Small Cell Lung Cancer Models Research Articles

Evaluating CD133 as a Radiotheranostic Target in Small-Cell Lung Cancer.

Despite decades of work, small-cell lung cancer (SCLC) remains a frustratingly recalcitrant disease. Both diagnosis and treatment are challenges: low-dose computed tomography (the approved method used for lung cancer screening) is unable to reliably detect early SCLC, and the malignancy's 5 year survival rate stands at a paltry 7%. Clearly, the development of novel diagnostic and therapeutic tools for SCLC is an urgent, unmet need. CD133 is a transmembrane protein that is expressed at low levels in normal tissue but is overexpressed by a variety of tumors, including SCLC. We previously explored CD133 as a biomarker for a novel autoantibody-to-immunopositron emission tomography (PET) strategy for the diagnosis of SCLC, work that first suggested the promise of the antigen as a radiotheranostic target in the disease. Herein, we report the in vivo validation of a pair of CD133-targeted radioimmunoconjugates for the PET imaging and radioimmunotherapy of SCLC. To this end, [89Zr]Zr-DFO-αCD133 was first interrogated in a trio of advanced murine models of SCLC─i.e., orthotopic, metastatic, and patient-derived xenografts─with the PET probe consistently producing high activity concentrations (>%ID/g) in tumor lesions combined with low uptake in healthy tissues. Subsequently, a variant of αCD133 labeled with the β-emitting radiometal 177Lu─[177Lu]Lu-DTPA-A″-CHX-αCD133─was synthesized and evaluated in a longitudinal therapy study in a subcutaneous xenograft model of SCLC, ultimately revealing that treatment with a dose of 9.6 MBq of the radioimmunoconjugate produced a significant increase in median survival compared to a control cohort. Taken together, these data establish CD133 as a viable target for the nuclear imaging and radiopharmaceutical therapy of SCLC.

Abstract A019: ATR inhibitor efficacy depends on CD8+ T-cell recruitment and MHC class-I upregulation via intratumoral STING pathway activation in small cell lung cancer

Abstract Introduction: Small cell lung cancer (SCLC) is the most aggressive subtype of lung cancer. Recent clinical trials of immune checkpoint blockade (ICB) combined with chemotherapy delivered only very modest benefits. Using genetic screens, we identified inhibition of G2/M cell cycle regulator, ataxia telangiectasia, and rad3 related (ATR), as a promising therapeutic target in small cell lung cancer (SCLC). In this study, we investigated the effect of targeting ataxia telangiectasia and rad3-related (ATR), the primary activator of the replication stress response, on the immune microenvironment in SCLC. We further confirm the efficacy of combining ATR inhibition with immune checkpoint blockade in SCLC. Methods: In this study, we performed genetic and pharmacological inhibition of ATR in a panel of human and murine SCLC cell lines. Furthermore, we investigated the effect of ATR inhibition either alone or in combination with PD-L1 blockade in multiple immunocompetent mouse models of SCLC. The downstream effects of ATR inhibition was assessed by bulk RNA sequencing, multicolor flow cytometry, western blot analysis and real-time qRT-PCR. The SCLC clinical samples from treatment naïve and patients treated with an ATR inhibitor we analysis by single cell and bulk RNA sequencing to ascertain the effect of ATR on immune subsets. Results: In multiple immunocompetent SCLC mouse models, ATR inhibition (ATRi) remarkably enhanced the anti-tumor effect of PD-L1 blockade. We next tested the ATR inhibition either alone or in combination with PD-L1 in the second-line regimen for SCLC. We observed that ATR inhibition in combination with PD-L1 blockade significantly reduced tumor volume and prolonged survival of aggressive mice models when compared to PD-L1 alone. Targeting ATR enhanced the expression of PD-L1, activated the cGAS/STING pathway, induced the expression of Type I and II interferon pathways, and caused significant infiltration of cytotoxic and memory/effector T-cells into tumors. Interestingly, ATRi also led to significant induction of MHC class I in SCLC in vitro and in vivo models. Single-cell analysis of patient samples confirms immunosuppressed phenotype in SCLC. Analysis of pre-and post-treatment clinical samples from a proof-of-concept study of a first-in-class ATR inhibitor, M6620 (VX970, berzosertib), and TOP1 inhibitor topotecan, in patients with relapsed SCLCs, validated the induction of MHC class I and interferon pathway genes, for the first time in this disease. Conclusion: Our findings highlight ATRi as a potentially transformative vulnerability of SCLC, paving the way for combination clinical trials with anti-PD-L1. We are the first to show that ATR inhibition can activate MHC class I in SCLC clinical samples. Given the increasing importance of immunotherapy for the management of SCLC and that ATR inhibitors are already in clinical trials, combining an ATR inhibitor with PD-L1 blockade may offer a particularly attractive strategy for the treatment of SCLC and contribute to the rapid translation of this combination into the clinic. Citation Format: Triparna Sen. ATR inhibitor efficacy depends on CD8+ T-cell recruitment and MHC class-I upregulation via intratumoral STING pathway activation in small cell lung cancer [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: DNA Damage Repair: From Basic Science to Future Clinical Application; 2024 Jan 9-11; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2024;84(1 Suppl):Abstract nr A019.

Genetically-engineered mouse models of small cell lung cancer: the next generation.

