Topoisomerase Inhibitors Research Articles

Abstract 500: Liposomal two-tailed topotecan (L-2TT) induces more apoptosis than topotecan hydrochloride on neuroblastoma xenografts

Abstract Background: Neuroblastoma (NB) is the second most common malignancy diagnosed in infants, accounting for 15% of pediatric tumor deaths. High risk NB have a <50% 5-year survival and often resist treatment, with acute and long-term toxicities. Topotecan, part of the standard of care in NB is a Topoisomerase1 inhibitor with a short half-life in circulation (30 minutes). We esterified phospholipid to topotecan at the phenolic hydroxyl group, producing the prodrug 2T-T. 2T-T was loaded onto liposome membranes (termed L-2TT); thus preventing drug leakage. We hypothesized L-2TT would be more efficient at inducing apoptosis than topotecan in NB models (in vitro and in vivo) in part due to its extended circulation time and endocytic uptake. Methods: IC50 was determined on 8 NB cell lines using a WST assay, comparing equal dosages of L-2TT to topotecan (empty liposomes were assessed as controls). NB cells were imaged with DiD-tagged liposomes together with lysotracker green, under confocal microscopy 24 hrs. Non-tumor bearing mice received increasing L-2TT doses, assessing weight, body score over five days. Drug circulation time was estimated by following DiR-liposomes in vivo (IVIS) over 72 hrs. Nude mice received 1 × 10^6 NGP cells (NB cells) intrarenally. When tumors reached 1 gram, xenografts received 10mg/kg L-2TT (containing 3.33mg/kg topotecan) via retroorbital injection, 3.33 mg/kg topotecan-hcl or no drug. Tumors were harvested 24 hrs. later, immunohistochemical analysis (apoptosis marker TUNEL), counting the % of positive cells of total tumor area. Some mice received DiR-liposomes together with L-2TT, fixed in PFA and 50mm sections captured total DiR under confocal microscopy. Finally, we interrogated L-2TT vs. Topotecan-HCl tumors via RNAseq for chemoresistance pathways. Results: IC50 values of L-2TT were lower than topotecan-HCl by almost 3-fold in 7/8 cell lines (empty liposomes at equal concentrations had no effect). DiD-tagged liposomes formed a punctate pattern and colocalized with lysotracker green, confirming liposomes are endocytosed by NB cells in vitro. L-2TT caused no changes adverse effects on mice. Drug circulation time remained stable over 48 hours and was still detectable at 72hrs after liposomal delivery. L-2TT resulted in 3-fold higher tumor apoptosis than Topotecan-hcl (p<0.0001), and itself 3-fold higher than controls (p<0.001, n=5). Mice receiving L-2TT+L-DiR resulted in 2-fold higher DiR signal than L-DiR only (p<0.05, n=3. Finally, RNAseq suggests L-2TT elicits less chemoresistance pathways than topotecan. Conclusions: L-2TT is more potent than topotecan in vitro and in vivo. Mechanisms for these effects could be longer circulation times, different tumor cell uptake, as well as changes in tumor vascular permeability. These drug modifications could provide potent alternative for NB treatment as well as other solid tumor treatment. Citation Format: Sonia L. Hernandez, Isabella Iwanicki, Paula Viza-Gomes, Lydia Wu, Mendi Marquez, Fernando Flores-Guzman, Rachael Sundland, Michaelann Tartis. Liposomal two-tailed topotecan (L-2TT) induces more apoptosis than topotecan hydrochloride on neuroblastoma xenografts [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 500.

Abstract 1899: Novel combinations of aplitabart, a DR5 agonist IgM antibody, with ADCs or chemotherapeutic agents lead to robust anti-tumor responses in solid tumor models

Abstract Agonism of death receptor 5 (DR5), a tumor necrosis factor receptor superfamily member, induces the killing of tumor cells via the extrinsic apoptotic pathway upon receptor multimerization. We have engineered a multivalent IgM DR5 agonist antibody, aplitabart (IGM-8444), that induces robust anti-tumor activity in both in vitro and in vivo preclinical models. We also demonstrated potent synergistic in vitro activity of aplitabart with different classes of chemotherapeutic agents including microtubule inhibitors, nucleoside analogs and topoisomerase inhibitors in a range of solid cancer cell lines. Preliminary results from an ongoing phase 1a/ab clinical study show that aplitabart has an encouraging safety profile and promising activity in combination with FOLFIRI ± bevacizumab in heavily pretreated metastatic colorectal cancer patients. To further explore the combination therapies for aplitabart in lung and breast cancers, we evaluated standard of care chemotherapies, such as paclitaxel, carboplatin, and antibody drug conjugates (ADCs) in vitro on a range of human lung and breast cancer cell lines. We observed dose-dependent synergistic cytotoxic effects of aplitabart on tumor cells when combined with these agents. Additionally, these agents increased the expression of DR5 on tumor cells and could explain their synergistic combinatorial activity with aplitabart. Representative cancer cell lines were selected to evaluate these combinations in vivo using xenograft mouse models where robust anti-tumor responses were demonstrated in the xenograft lung and breast cancer models, resulting in enhanced tumor growth inhibition and extended survival. Our findings demonstrate potent in vitro synergistic cytotoxicity and enhanced anti-tumor response in preclinical models in vivo by combining aplitabart with ADCs, or carboplatin and paclitaxel. These results support the combination of DR5 agonist IgM antibodies with agents known to upregulate DR5 expression on solid tumors. Aplitabart is currently under evaluation in a randomized clinical study in combination with FOLFIRI + bevacizumab in comparison with FOLFIRI + bevacizumab in patients with colorectal cancer (NCT04553692). Citation Format: Mélanie Desbois, Susan E. Calhoun, Kevin C. Hart, Carolyn R. Denson, Poonam Yakkundi, Thomas J. Matthew, Maya K. Leabman, Sanela Bilic, Genevive Hernandez, Eric W. Humke, Albert F. Candia, Bruce Keyt, Angus M. Sinclair, Maya F. Kotturi, Beatrice T. Wang. Novel combinations of aplitabart, a DR5 agonist IgM antibody, with ADCs or chemotherapeutic agents lead to robust anti-tumor responses in solid tumor models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1899.

Abstract 3753: Co-expression proteomic analysis of antibody drug conjugate receptor and payload biomarkers in breast cancer

