Colorectal Cancer Patient-derived Xenograft Models Research Articles

Abstract 2362: Preclinical efficacy and safety of M9140, a novel antibody-drug conjugate (ADC) with topoisomerase 1 (TOP1) inhibitor payload targeting carcinoembryonic antigen-related cell adhesion molecule 5 (CEACAM5)-expressing colorectal tumors

Abstract Background: M9140 is the first clinical-stage TOP1 inhibitor payload ADC directed against CEACAM5, which is expressed in colorectal cancer (CRC) and other cancer indications. M9140 is composed of a CEACAM5-specific antibody conjugated to eight, highly stable and hydrophilic ß-glucuronide-exatecan linker-payloads. After linker cleavage, the highly potent and membrane permeable TOP1 inhibitor exatecan is released. Methods: M9140 potency was tested in viability assays using cancer cell lines with different levels of CEACAM5 expression. Potency shift viability assays were conducted using two CRC cell lines, with zosuquidar used as multidrug resistance-1 (MDR-1) inhibitor. The M9140 bystander effect was assessed in co-culture experiments with CEACAM5-negative and -positive cancer cells. Antitumor efficacy and safety were evaluated in patient-derived xenograft (PDX) mouse models and in cynomolgus monkeys, respectively. Results: M9140 demonstrated specific binding to CEACAM5 and selective killing of target-positive cancer cells with potencies between 0.09 nM and 0.62 nM. A potent bystander effect of M9140 was demonstrated in co-culture experiments indicating the potential to treat tumors with heterogeneous target expression. Unlike other ADC payloads such as monomethyl auristatin E (MMAE) and the maytansine derivative DM4, exatecan potency was not affected by MDR-1 inhibition, indicating that this drug efflux resistance mechanism may not be relevant for exatecan. A single treatment with 10 mg/kg M9140 caused strong antitumor effects in all 14 CRC PDX models tested, with tumor stasis in 10 models and tumor regression in four models as the best response. The TOP1 inhibitor-based ADC M9140 caused strong antitumor efficacy with a tumor volume reduction of 74% and 88% as best response in two CRC PDX models where a maytansine-based CEACAM5 ADC was not effective. In cynomolgus monkeys, M9140 showed dose-dependent hematolymphoid and intestinal effects, consistent with exatecan payload, with no indication of any other toxicities such as interstitial lung disease (ILD) or ocular toxicity. Conclusions: M9140 demonstrated high potency, strong antitumor activity, and bystander effect in preclinical models. The side effect profile in monkeys was favorable and in line with the expected toxicity of exatecan. Notably, ILD and ocular toxicity, which are known adverse effects of deruxtecan and maytansine-based ADCs respectively, were absent. A first-in-human study to evaluate the safety, tolerability, pharmacokinetics, and preliminary clinical activity of M9140 in advanced solid tumors is ongoing (NCT05464030). Citation Format: Sabine Raab-Westphal, Felix Hart, Willem Sloot, Min Shan, Nicolas Rasche, Christiane Amendt, Jan Anderl. Preclinical efficacy and safety of M9140, a novel antibody-drug conjugate (ADC) with topoisomerase 1 (TOP1) inhibitor payload targeting carcinoembryonic antigen-related cell adhesion molecule 5 (CEACAM5)-expressing colorectal 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 2362.

Abstract 2118: SGN-CEACAM5C/SAR445953, a novel topoisomerase I inhibitor antibody-drug conjugate targeting CEACAM5, has potent anti-tumor activity in CRC, PDAC, GC and lung cancer tumor models

Abstract Carcinoembryonic antigen cell adhesion molecule 5, CEACAM5, is a glycosylphosphatidylinositol-anchored glycoprotein expressed on the cell surface of most of the colorectal cancer (CRC) and pancreatic ductal adenocarcinoma (PDAC) and of more than 2/3 of gastric cancer (GC) and non-small cell lung cancer (NSCLC) while normal tissue expression is limited. The high prevalence of CEACAM5 expression prompted us to develop a novel CEACAM5 topoisomerase I inhibitor (Topo1i) antibody drug conjugate (ADC) with a DAR of 8, SGN-CEACAM5C/SAR445953. The anti-CEACAM5 antibody was chosen based on its high selectivity for CEACAM5 and its potential to direct cytotoxic payloads to tumor. The Topo1i payload was optimized for potency and enhanced bystander activity. SGN-CEACAM5C/SAR445953 is rapidly internalized and demonstrates in vitro cytotoxicity with EC50 values in the sub-nM range while it induces no toxicity on CEACAM5-negative cells. The potent anti-tumor activity is mediated by direct cytotoxicity on CEACAM5-expressing tumor cells and by a strong bystander effect due to the diffusion of the payload to the neighboring CEACAM5-negative tumor cells. Accordingly, the ADC incubated in a co-culture of CEACAM5-positive and -negative cells at a ratio of 1/1 induces a ~50% growth inhibition of CEACAM5-negative cells. Interestingly, with incubated ADC, only 1% of CEACAM5-positive cells in co-culture are sufficient to provide 11% growth inhibition of CEACAM5-negative cells. In vivo, SGN-CEACAM5C/SAR445953 is stable in circulation in SCID mice with a t1/2 close to 15 days. In vivo efficacy at 1, 3 and 10 mg/kg (single administration) was evaluated in panels of 4 CRC, 3 PDAC, 4 NSCLC and 3 GC patient-derived xenograft (PDX) models. At 10 mg/kg, the ADC elicits antitumor regression in 14/14 models. At 3 mg/kg, tumor regression occurs in 12/14 models. This potent, specific and dose dependent anti-tumor activity was further confirmed in Single Mouse Trials (SMT) of 20 CRC PDX models, 31 lung cancer PDX models and 19 gastric cancer PDX models. SMT consists in use of one animal per PDX model per treatment arm and for which the evaluation of efficacy is based on RECIST (Response Evaluation Criteria In Solid Tumors) criteria used in clinic. In CRC, gastric and lung cancer SMT, disease control rates are 95%, 84% and 87%, respectively with overall response rates of 55%, 68% and 71% including 15%, 10% and 26% of complete responses, respectively. The high anti-tumor activity across panels of PDX models of several CEACAM5 positive indications supports further evaluation of SGN-CEACAM5C/SAR445953 in patients with CRC, PDAC, GC and lung cancers (NCT06131840). Citation Format: Yves Baudat, Celine Nicolazzi, Johann Petur Sigurjonsson, Celine Amara, Astrid Clarke, Ryan lyski, Dave Meyer, Valeria Fantin, Marielle Chiron, Stephanie Decary. SGN-CEACAM5C/SAR445953, a novel topoisomerase I inhibitor antibody-drug conjugate targeting CEACAM5, has potent anti-tumor activity in CRC, PDAC, GC and lung cancer 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 2118.

