Small Cell Lung Cancer Cell Research Articles

Abstract 1108: Evaluation of heme inhibitory therapy in combination with chemotherapy drugs on SCLC progression

Abstract Lung cancer is the leading cause of cancer-related death in the US. It is mainly divided in two types: small cell lung cancer and non-small cell lung cancer. About 85-90% of cases are classified as non-small cell lung cancer (NSCLC). Small cell lung cancer (SCLC) is an aggressive neuroendocrine lung tumor representing 15% of lung cancers. Despite the advent of targeted therapies and chemotherapies, effective therapies for lung cancer are an unlikely outcome for most patients. SCLC is initially highly responsive to cisplatin and etoposide chemotherapy but, in almost every case, becomes rapidly chemo resistant. However, the mechanisms underlying initial sensitivity and subsequent resistance are not well investigated. Thus, alternative approaches and combination therapy is required for treating SCLCs. Recent studies in our lab show that NSCLC cells demonstrate elevated levels of heme via increased heme uptake and synthesis, and elevated oxidative phosphorylation (OXPHOS) and ATP generation which fuels NSCLC proliferation. Also, limiting heme via inhibition of heme uptake using heme sequestering peptides (HeSP2) can delay growth and progression of NSCLC tumors. This HeSP2 can also effectively inhibit angiogenesis, normalize tumor vasculature, and alleviate tumor hypoxia in NSCLC tumors and thereby inhibit lung tumor growth and progression. Tumor heterogeneity is critical for tumor growth, metastasis, and acquired therapeutic resistance. To understand if heme can effectively reduce tumor cell proliferation and growth and improve tumor microenvironment, we treated chemo resistant SCLCs with HeSP2 and in combination with commonly used chemo drugs cisplatin and etoposide. Our data shows that HesP2 can strongly inhibit cell proliferation and decreases oxygen consumption rate along with ATP generation in SCLCs. To gain insights into mechanism by which the heme sequestering peptides limit tumor growth and progression, we implanted subcutaneous or SCLC cell lines in NOD/SCID mice. Mice were treated with saline (control), HeSP2, HeSP2 and cisplatin, HeSP2 and etoposide. Tumor growth was monitored using caliper measurements. Tumors tissues were harvested, processed and paraffin embedded for immunohistochemistry (IHC) and histology experiments. These results indicate that heme sequestration can be a powerful strategy for suppressing lung tumors likely drug-resistant tumors that rely on oxidative phosphorylation for survival. Citation Format: Adnin Ashrafi, Narges Salamat, Li Zhang. Evaluation of heme inhibitory therapy in combination with chemotherapy drugs on SCLC progression [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 1108.

Abstract 2557: Slit2 inhibits small cell lung cancer by targeting tumor microenvironment

Abstract Small cell lung cancer (SCLC) is the deadliest subtype of lung cancer with a 5-year survival rate of <5% in extensive-state disease and is designated by US Congress as a “recalcitrant cancer”. Recently approved by FDA, immune checkpoint blockade (ICB) immunotherapy showed marginally improved survival and only in a few patients, suggesting an inert immune tumor microenvironment (TME) and the existence of SCLC subtypes. Therefore, there is a significant need to develop more effective therapies for SCLC. In addition to the nearly universal biallelic inactivation of Rb and Tp53 genes in human SCLC tumors, comprehensive genome-wide screening studies have identified major co-occurring mutations in PTEN, CREBBP, EP300, SLIT2, MLL, COBL, and EPHA7 genes. Among them, SLIT2 showed the highest level of genomic abnormalities defined by a pronounced clustering of mutations and frequent genomic loss. However, the role of Slit2 in SCLC has not been defined yet. By using genetically engineered human SCLC cells overexpressing Slit2 or recombinant Slit2 (rSlit2) protein, we show that Slit2 inhibits SCLC cells proliferation, migration, and invasion properties and tumor sphere formation ability of drug-resistant SCLC cells in vitro. The mechanistic studies have identified inhibition of AKT and β-catenin mediated signaling pathways by Slit2 overexpression. Next, we implanted human SCLC cell lines into the immunocompromised NSG mice subcutaneously followed by treatment with rSlit2 or sterile saline. Analysis of tumor volume over the 4 weeks showed that rSlit2 treatment significantly reduced the growth of SCLC tumors. Further analysis of tumors showed that rSlit2 treated tumors harbor less M2-like CD206+ macrophages. Overall, these results suggest that Slit2 possesses tumor suppressive properties and could be developed as a novel therapeutic agent against SCLC. Citation Format: Dinesh K. Ahirwar, Manish Charan, Swati Misri, Konstantin Shilo, Ramesh Ganju. Slit2 inhibits small cell lung cancer by targeting tumor microenvironment [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 2557.

Abstract LB030: Mechanisms of ERK action in MEK inhibitor-insensitive lung cancers

Abstract Small cell lung cancer (SCLC) and other neuroendocrine (NE) lung tumors account for 25% of all lung cancers, they are the most aggressive type and have the poorest prognosis. SCLC does not present driver oncogenes involved in the regulation of kinase signaling, which makes these tumors hard to treat. The few available treatments yield responses early, but relapse occurs and they become resistant. Due to the poor efficacy of therapies, research in SCLC had been moved to the background, with basically no progress over the past decades. Mutations in the RAS-ERK pathway, elevating ERK activity and enhancing tumorigenesis, are common in other types of cancer, including NSCLC. Nevertheless, they are rare in SCLC. Indeed, previous studies demonstrated that ERK activation interferes with growth of SCLC. However, the mechanism by which ERK hinders tumor progression has not been defined yet. One of the most important players in SCLC and other NE tumors is the transcription factor ASCL1, essential for their survival. It has been reported that ASCL1 increases DUSP6 transcription with the consequent ERK activity suppression. Its downregulation affects cell cycle progression and survival. Conversely, inhibition of ERK activation by MEK inhibitors increases ASCL1 mRNA levels. Previous studies in our laboratory suggested that DUSP6 has a major role in a subset of SCLC and NSCLC-NE cell lines. Inhibition of DUSP6 enhances ERK signaling and significantly decreases survival of NE lung tumor cells. We have considered DUSP6 a good candidate to try to understand the mechanism by which ERK interferes with survival. However, hurdles in studying DUSP6 in SCLC include off-target effects of inhibitors and difficulty of gene-edited cell lines. To date, we have been able to generate a DUSP6 KO NSCLC-NE cell line which shows a clear drop in proliferation. Also, the overexpression of ERK or a constitutively active MEK1 mutant in a few SCLC, NE-NSCLC and MEK inhibitor-insensitive squamous lung cancer cell lines render a decrease in survival. DUSP6 is a cytoplasmic anchor for ERK and may reduce the ability of ERK to suppress ASCL1 transcription. For this reason, we are working on studying the effect on survival of ERK localization in the nucleus or the cytoplasm. With our ongoing experiments we are defining the conditions to examine transcriptional impact of ERK on SCLC. Discovering molecular events antagonized by the ERK pathway in SCLC will reveal novel targets controlling the inhibitory mechanisms. One of the SCLC major questions of translational relevance is what are the mechanisms upholding the development of chemoresistance, where the ERK pathway seems to be involved. Hence, the definition of the underlying mechanisms of tumorigenesis and therapy resistance will uncover new potential antitumor targets that currently escape our notice. A better understanding of the molecular biology of SCLC will let us find new therapeutic strategies to overcome the impasse in chemotherapy. Citation Format: Ana Martin-Vega, Svetlana Eartnest, John D. Minna, Jane E. Johnson, Melanie H. Cobb. Mechanisms of ERK action in MEK inhibitor-insensitive lung cancers [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 LB030.

