Antitumor Activity In Preclinical Models Research Articles

Abstract LB063: Anti-tumor activity in preclinical models utilizing a conditional bispecific redirected activation molecule (COBRA) targeting Her2

Abstract Among strategies to recruit cytotoxic T-cells into the tumor micro-environment (TME) are the use of T-cell engager molecules. One such therapeutic modality are molecules that recognize specific tumor associated antigens (TAA) but are activated preferentially in the TME. Conditional Bispecific Redirected Activation molecules (COBRA) are designed to be administered as a prodrug, and cleaved via matrix metalloproteinase to engage with both a tumor TAA and CD3 (Panachi, et.al. MAbs 2020 12(1) 1792130). In this study, we sought to determine the preclinical efficacy of a COBRA molecule targeting the Her2 receptor. Sub-cutaneous xenograft models (SCID mice using adoptive T-cell transfer) were utilized representing various levels of the TAA (HT-55, SNU-16, JIMT-1, and HCC827) to measure both efficacy and mechanism of action (T-cell extravasation). The COBRA molecule was dosed at 0.03, 0.1, 0.3, and 1 mg/kg using a Q3dx7 schedule. A non-cleavable COBRA molecule with the Her2 TAA was included as a control at 1 mg/kg. Efficacy was determined by caliper measurements of sub-cutaneous tumor size twice per week after dosing, and T-cell extravasation into the TME was measured by immunohistochemistry (IHC) at days 10, 19, and termination. IHC data was quantified using HALO imaging software. In our study, we measured dose-dependent tumor regression and/or stasis in all models tested. No anti-tumor activity was measured after dosing with the non-cleavable COBRA molecule. T-cell extravasation as measured by IHC and Halo analysis followed a dose and time dependent course. Comparison of Day 19 T-cell extravasation (one day after the last dose) showed a linear relationship to TAA expression. Our data indicate that treatment with a COBRA molecule in preclinical models with a Her2 TAA results in anti-tumor activity as measured by tumor stasis/regression, and exhibit the expected mechanism of action as evaluated by T-cell extravasation into the TME. Citation Format: Bradley Stringer, Johara Chouitar, Jacqualine Cerbone, Sarah Fortin, Alina Ainbinder, Cassie Kysilovsky, Brittany Scott, Antara Banerjee. Anti-tumor activity in preclinical models utilizing a conditional bispecific redirected activation molecule (COBRA) targeting Her2 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB063.

Abstract SY12-01: Targeting validated but un-drugged oncogenes with small molecule protein degraders

Abstract SY12-01: Targeting validated but un-drugged oncogenes with small molecule protein degraders

Abstract CT162: Trial in progress: A phase I, open-label, multicenter study of ZL-1218, an anti-CCR8 IgG1, as a single agent and as combination therapy with anti-PD-1 antibody to evaluate the safety, tolerability, and pharmacokinetics in subjects with advanced solid tumor

Abstract Background ZL-1218 is an anti-chemokine receptor 8 (CCR8) humanized IgG1 antibody with enhanced antibody-dependent cellular cytotoxicity (ADCC) activity. CCR8 demonstrates a preferential expression in tumor-associated Tregs over peripheral Tregs. Thus, targeting CCR8 may allow for specific depletion of intratumoral Tregs without impacting peripheral Tregs/other immune cells. ZL-1218 is intended to decrease the intratumoral Tregs by binding to both high- and low-expressing CCR8+ cells and eliciting potent ADCC activity. ZL-1218 blocked CCR8 ligand CCL1 from binding to CCR8, and reduced Treg recruitment by blocking chemotaxis of CCR8+ cells (unpublished data). Additionally, ZL-1218 demonstrated enhanced antitumor activity in preclinical models in combination with anti-PD-1. Methods This is a Phase I study of ZL-1218 as a single agent and in combination with pembrolizumab (P) to evaluate the safety, tolerability, pharmacokinetics/pharmacodynamics, and preliminary antitumor activity in subjects with advanced solid tumor malignancies. The study consists of Part 1 Dose Escalation and Part 2 Cohort Expansion. In Part 1, subjects will be treated with escalating doses of ZL-1218 alone and in combination with a fixed dose of P to identify the maximum tolerated dose (MTD) and/or the recommended expansion dose (RD). The Bayesian optimal interval (BOIN) design is used and adopted with overdose control. Upon progression in the single agent group, a subject may enroll into combination therapy of ZL-1218 with P. Subjects will start at their respective single agent dose or the cleared combination dose level, whichever is lower. Part 2 will explore the combination with pembrolizumab in subjects with selected tumor types, with or without prior CPI therapy. Major inclusion criteria include: (1) Subjects must have histologically confirmed and documented diagnosis of locally advanced unresectable/metastatic advanced solid tumor that is refractory/intolerant to standard treatment, or for which no standard treatment exists, and no greater than 3 prior lines of therapy in the relapse/refractory setting (2). Subjects must have at least one target lesion as defined by RECIST v1.1 on CT, PET/CT, or MRI scan. (3) Subjects must have a site of disease which is not previously irradiated and is safe and amenable to biopsy. Major exclusion criteria include: (1) Prior exposure to CCR8 inhibitor, or severe hypersensitivity (≥ Grade 3) to P and/or any of its excipients. (2) Subjects with symptomatic or uncontrolled brain metastasis requiring concurrent treatment, impaired major organ functions, active autoimmune disease, or active infections. Part 1 Dose Escalation is ongoing in the US and EU. Citation Format: Elena Garralda, Valentina Boni, David Vincente Baz, Arvind Chaudhry, Ignacio Gil Bazo, Martin Gutierrez, Jyoti Malhotra, Casal Guzman Alonso, Valentina Gambardella, Michael Chisamore, Renke Zhou, Maria Tea, Deborah Doroshow. Trial in progress: A phase I, open-label, multicenter study of ZL-1218, an anti-CCR8 IgG1, as a single agent and as combination therapy with anti-PD-1 antibody to evaluate the safety, tolerability, and pharmacokinetics in subjects with advanced solid tumor [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr CT162.

