Murine Orthotopic Xenograft Model Research Articles

HGG-46. PEDIATRIC RADIATION-INDUCED GLIOMA PATIENT SAMPLES AND NOVEL PATIENT-DERIVED MODELS REVEAL TRANSLATIONALLY RELEVANT TREATMENT SUSCEPTIBILITIES AND POTENTIAL GERMLINE RISK FACTORS

Abstract BACKGROUND Pediatric radiation-induced glioma (RIG) is an incurable secondary high-grade glioma (HGG) afflicting up to 4% of children who previously received cranial radiotherapy (RT) for other malignancies. RIG accounts for up to 10% of pediatric brain tumor deaths. It has no known genetic risk factors nor effective treatment and is uniformly fatal, partly due to extremely limited available models. Our recent molecular characterization of patient samples showed that while RIG and primary pediatric HGG share histological similarities, their genetic alterations and gene expression profiles differ. METHODS We obtained germline DNA sequencing from 28 RIG patients and 112 matched controls who received RT but did not develop RIG. In addition, we developed cell culture and murine orthotopic patient-derived xenograft (PDX) models from four RIGs. We conducted single-cell RNA-seq (scRNA-seq), drug screening/validation, and CRISPR functional screening on our novel models. RESULTS Germline mutations in TP53, PARP10, POLI, DCLRE1A, and MLH3 were more common in RIG patients than controls (p<0.002). Our matched cell culture and PDX models of RIG represent the genetic diversity of the disease. The PDX models form tumors in 30-120 days and closely recapitulate human RIG by histology and scRNA-seq. They show susceptibility across models to DNA-damaging treatments (etoposide, irinotecan, radiation), as well as MEK, PARP, and proteasome inhibition, with orthogonal supporting findings via CRISPR screening. Several two-treatment combinations also show efficacy and synergy across models, including radiation and trametinib in vivo (logrank p=0.029). Discussion: RIG is an understudied but major cause of pediatric CNS tumor mortality that differs genetically from primary pediatric HGG. Our findings suggest specific germline alterations in DNA repair pathways may put some patients at higher risk of developing RIG after cranial RT. We also introduce the first set of patient-derived RIG models in order to advance translational RIG research, with characterization of translationally relevant treatment susceptibilities.

Construction of An Orthotopic Xenograft Model of Non-small Cell Lung Cancer Mimicking Disease Progression and Predicting Drug Activities.

Non-small cell lung cancer (NSCLC) is a highly lethal disease with a complex and heterogeneous tumor microenvironment. Currently, common animal models based on subcutaneous inoculation of cancer cell suspensions do not recapitulate the tumor microenvironment in NSCLC. Herein we describe a murine orthotopic lung cancer xenograft model that employs the intrapulmonary inoculation of three-dimensional multicellular spheroids (MCS). Specifically, fluorescent human NSCLC cells (A549-iRFP) were cultured in low-attachment 96-well microplates with collagen for 3 weeks to form MCS, which were then inoculated intercostally into the left lung of athymic nude mice to establish the orthotopic lung cancer model. Compared with the original A549 cell line, MCS of the A549-iRFP cell line responded similarly to anticancer drugs. The long-wavelength fluorescent signal of the A549-iRFP cells correlated strongly with common markers of cancer cell growth, including spheroid volume, cell viability, and cellular protein level, thus allowing dynamic monitoring of the cancer growth in vivo by fluorescent imaging. After inoculation into mice, the A549-iRFP MCS xenograft reliably progressed through phases closely resembling the clinical stages of NSCLC, including the expansion of the primary tumor, the emergence of neighboring secondary tumors, and the metastases of cancer cells to the contralateral right lung and remote organs. Moreover, the model responded to the benchmark antilung cancer drug, cisplatin with the anticipated toxicity and slower cancer progression. Therefore, this murine orthotopic xenograft model of NSCLC would serve as a platform to recapitulate the disease's progression and facilitate the development of potential anticancer drugs.

Abstract 6565: Improving survival of atypical teratoid/rhabdoid tumor orthotopic xenografts through the combination of PI3K inhibitor paxalisib and nucleoside analog gemcitabine