Small cell lung cancer (SCLC) remains the most fatal form of lung cancer, with patients in dire need of new and effective therapeutic approaches. Modeling SCLC in an immunocompetent host is essential for understanding SCLC pathogenesis and ultimately discovering and testing new experimental therapeutic strategies. Human SCLC is characterized by near universal genetic loss of the RB1 and TP53 tumor suppressor genes. Twenty years ago, the first genetically-engineered mouse model (GEMM) of SCLC was generated using conditional deletion of both Rb1 and Trp53 in the lungs of adult mice. Since then, several other GEMMs of SCLC have been developed coupling genomic alterations found in human SCLC with Rb1 and Trp53 deletion. Here we summarize how GEMMs of SCLC have contributed significantly to our understanding of the disease in the past two decades. We also review recent advances in modeling SCLC in mice that allow investigators to bypass limitations of the previous generation of GEMMs while studying new genes of interest in SCLC. In particular, CRISPR/Cas9-mediated somatic gene editing can accelerate how new genes of interest are functionally interrogated in SCLC tumorigenesis. Notably, the development of allograft models and precancerous precursor models from SCLC GEMMs provides complementary approaches to GEMMs to study tumor cell-immune microenvironment interactions and test new therapeutic strategies to enhance response to immunotherapy. Ultimately, the new generation of SCLC models can accelerate research and help develop new therapeutic strategies for SCLC.

Abstract B027: ATR inhibition upregulates PD-L1 and potentiates the antitumor immune response to chemoimmunotherapy in small-cell lung cancer

Abstract Introduction: Small cell lung cancer (SCLC) is the most aggressive subtype of lung cancer, with a very poor prognosis and limited therapeutic options. Recent clinical trials of immune checkpoint blockade (ICB) combined with chemotherapy delivered only very modest benefit. Here, we identified that ataxia telangiectasia and rad3 related (ATR), the primary activator of the replication stress response, is highly enriched in SCLC and inhibition of ATR induced DNA damage and apoptosis in multiple SCLC models. Methods: In this study, we performed genetic and pharmacological inhibition of ATR in a panel of human and murine SCLC models. Furthermore, we investigated the effect of ATR inhibition either alone or in combination with PD-L1 blockade either as a first-line or a second-line treatment in multiple immunocompetent mouse models of SCLC. The downstream effects of ATR inhibition was assessed by single-cell RNA sequencing, multicolor flow cytometry, western blot analysis, IHC, and genomic analysis. Results: In multiple immunocompetent SCLC mouse models, ATR inhibition (ATRi) remarkably enhanced the anti-tumor effect of PD-L1 blockade. We next tested the ATR inhibition either alone or in combination with PD-L1 in the second-line regimen for SCLC. We observed that ATR inhibition in combination with PD-L1 blockade significantly reduced tumor volume and prolonged survival of aggressive mice models when compared to PD-L1 alone. Targeting ATR enhanced the expression of PD-L1, activated the cGAS/STING pathway, induced the expression of Type I and II interferon pathways, and caused significant infiltration of cytotoxic and memory/effector T-cells into tumors. Interestingly, ATRi also led to significant induction of MHC class I in SCLC in vitro and in vivo models. Analysis of pre- and post-treatment clinical samples from a proof-of-concept study of a first-in-class ATR inhibitor, M6620 (VX970, berzosertib), and TOP1 inhibitor topotecan, in patients with relapsed SCLCs validated the induction of MHC class I and interferon pathway genes, for the first time in this disease. Conclusion: Our findings highlight ATRi as a potentially transformative vulnerability of SCLC, paving the way for combination clinical trials with anti-PD-L1. Given the increasing importance of immunotherapy for the management of SCLC and that ATR inhibitors are already in clinical trials, combining an ATR inhibitor with PD-L1 blockade may offer a particularly attractive strategy for the treatment of SCLC and contribute to the rapid translation of this combination into the clinic. Citation Format: Triparna Sen. ATR inhibition upregulates PD-L1 and potentiates the antitumor immune response to chemoimmunotherapy in small-cell lung cancer [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Tumor Immunology and Immunotherapy; 2023 Oct 1-4; Toronto, Ontario, Canada. Philadelphia (PA): AACR; Cancer Immunol Res 2023;11(12 Suppl):Abstract nr B027.

Abstract B028: WEE1 inhibition enhances the antitumor immune response to PD-L1 blockade by the concomitant activation of STING and STAT1 pathways in small cell lung cancer

Abstract Background: Small cell lung cancer (SCLC) is a poorly immunogenic, high-grade neuroendocrine carcinoma arising in the lung. Immune checkpoint blockade (ICB) added to chemotherapy is now the standard upfront therapy for SCLC but leads to a modest increase in overall survival and progression-free survival. These modest benefits underscore the critical need to identify pathways and targets that can durably enhance the antitumor responses of ICB in SCLC. SCLC is characterized by a ubiquitous loss of TP53 which disrupts the G1-S cell cycle checkpoint and as a result, most SCLC is dependent on G2-M cell cycle checkpoint regulators including WEE1. We and others have shown that DNA damage response (DDR) components are overexpressed in SCLC and targeting DDR could be an effective therapeutic strategy in SCLC. Methods: In this study, we have performed WEE1 inhibition either alone or in combination with PD-L1 blockade in a panel of SCLC models. Results: We demonstrate that inhibition of WEE1 induces G2/M cell cycle arrest, DNA damage, and cytosolic DNA accumulation in SCLC models. We further show that WEE1 targeting activates the STING-TBK1-IRF3 pathway which increases type I interferons (IFN-α and IFN-β) and pro-inflammatory chemokines (CXCL10 and CCL5), facilitating an immune response via CD8+ cytotoxic T-cell infiltration. We further show that WEE1 inhibition concomitantly activates the STAT1 pathway, increasing IFN-γ and PD-L1 expression. Consistent with these findings, combined WEE1 inhibition (AZD1775) and PD-L1 blockade caused remarkable tumor regression, activation of type I and II interferon pathways, and infiltration of cytotoxic T-cells in multiple immunocompetent SCLC genetically engineered mouse models, including an aggressive model with stabilized MYC. Conclusions: Our study demonstrates the cell-autonomous and immune-stimulating activity of WEE1 inhibition in SCLC. Given the increasing importance of immunotherapy for the management of SCLC and that WEE1 inhibitors are already in clinical trials, combining a WEE1 inhibitor with PD-L1 blockade may offer a particularly attractive strategy for the treatment of SCLC and contribute to the rapid translation of this combination into the clinic. Citation Format: Triparna Sen. WEE1 inhibition enhances the antitumor immune response to PD-L1 blockade by the concomitant activation of STING and STAT1 pathways in small cell lung cancer [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Tumor Immunology and Immunotherapy; 2023 Oct 1-4; Toronto, Ontario, Canada. Philadelphia (PA): AACR; Cancer Immunol Res 2023;11(12 Suppl):Abstract nr B028.

