TMIC-40. TRANSCRIPTOMIC CHARACTERIZATION OF PATIENT GLIOMAS AND DERIVED MODEL SYSTEMS REVEALS ENVIRONMENTAL INFLUENCE ON NEURODEVELOPMENTAL CELLULAR STATES

Bulk tumor and single-cell RNA sequencing have revealed the remarkable molecular heterogeneity and plasticity of gliomas, leading to the definition of tumor subtypes and cellular states describing inter- and intra-tumoral levels of heterogeneity respectively. While there has been great interest in creating and revising these classifications, the combination of selective pressures from molecular alterations within the tumor cell as well as extrinsic factors within the tumor microenvironment (TME) driving these levels of heterogeneity remain to be fully described. The brain TME is a complex, regionally heterogeneous ecosystem of communicating non-malignant and malignant cell types and scavenge-able nutrients and metabolites. We hypothesized that distinct environmental contexts within and across tumors may drive the intra- and inter-tumoral heterogeneity of gliomas. To identify tumorigenic programs impacted by environmental context, we performed bulk RNA sequencing of over 40 triplets of patient glioma samples and their matched derivative models established in direct orthotopic mouse xenografts and conventional gliomasphere cultures. Comparative analyses revealed environment-associated programs including in vivo immune and neuroglial signaling as well as altered in vitro lipid metabolism and upregulated cell migration. Next, to investigate associations between tumor cellular state and environment-associated programs we performed single-cell RNA sequencing of 4 patient and model system triplets. By annotating single cell profiles with previously defined single cell atlases of the developing and adult brain, 9 major states reflecting neurodevelopmental cell types were identified. Single cell profiling further revealed cell state-specific expression of environment-associated programs. We simultaneously observed the divergence of model cellular state compositions towards states expressing programs associated with their environment. We conclude that the transcriptional evolution of cellular states is connected to their ecological role within the TME. Consequently, we find grade- and diagnosis-associated composition differences between patient tumors predictive of their ability to establish a model in vitro.

EPCO-10. INTRATUMORAL HETEROGENEITY OF ENVIRONMENT-INDUCED EXPRESSION PROGRAMS IN GLIOMA PATIENTS AND DERIVED MODEL SYSTEMS

Bulk tumor and single-cell RNA sequencing have revealed the remarkable molecular heterogeneity and plasticity of gliomas. This has led to the creation of tumor subtypes and cellular states describing inter- and intra-tumoral heterogeneity, respectively. While there has been great interest in creating and revising new classifications, the biological reasons for this degree of heterogeneity and the selective pressures driving it remain to be fully described. The brain tumor microenvironment (TME) is a complex, regionally heterogeneous ecosystem of communicating normal and malignant cell types and scavenge-able nutrients and metabolites. We hypothesized that distinct cellular interactions and metabolic flux in the TME may drive the inter- and intra-tumoral heterogeneity of gliomas. To identify tumorigenic programs impacted by environmental context we performed bulk RNA sequencing of over 35 triplets of patient glioma samples and their matched derivative models established in direct orthotopic mouse xenografts (DPDOX) and conventional gliomasphere cultures (GS). This analysis revealed environment-specific programs including in vivo immune and neuroglial signaling, in vitro lipid metabolism, and cell migration altered in model systems. These environmental programs are enriched in specific tumor subtypes and neuroglial signaling programs lost in vitro are dynamically upregulated upon re-transplantation in vivo. To further investigate associations between tumor cellular state and environment-driven programs we performed single-cell RNA sequencing of 3 patient and model system triplets. By annotating with brain cell atlases from previous single-cell characterizations, 6 major clusters and over 20 sub-clusters of tumor cell states and hybrid states were identified. Overlaying results from bulk sequencing revealed cell state-specific expression of environment-induced programs. Further, these cellular state “niches” diverge in model environments suggesting that environmental factors modulate not only the composition of cellular states but also their biological roles within gliomas.