Abstract 2153: ATR inhibition augments the efficacy of the lurbinectedin in small cell lung cancer

Abstract Small cell lung cancer (SCLC) is a recalcitrant disease with only a 9% five-year survival rate. SCLCs display intertumoral heterogeneity; high neuroendocrine (NE) tumors evolve with treatment and time in a largely MYC driven manner to a chemotherapy resistant non-NE state. Lurbinectedin, an RNA Pol-II inhibitor which causes DNA damage through binding ERCC5 was approved as second line therapy in 2020, with an overall response rate of 35% in patients with relapsed SCLC. However, these responses are short-lived and the majority of patient still succumb to their disease. A trial testing the combination of lurbinectedin and doxorubicin failed to improve survival compared with standard-of-care. We assessed lurbinectedin in combination with 43 other agents in SCLC cells. The top synergistic hit was the clinically relevant ATR inhibitor berzosertib which was 4-fold more synergistic than doxorubicin. Compared with lurbinectedin alone, the combination with berzosertib caused a 3.5-fold increase in DNA damage while significantly reducing the ability of cells to sense this damage by inhibiting γH2AX induction. This led to continued DNA replication even in the presence of lurbinectedin induced DNA damage, causing mitotic catastrophe and cell death. The combination was highly synergistic in 6 of 9 SCLC cell lines tested. Synergy was inversely correlated with p21 RNA and protein expression. The canonical role of p21 is to inhibit G1/S transition, and we found that thymidine induced G1 arrest inhibited synergy, while p21 knock-down increased the synergy. Interestingly, we observed synergy was inversely correlated with NE differentiation. In a high NE high p21 mouse model of SCLC, lurbinectedin alone was highly effective, with the combination showing little improvement. Conversely in a non-NE low p21 mouse model, lurbinectedin treatment alone was less effective, however the addition of berzosertib was synergistic and significantly improved efficacy. Overall, this work demonstrated berzosertib augments lurbinectedin efficacy in the recalcitrant non-NE SCLC subsets, and supported the development of a clinical trial testing lurbinectedin and berzosertib in SCLC patients NCT04802174. Citation Format: Christopher William Schultz, Yang Zhang, Haiqing Fu, Yasuhisa Murai, Darawalee Wangsa, Devon Atkinson, Liton Saha, Brian Elenbaas, Chien-Fei Lee, Astrid Zimmerman, Thomas Ried, Frank Zenke, Zoe Weaver, Rajaa Elmeskini, Yves Pommier, Anish Thomas. ATR inhibition augments the efficacy of the lurbinectedin in small cell lung cancer [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 2153.

Abstract 2908: PT217, an anti-DLL3/anti-CD47 bispecific antibody, exhibits anti-tumor activity through novel mechanisms of action

Abstract Small cell lung cancer (SCLC) is the most lethal subtype of lung cancers with few patients surviving more than 5 years from diagnosis. While SCLC initially responds well to standard chemotherapy treatment, chemotherapy-resistant recurrence is characteristic and available treatment options for recurrent and refractory diseases are limited. Immunotherapy as an alternative or additional treatment has been very successful in treating many cancers, yet it has shown disappointingly limited benefits in SCLC and notable treatment related toxicities have been observed. Delta like 3 (DLL3) is an attractive target for SCLC immunotherapy, as its expression is highly restricted to SCLC and can therefore be used for targeting purposes. On the other hand, CD47 is also strongly expressed on the surface of SCLC cells, where it inhibits macrophage-mediated tumor cell killing. We have developed PT217, a DLL3/CD47 bispecific antibody with effector effect competent Fc to specifically target SCLC cells via two mechanisms. First, PT217 blocks the CD47-SIRPα interaction and stimulates phagocytosis of tumor cells by macrophage. Second, PT217 exhibits robust effector effect (ADCC by NK cells and ADPC by macrophage) mediated by the functional Fc of PT217. Interestingly, it appears that the tumor cells targeted by NK cells are subsequently engulfed by macrophage. Elevated phagocytosis of the tumor cells by macrophages and dendritic cells is expected to increase the presentation of tumor neoantigens that may eventually lead to T cell-mediated killing of tumor cells that do not expression DLL3. In vivo, PT217 demonstrated tumor suppression activity in xenograft mouse models. In addition to the strong tumor killing activity, PT217 also demonstrated good safety profile in NHP studies. Furthermore, PT217 exhibits regular mAb-like manufacturability in process development and CMC. We expect to initiate a phase 1 trial to target SCLC in the first half of 2022. Citation Format: Haiqun(John) Jia, Dorthy Fang, Molly Lobsinger, Yan Long, Kelan Chen, Albert Lam, Yangyang Guo, Kaisa Selesniemi, Ming Wang, Hui Zou. PT217, an anti-DLL3/anti-CD47 bispecific antibody, exhibits anti-tumor activity through novel mechanisms of action [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 2908.

Abstract 921: The Nrf2E79Q activating mutation accelerates growth of pure-small cell lung cancer but not combined small cell lung cancer Tp53floxed/floxed/Cdkn2afloxed/floxed mice