Abstract Atypical teratoid/rhabdoid tumors (AT/RT) are an aggressive infantile brain tumor with a dismal four-year event-free survival of 37%. We have previously identified high activation of mTORC1 and mTORC2 within AT/RT and shown that the highly brain penetrant PI3K inhibitor paxalisib is capable of simultaneously inhibiting mTORC1/2 by acting upstream of both complexes. In two orthotopic xenograft models, paxalisib slowed tumor growth and significantly extended survival (CHLA-06: 40 to 54 days, p=0.001; BT-12: 21 to 35 days, p=0.02). RNAseq analysis following mTOR inhibition in AT/RT cell lines showed an upregulation of genes involved in the activation of the integrated stress response (ISR) (ATF4, CHOP, PPP1R15A t-test p<0.05). Analysis of primary pediatric brain tumors through the Children’s Brain Tumor Network showed increased levels of ATF4 mRNA and eIF2α protein and mRNA in AT/RT compared to other indolent pediatric brain tumors. Increased expression of ISR components suggests this pathway may be a dependency in AT/RT. Activation of this pathway is known to be cytoprotective, however persistent over-activation drives cell death through induction of pro-apoptotic factors. Gemcitabine is a pyrimidine analog functioning to inhibit DNA synthesis and induce DNA damage; notably, recent literature has correlated DNA damage to activation of the ISR with downstream phosphorylation of eIF2α. We hypothesize that due to high baseline activation of ISR for AT/RT, paxalisib combined with gemcitabine will result in an over-activation of the ISR leading to AT/RT cell death. Western blot analysis of combination therapy compared to DMSO control showed induction of phospho-eIF2α, ATF4, and CHOP, denoting an activation of the ISR. Combination therapy in AT/RT cells induces cell death (Western blot analysis cPARP, MUSE Annexin V assay, SynergyFinder BLISS score [viability] CHLA-06: 21.50, CHLA-266: 22.60) and synergizes to decrease cell growth (SynergyFinder BLISS score [inhibition] CHLA-06: 16.80, BT-12: 14.30, CHLA-266: 13.90, BT-37: 11.40, CHLA-05: 10.40). Paxalisib/gemcitabine combination therapy in murine orthotopic xenograft models of AT/RT has slowed tumor growth (bioluminescent imaging) and led to significant extension of survival. Mice bearing BT-37 orthotopic xenografts and treated with vehicle control had a median survival of 56 days, while all of the paxalisib/gemcitabine treated mice were alive at 100 days of treatment (p<0.0001). In CHLA-06 orthotopic tumors combination therapy extended median survival from 22 days for control to 82.5 days (p<0.0001). Based on these findings, the Pacific Pediatric Neuro-Oncology Consortium (PNOC) is planning to include paxalisib/gemcitabine combination therapy in the next international clinical trial for patients with relapsed/recurrent AT/RT. Citation Format: Tyler Findlay, Kristen Malebranche, Anupa Geethadevi, Charles Eberhart, Jeffrey Rubens, Eric Raabe. Improving survival of atypical teratoid/rhabdoid tumor orthotopic xenografts through the combination of PI3K inhibitor paxalisib and nucleoside analog gemcitabine [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6565.

CR5/CCL5 axis is linked to a poor outcome, and inhibition reduces metastasis in oral squamous cell carcinoma.

The CCR5/CCL5 axis is essential for interactions between malignant cells and microenvironment components, promoting tumor progression in oral squamous cell carcinoma (OSCC). This study aims to evaluate the association of CCL5 and CCR5 with the behavior of oral cancer and assess the therapeutic potential of a CCR5 antagonist. A retrospective study to analyze CCR5 and CCL5 expression on paraffin-embedded tissues was performed. In cell lines, rhCCL5 was added to induce CCR5-related pathways, and Maraviroc and shRNA against CCR5 were used to neutralize the receptor. Finally, an in vivo murine orthotopic xenograft model of tongue cancer was used to evaluate Maraviroc as an oncologic therapy. After 15days, the mice were killed, and the primary tumors and cervical lymph nodes were analyzed. The expression of CCR5 was associated with clinical stage and metastasis, and CCL5 was related to overall survival. Adding rhCCL5 induced cell proliferation, while shRNA and Maraviroc reduced it in a dose-dependent manner. Maraviroc treatment also increased apoptosis and modified cytoskeletal organization. In vivo, Maraviroc reduced neck metastasis. The effects of CCR5 antagonists in OSCC have been poorly studied, and this study reports in vitro and in vivo evidence for the effects of Maraviroc in OSCC. Our results suggest that the CCR5/CCL5 axis plays a role in oral cancer behavior, and that its inhibition is a promising new therapy alternative.

Development of constitutively synergistic nanoformulations to enhance chemosensitivity in T-cell leukemia

Advances in multiagent chemotherapy have led to recent improvements in survival for patients with acute lymphoblastic leukemia (ALL); however, a significant fraction do not respond to frontline chemotherapy or later relapse with recurrent disease, after which long-term survival rates remain low. To develop new, effective treatment options for these patients, we conducted a series of high-throughput combination drug screens to identify chemotherapies that synergize in a lineage-specific manner with MRX-2843, a small molecule dual MERTK and FLT3 kinase inhibitor currently in clinical testing for treatment of relapsed/refractory leukemias and solid tumors. Using experimental and computational approaches, we found that MRX-2843 synergized strongly—and in a ratio-dependent manner—with vincristine to inhibit both B-ALL and T-ALL cell line expansion. Based on these findings, we developed multiagent lipid nanoparticle formulations of these drugs that not only delivered defined drug ratios intracellularly in T-ALL, but also improved anti-leukemia activity following drug encapsulation. Synergistic and additive interactions were recapitulated in primary T-ALL patient samples treated with MRX-2843 and vincristine nanoparticle formulations, suggesting their clinical relevance. Moreover, the nanoparticle formulations reduced disease burden and prolonged survival in an orthotopic murine xenograft model of early thymic precursor T-ALL (ETP-ALL), with both agents contributing to therapeutic activity in a dose-dependent manner. In contrast, nanoparticles containing MRX-2843 alone were ineffective in this model. Thus, MRX-2843 increased the sensitivity of ETP-ALL cells to vincristine in vivo. In this context, the additive particles, containing a higher dose of MRX-2843, provided more effective disease control than the synergistic particles. In contrast, particles containing an even higher, antagonistic ratio of MRX-2843 and vincristine were less effective. Thus, both the drug dose and the ratio-dependent interaction between MRX-2843 and vincristine significantly impacted therapeutic activity in vivo. Together, these findings present a systematic approach to high-throughput combination drug screening and multiagent drug delivery that maximizes the therapeutic potential of combined MRX-2843 and vincristine in T-ALL and describe a novel translational agent that could be used to enhance therapeutic responses to vincristine in patients with T-ALL. This broadly generalizable approach could also be applied to develop other constitutively synergistic combination products for the treatment of cancer and other diseases.