Macrophage Mediated Abscopal Effects of Radiation Therapy

Radiation therapy (RT) can activate both innate and adaptive immune responses, and the combination of RT and immunotherapy is thought to be a promising strategy. We found that the "don't-eat-me" molecule CD47 is highly expressed on the surface of small cell lung cancer (SCLC) cells, a highly metastatic form of lung cancer, and that blockade of CD47 can enhance the phagocytosis of SCLC cells by macrophages. In this study, we investigated whether combining CD47 blockade and RT could synergize to inhibit the tumor growth of SCLC as well as other cancers in preclinical models. We evaluated efficacy and immune responses by RT and CD47 blockade in SCLC preclinical models as well as in colon cancer and lymphoma preclinical models. We engrafted cancer cells into both flanks of recipient mice and irradiated only one side of tumors with or without CD47 antibodies to investigate local and systemic effects of RT and CD47 blockade. We also used liver metastases models and endogenous lung tumor models to investigate anti-tumor effects and immune responses in their tumor microenvironments. In human patients, we investigated immune responses after RT using CIBERSORTx. We found CD47 blockade potently enhances the local antitumor effects of RT in all the pre-clinical models of SCLC we tested. Strikingly, CD47 blockade also stimulates systemic "abscopal" effects inhibiting non-irradiated SCLC tumors in mice receiving RT. These effects are observed in liver metastases models and endogenous lung tumor models as well as subcutaneous tumor models. Surprisingly, these abscopal effects are independent of T cells but require macrophages that migrate into non-irradiated tumor sites in response to inflammatory signals produced by RT and are locally activated by CD47 blockade to phagocytose cancer cells. Similar abscopal antitumor effects were observed in other cancer models treated with RT and CD47 blockade. We also found that RT increases tumor infiltrating macrophages in human cancer patients. Interestingly, these abscopal antitumor effects are enhanced by PD-1 blockade in some models. Our data clearly demonstrate macrophage-mediated abscopal responses of RT when combined with CD47 blockade in a range of cancer models. The systemic activation of antitumor macrophages following radiation and CD47 blockade may be particularly important in cancer patients who suffer from metastatic disease. RT is a part of standard-of-care and CD47-blocking strategies are in clinical trials, therefore our observations may be rapidly translatable to cancer patients.

P53 restoration in small cell lung cancer identifies a latent cyclophilin-dependent necrosis mechanism

The p53 tumor suppressor regulates multiple context-dependent tumor suppressive programs. Although p53 is mutated in ~90% of small cell lung cancer (SCLC) tumors, how p53 mediates tumor suppression in this context is unknown. Here, using a mouse model of SCLC in which endogenous p53 expression can be conditionally and temporally regulated, we show that SCLC tumors maintain a requirement for p53 inactivation. However, we identify tumor subtype heterogeneity between SCLC tumors such that p53 reactivation induces senescence in a subset of tumors, while in others, p53 induces necrosis. We pinpoint cyclophilins as critical determinants of a p53-induced transcriptional program that is specific to SCLC tumors and cell lines poised to undergo p53-mediated necrosis. Importantly, inhibition of cyclophilin isomerase activity, or genetic ablation of specific cyclophilin genes, suppresses p53-mediated necrosis by limiting p53 transcriptional output without impacting p53 chromatin binding. Our study demonstrates that intertumoral heterogeneity in SCLC influences the biological response to p53 restoration, describes a cyclophilin-dependent mechanism of p53-regulated cell death, and uncovers putative mechanisms for the treatment of this most-recalcitrant tumor type.

De Novo and Histologically Transformed Small-Cell Lung Cancer Is Sensitive to Lurbinectedin Treatment Through the Modulation of EMT and NOTCH Signaling Pathways.

Small-cell lung cancer (SCLC) is a high-grade neuroendocrine tumor with dismal prognosis and limited treatment options. Lurbinectedin, conditionally approved as a second-line treatment for metastatic SCLC, drives clinical responses in about 35% of patients, and the overall survival (OS) of those who benefit from it remains very low (∼9.3 months). This finding highlights the need to develop improved mechanistic insight and predictive biomarkers of response. We used human and patient-derived xenograft (PDX)-derived SCLC cell lines to evaluate the effect of lurbinectedin in vitro. We also demonstrate the antitumor effect of lurbinectedin in multiple de novo and transformed SCLC PDX models. Changes in gene and protein expression pre- and post-lurbinectedin treatment was assessed by RNA sequencing and Western blot analysis. Lurbinectedin markedly reduced cell viability in the majority of SCLC models with the best response on POU2F3-driven SCLC cells. We further demonstrate that lurbinectedin, either as a single agent or in combination with osimertinib, causes an appreciable antitumor response in multiple models of EGFR-mutant lung adenocarcinoma with histologic transformation to SCLC. Transcriptomic analysis identified induction of apoptosis, repression of epithelial-mesenchymal transition, modulation of PI3K/AKT, NOTCH signaling associated with lurbinectedin response in de novo, and transformed SCLC models. Our study provides a mechanistic insight into lurbinectedin response in SCLC and the first demonstration that lurbinectedin is a potential therapeutic target after SCLC transformation.