Abstract Inactivating mutations in TP53/P16 are found in most types of non-small cell lung cancer while RB1/P16 losspredominates in small cell lung cancer (SCLC). NRF2 activating mutations are also found frequently in lungcancer, especially in lung squamous cell carcinoma. However, how concurrent mutations in these genes maycontribute to lung cancer development is not fully understood. To address this problem, we compared lung tumordevelopment in a genetically-engineered mouse model (GEMM) with dual Trp53/p16 deficiency, +/- expressionof one of the most common mutations in NRF2 found in human tumors, Nrf2E79Q/+. Surprisingly, both groups,Nrf2E79Q/+ and Nrf2+/+, developed combined-SCLC (C-SCLC): a mixture of SCLC and large cell neuroendocrine(NE) carcinoma along with pure-SCLC (P-SCLC). The appearance of C-SCLC implicates Trp53/p16 double lossin the development of this type of lung cancer. Both groups developed C-SCLC at the same penetrance andincidence; all tumors labeled positive for NE-markers by immunohistochemistry (IHC) including ASCL1, SYP andINSM1. However, C-SCLCs developed by Nrf2E79Q/+ mice did not show NRF2 labeling by IHC, despiterecombination of the Nrf2E79Q/+ allele. In contrast, the Nrf2E79Q/+ mice showed significantly higher incidence of P-SCLC compared to Nrf2+/+ mice. All P-SCLC from Nrf2E79Q/+ mice were NRF2-positive by IHC, while the fewtumors developed by Nrf2+/+ mice were negative. All P-SCLC lesions labeled positive for NE-markers includingASCL1, CGRP & SYP. Both C-SCLCs & P-SCLCs were positive for NKX1.2 (lung cancer-marker) and negativefor P63 (squamous cell-marker). Interestingly, phospho-RB1 was positive for both C-SCLCs & P-SCLCs,suggesting the loss of p16 in our GEMM inactivates Rb1 through loss of inhibition of the cyclin dependent kinases4/6 (CDK4/6). This is the first study showing that the concurrent inactivation of Trp53/p16 in mice drivesdevelopment of C-SCLC. Our study also implicated activation of NRF2 signaling in the progression of SCLC.Our next studies will dissect the mechanisms by which NRF2 activation contributes to the development of SCLCdevelopment. Citation Format: Samera Hamad, Stephanie A. Montgomery, Jeremy M. Simon, Brittany M. Bowman, Kyle B. Spainhower, Ryan M. Murphy, Agnieszka Witkiewicz, Suzanne E. Fenton, Scott H. Randell, Neil Hayes, Erik Knudsen, Trudy G. Oliver, Ben Major, Bernard E. Weissman. The Nrf2E79Q activating mutation accelerates growth of pure-small cell lung cancer but not combined small cell lung cancer Tp53floxed/floxed/Cdkn2afloxed/floxed mice [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 921.

Abstract 3098: The first circulating tumor cell-derived explant (CDX) model of a Merkel cell carcinoma

Abstract NeuroEndocrine Carcinomas (NECs) are rare yet lethal diseases; they are frequently metastatic and have limited treatment options. Whilst progress has been made in understanding the biology of Small Cell Lung Cancer (SCLC), the most studied NEC, research on NECs from other anatomical sites lags behind. In SCLC, circulating tumor cells (CTCs) can be used to generate patient-relevant mouse models; termed CTC-Derived eXplants (CDX) which are faithful in biology and chemotherapy response to donor patients1,2. A pilot prospective study is on-going to assess the potential utility of cell-free DNA (cfDNA) and/or CellSearch (CS) CTCs (EpCAM/cytokeratin positive) as liquid biopsies and feasibility of CDX generation from patients with advanced stage extrapulmonary NECs undergoing palliative chemotherapy. CS CTCs are enumerated before and during treatment and marker-independent RosetteSep-enriched CTCs from parallel blood samples are implanted in immunodeficient mice to attempt CDX generation. Twenty-seven patients were recruited from Jun-19 to Nov-21. CS-CTCs were present in 19/27; 70% pre-treatment samples (mean 57, median 2, range 0-685 CTCs per 7.5mL of blood). CDX generation was successful from a pre-treatment CTC sample from a patient originally diagnosed with a NEC of unknown origin who responded to Platinum/Etoposide. Whole-exome sequencing of this CDX and matched pre-treatment cfDNA from the donor revealed largely overlapping copy number changes and common mutations including an activating PIK3CA mutation. In addition, there was no evidence of TP53 or RB1 loss (hallmarks of SCLC) in neither the CDX nor the donor’s cfDNA. Immunohistochemical (IHC) analysis of this CDX showed a small cell NEC morphology, 90% Ki-67 positive cells, expression of EpCAM, pan-cytokeratins and neuroendocrine (NE) diagnostic markers, concordant with the donor’s biopsy. Further IHC and RNA sequencing revealed expression of the NE transcription factor atonal homolog 1 (ATOH1)2, CK20 and abundant Merkel cell polyomavirus (MCPyV) transcripts. These characteristics prompted reclassification of the original patient diagnosis as Merkel cell carcinoma (MCC). There was only 1 CS-CTC in the parallel pre-treatment blood sample implying that EpCAM-negative CTCs may have given rise to the CDX. The CDX showed in vivo sensitivity to Platinum/Etoposide, mirroring treatment response of the donor. Ex vivo cultures from CDX-derived cells grow as suspension clusters similar to ‘classic’ SCLC and MCPyV-positive MCC cell lines. In summary, this first Merkel Cell Carcinoma CDX recapitulates the biology of the donor’s tumor. As the donor remains alive 25 months from diagnosis of advanced disease, their CDX can serve as an avatar to guide future treatment. 1. Hodgkinson et al., Nature Med 2014, 20: p. 897-903. 2. Simpson et al., Nature Cancer 2020, 1: p. 437-451. Citation Format: Melissa Frizziero, Elaine Kilgour, Kathryn L. Simpson, Dominic Rothwell, Kristopher Frese, Melanie Galvin, Yitao Chen, Alastair Kerr, Sam Humphrey, Mukarram Hossain, Juan W. Valle, Mairéad G. McNamara, Caroline Dive. The first circulating tumor cell-derived explant (CDX) model of a Merkel cell carcinoma [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 3098.

Abstract 2360: The role of the neurogenic transcription factor ATOH1 in small cell lung cancer

Abstract SCLC is an aggressive neuroendocrine (NE) cancer with a 7% 5-year survival rate. SCLC is treated as a clinically homogenous disease, but evidence of its intra- and inter-tumor heterogeneity is increasing. This is partly attributed to expression of neurogenic transcription factors (TFs) ASCL1 and NEUROD1, which correlate with SCLC pathogenesis and NE status, and are now included in a consensus for SCLC classification1. Our Circulating tumor cell patient Derived eXplant (CDX) models recapitulate disease heterogeneity in terms of neurogenic TF expression; furthermore, we recently identified a previously unrecognized subset within our CDX biobank expressing another neurogenic TF, ATOH12. ATOH1 function has been inferred from mouse embryonic and neonatal developmental mouse models, where Atoh1 governs the formation of cerebellar granule cells, auditory hair cells and Merkel cells. In human settings, ATOH1 reprograms pluripotent stem cells to a neuronal lineage and has context-dependent activity in cancer, being considered an oncogene in medulloblastoma and a tumor suppressor in the intestine3. I am investigating the role of ATOH1 in SCLC, to refine disease classification and explore new therapeutic approaches stratified to SCLC phenotypes. To interrogate the role of ATOH1 in SCLC, we developed an in-house antibody and established stable SCLC CDX and cell lines in which ATOH1 can be inducibly depleted in vitro and in vivo. To understand the transcriptional profile mediated by ATOH1, we performed ChIP-Seq and RNA-Seq in ATOH1-competent and depleted cells and integrated the datasets to infer ATOH1 direct transcriptional targets. In concordance with its role in development, ATOH1 direct transcriptional targets are enriched for processes regulating neurogenesis and inner ear hair cell differentiation. ATOH1 depletion in vitro in CDX17P resulted in elevated expression of Non-NE marker genes and NE to Non-NE phenotype transition, confirmed by gene set enrichment analysis, which implicated a possible role for ATOH1 in regulating neuroendocrine plasticity in SCLC. ATOH1 depletion resulted in a significant increase in apoptosis-independent cell death (p < 0.003), and whilst ATOH1 depletion did not affect cell proliferation in CDX17P, there was decreased S-phase progression in CDX30 and HCC33 cells. Depletion of ATOH1 in CDX17P In vivo did result in slower tumor growth and further studies will investigate the impact of ATOH1 on cell death, proliferation and NE to Non-NE transition in vivo. In summary, we have characterized a rare subset of SCLC expressing ATOH1 and found that ATOH1 is necessary for cell survival in vitro and ablation of ATOH1 slows tumor growth in vivo. Ongoing studies focus on investigating possible therapeutic approaches to modulate ATOH1 expression. Citation Format: Alessia Catozzi, Mitchell Revill, Jordan Roebuck, Sam Humphrey, Melanie Galvin, Fiona Blackhall, Kathryn Simpson, Alastair Kerr, Kristopher Frese, Caroline Dive. The role of the neurogenic transcription factor ATOH1 in small cell lung cancer [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 2360.