DIPG-16. ACUTE VERSUS PROLONGED CONVECTION-ENHANCED DELIVERY OF ALISERTIB INTO H3 K27M-MUTANT MODELS OF DIFFUSE MIDLINE GLIOMA

Abstract Convection-enhanced delivery (CED) is a potentially promising strategy to administer therapeutics directly into the brainstem of children harboring H3 K27-altered diffuse midline glioma (DMG). While early-phase clinical trials have demonstrated the safety of this technique, efficacy has yet to be achieved. Here, we describe how different variations of CED may be exploited to extend survival in a DMG murine patient-derived orthotopic xenograft model. Either 1-day (8 µL/hr) or 7-day (1 µL/hr) continuous CED infusions were performed to deliver an equivalent volume of the aurora kinase inhibitor alisertib to the mouse brainstem. Bioluminescence and magnetic resonance images were acquired to monitor tumor progression, validate CED catheter positioning, and analyze infusion-related imaging changes. Both infusion regimens significantly prolonged survival versus control (median survival benefit of 6.5 and 8 days, p=0.03 and p=0.01, for 1-day and 7-day CED, respectively). Postmortem examination of brains revealed no signs of tissue necrosis, cavitary lesions, or cellular (inflammatory) infiltrate at the site of infusion. However, the tumor parenchyma surrounding the cannula tract was markedly hypocellular in treated animals. Alisertib induced a robust increase in H3 K27 trimethylation along with decreased H3 K27M and Ki-67. Our findings indicate that CED of alisertib is well tolerated and effective, in both the acute and prolonged setting, underscoring the potential of this approach in the management of DMG.

ATRT-09. COMBINATION OF THE PI3K INHIBITOR PAXALISIB WITH THE NUCLEOSIDE ANALOG GEMCITABINE ACTIVATES THE INTEGRATED STRESS RESPONSE AND EXTENDS SURVIVAL IN ORTHOTOPIC MODELS OF ATYPICAL TERATOID/RHABDOID TUMORS

Abstract Relapsed atypical teratoid/rhabdoid tumors (AT/RT) are a deadly disease without a known cure. The Pacific Pediatric Neuro-Oncology Consortium (PNOC) is looking for effective combination therapies for an upcoming clinical trial to better treat relapsed AT/RT. We have previously identified that AT/RT are dependent on activation of mTORC1 and mTORC2 for growth and survival. Paxalisib is a highly brain penetrant PI3k inhibitor which acts upstream of mTOR to simultaneously inhibit mTORC1/2. In murine orthotopic xenograft models of AT/RT, Paxalisib significantly extends survival as a single agent therapy (CHLA-06: 40 to 54 days, p=0.001; BT12: 21 to 35 days, p=0.02). However, to improve the durability of this single agent therapy, we evaluated the efficacy of rational therapeutic partners. Analysis of RNAseq following mTOR inhibition (mTORi) showed an upregulation of genes associated with the integrated stress response (ISR) (ATF4, CHOP, PPP1R15A; t-test p<0.05). Gemcitabine is a pyrimidine nucleoside prodrug, which inhibits DNA synthesis and induces DNA damage, also leading to ISR activation. While the ISR can be protective, intense or prolonged activation leads to cell death. We therefore hypothesized that Paxalisib would combine with Gemcitabine to over-activate the ISR and drive AT/RT cell death. Through protein analyses, we demonstrate that combination therapy further activates the ISR compared to DMSO control (Western Blot: phospho-eIF2α, ATF4, and CHOP). Combination therapy also increases apoptosis (Western blot cPARP, MUSE Annexin V Assay) and synergizes to decrease AT/RT cell growth (SynergyFinder BLISS score CHLA-06: 16.8, BT12: 14.3, CHLA-266: 13.9). In mice bearing CHLA-06 orthotopic tumors, Paxalisib/Gemcitabine combination therapy slows tumor growth (Bioluminescent imaging) and extends median survival from 22 to 82.5 days (p<0.0001) compared to vehicle control treated mice. We aim to translate these results in this upcoming PNOC clinical trial to treat relapsed AT/RT.

Abstract 2474: Uncovering a new therapeutic vulnerability for preventing brain metastases

Abstract INTRO: Patients with brain metastases (BM) face a 90% mortality rate within one year of their diagnosis and they lack targeted therapeutic options, particularly preventative or interceptional ones. METHODS: The Singh lab has generated a large in-house biobank of patient-derived BM cell lines that are established from patient-derived BM from primary lung and breast cancers and melanoma. We use these BM cell lines to generate murine orthotopic xenograft models of BM and interrogate the biological processes that lead to BM. These models have successfully recapitulated all the stages of their respective metastatic cascades and allowed characterization of a “premetastatic” population of BM cells that have just seeded the brains of mice before forming mature, clinically detectable tumors. Pre-metastatic cell populations are impossible to detect in human patients but present a therapeutic window wherein metastasizing cells can be targeted and eradicated before establishing clinically detectable and difficult to treat brain tumors. RESULTS: Targeting premetastatic BM cells is a feasible interceptional strategy to block BM, but druggable targets are still very limited. Here, we applied RNA sequencing of premetastatic BM cells to reveal a unique deregulated transcriptomic profile that is specific to premetastatic cells regardless of primary tumor origin. Subsequent Connectivity Map analysis revealed compounds that we biologically characterized in vitro for selective anti-BMIC phenotypes. This effort led us to identify a tool compound that exhibits anti-BM activity in vitro, while remaining ineffective against normal brain cell controls. Follow up preclinical studies showed that treatment with this tool compound reduces the tumor burden of mice compared to placebo, while providing a significant survival advantage. Mass spectrometry-based metabolomics and CRISPR knock-out studies directly validated our tool compound’s target, Target X, as a targetable therapeutic vulnerability in BM, where pharmacological and genetic perturbation of Target X attenuates BM cell proliferation both in vitro and in vivo. We have now begun a large-scale medicinal chemistry campaign to develop a novel, brain penetrant Target X-inhibitor with a drug-like pre-clinical profile validated by our in vivo experimental models. This advanced drug candidate will be ready for later stage preclinical development and subsequent clinical development. CONCLUSION: This potential first-in-class anti-metastatic therapy may provide an alternative interceptional treatment strategy for patients experiencing BM that are otherwise limited to palliation. Our work provides a new model for target discovery and validation to develop more effective preventative therapeutic strategies for patients with metastatic disease. Citation Format: Agata M. Kieliszek, Daniel Mobilio, Blessing I. Bassey-Archibong, Jarrod Johnson, Nikoo Aghaei, William Gwynne, Dillon McKenna, Minomi K. Subapanditha, Chitra Venugopal, Jakob Magolan, Sheila K. Singh. Uncovering a new therapeutic vulnerability for preventing brain metastases [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2474.