First-in-human study of ABBV-011, a seizure-related homolog protein 6 (SEZ6)–targeting antibody-drug conjugate, in patients with small cell lung cancer.

3002 Background: Small cell lung cancer (SCLC) has a dismal prognosis and new therapies are urgently needed. SEZ6 is a transmembrane protein expressed in SCLC tumors that may be used as a therapeutic target. ABBV-011 is an antibody-drug conjugate (ADC) targeting SEZ6 with a calicheamicin payload, which has shown antitumor activity in preclinical models of SCLC. Preliminary results from the monotherapy dose-escalation and -expansion cohorts of the first-in-human ABBV-011 study are presented. Methods: Phase 1, open-label, multicenter study (NCT03639194) of ABBV-011 alone or in combination with budigalimab, a programmed cell death 1 inhibitor. Primary objectives were to assess the safety and tolerability and to determine the maximum tolerated dose (MTD) and/or recommended phase 2 dose of ABBV-011. Adults (≥18 years) with relapsed/refractory SCLC (1–3 lines of prior therapy) were enrolled. Dose escalation was guided by Bayesian continual reassessment method. ABBV-011 was administered intravenously at doses from 0.3 to 2.0 mg/kg once every 3 weeks. Dose expansion was conducted in SEZ6-selected patients. Results: At data cutoff on August 22, 2022, 99 patients were treated with ABBV-011 monotherapy. Median age was 63 years (range, 41–79), 50% of patients were male, and 68% had received ≥2 prior therapies. ABBV-011 ADC pharmacokinetics were approximately dose-proportional with an elimination half-life of 4.6 days across the dose range of 0.3–2.0 mg/kg. In dose escalation (n=26), 1 patient had a dose-limiting toxicity of grade (G) 3 fatigue at 2.0 mg/kg. We report safety and efficacy results for 40 patients in the dose-expansion 1.0-mg/kg ABBV-011 cohort. Median duration of treatment was 12 weeks (range, 1.9–63.3). Treatment-emergent adverse events (TEAEs) occurred in 39 (98%) patients, the most frequent being fatigue (48%), nausea (45%), anorexia (38%), thrombocytopenia (38%), and vomiting (35%). G3 TEAEs occurred in 18 (45%) patients, the most frequent being fatigue, thrombocytopenia, and neutropenia (10% each); 1 G4 TEAE of dyspnea was reported. Seven patients died due to malignant neoplasm/disease progression (n=6) or respiratory distress (n=1); none were related to ABBV-011. Hepatotoxicity was observed, including G≥2 TEAEs of hyperbilirubinemia (18%), increased gamma-glutamyltransferase (8%), ascites (5%), veno-occlusive liver disease (3%), and portal hypertension (3%). Confirmed objective response rate was 25% (10 partial responses [PR]), with median duration of response of 4.2 months (95% CI: 2.6, 6.7). Clinical benefit rate (CBR) was 65% (10 PR and 16 stable disease) and CBR lasting >12 weeks was 43%. The median progression-free survival was 3.5 months. Conclusions: The MTD was not reached and ABBV-011 was well tolerated at 1.0 mg/kg with promising antitumor activity observed. Further evaluation of ABBV-011 is ongoing. Clinical trial information: NCT03639194 .

Single-Cell Evolutionary Analysis Reveals Drivers of Plasticity and Mediators of Chemoresistance in Small Cell Lung Cancer.

Understanding the evolutionary dynamics of SCLC can shed light on key mechanisms such as cellular plasticity, heterogeneity, and chemoresistance.

IL-18-secreting CAR T cells targeting DLL3 are highly effective in small cell lung cancer models.

Patients with small cell lung cancer (SCLC) generally have a poor prognosis and a median overall survival of only about 13 months, indicating the urgent need for novel therapies. Delta-like protein 3 (DLL3) has been identified as a tumor-specific cell surface marker on neuroendocrine cancers, including SCLC. In this study, we developed a chimeric antigen receptor (CAR) against DLL3 that displays antitumor efficacy in xenograft and murine SCLC models. CAR T cell expression of the proinflammatory cytokine IL-18 greatly enhanced the potency of DLL3-targeting CAR T cell therapy. In a murine metastatic SCLC model, IL-18 production increased the activation of both CAR T cells and endogenous tumor-infiltrating lymphocytes. We also observed an increased infiltration, repolarization, and activation of antigen-presenting cells. Additionally, human IL-18-secreting anti-DLL3 CAR T cells showed an increased memory phenotype, less exhaustion, and induced durable responses in multiple SCLC models, an effect that could be further enhanced with anti-PD-1 blockade. All together, these results define DLL3-targeting CAR T cells that produce IL-18 as a potentially promising novel strategy against DLL3-expressing solid tumors.

