clonal cell lines were selected in the presence of 6 and 10 μM osimertinib (one each) or in 5 μM osimertinib plus 10 μM verapamil (3 cell lines). These clonal lines were, respectively, 90-, 95-, 38-, 227-, and 244-fold resistant to osimertinib. The RAD51 inhibitor 2-(benzylsulfonyl)-1-(1H-indol-3-yl)-1,2-dihydroisoquinoline (IBR2), which enhances cytotoxicity of several EGFR inhibitors against numerous cell lines (Ferguson et al., JPET 2017, doi.org/10.1124/jpet.117.241661), decreased osimertinib-resistance by up to 80% in these cell lines. Sequence analysis indicates that cell line H1975/osi-6b retained the same EGFR sequence as that in the parent cell line. H1975/osi-5b/VPL appears to have undergone epithelial-to-mesenchymal transition. Further analyses of the resistant cell lines are being undertaken. These cell lines are a valuable resource in which to test methods to circumvent resistance to third generation EGFR TKIs.

Citation Format: Peter J. Ferguson, Mark D. Vincent, James Koropatnick. Establishment and characterization of non-small cell lung cancer cell line variants selected for resistance to osimertinib [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1817.
Abstract 1819: Acquired T790M mutation after first generation EGFR tyrosine kinase retreatment
Authors: Lee Sung Yong , OH Jee Youn , Shim Jae Jeong , Kang Kyung Ho , Min Kyung Hoon
Published: August 2018

Introduction The first or second generation EGFR TKI drugs showed good overall response and progression free survival rates in EGFR mutation positive patients. However, most of them progress within 12 months from treatment start due to acquired resistance. In clinical practice, many physicians frequently offer these patients retreatment with EGFR TKIs after a chemotherapy break, because EGFR TKI retreatment can reduce the regrowing EGFR TKI sensitive clones. We evaluated induction of T790M mutation in previously sensitive EGFR mutation positive cancer patients that repeatedly treated EGFR TKIs. Method We reviewed the medical records of patients who were rechallenged with first generation EGFR TKIs. Those patients were previously responded to gefitinib or erlotinib and progressed after several chemotherapies. We analyzed the clincopathological characteristics, treatment modality and their outcome, and development of T790M mutation. EGFR mutations in exons 18, 19, 20, and 21 were evaluated with PNA mediated PCR clamping method. Results Three patients showed acquired T790M mutation after first generation EGFR TKIs retreatment. The acquired T790M mutation was detected in the tumor tissue in two patients and in the bronchoalveolar lavage fluid in the other patient. Three patients were taking osimertinib or olmutinib, two patients showed good clinical efficacy and low adverse events, however the other patient showed serious adverse event (interstitial lung disease). Conclusions Re-treatment with first generation EGFR TKIs after drug holiday in sensitizing EGFR mutant patients are considered to be an effective option, because EGFR TKI retreatment can reduce the regrowing EGFR TKI sensitive clones. Moreover, retreatment of first generation EGFR TKI may also induce or expand EGFR TKI resistance by T790M mutation and it could be treated with third generation EGFR TKI.

Citation Format: Sung Yong Lee, Jee Youn OH, Jae Jeong Shim, Kyung Ho Kang, Kyung Hoon Min. Acquired T790M mutation after first generation EGFR tyrosine kinase retreatment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1819.
Abstract 1825: PIK3CA E542K mutation in bladder cancer confers resistance to PI3K targeted therapy but synergy with BET inhibition
Authors: Elbanna May Faek , Damayanti Nur , Chintala Sreenivasulu , Pili Roberto
Published: August 2018