Abstract A097: HBI-2438, HUYABIO selective KRASG12C inhibitor with BBB penetration, inhibited tumor growth in a metastatic brain model as single agent and also displayed synergy in combination with HBI-2376 (HUYABIO SHP2 inhibitor) in a CRC PDX model

Abstract Recent advances in targeting KRASG12C mutation and approval of sotorasib and adagrasib provided new treatment avenues for cancer patients. Additionally, about 10% of NSCLC (non-small cell lung cancer) patients carrying KRASG12C mutation are diagnosed with brain metastasis. Nearly 50% of NSCLC patients with recurrent disease also have metastatic lesions in the brain. This further signifies the therapeutic value of KRASG12C inhibitors with BBB (blood brain barrier) penetration properties. Early studies showed HBI-2438, HUYABIO selective and potent KRASG12C inhibitor, was detectable and quantifiable in CSF when administered orally. Here we tested efficacy of HBI-2438 in an intra-carotid brain metastatic model and compared its efficacy vs. AMG510 and MRTX849 in similar dose and intervals. Bioluminescent imaging and quantification showed major tumor regression in tumors treated with HBI-2438 and MRTX849 and to a lesser extent in AMG510 treated tumors, all at 30 mg/kg. Consistent with preclinical data, HBI-2438 monotherapy showed early clinical efficacy signal in Cohort 1 (150 mg) and Cohort 2 (300 mg). HBI-2438 was well tolerated and did not show any SAEs or DLTs in these early cohorts. SHP2 signaling is one of the main components of the RAS/MAPK pathway and is acting upstream of KRAS. Therefore, and has been shown recently, targeting both KRAS and SHP2 in combination therapy may enhance the response to either agent as monotherapy. Here we tested combination of HBI-2438 and HBI-2376 (HUYABIO selective SHP2 inhibitor) in a KRASG12C CRC (colorectal cancer) PDX (patient derived xenograft) model that has demonstrated partial resistance to treatment with KRASG12C inhibitors. As expected, tumor bearing mice treated with HBI-2438 or MRTX849 monotherapy showed partial tumor growth inhibition in this model. However, combination treatment, HBI-2438 (10 or 30 mpk) plus HBI-2376 (5 mpk), showed significant inhibition in tumor growth. Additionally, the combination therapy at a higher dose (HBI-2438 at 100 mpk plus HBI-2376 at 5 mpk) achieved complete tumor regression vs. MRTX849+TNO155 demonstrating synergy between the two compounds in this model. These data further demonstrated greater inhibition of KRAS/MAPK pathway leading to a better tumor growth inhibition and justifies testing combination of HUYABIO KRAS G12Ci plus SHP2i in the clinic. Therefore, we believe HBI-2438 is a well differentiated KRAS G12C inhibitor vs. the competitors due to i) BBB penetration ii) superiority in combination therapy with SHP2 inhibitor and iii) efficacy signal in early cohorts in the clinic. Citation Format: Farbod Shojaei, Jill M Ricono, Che Fang, John Ning, Gloria Lee, Mireille Gillings. HBI-2438, HUYABIO selective KRASG12C inhibitor with BBB penetration, inhibited tumor growth in a metastatic brain model as single agent and also displayed synergy in combination with HBI-2376 (HUYABIO SHP2 inhibitor) in a CRC PDX model [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 A097.

Abstract B147: Preclinical evaluation of XPO1 inhibition with topoisomerase-I (topo-I) inhibition in colorectal cancer (CRC) cell lines and patient-derived xenograft (PDX) models

Abstract Background: Resistance to topo-I inhibitors is of significant importance in treating patients with metastatic CRC (mCRC). Selinexor and eltanexor are selective inhibitors of nuclear export, by binding to exportin 1 (XPO1, the primary nucleic export receptor, and is overexpressed in CRC). Eltanexor is an investigational XPO1 inhibitor, with similar mechanism and potency but improved tolerability in animal models. XPO1 inhibition results in nuclear localization of tumor suppressor proteins, oncoprotein mRNAs, and topoisomerases, and decreases DNA damage repair (DDR) response. Irinotecan is a topo-I inhibitor which induces DNA damage and is commonly used in mCRC. We hypothesized that XPO1 inhibition may improve response to topo-I inhibitor in mCRC by impairing the DDR response. Methods: The synergism of XPO1 inhibition (selinexor or eltanexor) with SN38 was assessed in CRC cell lines by CellTiter-Glo 2.0 and quantitated using Bliss Additivity Model using Synergy Finder 2.0. Each condition was plated either concurrent (both drugs for 72 hours) or sequential (SN38 for 24 hours then removed, followed by XPO1 inhibitor for 48 hours). Nude mice were implanted with one microsatellite stable CRC PDX model in the flanks followed by treatment with vehicle, XPO1 inhibitor, irinotecan (15 mg/kg intraperitoneal weekly), or combination. Tumor growth was measured by specific growth rate (SGR), within an IACUC-approved protocol. Tumor tissue was collected at day 7 for molecular analysis. Tissues were lysed and protein was run on 4%-12% SDS-PAGE Gel. p21 Waf/Cip and P-Histone H2A.X were used to determine DNA damage by western blot. P-Histone H2AX (pH2AX) was evaluated by immunofluorescence using primary conjugated P-Histone H2A.X antibody and DAPI for nuclear counter stain. Slides were imaged using Olympus iX83 microscope and analysis was performed using Olympus CellSens software. Results: In CRC cell lines, concurrent combination eltanexor and SN38 did not synergistically decrease viability but increased pH2AX compared to SN38 alone (~30-fold). However, sequential SN38 followed by eltanexor synergistically decreased viability at multiple dose levels; evaluation of pH2AX is ongoing. In PDX model CRC254, eltanexor (10 mg/kg and reduced to 7.5 mg/kg on day 8 to improve tolerability, orally 5 days per week) with irinotecan decreased SGR compared to irinotecan alone (SGR=0.007 vs 0.026, respectively, p=0.0003) and compared to eltanexor alone (SGR=0.029, p <0.0001). Combination treatment increased pH2AX and increased p21 expression compared to either single-agent treatment. Similar SGR results were observed with selinexor (5 mg/kg orally twice weekly). Conclusions: XPO1 inhibition and topo-I inhibition decreased CRC tumor growth in PDX models, presumably by increasing DNA double strand breaks. Cell line data suggests sequential dosing of topo-I inhibition followed by XPO1 inhibition may be effective. This work supports continued development of this combination in mCRC. Citation Format: Robert W Lentz, Adrian Dominguez, Stacey Bagby, Cameron Binns, Alexis Leal, Sunnie Kim, Sarah Lindsey Davis, Christopher H Lieu, Wells A Messersmith, Todd M Pitts. Preclinical evaluation of XPO1 inhibition with topoisomerase-I (topo-I) inhibition in colorectal cancer (CRC) cell lines and patient-derived xenograft (PDX) models [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 B147.