Abstract 4056: ONC201 in combination with carboplatin and etoposide as a novel triple drug treatment for small cell lung cancer (SCLC)

Abstract Lung cancer is the leading cause of cancer death in both men and women according to the American Cancer Society, with more deaths than colon, breast, and prostate cancer combined. Small cell lung cancer (SCLC) comprises about 10 to 15 percent of all lung cancer diagnoses. Frequent loss of RB1 and mutations in p53 in SCLC make it rather difficult to develop targeted therapies. Many current therapies rely on toxic chemotherapy or immunotherapy to combat the aggressive nature of SCLC; however, even with the advent of new therapies, the median survival rate has remained relatively low at 12 to 16 months. SCLC is also characterized by a high mutation rate, resulting in patients becoming increasingly resistant to treatments. This calls for a novel combination to extend patient life expectancy. ONC201 is an imipridone that is currently in clinical trials for its proapoptotic effects in several cancer types. We propose that combining ONC201 with standard first-line chemotherapeutic agents etoposide and carboplatin will result in a synergistic effect and serve as a novel treatment plan for SCLC patients. SCLC cell lines H1048 and H1105 were treated with the novel triple drug combination ONC201, etoposide, and carboplatin. Cell-Titer Glo cell viability assays were conducted for 72 hours to see the additive and/or synergistic effect of novel triple drug treatment. Western blots were also run to evaluate the expression of proapoptotic protein cleaved PARP or expression of cellular metabolic stress protein ATF4 to explore the synergistic effect of triple drug treatments in SCLC cell lines. Cell viability after the triple drug treatment in both cell lines H1048 and H1105 may indicate a potential synergistic effect. Preliminary western results indicate that the triple drug treatment results in an increase in cPARP or ATF4 expression relative to the vehicle, suggesting a synergistic effect of the triple drug treatment. We are currently exploring the novel combination and potential underlying mechanisms behind the synergistic effects of the triple drug treatment. Future studies will evaluate this triple drug combination treatment in mouse models of SCLC. Citation Format: Young S. Lee, Lanlan Zhou, Christopher Azzoli, Wafik S. El-Deiry. ONC201 in combination with carboplatin and etoposide as a novel triple drug treatment for small cell lung cancer (SCLC) [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 4056.

Abstract 5479: Discovery and evaluation of GT19630, a c-Myc/GSPT1 cereblon E3 ligase modulator (CELMoD), for targeting Myc-driven blood cancers and small cell lung cancers (SCLC)

Abstract c-Myc is an oncogenic transcriptional factor driving tumor initiation, progression and poor prognosis in 80% of all tumor types, especially in B-cell malignancies and small cell lung cancer (SCLC) with Myc genomic alterations. Myc dysregulation have been directly linked to the poor clinical outcome in these cancers. Therefore, it is highly warranted to discover and develop novel Myc therapeutical agents for targeting Myc driven cancers. Here we described GT19630, a GSPT1/Myc CELMoD. GT19630 was discovered through an SAR effort for c-Myc degrader by using c-Myc ELISA and Western blot assays in c-Myc driven HL60 AML cells. GT19630 selectively degraded c-Myc proteins in HL60 cells (IC50=1.5 nM) as compared to growth-factor regulated c-Myc erythroid progenitor cells (TF-1 cells) with IC50=52.5 nM. GT19630 also selectively inhibited HL60 cell proliferation (IC50= 0.33 nM), as compared to its IC50 (26.2 nM) in GM-CSF-TF-1 proliferation, as well as in bone marrow colony-forming cell assays (myeloid=40.2 nM), suggesting>100X selectivity for HL60 cells over normal blood cells. Through the SAR for Myc degrader, GT19630 has been evolved as a leading molecule sharing chemical properties to CELMoDs. Therefore, this compound was further evaluated by proteomics and western blot, GT19630 was confirmed to selective degradation of CELMoD targets, GSPT1/GSPT2 (translation termination factor G1 to S phase transition proteins 1 and 2) with IC90<1 nM and CK1 alpha (IC90<10 nM), but not IKZF1/Ikaros. In silico modeling of GT19630 was performed in the DDB1−CRBN−CC-885−GSPT1 complex and confirmed the docking similarity with CELMoDs. Further, GT19630 inhibited the cell proliferation with IC50<10 nM in 74% B-cell malignant cell lines (20/27) bearing deregulated c-Myc and in 79% of SCLC cell lines (4/19) carrying deregulated Myc (c-Myc, N-Myc or L-Myc) tested. Moreover, GT19630 completely degraded Myc proteins in AML, lymphoma and multiple myeloma (c-Myc) and SCLC (c-Myc and N-Myc) xenograft tumors at the lowest dose of 1.0 mg/kg and induced complete tumor regression (lowest dose=0.3 mg/kg) tested. Furthermore, this compound eradicated lymphoma cells in Daudi-induced liquid lymphoma mouse models. In addition, GT19630, as a potent GSPT1/Myc CELMoD, demonstrated an even-driven pharmacology in vivo and induced complete tumor regression with a dosing regimen of 3 day on/7 day off. Remarkably, GT19630 selectively degraded Myc proteins in HL60 and DMS114 SCLC xenograft tumors as compared to a much less potency at degrading c-Myc in rat spleen. Finally, GT19630 demonstrated favorable PK and safety profiles (an 8-fold safety therapeutic windows) with no effect on myeloid lineages in rats at the dose of 6 mg/kg for 14 days, indicating GT19630 lacks myelosuppression as reported for other CELMoDs. Currently, GT19630 has been advanced into IND enabling stage. Citation Format: Liandong Ma, Youzhi Tong, Zhaohui Yang, Qianxiang Zhou, Hongha Yan, Ru Xu, Jie Chen, Jie Pan, Huiyuan Wang, Jiangwei Li, Dong Chen, Xiang Cai, Jie Qu, Yini Wang, Jun Qin, Yuki Nishida, Michael Andreeff, Qilnli Guo, Yuki Nishida, Michael Andreeff. Discovery and evaluation of GT19630, a c-Myc/GSPT1 cereblon E3 ligase modulator (CELMoD), for targeting Myc-driven blood cancers and small cell lung cancers (SCLC) [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 5479.