Abstract The use of antibody drug conjugates (ADC) targeting HER2, and Trop 2 has made a great difference in the treatment of breast cancer. Such agents consist of an antibody targeting the receptor which is conjugated to a payload chemotherapy agent. Chemotherapy involves the use of anti-tubulin agents (e.g. docetaxel), topoisomerase inhibitors etc. We examined 507 breast cancer samples using targeted proteomics to quantitate biomarkers for ADC targets such as HER2, HER3, EGFR and Trop2 in our clinical proteomics (CLIA) laboratory. We also measured biomarkers that are associated with response and biomarkers that are associated with resistance to chemotherapeutic agents. Resistance markers include TUBB3 (taxanes), and response markers include TOPO1 (irinotecan, topotecan). Methods: Formalin fixed, paraffin embedded (FFPE) tissues blocks of breast cancer were sectioned, marked for tumor, laser capture microdissected, digested and analyzed by LC-selected reaction monitoring mass spectrometry. Seventy-two proteins were quantitated. Discussion:In our previous work, we have determined that >740 amol/µg HER2 corresponds to IHC 3+/2+ and FISH +. Based on the HER2 quantitation for each sample, the samples were segregated into three groups. Negative (Group A, <150 amol/µg), High expressors (Group C, >740 amol/µg), and Detected (Group B, 151-739 amol/µg). Groups A, B, and C were 39%, 46%, and 43% of the cases respectively. In Group A (HER2 negative), HER3 was detected in 14% of cases with a 3x range (181-602 amol/µg), EGFR was detected in 53% of samples with 139x range (108-14986 amol/µg), Trop2 was detected in 59% of cases ranging from 256 to 11900 amol/µg, Topo1 was detected in 86% of cases with a 12x range (402-4870 amol/µg) and TUBB3 was detected in 63% of cases at levels ranging from 755 to 11750 amol/µg. In Group B (HER2 detected), HER3 was detected in 38% with a 3x range (178-565 amol/µg), EGFR was detected in 34% at levels ranging from 104-7040 amol/µg, Trop2 was detected in 63% ranging from 157 to 12808 amol/µg, Topo1 was detected in 94% with a 12x range (413-5100 amol/µg), and TUBB3 was detected in 51% of cases at levels ranging from 757 to 9311 amol/µg.In Group 3 (HER2 highly expressed), HER3 was detected in 43% with a 5x range (189- 890 amol/µg), EGFR was detected in 30% at levels ranging from 101 to 565 amol/µg, Trop2 was detected in 68% ranging from 310 to14650 amol/µg, Topo1 was detected in 95% with a 6x range (487- 2885 amol/µg), and TUBB3 was detected in 64% of samples at levels ranging from 829 to 2300 amol/µg. Conclusion:The capacity to multiplex 72 protein biomarkers from 2-3 FFPE sections will help in design of ADCs bispecific antibodies and/or bispecific ADCs. Citation Format: Negin Ghafourian, Sheeno P. Thyparambil, Richard Mortensen, James Chou, Robert Heaton, Xuefeng B. Ling. Co-expression proteomic analysis of antibody drug conjugate receptor and payload biomarkers in breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3753.

Abstract 4234: Personalized therapeutic screening in patient derived organoids for gastroenteropancreatic neuroendocrine tumors

Abstract Introduction Gastroenteropancreatic Neuroendocrine Neoplasms (GEP-NENs) are a rare subset of cancers which nevertheless are a rising health burden. Development of new therapies suffers from several bottlenecks, including low patient accrual and poor understanding of tumor characteristics. Patient tumor organoids (PTOs) are a novel model capable of improving screening of patient tissue in an accurate, standardized, and high-throughput capacity. In this study, we utilized patient tumors for creation of high-fidelity PTOs from a variety of GEP-NEN primary origins to evaluate therapy responses. Methods Tumors from patients undergoing clinically guided surgeries were processed within two hours of resection and dissociated into single-cell suspension. Cells were encapsulated into Matrigel and cultured into two groups. The first group was grown for 10 days to assess viability then treated with a panel of clinically approved therapies and novel treatments recommended by high throughput NEN cell line screening for treatment sensitivity using the MIPE 5.0 library. The second group was grown for long-term expansion and biobanking, followed by characterization using immunohistochemistry and genetic profiling to ensure tumor cell maintenance. Results From March 2023-November 2023, 14 patients provided 30 tumors for PTO development. These included small intestine (n=5), pancreatic (n=8), and gastric (n=1) neuroendocrine tumors. Long-term culture (>3 passages) was successful for 23/30 (77%) specimens, with passage timing related to tumor grade. PTOs maintained immunohistochemical characteristics of the parent tumor types and demonstrated similar genetic profiles, including neuroendocrine tumor cell markers synaptophysin, chromogranin A, and matched grade-based Ki67 proliferative index. The early-stage therapeutic screening was performed for 12/14 (86%) patients, demonstrating tumor grade dependent treatment efficacy and showing clinically dose relevant sensitivity towards approved small molecule inhibitor therapies including cabozantinib and sunitinib in a patient and tumor origin-dependent manner. Testing of effective therapy classes recommended by cell line treatment panels suggested high level treatment efficacy for proteosome inhibitors, MEK inhibitors, and topoisomerase inhibitors. Conclusion Development of GEP-NEN PTOs is feasible for long term culture and standard of care therapy testing. Further study demonstrated the successful application of novel therapeutic options in PTOs for patients with GEP-NENs. Citation Format: Steven D. Forsythe, Srujana V. Yellapragada, Stephen G. Andrews, Jaydira del Rivero, Jonathan M. Hernandez, Naris Nilubol, James P. Madigan, Samira M. Sadowski. Personalized therapeutic screening in patient derived organoids for gastroenteropancreatic neuroendocrine tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4234.

Abstract 5857: Trastuzumab deruxtecan resistance can be mediated by payload resistance or secondary extracellular ERBB2 mutations but sensitivity to HER2 tyrosine kinase inhibitors is maintained

Abstract Among NSCLC patients, the most common HER2 mutation is the exon 20 insertion mutation, Y772dupYVMA, which accounts for over 40% of all HER2 mutations in lung cancer. Trastuzumab deruxtecan (T-DXd), a HER2 antibody-drug conjugate (ADC), received FDA approval for the treatment of HER2 mutant NSCLC yielding a confirmed objective response of 52% and a median duration of response of greater than 9 months. Unfortunately, patients that initially respond to T-DXd will eventually acquire resistance, and the mechanisms of resistance as well as effective targeting strategies to overcome resistance are not yet elucidated. We generated Ba/F3 cells expressing the HER2 YVMA insertion mutation with acquired resistance to T-DXd by culturing cells in T-DXd until resistance occurred. T-DXd resistant cells retained expression of HER2, but were resistant to the payload, deruxtecan, as well as other topoisomerase inhibitors. T-DXd resistant cells exhibited loss of topoisomerase I, a previously reported mechanism of topoisomerase inhibitor resistance. In parallel, we generated a PDX model of acquired T-DXd resistance and observed sustained expression of HER2 but loss of TOP1 in resistant tumors. T-DXd resistant cell lines were sensitive to payloads with alternate mechanisms of action including maytansine and likewise retained sensitivity to the HER2 ADC trastuzumab emtansine (T-DM1) which utilizes DM1 as a payload. Given that T-DXd resistant cells retained HER2 expression, we assessed whether they were sensitive to HER2 tyrosine kinase inhibitors (TKI). T-DXd resistant cells remained highly sensitive to HER2 TKIs including poziotinib, afatinib, BI-4142, and BI-1622. To investigate whether genomic alterations of HER2 could facilitate HER2 ADC resistance, we utilized the LentiMutate approach which employs an error-prone HIV-1 reverse transcriptase to produce a high frequency of mutations to identify resistance-associated mutations in cells treated with a HER2 ADC. Sequencing analysis revealed that resistant cells had an enrichment in point mutations within HER2 domain IV (D582N, F595C/S, E580K, C623Y), which includes the binding site of trastuzumab. To validate the impact of these mutations on HER2 ADC resistance, we generated cells expressing a HER2 exon 20 insertion in combination with the observed domain IV mutations. D582N and F695C/S co-mutations conferred resistance to T-DXd and T-DM1 but not to HER2 TKIs. These data demonstrate that resistance to T-DXd can be mediated by loss of sensitivity to the ADC payload in which case ADCs bearing payloads with alternate mechanisms of action as well as HER2 TKIs retain anti-tumor cell activity. Moreover, resistance to trastuzumab-based ADCs can also be mediated by secondary mutations within domain IV of HER2. However, these resistance mutations do not diminish HER2 TKI activity. Citation Format: Monique B. Nilsson, Xiuning Le, Junqin He, Xiaoxing Yu, Xiaofang Huo, Ashwani Kumar, Alissa Poteete, Qian Huang, Ralf Kittler, John Heymach. Trastuzumab deruxtecan resistance can be mediated by payload resistance or secondary extracellular ERBB2 mutations but sensitivity to HER2 tyrosine kinase inhibitors is maintained [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5857.