Characterization of a novel anti-PVRIG antibody with Fc-competent function that exerts strong antitumor effects via NK activation in preclinical models

Poliovirus receptor-related immunoglobulin domain-containing protein, or PVRIG, is a newly discovered immune checkpoint that has emerged as a promising target for cancer immunotherapy. It is primarily expressed on activated T and natural killer (NK) cells, and once engaged with its ligand, PVRL2, it induces inhibitory signaling in T cells, thereby promoting the functional exhaustion of tumor-infiltrating lymphocytes (TILs). Here, we characterized IBI352g4a, a novel humanized anti-PVRIG antibody with Fc-competent function, explored the mechanism of its antitumor activity in preclinical models, and systemically evaluated the contribution of FcrR engagement to PVRIG blockade-induced antitumor activity. IBI352g4a binds to the extracellular domain of human PVRIG with high affinity (Kd = 0.53 nM) and specificity, and fully blocks the interaction between PVRIG and its ligand PVRL2. Unlike other immune checkpoints, IBI352g4a significantly induced NK cell activation and degranulation, but had a minimal effect on T-cell activation in in vitro functional assays. IBI352g4a induced strong antitumor effect in several preclinic models, through in vivo mechanism analysis we found that both NK and T cells contribute to the antitumor effect, but NK cells play predominant roles. Specifically, a single dose of IBI352g4a induced significant NK cell activation in TILs, but T-cell activation was observed only after the second dose. Moreover, the Fc effector function is critical for both NK cell activation and treatment efficacy in vitro and in vivo. Our study, for the first time, demonstrates that both NK activation and FcrR engagement are required for antitumor efficacy induced by PVRIG blockade.

Abstract 6579: DS-3939a, a novel TA-MUC1-targeting antibody-drug conjugate (ADC) with a DNA topoisomerase I inhibitor DXd, exhibits potent antitumor activity in preclinical models

Abstract Background: Tumor-associated mucin-1 (TA-MUC1) is a tumor-specific transmembrane glycoprotein with aberrant glycosylation. It is highly expressed in various human epithelial cancers, making it an attractive target for cancer therapy. DS-3939a is a TA-MUC1 targeting antibody-drug conjugate (ADC) structurally composed of a humanized anti-TA-MUC1 antibody, an enzymatically cleavable tetrapeptide-based linker, and a DNA topoisomerase I inhibitor (DXd) with a high drug-to-antibody ratio (DAR). In this study, the pharmacological activity of DS-3939a was evaluated using preclinical in vitro and in vivo models. Methods: TA-MUC1 expression was assessed by immunohistochemistry and flow cytometry. Binding specificity of DS-3939a was confirmed by enzyme-linked immunosorbent assay. Induction of DNA damage and apoptosis to cancer cells by DS-3939a treatment were detected by Simple Western System. In vitro cell growth inhibitory and in vivo antitumor activities of DS-3939a were evaluated using various cancer cell lines and patient-derived xenograft (PDX) models. Results: Many specimens across multiple cancer types showed positive staining for TA-MUC1, with a particularly high positive rate observed in bladder, lung, and breast cancers. DS-3939a specifically bound to aberrantly glycosylated MUC1 peptides by recognizing both the glycan and backbone peptide moiety of MUC1. In vitro, DS-3939a inhibited the growth of TA-MUC1-positive cancer cells but not of TA-MUC1-negative cancer cells. Neither a parental anti-TA-MUC1 antibody nor isotype control ADC inhibited the growth of these cells. In addition, treatment with DS-3939a and DXd alone induced DNA damage and apoptosis in cancer cells. These results demonstrate that DS-3939a exhibits TA-MUC1-dependent cell growth inhibition through DXd-mediated cytotoxic effect. Moreover, DS-3939a exhibited significant antitumor effects in the several TA-MUC1-positive cancer cell line-derived xenograft models and various PDX models. DS-3939a also induced strong tumor regression even after treatment of other cytotoxic ADCs in several xenograft models. Conclusion: Based on these preclinical results, DS-3939a could provide valuable therapy with potential benefits for patients with TA-MUC1-expressing tumors. A first-in-human phase 1/2 study in patients with advanced solid tumors is currently in progress (NCT05875168). Citation Format: Mayuko Yukiura, Kohei Takano, Kazuki Takahashi, Akiko Zembutsu, Michiko Kitamura, Yoshinobu Shiose, Kokichi Honda, Kazunori Oyama, Wataru Obuchi, Makiko Yamada, Riki Goto, Ken Sakurai, Kazuyoshi Kumagai, Takashi Kagari, Yuki Abe, Toshinori Agatsuma. DS-3939a, a novel TA-MUC1-targeting antibody-drug conjugate (ADC) with a DNA topoisomerase I inhibitor DXd, exhibits potent antitumor activity in preclinical 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 6579.

Abstract 1656: ISM6331, a novel and potent pan-TEAD inhibitor, exhibits strong anti-tumor activity in preclinical models of Hippo pathway-dysregulated cancers

Abstract The Hippo-YAP/TAZ-TEAD signaling pathway plays critical roles in tumorigenesis and tumor progression. Genetic alterations of Hippo pathway regulators, such as NF2 or LATS1/2, have been shown to induce YAP/TAZ-TEAD transcriptional activity, promoting initiation and progression of many solid tumors. In addition, many studies have shown that YAP/TAZ-TEAD activation mediates resistance to multiple targeted therapies, particularly EGFR-KRas-MAPK pathway inhibitors. The TEAD family of transcription factors (TEAD1/2/3/4) share structural similarity and have overlapping functions in tumor development and TEAD auto-palmitoylation is critical for its interaction with YAP/TAZ and its transcriptional function. Therefore, blocking TEAD palmitoylation and allosterically disrupting YAP/TAZ-TEAD-mediated transcriptional regulation, is emerging as a promising approach for the treatment of tumors with Hippo pathway dysregulation. In this work, ISM6331, a novel and potent TEAD inhibitor with excellent inhibition against TEAD1/2/3/4 was identified leveraging an AI generative model. ISM6331 reversibly binds to the TEAD palmitoylation site and significantly suppresses TEAD transcriptional activity. ISM6331 potently and selectively inhibited the growth of many Hippo pathway-dysregulated tumor cells and dose-dependently suppressed the expression of TEAD target genes in vitro. In NF2-deficient or LATS1/2-mutant in vivo mesothelioma models, ISM6331 exhibited promising anti-tumor efficacy as monotherapy in a dose-dependent manner from 3 to 30mg/kg. ISM6331 also showed synergism with EGFR or KRasG12C inhibitors in inhibiting tumor cell growth and overcame drug resistance in in vitro and in vivo models. In addition, ISM6331 showed excellent pharmacokinetic properties in multiple preclinical species and was well-tolerated in GLP-toxicity studies. In summary, ISM6331 has promising potential to treat Hippo pathway-dysregulated tumors as monotherapy as well as in combination with targeted therapies. Citation Format: Qi Li, Jainfei Wan, Jinxin Liu, Jing Shang, Jiaojiao Yu, Wei Zhu, Celia X.-J. Chen, Junwen Qiao, Ling Wang, Man Zhang, Xiao Ding, Supriya Bavadekar, Sujata Rao, Feng Ren, Alex Zhavoronkov. ISM6331, a novel and potent pan-TEAD inhibitor, exhibits strong anti-tumor activity in preclinical models of Hippo pathway-dysregulated 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 1656.