Abstract 5709: Transcriptional circuitry of NKX2-1 and SOX1 defines a previously unrecognized lineage subtype of small cell lung cancer

Abstract Introduction: The current molecular classification of small cell lung cancer (SCLC) based on expression of four lineage transcription factors, SCLC-A (ASCL1), SCLC-N (NEUROD1), SCLC-P (POU2F3), and SCLC-Y (YAP1) still leaves its major subtype SCLC-A as a large heterogeneous group, necessitating more precise characterization of lineage subclasses. Experimental procedure: To refine the current SCLC classification and to identify specific lineage features of the SCLC subtypes, we performed unsupervised hierarchical clustering of H3K27ac profiles on transcriptional regulators from 25 SCLC cell lines and determined the epigenomic features for each cluster. Functional significance of the transcriptional lineage regulators for the identified cluster was evaluated by cell growth, apoptosis and xenograft using CRISPR-Cas9-mediated deletion. The specific cistromic profiles by ChIP-seq and its functional transcriptional partners using co-immunoprecipitation followed by mass spectrometry were determined to reveal their functional output in the identified subtype. Rb1fl/flTrp53fl/fl and Rb1fl/flTrp53fl/flNkx2-1fl/fl genetic engineered mouse model were generated to explore the function of Nkx2-1 in tumor initiation and differentiation. H3K27ac profiles were further analyzed to reveal 6 human SCLC specimen and 20 mice tumors epigenomic landscapes. Summary: We identified previously uncharacterized epigenomic sub-clusters of the major SCLC-A subtype, named SCLC-A1 and SCLC-A2. SCLC-A1 was characterized by the presence of a super-enhancer at the NKX2-1 locus, which was observed in human SCLC specimens and a murine SCLC model. We found NKX2-1, a dual lung and neural lineage factor, is uniquely relevant in SCLC-A1, where it maintains neural lineage rather than pulmonary epithelial identity. We further found maintenance of this neural identity in SCLC-A1 is mediated by collaborative transcriptional activity with another neuronal transcriptional factor SOX1. ? Conclusions: We comprehensively describe an additional epigenomic heterogeneity of the major SCLC-A subtype, and define SCLC-A1 subtype by the core regulatory circuitry representing NKX2-1 and SOX1 super-enhancers and their functional collaborations to maintain a neuronal linage state. Citation Format: ranran kong, Ayushi S. Patel, Takashi Sato, Seungyeul Yoo, Abhilasha Sinha, Yang Tian, Feng Jiang, Charles A. Powell, Eric Snyder, Jiantao Jiang, Shaomin Li, Hideo Watanabe. Transcriptional circuitry of NKX2-1 and SOX1 defines a previously unrecognized lineage subtype of small cell lung cancer [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 5709.

Abstract 2303: The WEE1 inhibitor Debio 0123 enhances the efficacy of standard of care DNA damaging agents in lung cancer models

Abstract Introduction: The WEE1 tyrosine kinase is activated upon DNA damage and regulates the G2-M and S phase cell cycle checkpoints. Inhibition of WEE1, in conjunction with genetic alterations and/or addition of a DNA damaging agent, results in mitotic catastrophe and apoptosis of cancer cells, offering an attractive approach to treating cancer. Debio 0123 is a WEE1 specific inhibitor previously shown to sensitize cancer cells to DNA damaging agents which is currently being assessed in combination with carboplatin in patients with advanced solid malignancies. Small cell lung cancer (SCLC) is an aggressive disease with poor clinical outcomes that carries a high mutational burden and genomic instability. Here we investigated the ability of Debio 0123 to enhance SCLC response to standard of care (SOC) DNA damaging agents carboplatin and etoposide in vitro and in vivo. Methods: SCLC cell lines were treated with Debio 0123 alone or in combination with etoposide or carboplatin in vitro and apoptosis assessed by flow cytometry. In vivo SCLC patient derived- or cell line derived-xenograft (PDX or CDX, respectively) models were treated with Debio 0123 orally in combination with either carboplatin or etoposide alone or as a triple combination. Tumor growth inhibition was assessed over 3 cycles of treatment and tolerability of the combinations evaluated by monitoring body weight changes. Results: Debio 0123 synergized with carboplatin and etoposide in vitro leading to a significant increase in the induction of apoptosis. Additionally, Debio 0123 significantly improved the tumor growth inhibitory effect of etoposide and carboplatin in both PDX and CDX models of SCLC in vivo. Triple combination of carboplatin, etoposide and Debio 0123 was well tolerated at therapeutically relevant dosing and resulted in significantly improved tumor response when compared to carboplatin and etoposide treatments alone or to the double combination. Conclusions: Taken together these results highlight that inhibiting WEE1 with Debio 0123 significantly improves tumor response to SOC DNA damaging agents in models of SCLC, providing the foundation for future clinical exploration of Debio 0123 in SCLC. Citation Format: Luke Piggott, Anne Vaslin-Chessex, Noemie Luong, Benjamin Tschumi, Gregoire Vuagniaux. The WEE1 inhibitor Debio 0123 enhances the efficacy of standard of care DNA damaging agents in lung cancer models [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 2303.

Abstract 6238: Profiling of the circulating cell-free DNA methylome for detection and subtyping of small cell lung cancers

Abstract Introduction: Small-cell lung cancer (SCLC) is a high-grade neuroendocrine carcinoma characterised by high proliferation rate and early, rapid metastatic spread. Although SCLC is treated as a homogenous disease, recent studies revealed morphologic and transcriptomic heterogeneity with several molecular subtypes described based on predominant transcription factor expression (ASCL1, NEUROD1, ATOH1, POU2F3, YAP1) (Rudin et al., 2019; Simpson et al., 2020) which in preclinical studies exhibit differing vulnerabilities raising the potential of stratified therapy. DNA methylation is also thought be an important regulator of SCLC biology (Gazdar et al., 2017) and epigenetically distinct subtypes derived from SCLC primary tumour samples reported (Poirier et al., 2015). Here, we developed a robust workflow for genome-wide DNA methylation profiling to examine the potential use of cfDNA methylation profiling for detection and subtyping of SCLC. Results: To evaluate SCLC genome-wide DNA methylation patterns we employed a bisulfite-free enrichment-based approach (T7-MBD-seq). We tested this approach on tissue samples from preclinical models and from normal lung (n=110) and on cfDNA samples from both patients with SCLC and from non-cancer controls (n=157). Methylation profiles from preclinical models (patient-derived xenografts (PDX) and CTC derived explant (CDX) models) were comparable to previously described methylation patterns from SCLC primary tumours and were recapitulated in patients’ cfDNA samples. A tumour/normal classifier, based on 4,061 genomic regions detected as being hypermethylated in SCLC preclinical models, correctly assigned 93% and 100% cfDNA samples from patients with limited and extensive stage SCLC respectively, with a statistically significant correlation of prediction scores with disease stage (P=0.0076). Finally, to determine whether cfDNA methylation profiling could subtype SCLC patients, we built a subtype classifier, based on methylation signatures derived from 59 established SCLC cell lines. We applied the classifier to cfDNA samples from 56 patients and 10/11 with known subtypes (identified from a donor matched CDX model) were correctly classified. Overall, 73% of cfDNA samples were classified as ASCL1, 13% were classified as NEUROD1 and 14% were classified as being double negative with the distribution of the subtypes correlating closely to previously published IHC data from SCLC tissue samples (Baine et al., 2020). Conclusions: Our data reveal two potential clinical utilities of cfDNA methylation profiling; a universally applicable liquid biopsy approach for more sensitive detection and monitoring of SCLC and molecular subtyping to ease the path to future clinical trials of subtype stratified treatments for patients with SCLC. Citation Format: Dominic G. Rothwell, Francesca Chemi, Simon Pearce, Alex Clipson, Steven Hill, Alicia Marie Conway, Sophie Richardson, Katarzyna Murat, Rebecca Caeser, Jacklynn Egger, John T. Poirier, Alastair Kerr, Fiona Blackhall, Charles M. Rudin, Caroline Dive. Profiling of the circulating cell-free DNA methylome for detection and subtyping of small cell lung cancers [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 6238.