Abstract 5490: Combination of the PI3k inhibitor Paxalisib with the nucleoside analog Gemcitabine over-activates the integrated stress response and induces atypical teratoid/rhabdoid tumor cell death

Abstract We have previously identified high activation of both mTORC1 and mTORC2 in the aggressive infantile brain tumor, atypical teratoid/rhabdoid tumor (AT/RT). Paxalisib is a highly brain penetrant PI3k inhibitor which acts upstream of mTOR to simultaneously inhibit mTORC1/2. Paxalisib is well-tolerated in ongoing pediatric clinical trials. In murine orthotopic xenograft models of AT/RT, Paxalisib significantly extended survival (CHLA-06: 40 to 54 days, p=0.001; BT12: 21 to 35 days, p=0.02). However, to improve the durability of this single agent therapy, we evaluated the efficacy of rational therapeutic partners. Analysis of RNAseq following mTOR inhibition (mTORi) of 4 cell lines representative of AT/RT showed an upregulation of genes associated with the integrated stress response (ISR), (ATF4: CHLA-06, t-test p<0.05; CHOP: CHLA-02, CHLA-06 t-test p<0.001). The activation of the ISR is further suggested through induction of PPP1R15A, a gene whose activation is closely associated with stress events and leads to downstream cell growth arrest and apoptosis (BT37 t-test p<0.001, CHLA-02, CHLA-06, CHLA-266, t-test p<0.01). Gemcitabine is a pyrimidine nucleoside prodrug, which inhibits DNA synthesis and induces DNA damage. As a result, Gemcitabine also induces phosphorylation of eIF2α and the activation of the ISR. While the ISR can be protective, intense or prolonged activation leads to cell death. We therefore hypothesized that Paxalisib would combine with Gemcitabine to hyper-activate the ISR and drive AT/RT cell death. Through Western blot analysis, we demonstrate that combination therapy increases phospho-eIF2α, ATF4, and CHOP compared to DMSO control. Furthermore, we demonstrate that combination therapy increases apoptosis (Western blot cPARP, MUSE Annexin V Assay) and synergizes to decrease AT/RT cell growth (SynergyFinder BLISS score CHLA-06: 16.8, BT12: 14.3, CHLA-266: 13.9, BT37: 11.4, CHLA-05: 10.4). Ongoing treatment of mice bearing CHLA06 orthotopic tumors demonstrate that combination therapy further extends median survival. Our studies suggest that pharmacologically activating the ISR may be an effective strategy to target AT/RT and combination of Paxalisib and Gemcitabine may be an effective treatment to help extend survival in this deadly disease. Citation Format: Tyler Findlay, Kristen Malebranche, Anupa Geethadevi, Eric Raabe, Charles Eberhart, Jeffrey Rubens. Combination of the PI3k inhibitor Paxalisib with the nucleoside analog Gemcitabine over-activates the integrated stress response and induces atypical teratoid/rhabdoid tumor cell death. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5490.

Next-Generation Sequencing of Newly-Diagnosed Primary CNS Lymphoma Reveals Alterations in BTG1, ETV6, and 6p Are Associated with Chemoresistance and Inferior Progression-Free Survival