Abstract 530: Preclinical evaluation of avutometinib (VS-6766; RAF/MEK clamp) in combination with EGFR inhibition in colorectal cancer patient-derived xenograft (PDX) models harboring KRAS mutations

Abstract Background KRAS mutation (mt) occurs in ~43% of patients with colorectal cancer (CRC) with KRAS G12D, G12V and G13D being most prevalent. Avutometinib (avuto, VS-6766) is a unique RAF/MEK clamp that inhibits MEK kinase activity and induces dominant negative RAF/MEK complexes preventing the re-activation of MEK by RAF. Preclinically, avuto inhibited proliferation of KRAS mt CRC cell lines. Clinically, avuto monotherapy produced clinical responses in gynecological cancers and KRAS mt non-small cell lung cancer. Methods 3D proliferation assays were used to quantify synergy between avuto and agents targeting other nodes in the MAPK pathway or parallel signaling pathways. We evaluated the antitumor effects of avuto alone or in combination with panitumumab in CRC PDX models with KRASG12V, concurrent KRASG12V and PIK3CA, or KRASG12D mutations. Mice bearing PDX tumors were randomized into groups of 6 mice treated with avuto alone or in combination with panitumumab for 21 days with tumor volume measured twice weekly. Results In 3D proliferation assays with a panel of KRAS mt CRC cell lines (including G12D, G12V and G13D mutations), the EGFR/ErbB family inhibitor afatinib showed the strongest synergy score with avuto relative to inhibitors of SHP2, ERK1/2, mTOR or CDK4/6. Based on the synergy of avuto with afatinib, the combination of avuto with the anti-EGFR antibody panitumumab was tested in KRAS mt CRC PDX models. In a KRASG12V PDX model, tumor regression (11%) was seen in 1/6 mice treated with avuto alone. No tumor regression was seen in mice treated with panitumumab monotherapy. The combination of avuto and panitumumab led to significant tumor regression (>40%) in 5/6 mice following 21 days of treatment. In a KRASG12V PDX model with concurrent PIK3CA mutations, no tumor regression was seen in mice treated with either avuto or panitumumab alone. The combination of avuto and panitumumab led to initial tumor stabilization followed by tumor growth in 3/6 mice. In a KRASG12D PDX model, tumor regression (17%) was seen in 1/6 mice treated with avuto and 0/6 with panitumumab. Tumor regression (13% and 18%) was noted in 2/6 mice treated with the combination of avuto and panitumumab. Conclusion In KRAS mt CRC cell lines, strong synergy was observed between avuto and afatinib. In KRAS mt CRC PDX models in vivo, avuto monotherapy showed tumor growth inhibition but limited tumor regression, and panitmumab monotherapy failed to show tumor regressions. The combination of avuto and panitumumab showed significant anti-tumor activity in a CRC PDX model harboring KRASG12V with less tumor regression observed in a KRASG12D PDX model or in a KRASG12V PDX model with concurrent PIK3CA mutation. These results support the ongoing clinical evaluation of avutometinib in combination with the anti-EGFR antibody cetuximab for treatment of KRAS mt CRC (NCT05200442). Citation Format: Chongkai Wang, Silvia Coma, Jonathan Pachter, Marwan Fakih. Preclinical evaluation of avutometinib (VS-6766; RAF/MEK clamp) in combination with EGFR inhibition in colorectal cancer patient-derived xenograft (PDX) models harboring KRAS mutations [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 530.

Abstract 5486: Combining bromodomain and extraterminal (BET) protein inhibitor treatment with standard MAPK inhibitors improved MAPK signaling inhibition in colorectal cancer

Abstract Background: Overexpression and activation of the MAPK signaling pathway is known to play a key role in colorectal cancer (CRC) progression. Substantial efforts have been made to target MAPK signaling pathways in CRC, particularly blocking oncogenic mutations in KRAS or BRAF. However, standard treatments targeting MAPK signaling have demonstrated limited activities in CRC patients and are in strong need of improved efficacies. Thus, we investigated how the combination of BET inhibitor treatment could affect MAPK signaling activation. Methods: We performed a wide-scale drug combination study testing 15 drug combinations using CRC patient-derived xenograft (PDX) models. PDX models were treated for 21 days, and tumor volume and body weight changes were measured for assessment of treatment responses and toxicities. For the BET inhibitor (iBET-151) plus MEK inhibitor (binimetinib or trametinib) combination, RNA-seq and RPPA was performed on PDX tumor tissues collected after 7 days of treatment for pharmacodynamics study (n=3 per treatment condition). Tumors collected on day 21 were sequenced for H3K27Ac ChIP-seq and IHCs for understanding epigenomic changes in active enhancers and target validations. Results: Our preliminary screening of 15 drug combinations in CRC PDX models have shown the most promising and active responses in a combination of BETi with MEKi (5 out of 20 PDXs obtained tumor regression). Preclinical H3K27ac ChIP-seq data has shown lost enhancer peaks after BET inhibition were significantly associated with RAS signaling pathways (q<0.05). Gene set enrichment analysis on preclinical transcriptomic data also demonstrated downregulation of KRAS-signaling in BETi plus MEKi combination treatment compared to MEKi as monotherapy (p<0.05). MAPK activation scores (MPAS) were also significantly downregulated in transcriptomic and enhancer levels under BETi plus MEKi combinations compared to MEKi. Downstream transcription factors of MAPK signaling pathways, such as MYC and FOSL1, were synergistically downregulated in combination with BETi. Also, we found downregulation of EREG, a member of the epidermal growth factor (EGF) family, under BET inhibition which may play a role in MAPK downregulation together with standard therapy. Conclusions: Some studies have shown MAPK signaling activation as a resistance mechanism of BET inhibition in multiple cancer types. However, the understanding of the crosstalk between the activity of BET inhibition in a combination with MAPK signaling inhibition is limited in CRC. We found BET inhibition induces deeper inhibition of MAPK pathway activation together with standard targeted therapies. Our data demonstrated transcriptomic and epigenetic levels of the mechanism of BETi activity together with MAPK inhibition in CRC. Citation Format: Hey Min Lee, Alexey Sorokin, Preeti Kanikarla Marie, Saikat Chowdhury, Anand Singh, Amanda Anderson, Jumanah Yousef Alshenaifi, Funda Meric-Bernstam, Kunal Rai, Scott Kopetz. Combining bromodomain and extraterminal (BET) protein inhibitor treatment with standard MAPK inhibitors improved MAPK signaling inhibition in colorectal cancer. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5486.