Abstract 3888: TOP1 mutations mediate cross resistance to ADCs in metastatic breast cancer

Abstract Background: Antibody-drug conjugates (ADCs) have improved survival for patients with metastatic breast cancer (MBC). In patients with HER2 negative MBC, two ADCs have FDA approval: sacituzumab govitecan (SG) and trastuzumab deruxtecan (T-DXd), both with topoisomerase-I (topo-I) inhibitor payloads. Given the many other ADCs in development, there is great interest in using ADC after ADC to maximize treatment benefit for patients. However, there is limited understanding regarding resistance mechanisms to ADCs and impact on ADC sequencing. We conducted a translational study to address this, and here we report the incidence of TOP1 mutations and clinical impact on ADC sequencing. Methods: All patients with MBC treated with ADCs at a large academic medical institution (Massachusetts General Hospital) who had comprehensive plasma-based genotyping (500 gene GuardantOMNI panel) were included. Since both SG and T-DXd have topo-I inhibitor-based payloads, we particularly focused on TOP1 mutations, variant allele frequency (VAF), and germline/somatic characterization. Incidence of TOP1 mutations in the ADC cohort was compared to The Cancer Genome Atlas (TCGA). Clinical “cross-resistance” was defined as progressive disease (PD) as best response to second ADC (ADC2) or treatment time on ADC2 of less than 60 days. Results: Based on comprehensive plasma-based genotyping we identified 4 distinct TOP1 mutations: S57C, R364H, W401C, G359E, at a frequency of 6.0% (4/67) at the time of disease progression on ADC compared to a frequency of 0.5% described in primary breast cancer in TCGA. Two of the amino acids found to be mutated are known to form direct interactions with the DNA backbone (G359) or the topoisomerase inhibitor itself (R364). For clinical resistance, one patient was briefly on ADC2 but stopped after 1 dose for toxicity; among the other 3 patients, two had cross-resistance to ADC after ADC, with both ADCs containing topo-I inhibitor payloads. Median duration on first ADC was 455 days compared to a median of 52 days for ADC2. Finally, one patient treated sequentially with 3 ADCs (all with topo-I inhibitor payloads) was found to have rising TOP1 VAF with progressive ADC treatments. Conclusion: This is the first report describing emergence of TOP1 mutations under selective pressure from ADCs and the impact on mediating cross-resistance to ADC after ADC with topo-I inhibitor payloads. Novel ADCs with alternative payloads may potentially be more effective when used sequentially after an ADC with a topo-I inhibitor. Further biomarker research is needed to optimize ADC sequencing for patients with TOP1 mutant MBC. Citation Format: Rachel Occhiogrosso Abelman, Haley Barnes, Arielle J. Medford, Annika Putur, Bogang Wu, Caroline Weipert, Geoffrey Fell, Laura M. Spring, Seth A. Wander, Beverly Moy, Andreas Varkaris, Dejan Juric, Leif Ellisen, Ryan Corcoran, Aditya Bardia. TOP1 mutations mediate cross resistance to ADCs in metastatic breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3888.

Abstract 5814: EPriL macrocycles as a platform for the rapid generation of effective kinase degrader antibody conjugates (DACs)

Abstract The therapeutic success of antibody drug conjugates (ADCs) drives a continuous search for novel payloads that can increase therapeutic window and thereby widen the applications for ADCs. Recently, heterobifunctional degraders have gained great interest as payloads, and degrader antibody conjugates (DACs) are seen as a novel therapeutic modality. Heterobifunctional degraders consist of a small molecule ligand that binds a target (protein of interest or POI), a spacer and an E3 ligase ligand, which can catalyze target degradation. Owing to their catalytic activity, degraders can have better potency than the equivalent inhibitors, making them suitable as ADC payload [1]. Degrader payloads can target a wider variety of mechanisms than classic payloads, which use the same antitumor strategies as chemotherapy, such as tubulin binding or topoisomerase inhibition. Since many FDA-approved targeted therapies are based on the inhibition of protein kinases, we investigated degraders of these kinases as DAC payloads. Kinase DACs could bring enhanced targeting and therefore better therapeutic window to a field where classic ADC payloads have often shown substantial toxicities. As many heterobifunctional degraders show poor cell membrane penetration, their inhibitory potential could be increased as part of a DAC, where endocytic uptake is followed by intracellular release of the degrader payload. To identify kinase degrader payloads, we present a workflow based on a platform called Energetically Privileged Ligands (EPriLs). EPriLs are macrocycle scaffolds that bind non-covalently in the kinase ATP pocket. Their unique binding mode avoids contacts with amino acid positions where resistance to kinase inhibitors frequently occurs. EPriL macrocycles can be decorated appropriately to rationally design specific inhibitors for many therapeutically relevant kinases, and provide synthetic handles to couple them to VHL or CRBN ligands to generate effective kinase degraders. Here we describe how EPriL kinase degraders can be developed into effective DACs, using consecutive libraries of EPriL ligands, spacers, E3 ligase ligands and linkers. First, suitable degraders are identified, based on rapid and deep target degradation and potent antiproliferative activity on target cell lines. Degraders are then transformed into maleimide-linked degraders using convenient attachment of enzymatically cleavable linkers. In a medium throughput fashion, these maleimides are coupled to antibodies to generate DACs, which are tested for stability and biological potency. Applying this workflow to various well-validated kinase targets in oncology resulted in a promising kinase targeting DAC with favorable ADME properties, clear potentiation compared to the parent degrader, and increased selectivity for tumor cell lines. 1] Dragovich et al., Chem. Soc. Rev. (2022) 51, 3886-3897. Citation Format: Joost C. Uitdehaag, Jos e Man, Michelle Muller, Freek an Cauter, Sander an Gemert, Milan Hoffmann, Yvonne G. an Mil, Winfried R. Mulder, Martine B. Prinsen, Jan Gerard Sterrenburg, Diep Vu, Joeri e Wit, Erik Ensing, Rogier C. Buijsman. EPriL macrocycles as a platform for the rapid generation of effective kinase degrader antibody conjugates (DACs) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5814.

Abstract 5819: An anti-TROP2-CPT113 ADC, exhibits potent targeted antitumor activity and favorable pharmacokinetic properties

Abstract Trophoblast cell surface antigen 2 (TROP2) is highly expressed in a number of epithelial cancer types and is considered to be a poor prognostic marker. We have developed an anti-TROP2 antibody-drug conjugate, DXC1002, that contains a potent inhibitor of DNA topoisomerase I payload (CPT113) attached to the antibody mainly in the Fab region via a unique hydrophilic CrossConju™ linker. The anti-tumor activities of DXC1002 were studied in various human cancer cell lines and xenograft mouse models and pharmacokinetic profile of DXC1002 were evaluated in cynomolgus monkeys and rats. DXC1002 demonstrated potent anti-tumor activity in TROP2 tumor cells of various expression levels in vitro, and at low dose of 1 mg/kg for one injection, in both high and moderate Trop2 expression xenograft models. In plasma stability studies, wherein DXC1002 was incubated in the plasma of five different species for 168 hours (7 days) at 37 oC, over 90% ADC was intact, exhibiting good stability of the CrossConju™ linker. Pharmacokinetic studies of DXC1002 in monkeys (TROP2 cross-species) and rats (non-TROP2 cross-species) showed half-lives of about 61.27 and 236.77 hours, respectively. Systemic clearance in monkey and rat was 0.41-0.67 and 0.279-0.309 mL/h/kg, respectively. The longer half-lives and slower clearance observed in rats the results offered a more direct assessment of the linker stability as target-mediated clearance played no role in rats. In summary, with the conjugation of a DNA topoisomerase I inhibitor payload to Trop2 antibody via the CrossConju™ linker, DXC1002 demonstrates remarkable anti-tumor properties and pharmacokinetic profile, with a potential to be further validated in clinical applications. Citation Format: Huihui Guo, Xiangfei Kong, Yong Du, Zhicang Ye, Yongxiang Chen, Zhixiang Guo, Lingli Zhang, Lu Bai, Junxiang Jia, Yunxia Zheng, Wei Zheng, Jun Zheng, Wenjun Li, Yuanyuan Huang, Zhongliang Fan, Mengmeng Liu, Binbin Chen, Meng Dai, Juan Wang, Miaomiao Chen, Qingliang Yang, Robert Y. Zhao. An anti-TROP2-CPT113 ADC, exhibits potent targeted antitumor activity and favorable pharmacokinetic properties [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5819.