Abstract 3874: Engineered microphysiological systems for testing effectiveness of cell-based cancer immunotherapies in small cell lung cancer

Abstract Background: Immune cell trafficking into solid tumors has proven challenging due to immune cell exclusion by vascular barriers. Additionally, testing next-generation immune therapies remains difficult in animal models and requires sophisticated ex vivo systems to study human tumor biology and predict treatment response in real time. SCLC comprises approximately 15% of all lung cancer cases and despite recent incorporation of immune checkpoint blockade (ICB) into first line treatment, patients with SCLC continue to have a poor prognosis and limited treatment options. Notably, recent transcriptomic profiling of SCLC has indicated significant inter-tumoral and intra-tumoral heterogeneity. We have previously demonstrated that neuroendocrine SCLC subpopulations downregulate MHC I, whereas non-neuroendocrine SCLC subpopulations exhibit increased innate immune signaling and robust upregulation of MHC I antigen presentation. Here we interrogate the vulnerability of SCLC populations to NK cells and investigate their trafficking using a novel microphysiological ex vivo model. Methods: We developed a 3-dimensional (3D) microphysiological TME model of vascularized SCLC, comprising tumor spheroids embedded in a microvascular network self-assembled by endothelial cells and lung fibroblasts. Real time fluorescence imaging, cell-titer Glo and flow cytometry were used to quantify tumor cell viability in 2D and 3D microfluidic co-culture cytotoxicity assays, using primary NK cells and the NK92 cell line. Results: We demonstrated robust targeting of MHC-I low SCLC cells by primary human NK cells and NK92, and found that MHC-I high SCLC subpopulations show resistance to NK cell-mediated killing. To dissect the influence of vascular barriers on immune cell trafficking, we developed a 3D microphysiological TME model of vascularized SCLC, which successfully recapitulated tumor-vascular-immune interactions in a human-relevant platform as evidenced by vascular perfusion by NK cells. Using this model, we were able to demonstrate that the activation of cGAS-STING signaling in endothelial cells results in the secretion of CXCL10 and upregulation of adhesion molecules (ICAM-1, VCAM-1, E-selectin), promoting immune cell recruitment. Conclusions: We successfully developed a 3D microphysiological model of vascularized SCLC TME and show proof of principle that this model can be used for preclinical studies of cell therapies. Using this novel microphysiological system, we revealed that co-opting STING signaling can promote NK cell recruitment to the SCLC TME. Taken together, we show that microphysiological systems can be used to identify and test therapeutic vulnerabilities while studying immune infiltration and killing in the TME, offering an accurate and adaptable platform for biologic discovery and therapeutic development. Citation Format: Marco Campisi, Minyue Chen, Nathaniel Spicer, Patrick Lizotte, Erik H. Knelson, Cloud P. Paweletz, David A. Barbie, Navin R. Mahadevan. Engineered microphysiological systems for testing effectiveness of cell-based cancer immunotherapies in small cell lung cancer [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 3874.

Abstract 2602: Combined inhibition of AXL and ATR enhances cell death and immune response in small cell lung cancer

Abstract Small cell lung cancer (SCLC) is an aggressive lung tumor of neuroendocrine origin with a dismal 5-year survival rate. Despite high response rates to initial therapy, rapid development of therapeutic resistance limits overall survival. There are also limited treatment options, particularly in the relapsed setting. Our group and others have shown that AXL, a TAM family receptor tyrosine kinase that is highly expressed in mesenchymal tumors, mediates resistance to chemotherapy, radiation and targeted therapies in SCLC, non-small cell lung cancer and other cancers, through its roles in driving epithelial to mesenchymal transition and DNA damage repair. AXL has also been implicated in immune escape. Based on these findings, we hypothesize that AXL targeting may be a potential therapeutic approach in SCLC. We screened BGB324 (bemcentinib), a selective small-molecule AXL inhibitor in clinical trials for various advanced solid tumors, in a panel of 60 human SCLC cell lines using cell viability assays. The SCLC cell lines showed a range of sensitivities, with IC50 values ranging from 41 nM to 10 µM (median IC50 3.1 µM) with NeuroD1-driven SCLC cell lines being highly sensitive to BGB324 (ANOVA p<0.05). BGB324 also showed potent inhibition of tumor growth in an in vivo SCLC model. BGB324 further combined synergistically with an ATR inhibitor (AZD3738) and induces significant DNA damage. In a syngeneic model of SCLC, the combination of BGB324, AZD6738 and an anti-PDL1 antibody combination also induced significant tumor regression. Together, these promising findings show that AXL inhibition may be effective in SCLC and support further investigation of AXL and ATR inhibitor combinations with immune checkpoint blockade. Citation Format: Kavya Ramkumar, Azusa Tanimoto, C. Allison Stewart, Qi Wang, Li Shen, Robert J. Cardnell, B. Leticia Rodriguez, Don L. Gibbons, Jing Wang, Carl M. Gay, Lauren A. Byers. Combined inhibition of AXL and ATR enhances cell death and immune response in small cell lung cancer [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 2602.