Preparation and application of patient-derived xenograft mice model of colorectal cancer.

Patient-derived xenograft (PDX) model becomes a more and more important tool for tumor research. This study aimed to establish a colorectal cancer PDX model and verify its applicability. Fresh human colorectal cancer tissue was surgically removed and subcutaneously inoculated into immunodeficient mice to establish the PDX model. Hematoxylin and eosin (HE) staining and immunohistochemical staining were used to evaluate the model. The successful PDX model was selected to study the efficacy of capecitabine in treating colorectal cancer. HE staining showed that the PDX mice model of colorectal cancer could preserve the histological characteristics of the primary tumor. Immunohistochemistry staining showed α-fetoprotein (AFP), carcinoembryonic antigen (CEA), and E-cadherin were strongly positively expressed in primary human and PDX tumor tissues, with a high degree of similarity. Capecitabine significantly inhibited PDX tumor growth and reduced the expression of AFP and CEA proteins in the tumor tissues (all P s<0.05). We successfully established a colorectal cancer PDX model, and the PDX model could retain the histological and biological characteristics of the primary tumor. Using this PDX model, we revealed that capecitabine at a dose of 300-400 mg/kg can effectively treat colorectal cancer, and no significant difference in toxicity was found among different dose groups. The current work provides a feasible framework for establishing and validating the PDX tumor model to better facilitate the evaluation of drug efficacy and safety.

Patient-derived xenograft model in colorectal cancer basic and translational research.

Colorectal cancer (CRC) is one of the most popular malignancies globally, with 930 000 deaths in 2020. The evaluation of CRC-related pathogenesis and the discovery of potential therapeutic targets will be meaningful and helpful for improving CRC treatment. With huge efforts made in past decades, the systematic treatment regimens have been applied to improve the prognosis of CRC patients. However, the sensitivity of CRC to chemotherapy and targeted therapy is different from person to person, which is an important cause of treatment failure. The emergence of patient-derived xenograft (PDX) models shows great potential to alleviate the straits. PDX models possess similar genetic and pathological characteristics as the features of primary tumors. Moreover, PDX has the ability to mimic the tumor microenvironment of the original tumor. Thus, the PDX model is an important tool to screen precise drugs for individualized treatment, seek predictive biomarkers for prognosis supervision, and evaluate the unknown mechanism in basic research. This paper reviews the recent advances in constructed methods and applications of the CRC PDX model, aiming to provide new knowledge for CRC basic research and therapeutics.

Patient-derived xenograft models for gastrointestinal tumors: A single-center retrospective study.

Patient-derived xenograft (PDX) models have shown a great efficiency in preclinical and translational applications. Gastrointestinal (GI) tumors have a strong heterogeneity, and the engraftment rate of PDX models remarkably vary. However, the clinicopathological and molecular characteristics affecting the engraftment rate still remain elusive. A total of 312 fresh tumor tissue samples from patients with GI cancer were implanted into immunodeficient mice. The median follow-up time of patients was 37 months. Patients' characteristics were compared in terms of PDX growth and overall survival. PDX models of 3-6 generations were used for drug evaluation. In total, 171 (54.8%, 171/312) PDX models were established, including 85 PDX models of colorectal cancer, 21 PDX models of esophageal cancer, and 65 PDX models of gastric cancer. Other than tumor site, histology, differentiation degree, and serum alpha-fetoprotein (AFP) level, no significant differences were found between transplantation of xenografts and patients' characteristics. For patients who had undergone neoadjuvant therapy, the incidence of tumor formation was higher in those with progressive disease (PD) or stable disease (SD). In gastric cancer, the results showed a higher transplantation rate in deficient mismatch repair (dMMR) tumors, and Ki-67 could be an important factor affecting the engraftment rate. The gene mutation status of RAS and BRAF, two important molecular markers in colorectal cancer, showed a high degree of consistency between patients' tumors and PDXs. However, no significant effects of these two mutations on PDX engraftment rate were observed. More importantly, in this study although KRAS mutations were detected in two clinical cases, evident tumor inhibition was still observed after cetuximab treatment in both PDX models and patients. A large-scale PDX model including 171 cases was successfully established for GI tumors in our center. The relationship between clinicopathological and molecular features and engraftment rates were clarified. Furthermore, this resource provides us with profound insights into tumor heterogeneity, making these models valuable for PDX-guided treatment decisions, and offering the PDX model as a great tool for personalized treatment and translation research.

Cabozantinib Enhances Anti-PD1 Activity and Elicits a Neutrophil-Based Immune Response in Hepatocellular Carcinoma.