Abstract 2605: STX-1, a potent first-in-class ADC directed against DPP4 (CD26) as a biomarker of senescent tumor cells

Abstract Dipeptidyl Peptidase 4 (DPP4/CD26) is a membrane glycoprotein involved in particular chemotactic and inflammatory responses, via its N-terminal protein cleavage enzymatic activities. DPP4 expression is found in various cell types, in certain subsets of lymphocytes and frequently overexpressed in primary tumors and metastases where its role remains still poorly understood. Recently, DPP4 was identified as a novel biomarker of senescent cells. In cancers, the harmful effect of senescent tumor cells is well recognized and mediated by the local production of pro-inflammatory cytokines, soluble immunosuppressive factors and metalloproteinases, called ‘SASP’ phenotype which could be induced by many chemotherapy and radiation regimens. This deleterious microenvironment promotes tumor growth, invasion and neoangiogenesis which can lead to treatment resistance, relapses and poor prognosis in many cancers, especially at advanced stages. STX-1 is a leading first-in-class ADC platform based on a proprietary anti-DPP4 mAb generated after a screen between normal and senescence-induced cells identifying DPP4 as a candidate for cancer targeting. Other biomarkers of interest were also identified as being selectively expressed for further preclinical evaluation. This IgG1/k mAb has potent in vitro activities on DPP4+ cells: i) in a bleomycin-induced senescent fibroblasts model; ii) on DPP4-expressing and chemotherapy- or radiotherapy-induced senescent human tumor cell lines with overexpression of DPP4; iii) binding of the mAb to its target results in its internalization into the endolysosomal compartment of cells. The first formulations of STX-1 are undergoing preclinical evaluation in vitro and in vivo and consist of a classical maleimide-based conjugation, an enzymatically cleavable cathepsin-dipeptide linker comprising a self-immolative spacer and either inhibitor of tubulin (MMAE/DAR4) or topoisomerase I inhibitor (exatecan/DAR8) payloads. Plasma stability and affinity, dose-response potency and permeability bystander activity on human tumor cell lines were evaluated in vitro. Preliminary efficacy is demonstrated in vivo on tumor xenograft models with various DPP4 expressions (constitutive or chemo/radio-induced to senescence) based on a 21-28 days weekly infusion schedule (3 or 5 µg/kg). The indications selected for further therapeutic development are prostate, liver and colorectal carcinoma models. Data on antitumor efficacy, tolerability and pharmacokinetics will be presented. Further studies will include optimization of the best STX-1 formulation, NHP studies and GMP scale-up with planned IND submission expected in Q3-2024. Exploiting the targeting of senescent cells in cancer based on selected biomarkers such as DPP4 constitutes a new therapeutic avenue to counteract tumor dormancy, recurrences and resistance to conventional chemo/radiotherapies. Citation Format: Eric Angevin, Virginie Lelarge, Remi Capelle, Justine Choeur, Thierry Mathieu, Benjamin Le Calvé. STX-1, a potent first-in-class ADC directed against DPP4 (CD26) as a biomarker of senescent tumor cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2605.

Abstract 5964: Design and anticancer biological evaluation of novel 7-aza-8,9-methylenedioxyindenoisoquinoline derivatives that inhibit MYC and topoisomerase I

Abstract MYC is one of the most validated driver oncogenes and is overexpressed in most human cancers. However, the MYC protein is considered “undruggable” due to its disordered structure and difficulties associated with targeting transcription factors. The MYC gene promoter forms G- quadruplex, a four-stranded non-canonical DNA secondary structure. The MYC G-quadruplex functions as a transcription silencer and further inhibits MYC expression upon drug binding, representing an exciting approach for MYC-targeting cancer therapy. Indenoisoquinolines are topoisomerase I inhibitors with better physicochemical and biological properties than the clinical camptothecin drugs. We previously revealed a novel mechanism of action for active anticancer indenoisoquinolines by dual inhibition of MYC and topoisomerase I, where potent MYC inhibition was achieved through targeting its promoter G-quadruplex. Herein, we report the design, cellular activity, and in vivo efficacy of novel anticancer 7-aza-8,9-methylenedioxyindenoisoquinoline derivatives based on optimized substituents and π-π stacking interactions. Using biophysical, biochemical, and cellular assays, we demonstrated that the new indenoisoquinoline derivatives greatly stabilized the MYC promoter G-quadruplex, significantly lowered MYC protein and mRNA levels in cancer cells, and inhibited topoisomerase I activity. A MYC G-quadruplex mediated mechanism of action was evident by differential activities in Raji vs CA-46 cells. The importance of MYC targeting was corroborated by potent cytotoxicity against a panel of MYC-dependent cancer cell lines as well as the NCI-60 panel of human cancer cell lines. The top three candidates were evaluated for pharmacokinetics and in vivo anticancer properties. Excellent metabolic stability, bioavailability, and tumor accumulation were observed in xenograft mouse models. Potent and significant tumor growth inhibition was demonstrated in the aggressive RD-ES Ewing Sarcoma xenograft mouse model while the drugs were well-tolerated. In addition, favorable brain penetration and pharmacokinetics were established, which encourage future evaluations in difficult-to-treat brain tumors. In conclusion, we designed and developed 7-aza-8,9-methylenedioxyindenoisoquinoline derivatives that are dual inhibitors of MYC and topoisomerase I. Our drug candidates demonstrated excellent pharmacokinetics and in vivo anticancer activities with promising indications in MYC-dependent cancers. Citation Format: Yichen Han, Luying Chen, Adam Buric, Venkat Chintareddy, Pooran Chand, Randall Riggs, Mark Cushman, Danzhou Yang. Design and anticancer biological evaluation of novel 7-aza-8,9-methylenedioxyindenoisoquinoline derivatives that inhibit MYC and topoisomerase I [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5964.

