Competition Abstracts
Poster 1
Developing GPR56-Targeted Antibody-Drug Conjugates for Triple-Negative Breast Cancer Treatment
Yueh-Ming Shyu1,2, Joan Jacob3, Carla Godoy2, Treena Chatterjee2, Zhengdong Liang2, Kendra S. Carmon2
1The University of Texas MD Anderson Cancer Center UTHealth Houston Graduate School of Biomedical Sciences, Houston, TX 77030; 2Center for Translational Cancer Research, The Brown Foundation Institute of Molecular Medicine, The University of Texas Health Science Center at Houston, Houston, TX 77030; 3Pediatrics Oncology-AICT, Baylor College of Medicine, Houston, TX 77030
Triple-negative breast cancer (TNBC) poses a significant challenge in oncology, comprising 10-15% of all breast cancer cases. Its aggressive nature, high metastatic potential, and lack of targetable receptors result in limited treatment options and poor prognosis. The emergence of chemotherapy resistance further complicates TNBC management, underscoring the urgent need for novel therapeutic strategies. Antibody-drug conjugates (ADCs) have emerged as a promising approach for targeted cancer therapy. These innovative drugs combine monoclonal antibodies (mAbs) specificity with potent cytotoxic payloads, enabling precise delivery of chemotherapy drugs to cancer cells. This targeted approach potentially enhances efficacy while minimizing damage to healthy tissues, making ADCs an attractive option for developing more effective TNBC treatments.
Our research identified G protein-coupled receptor 56 (GPR56) as a promising target for ADC development in TNBC. Analysis of The Cancer Genome Atlas (TCGA) data revealed that high GPR56 expression correlates with poor overall survival in breast cancer patients and is significantly elevated in TNBC compared to non-TNBC. Notably, GPR56 demonstrated a higher tumor-to-normal tissue expression ratio than TROP2, an approved ADC target. A BioID screen revealed that GPR56 associates with β1 integrins that mediate resistance and loss of GPR56 inhibited tumor growth. Therefore, we hypothesize that GPR56 is a potential target for treating TNBC. We previously developed an anti-GPR56 ADC (10C7-Duo) by conjugating duocarmycin payload to a GPR56-specific mAb, 10C7, which had significant antitumor efficacy in colorectal cancer models. Importantly, 10C7-Duo showed high potency in TNBC cell lines with high GPR56 expression, exhibiting target-dependent cytotoxicity. Combination therapy studies revealed synergistic effects between 10C7-Duo and AZD5305, a PARP1 inhibitor, in TNBC cells. Though 10C7-Duo has robust antitumor efficacy, 10C7 mAb showed agonist activity that may have long-term tumor promoting capabilities. Therefore, we are currently developing a new and improved ADCs incorporating different drug payloads and an anti-GPR56 mAb, 9E3, which does not exhibit agonist activity. We are also investigating GPR56-integrin interactions and their impact on FAK-Src signaling. Future work will focus on both ADC single-agent and combination therapies using TNBC cell lines, patient-derived samples, and xenograft mouse models.
This study aims to develop novel GPR56-targeted ADCs for TNBC, potentially enhancing efficacy, reducing side effects, and overcoming therapy resistance. By addressing the urgent need for effective TNBC treatments, this approach could significantly improve outcomes for TNBC patients.
Poster 2
Integrating Membrane Dynamics, Fragment-Based Drug Discovery and High Throughput Virtual Screening to identify novel inhibitors of Small GTPase Rheb
Chase M. Hutchins1, Alemayehu A. Gorfe1
- McGovern Medical School, University of Texas Health Science Center at Houston, Department of Integrative Biology and Pharmacology, 6431 Fannin St., Houston, Texas 77030, USA
- UTHealth MD Anderson Cancer Center Graduate School of Biomedical Sciences, Houston, 6431 Fannin St., Texas 77030, USA
Background: Rheb is a small GTPase in the Ras superfamily that promotes cell growth and proliferation by directly activating mTORC1 and its dysregulation can worsen cancer initiation and progression. Although rapamycin and its analogs (rapalogs) inhibit mTORC1 and are approved for several cancers, prolonged treatment can lead to off-target inhibition of mTORC2. Consequently, selectively inhibiting mTORC1 via Rheb represents an attractive alternative therapeutic strategy; however there currently are no clinically approved inhibitors targeting Rheb. Recent studies in Ras proteins emphasize the critical role of membrane orientation dynamics and its potential as a therapeutically targetable process but the role of membrane reorientation in function and druggability in other small GTPases, including Rheb, remains largely unexplored. In this study, we explored the membrane orientation dynamics of Rheb and identify how orientation dynamics can be targeted to yield more clinically viable inhibitors.