Immune checkpoint inhibitors combined with antiangiogenic agents produce benefits in the treatment of advanced hepatocellular carcinoma (HCC). We investigated the efficacy and immunomodulatory activity of cabozantinib alone and combined with anti-PD1 in experimental models of HCC, and explored the potential target population that might benefit from this combination. C57BL/6J mice bearing subcutaneous Hepa1-6 or Hep53.4 tumors received cabozantinib, anti-PD1, their combination, or placebo. Tumor and blood samples were analyzed by flow cytometry, IHC, transcriptome, and cytokine profiling. Cabozantinib-related effects were validated in a colorectal cancer patient-derived xenograft model. Transcriptomic data from three human HCC cohorts (cohort 1: n = 167, cohort 2: n = 57, The Cancer Genome Atlas: n = 319) were used to cluster patients according to neutrophil features, and assess their impact on survival. The combination of cabozantinib and anti-PD1 showed increased antitumor efficacy compared with monotherapy and placebo (P < 0.05). Cabozantinib alone significantly increased neutrophil infiltration and reduced intratumor CD8+PD1+ T-cell proportions, while the combination with anti-PD1 further stimulated both effects and significantly decreased regulatory T cell (Treg) infiltration (all P < 0.05). In blood, cabozantinib and especially combination increased the proportions of overall T cells (P < 0.01) and memory/effector T cells (P < 0.05), while lowering the neutrophil-to-lymphocyte ratio (P < 0.001 for combination). Unsupervised clustering of human HCCs revealed that high tumor enrichment in neutrophil features observed with the treatment combination was linked to less aggressive tumors with more differentiated and less proliferative phenotypes. Cabozantinib in combination with anti-PD1 enhanced antitumor immunity by bringing together innate neutrophil-driven and adaptive immune responses, a mechanism of action which favors this approach for HCC treatment.

Abstract 1056: Potent in vivo anti-tumor activity of D-1553 as a single agent and in combination with targeted therapeutics in a broad spectrum of patient-derived xenograft tumor models with KRas G12C mutation

Abstract Ras protein plays a critical role in cell growth and proliferation by transmitting signal from cell surface receptor tyrosine kinase to downstream cellular proteins such as RAF and MEK. KRas is one of the most frequently mutated oncogenes, with mutations at residues G12, G13, and Q61, found in lung, colon, pancreatic and other solid malignancies. We have developed an orally bioavailable, covalent inhibitor of KRas G12C, D-1553, with potent in vitro biochemical, cellular activity and in vivo efficacy. Here we report the efficacy of D-1553 in a large panel of patient-derived xenograft (PDX) tumor models with KRas G12C mutation. In the lung cancer PDX models, D-1553 exhibited tumor growth inhibition (TGI) from 43.6% to 124.3%, with 4 out of 8 models showing tumor regression. In the colorectal cancer PDX models, the range of TGI was from 60.9% to 105.7%, with 3 out of 9 models showing regression. Combination treatment of D-1553 with chemotherapy and targeted agents demonstrated enhanced anti-tumor activity resulting in more tumor regression compared to single agent treatment. These observations from PDX models support the combination treatment as a key to increased overall response rate to KRas G12C inhibitor in clinical trial. D-1553 is currently in a Phase 1/2 clinical trial for patients with advanced solid tumors harboring KRas G12C mutation (NCT04585035). Citation Format: Zhe Shi, Jifang Weng, Xiaochong Fan, Qingqing Zhu, Emily Robb, Alyssa Moriarty, Michael Wick, Yueheng Jiang, Ling Zhang, Xing Dai, Yaolin Wang. Potent in vivo anti-tumor activity of D-1553 as a single agent and in combination with targeted therapeutics in a broad spectrum of patient-derived xenograft tumor models with KRas G12C mutation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1056.

Microsatellite instability-high colorectal cancer patient-derived xenograft models for cancer immunity research.

There is an increasing demand for appropriate preclinical mice models for evaluating the efficacy of cancer immunotherapies. Therefore, we established a humanized patient-derived xenograft (PDX) model using microsatellite instability-high (MSI-H) colorectal cancer (CRC) tissues and patient-derived peripheral blood mononuclear cells (PBMCs). The CRC tissues of patients scheduled for surgery were tested for MSI status, and CRC tumors were transplanted into NOD/LtSz-scid/IL-2Rg-/-(NSG) mice to establish MSI-H PDX models. PDX tumors were compared to the original patient tumors in terms of histological and genetic characteristics. To humanize the immune system of MSI-H PDX models, patient PBMCs were injected through the tail vein. PDX models were established from two patients with MSI-H CRC; one patient had a germline mutation in MLH1 (c.1990-2A > G), and the other patient had MLH1 promoter hypermethylation. PDX with the germline mutation was histologically similar to the patient tumor, and retained the genetic characteristics, including MSI-H, deficient mismatch repair (dMMR), and MLH1 mutation. In contrast, the histological features of the other PDX from a tumor with MLH1 promoter hypermethylation were clearly different from those of the original tumor, and MLH1 promoter hypermethylation and MSI-H/dMMR were lost in the PDX. When T cells from the same patient with MLH1 mutation were injected into the PDX through the tail vein, they were detected in the PDX tumor. The MSI-H tumor with an MMR mutation is suitable for MSI-H PDX model generation. The PBMC humanized MSI-H PDX has the potential to be used as an efficient model for cancer immunotherapy research.

Implementing Systems Modelling and Molecular Imaging to Predict the Efficacy of BCL-2 Inhibition in Colorectal Cancer Patient-Derived Xenograft Models.