Abstract 3148: ABBV-706 is a novel SEZ6-targeted topoisomerase 1 inhibitor ADC for SCLC and other neuroendocrine cancers

Abstract Lung cancer has the highest rates of incidence (2.1 million cases/year) and mortality (1.8 million deaths/year) among all cancers worldwide. Approximately 15% of lung cancers are small cell lung cancer (SCLC). SCLC is typically diagnosed at late stages, with approximately 70% of patients having extensive stage disease at time of diagnosis. Unfortunately, these patients have a dismal 5-year survival rate of approximately 3%. In contrast to non-small cell lung cancer (NSCLC), there has been little advancement in the treatment of SCLC, with no biomarker directed therapies available for patients. SEZ6 is overexpressed in most SCLC’s and other neuroendocrine tumor types. This overexpression and limited normal tissue expression suggest SEZ6 would be a good target for the development of an antibody drug conjugate (ADC). Validation of SEZ6 as an ADC target was supported by signs of clinical activity for ABBV-011, a SEZ6-targeting calicheamicin ADC. Preclinical and clinical data suggest an increased therapeutic index for Top1i ADCs relative to calicheamicin ADCs. Furthermore, Top1i inhibition is an effective mechanism of action in SCLC with topotecan approved in 2L, although significant toxicity limits broad utility. As such, we hypothesized that a SEZ6-Top1i ADC would enable effective Top1 inhibition in tumor cells and reduce toxicity relative to ABBV-011 or systemic chemotherapy, driving increased therapeutic benefit. ABBV-706 is an ADC comprised of the same SEZ6 targeting antibody as ABBV-011 conjugated to AbbVie’s topoisomerase-1 (Top1) inhibitor. ABBV-706 is a potent anti-proliferative agent in SEZ6 positive SCLC cell lines, with sub- to low-nanomolar activity. SEZ6 dependence was demonstrated by the correlation of SEZ6 mRNA expression to ABBV-706 growth inhibition. On-target Top1i activity was confirmed in cells treated with ABBV-706 as measured by dose-dependent induction of γ-H2AX, a marker of DNA damage, and G2/M arrest. ABBV-706 possessed superior anti-tumor activity compared to ABBV-011 in a panel of SCLC cell line-derived xenograft (CDX) and patient-derived xenograft (PDX) models with a range of SEZ6 expression levels. In addition, ABBV-706 had activity in the setting of resistance to cisplatin/etoposide (1L SoC in SCLC), in combination with cisplatin, and in SEZ6-expressing neuroendocrine liver and cervical PDX models. ABBV-706 has favorable pharmacokinetics and is well-tolerated in cynomolgus monkeys with bone marrow and gastrointestinal tract toxicities common to other Top1 inhibitors. ABBV-706 shows promise as an agent for the treatment of SCLC and other difficult to treat SEZ6 expressing neuroendocrine tumors. ABBV-706 has completed dose escalation, and dose expansion is currently ongoing in a Phase 1 FIH clinical study (NCT05599984). Citation Format: Emily J. Faivre, Marybeth A. Pysz, Eoghainín Ó hAinmhire, Laura Kreckler, Kelly Doyle, Aloma D'Souza, Zhiyong Ding, Trusha Sondkar, Dolonchampa Maji, Fan Zhao, Andrew Phillips. ABBV-706 is a novel SEZ6-targeted topoisomerase 1 inhibitor ADC for SCLC and other neuroendocrine cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3148.

Abstract 2099: PELP1 inhibition enhances the therapeutic efficacy of topoisomerase inhibitors in triple-negative breast cancer

Abstract BACKGROUND: Triple negative breast cancers (TNBCs) account for 15-24% of breast cancer deaths and are characterized by aggressive clinical course, a worse prognosis, and a higher propensity to metastasize. Proline, glutamic acid-, and leucine-rich protein 1 (PELP1) is an oncogene, its expression is deregulated in TNBC, and its status is a prognostic indicator of poor TNBC survival. Recently, a small molecule inhibitor of PELP1 (SMIP34) which binds to and degrades PELP1 was developed. The Objective of this proposal is to define the mechanism of action of PELP1 inhibitor SMIP34 in TNBC progression and to pave the path for a novel combination therapy. METHODS: We tested the effectiveness of PELP1 inhibitor, SMIP-34, in combination with 140 FDA-approved medications on cell survival of multiple TNBC cell lines. The effect of SMIP34 combination therapy on cell survival was measured using MTT, colony formation, and Annexin V apoptosis assays. Mechanistic studies were done using RT-qPCR, immunoprecipitation, proximity ligation, mass spectrometry, gene reporter, immunofluorescence, and comet assays. Furthermore, the preclinical utility of combination therapy was evaluated using MDA-MB-231 xenografts, patient-derived organoids (PDOs) and explants (PDEs). RESULTS: We performed an in vitro screening of 140 FDA-approved drugs in combination with SMIP34. Results revealed that SMIP34 sensitized TNBC cells to five FDA approved drugs. Of the five drugs, the three drugs Gemcitabine, Valrubicin, and Mitoxantrone, induced DNA damage by inhibiting topoisomerase, a protein that cleaves and reconnects DNA during replication. We validated the ability of SMIP34 to enhance the efficacy of TIs using two additional TNBC cell lines and confirmed their synergistic activity using several in vitro assays including cell viability, colony formation, and apoptosis. In agreement with the role of PELP1 in DNA damage response, Western blotting analyses showed higher levels of γ-H2AX in SMIP34+TI combination therapy when compared to monotherapy. Results from the comet assays further demonstrate increased DNA damage caused by the SMIP-34 + TIs combination therapy. Mechanistic studies using Proximity labelling followed by immunoprecipitation identified topoisomerase 2A and 2B (TOP2A and TOP2B) as potential interactors of PELP1. Furthermore, gene correlation analysis using TCGA datasets revealed that PELP1 expression is positively correlated with TOP2A, and TOP2B in TNBC. SMIP34 plus Mitoxantrone (TI) combination treatment significantly reduced the growth of TNBC PDEXs, and PDOs in vitro, and MDA-MB-231 xenograft tumor growth in vivo, compared to vehicle or monotherapy treatment. CONCLUSION: Together, these results suggest a novel targeted therapy for the treatment of TNBC, involving the combination of topoisomerase inhibitors and the PELP1 inhibitor SMIP34. Citation Format: Khaled Mohamed Nassar, John R. Sanchez, Durga Meenakshi Panneerdoss, Behnam Ebrahimi, Yang Xue, Uday P. Pratap, Salvador C. Alejo, Gangadhara R. Sareddy, Suryavathi Viswanadhapalli, Ratna K. Vadlamudi. PELP1 inhibition enhances the therapeutic efficacy of topoisomerase inhibitors in triple-negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2099.

Abstract 381: DUSP12 in glioblastoma: Insights into nucleolar stress and DNA damage response

Abstract Glioblastoma (GBM), an extremely aggressive brain tumor, presents molecular complexities that require enormous challenges for its better understanding. The relatively unexplored dual-specificity phosphatase 12 (DUSP12) is an attractive target due to its zinc finger-like domain suggesting potential interactions with nucleic acids and ribonucleoproteins. This highly conserved enzyme plays a pivotal role in ribosome biogenesis across eukaryotes. Importantly, cell cycle arrest induced by DNA damage often coincides with alterations in ribosome biogenesis, a phenomenon termed nucleolar stress, linked to changes in the localization and activity of nucleophosmin (NPM) and p53 proteins. Bioinformatic analysis of public databases revealed elevated DUSP12 expression in glioblastoma samples compared to normal tissue, displaying strong positive correlations with p53 and NPM. While DUSP12 expression did not impact tumor progression in wild-type p53 patients, its lower expression was associated with increased tumor progression in p53-mutant cases, emphasizing the significance of p53 status in understanding DUSP12's roles in GBM. Gene ontology analysis of DUSP12-correlated genes in glioblastoma patients showed robust enrichment in biological processes like ribosome biogenesis, chromosome organization, cell cycle, and DNA repair, with a substantial number of nucleoplasmic and nucleolar proteins being recently identified by our group through mass spectrometry as DUSP12 partners in other tumor models. A substantial difference in DUSP12 protein levels between the GBM cell lines U87MG (wild-type p53) and U138MG (mutant p53) was observed, with the latter presenting higher levels of this phosphatase. Some biological responses of these cell lines were assessed after exposure to the topoisomerase inhibitors doxorubicin (DX) and camptothecin (CPT) through viability assays in adherent and spheroid cultures, γH2AX foci formation, and ATM/Chk2 activation, showing marginal differences between the cell lines. Notably, DX treatment displayed strong nucleolar stress features, such as alterations in the number and size of nucleoli observed by NPM subcellular distribution changes in both cell lines, and induction of p21 expression only in the p53-profficient U87MG. These alterations were accompanied by nuclear accumulation of DUSP12, underlining its potential regulatory role in this process. The knockdown of DUSP12 with specific siRNA led to a substantial decrease of the treatment responsiveness in U138MG, consistent with the lower levels of this phosphatase associated with a more aggressive phenotype in mutant p53 patients. In summary, DUSP12 emerges as a pivotal player in glioblastoma, influencing nucleolar stress dynamics and tumor aggressiveness, particularly in the context of p53 mutations. Citation Format: Viktor Kalbermatter Boell, Fábio Luís Forti. DUSP12 in glioblastoma: Insights into nucleolar stress and DNA damage response [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 381.