Abstract 20: KSQ-001EX: An engineered TIL therapy manufactured from a clinical-scale, feeder-free process for the treatment of solid tumor indications

Abstract Tumor Infiltrating Lymphocyte (TIL) therapy is an autologous adoptive cell therapy involving the isolation, ex vivo expansion and infusion of tumor infiltrating lymphocytes (TIL) into late-stage cancer patients for therapeutic benefit. While clinical responses to TIL therapy have been observed in metastatic melanoma, efficacy in other tumor types including non-small cell lung cancer (NSCLC), and head and neck squamous cell carcinoma (HNSCC) [SM1] is limited by the intrinsic functionality and persistence of transferred T cells and the immunosuppressive tumor microenvironment. To improve the clinical outcome of TIL therapy, we have developed KSQ-001EX, an engineered TIL therapy using CRISPR/Cas9 technology to knockout the SOCS1 gene, for the treatment of solid tumors. SOCS1 is a negative regulator of cytokine signaling in T cells that we previously identified as a top target restraining T cell anti-tumor function and persistence using genome-wide in vivo CRISPR screens. To streamline and shorten TIL manufacture, we established a next-generation manufacturing process with resected tumors or core biopsies as starting materials that eliminates the use of feeder cells and REP, shortening the length of manufacture to 22 days. We demonstrated robust manufacture of cryopreserved KSQ-001EX at clinical scale from NSCLC, HNSCC, checkpoint refractory melanoma, and heavily pre-treated colorectal carcinoma (CRC). KSQ-001EX manufactured from clinical-scale runs were highly viable (>90%) following cryopreservation and thaw, with > 90% SOCS1 on-target editing and complete knockdown of SOCS1 at the protein level. Importantly, KSQ-001EX across all indications assessed showed high frequency of CD8 (median ~80%), an attribute associated with TIL clinical responses. KSQ-001EX also retained high diversity of TCR repertoire. Consistent with the biology of SOCS1 editing, KSQ-001EX exhibited greater cytotoxicity and higher IFNγ production against tumor spheroids in comparison to TIL and enhanced induction of pSTAT4 upon IL-12 stimulation, demonstrating heightened sensitivity of KSQ-001EX to cytokines. In conclusion, KSQ-001EX, an engineered TIL therapy with CRISPR/Cas9 mediated inactivation of SOCS1, can be manufactured at clinical doses from surgical resections or core biopsies within 22 days using a simplified feeder-free manufacturing process from multiple indications. KSQ-001EX exhibits heightened anti-tumor activity in preclinical models, with therapeutic benefit to be evaluated in a planned clinical trial in patients with treatment-refractory melanoma, NSCLC, and HNSCC. [SM1]Spell out these at first instance? Citation Format: Sharon Lin, Gustavo Martinez, Marie-Andrée Forget, Katrina Adlerz, Mitali Ghose, Leila Williams, Paul Dunbar, Frank Thompson, Fiona Sharp, Hugh Gannon, Conor Calnan, Ashish Yeri, Dipen Sangurdekar, Donald Sakellariou-Thompson, Samantha Fix, Tamara Griffith, Ellie Jafari, Jane Zulovich, Priya Balasubramanian, Erin Willert, MIcah Benson, Chantale Bernatchez, Karrie Ka Wai Wong. KSQ-001EX: An engineered TIL therapy manufactured from a clinical-scale, feeder-free process for the treatment of solid tumor indications [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 20.

Abstract 5988: The role of the deubiquitinase USP7 and the E3/E4 ubiquitin ligase complex ITCH/UBE4B in the regulation of cell death in neuroblastoma

Abstract Dysregulation of the Ubiquitin Proteasome System has been linked to many human diseases, including cancer. Expression of UBE4B ubiquitin ligase is associated with neuroblastoma patient outcomes and its functional roles in neuroblastoma pathogenesis are not known. We have recently identified a ubiquitin complex ITCH/UBE4B which mediates ubiquitination of Ku70 and c-FLIPL proteins for proteasomal degradation allowing HDAC inhibitor-mediated caspase-8 dependent apoptosis. We also confirmed that the deubiquitinase USP7, critical player in tumor suppression and DNA repair, can be a potential therapeutic target for neuroblastoma. Highly selective USP7 inhibitors have demonstrated significant antitumor activity in preclinical models of adult cancer, and we reported that these inhibitors alone can be more effective against neuroblastoma tumor growth. Our hypothesis is that USP7 inhibition will be more effective against neuroblastoma tumors through destabilization of ITCH/UBE4B complex protein targets allowing a stronger induction of cell death in response to treatment for the children. To evaluate efficacy of USP7 inhibitors in combination with HDAC inhibitors or chemotherapy against neuroblastoma tumor growth, neuroblastoma cell lines depleted for UBE4B or USP7 were treated with increasing concentrations of USP7 inhibitors alone or in combination with chemotherapy or with HDAC inhibitors. Cell proliferation was measured using continuous live cell imaging and apoptosis by caspase cleavage and PARP cleavage detection by western blot. We have evaluated also, whether ubiquitination/deubiquitination and degradation rates of p53, Ku70 and c-FLIPL proteins could modulate induction of apoptosis and necroptosis. USP7 inhibition resulted in decreases in cell viability in p53 wild-type neuroblastoma cell lines. USP7 inhibition induced apoptosis and necroptosis by increasing phosphorylation of MLKL, RIPK3 and RIPK1. In UBE4B or USP7 depleted cells, a huge induction of necroptosis and a small rate of apoptosis were observed. We also identified USP7 as a deubiquitinase of Ku70, stabilizing Ku70 at the basal level, leading to stabilization of Ku70/c-FLIPL/Bax complex. USP7 inhibition destabilizes ku70 and c-FLIPL for protein degradation leading to induction of apoptosis as well as necroptosis. UBE4B depletion in neuroblastoma inhibits HDAC inhibitors mediated caspase-8 mediated apoptosis but enhances necroptosis, due to the inhibition of Ku70 and c-FLIPL proteins degradation leading to the blockade of caspase-8 activation and the activation of the necroptosome. Our data suggests that USP7 and ITCH/UBE4B can control the switch between apoptosis and necroptosis in response to USP7 and HDAC inhibitors. USP7 inhibition and ITCH/UBE4B activation by HDAC inhibitors could be a promising therapeutic strategy for children with high-risk and relapsed neuroblastoma. Citation Format: Christophe Le Clorennec, CARLA SAMPAIO, PETER E. ZAGE. The role of the deubiquitinase USP7 and the E3/E4 ubiquitin ligase complex ITCH/UBE4B in the regulation of cell death in neuroblastoma [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 5988.