Methods: To investigate how membrane orientation influences Rheb function and druggability, we employed a multi-tiered, integrated computational strategy. First, we performed microsecond-scale molecular dynamics (MD) simulations to map Rheb’s orientation dynamics at the atomic resolution. Next, probe-based MD simulations were used to identify novel binding pockets and orientation‐dependent changes in Rheb’s allosteric druggable surface. Finally we targeted the most druggable binding pockets identified by probe-based simulations to conduct a high‐throughput virtual screen of large, pocket-tailored chemical libraries to discover novel inhibitors targeting Rheb.
Results: We identified three meta-stable membrane orientations of Rheb, with each orientation state differing in allosteric druggable surface, pocket geometry and druggabiltiy rating. Leveraging these insights, we then selected the most druggable pocket conformations and virtually screened a pocket-tailored library of ~2 million molecules targeting the most druggable conformational states of Rheb from our probe-based MD simulations.
Conclusions: Our findings reveal that Rheb’s membrane orientation dynamics influence its druggability and present an untapped avenue for inhibitor development. Targeting Rheb directly could offer a more selective approach to modulating mTORC1 activity in cancer, potentially reducing off-target effects associated with long-term rapalog therapy.
Poster 3
Targeting Colorectal Cancer Stem Cells with an Antibody-Drug Conjugate-Based Combination Therapy to Overcome Relapse
Shraddha Subramanian1,2, Zhengdong Liang1, Peyton High1,2, Adela Aldana1, and Kendra S. Carmon1,2
1Center for Translational Cancer Research, The University of Texas Health Science Center, Houston, TX, USA
2The University of Texas MD Anderson Cancer Center UTHealth Houston Graduate School of Biomedical Sciences, Houston, TX, USA
A significant hurdle in colorectal cancer (CRC) treatment is the relapse of residual disease, which can be attributed to cancer stem cells (CSCs). CSCs potentiate metastatic progression by exploiting their capacity to self-renew and differentiate. Furthermore, this immortal cell population exhibits plasticity, allowing cells to alter their phenotype in response to environmental cues that bolster inherent drug resistance. As a bona fide CSC marker, LGR5 is a promising drug target. We generated anti-LGR5 antibody-drug conjugates (ADCs) that inhibited tumor growth yet failed to prevent relapse following treatment completion. Follow-up studies indicate recurrent tumors evade therapy by converting into a drug-resistant LGR5-negative (LGR5–) state and, at least in part, depend on MET-STAT3 cascade activation for survival.
We demonstrated the coupling of LGR5 to IQGAP1, a scaffolding protein that promotes poor disease prognosis in multiple cancer subtypes. Interestingly, our pull-down assays revealed that LGR5 knockdown (KD) enhances IQGAP1 interaction with MET and STAT3, highlighting a potential role for IQGAP1 in mediating MET-STAT3 activation. To eliminate drug-resistant LGR5– cells, we generated MET-targeted ADCs by conjugating a highly selective MET monoclonal antibody (mAb) backbone to the DNA-crosslinking payload pyrrolobenzodiazepine via a site-specific conjugation methodology. The MET ADC was evaluated for cancer cell-killing efficacy in parallel with MET mAb, non-targeting control mAb (cmAb), and control ADC (cADC). MET ADC demonstrated high efficacy and potency in MET-expressing CRC cells in vitro, while unconjugated MET mAb, cmAb, and cADC exhibited minimal effects. Additionally, MET ADC had no impact on MET KD CRC cells, demonstrating its specificity. Safety studies in immunocompetent mice showed the MET ADC was well-tolerated with minimal toxicity. Moreover, when evaluated in CRC cell line and patient derived xenografts, the MET ADC induced significant tumor regression and prolonged overall survival. However, MET ADC monotherapy alone did not effectively prevent tumor relapse. Thus, an ADC combination strategy dual-targeting LGR5– and LGR5+ cells is a more promising approach to eliminating heterogeneous tumors. Pilot cytotoxicity assays evaluating the combination of MET ADCs with next-generation LGR5 ADCs showed moderate synergistic effects in vitro. The improved iteration of our LGR5 ADC was produced by attaching a topoisomerase I inhibitor derivative to a previously characterized LGR5 mAb backbone in a site-specific manner.
Future work involves investigating the efficacy of combining MET ADCs and LGR5 ADCs in patient-derived xenograft (PDX) models of CRC. These findings present a novel mechanism underpinning CRC plasticity and a rationale for an ADC-based treatment strategy to overcome colorectal tumor resistance and heterogeneity.