Introduction: There is a significant unmet need for the development of reliable genetic biomarkers that identify patients with newly-diagnosed primary CNS lymphoma (PCNSL) who are at high risk of progression, both during standard methotrexate-based induction as well as delayed progression after receipt of dose-intensive consolidation. Currently, little is known about the genetic subtypes of PCNSL and the basis for differences in chemo-immunotherapeutic response. We hypothesized that an integrated clinical-genomic analysis may reveal new determinants of tumor progression and may ultimately guide a precision medicine-based approach to the selection of effective treatment regimens. Methods: We performed targeted next-generation sequencing of 529 pan-cancer genes of pre-treatment, formalin-fixed, paraffin-embedded tumors from 52 patients with CNS diffuse large B-cell lymphoma. We identified structural variants including single nucleotide variants, small insertions and deletions, and copy-number alterations. Clinical records were retrospectively reviewed to determine patients' baseline characteristics, IELSG index, and progression-free survival (PFS). 44 EBV-negative PCNSL patients treated with methotrexate, temozolomide, rituximab (MTR) induction with adequate genomic samples were available for complete analysis. Statistical testing was performed using R. Results: We identified three candidate genomic alterations that were significantly associated with chemotherapy resistance in PCNSL: (1) Alterations at 6p21.3, including both copy neutral loss of heterozygosity (CN LOH) at the HLA Class I (HLA-A, B, C) and Class II loci (HLA-DR, DP, DQ, TAP1) as well as homozygous deletion of HLA Class II; (2) Mutations of tumor suppressor genes BTG-1 and ETV6 (Fisher's exact, p < 0.01). Overall, these genomic alterations were detected in 18 out of 19 progression events in the cohort (Fisher's exact, p < 0.001). 7 of 9 tumors with 6p CN LOH also contained mutations at BTG-1 and/or ETV6. Kaplan-Meier survival analysis shows three subgroups stratified by alteration type with distinct PFS outcomes (Figure 1). The subgroup with either CN LOH or homozygous deletion at 6p had the earliest progression, followed by the subgroup with mutations at either BTG-1/ETV6 and no 6p CN LOH or homozygous deletion, compared to no alterations at these 3 loci (Log-rank, p < 0.01). Patients with hemizygous loss at 6p exhibited a trend towards worse outcome compared to no 6p loss. Furthermore, multivariate Cox proportional hazard analysis demonstrated a statistically significant 2.7-fold increased risk of progression with 6p CN LOH/homozygous deletion or mutations involving BTG-1/ETV6 (Table 1). While etoposide-cytarabine consolidation and maintenance lenalidomide were each significantly associated with a decreased risk of progression, age at diagnosis, Karnofsky performance status, intraocular disease status, and IELSG index were not significantly associated with PFS. Conclusions: Through harmonizing clinical and next-generation sequencing data, in this retrospective analysis we identify pathogenic alterations involving BTG-1 and ETV6, as well as major alterations at 6p21.3, that correlated with accelerated disease progression and an early tumor resistance phenotype in PCNSL. While 6p loss has been identified as a mechanism of tumor immune escape in PCNSL, our results suggest that 6p CN LOH may be a novel mechanism associated with early progression. Of note, in a parallel investigation using patient-derived CNS lymphoma tumor cells engrafted in a murine orthotopic xenograft model, we have demonstrated that lenalidomide significantly induces transcription of 6p21.3 genes involved in antigen presentation and immunomodulation, including HLA-A, TAP-1, and lymphotoxins. Taken together, 6p21.3 copy number loss, in particular CN LOH and homozygous deletion, as well as mutations in BTG-1 and ETV6 may be a promising biomarker set, potentially useful in risk stratification in clinical trials as well as to identify high risk patients more likely to derive benefit from lenalidomide. Prospective validation studies are planned to confirm these results. Supported by NCI. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

DDDR-03. DEVELOPMENT OF NOVEL ANTI-BRAIN METASTASIS INHIBITORS

Abstract The current standard of care for (surgery and radiation) for brain metastases (BM) is inadequate as BM have a 90% mortality rate within one year of diagnosis, posing a large unmet clinical need. The Singh lab has generated a large in-house biobank of patient-derived BM cell lines that are established from BM patient tumor samples. We use these BM cell lines to generate murine orthotopic xenograft models of BM and interrogate the biological processes that lead to BM. These models have successfully recapitulated all the stages of their respective BM cascades and additionally captured a “premetastatic” population of BM cells that have just seeded the brains of mice before forming mature, clinically detectable tumors. Pre-metastatic cell populations are impossible to detect in human patients but represent a therapeutic window wherein metastasizing cells can be targeted and eradicated before establishing clinically detectable and difficult to treat brain tumors. RNA sequencing of pre-metastatic BM cells revealed a unique deregulated transcriptomic profile that is specific to pre-metastatic cells despite the tumor of origin. Connectivity Map analysis was applied to the gene expression signatures of pre-metastatic BM cells to identity a compound (Drug A) which selectively inhibits BM cell proliferation but is not blood-brain barrier (BBB) penetrant and has not been previously considered in the context of brain metastasis. We synthesized a BBB-penetrant analogue of Drug A and found, using our patient-derived xenograft (PDX) models, that it increased survival benefit relative to both placebo and Drug A. Beginning with this promising scaffold, we will conduct structure-activity hypothesis-driven medicinal chemistry campaigns to optimize this scaffold for brain permeation while maintaining selective anti-BM activity. Development of novel small molecules that target premetastatic BM cells could slow or prevent the formation of BM and dramatically improve the prognosis of at-risk cancer patients.

BSCI-13 DEVELOPMENT OF NOVEL ANTI-BRAIN METASTASIS INHIBITORS

Abstract The current standard of care (surgery and radiation) for brain metastases (BM) is inadequate as BM have a 90% mortality rate within one year of diagnosis, posing a large unmet clinical need. The Singh lab has generated a large in-house biobank of patient-derived BM cell lines that are established from BM patient tumor samples. We use these BM cell lines to generate murine orthotopic xenograft models of BM and interrogate the biological processes that lead to BM. These models have successfully recapitulated all the stages of their respective BM cascades and additionally captured a “pre-metastatic” population of BM cells that have just seeded the brains of mice before forming mature, clinically detectable tumors. Pre-metastatic cell populations are impossible to detect in human patients but represent a therapeutic window wherein metastasizing cells can be targeted and eradicated before establishing clinically detectable and difficult to treat brain tumors. RNA sequencing of pre-metastatic BM cells revealed a unique deregulated transcriptomic profile that is specific to pre-metastatic cells despite the tumor of origin. Connectivity Map analysis was applied to the gene expression signatures of pre-metastatic BM cells to identity a compound (Drug A) which selectively inhibits BM cell proliferation but is not blood-brain barrier (BBB) penetrant and has not been previously considered in the context of brain metastasis. We synthesized a BBB-penetrant analogue of Drug A and found, using our patient-derived xenograft (PDX) models, that it increased survival benefit relative to both placebo and Drug A. Beginning with this promising scaffold, we will conduct structure-activity hypothesis-driven medicinal chemistry campaigns to optimize this scaffold for brain permeation while maintaining selective anti-BM activity. Development of novel small molecules that target pre-metastatic BM cells could slow or prevent the formation of BM and dramatically improve the prognosis of at-risk cancer patients.