Abstract 1661: Preclinical characterization of HMPL-295, a potent and selective ERK 1/2 inhibitor

Abstract Background: Although therapeutic agents targeting alterations in the MAPK pathway have achieved great clinical success, the overall benefit is still suboptimal. Several studies have shown that reactivation of MAPK signaling is the main basis to compromise the efficacy. Thus, co-inhibition of ERK, the terminal master kinase of MAPK pathway, and the upstream targets may effectively shut down the MAPK signaling cascade and induce deeper and more durable anti-tumor activities. Herein, we present the preclinical characterization of HMPL-295, a potent and selective ERK 1/2 inhibitor, discovered and being currently developed in phase I clinical trial (NCT04908046) by HUTCHMED. Methods: The inhibition on ERK 1/2 kinase was determined using Z-LYTE™ kinase assay. The selectivity of HMPL-295 was evaluated against 394 kinases (KinaseProfilerTM) and 86 safety-related proteins (SafetyScreen87TM) by Eurofins. Cellular target inhibition on phosphorylation of RSK (p-RSK) was detected by ELISA. In vitro anti-proliferation activity of HMPL-295 as a single agent was measured by CCK-8 or CellTiter-Glo luminescent assay. Colony formation assay was used to evaluate the combination effect of HMPL-295 with targeted therapy. Multiple tumor models with RAS/RAF/MAPK pathway activation were applied in immune-deficient mice to investigate the anti-tumor activity of HMPL-295 as a single agent or in combination with either chemotherapy or targeted therapy. Results: HMPL-295 strongly inhibited ERK1 and ERK2 kinase activities with equal IC50 at 4 nM. In human colon cancer cell line COLO 205 harboring BRAFV600E mutation, HMPL-295 inhibited p-RSK, a direct substrate of ERK1/2, with an average IC50 of 180 nM from 3 independent experiments. With the inhibition of ERK and its downstream substrates, HMPL-295 treatment induced tumor cells arresting at G0/G1 phase via down-regulation of cyclin D1/p-RB signaling and consequently attenuated cell growth in a panel of MAPK pathway dysregulated tumor cell lines, but barely affected the growth of normal cells. Furthermore, HMPL-295 demonstrated favorable selectivity in the kinase and safety pharmacology profiling, indicating a low off-target risk. For in vivo studies, oral administration of HMPL-295 induced time- and dose-dependent inhibition of p-RSK and resulted in dose-dependent anti-tumor activity in several tumor models harboring KRAS or BRAF mutations. Moreover, HMPL-295 significantly improved the anti-tumor activity of standard-of-care chemotherapy as well as targeted agents in KRAS- or BRAF-mutant tumor models both in vitro and in vivo. Conclusion: HMPL-295 is a potent and selective ERK1/2 inhibitor which demonstrates strong anti-tumor activity in preclinical models, supporting further clinical evaluation. Citation Format: Jia Hu, Jun Ni, Yuanzhi Lv, Wenjun Li, Hui Zhang, Xin Li, Ying Yu, Zeyu Zhong, Jian Wang, Yang Sai, Weiguo Qing, Yongxin Ren, Michael Shi, Weiguo Su. Preclinical characterization of HMPL-295, a potent and selective ERK 1/2 inhibitor [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 1661.

Abstract 5909: Sulindac exhibits anti-proliferative effects in pre-clinical models of ovarian cancer

Abstract Objectives: Given the intricate relationship between inflammation and ovarian cancer (OC) development and progression, anti-inflammatory drugs may have potential in the prevention and treatment of OC. Sulindac exhibits potent anti-inflammatory effects through inhibition of COX1/COX2 pathways and promising anti-tumor activity in pre-clinical models of colorectal and endometrial cancer. Thus, we investigated the efficacy of sulindac as an anti-tumorigenic agent in OC pre-clinical cell and mouse models. Methods: The human OC cell lines, MES and OVCAR5, and the K18-gT121+/-;p53fl/fl;Brca1fl/fl (KpB) mouse model of high-grade serous OC were used. Cellular proliferation was assessed by MTT and colony count assays. Apoptosis was assessed using cleaved caspase 3, 8, and 9 assays. To measure cellular stress, production of reactive oxygen species was measured by DCFH-DA assay, and the JC1 assay was used to assess changes in mitochondrial membrane potential. Cellular adhesion was evaluated by laminin assay, and cellular migration was determined by wound healing assay. Western immunoblotting was used to assess the effects of sulindac on downstream targets related to cellular stress, apoptosis, cellular invasion potential, cell cycle control, and inflammation. The KpB mice were treated with sulindac (7.5 mg/kg, oral gavage, daily) or placebo for four weeks. Results: Sulindac inhibited cellular proliferation in a dose-dependent manner in the MES and OVCAR5 cells, with IC50s of 75.3 and 75.69 μM, respectively. Sulindac (100 μM) reduced colony formation by 81% in the MES cells and by 49% in the OVCAR5 cells (p<0.01). Treatment of MES and OVCAR5 cells with sulindac increased ROS production and decreased mitochondrial membrane potential, in a dose-dependent manner (p<0.01). Sulindac induced activity of cleaved caspase 3, 8, and 9, in MES and OVCAR5 cells (p<0.01). In addition, sulindac (100 μM) effectively decreased cellular adhesion by 31% in MES cells and by 23% in OVCAR5 cells (p<0.01). These results were confirmed by Western immunoblotting demonstrating that sulindac downregulated the anti-apoptotic proteins Bcl-xl and Mcl-1 and upregulated the pro-apoptotic proteins Bax and cellular stress proteins Bip, ATF-4, and PDI, in both cell lines. Sulindac downregulated expression of several epithelial-mesenchymal transition proteins in both cell lines, including beta-catenin, snail, and slug. Sulindac also downregulated expression of cell cycle proteins CDK4, CDK5, and Cyclin D1 and inflammatory protein COX-2 in both cell lines. After 4 wks of treatment, sulindac significantly inhibited tumor growth by 71% (1.89 g vs 0.54 g, p<0.01) in KpB mice. Conclusions: Our results find that sulindac exhibited anti-tumorigenic effects in OC cell lines and the KpB OC mouse model. Given these promising pre-clinical results, further studies on the repurposing of sulindac for the prevention and treatment of OC is warranted. Citation Format: Nikita Sinha, Shuning Chen, Jennifer Haag, Xiaochang Shen, Boer Deng, Ziyi Zhao, Chunxiao Zhou, Victoria Bae-Jump. Sulindac exhibits anti-proliferative effects in pre-clinical models of ovarian 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 5909.