Simple SummaryDrugs that sensitise tumours to chemotherapy by enhancing cell death signalling are of significant clinical interest. However, it is challenging to determine which colorectal cancer patients may benefit from such sensitisers. The ability to predict this would be advantageous. Here we show that protein profiling combined with mathematical modelling identifies responsive tumours. Using our modelling method, we predicted the effect of adding a sensitizer drug to chemotherapy in two patient-derived colorectal tumours. We grew the tumours in mice, treated animals with these drugs and performed PET/CT imaging. The predicted “sensitive” tumours were smaller when the sensitising drug was added to chemotherapy whilst it did not further reduce tumour size in “non-sensitive” tumours, thus validating our prediction. PET imaging also supported our predictions. CT analysis (radiomics) revealed features that distinguished the two tumours. This was the first application of radiomic analyses to PDX derived CT data.Resistance to chemotherapy often results from dysfunctional apoptosis, however multiple proteins with overlapping functions regulate this pathway. We sought to determine whether an extensively validated, deterministic apoptosis systems model, ‘DR_MOMP’, could be used as a stratification tool for the apoptosis sensitiser and BCL-2 antagonist, ABT-199 in patient-derived xenograft (PDX) models of colorectal cancer (CRC). Through quantitative profiling of BCL-2 family proteins, we identified two PDX models which were predicted by DR_MOMP to be sufficiently sensitive to 5-fluorouracil (5-FU)-based chemotherapy (CRC0344), or less responsive to chemotherapy but sensitised by ABT-199 (CRC0076). Treatment with ABT-199 significantly improved responses of CRC0076 PDXs to 5-FU-based chemotherapy, but showed no sensitisation in CRC0344 PDXs, as predicted from systems modelling. 18F-Fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG-PET/CT) scans were performed to investigate possible early biomarkers of response. In CRC0076, a significant post-treatment decrease in mean standard uptake value was indeed evident only in the combination treatment group. Radiomic CT feature analysis of pre-treatment images in CRC0076 and CRC0344 PDXs identified features which could phenotypically discriminate between models, but were not predictive of treatment responses. Collectively our data indicate that systems modelling may identify metastatic (m)CRC patients benefitting from ABT-199, and that 18F-FDG-PET could independently support such predictions.

Abstract 2798: Cancer stem cells profiling of the colorectal cancer patient-derived xenograft model and corresponding in vitro organoid model by multiplex IHC

Abstract Background. Organoids are derived from stem cells from patient tissue, with self-capability as well as self-organization [1] and have been reported to mimic the structural and functional features of their in vivo counterpart[2]. Patient-derived xenografts (PDXs) are considered predictive in vivo cancer model for preclinical research and we have built and characterized a large library of PDX biobank. We recently have also established a large biobank of PDX-derived organoids (PDXOs) from our PDX biobank (&amp;gt;200) using the Hubrecht Organoid Technology (HUB), with evidence of “biological equivalence” to their parental PDXs, sharing similar profiles of genomics and pathology, as well as pharmacology. PDX and the derived PDXO thus constitute matched in vivo and in vitro model pairs, with great potential pharmaceutical applications. This report attempted to verify and characterize the CSC components of both models by multiplex IHC. Method. Five CRC PDX/PDXO pairs (CR1250, CR2258, CR3310,CR5048, CR11372) were subjected to histopathology (HE staining) and CSCs (Multiplex IHC staining) analysis. TSA-based multiplex IHC staining in Leica Bond Rx automatic platform was performed using a 4-plex CSC panel: DAPI (Sigma, #9542), CD133 (Cell Signaling, #86781), CD44 (abcam, ab51037), SOX2 (Cell Signaling, #14962) and basal cell marker pan-CK (Cell Signaling, #4545), followed by whole slide scan using Vectra® Polaris™ automated quantitative pathology imaging system (PerkinElmer) and quantified by HALO image analysis (Indica labs). Results. H&amp;E staining of the five CRC-PDXOs showed typical adenocarcinoma histology structure, e.g. recognizable adenocarcinoma cells in tubular or vesicular glands, similar to those of the matched PDXs. The presence of the basal cells marker (pan-CK) was observed predominantly on the cell surface with broader pattern in corresponding matched models. Similarly, CD44, a known dominant marker for CRC CSC was observed broadly on the surface of tumor cells in both models. Moreover, pan-CK and CD44 showed universal co-localization, thus suggesting that pan-CK+CD44+ cells become the primary cellular composition of CRC PDXOs and PDXs. Interestingly, CD133, another marker of CSC, displayed distinct staining patterns between PDXOs and PDXs: predominantly outside of tumor glandular in PDXs (periglandular-like) vs. intraglandular in PDXOs (intraglandular-like). SOX2, a key transcription factor for CSCs and vital to CSC development, was also broadly present in all PDXOs and PDXs with similar pattern. Conclusion. Multiplex IHC could be a powerful tool to investigate CSC component in tumors and tumor models. Our preliminary data seem to show that most cells, in both PDX and PDXO models, resemble basal cell layer where pan-CK+/CD44+ CSCs also co-localized, consistent with hypothesis of both being CSC-driven disease models.

Activity of SY-5609, an oral, noncovalent, potent, and selective CDK7 inhibitor, in preclinical models of colorectal cancer.

3585 Background: Colorectal cancer (CRC) is driven by genetic alterations that result in constitutive activation of oncogenic transcription factors (eg β-catenin, MYC) and of mitogenic signaling and cell cycle progression (driven by oncogenic mutations in KRAS and BRAF). CDK7 is a key regulator of transcription, through phosphorylation of the CTD domain of RNA Polymerase II, and of cell cycle progression, through phosphorylation of the cell cycle kinases CDK1, 2, 4, and 6. This dual role of CDK7 suggests inhibitors of CDK7 may be effective in the treatment of CRC. SY-5609 is an oral, noncovalent, potent and highly selective CDK7 inhibitor in phase 1 clinical development for patients with advanced solid tumors including CRC (NCT04247126). Here we report on the activity of SY-5609 in patient-derived xenograft (PDX) models of CRC. Methods: SY-5609 was administered once daily (QD) by oral gavage for 21 days (end of treatment, EOT) to mice bearing PDX models of CRC. The relationship between SY-5609 dose, pharmacodynamic (PD) changes in xenograft tissue, tumor growth inhibition (TGI), and mouse body weight (BW) was evaluated across a range of doses. SY-5609 TGI activity was also evaluated at sub-maximum-tolerated-dose levels across a panel of 30 independent CRC models including BRAF-, KRAS-, and non-BRAF/KRAS-mutant (wild type) models (n = 10 per group). Results: SY-5609 induced dose-dependent TGI in BRAF-mutant CRC PDX tumors, with tumor regressions observed at well tolerated doses (no BW loss at EOT), and no tumor regrowth for 2+ weeks after treatment was discontinued. Dose-dependent TGI was associated with dose-dependent PD changes in PDX tumor tissue. Across 30 PDX models, SY-5609 at well-tolerated doses (average BW loss of 0% at EOT across all models) induced ≥50% TGI in 67% (20/30) of models. Deep responses (≥90% TGI or regressions) were observed in 23% (7/30) of models, with enrichment for deep responses in BRAF mutant models (50%, 5/10) relative to KRAS mutant (10%, 1/10), and wild type (10%, 1/10) models. Conclusions: Daily oral dosing of the CDK7 inhibitor SY-5609 induces robust TGI, including regressions, in CRC PDX models at well-tolerated doses. Dose-dependent TGI is associated with dose-dependent PD changes in CRC PDX tumor tissue. These results highlight the therapeutic potential of SY-5609 in CRC and support the evaluation of SY-5609 in CRC patients in early phase clinical trials. SY-5609 is in phase 1 clinical development for patients with advanced solid tumors including CRC (NCT04247126).