Abstract 3130: In vitro characterization of a novel TROP2-targeting antibody-drug conjugate OBI-992

Abstract BACKGROUND TROP2, a transmembrane glycoprotein widely expressed on epithelial cancers, has emerged as an attractive target for antibody-drug conjugate (ADC) development. Sacituzumab govitecan, a TROP2 ADC conjugated to topoisomerase inhibitor (TOP1) SN-38, has been approved for patients with triple-negative breast cancer. This study aims to investigate the characteristics of a novel TROP2 antibody (R4702) and its ADC OBI-992, which is derived from the conjugation of R4702 with a TOP1 inhibitor exatecan. METHODS Clinical study: Prognostic roles of TROP2 and TOP1 in patients were accessed through the “Kaplan-Meier plotter” database from more than 1055 colon cancer patients. In vitro study: An ELISA study was conducted to investigate the binding epitope of R4702. Cell binding assay and Surface Plasmon Resonance were carried out to measure non-specific binding activity and binding affinity, respectively. DNA damage activity, cytotoxicity, and immunogenic cell death (ICD) effects of three TOP1 inhibitors exatecan, deruxtecan (Dxd), and SN-38, were evaluated. Cytotoxicity of OBI-992 along with other ADC was measured in both 2D and 3D spheroids cancer cells (gastric cancer NCI-N87, pancreatic cancer Capan1, and prostate cancer DU145). TROP2 and BCRP expression as well as potential mutations in TOP1 were investigated in TROP2 ADCs-induced resistant colon cancer cells. The synergistic effects of the combination of OBI-992 with PARP inhibitors were evaluated. RESULTS Clinical study: Positive correlations between high mRNA expressions of both TROP2 (p=0.0075) and TOP1 (p=0.043) with poor overall survival for colon cancer patients were found. In vitro: The R4702 antibody displayed different binding epitopes from sacituzumab and datopotamab. In addition, R4702 showed lower non-specific binding and better binding affinity to TROP2 antigen than datopotamab. The payload exatecan demonstrated excellent ICD effects. Relatively higher cytotoxicity was observed by exatecan when compared to that of Dxd and SN-38. OBI-992 exhibited excellent activities on cell growth inhibition in 2D cell cultures and 3D cell spheroids. TROP2 down-regulation and BCRP upregulation were not found in OBI-992-induced resistant cells. A mutation R364H was identified in TOP1 in the resistance study with OBI-992, which is critical for the binding to TOP1 inhibitors camptothecin analogs. Finally, a synergistic effect of OBI-992 and PARP inhibitors (talazoparib, rucaparib, niraparib, and olaparib) on the enhancement of cancer cell killing and DNA damage was observed. CONCLUSION High expression of both TROP2 and TOP1 is associated with poor survival in patients with colon cancer. R4702 is a novel TROP2 antibody with a unique binding epitope and low non-specific binding. Exatecan and exatecan-conjugated ADC OBI-992 showed high cytotoxic activities. Combination of OBI-992 with PARP inhibitors have potential in TROP2-expressing malignancies. Citation Format: Tzer-Min Kuo, Ting-Yu Chang, Jye-Yu Huang, Wei-Chien Tang, Chun-Jung Lin, Yi-Chen Wu, Chi-Huan Lu, Hao-Cheng Weng, Yu-Jung Chen, Yu-Hsuan Tsao, Cheng-Yen Wei, Lifen Shen, Wan-Fen Li, Ming-Tain Lai. In vitro characterization of a novel TROP2-targeting antibody-drug conjugate OBI-992 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3130.

Abstract 1872: A next generation treatment for Nectin-4 positive cancers - Preclinical characterization of LY4052031, an anti-Nectin-4 antibody, conjugated to a novel camptothecin payload

Abstract Nectin-4 is an immunoglobulin-like antigen overexpressed in a variety of cancers including bladder, breast, NSCLC, and gastric. Normal tissues including skin, salivary glands, bladder and esophagus express only low to medium levels of Nectin-4 making the protein an attractive target for cancer therapies. The approval of enfortumab vedotin-ejfv, an anti-Nectin-4 based antibody-drug conjugate (ADC) with a microtubule inhibitor payload, either as a single agent or in combination with pembrolizumab has been a significant advancement in the treatment of metastatic urothelial cancer. We have developed a novel anti-Nectin-4 ADC with a novel topoisomerase I (TOPO 1) inhibitor drug payload. Topoisomerase inhibitor payload-based ADCs offer potential advantages compared to microtubule payload-based ADCs including a different toxicity profile and the differentiated susceptibility to resistance mechanisms, such as P-gp mediated drug efflux. LY4052031 is a fully human monoclonal anti-Nectin-4 antibody conjugated to a novel TOPO 1 inhibitor by a cleavable peptide linker at a homogeneous drug antibody ratio (DAR) of 8:1. In vitro, both LY4052031 and its unconjugated parental antibody specifically bind to Nectin-4 expressing cell lines and are quickly and efficiently internalized. LY4052031 demonstrated potent cytotoxicity on tumor cells with high and low Nectin-4 expression. Additionally, bystander activity exerted by LY4052031 on antigen negative cells co-cultured with antigen positive cells was greater than that observed with the clinical benchmark enfortumab vedotin-ejfv. In vivo studies in xenografts expressing low to high levels of Nectin-4 showed significant tumor growth inhibition following treatment with LY4052031 as monotherapy. Overall, LY4052031 exhibits specificity, selectivity, potency, and effectiveness as a next generation therapy to treat Nectin-4 positive tumors. An IND submission is planned for 2024. Citation Format: Divya Sagar, Mohan Srinivasan, Kevin Lindquist, Qianxu Guo, Wailin Wong, Maria B. Lebron, Rose Marie Sattler, Jieyu Zhou, Whitney Helms, Jeffrey Boyles, Petra Verdino, Xuan Zhao, Yvonne Mak, Joshua Park, Rikke Holmgaard, Kyla Driscoll, Omar Duramad, Kristin Bedard. A next generation treatment for Nectin-4 positive cancers - Preclinical characterization of LY4052031, an anti-Nectin-4 antibody, conjugated to a novel camptothecin payload [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1872.