Anti-CD47 and Anti-PDL1 Immunotherapy Synergize for Anti-tumor Activity in Preclinical Models of Head and Neck Cancer

Anti-CD47 and Anti-PDL1 Immunotherapy Synergize for Anti-tumor Activity in Preclinical Models of Head and Neck Cancer

Phase I study of the Syk inhibitor sovleplenib in relapsed or refractory mature B-cell tumors.

Sovleplenib (HMPL-523) is a selective spleen tyrosine kinase (Syk) inhibitor with antitumor activity in preclinical models of B-cell malignancy. We conducted a dose-escalation and dose-expansion phase I study of sovleplenib in patients with relapsed/refractory mature Bcell tumors. Dose escalation followed a 3+3 design; patients received oral sovleplenib (200-800 mg once daily [q.d.] or 200 mg twice daily [b.i.d.], 28-day cycles). During dose expansion, patients were enrolled into four cohorts per lymphoma classification and treated at the recommended phase 2 dose (RP2D). Overall, 134 Chinese patients were enrolled (dose escalation, n=27; dose expansion, n=107). Five patients experienced dose-limiting toxicities: one each of amylase increased (200 mg q.d.), febrile neutropenia (800 mg q.d), renal failure (800 mg q.d.), hyperuricemia and blood creatine phosphokinase increased (200 mg b.i.d.) and blood bilirubin increased and pneumonia (200 mg b.i.d.). RP2D was determined as 600 mg (>65 kg) or 400 mg (≤65 kg) q.d. The primary efficacy end point of independent review committee-assessed objective response rate in indolent B-cell lymphoma was 50.8% (95% CI, 37.5-64.1) in 59 evaluable patients at RP2D (follicular lymphoma: 60.5%, marginal zone lymphoma: 28.6%, lymphoplasmacytic lymphoma/Waldenström macroglobulinemia, 0%). The most common (≥10% patients) grade ≥3 treatment-related adverse events in the doseexpansion phase were decreased neutrophil count (29.9%), pneumonia (12.1%) and decreased white blood cell count (11.2%). Pharmacokinetic exposures increased doseproportionally with ascending dose levels from 200-800 mg, without observed saturation. Sovleplenib showed antitumor activity in relapsed/refractory B-cell lymphoma with acceptable safety. Further studies are warranted.

New Emerging Targets in Cancer Immunotherapy: The Role of B7-H3.

Immune checkpoints (ICs) are molecules implicated in the fine-tuning of immune response via co-inhibitory or co-stimulatory signals, and serve to secure minimized host damage. Targeting ICs with various therapeutic modalities, including checkpoint inhibitors/monoclonal antibodies (mAbs), antibody-drug conjugates (ADCs), and CAR-T cells has produced remarkable results, especially in immunogenic tumors, setting a paradigm shift in cancer therapeutics through the incorporation of these IC-targeted treatments. However, the large proportion of subjects who experience primary or secondary resistance to available IC-targeted options necessitates further advancements that render immunotherapy beneficial for a larger patient pool with longer duration of response. B7-H3 (B7 Homolog 3 Protein, CD276) is a member of the B7 family of IC proteins that exerts pleiotropic immunomodulatory effects both in physiologic and pathologic contexts. Mounting evidence has demonstrated an aberrant expression of B7-H3 in various solid malignancies, including tumors less sensitive to current immunotherapeutic options, and has associated its expression with advanced disease, worse patient survival and impaired response to IC-based regimens. Anti-B7-H3 agents, including novel mAbs, bispecific antibodies, ADCs, CAR-T cells, and radioimmunotherapy agents, have exhibited encouraging antitumor activity in preclinical models and have recently entered clinical testing for several cancer types. In the present review, we concisely present the functional implications of B7-H3 and discuss the latest evidence regarding its prognostic significance and therapeutic potential in solid malignancies, with emphasis on anti-B7-H3 modalities that are currently evaluated in clinical trial settings. Better understanding of B7-H3 intricate interactions in the tumor microenvironment will expand the oncological utility of anti-B7-H3 agents and further shape their role in cancer therapeutics.

Abstract A044: The discovery of potent KAT6 inhibitors that demonstrate anti-tumor activity in preclinical models of ER+ breast cancer

Abstract KAT6 paralogs KAT6A (MOZ; MYST3) and KAT6B (MORF; MOZ2; MYST4) are histone acetyltransferase (HAT) enzymes that acetylate histone H3 and thereby epigenetically regulate gene transcription by altering chromatin structure. Dysregulation of KAT6 activity (gene amplification, overexpression, fusion, mutation, etc.) is observed in breast and other cancers. In several subtypes of breast cancer, KAT6A is amplified as part of the 8p11-p12 amplicon and/or is overexpressed in 11 to 15% of overall breast cancer population. Overexpression of KAT6 correlates with worse clinical outcome in ER+/HER2− breast cancers. Here we present the discovery of novel and potent KAT6 inhibitors with robust in vitro and in vivo anti-tumor efficacy and high selectivity against other KAT family members KAT5 and KAT8. Our lead KAT6 inhibitor compounds demonstrate strong anti-proliferative effects in ER positive breast cancer cell lines with KAT6 dysregulation while demonstrating robust target engagement biomarker activity (inhibition of histone H3 acetylation at lysine residue 23). In addition, these compounds exhibit desirable ADME and pharmacokinetic properties including good oral bioavailability in tested species, supporting potential once daily dosing in humans. The lead compounds also demonstrate enhanced in vitro cellular efficacy in breast cancer cell lines when combined with OP-1250, a complete ER antagonist (CERAN), and CDK4/6 inhibitors, illustrating their combination potential. In addition, these lead compounds demonstrate excellent dose-dependent anti-tumor activity resulting in tumor growth inhibition and tumor regression in a KAT6A amplified ER+ breast cancer xenograft model, highlighting their potential as a novel therapy in ER+ breast cancer. Additional nonclinical efficacy testing, and safety profiling of these lead compounds is currently underway to select a clinical candidate. Citation Format: Gopinath S. Palanisamy, Chandregowda Venkateshappa, Megha Goyal, Susanna A. Barratt, Brian R. Hearn, Girish Daginakatte, Aravind A B, Samiulla D S, Kalisankar Bera, Sangeetha S, Leena Khare, Alison D. Parisian, Dirk A. Heerding, Raymond A. Ng, Cyrus L. Harmon, Susanta Samajdar, Murali Ramachandra, David C. Myles. The discovery of potent KAT6 inhibitors that demonstrate anti-tumor activity in preclinical models of ER+ breast cancer [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr A044.