Abstract CT218: A phase II trial of niraparib plus dostarlimab in relapsed small cell lung cancer and other high-grade neuroendocrine carcinomas

Abstract Objectives: Small cell lung cancer (SCLC) and high-grade neuroendocrine carcinomas (NECs) share many clinical features, including limited response to immune checkpoint inhibitors (ICIs). However, preclinical data suggest synergistic response with combined ICI and poly (ADP-ribose) polymerase inhibitors (PARPi) in SCLC models. This single-institution, phase II trial (NCT04701307) assessed the efficacy of a combination of the anti-PD-1 monoclonal antibody, dostarlimab, with the selective PARPi, niraparib, in patients with relapsed SCLC or NECs. Methods: Eligible patients with SCLC (Cohort 1) or NECs (Cohort 2) had received at least one prior line of therapy and were treated with niraparib 300 mg (or 200 mg if <77kg or platelets < 150,000/µL) PO daily, and dostarlimab 500 mg IV q21d (1000mg IV q42d starting with Cycle 5). Co-primary endpoints were objective response rate (ORR) by RECISTv1.1 and 6-month progression free-survival (PFS6). Using a Bayesian Optimal Phase 2 (BOP2) design, interim futility analyses were planned after enrolling up to 15 SCLC and 9 NEC patients (NEC), respectively. Adverse events (AE) were monitored continuously. Patients underwent biopsies, if feasible, at Cycle 1 and Cycle 3, as well as longitudinal plasma collection for translational studies. Results: From Feb 2021 to Aug 2021, 14 and 9 patients enrolled with SCLC and NEC, respectively. NECs included tumors from gynecological, head/neck, and gastrointestinal sites. In Cohort 1 (SCLC), 12 of 14 patients were evaluable by RECISTv1.1, including 1 complete response (CR), while 4 patients not achieving partial response (PR) had minor responses (-2%, -14%, -19%, and -24% from baseline). Only 1 patient in this cohort achieved PFS6, though 2 additional patients progressed between 5 and 6 months. In Cohort 2 (NEC), 6 of 9 patients were evaluable by RECISTv1.1 and no CR/PRs were observed. One patient did experience durable minor response (-21%), but no patients achieved PFS6. Dose-limiting, niraparib-related hematological AEs, typically thrombocytopenia, occurred in 12 of 23 patients. Non-hematological, treatment-related serious AEs occurred in only 1 patient (Grade 3 inflammatory arthritis), while 1 additional patient experienced brief dose-interruption due to Grade 2 pneumonitis. Preliminary translational data, including bulk and single-cell RNAseq, indicate molecular features, such as transcriptional subtype, are shared across SCLC and NECs and may predict response to this combination. Conclusions: In heavily pre-treated patients across SCLC and NEC cohorts, combined niraparib and dostarlimab failed to exceed interim futility criteria. However, multiple SCLC patients experienced durable disease control, including one patient with sustained CR and associated translational studies point to potential biomarker-driven approaches in the future. Trial supported by GlaxoSmithKline. Citation Format: Carl M. Gay, C. Allison Stewart, Michael Frumovitz, Junya Fujimoto, Yuann xi, Qi Wang, Runsheng Wang, Veronica Novegil, Mehmet Altan, Tina Cascone, Arvind Dasari, Yasir Y. Elamin, Frank V. Fossella, Bonnie S. Glisson, Charles S. Lu, Marcelo V. Negrao, Ferdinandos Skoulidis, Natalie Vokes, Robert J. Cardnell, Ignacio I. Wistuba, Jing Wang, John V. Heymach, Lauren A. Byers. A phase II trial of niraparib plus dostarlimab in relapsed small cell lung cancer and other high-grade neuroendocrine carcinomas [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr CT218.

Abstract LB233: Preclinical analysis identifies predictive biomarker and potential pathways of resistance to lurbinectedin treatment in small cell lung cancer

Abstract Background: Small cell lung cancer (SCLC) is an exceptionally aggressive disease with limited treatment options that typically result in transient responses. SCLC is responsible for approximately 250,000 deaths globally per year. Major hurdles to improving SCLC treatment include the development of rapid chemo-resistance and limited second-line therapies. Lurbinectedin is FDA approved as a second-line treatment for SCLC but shows a response in a subset of patients. Therefore, improved mechanistic understanding and identifying predictive biomarkers of lurbinectedin treatment is a major unmet clinical need. Methods: We treated SCLC cell lines and patient-derived xenograft (PDX) models from all major SCLC subtypes with lurbinectedin. Lurbinectedin-mediated changes in signaling pathways were studied by bulk RNA sequencing, western blot, and flow cytometry. Anti-tumor efficacy and toxicity studies were performed in vivo. Result: All human and PDX-derived SCLC cell lines showed sensitivity to lurbinectedin at a nano-molar concentration ranging from 1.905 to 30 nM. Bulk RNA-seq analysis showed lurbinectedin induced changes in neuroendocrine phenotype, DNA damage response and tumor progression markers in vitro. Single agent treatment of lurbinectedin showed remarkable anti-tumor efficacy in an ASCL1-driven PDX model. RNA sequencing analysis identified modulation of genes in multiple signaling pathways including PI3K-AKT, apoptosis and EMT to be significantly associated with the lurbinectedin response in PDX models. Conclusion: There is an immediate need to understand the subsets of SCLC that would be most sensitive to lurbinectedin and identify predictive biomarkers. We demonstrate MYC as a predictive biomarker for lurbinectedin response. We are the first to show that single agent lurbinectedin shows remarkable anti-tumor efficacy in a ASCL1-driven PDX models of SCLC. Furthermore, our pre and post-lurbinectedin treatment transcriptomic analysis identify the pathways that may contribute to primary or acquired resistance to lurbinectedin in SCLC. Finally, we identity candidate targets that would guide the design of future combination clinical trials with lurbinectedin in SCLC. Citation Format: Subhamoy Chakraborty, Charles Coleman, Deniz Demircioglu, Dan Hasson, Triparna Sen. Preclinical analysis identifies predictive biomarker and potential pathways of resistance to lurbinectedin treatment in small cell lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr LB233.