Background: We have previously reported that two bladder cancer PDX models that carry distinct PIK3CA helical domain (HD) mutations respond differently to dual PI3K/mTOR inhibitor (LY3023414), where one model is sensitive (RP-B-02, PIK3CA E545K MUT) while the other is resistant (PIK3CA, E542K MUT) (Wei L et al Oncotarget 2016). Thus, we transduced these mutations in isogeneic cells to determine whether each mutation is indeed associated with a distinct oncogenic potential, as well as differential therapeutic response. Subsequently, we tested rational drug combinations capable of overriding resistance to PI3K targeted therapy (i.e. bromodomain inhibitor). Methods: Isogeneic HEK cells and urothelial cells (SV-HUC) were transduced with plasmids carrying either wild type (WT) or mutant PIK3CA (E545K and E542K mutants). Proliferation and growth were compared both in 2D and 3D culture respectively. We tested the therapeutic response to LY3023414 in 2D and 3D culture. Western blotting was used to test target modulation in the PI3K/mTOR pathway in response to treatment. JQ1 and LY3023414 combination studies were done in vitro. Calcusyn™ was used to determine whether synergy between the two agents exists in the context of either mutation. Results: PIK3CA E542K mutation has a growth advantage compared to the E545K mutation. This observation was more significant in 3D culture, which more faithfully represents the complexity of the tumor microenvironment. Isogeneic HEK cells expressing the E542K mutation were significantly more resistant to LY3023414 treatment both in 3D and 2D. This resonates with the resistance we initially reported in the bladder cancer PDX models carrying the E542K mutation. Interestingly, LY3023414+JQ1 combination was synergistic in the RP-B-01 (E542K MUT, but not in the RP-B-02 cell line (E545K MUT). Conclusion: PIK3CA mutation status is predictive of response to PI3K targeted therapy in bladder cancer, where PIK3CA E542K mutation confers resistance to PI3K targeted therapy. The synergistic combination of LY3023414 and the bromodomain inhibitor JQ1 can override resistance to PI3K targeted therapy. This drug combination may be of clinical significance in the context of PIK3CA E542K, but not E545K mutation.

Citation Format: May Faek Elbanna, Nur Damayanti, Sreenivasulu Chintala, Roberto Pili. PIK3CA E542K mutation in bladder cancer confers resistance to PI3K targeted therapy but synergy with BET inhibition [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1825.
Abstract 1826: Oncogenic KRAS mediates resistance to MET targeted therapy in non-small cell lung cancer (NSCLC) with MET mutations that induce exon14 skipping
Authors: Suzawa Ken , Offin Michael D. , Kurzatkowski Christopher , Liu Daniel , Vojnic Morana , Smith Roger S. , Mattar Marissa , Khodos Inna , Stanchina Elisa de , Sabari Joshua K. , Lockwood William W. , Drilon Alexander E. , Ladanyi Marc , Somwar Romel
Published: August 2018

Mutations in MET that induce skipping of exon 14 and lead to reduced ubiquitin ligase-mediated turnover of this receptor tyrosine kinase (RTK) are detected in 3-4% of non-small cell lung cancer (NSCLC), approaching the prevalence of ALK-rearranged lung cancers. Preclinical and clinical studies have revealed that MET exon14 alterations are actionable oncogenic drivers that are amenable to therapy with MET kinase inhibitors such as crizotinib. However, similar to most kinase-driven cancers, despite initial benefit, acquired resistance to therapy is inevitable. Next-generation sequencing (MSK-IMPACT 468 gene panel) was performed on samples from 81 NSCLC patients with MET exon14 alterations, including 7 with paired pre- and post-treatment tumor samples. A concurrent KRAS G12 mutation was identified in 5 patients. In 4 of these patients, the KRAS mutation was present prior to receiving crizotinib. The KRAS mutation was acquired post-crizotinib in the remaining patient. These findings implicate KRAS activation as a potential mechanism of acquired resistance. Using isogenic and patient-derived in vitro and in vivo models harboring MET exon14 skipping alteration, we confirmed that the KRAS mutation results in constitutive activation of RAS/ERK signaling and cells expressing both MET exon14 skipping and KRAS mutations are refractory to MET inhibition. Dual inhibition of MET and MEK with crizotinib and trametinib, respectively, has an additive effect in cell line and xenograft models. Whereas concurrent KRAS mutation is an extremely rare event in EGFR- and ALK-driven NSCLC, our findings confirm KRAS mutation as a recurrent mechanism of primary or secondary resistance to MET-directed therapies in lung cancers harboring MET exon14 alterations. We provide a new potential therapeutic strategy for NSCLC patients with both MET exon14 alterations and KRAS mutations.

Citation Format: Ken Suzawa, Michael D. Offin, Christopher Kurzatkowski, Daniel Liu, Morana Vojnic, Roger S. Smith, Marissa Mattar, Inna Khodos, Elisa de Stanchina, Joshua K. Sabari, William W. Lockwood, Alexander E. Drilon, Marc Ladanyi, Romel Somwar. Oncogenic KRAS mediates resistance to MET targeted therapy in non-small cell lung cancer (NSCLC) with MET mutations that induce exon14 skipping [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1826.
Abstract 1835: PPARγ agonist in combination with bcr/abl tyrosine kinase inhibitors in patients of chronic myeloid leukemia in chronic phase with suboptimal molecular response
Authors: Malhotra Hemant , Yadav Ajay , Mathur Ashwin , Biswas Debashish , Malhotra Bharti
Published: August 2018