Abstract A052: Discovery and characterization of a p300-selective degrader demonstrates potent anti-tumor activity in preclinical models of prostate cancer

Abstract Strategies targeting androgen receptor (AR) in the treatment of prostate cancer (PrCa) have shown clear clinical benefit. However, a variety of AR-signaling bypass mechanisms ultimately result in progression to metastatic castrate resistant prostate cancer (mCRPC), and therapies for these patients remain an urgent unmet need. The histone acetyltransferase paralogs p300 and CBP, key coactivators of AR, are currently under investigation as attractive therapeutic targets to abrogate aberrant AR signaling but face a challenging clinical toxicity profile in hematopoietic cells. We postulate that p300 serves as a key regulator of AR signaling, and by sparing CBP we should retain potency against AR-driven PrCa while providing a larger safety margin. We discovered potent heterobifunctional degraders with demonstrated selectivity for p300 over CBP. Our tool compound exhibits degradation of p300 within 2 hours (DC50 = 7.5nM, Dmax = 79%) with minimal impact on CBP at 48 h (DC50 >1uM, Dmax = 5%). The AR/ARv7 driven VCaP PrCa cell line demonstrated exceptional sensitivity to this p300 degrader in proliferation assays (gIC50 = 0.8 nM) comparable to the dual p300/CBP inhibitor, CCS-1477, or the AR degrader, ARV-110 and undergoes a cytotoxic response. Profiled against known AR target genes, our degrader was able to suppress KLK2, KLK3 and FKBP5 transcript levels akin to CCS-1477 in both LNCaP and VCaP PrCa cell lines, supporting the hypothesis that p300, not CBP, acts as the primary coactivator of AR signaling. In addition, our compound led to greater downregulation of full-length AR, ARv7 and cMyc compared to CCS-1477. Subsequent assessment in an in vivo model (VCaP CDX) demonstrated tumor growth inhibition at the highest dose tested (88%; p=2.6e-4). Lastly, we profiled our p300 degrader in human bone marrow derived hematopoietic progenitor colony-forming assays where we observed a significant reduction in toxicity (IC50 = 3.9uM) compared to either CCS-1477 (IC50 = 121nM) or a dual degrader tool compound (IC50 = 16nM), supporting the hypothesis that a p300-specific mechanism will offer an improved therapeutic index. Treatment with our p300-specific degrader resulted in a potent anti-tumor effect on PrCa cells both in vitro and in vivo, comparing favorably to both dual p300/CBP inhibitor or AR degrader strategies. Furthermore, selective degradation of p300 has the potential to minimize toxicity to hematopoietic cells commonly observed with dual targeting of CBP and p300. Taken together, these results support the role p300 may play in driving AR-mediated signaling in PrCa and demonstrate that a p300-specific degrader may serve as an effective therapeutic modality in this disease setting. Citation Format: Mike Russell, Cassandra L Lowenstein, Xuqing Zhang, Jeremy Roach, Jianing Song, Rakesh Nagilla, Peter Orth, Matt Tudor, Qiaolin Deng, Zhihua Sui, Corey Strickland, Larry J Jolivette, E Scott Priestley, Helai P Mohammad. Discovery and characterization of a p300-selective degrader demonstrates potent anti-tumor activity in preclinical models of prostate cancer [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr A052.

Abstract C145: ANS014004, a novel small-molecule type II c-Met inhibitor effectively overcomes clinical-resistance MET mutations and exhibits antitumor activity in preclinical models of MET-amplified non-small cell lung cancer (NSCLC) and gastric cancer

Abstract Mesenchymal epithelial transition (MET) proto-oncogene receptor tyrosine kinase (RTK) is a cell surface receptor selective for hepatocyte growth factor (HGF), and is involved in embryogenesis regulation, wound healing, organ regeneration, angiogenesis, and immunomodulation. Aberrant MET oncogenic alterations include: MET exon 14 skipping (MET∆ex14) mutations; activating mutations in the kinase domain; MET gene amplification; MET fusions; and MET protein overexpression. These oncogenic alterations occur in a wide range of human solid cancers. Small-molecule type I c-Met inhibitors bind to the active (Asp-Phe-Gly “DFG-in” state) of c-Met within the adenosine triphosphate (ATP) binding pocket via the Y1230 residue, resulting in down-regulation of multiple pro-oncogenic downstream factors. Presently, type I c-Met inhibitors such as Capmatinib are used as monotherapies in patients with locally advanced or metastatic NSCLC with MET∆ex14 mutations. However, development of post-treatment resistance to type I c-Met inhibitors occurs clinically, including through acquired mutations in codons D1228 and Y1230. No drugs have been approved globally for MET alteration indications other than MET∆ex14 mutations. Next generation MET inhibitors are thus needed to treat patients harboring various MET oncogenic alterations beyond MET∆ex14, including post-treatment acquired mutations. ANS014004 is a newly developed small-molecule type II inhibitor of c-Met, binding to the inactive state of c-Met (“DFG-out”) in the ATP pocket. ANS014004 showed greater kinase inhibition activity against c-Met mutant kinases Y1230H and D1228A in vitro (IC50’s = 2.596 and 2.971 nM, respectively), when compared with Capmatinib, Cabozantinib, and Merestinib (IC50 values = >5000, ~10, and ~5 nM respectively). Further, ANS014004 showed a stronger anti-proliferative effect in MET mutant Ba/F3 cells TPR-Met D1228A and TPR-Met-Y1230H in vitro (IC50’s = 49.34 nM and 30.32 nM, respectively), when compared with Capmatinib (IC50 values>10000nM) and Merestinib (IC50 values: 37~100 nM). ANS014004 also showed potent antitumor effects in vitro in the human cancer tumor cell lines harboring various pathogenetic MET alterations: Hs-746T (gastric); MKN-45 (gastric); EBC-1 (NSCLC); NCI-H1993 (NSCLC); with IC50 ranging from 6.38~62.32 nM. In several subcutaneous xenograft tumor model studies using these same cell lines implanted in BALB/c nude mice, orally administered ANS014004 produced significant dose-dependent tumor growth inhibition, and the corresponding exposures of ANS014004 in plasma, tumor and brain samples increased with increasing dose. ANS0104001 was also observed to induce tumor regression in a MET-amplified intracranial xenograft model. Overall, the non-clinical studies of ANS014004 demonstrated it is a potent, orally-bioavailable type II c-Met inhibitor with activity against various pathogenetic MET alterations and with favorable absorption, distribution, pharmacokinetic, efficacy, and tolerability profiles in vivo. The molecule will enter a Phase 1 clinical study in the US soon. Citation Format: Gong Li, Hepeng Shi, Peilong Zhang, Xiangqiu Li, Wenli Lan, Linna Li, David Chung, Kevin Schaab. ANS014004, a novel small-molecule type II c-Met inhibitor effectively overcomes clinical-resistance MET mutations and exhibits antitumor activity in preclinical models of MET-amplified non-small cell lung cancer (NSCLC) and gastric cancer [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr C145.