Abstract 2145: High SLFN11 expression correlates with sensitivity to lurbinectedin in small cell lung cancer (SCLC) models

Abstract Background: Lurbinectedin monotherapy received accelerated FDA approval for adults with metastatic SCLC with disease progression on or after platinum-based chemotherapy. Lurbinectedin binds to GC-rich areas of gene promoters, blocks RNA-polymerase-II and induces degradation via ubiquitin/proteasome machinery. DNA binding of lurbinectedin results in double stranded DNA breaks and DNA damage that leads to cellular apoptosis. Schlafen 11 (SLFN11), a putative DNA/RNA helicase irreversibly binds to DNA replication forks resulting in replication block and is a predictive biomarker of response to therapeutics that elicit DNA damage including cisplatin, topoisomerase I/II inhibitors and PARP inhibitors. Objective: Evaluate the role of SLFN11 expression in predicting response to lurbinectedin, a DNA damaging agent, in human SCLC cell lines and in vivo models. Methods: Cytotoxicity assays: SCLC cell lines DMS 53, DMS 114, NCI-H69, NCI-H82, NCI-H196, NCI-H209, NCI-H211, NCI-H446, NCI-H526, NCI-H841, NCI-H889, NCI-H1048, and SHP-77 were tested with lurbinectedin dose range from 100 nM to 0.01 nM. Cell viability was determined by measuring intracellular ATP to determine percent cellular viability and IC50 of lurbinectedin. SLFN11 expression of 13 SCLC cell lines were retrieved as RNAseq values from the DepMap database. RNAseq value >2 was assigned as SLFN11 high, values <2 assigned as low. Western blot analysis was used to confirm protein expression. The difference in 10log IC50 between SLFN11 high and low lines is determined using Mann-Whitney test. In vivo efficacy studies: High SLFN11 (NCI-H1048) and low SLFN11 (NCI-H889 and NCI-H69) SCLC cell lines were used for xenograft studies in BALB/c nude mice. Mice were randomly allocated to 4 groups (n=8) as tumors reached a volume of 100 - 150 mm3. Groups received either vehicle or lurbinectedin at doses of 0.06, 0.12 or 0.18 mg/kg IV, QWx 3 weeks. Immunohistochemistry was used to assess SLFN11 protein expression on xenograft tissue. Results and Conclusions: Cell viability assays in 13 SCLC models confirm high SLFN11 expressing cell lines are 4-fold more sensitive to lurbinectedin compared to low SLFN11 expressing cell lines (ΔpIC50 = 0.64; p = 0.0451). The in vivo efficacy data confirms that the SLFN11 high NCI-H1048 model is more responsive with 90% TGI compared to 35% observed in SLFN11 low models (NCI-H889 and NCI-H69) at the highest lurbinectedin dose (p-value = 0.006). Efficacy data confirms correlation to SLFN11 protein expression, consistent with the RNA level association. Both in vitro cytotoxicity and in vivo efficacy studies in SCLC models confirm that high SLFN11 expression predicts response to lurbinectedin. Cell viability studies demonstrate that a limited set of SLFN11 low expressing cell lines are sensitive to lurbinectedin, suggesting a role for other genes. Proteomics and genomics work is underway to define additional response biomarkers Citation Format: Aparna Gupta, Kedar S. Vaidya, Janneke J.T.M. Melis, Robert Hauptschein, Graham Brock, Robin Humphreys. High SLFN11 expression correlates with sensitivity to lurbinectedin in small cell lung cancer (SCLC) models [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 2145.

Abstract 6155: Lurbinectedin exhibits combinatorial activity with BCL2/BCL2L1 inhibitors in vitro and in vivo by modulation of MCL1 expression

Abstract Lurbinectedin (Zepzelca) is a marine-derived anti-tumor agent currently approved for metastatic small cell lung cancer (SCLC). Lurbinectedin has been previously shown to exert its anti-tumor effect by binding to the minor groove of DNA and inhibition of nucleotide excision repair. In addition, lurbinectedin inhibits transcription by inducing degradation of RNA polymerase II. While these activities hint towards a general mechanism, specific molecular targets for lurbinectedin remain obscure. We demonstrate that in vitro, Lurbinectedin specifically induced downregulation of MCL1 protein, a member of the BCL2 family of pro-survival proteins, in a dose- (0-30 nM) and time-dependent manner (0-24 h) by Western analysis. Expression of other pro-survival proteins BCL2 and BCL2L1 were not affected. The downregulation of MCL1 was consistent in all nine tumor cell lines tested regardless of indication. Increased activity or expression of MCL1 is a known compensatory mechanism to offset loss of BCL2 or BCL2L1. We therefore hypothesized that lurbinectedin induced MCL1 loss, along with inhibition of the pro-survival proteins BCL2 and BCL2L1 would lead to an enhancement in cell killing. Consistent with the dominant pro-survival role of BCL2 in SCLC, the combination of lurbinectedin with a specific BCL2 inhibitor (venetoclax) in vitro induced synergistic cytotoxicity (measured by Bliss Sum analysis) in a panel of small cell lung cancer lines. In solid tumor lines other than SCLC, the combination of lurbinectedin with a specific BCL2L1 inhibitor (A-1331852) was also synergistic. Correspondingly in vivo, enhancement in the efficacy of lurbinectedin was observed in combination with venetoclax in SCLC models, while in solid tumor models other than SCLC the combination with a specific BCL2L1 inhibitor enhanced efficacy. Collectively, these data identify MCL1 as a specific lurbinectedin target and suggest that combinations that target other pro-survival proteins may represent a viable strategy to enhance the anti-tumor activity of lurbinectedin. Citation Format: Kedar S. Vaidya, Aparna Gupta, Robert Hauptschein, Robin C. Humphreys. Lurbinectedin exhibits combinatorial activity with BCL2/BCL2L1 inhibitors in vitro and in vivo by modulation of MCL1 expression [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 6155.