Prospective phase 2 trial of PSMA-targeted molecular RadiothErapy with 177Lu-PSMA-617 for metastatic castration-reSISTant Prostate Cancer (RESIST-PC): efficacy results of the UCLA cohort

The objective of this study was to determine prospectively the efficacy profile of 2 activity regimens of ¹⁷⁷Lu-PSMA therapy in patients with progressive metastatic castrate-resistant prostate cancer (mCRPC): 6.0 vs. 7.4 GBq. Methods: RESIST-PC (NCT03042312) was a prospective multicenter phase 2 trial. Patients with progressive mCRPC after ≥ 1 novel androgen-axis drug, either chemotherapy naïve or postchemotherapy, with sufficient bone marrow reserve, normal kidney function, and sufficient PSMA expression by PSMA PET were eligible. Patients were randomized (1:1) into 2 activity groups (6.0 or 7.4 GBq) and received up to 4 cycles every 8 wk. The primary endpoint was the efficacy of ¹⁷⁷Lu-PSMA measured by the prostate-specific antigen (PSA) response rate (RR) after 2 cycles (≥50% decline from baseline). Secondary endpoints included the PSA RR (≥50% decline) at any time (best response), and overall survival (OS). Results: The study was closed at enrollment of 71/200 planned patients because of sponsorship transfer. We report here the efficacy of the University of California Los Angeles cohort results only (n = 43). The PSA RRs after 2 cycles and at any time were 11/40 (28%, 95% CI 15-44), 6/13 (46%, 95% CI 19-75), and 5/27 (19%, 95% CI 6-38), and 16/43 (37%, 95% CI 23-53), 7/14 (50%, 95% CI 23-77), and 9/29 (31%, 95% CI 15-51) in the whole cohort, the 6.0-GBq group, and the 7.4-GBq group, respectively (P = 0.12 and P = 0.31). The median OS was 14.0 mo (95% CI 10.1-17.9), 15.8 (95% CI 11.8-19.4), and 13.5 (95% CI 10.0-17.0) in the whole cohort, the 6.0-GBq group, and the 7.4 GBq group, respectively (P = 0.87). OS was longer in patients who experienced a PSA decline ≥ 50% at any time than in those who did not: median, 20.8 versus 10.8 mo (P = 0.005). Conclusion: In this prospective phase 2 trial of ¹⁷⁷Lu-PSMA for mCRPC, the median OS was 14 mo. Despite the heterogeneous study population and the premature study termination, the efficacy profile of ¹⁷⁷Lu-PSMA appeared to be favorable and comparable with both activity regimens (6.0 vs. 7.4 GBq). Results justify confirmation with real-world data matched-pair analysis and further clinical trials to refine and optimize the ¹⁷⁷Lu-PSMA therapy administration scheme to improve tumor radiation dose delivery and efficacy.

Antibody Drug Conjugates in Lung Cancer: State of the Current Therapeutic Landscape and Future Developments

While both targeted therapy and immunotherapy-based strategies have emerged as frontline standard-of-care for patients with advanced lung cancer, acquired resistance and disease progression remain inevitable in most cases. Chemotherapy is a common salvage option in this scenario, but is limited by a relatively narrow therapeutic index. The emergence of antibody-drug conjugates (ADCs) offer an appealing alternative. ADCs couple the specificity of a monoclonal antibody with the cytotoxic effects of chemotherapy to facilitate the targeted delivery of cytotoxic payloads directly to cancer cells. Here, we review the general structure and function of ADCs, followed by a discussion of emerging ADCs in lung cancer and the future applications of this increasingly relevant class of novel agents.

TAMI-48. ENGRAFTMENT PHENOTYPES IN PRECLINICAL MODEL SYSTEMS REVEAL A FUNCTIONAL SUBGROUP OF PATIENT TUMORS DEPENDENT ON THE BRAIN TUMOR MICROENVIRONMENT FOR GROWTH

The derivation of model systems from patient tumors is a requisite for reproducible and high throughput translational cancer research. However, not all tumors can form a model and those that do often fail to capture the molecular diversity specific to their cancer. The potential tumor-intrinsic underpinnings remain largely unknown. In gliomas, the brain tumor microenvironment (TME) is increasingly acknowledged as a regulator of tumor proliferation, invasion, and therapy response. The dissimilar environment of in vitro and heterotopic xenograft models could potentially play a role in the limited fidelity of these model systems. Here we established a culture-free workflow and biobank of 144 glioma direct-from-patient orthotopic xenografts (DPDOX) and 51 parallel gliomasphere cultures (GS). Our direct-from-patient workflow enabled the exclusive in vivo establishment of several gliomas – hereafter termed TME-dependent tumors – including low and high grade mtIDH gliomas and histone H3.3 G34 glioblastomas notoriously difficult to culture in vitro. Through molecular profiling of over 75 patient tumors and their matched derivative models, we find that DPDOX tumors preserve a gene expression signature of neural and glial interactions not found in GS and enriched in brain TME-dependent patient tumors. While these patient tumors span a diversity of clinical diagnoses, network-based inferred transcription factor activity suggests that they converge on shared master regulators of self-renewal driving proneural and OPC/NPC-like cellular state enrichment. Integrating multi-omic profiling from TCGA and other publicly available datasets reveals that this expression signature corresponds to a shared DNA methylation signature across disparate epigenetic subgroups. These findings suggest a brain TME dependence in patient tumors across multiple molecular and clinical classifications of glioma which leads to a lack of representation in model systems failing to recapitulate tumor-promoting components of the TME. Further this work provides a resource to guide translational investigations accounting for influences of the model environment.