Abstract C162: Assessment of the potential for QTc prolongation by the investigational ATR inhibitor tuvusertib in patients with advanced solid tumors using integrated nonclinical and clinical assessments

Abstract Background: Tuvusertib (M1774) is a potent, selective, orally administered inhibitor of ataxia telangiectasia and Rad3-related protein kinase (ATR) with demonstrated antitumor activity in preclinical models. Tuvusertib is currently being evaluated in phase I and II trials as monotherapy and in combination with other DNA damage response inhibitors and immune checkpoint inhibitors. Assessment of an investigational agent’s potential to cause delayed ventricular repolarization (QTc prolongation) is essential in drug development. QTc prolongation is assessed using nonclinical studies and concentration-QTc (c-QTC) analysis of phase I clinical data across a wide dose range and/or a thorough QT/QTc (TQT) clinical study. Here, we assess tuvusertib’s potential to cause QTc prolongation by integrating nonclinical evaluations and clinical c-QTc analyses. Methods: Nonclinical evaluations included in vitro binding of tuvusertib to the ether-a-go-go-related gene (hERG) channel and telemetry of tuvusertib in male beagle dogs and minipigs. Pharmacokinetics-time-matched triplicate electrocardiograms were collected in patients with advanced solid tumors from the first-in-human (FIH) trial (NCT04170153) for tuvusertib 5−270 mg QD along with intermittent dosing regimens. Based on exploratory analyses, a linear mixed-effect model (Garnett C, et al. J Pharmacokinet Pharmacodyn 2018;45:383–97) was chosen to describe the relationship between tuvusertib plasma concentrations and selected heart rate (HR)-corrected QT using the Fridericia correction (QTcF). Results: In vitro hERG channel binding potency for tuvusertib 0.3–10.0 µM was calculated with a half-maximal inhibitory concentration (IC50) of 2.8 µM. Nonclinical telemetry studies showed no treatment effect on QT/QTc prolongation at doses of up to 3 mg/kg in male beagle dogs and minipigs. c-QTc analyses in 55 patients from the FIH trial revealed a small positive slope of drug effect (slope estimate [95% CI] = 0.00244 [0.000708, 0.00417] ms/(ng/mL)). This increase in model-predicted QTcF from baseline was not considered to be clinically meaningful (<20 ms threshold) at steady-state maximum concentration (Cmax) achieved with the recommended dose for expansion (RDE) of 180 mg QD 2w on/1w off (mean [upper bound of 95% CI] = 3.4 [5.5] ms) and up to 3 times the RDE (10.3 [16.5] ms). Concentration-HR modeling found no relationship between tuvusertib concentration and HR, suggesting the absence of an effect. Conclusions: Integrating nonclinical and clinical assessments revealed no clinically meaningful effect of tuvusertib on QTc at concentrations achieved with the RDE and up to 3-times higher concentrations. Citation Format: Jatinder Kaur Mukker, Timothy A. Yap, Anthony W. Tolcher, Johann S. de Bono, Ruth Plummer, Rohan Kulkarni, Han Witjes, Paul Matthias Diderichsen, Axel Krebs-Brown, Rainer Strotmann, Zoltan Szucs, Ioannis Gounaris, Karthik Venkatakrishnan. Assessment of the potential for QTc prolongation by the investigational ATR inhibitor tuvusertib in patients with advanced solid tumors using integrated nonclinical and clinical assessments [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr C162.

Abstract IA010: Engineering human sialidase as novel cancer therapeutics by targeting sialoglycans

Abstract Immune checkpoint blockade has revolutionized cancer treatment, but resistance remains a significant hurdle for many patients. Sialoglycans, as new immune checkpoints on tumors, present a promising therapeutic opportunity to enhance immune response. Cleaving off sialoglycans from tumors using a tumor-associated antigen (TAA) targeted antibody-bacterial sialidase conjugate has shown antitumor activity in preclinical models. Recognizing the immunogenicity risk of bacterial enzymes, we've engineered a human sialidase for therapeutic development. By investigating the roles of sialoglycans on immune cells, we've found that cleaving T cell surface sialoglycans boosts antitumor immunity. Additionally, we've demonstrated the efficacy and tolerability of the untargeted engineered human sialidase Fc fusion (Bi-Sialidase) as a potential immunotherapy. These advancements have led to the development of the EAGLE (enzyme antibody glycan editing) technology platform, which restores antitumor immunity by stripping sialic acids from immunosuppressive sialoglycans on both tumor and immune cells. Citation Format: Li Peng. Engineering human sialidase as novel cancer therapeutics by targeting sialoglycans [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr IA010.