Abstract 5042: Anti-tumor activity of RYZ101 (Ac-225 DOTATATE) in somatostatin receptor-expressing preclinical models of small-cell lung cancer

Abstract Introduction: Overexpression of somatostatin receptors (SSTRs), particularly SSTR2, is found in gastroenteropancreatic neuroendocrine tumors (GEP-NETs), and subsets of other solid tumors such as small-cell lung cancer (SCLC). β-emitting radiopharmaceutical therapy Lu-177 DOTATATE has been approved for SSTR-expressing (SSTR+) GEP-NETs, but the relatively low objective response rate and frequent post-treatment progression represent an unmet medical need. Based on preliminary clinical anti-tumor efficacy, RYZ101 (Ac-225 DOTATATE) is being developed for inoperable SSTR+ well-differentiated GEP-NETs with disease progression following Lu-177-somatostatin analogue (SSA) therapy (ACTION-1, NCT05477576). SCLC accounts for approx. 13% of lung cancer and lacks effective therapeutic options. Immunohistochemistry analysis indicates that ~50% of SCLC tumors are SSTR2+, with a substantial subset showing high and homogenous expression. The goal of this study was to provide preclinical support for RYZ101, as a single-agent or in combination with carboplatin and etoposide, for SSTR+ SCLC. Methods: RYZ101 is comprised of the α-emitting radioisotope actinium-225, chemical chelator DOTA, and SSA octreotate (TATE). Binding affinity to human SSTR1-5 was determined using a competitive radioligand binding assay in engineered cell lines expressing individual SSTR. Internalization was measured by PathHunter SSTR2 Activated GPCR Internalization Assay. The preclinical biodistribution of RYZ101 was carried out in non-tumor-bearing BALB/c mice of both sexes. The efficacy studies were performed in cell line-derived and patient-derived xenograft (PDX) models of SCLC. Results: In preclinical studies where Lanthanum (La3+) was used as a surrogate for Ac-225, RAYZ-10001-La (La-DOTATATE) had high binding affinity (Ki=0.057nM) to human SSTR2 (>600-fold more potent than other SSTR subtypes) and exhibited efficient internalization. In a preclinical biodistribution study, RYZ101 performed similarly to Lu-177 DOTATATE. In multiple SCLC xenograft models, RYZ101 significantly inhibited tumor growth and prolonged survival, with deeper responses, including sustained regression, observed in the models with higher SSTR2 level. The anti-tumor effect was further enhanced when combining RYZ101 with carboplatin and etoposide at clinically relevant doses. Conclusions: In summary, RYZ101 is a first-in-class, highly potent, α-emitting radiopharmaceutical therapy being developed for the treatment of SSTR+ solid tumors. Preclinical data demonstrate the potential of RYZ101 for the treatment of patients with SSTR+ SCLC. Citation Format: Guangzhou Han, Eunmi Hwang, Fanching Lin, Renee Clift, Daniel Kim, Eric Bischoff, Susan Moran, Gary Li. Anti-tumor activity of RYZ101 (Ac-225 DOTATATE) in somatostatin receptor-expressing preclinical models of small-cell lung cancer. [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 5042.

Abstract 5727: Identification of synthetic lethal vulnerabilities in cancers with loss of function mutations in NOTCH

Abstract Loss of Function (LOF) mutations in the NOTCH receptors are found in several different cancers most notably in small cell lung cancer (SCLC) and squamous cell carcinomas (SCC). We previously developed genetically engineered mouse models (GEMM) of SCLC using CRISPR/Cas9 engineered to be NOTCH1-Mutant, NOTCH2-Mutant, and NOTCH-WT. Synthetic lethality provides a paradigm for targeting cancers with LOF mutations in tumor suppressor genes. In applying this paradigm, one looks for specific vulnerabilities that are created upon loss of the gene of interest. Using 6 cell lines developed from these CRISPR-based SCLC GEMMs which are isogenic to NOTCH, we performed CRISPR/Cas9 LOF negative selection screens (using an sgRNA library enriched in druggable enzymes) to identify synthetic lethal interactors with LOF NOTCH mutations. Our CRISPR/Cas9 screen identified TRIM28 (Tripartite Motif Containing 28, or KAP1) as a highly significant synthetic lethal interactor with NOTCH1 or NOTCH2. We validated the synthetic lethal interaction between NOTCH1/2 and TRIM28 using both human and mouse NOTCH-isogenic cell lines. Interestingly, RNA-sequencing of NOTCH2-Mutant or NOTCH-WT SCLC cell lines after TRIM28 CRISPR inactivation showed robust increases in endogenous retroviral (ERV) expression and the MDA5/RIG-I/MAVS RNA-sensing machinery leading to hyperactivation of the TBK1/IRF3/7 innate immune signaling pathway and the pro-inflammatory cytokine CXCL10 selectively in cells with NOTCH inactivated. Notably, inactivation of TBK1 activity or JAK-STAT activity using specific small molecule inhibitors of TBK1 or JAK completely reversed the synthetic lethality between NOTCH and TRIM28 suggesting that the synthetic lethality phenotype is a consequence of hyperactivation of innate immune signaling, which is known to be cytotoxic. Together our findings uncover a novel vulnerability in SCLCs with LOF NOTCH mutations and perhaps other cancers with LOF NOTCH mutations and suggest a strategy that could also potentiate anti-tumor immunity by increasing innate immune signaling in tumor cells. Citation Format: Deli Hong, Matthew A. Booker, Sidrah Anjum, Yixiang Li, Tran C. Thai, Michelle Y. Wang, David A. Barbie, Michael Y. Tolstorukov, Jun Qi, Matthew G. Oser. Identification of synthetic lethal vulnerabilities in cancers with loss of function mutations in NOTCH. [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 5727.