Introduction & background:

Ten to 20 % of patients of Chronic Myeloid Leukemia in chronic phase (CML CP) have suboptimal molecular response (MR) to first line Imatinib maleate (IM). Treatment options include IM dose increase or switch to a 2nd generation tyrosine kinase inhibitor (TKI), Nilotinib or Dasatinib. Recently, synergy has been demonstrated when PPAR γ agonists are added to TKIs. We describe our initial results on 15 patients of CML CP treated with the combination of IM and pioglitazone, a PPAR γ agonist.

Patients and methods:

Fifteen patients of CML CP with suboptimal MR (bcr/abl:abl RQ-PCR between 1 to 10) after more than two years of IM were recruited in this pilot study. Because of economic considerations, these patients were not candidates for 2nd gen. TKIs. Patients given IM 600 mg/day and pioglitazone 30 mg/day. Blood counts and biochemistry monitored monthly, bcr/abl tested every 3 months using a cartridge based IS assay using the Cepheid GenXpert.

Results & conclusions:

Twelve of the 15 patients achieved significant MR, with 6/16 achieving a major MR at 9 months. Only 3/15 did not show a response (Table). Treatment with pioglitazone was well tolerated. One patient was not analysed due to intolerance to pioglitazone are first dose. Two patients had grade 1 elevation of hepatic enzymes which returned to normal after one week treatment cessation.

We conclude that the combination of imatinib with pioglitazone is effective and well tolerated in patients with a sub-optimal MR to TKI in patients with CML-CP. The combination could be a cost-effective strategy in treating imatinib non/sub-optimal responders in the developing world. The combination needs further and larger studies for confirmation and evaluation of the mechanisms of the synergy.

S. No.Patient ID/SexDiagnosis dateBCR-ABL (Before Pio)BCR-ABL (After Pio)At 3 monthAt 6 monthAt 9 month1SCM/MOct 20125.352.741.830.0052MD/FAug 20061.130.880.480.13GPJ/MJan 20142.860.43ND0.54RRC/MOct 20082.861.070.25ND5RK/MMar20081.390.770.350.416RDS/FOct 200010.15.994.870.677RDR/FApril 20039.045.780.360.058MM/MMay 20114.48NDND0.149RD/FJuly 20108.331.290.440.7310RB/FJuly 20153.253.022.891.3911BRR/MJan 20107.135.613.821.7712BK/FNov 20042.060.040.030.0713DPS/MJan 20116.155.471.020.8414JKM/MApril 20074.2215.49.117.6215CS/MOct 20121.721.170.840.08

Citation Format: Hemant Malhotra, Ajay Yadav, Ashwin Mathur, Debashish Biswas, Bharti Malhotra. PPARγ agonist in combination with bcr/abl tyrosine kinase inhibitors in patients of chronic myeloid leukemia in chronic phase with suboptimal molecular response [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1835.
Abstract 1836: Induction of secreted soluble decoy EGFR variants by splicing interference overcomes drug resistance in human non-small cell lung cancer
Authors: Park Jeong Eun , Spraggon Lee , Stanchina Elisa de , Cartegni Luca
Published: August 2018

Activation of the epidermal growth factor receptor (EGFR) is involved in the oncogenesis of multiple cancers, particularly lung cancer. Current treatments are limited by the appearance of TKI resistance from secondary somatic mutations in the EGFR gene, such as the T790M mutation (>50% of biopsies) in the EGFR kinase domain following erlotinib or gefitinib treatment. As these tumors are still EGFR-dependent, EGFR remains a prime therapeutic target in NSCLC. We have recently described multiple natural soluble decoy isoforms for multiple RTKs, including EGFR, which depend on the differential inclusion of functional domains by alternative splicing. We employ antisense oligo nucleotide (ASO) to reprogram EGFR pre-mRNA processing in order to increase expression of mRNA variants that encode for dominant-negative, soluble decoys EGFR (sdEGFR), at the expense of the oncogenic full-length EGFR receptor. These alternative splicing isoforms are generated via intronic polyadenylation (IPA) of pre-mRNA in a U1-snRNP (U1)-dependent manner. More specifically, we are able to induce the sdEGFR variants by using specific ASOs, designed to block the upstream U1 binding site and thus activate the appropriate IPA sites. Here, we show that our novel strategy effectively induces the expression of potent natural inhibitors of EGFR signaling in treatment-refractory lung cancer models in vitro and in vivo, leading to suppression of downstream pathways and tumor growth inhibition. The ASO-induced natural sdEGFR compounds function in a dominant-negative manner and induce dramatic cell death in NSCLC cells harboring multiple activating and resistance EGFR mutations, and thus provides a novel alternative strategy for treatment of refractory NSCLC, to overcome resistance mediated by the EGFR secondary mutations (including T790M, C797S and others).