Abstract C020: First-in-human phase 1/1b trial of the first-in-class bi-steric mTORC1-selective inhibitor RMC-5552 in patients with advanced solid tumors

Abstract Activation of the mTOR pathway plays a role in the oncogenesis and progression of many cancer types, and is frequently co-altered in RAS-driven tumors. First-generation mTORC1-selective inhibitors were limited by incomplete inhibition of 4EBP1 phosphorylation, while second-generation pan-mTOR inhibitors had a low therapeutic index due to mTORC2-mediated toxicity such as hyperglycemia. RMC-5552 is a first-in-class third-generation bi-steric mTOR inhibitor that is mTORC1-selective via its FKBP12-binding moiety and potently inhibits phosphorylation of the 4EBP1 tumor suppressor via a linked ATP-competitive moiety, addressing these key limitations of prior mTOR inhibitors in preclinical models. RMC-5552 is being investigated in a Phase I/Ib study (NCT04774952). Eligible patients (pts) were ≥18 yrs old with ECOG 0-1 and had advanced solid tumors that had failed or were ineligible for standard-of-care treatments. Pts received RMC-5552 as a weekly infusion. To address mucositis, a common toxicity in pts treated with mTOR inhibitors, pts prophylactically used dexamethasone mouthwash either alone or with tacrolimus mouthwash (TM), which binds to the RMC-5552 presenter protein FKBP12. Objectives included assessment of safety/tolerability (CTCAEv5), defining the maximum tolerated and recommended Phase 2 doses, pharmacokinetics, and preliminary efficacy (RECIST v1.1). As of June 12, 2023, 47 pts have been evaluated at 6 dose levels from 1.6 mg to 12 mg. The most common (> 20%) treatment-related adverse events (TRAE, any grade) were stomatitis/mucositis (45%), fatigue (40%), nausea (38%), decreased appetite (32%), and vomiting (23%). Treatment-related events of hyperglycemia occurred in 4% of pts (both grade 2) and were not dose limiting. The most common grade 3 TRAE at dose levels ≥6 mg was mucositis/stomatitis, which was dose-dependent and limited tolerability in the absence of TM. Between 8 and 12 mg, the rate of treatment related stomatitis/mucositis was 65% (15% grade 3) in pts treated without TM (N = 20) versus 30% (no grade 3) in pts treated with TM (N = 10). TM prophylaxis enabled dose escalation beyond dose levels previously considered intolerable due to mucositis (10-12 mg; escalation ongoing), and unbound plasma exposures at 8-12 mg were within the range that induced significant anti-tumor activity in preclinical models. The disease control rate was 67% among efficacy evaluable pts (N = 39). One pt with a salivary gland tumor harboring a PTEN mutation had a confirmed partial response (PR) with 78% reduction and 16 months duration of response. In addition, molecular responses of circulating tumor DNA were observed in pts with mTOR pathway variants. Updated efficacy results will be presented. These early data indicate that RMC-5552 monotherapy is tolerated at doses predicted to be efficacious, and that selective inhibition of mTORC1 alleviates mTORC2-mediated toxicity. Dose escalation is ongoing, and mucositis prophylaxis has enabled further dose intensification for future combination studies with RAS(ON) inhibitors. Citation Format: Alison M Schram, Abdul Rafeh Naqash, Eric B Haura, Jonathan W Riess, Susanna V Ulahannan, Sai-Hong I Ou, Anna Capasso, Pamela N Munster, Michael L Cheng, W Clay Gustafson, Bojena Bitman, Sumit Kar, Zhican Wang, Lin Tao, Justin G Meyerowitz, Howard A Burris. First-in-human phase 1/1b trial of the first-in-class bi-steric mTORC1-selective inhibitor RMC-5552 in patients with advanced solid tumors [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr C020.

Abstract C132: SGN-35T: A novel CD30-directed antibody-drug conjugate for the treatment of lymphomas

Abstract Antibody-drug conjugates (ADCs) employing the vedotin drug linker are effective anti-cancer agents in multiple indications including Hodgkin lymphoma, cervical cancer, and bladder cancer. While vedotin ADCs have demonstrated efficacy for the treatment of a wide variety of solid and hematologic cancers, some side effects, including dose-limiting neutropenia, are commonly observed. To improve the tolerability while leveraging the known activity of brentuximab vedotin, an ADC approved for the treatment of advanced classical Hodgkin lymphoma and other CD30-expressing lymphomas, alternative ADC structural components are under exploration. A novel cleavable linker containing a tripeptide molecule comprised of D-leucine-alanine-glutamate (DLAE) was developed and used to generate SGN-35T, an anti-CD30 ADC with the same mAb backbone and cytotoxic monomethyl auristatin E (MMAE) payload as brentuximab vedotin. SGN-35T was investigated for both anti-tumor activity and effects on hematopoiesis using in vitro and in vivo assays. SGN-35T displayed comparable activity to brentuximab vedotin against three lymphoma cell lines in vitro, and complete or near-complete tumor growth inhibition in five lymphoma xenograft models including a CD30-heterogeneous model. SGN-35T led to cell cycle arrest at the G2/M phase leading to apoptosis, in concordance with the established mechanism of action of MMAE. Introduction of the tripeptide linker in SGN-35T maintained the induction of immunogenic cell death hallmarks observed with brentuximab vedotin and other vedotin-based ADCs. SGN-35T demonstrated reduced potency on hematopoiesis compared to brentuximab vedotin in a human bone marrow colony-forming unit assay. In cynomolgus monkey toxicity studies, administration of SGN-35T had a reduced impact to neutrophils counts at matched dose levels and a two-fold improvement in tolerability compared to brentuximab vedotin, with a highest non-severely toxic dose (HNSTD) of 6 mg/kg versus an HNSTD of 3 mg/kg for brentuximab vedotin when administered Q3Wx4. Together, these data demonstrate that SGN-35T exhibits anti-tumor activity in preclinical models and may reduce the severity of hematopoietic toxicities while retaining anti-tumor activity observed with brentuximab vedotin. A Phase 1, first-in-human study is planned to evaluate the safety and anti-tumor activity of SGN-35T in lymphoid malignancies. Citation Format: Kevin J Hamblett, Steven Jin, Roma Yumul, Yufei Chen, John Kwon, Jessica Simmons, Clark Henderson, Hao Sun, Jason P Schrum, Andrea R Lim, Noah A Bindman, Melissa Conerly, Astrid Clarke. SGN-35T: A novel CD30-directed antibody-drug conjugate for the treatment of lymphomas [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr C132.