Abstract 4708: Potency and selectivity of ERBB2-targeting antibody drug conjugates in vitro

Abstract Previously we have reported on the relevance of the joint ProLiFiler and Cancer DataMiner platforms when studying the antitumor efficacy of novel antibody-drug conjugates (ADCs), such as Sacituzumab govitecan. In this study, we use our platforms to investigate and compare the selectivity of two FDA-approved Trastuzumab-based ADCs targeting ERBB2: Kadcyla, the first-in-class ADC employing a microtubule inhibitor bound via a non-cleavable linker, and Enhertu, which combines a topoisomerase inhibitor with a protease-cleavable linker. We performed a cell proliferation and survival assay using the ProLiFilerTM (Reaction Biology) to characterize the in vitro antitumor effects of Enhertu, Kadcyla, and their individual cytotoxins, deruxtecan & mertansine on 160 human cancer cell lines (CLs). The resulting data were uploaded to 4HF´s Cancer DataMiner platform for data analysis. First, we confirmed high potency and limited selectivity of mertansine, as it displayed an IC50 < 250 nM (mean: 27.3 nM) in 95% of cell lines (CLs). A COMPARE analysis confirmed that mertansine data correlated best with those of other microtubule inhibitors in our drug databases (e.g., MMAE, Spearman rho = 0.79, p=9.6E-27). Conversely, a paired analysis showed that CLs were less sensitive to Kadcyla than to mertansine except for CLs overexpressing ERBB2. The 160-CL panel included a total of nine CLs (six mammary, two gastric, one ovarian) with strong ERBB2 overexpression (Affymetrix data >10), mostly associated with ERBB2 gene amplification; seven of them were the most sensitive CLs to Kadcyla (IC50 < 6 nM). Focusing solely on breast cancer cell lines (breast cancer is the approved indication for Kadcyla), we observed a strong correlation between sensitivity to Kadcyla and ERBB2 expression (Spearman r = -0.78, p = 0.003). Interestingly, in line with published data, the ERBB2-overexpressing cell lines SNU-216 (stomach cancer) and JIM-T1 (breast cancer) were less sensitive to Kadcyla. In non-ERBB2-amplified CLs, Kadcyla sensitivity did not correlate with ERBB2 expression levels. Focusing on ERBB2-negative CLs such as hematological CLs, we unexpectedly observed consistent cell inhibition (mean IC50 =33 nM) with Kadcyla, suggesting that the ADC was cleaved, and the payload released into the medium. Overall, this study has demonstrated the relevance of our platforms to study and compare newly developed ADCs. Cytotoxic activities recorded for conjugates and free payloads, along with molecular data for the test cell lines, provides insight in the mode of action of conjugates and their target cell populations and hence can support the development of ADCs. Investigations are underway with Enhertu and its payload deruxtecan, and results will be compared with those obtained for Kadcyla and mertansine. Citation Format: Anne-Lise Peille, Kaja Holtorf, Pablo Anton Garcia, Nadine Obier, Daniel Feger, Thomas Metz, Sebastian Dempe, Heinz-Herbert Fiebig, Jan Ehlert, Vincent Vuaroqueaux. Potency and selectivity of ERBB2-targeting antibody drug conjugates in vitro [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4708.

Abstract 6392: Activity of HER2-and TROP2- antibody drug conjugates (ADCs) in small cell lung cancer (SCLC) models with SLFN11 as a predictive biomarker

Abstract Background: Small-cell lung cancer (SCLC) is a highly aggressive malignancy with its few treatment options devoid of biomarker selection, and a 5-year survival rate of less than 7%. Our group previously established four transcriptionally defined subtypes of SCLC, each with distinct cell surface targets (Gay et al, Cancer Cell 2021). Further, we identified SLFN11 (a putative DNA/RNA helicase) as a candidate biomarker of sensitivity to DNA-damaging agents, including topoisomerase inhibitors. Human epidermal growth factor receptor 2 (HER2/ERBB2) expression has been previously described in a subset of SCLCs and has been linked to poor prognosis. HER2 antibody-drug conjugates (ADCs) like trastuzumab deruxtecan (T-DXd) (where the payload is a topoisomerase I inhibitor) have received FDA approval for various solid tumors, highlighting their therapeutic potential. Similarly, TROP2 (TACSTD2) ADC sacituzumab govitecan has shown promising clinical efficacy in a SCLC (TROPiCS-03 basket trial). However, it is unclear what the predictive biomarkers are to these ADCs in SCLC. Methods: Expression of ERBB2 and TACSTD2 mRNA was analyzed using publicly available patient datasets. We also characterized surface expression of HER2 and TROP2 by flow cytometry in SCLC cell lines at baseline and after cisplatin/etoposide treatment. We then assessed the cytotoxicity of T-Dxd and sacituzumab govitecan in a panel of SCLC cell lines representative of each SCLC subtype, as well as SLFN11 status. Results: Analyses of HER2/ERBB2 and TROP2/TACSTD2 in SCLC cell lines and patient datasets showed a range of ERBB2 and TACSTD2 expression with enrichment in the non-neuroendocrine subtypes (SCLC-P and SCLC- I subtypes). We further validated HER2 and TROP2 surface levels by flow cytometry in a subset of SCLC cell lines. Intriguingly, we observed that surface expression of both HER2 and TROP2 increase after frontline chemotherapy cisplatin/etoposide treatment. As expected, T-Dxd and sacituzumab govitecan exhibit cytotoxicity in a subset of SCLC cell lines. We found a strong correlation between the in vitro cytotoxicity (IC50) of sacituzumab govitecan with SLFN11 (rho= 0.74, p=0.015). Importantly, SLFN11 is bimodally distributed in SCLC and we found ERBB2 and TACSTD2 to be enriched in the SLFN11-high group of SCLC patients. We also found ERBB2 and TACSTD2 to be correlated with each other (rho = 0.53, p <0.001). Conclusion: In this study, we demonstrate that HER2/ERBB2 and TROP2/TACSTD2 are enriched in a subset of SCLC. FDA-approved ADCs, T-DXd and sacituzumab govitecan each have preclinical activity in SCLC with SLFN11 as a predictive biomarker of payload cytotoxicity. We also found HER2 and TROP2 target levels increase after frontline chemotherapy (cisplatin/etoposide) in SCLC, which suggest their efficacy may be enhanced in relapsed SCLC where treatment options are extremely limited. Citation Format: Bingnan Zhang, Ali Ibrahim, C.Allison Stewart, Lixia Diao, Qi Wang, Li Shen, Yuann xi, Alejandra Serrano, Luisa M. Solis, Wei-Lien Wang, Kavya Ramkumar, Robert J. Cardnell, Runsheng Wang, Alberto Duarte, Jing Wang, Lauren A. Byers, Carl Gay. Activity of HER2-and TROP2- antibody drug conjugates (ADCs) in small cell lung cancer (SCLC) models with SLFN11 as a predictive biomarker [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6392.