Abstract 3594: Exportin 1 inhibition as a therapeutic strategy for small cell lung cancer

Abstract Small cell lung cancer (SCLC) is an aggressive disease characterized by early metastasis and exceptional lethality, comprising 13% of all lung cancer cases. With few treatment options, typically resulting in only transient responses, SCLC is responsible for approximately 250,000 deaths globally per year. The backbone of SCLC treatment over the past several decades has been platinum-based doublet chemotherapy, with the recent addition of immunotherapy to first-line chemotherapy showing limited benefit in a small subset of patients. Major hurdles to improving SCLC treatment include development of rapid chemoresistance and ineffective second line therapies. The identification of more durably effective therapeutic strategies is a major unmet clinical need. Here, we performed an in vitro CRISPR screen in SCLC cell lines from all major SCLC subtypes, including short-term cultured cells from patient-derived xenografts (PDXs), to identify potential therapeutic targets to enhance sensitivity to chemotherapy. Candidate hits were validated genetically and pharmacologically with in vitro synergy assays, in vivo clonal competition assays and pharmacologic assessments in PDX models. Signaling pathways were studied by RNA sequencing and western blot, and toxicity studies were performed in vivo to assess the safety of the agents at pharmacologically effective doses. We performed immunohistochemistry (IHC) to assess expression of candidate targets in tissue microarrays (TMAs). Our CRISPR screen revealed the nuclear exporter exportin 1 (encoded by the XPO1 gene) as a promising target sensitizing to chemotherapy, independently of the SCLC subtype. We found that XPO1 mRNA expression was higher in SCLC than in any other solid tumor or hematological malignancy, and demonstrated consistently high protein expression by IHC in clinical TMAs. A potent and selective exportin 1 inhibitor, selinexor, is approved for use in hematological malignancies. Combination of selinexor with cisplatin or irinotecan demonstrated synergy in vitro and efficacy in vivo in an array of chemonäive and chemoresistant SCLC PDXs, including all major SCLC subtypes. The combinations were well tolerated in mice. The chemo-sensitizing effects of selinexor were associated with suppression of chemotherapy-induced AKT activation. In conclusion, exportin 1 inhibition strongly enhances sensitivity of SCLC tumors to cisplatin and irinotecan, used in first line and second line treatment of SCLC tumors, respectively, and these effects are independent of the SCLC subtype. These results provide preclinical rationale for the combination of selinexor with cisplatin or irinotecan in naïve and relapsed SCLC. The clinical availability of selinexor will allow rapid clinical translation of these results in a disease setting with extremely limited therapeutic options. Citation Format: Alvaro Quintanal-Villalonga, Hirokazu Taniguchi, Yuan Hao, Andrew Chow, Yingqian A. Zhan, Fathema Uddin, Viola Allaj, Parvathy Manoj, Nisargbhai S. Shah, Umesh K. Bhanot, Juan Qiu, Elisa de Stanchina, Richard P. Koche, Triparna Sen, John T. Poirier, Charles M. Rudin. Exportin 1 inhibition as a therapeutic strategy for small cell lung cancer [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 3594.

Abstract 4204: CDK4/6 inhibition mitigates chemotherapy-induced immunosuppression and enhances the efficacy of chemo- immunotherapy in small cell lung cancer models

Abstract Small cell lung cancer (SCLC) is an aggressive form of lung cancer with a notably low survival rate. Chemotherapy and more recently its combination with immunotherapy are the standard of care for extensive stage SCLC. Although this combinatorial treatment provides clinical benefit, it can be hampered by the effect of chemotherapy on inducing immunosuppression. Cyclin dependent kinases 4/6 (CDK4/6) phosphorylate retinoblastoma (Rb) protein and promote proliferation of Rb-intact hematopoietic stem progenitor cells (HSPCs) by allowing cells to progress through S phase. Rb loss is a signature mutation in SCLC tumors, making these tumor cells unresponsive to CDK4/6 inhibition. Therefore, we hypothesized that CDK4/6 inhibitors could be utilized to block the proliferation of Rb-intact HSPCs and protected them from chemotherapy without altering the effect of chemotherapy on Rb-deficient SCLC cells. We treated Rb-deficient SCLC cancer cells and Rb-intact NK and T cells with increasing concentrations of cisplatin, etoposide and topotecan with or without the CDK4/6 inhibitor G1T28. Cell proliferation, apoptosis and cell cycle were analyzed using CellTiter-Glo, Annexin V staining, and PI-based cell cycle analysis. In vitro, CDK4/6 inhibition did not alter the impact of chemotherapy on Rb-deficient SCLC cell viability, whereas with Rb-intact NK and T cells, CDK4/6 inhibitor treatment induced cell cycle arrest and prevented apoptosis induced by chemotherapeutic agents. In the TKOTmG Rb-deficient mouse model of SCLC, CDK4/6 inhibition improved the efficacy of cisplatin plus etoposide. In vivo studies using the KP-1 syngeneic mouse models showed that treatment with a CDK4/6 inhibitor improved the efficacy of chemotherapy and immunotherapy individually or chemo-immunotherapy combinations by reducing the tumor growth rate and prolonging animal survival. CDK4/6i treatment prior to chemotherapy preserved white blood cell counts in comparison to chemotherapy alone. Tissue and blood immune marker analysis showed that CDK4/6 inhibitor treatment increased both the circulating and tumor-resident NK cells. Collectively, we demonstrated that CDK4/6 inhibition does not antagonize the therapeutic impact of chemotherapy on Rb-deficient SCLC cells but enhances the efficacy of chemotherapy and immunotherapy in KP-1 syngeneic SCLC mouse model. CDK4/6i also at least partially abrogated the chemotherapy-induced reductions in subpopulatons of immune cells. CDK4/6 inhibition may be considered as a therapeutic strategy for mitigating chemotherapy-induced immunosuppression and enhance antitumor immunity in SCLC patients. Citation Format: Thiruvengadam Arumugam, Irene G. Muñoz, Alissa Poteete, Fahoa Zhang, Monique Nilsson, John S. Yi, Jessica A. Sorrentino, Andrew P. Beelen, John V. Heymach. CDK4/6 inhibition mitigates chemotherapy-induced immunosuppression and enhances the efficacy of chemo- immunotherapy in small cell lung cancer models [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 4204.

Abstract 2565: CDK9 inhibitor KB-0742 is active in preclinical models of small-cell lung cancer

Abstract Small-cell lung cancer (SCLC) is a highly aggressive malignancy, with a 5-year survival rate below 5%. In contrast to non-small cell lung cancer, in which treatment advancements have shown much success, there has not been significant progress in the development of new therapies for SCLC over the last 40 years. Thus, an urgent need exists to identify new and effective pharmacological interventions for these patients. Recent advancements in the understanding of the pathology of the disease has shown that SCLC tumorigenesis and evolution is governed by increased expression of neuroendocrine-associated and other proto-oncogenic transcription factors such as ASCL1, NEUROD1, and MYC. Thus, targeting transcription may be an effective therapeutic strategy. Cyclin-dependent kinase 9 (CDK9) is a serine-threonine kinase that is involved in transcriptional elongation through the phosphorylation of the RNA polymerase II. Additionally, CDK9 interacts with transcription factors such as MYC to promote activation of target genes. Inhibition of CDK9 results in disrupted transcriptional networks and inhibition of cancer cell proliferation and survival, making CDK9 an attractive target for the treatment of SCLC. We have developed a highly selective and orally bioavailable inhibitor of CDK9, KB-0742. Here we present the evaluation of KB-0742 activity in preclinical models of SCLC. Using the Broad PRISM platform, we evaluated the sensitivity of 24 SCLC cell lines. We observed a correlation between MYC copy number amplification and sensitivity with amplified lines having smaller AUC values than non-amplified lines (Mann-Whitney-Wilcoxon; P>0.05). We observed a similar trend of lower IC50 values with increasing levels of MYC expression in a separate cell-line screen that included 5 SCLC lines (Pearson’s correlation; P=0.71). We then evaluated KB-0742 activity in a panel of 6 patient-derived organoid (PDO) SCLC models with different treatment histories and compared to 4 standard-of-care (SOC) compounds. KB-0742 was more active than the SOC compounds, with maximum inhibition rates of over 90% for 5 of the 6 models. In a separate study of 4 treatment-naïve PDO models, KB-0742 was active in 3 different transcription factor-driven subtypes of SCLC, and the response correlated significantly with c-MYC and MYCL expression. Lastly, we used 4 patient-derived xenograft (PDX) models to evaluate KB-0742 activity in vivo. The tumor growth inhibition (TGI) rate ranged from 54% to 92%, with tumor regressions observed in 2 of the 4 models, and 1 model showed greater TGI with KB-0742 than the SOC. These data support the development of KB-0742 as a potential treatment for SCLC. Patients with relapsed or refractory solid tumors or non-Hodgkin lymphoma are currently being enrolled in a phase 1/2 clinical trial of KB-0742 (NCT04718675) with an expansion arm for SCLC being planned after the recommended phase 2 dose is identified. Citation Format: Melinda A. Day, Douglas C. Saffran, Tressa Hood, Nikolaus Obholzer, Akanksha Pandey, Charles Y. Lin, Pavan Kumar, Jorge DiMartino. CDK9 inhibitor KB-0742 is active in preclinical models of small-cell lung cancer [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 2565.