Abstract 976: Interrogating the pre-metastastic gene signature to block brain metastases

Abstract BACKGROUND: The incidence of brain metastases (BM) is tenfold higher than that of primary brain tumors. BM predominantly originate from primary lung, breast, and melanoma tumors with a 90% mortality rate within one year of diagnosis, posing a large unmet clinical need to identify novel therapies against BM. The goal of this work is to uncover the molecular factors that drive the formation of BM and investigate whether we can slow down and ultimately block BM formation. METHODS: The Singh lab has generated a large in-house biobank of patient-derived BM cell lines that are established from BM patient tumor samples. We use these BM cell lines to generate murine orthotopic xenograft models of BM and interrogate the biological processes that lead to BM. These models have successfully recapitulated all the stages of their respective BM cascades and additionally captured a “pre-metastatic” population of BM cells that have just seeded the brains of mice before forming mature, clinically detectable tumors. Pre-metastatic cell populations are impossible to detect in human patients but represent a therapeutic window wherein metastasizing cells can be targeted and eradicated before establishing clinically detectable and difficult to treat brain tumors. RESULTS: RNA sequencing of pre-metastatic BM cells revealed a unique deregulated transcriptomic profile that is specific to pre-metastatic cells despite the tumor of origin. Subsequent Connectivity Map analysis revealed compounds that we biologically characterized in vitro for selective anti-BMIC phenotypes. This effort led to a lead compound that exhibits anti-BM activity in vitro, while remaining ineffective against normal brain cell controls. Preliminary in vivo work has shown that following both orthotopic and intracardiac injection of BM cells, treatment with this lead compound reduces the tumor burden compared to mice being treated by a vehicle control, while providing a significant survival advantage. Ongoing mechanistic investigations aim to delineate the protein target of this compound in the context of the observed selective anti-BM phenotype. CONCLUSION: Identification of novel small molecules that target premetastatic BM cells could slow or prevent the formation of BM and dramatically improve the prognosis of at-risk cancer patients. Citation Format: Agata Kieliszek, Blessing Bassey-Archibong, Chitra Venugopal, Sheila Singh. Interrogating the pre-metastastic gene signature to block brain metastases [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 976.

STEM-02. THERAPEUTIC INTERVENTION OF LUNG-, BREAST-, AND MELANOMA-BRAIN METASTASIS

Abstract BACKGROUND The incidence of brain metastases (BM) is tenfold higher than that of primary brain tumours. BM predominantly originate from primary lung, breast, and melanoma tumours with a 90% mortality rate within one year of diagnosis, posing a large unmet clinical need to identify novel therapies against BM.This unmet clinical need is largely attributed to a small population of cancer stem cells (CSCs), termed BM-initiating cells (BMICs), that are able to escape a primary tumour, drive metastasis and facilitate the formation of a secondary tumour in the brain. METHODS Using a large in-house biobank of patient-derived BMIC lines, the Singh Lab has generated murine orthotopic patient-derived xenograft models of BM and captured a “premetastatic” population of BMICs that have just seeded the brains of mice before forming clinically detectable tumours: a cell population that is impossible to detect in human patients but represents a therapeutic window wherein metastasizing cells can be targeted and eradicated before establishing clinically detectable tumours. RESULTS RNA sequencing of pre-metastatic BMICs from all three primary tumour models with subsequent Connectivity Map analysis identified a lead compound that exhibits selective anti-BM activity in vitro. Preliminary in vivo work has shown that this lead compound reduces the tumor burden of treated mice compared to vehicle control while providing a significant survival advantage. Ongoing mechanistic investigations aim to delineate the protein target of this compound in the context of the observed selective anti-BMIC phenotype. CONCLUSION Identification of novel small molecules that target premetastatic BM cells could prevent the formation of BM and dramatically improve the prognosis of at-risk cancer patients.

BSCI-19. Therapeutic intervention of lung-, breast-, and melanoma-brain metastasis

BackgroundThe incidence of brain metastases (BM) is tenfold higher than that of primary brain tumours. BM predominantly originate from primary lung, breast, and melanoma tumours with a 90% mortality rate within one year of diagnosis, posing a large unmet clinical need to identify novel therapies against BM.MethodsUsing a large in-house biobank of patient-derived BM cell lines, the Singh Lab has generated murine orthotopic patient-derived xenograft models of BM and captured a “premetastatic” population of BM cells that have just seeded the brains of mice before forming clinically detectable tumours: a cell population that is impossible to detect in human patients but represents a therapeutic window wherein metastasizing cells can be targeted and eradicated before establishing clinically detectable tumours.ResultsRNA sequencing of pre-metastatic BM cells from all three primary tumour models with subsequent Connectivity Map analysis identified a lead compound that exhibits selective anti-BM activity in vitro. Preliminary in vivo work has shown that this lead compound reduces the tumor burden of treated mice compared to vehicle control while providing a significant survival advantage. Ongoing mechanistic investigations aim to delineate the protein target of this compound in the context of the observed selective anti-BM phenotype.ConclusionTherapeutic targeting of premetastatic BM cells could prevent the formation of BM and dramatically improve the prognosis of at-risk cancer patients.