Dynamic alterations of genome and transcriptome in KRAS G13D mutant CRC PDX model treated with cetuximab

BackgroundKRAS mutations have been characterized as the major predictive biomarkers for resistance to cetuximab treatment. However, studies indicate that not all KRAS mutations are associated with equivalent treatment outcomes. KRAS G13D mutations were observed to account for approximately 16% of all KRAS mutations in advanced colorectal cancer patients, and whether these patients can benefit from cetuximab has not been determined.MethodsAn established KRAS G13D mutant colorectal cancer (CRC) patient-derived xenograft (PDX) model was treated with cetuximab. After repeated use of cetuximab, treatment-resistant PDX models were established. Tissue samples were collected before and during treatment, and multiomics data were subsequently sequenced and processed, including whole-exome, mRNA and miRNA data, to explore potential dynamic changes.ResultsCetuximab treatment initially slowed tumor growth, but resistance developed not long after treatment. WES (whole-exome sequencing) and RNA sequencing found that 145 genes had low P values (< 0.01) when analyzed between the locus genotype and its related gene expression level. Among these genes, SWAP70 was believed to be a probable cause of acquired resistance. JAK2, PRKAA1, FGFR2 and RALBP1, as well as 10 filtered immune-related genes, also exhibited dynamic changes during the treatment.ConclusionsCetuximab may be effective in KRAS G13D mutation patients. Dynamic changes in transcription, as determined by WES and RNA sequencing, occurred after repeated drug exposure, and these changes were believed to be the most likely cause of drug resistance.

Abstract A16: A GUCY2c-CD3 bispecific engages T cells to induce cytotoxicity in gastrointestinal tumors

Abstract Background: Guanylyl cyclase C (GUCY2C) is a regulator of intestinal homeostasis and is expressed in more than 90% of colorectal cancer (CRC), as well as in other gastrointestinal malignancies. Target expression in normal tissues is largely restricted to the apical side of intestinal epithelial tight junctions, which could allow for preferential uptake of GUCY2C-targeted biologics by tumors that have disrupted tight junction architecture. Here we demonstrate tumor-selective uptake and potent efficacy with a half-life extended, GUCY2C-CD3 bispecific molecule that recruits CD3-positive T cells to induce cytotoxicity of GUCY2C-expressing tumors in several CRC models in vivo. Additionally, to address immune evasion mechanisms, rational combinations of the bispecific are explored with immune checkpoint blockade agents, as well as by blocking angiogenesis, which has been reported to enhance T-cell infiltration into tumors. Methods: GUCY2C-CD3 mediated activity was evaluated in vivo in several cell line- and patient derived-xenograft models of CRC, using adoptive transfer of human T cells in established subcutaneous and orthotopic tumors. Immunohistochemistry was performed to demonstrate biodistribution of the drug and recruitment of activated T cells in GUCY2C-expressing tumors vs. normal tissues. We also performed CYTOF analyses on GUCY2C-CD3-treated tumors and tumor-infiltrating lymphocytes (TILs) to identify markers of immune evasion. Combination studies with anti PD-1/PD-L1 checkpoint blockade agents and with an anti VEGF-A antibody were performed using the adoptive transfer model. Results: GUCY2C-CD3 bispecific showed preferential biodistribution to GUCY2C-expressing xenograft tumors compared to normal tissue. The drug demonstrated potent dose-dependent efficacy in several CRC models with no signs of toxicity. Bispecific treated tumors not only showed recruitment of activated T cells to the tumor site, but also upregulated checkpoint mechanisms, such as PD-L1 on tumors and exhaustion markers on TILs. Consequently, anti PD-1/PD-L1 checkpoint blocking antibodies provided enhanced efficacy when combined with GUCY2C-CD3. Additionally, significant combination benefit was observed when GUCY2C-CD3 was combined with an anti VEGF-A blocking antibody. Conclusions: Our preclinical data demonstrate that a GUCY2C-CD3 bispecific can selectively target colorectal tumors, including those with KRAS or BRAF mutations, which are difficult to treat with currently approved therapies. This bispecific shows combination benefits with T-cell checkpoint blockade agents, as well as antiangiogenesis agents, indicating that single-agent activity with GUCY2C-CD3 can be further enhanced with mechanisms that address immune evasion. Citation Format: Divya Mathur, Adam Root, Bozena Bugaj-Gaweda, Xingzhi Tan, Wei Fang, Stephanie Bisulco, Jonathan Golas, Jessica Kearney, Eric Upeslacis, Johnny Yao, Edward Rosfjord, Chad Stevens, Lindsay King, Jatin Narula, Kerry Kelleher, Cynthia Rohde, Lioudmila Tchistiakova, Anhco Nguyen, Puja Sapra. A GUCY2c-CD3 bispecific engages T cells to induce cytotoxicity in gastrointestinal tumors [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2019 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(3 Suppl):Abstract nr A16.