Abstract 1489: MicroRNA-1 targets CXCR4/FOXM1/RRM2 axis regulating small cell lung cancer growth and metastasis

Abstract Small cell lung cancer (SCLC) is a high-grade neuroendocrine metastatic lung cancer subtype having a universal relapse and poor prognosis. Limited or extensive-stage SCLC patients have limited therapeutic options due to a lack of potential drug targets. In the quest for novel therapeutic molecules, we performed micro-RNA sequencing from the serum samples and also analyzed bulk RNA-sequencing data from tumors of SCLC patients. We found a consistent downregulation of miR-1 in SCLC. These results were recapitulated in SCLC cell lines and tumor tissues compared to their matched normal. To assess the therapeutic potential of miR-1, we overexpressed miR-1 in SCLC cell lines that translated into decreased cell growth and oncogenic signaling. Mechanistic studies revealed that CXCR4 is a direct target for miR-1 in SCLC. Intracardiac injection of SCLC cell lines in the mouse models showed that overexpression of miR-1 decreases the distant organ metastasis, whereas miR-1 sponging potentiates aggressiveness and metastasis. Furthermore, we identified FOXM1-RRM2 as a unique downstream target of the miR-1/CXCR4 axis involved in the growth and metastasis of SCLC. Our results showed that FOXM1 directly binds to the promoter site of RRM2 and regulates its activity. Overexpression of miR-1 decreases the expression and activity of FOXM1-RRM2 through CXCR4 that reduces cell growth and metastasis. Taken together, our results suggest that miR-1 decreases SCLC metastasis by targeting the CXCR4/FOXM1-RRM2 axis and has a high potential for the development of novel SCLC therapies. Citation Format: Parvez Khan, Jawed A. Siddiqui, Shailendra Kumar Maurya, Tamara Mirzapoiazova, Ranjana Kanchan, Ramakanth Chirravuri Venkata, Pranita Atri, Wemin Tang, NaveenKumar Perumal, Prakash Kshirsagar, Mahek Fatima, Md Arafat Khan, Sanjib Chaudhary, Asad Ur Rehman, Imayavaramban Lakshmanan, Sidharth Mahapatra, Prakash Kulkarni, Apar Kishor Ganti, Maneesh Jain, David Oupicky, Ravi Salgia, Surinder Kumar Batra, Mohd Wasim Nasser. MicroRNA-1 targets CXCR4/FOXM1/RRM2 axis regulating small cell lung cancer growth and metastasis [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 1489.

Abstract 3473: Use of DNA methylation from tumor and plasma to identify four major small cell lung cancer subtypes with distinct biology and therapeutic vulnerabilities

Abstract Small cell lung cancer (SCLC) is a highly aggressive cancer with limited treatment options and generally poor prognosis. Treatment of SCLC has not considerably changed over the last decades with therapeutic options focusing on unselected populations. Although in the past SCLC was thought to be a relatively homogenous malignancy, recent reports from our group and others identified four major distinct subgroups of SCLC, each with different therapeutic vulnerabilities. Three of the subtypes are defined by the expression of a specific transcription factor, ASCL1 (SCLC-A), NEUROD1 (SCLC-N) and POU2F3 (SCLC-P) while the fourth subtype is defined by an inflamed phenotype (SCLC-I). While our initial subtyping of SCLC is based on a gene expression signature comprised of ~1300 genes, which makes routine implementation challenging, we hypothesized that DNA methylation as a proxy to gene expression might be a more suitable approach for biomarker development in SCLC. We assembled a cohort of 105 SCLC formalin-fixed paraffin embedded (FFPE) samples (82/105 Stage > IIIb) and performed matched RNA-Sequencing (RNAseq) and methylation profiling using reduced-representation bisulfite sequencing (RRBS). To validate our findings and expand our analysis across different sample types, we profiled a panel of 59 fully characterized SCLC cell lines as well as 68 patient-derived xenograft models. We found that methylation levels differ markedly between the four subtypes, with the SCLC-N presenting with a hypermethylated phenotype and the SCLC-P with a hypomethylated phenotype across the genome, highlighting the profound differences in the underlying epigenetic regulation among the SCLC subtypes and supporting DNA methylation analysis as a potential readout for identifying SCLC subtypes. Furthermore, in order to subtype the clinical SCLC samples, we developed a predictive model using an extreme gradient boost model using RNA expression and DNA methylation, respectively, to allow the classification with 94.5% accuracy in the tissue testing cohort. Using a cohort of matched plasma samples, we further demonstrated that the DNA methylation differences were indeed preserved in cell-free DNA (cfDNA) allowing subtype classification with an accuracy of 87.5%. These data indicate that DNA methylation can be used for reliable subtyping of SCLC in tissue and in liquid biopsy samples. In summary, using a large cohort of predominantly extensive stage SCLC clinical samples, we were able to identify profound differences in DNA methylation that can be exploited as a novel biomarker for the classification of SCLC into four distinct subtypes with both tissue biopsy and non-invasive using plasma. Considering the previously shown therapeutic vulnerabilities of the four subtypes, these findings will enable the rapid initiation of personalized clinical trials in SCLC. Citation Format: Simon Heeke, Carl M. Gay, Marcos R. Estecio, Allison Stewart, Hai Tran, Bingnan Zhang, Ximing Tang, Gabriela Raso, Kyle Concannon, Luana Guimaraes De Sousa, Whitney E. Lewis, Monique Nilsson, Yuanxin Xi, Lixia Diao, Qi Wang, Jianjun Zhang, Jing Wang, Ignacio I. Wistuba, Lauren A. Byers, John V. Heymach. Use of DNA methylation from tumor and plasma to identify four major small cell lung cancer subtypes with distinct biology and therapeutic vulnerabilities [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 3473.