Citation Format: Jeong Eun Park, Lee Spraggon, Elisa de Stanchina, Luca Cartegni. Induction of secreted soluble decoy EGFR variants by splicing interference overcomes drug resistance in human non-small cell lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1836.
Abstract 1842: Novel KIF5B-RET+ NSCLC cell lines demonstrate differential responses to RET inhibitors
Authors: Schubert Laura , Le Anh T. , Doak Andrea E. , Doebele Robert C.
Published: August 2018

Chromosomal rearrangements involving the rearranged during transfection (RET) tyrosine kinase occur in 1-2% of NSCLCs. This results in the expression of a constitutively active fusion kinase that promotes cancer cell growth, proliferation and survival. In lung cancer, RET is most commonly fused to KIF5B, but can have many other 5' partners such as CCDC6, NCOA, TRIM33 and TRIM24. Clinical trials with several multi-kinase inhibitors, which potently inhibit RET, have had low response rates between 18-53%. Novel, more highly specific RET inhibitors are now in clinical development. Collectively, the clinical trial data suggest that patients with KIF5B-RET rearrangements have exceptionally low responses to RET inhibitors in relation to non-KIF5B-RET fusions. In order to understand the role of RET 5' partners in regulating response to RET inhibitors we have generated two novel KIF5B-RET+ patient-derived cell lines, CUTO22 (K23;R12) and CUTO32 (K15;R12). We have confirmed that each of these cell lines contain the KIF5B-RET fusion and express the RET fusion protein. MTS proliferation assays have revealed that the CUTO22 cell line is very sensitive to the highly specific RET inhibitor, CEP-32496/RXDX-105, and the multi-kinase inhibitor ponatinib. Conversely, the CUTO32 cell line is dramatically resistant to both RXDX-105 and ponatinib. Phospho-RET (pRET) is inhibited by RXDX-105 and ponatinib in a dose-dependent manner in both the CUTO22 and CUTO32 cell line. Interestingly, despite successful RET inhibition, downstream signaling in pERK and pAKT remains active. In a time-course experiment, pRET is inhibited for up to 24 hours while pERK and pAKT is sustained. Additionally, knockdown of RET with siRNA did not reduce downstream signaling activation in CUTO22 or CUTO32 cells. Combined inhibition of possible bypass pathways, EGFR or mTOR, did not significantly enhance sensitivity to RET inhibitors in CUTO22 and CUTO32 cell lines. To isolate the role of the 5' partners in response to RET inhibitors we have utilized CRISPR/Cas9 technology to generate Kif5b-Ret and Trim24-Ret rearrangements in Ba/F3 cells. We have confirmed with PCR or RT-PCR that these cell lines harbor the intended Ret fusions and express the RET protein. Both the Kif5b-Ret+ and Trim24-Ret+ Ba/F3 cell lines are highly sensitive to multiple RET inhibitors. In conclusion, these data suggest that RET inhibitors successfully inhibit the target protein, but not downstream signaling, suggesting that KIF5B-RET may have unique co-alterations or reliance on alternative pathways to promote growth and proliferation.

Citation Format: Laura Schubert, Anh T. Le, Andrea E. Doak, Robert C. Doebele. Novel KIF5B-RET+ NSCLC cell lines demonstrate differential responses to RET inhibitors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1842.
Abstract 1863: Ursolic acid sensitizes rhTRAIL-resistant triple negative breast carcinoma to rhTRAIL-induced apoptosis
Authors: Manouchehri Jasmine , Kalafatis Michael
Published: August 2018