Abstract 1645: JAB-2485: A potent, highly selective small-molecule Aurora kinase A inhibitor that targets cell division

Abstract Background: Aurora kinase A (AURKA), a crucial mitotic regulator, is frequently dysregulated in a wide range of cancers and contributes to clinical aggressiveness and poor patient survival. Abnormally activated AURKA promotes tumorigenesis through enhancing cancer cell proliferation, epithelial-mesenchymal transition, and cancer stem cell self-renewal, rendering it an attractive therapeutic target. We have developed JAB-2485, a highly selective small-molecule AURKA inhibitor. Methods: Biochemical and cell-based assays were performed to determine the IC50 of JAB-2485 on Aurora kinase family members. Fluorescence activated cell sorting (FACS) and caspase 3/7 assay were performed to detect JAB-2485-induced cell cycle arrest and apoptosis, respectively. The CellTiter-Glo assay was performed to evaluate the effect of JAB-2485 in multiple cancer cell lines. Finally, the antitumor effect of JAB-2485 either as a single agent or in combinations was investigated in tumor cell line-derived xenografts. Results: JAB-2485 is potent and highly selective on AURKA, with IC50 of 0.33nM and around 1700-fold selectivity over AURKB. Following treatment of JAB-2485, the level of AURKA phosphorylation as a pharmacodynamic marker was significantly decreased in a dose-dependent manner. As a single agent, JAB-2485 inhibited in vitro proliferation of small cell lung cancer (SCLC), triple-negative breast cancer (TNBC) and neuroblastoma cell lines along with induced G2/M cell cycle arrest and apoptosis, and significantly inhibited in vivo tumor growth on SCLC and neuroblastoma xenografts. Furthermore, JAB-2485 showed strong synergy with cisplatin and paclitaxel in SCLC and TNBC animal models, respectively. Conclusions: Taken together, preclinical results provide robust evidence supporting further evaluation of JAB-2485 both as a single agent and in combinations for treatment of various types of cancers. A Phase 1/2a clinical trial of evaluating JAB-2485 in adult patients with advanced solid tumors is enrolling patients in the US (NCT05490472). Citation Format: Guiqun Yang, Yanping Wang, Haijun Li, Mingming Chen, Yiwei Lin, Xin Sun. JAB-2485: A potent, highly selective small-molecule Aurora kinase A inhibitor that targets cell division [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 1645.

Abstract 2648: In vivo efficacy and preclinical safety profile of NN3201, an anti-cKIT antibody-drug conjugate, for treating SCLC and AML

Abstract Overexpression and activating mutations of cKIT are associated with tumor aggressiveness and poor prognosis in various cancer patients such as small cell lung cancer (SCLC), gastrointestinal stromal tumor (GIST), acute myeloid leukemia (AML), and mastocytoma. Since small molecule inhibitors including imatinib frequently have a limited therapeutic application due to eventual drug resistance and severe adverse events, we developed the cKIT-directed antibody-drug conjugate (ADC), NN3201, for the treatment of wild-type and mutant cKIT-positive cancers. NN3201 is an ADC conjugate of the antimitotic payload MMAE to the fully human 2G4 antibody, directed against cKIT, via the cysteine re-bridging technology ThioBridge® at a drug-to-antibody ratio (DAR) of 4. NN3201 displayed preferable biophysical properties and broadly potent in vitro antitumor activities across various cKIT-positive tumor cell lines. NN3201 exhibited potent in vivo antitumor activities in cKIT-positive tumor cell line xenograft and patient-derived tumor xenograft models of SCLC and AML, representing robust and durable antitumor responses. Furthermore, in a single-dose toxicity study with cynomolgus monkey, no significant or severe clinical toxicity signs were observed in animals dosed at 1, 2, and 3 mg/kg. Even though a decrease in reticulocyte, red cell mass (hemoglobin and red blood cell), neutrophil, and monocyte counts, along with bone marrow recovery and reticulocyte compensatory mechanism, red blood cell and white blood cell recovery were observed from day 14 in the low and medium dose groups and day 21 in the high dose group, dose-dependently. These preclinical results suggest that NN3201 is a potential therapeutic agent for the treatment of cKIT-positive cancers and support the further clinical evaluation in SCLC and AML. Citation Format: Han-Jik Ko, Sung Tae Kim, Jin Gu Cho, Jin-Ock Kim, Jung Tae Lee, Sang Gyu Park. In vivo efficacy and preclinical safety profile of NN3201, an anti-cKIT antibody-drug conjugate, for treating SCLC and AML [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 2648.

Onionin A inhibits small-cell lung cancer proliferation through suppressing STAT3 activation induced by macrophages-derived IL-6 and cell–cell interaction with tumor-associated macrophage

Tumor-associated macrophage (TAM)-derived IL-6 is involved in small-cell lung cancer (SCLC) progression and chemoresistance via the activation of signal transducer and activator of transcription 3 (STAT3) in the tumor microenvironment. This study aimed to identify natural compounds that suppress cell–cell interactions between TAMs and SCLC cells by inhibiting STAT3 activation. We used a library of natural compounds to identify candidate agents possessing anti-SCLC effects by inhibiting macrophage-induced tumor proliferation. SBC-3 and SBC-5, human SCLC cell lines, were used for in vitro experiments. Furthermore, we assessed the efficacy of these candidate agents in a murine xenograft model of human SCLC. Among the natural compounds examined, onionin A (ONA) inhibited IL-6-induced STAT3 activation and SCLC cell proliferation. ONA also reduced the secretion of IL-6 from macrophages and interfered with the direct effect of cell–cell interactions between macrophages and SCLC cells. Furthermore, ONA administration suppressed tumor progression in a tumor-bearing mouse model. ONA was identified as the most useful candidate for targeting cell–cell interactions between cancer cells and TAMs for anti-SCLC therapy.