Abstract 5111: Rational synergistic radiosensitization strategies for group 3 medulloblastoma

Abstract Medulloblastoma (MB) is the most common malignant pediatric brain tumor. MB is comprised of 4 groups, termed Wnt, Shh, Group 3 and Group 4, each characterized by distinct molecular and clinical profiles. MYC-amplified Group 3 MB is associated imminent fatal metastatic relapse following standard treatment approaches, which currently include surgery, craniospinal irradiation and chemotherapy, highlighting an urgent need for identification of therapeutic vulnerabilities for these tumours. As such, using 4 novel patient-derived models of Group 3 MB that faithfully recapitulate the molecular and histological tumor characteristics, we characterised response to radiation of Group 3 MB in vitro to show that these tumors do not possess intrinsic radiation resistance. Furthermore, cumulative radiation experiments do not increase bulk radiation resistance in MB cells, highlighting the contribution of dynamic cell states to radiation response. In contrast, exposure to radiation leads to changes in cell clonogenic capacity as measured by limited dilution assays. Furthermore, RNA-seq data uncovered altered transcriptomic programs in response to cumulative radiation treatment. In particular, we observe differential regulation of genes encoding potassium ion channels and their regulators as well as genes encoding ECM and cell adhesion proteins. As part of our goal to evaluate the current multimodal treatment strategy of MB, we also show that a set of standard chemotherapeutic agents (etoposide, thiotepa and lomustine) currently used in the clinic do not produce a potent response at optimal doses in vitro, potentially accounting for abysmal survival outcomes seen in chemotherapy treated MB patients. As such, we conducted a screen of 144 FDA approved cancer drugs and identified therapeutics that selectively target Group 3 MB cells in contrast to normal tissue controls (foetal neural stem cells) in the low nanomolar dose range. In particular, topoisomerase inhibitor topotecan produces a potent response specific to MYC-amplified Group 3 MB, and sensitizes 2 patient-derived MB models to gamma irradiation. Altogether, our data characterizes Group 3 MB molecular and cellular responses to current treatment modalities and provides rationale for new clinical strategies to sensitize patients to radiation that will potentially allow to reduce the required radiation doses to treat these aggressive tumors, reduce the incidence of radiation treatment-related morbidity as well as improve cure rates. Citation Format: Julija Povilaikaite, Kaitlin Stitz, Nikhita Austin, Vijay Ramaswamy. Rational synergistic radiosensitization strategies for group 3 medulloblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5111.

Abstract 642: Flavopiridol inhibits cell proliferation, migration, and invasion via downregulation of FOXM1 in triple negative breast cancer

Abstract Triple-negative breast cancer (TNBC) represent 15-20% of all breast cancers and is the subtype of breast cancer that is not responsive to targeted breast cancer treatments such as anti-estrogens (tamoxifen) or HER2 targeted antibodies due to the lack of ER, PR, and HER2 receptors. TNBC is associated with poor prognosis, early relapse, and distant metastasis and drug resistance. With the use of standard chemotherapeutics in the neoadjuvant setting, unfortunately the majority of patients (~60%) with TNBC do not achieve complete remission and 40% of the patients with regional (Stage II) and 90% of the patients with distant metastasis (Stage IV) die within 5-years. Currently, there is no effective targeted therapy for TNBC patients for targeting oncogenic pathways. Although recently the FDA approved sacituzumab (govitecan), a Trop-2-receptor directed antibody conjugated with chemotherapeutic agent topoisomerase inhibitor in metastatic TNBC, and response rate was 30% and the median duration of response is 7.7 months, and the majority of patients did not maintain response longer than 12 months. Therefore, identifying novel molecular targets and developing alternative therapeutic strategies are urgently needed. FOXM1 is a protooncogenic transcription factor suppressed by p53 and drives expression of genes, which play a crucial role in promoting cancer cell proliferation, metastasis, progression, tumorigenesis of TNBC. We previously demonstrated for the first time that in vivo targeting of FOXM1 suppresses TNBC tumor growth in mice. Here, analyzing TCGA patient database we found that FOXM1 expression correlates with shorter patient survival and prognosis in TNBC patients. Overall data suggest that FOXM1 is a potential molecular target. However, currently, there is no FDA approved inhibitor of FOXM1. To identify potential inhibitors, utilizing silico docking and molecular dynamics studies we screened the FDA-approved compounds found that flavopiridol interacts with FOXM1. Flavopiridol is a small molecule inhibitor for CDKs and is approved by the FDA for the treatment of Acute Myeloid Leukemia. We demonstrated that flavodilol inhibits FOXM1 expression at nanomolar concentration and cell proliferation, migration, invasion, and induces apoptosis in TNBC cells. We are currently testing favopridol in MDA-MB-231 (human) and 4T1 mouse mammary) TNBC tumor models. In conclusion, our studies suggest that flavopiridol is a highly potent FOXM1 inhibitor and is a promising agent for repurposing to target FOXM1 and for the treatment of TNBC. Citation Format: Sayra Dilmac, Nermin Kahraman, Ferah Comert Onder, Zuhal Hamurcu, Bulent Ozpolat. Flavopiridol inhibits cell proliferation, migration, and invasion via downregulation of FOXM1 in triple negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 642.

Abstract 7168: PBI-410 (GQ1010), A novel Trop-2-targeted ADC demonstrates a favorable safety and toxicokinetic profile in multiple preclinical assessments

Abstract Introduction: Trop-2-targeting ADCs (Trop-2 ADC) have demonstrated notable clinical efficacy; however, safety concerns necessitate frequent dose adjustments or discontinuations. PBI-410 (GQ1010) is a next-generation TROP-2 ADC developed using GeneQuantum's Ligase-Dependent Conjugation (iLDC) technology, that integrates a highly stable linker and a novel camptothecin analogue payload, TopoIx. This study included comprehensive preclinical evaluations that demonstrated a favorable safety and TK profile and potential for broader therapeutic margin versus other Trop-2 ADCs approved or in development. Methods: TopoIx underwent extensive Good Laboratory Practice toxicity assessments in Sprague-Dawley (SD) rats (payload alone) and as part of the intact ADC in Non-Human Primates. Rats were administered repeated intravenous infusions of 0.5, 1.25, and 2.5 mg/kg of H0011 once a week over 5 doses. The potential toxicity profile of PBI-410 was evaluated in cynomolgus monkeys via repeated intravenous infusions of 10, 30, and 60 mg/kg doses every 3 weeks for 3 doses, followed by a six-week recovery phase. Results: TopoIx administration in SD rats exhibited good tolerance, with slight reductions in body weight gain and food consumption. Microscopic tissue changes resolved post-drug withdrawal, except for persistent findings in the sciatic nerve. Repeated doses of PBI-410 in cynomolgus monkeys were well-tolerated, primarily manifesting as skin pigmentation and associated microscopic alterations in specific tissues, such as eyes, esophagus, thymus, and lymph nodes typical for topoisomerase inhibitors. Importantly, these changes were reversible upon drug cessation. The HNSTD/NOAEL for PBI-410 was determined to be 60 mg/kg. This corresponds to mean Cmax of 1760 µg/mL and AUCinf of 235000 µg*hr/mL for ADC and for TopoIx mean Cmax of 16.4 ng/mL and AUCinf of 2610 ng*hr/mL. The lower exposure of TopoIx suggests minimum payload shedding in the systemic circulation. Notably, PBI-410 demonstrated a significantly enhanced safety profile compared to other Topo1-based Trop-2 ADCs, including an absence of hematopoietic and intestinal toxicities, and no pulmonary toxicity or interstitial lung disease (ILD) observed. Conclusion: PBI-410 demonstrated a favorable and differentiated nonclinical safety profile and favorable TK relative to those reported to date for other Trop-2 ADCs in development. This profile, in addition to the potent anti-tumor response and synergistic activity in combination with anti-PD1 reported previously, position PBI-410 as a best-in-class potential Trop-2 ADC and partner of choice for anti-PD1 combination therapy. Additionally, TopoIx has displayed excellent properties among the TOP1 inhibitors, making it suitable for a broader therapeutic application based on exceptional potency while maintaining a favorable safety profile. Citation Format: Yajun Sun, Vijayapal Reddy, Palaniappan Kulanthaivel, Yanwen Feng, Jie Zhao, Zhiyan Chi, Junhao Wang, Lili Shi, Gang Qin, Paul H. Song. PBI-410 (GQ1010), A novel Trop-2-targeted ADC demonstrates a favorable safety and toxicokinetic profile in multiple preclinical assessments [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 7168.