Recombinant human tumor necrosis factor-related apoptosis-inducing ligand (rhTRAIL) possesses the ability to induce apoptosis in cancer cells independent of their p53 status while exhibiting minimal toxicity to normal, non-transformed cells, and thus, it is a promising anti-cancer therapeutic. However, rhTRAIL-induced apoptosis is not as effective in a majority of breast cancers due to the up-regulation of anti-apoptotic proteins, down-regulation of pro-apoptotic proteins, and/or down-regulation of death receptors (DRs) 4 and 5. A combinatorial approach of rhTRAIL with the “mother nature”-derived compound ursolic acid (UA) has been applied to sensitize rhTRAIL-resistant triple negative breast carcinoma. UA is derived from the leaves and berries of various plants and found in the coatings of fruits and does not exhibit toxicity to normal, non-transformed cells. UA has been revealed to possess the ability to up-regulate DR5 and diminish the expression of anti-apoptotic proteins survivin and FLIP in cancer cells and thereby, making UA an encouraging choice to be utilized as a sensitizing agent. The aim of this study was to determine the capacity of UA to sensitize rhTRAIL-resistant triple negative breast cancer (TNBC) BT-20 and HCC1937 cells to rhTRAIL-induced apoptosis and elucidate the underlying mechanisms for UA's sensitization. The combinatorial treatment of UA and rhTRAIL augmented the induction of apoptosis when compared to single agent UA and rhTRAIL treatments as detected by Annexin V/PI assays and through by the execution of the extrinsic pathway as marked by the activation of caspase 8, activation of the executioner caspases 3 and 7, and eventual PARP cleavage (a hallmark of apoptosis). The underlying mechanisms for UA's sensitization of rhTRAIL-resistant TNBCs were established to be through the down-regulation of the anti-apoptotic protein FLIP and through the up-regulation of DR4 and DR5. Overall, these findings reveal that UA is an efficacious sensitizing agent for rhTRAIL-resistant TNBCs.

Citation Format: Jasmine Manouchehri, Michael Kalafatis. Ursolic acid sensitizes rhTRAIL-resistant triple negative breast carcinoma to rhTRAIL-induced apoptosis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1863.
Abstract 1891: Cross-resistance and synergy between idelalisib and bendamustine in chronic lymphocytic leukemia
Authors: Kost Sara E. F. , Saleh Ali , Mejia Edgard M. , Mostafizar Marina , Bouchard Eric D. J. , Banerji Versha , Marshall Aaron J. , Gibson Spencer B. , Katyal Sachin , Johnston James B.
Published: August 2018

Idelalisib (IDE) is an inhibitor of the δ isoform of PI3 kinase and has shown high activity in chronic lymphocytic leukemia (CLL) either when given alone or in combination with bendamustine (BEN) /rituximab (BR). In the present study, we have determined whether there is cross-resistance between BEN and IDE in primary CLL cells in vitro and whether synergy is observed upon combining these agents. In primary CLL cells in vitro, cross-resistance was not observed between BEN and IDE suggesting different modes of cytotoxicity. In contrast to BEN, sensitivity to IDE was not influenced by prior clinical treatment or the presence of a del 17p. Marked synergy in cytotoxicity was seen between BEN and IDE, which was paralleled by changes in γ-H2AX staining. These findings suggest that the synergistic antitumor effect was related to enhanced DNA damage by the drug combination. The degree of cytotoxic synergy varied and synergy was observed in some cases that were resistant to BEN or IDE, and those with del 17p. Synergy between BEN and IDE was also seen in the B cell lines, BJAB and I83, and in healthy donor peripheral blood mononuclear cells indicating that the phenomenon was not CLL-specific. To simulate the microenvironment, CLL cells were pre-stimulating with CD40L and IL4 prior to drug treatment. Interestingly this treatment caused the cells to become resistant to IDE, but BEN sensitivity was unaffected. However, combining BEN and IDE produced greater synergy than observed when cells were incubated without IL4/CD40. To examine the role of PI3Kδ for synergy, B cells from C57 BL/6 mice, both wild type and with non-functioning PI3Kδ protein, were exposed to BEN and/or IDE. Cells with the non-functioning PI3Kδ protein were more resistant to IDE than the wild-type cells and showed lesser synergy confirming the importance of this protein for the synergistic effect. In summary, these results confirm that IDE can be active against BEN-resistant CLL cells, while BEN may remain active against IDE-resistant samples, demonstrating different modes of anti-tumor activity. However, the unique yet inconsistent synergy seen between these two agents suggest an overlapping mechanism of action. Ongoing studies are evaluating the mechanism for this synergy.

Citation Format: Sara E. F. Kost, Ali Saleh, Edgard M. Mejia, Marina Mostafizar, Eric D. J. Bouchard, Versha Banerji, Aaron J. Marshall, Spencer B. Gibson, Sachin Katyal, James B. Johnston. Cross-resistance and synergy between idelalisib and bendamustine in chronic lymphocytic leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1891.