Abstract 928: Glypican-3 targeted thorium-227 alpha therapy reduces tumor burden in an orthotopic xenograft model of hepatocellular carcinoma

Abstract The purpose of this study is to develop a thorium-227 (227Th) antibody radioimmunoconjugate targeting glypican-3 (GPC3) and to test its therapeutic efficacy in a hepatocellular carcinoma (HCC) orthotopic xenograft model. GPC3 targeting antibody (αGPC3) was conjugated to bifunctional chelator p-SCN-Bn-H4octapa (octapa), and αGPC3-octapa binding affinity for GPC3 was evaluated by flow cytometry. 227Th radiolabeling of this conjugate was optimized, and in vitro stability of 227Th-αGPC3-octapa was evaluated in PBS with and without free radical scavenging agent over 14 days. For in vivo evaluation, an orthotopic xenograft model was generated by hepatic subcapsular injection of human HCC HepG2 cells. In vivo biodistribution was assessed in blood, tumor and organs at 1, 7 and 21 days after tail vein injection of 227Th-αGPC3-octapa (500 KBq/kg). To test therapeutic efficacy, tumor-bearing animals were injected with 227Th-αGPC3-octapa (250 kBq/kg or 500 kBq/kg) and compared to an irrelevant control antibody, 227Th-αBHV1-octapa (500 kBq/kg), and to a no-treatment control. Tumor burden was assessed with serial serum alpha-fetoprotein (AFP) measurements, a marker of tumor burden validated in this model. Toxicity to 227Th-αGPC3-octapa was measured by serum comprehensive metabolic panel obtained 21 days after injection. GPC3 binding affinity was highest after conjugation of αGPC3 with 10 equivalents of octapa. The protein recovery from the conjugation process was &amp;gt;85%, and mass spectral analysis indicated an average of 3.3 octapa moieties per molecule of αGPC3-octapa. After two weeks, &amp;gt;98% of αGPC3-octapa and αBHV1-octapa had 227Th bound in the presence of scavenging agent. αGPC3-octapa maintained high affinity for GPC3 as measured by flow cytometry, indicating the octapa conjugation reaction did not alter immunoreactivity of αGPC3. In vivo, 227Th-αGPC3-octapa accumulated in the tumor over time and cleared from normal tissues with a %ID/g of &amp;lt;5% by 21 days after injection. Significant antitumor activity was observed after treatment with 227Th-αGPC3-octapa (500 kBq/kg) with mean AFP level of 10,696 ± 19,754ng/mL compared to 308,175 ± 362,372ng/mL and 145,154 ± 166,780ng/mL in the 227Th-αBHV1-octapa and no-treatment control group, respectively. Reductions in serum AFP was observed in all but one tumor-bearing mouse after 500kBq/kg 227Th-αGPC3-octapa therapy. Organ-specific toxicity was not observed after treatment with 227Th-αGPC3-octapa (500 KBq/kg) compared to no-treatment control. In conclusion, we report the development of a GPC3 targeted thorium conjugate and demonstrate its in vivo therapeutic efficacy in a murine orthotopic xenograft model of hepatocellular carcinoma. Citation Format: Kevin P. Labadie, Donald K. Hamlin, Aimee Kenoyer, Sara K. Daniel, Alan F. Utria, Andrew D. Ludwig, Heidi L. Kenerson, Delphine L. Chen, Johnnie Orozco, Raymond S. Yeung, Lily Li, Chris Orvig, Yawen Li, D Scott Wilbur, James O. Park. Glypican-3 targeted thorium-227 alpha therapy reduces tumor burden in an orthotopic xenograft model of hepatocellular carcinoma [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 928.

HYBID derived from tumor cells and tumor-associated macrophages contribute to the glioblastoma growth

Glioblastoma is the most malignant tumor of the brain associated with poor prognosis and outcome, and hence there is an urgent need to develop novel treatments for glioblastoma. In this study, we focused on hyaluronan binding protein (HYBID, as known as CEMIP/KIAA1199), a protein involved in hyaluronan depolymerization in chondrocytes and synoviocytes. We previously reported that Hybid-deficient (KO) mice show accumulation of hyaluronan in the brain, and memory impairment. To elucidate the role of HYBID in glioblastoma pathogenesis, we knocked down HYBID in human glioblastoma cells using siRNAs and developed a murine orthotopic xenograft model in the Hybid KO mice. Downregulation of HYBID in glioblastoma cells resulted in inhibition of cell proliferation and migration, and increased cell death. The growth of glioblastoma cells implanted in the mouse brain was suppressed in Hybid KO mice compared to that in the wild-type mice. Interestingly, infiltration of macrophages in the glioblastoma tissue was decreased in Hybid KO mice. Using intraperitoneal macrophages derived from Hybid KO mice and glioma cell supernatants, we examined the role of HYBID in macrophages in the tumor environment. We showed that HYBID contributes to macrophage migration and the release of pro-tumor factors. Moreover, we revealed that HYBID can be a poor prognostic factor in glioma patients by bioinformatics approaches. Our study provides data to support that HYBID expressed by both glioblastoma cells and tumor-associated macrophages may contribute to glioblastoma progression and suggests that HYBID may be a potential target for therapy that focuses on the tumor microenvironment of glioblastoma.