NSG mice as hosts for oncological precision medicine

Patient-derived xenograft (PDX) models have been rediscovered as meaningful research tool. By using severely immunodeficient mice, high-engraftment rates can be theoretically achieved, permitting clinical stratification strategies. Apart from engraftment efficacy, tolerability towards certain cytostatic drugs varies among individual mouse strains thus impeding large-scale screenings. Here, we aimed at optimizing an in vivo treatment schedule using the widely applied cytostatic drug 5-fluoruracil (5-FU) for exemplary response prediction in colorectal cancer (CRC) PDX models. Four different individual CRC PDX models were engrafted into NOD.Cg-PrkdcscidIl2rgtm1Wjl (NSG) mice. Mice with established PDX were allocated to different treatment groups, receiving 5-FU, the oral prodrug Capecitabine, or 5-FU/leucovorin (LV) at different doses. Body weight, tumor size, and general behavior were assessed during therapy. Ex vivo analyses were done from blood samples, liver, as well as tumor resection specimen. Engraftment efficacy was high as expected in NSG mice, yielding stable PDX growth for therapy stratification. However, overall tolerability towards 5-FU was unexpectedly low, whereas the prodrug Capecitabine as well as the combination of 5-FU/LV at low doses were well tolerated. Accompanying plasma level determination of DYPD, the rate-limiting enzyme for 5-FU-mediated toxicity, revealed reduced activity in NSG mice compared with other common laboratory mouse strains, offering a likely explanation for the drug incompatibility. Also, the De Ritis quotient was highly elevated in treated mice, reflecting overall organ injury even at low doses. Summarizing these findings, NSG mice are ideal hosts for in vivo engraftment studies. However, the complex immunodeficiency reduces tolerance to certain drugs, thus making those mice especially sensitive. Consequently, such dose finding and tolerance tests constitute a necessity for similar cancer precision medicine approaches.

Oxidative stress-driven DR5 upregulation restores TRAIL/Apo2L sensitivity induced by iron oxide nanoparticles in colorectal cancer

There exists an emergency clinical demand to overcome TRAIL/Apo2L (tumor necrosis factor-related apoptosis-inducing ligand) resistance, which is a major obstacle attributed to insufficient level or mutation of TRAIL receptors. Here, we developed an iron oxide cluster-based nanoplatform for both sensitization and MR image-guided evaluation to improve TRAIL/Apo2L efficacy in colorectal cancer, which has an inadequate response to TRAIL/Apo2L or chemotherapy. Specifically, NanoTRAIL (TRAIL/Apo2L-iron oxide nanoparticles) generated ROS (reactive oxygen species)-triggered JNK (c-Jun N-terminal kinase) activation and induced subsequent autophagy-assisted DR5 upregulation, resulting in a significant enhanced antitumor efficacy of TRAIL/Apo2L, which confirmed in both TRAIL-resistant HT-29, intermediately resistant SW-480 and sensitive HCT-116 cells. Furthermore, in a subcutaneous colorectal cancer mouse model, the in vivo tumor retention of NanoTRAIL can be demonstrated by MR T2 weighted contrast imaging, and NanoTRAIL significantly suppressed tumor growth and prolonged the survival time without observable adverse effects compared with control and TRAIL/Apo2L monotherapy. Importantly, in the study of colorectal cancer patient-derived xenograft models, we found that the NanoTRAIL treatment could significantly improve the survival outcome with consistent ROS-dependent autophagy-assisted DR5 upregulation and tumor apoptosis. Our results describe a transformative design that can be applied clinically to sensitize Apo2L/TRAIL-resistant patients using FDA-approved iron oxide nanoparticles.

Abstract 225: TR1801-ADC, an optimized anti cMet PBD ADC with high efficacy in solid tumors of the GI tract and head &amp; neck cancer

Abstract cMet is a well-characterized oncogene that is the target of many drugs including small molecule and biologic pathway inhibitors, and more recently, antibody drug conjugates (ADCs). However, clinical benefit from c-Met targeted therapy has been limited up to this point. We developed an optimized c-Met targeted antibody drug conjugate TR1801-ADC that utilized optimization at all steps including specificity, stability, internalization, toxin linkers, conjugation site, PK, and in vivo efficacy. The results were a highly potent c-Met ADC that was superior in comparison to a conventional MMAE (monomethylauristatin E) cMet ADC in potency, efficacy and duration of response. TR1801-ADC is site-specifically conjugated to a PBD-toxin linker and has low picomolar activity in multiple cancer cell lines derived from different solid tumors including lung cancer, colorectal cancer and gastric cancer. The potency of our cMet ADC is independent of MET gene copy number and its activity was high not only in high cMet cell lines but also in medium to low cell lines (100,000 to 40,000 cMet/cell). We identified potential Phase 1 cancer indications based on IHC and cMet H-score from tissue micro arrays (TMAs). 3 cancer indications (gastric, colorectal and head &amp; neck cancer) were chosen based on high abundance of high cMet expression (&amp;gt;20% abundance of H-Score higher than 150) and were used to assess the efficacy of our cMet ADC in PDX models. For each indication 10 PDX (patient-derived xenograft) models were chosen based on their cMet expression. TR1801-ADC was administered in all models as single i.v. dose at 1, 0.5, 0.25 and 0.125 mg/kg. Control ADC was administered at 1mg/kg. Tumor growth inhibition varying from &amp;gt;100% to around 40% was seen in all gastric cancer PDX models with single dose injections of 1 mg/kg and 0.5 mg/kg. Complete tumor regression was seen in 70% of the 1 mg/kg group, in 50% of the 0.5 mg/kg group and in 40% of the 0.25 mg/kg group. TR1801-ADC produced statistically significant growth inhibition in comparison to untreated controls in 9 colorectal cancer PDX models. Complete tumor regression was observed in 40% (4/10) PDX models when treated with 1 mg/kg TR1801-ADC. The further 50% showed partial regression (5/10 models) and one showed no significant tumor response. The head &amp; neck cancer PDX models were in general least sensitive to TR1801-ADC. TR1801-ADC produced statistically significant growth inhibition in comparison to untreated controls in 8/10 head &amp; neck cancer PDX models. Complete tumor regression was observed in 30% (3/10) PDX models when treated with 1 mg/kg TR1801-ADC. 50% showed statistical significant partial regression while two models (20%) showed no significant tumor inhibition. Altogether, TR1801-ADC is a novel highly potent cMet ADC that shows very promising efficacy in PDX models of gastric, colorectal and head &amp; neck cancer with long lasting anti-tumor effect with a single dose. Citation Format: Marco Gymnopoulos, Oscar Betancourt, Vincent Blot, Ryo Fujita, Diana Ly, Sophie Nguyen, Jeanette Snedden, Jose Villicana, Jon Wojciak, Eley Wong, Neki Patel, Francois D'Hooge, Balakumar Vijayakrishnan, Conor Barry, John A. Hartley, Phil W. Howard, Roland Newman, Julia Coronella. TR1801-ADC, an optimized anti cMet PBD ADC with high efficacy in solid tumors of the GI tract and head &amp; neck cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 225.