Overall survival after 177Lu-PSMA-617 molecular radiotherapy in patients with metastatic castrate-resistant prostate cancer: Post-hoc analysis of a prospective phase II trial

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Background: This was an open-label randomized prospective bi-centric single-arm phase II clinical trial of 177Lu-PSMA-617 molecular radiotherapy in patients with progressive metastatic castrate-resistant prostate cancer (mCRPC) conducted at University of California Los Angeles (USA) and Excel Diagnostics & Nuclear Oncology Center (Houston, TX, USA) (NCT03042312). The study was investigator-initiated under an investigational new drug approval protocol (IND#133661) with authorization of charging for investigational drug (cost-recovery, Title 21 CFR 312.8). We report here the post-hoc analysis of overall survival (OS) in a single-study site cohort (UCLA). Methods: Patients with progressive mCRPC (biochemical, radiographic, or clinical) after ≥1 novel androgen axis drug (NAAD), either chemotherapy (CTX) naïve or post-CTX, with sufficient bone marrow reserve, normal kidney function, and sufficient PSMA-target expression by PET were eligible. Patients received up to 4 cycles of 177Lu-PSMA-617 every 8±1 weeks and were randomized into 2 treatment activities groups (6.0 or 7.4 GBq). Efficacy was defined as serum PSA decline of ≥50% from baseline and served as primary endpoint (hypothesis: ≥40% of responders after 2 cycles). Results: 43 patients were randomized to the 6.0 GBq (n= 14) and 7.4 GBq (n=29) treatment arms. 11/43 (26%) were CTX naïve while 10/43 (23%), 12/43 (28%), 5/43 (12%) and 5/43 (12%) had received 1, 2, 3 or 4 CTX regimens. Median baseline PSA was 29.2 ng/ml (mean 228.8, range 0.5-2082.6). 21/43 (49%) completed 4 cycles of 177Lu-PSMA-617 whereas 4/43 (9%), 13/43 (30%) and 5/43 (12%) underwent 1, 2 and 3 cycles. PSA decline of ≥50% was observed in 11/43 of patients (26%) after 2 cycles and in 16/43 (37%) at any time (best PSA response). 9/43 (21%) had a PSA decline of ≥90% and 23/43 (53%) had any PSA decline (>0%). After a median follow-up of 19.5 months the median OS was 14.8, 15.7 and 13.5 months in the whole cohort, the 6.0 GBq and 7.4 GBq treatment arms, respectively (p=0.68). Patients showing a PSA decline of ≥50% after 2 cycles and at any time had a longer OS: median 20.1 months vs. 13.6 (p=0.091) and 20.1 vs. 11.6 (p=0.002), respectively. Conclusions: In this post-hoc analysis of a single-site cohort of 43 patients included in a prospective phase II trial the median OS after 177Lu-PSMA-617 molecular radiotherapy in patients with progressive mCRPC was 14.8 months. There was no difference of efficacy between the 6.0 GBq and 7.4 GBq treatment arms. Clinical trial information: NCT03042312 .

TMIC-26. PRECLINICAL MODEL SYSTEMS OF GLIOBLASTOMA REVEAL MICROENVIRONMENTAL PROGRAMS AND DEPENDENCIES IN PATIENT TUMORS

Patient-derived model systems serve as a platform for translational research representing the heterogeneity of human cancers, and their success in recapitulating disease-driving genomic alterations is well-documented. While recent studies have demonstrated genomic and functional divergence in patient-derived models with passaging, the need for accurate preclinical models remains. Glioblastoma (GBM) is the most common and aggressive primary brain tumor, and thus far preclinical models have failed to consistently replicate the responses found in patients. We therefore aimed to evaluate the multi-omic fidelity of low-passage GBM model systems across in vitro and in vivo environments and to elucidate the molecular features in which they differ. To this end we established a biobank of glioma direct-from-patient orthotopic xenograft (GliomaPDOX) models and primary gliomasphere cultures (GSCs) and performed whole-exome and RNA sequencing of over 40 purified patient tumors and their matched GliomaPDOXs and GSCs to facilitate paired comparisons across a gradient of full tumor microenvironment (TME) presence. We observed global genomic and transcriptomic fidelity in both systems, but specific programmatic gene expression differences associated with cell-cell interactions in the brain TME, glial cell identity, and in vitro GSC-forming ability. GSCs and GSC-forming ability are strongly associated with an astrocytic gene expression signature, while more stem-like and oligodendrocytic patient tumors including IDH- and H3F3A-mutant GBMs more successfully engraft in GliomaPDOXs. This result implicates the brain TME as a support system for these more stem/oligo-like tumors. Transcription factor network analysis identified regulators of the NOTCH and MYC pathways as strongly enriched in this subgroup of patient tumors and their derivative xenografts, and provides potential targets for therapeutic intervention in near future experiments. Collectively, these findings underline the critical role of the TME in defining GBM cell state, reveal the heterogeneity of TME dependence across patient tumors, and link this dependency to therapeutically actionable molecular features.