The multi-target small-molecule inhibitor SB747651A shows in vitro and in vivo anticancer efficacy in glioblastomas

Glioblastoma multiforme is the most common primary brain tumor and among the most lethal types of cancer. Several mono-target small molecule-inhibitors have been investigated as novel therapeutics, thus far with poor success. In this study we investigated the anticancer effects of SB747651A, a multi-target small-molecule inhibitor, in three well characterized patient-derived glioblastoma spheroid cultures and a murine orthotopic xenograft model. Concentrations of 5–10 µM SB747651A reduced cell proliferation, spheroid formation, migration and chemoresistance, while apoptotic cell death increased. Investigation of oncogenic kinase signaling showed decreased phosphorylation levels of mTOR, CREB, GSK3 and GYS1 leading to altered glycogen metabolism and formation of intracellular reactive oxygen species. Expression levels of cancer stemness marker SOX2 were reduced in treated tumor cells and SB747651A treatment significantly prolonged survival of mice with intracranial glioblastoma xenografts, while no adverse effects were observed in vivo at doses of 25 mg/kg administered 5 days/week for 8 weeks. These findings suggest that SB747651A has anticancer effects in glioblastoma. The cancer-related pathophysiological mechanisms targeted by SB747651A are shared among many types of cancer; however, an in-depth clarification of the mechanisms of action in cancer cells is important before further potential application of SB747651A as an anticancer agent can be considered.

Glypican-3 targeted delivery of 89Zr and 90Y as a theranostic radionuclide platform for hepatocellular carcinoma

Glypican-3 (GPC3) is a tumor associated antigen expressed by hepatocellular carcinoma (HCC) cells. This preclinical study evaluated the efficacy of a theranostic platform using a GPC3-targeting antibody αGPC3 conjugated to zirconium-89 (89Zr) and yttrium-90 (90Y) to identify, treat, and assess treatment response in a murine model of HCC. A murine orthotopic xenograft model of HCC was generated. Animals were injected with 89Zr-labeled αGPC3 and imaged with a small-animal positron emission/computerized tomography (PET/CT) imaging system (immuno-PET) before and 30 days after radioimmunotherapy (RIT) with 90Y-labeled αGPC3. Serum alpha fetoprotein (AFP), a marker of tumor burden, was measured. Gross tumor volume (GTV) and SUVmax by immuno-PET was measured using fixed intensity threshold and manual segmentation methods. Immuno-PET GTV measurements reliably quantified tumor burden prior to RIT, strongly correlating with serum AFP (R2 = 0.90). Serum AFP was significantly lower 30 days after RIT in 90Y-αGPC3 treated animals compared to those untreated (p = 0.01) or treated with non-radiolabeled αGPC3 (p = 0.02). Immuno-PET GTV measurements strongly correlated with tumor burden after RIT (R2 = 0.87), and GTV of animals treated with 90Y-αGPC3 was lower than in animals who did not receive treatment or were treated with non-radiolabeled αGPC3, although this only trended toward statistical significance. A theranostic platform utilizing GPC3 targeted 89Zr and 90Y effectively imaged, treated, and assessed response after radioimmunotherapy in a GPC3-expressing HCC xenograft model.

MODL-31. RADIATION-DERIVED TREATMENT-RESISTANT PDX AND CELL CULTURE MODELS RECAPITULATE THE CHARACTERISTICS OF MATCHED PRIMARY/RECURRENT PEDIATRIC HIGH-GRADE GLIOMA

BACKGROUNDPediatric high-grade glioma (pHGG) is the most common cause of childhood cancer death. Recurrence after therapy is a major challenge, since recurrent pHGG proliferates aggressively and resists therapy. We developed and validated preclinical models of matched primary and recurrent tumors, providing a method to study recurrence and potential therapies.METHODSWe irradiated H3K27M thalamic pHGG cells (BT245) (8 Gy/week,2Gy fractions x3 weeks) and propagated the surviving cells (BT245R). We developed a murine recurrence model by orthotopically implanting BT245 cells, irradiating the resultant tumors (4 Gy/day x2d) and propagating irradiated (BT245RM) or control (BT245CM) tumor cells at endpoint. We performed phenotypic analyses, RNA-Seq, and drug testing.RESULTSBT245R cells were more stemlike than BT245, with an 8-fold greater rate of neurosphere formation (p<0.03). Geneset enrichment analysis showed similar molecular changes in BT245RM cells and primary/recurrent H3K27M pHGG patient sample pair, including relaxation of the G2/M cell cycle checkpoint (Hallmark_G2M_Checkpoint: BT245RM NES=-5.95, FDR=0.0; patient NES=-5.86, FDR=0.0), downregulation of MYC targets (Hallmark_MYC_Targets_V1: BT245RM NES=-7.43, FDR=0.0; patient NES=-5.86, FDR=0.0), and decreased differentiation (Go_Regulation_of_Stem_Cell_Differentiation: BT245RM NES=-3.35, FDR=0.0; patient NES=-3.15, FDR=0.0). Enrichment of the protein_kinase_C_signaling in BT245RM (NES=2.18,FDR=0.03) suggested response to MAPK pathway inhibition. BT245R cells were twice as sensitive as BT245 cells to the MEK inhibitor trametinib (p<0.05).CONCLUSIONSOur neurosphere and murine orthotopic patient-derived xenograft models recapitulate gene expression changes of matched primary/recurrent pHGG. RNA-Seq analysis validated the model against patient samples and identified trametinib as potentially effective in recurrent pHGG.