PK-M2-mediated metabolic changes in breast cancer cells induced by ionizing radiation

PURPOSE

Radiotherapy (RT) constitutes an important part of breast cancer treatment. However, triple negative breast cancers (TNBC) exhibit remarkable resistance to most therapies, including RT. Developing new ways to radiosensitize TNBC cells could result in improved patient outcomes. The M2 isoform of pyruvate kinase (PK-M2) is believed to be responsible for the re-wiring of cancer cell metabolism after oxidative stress. The aim of the study was to determine the effect of ionizing radiation (IR) on PK-M2-mediated metabolic changes in TNBC cells, and their survival. In addition, we determine the effect of PK-M2 activators on breast cancer stem cells, a radioresistant subpopulation of breast cancer stem cells.

METHODS

Glucose uptake, lactate production, and glutamine consumption were assessed. The cellular localization of PK-M2 was evaluated by western blot and confocal microscopy. The small molecule activator of PK-M2, TEPP46, was used to promote its pyruvate kinase function. Finally, effects on cancer stem cell were evaluated via sphere forming capacity.

RESULTS

Exposure of TNBC cells to IR increased their glucose uptake and lactate production. As expected, PK-M2 expression levels also increased, especially in the nucleus, although overall pyruvate kinase activity was decreased. PK-M2 nuclear localization was shown to be associated with breast cancer stem cells, and activation of PK-M2 by TEPP46 depleted this population.

CONCLUSIONS

Radiotherapy can induce metabolic changes in TNBC cells, and these changes seem to be mediated, at least in part by PK-M2. Importantly, our results show that activators of PK-M2 can deplete breast cancer stem cells in vitro. This study supports the idea of combining PK-M2 activators with radiation to enhance the effect of radiotherapy in resistant cancers, such as TNBC.

Processing of Primary Patient Tumors and Subsequent Generation of Primary Cell Lines

Patient tumor tissue processing is an important step in the generation of clinically relevant specimens for in vitro and in vivo studies. Proper disassociation and tissue sample cleanup is a multistep, time-consuming process that ultimately effects the generation of patient derived xenografts and neurosphere cultures. Here we describe a detailed protocol on how to process and disassociate patient glioma tissue and subsequent steps on orthotopic implantation and in vitro generation of neurospheres.

Biosafety and Biohazards: Understanding Biosafety Levels and Meeting Safety Requirements of a Biobank

When it comes to biobanking and working with different types of laboratory specimens, it is important to understand potential biohazards to ensure safety of the operator and laboratory personnel. Biological safety levels (BSL) are a series of designations used to inform laboratory personnel about the level of biohazardous risks in a laboratory setting. There are a total of four levels ranked in order of increasing risk as stipulated by the Center of Disease Control and Prevention (CDC) (Biosafety in microbiological and biomedical laboratories, 5th edn. HHS publication no. (CDC) 21-1112. https://www.cdc.gov/biosafety/publications/bmbl5/bmbl.pdf . Accessed 2 Jan 2016, 2009). We will address the main distinctions between these levels including briefly introducing hazards characteristics that classify biohazardous agents, as well as define the essentials in meeting safety requirements.

Harnessing Preclinical Molecular Imaging to Inform Advances in Personalized Cancer Medicine

Comprehensive molecular analysis of individual tumors provides great potential for personalized cancer therapy. However, the presence of a particular genetic alteration is often insufficient to predict therapeutic efficacy. Drugs with distinct mechanisms of action can affect the biology of tumors in specific and unique ways. Therefore, assays that can measure drug-induced perturbations of defined functional tumor properties can be highly complementary to genomic analysis. PET provides the capacity to noninvasively measure the dynamics of various tumor biologic processes in vivo. Here, we review the underlying biochemical and biologic basis for a variety of PET tracers and how they may be used to better optimize cancer therapy.