About

Kelton Schleyer, Ph.D., M.S., is a Research Assistant Professor in the Department of Medicinal Chemistry at the College of Pharmacy, University of Florida. He completed his B.S. in Chemistry at Harding University in Searcy, Arkansas, and pursued graduate studies at the University of New Mexico in the department of Chemistry and Chemical Biology under Dr. Lina Cui, earning an M.S. in Chemistry. He then joined the University of Florida's Department of Medicinal Chemistry to complete his Ph.D. in 2021. Following his doctoral studies, Dr. Schleyer conducted post-doctoral research with Dr. Ralph Weissleder at the Center for Systems Biology at Massachusetts General Hospital. In 2025, he returned to the College of Pharmacy at UF as a Research Assistant in the Cui lab, continuing his research in medicinal chemistry.

Research topics

• Chemistry
• Biochemistry
• Biology
• Computational biology
• Nanotechnology
• Organic chemistry
• Materials science
• Biophysics
• Combinatorial chemistry

Selected publications

• γ‐Butyrolactone Derivatives of MSA‐2 are STING Prodrugs

  ChemMedChem · 2024-06-18 · 2 citations

  articleOpen access1st author

  STING agonists are potent enhancers of a pro-inflammatory response and, thus, potentially useful therapeutics. Unfortunately, many agonists developed to date require complex drug delivery formulations and often have poor water solubility, limiting their use for systemic administration. Here, we report the discovery and chemical characterization of lactones of MSA-2 as new STING prodrugs with enhanced properties. We show that these prodrugs form efficient inclusion complexes with tumor myeloid cell targeting cyclodextrin nanoparticles and propose a new mechanism of formation and hydrolysis.

  PublisherOA PDFDOI

• FAP-Targeted Fluorescent Imaging Agents to Study Cancer-Associated Fibroblasts In Vivo

  Bioconjugate Chemistry · 2024-12-12 · 6 citations

  articleOpen access

  Cancer-associated fibroblasts (CAFs) expressing fibroblast activation protein alpha (FAP) are abundant in tumor microenvironments and represent an emerging target for PET cancer imaging. While different quinolone-based small molecule agents have been developed for whole-body imaging, there is a scarcity of well-validated fluorescent small molecule imaging agents to better study these cells in vivo. Here, we report the synthesis and characterization of a series of fluorescent FAP imaging agents based on the common quinolone azide inhibitor. Our data show excellent performance of some synthesized FAP Targeting Fluorescent probes (FTFs) for both topical application and intravenous delivery to label CAF populations in solid tumors. These results suggest that FTF can be used to study CAF biology and therapeutic targeting in vivo.

  PublisherDOI

• Pharmacological Polarization of Tumor‐Associated Macrophages Toward a CXCL9 Antitumor Phenotype

  Advanced Science · 2024-02-11 · 10 citations

  articleOpen access

  TAM has recently been described to have an antitumor phenotype and is linked to immune checkpoint response. Despite the emerging understanding of the unique antitumor TAM phenotype, there is a lack of TAM-specific therapeutics to exploit this new biological understanding. Here, the discovery and characterization of multiple small-molecule enhancers of chemokine ligand 9 (CXCL9) and their targeted delivery in a TAM-avid systemic nanoformulation is reported. With this strategy, it is efficient encapsulation and release of multiple drug loads that can efficiently induce CXCL9 expression in macrophages, both in vitro and in vivo in a mouse tumor model. These observations provide a window into the molecular features that define TAM-specific states, an insight a novel therapeutic anticancer approach is used to discover.

  PublisherOA PDFDOI

• Abstract 2395: A bioluminescent probe for detection and imaging of heparanase enzymatic activity

  Cancer Research · 2023-04-04 · 1 citations

  article

  Abstract Cancers of all types have been shown to overexpress the carbohydrate-processing enzyme heparanase during angiogenesis and invasion, and this enzymatic activity correlates positively with tumor stage and the presence of metastases. While detection of heparanase enzymatic activity holds potential for cancer diagnosis and staging, no probe has been achieved for in vivo systems. We have recently developed fluorogenic heparanase probes for single-step detection of in vitro heparanase enzymatic activity, drastically simplifying the detection of heparanase activity. The modular chemistry allows us to extend the utility further to improve the sensitivity of in vitro heparanase activity detection and enable in vivo detection. Thus, we have developed a bioluminescent heparanase probe, which upon activation by heparanase produces a substrate of firefly luciferase, a standard reporter enzyme for in vivo monitoring of tumor progression. This probe will be validated in multi-well assays of heparanase activity, and applied in real-time correlation of heparanase activity and tumor progression in, fLuc+ tumors in animal models. These studies hold promise in enabling highly sensitive detection of heparanase activity both in vitro and in vivo, and in allowing future research of real-time monitoring of heparanase activity with the tumor progression. Citation Format: Johnathan Somers, Kelton Schleyer, Jun Liu, Zhishen Wang, Arjun Kafle, Lina Cui. A bioluminescent probe for detection and imaging of heparanase enzymatic activity [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 2395.

  PublisherDOI

• A Universal and Modular Scaffold for Heparanase Activatable Probes and Drugs

  Bioconjugate Chemistry · 2022-11-08 · 3 citations

  articleOpen access1st author

  Heparanase (HPSE) is an endo-β-glucuronidase involved in extracellular matrix remodeling in rapidly healing tissues, most cancers and inflammation, and viral infection. Its importance as a therapeutic target warrants further study, but such is hampered by a lack of research tools. To expand the toolkits for probing HPSE enzymatic activity, we report the design of a substrate scaffold for HPSE comprised of a disaccharide substrate appended with a linker, capable of carrying cargo until being cleaved by HPSE. Here exemplified as a fluorogenic, coumarin-based imaging probe, this scaffold can potentially expand the availability of HPSE-responsive imaging or drug delivery tools using a variety of imaging moieties or other cargo. We show that electronic tuning of the scaffold provides a robust response to HPSE while simplifying the structural requirements of the attached cargo. Molecular docking and modeling suggest a productive probe/HPSE binding mode. These results further support the hypothesis that the reactivity of these HPSE-responsive probes is predominantly influenced by the electron density of the aglycone. This universal HPSE-activatable scaffold will greatly facilitate future development of HPSE-responsive probes and drugs.

  PublisherOA PDFDOI

• Abstract 2925: Expanding the library of small molecule imaging probes for heparanase

  Cancer Research · 2022-06-15

  article1st authorCorresponding

  Abstract Heparanase is an enzyme highly involved in the progression of many types of cancer through its enzymatic processing of heparan sulfate proteoglycans. Unfortunately, research and clinical investigation of this target is hampered by the lack of simple, effective tools to detect its enzymatic activity. Despite the natural preference of heparanase to cleave polysaccharide substrates, we previously developed the first disaccharide-based fluorogenic probe for heparanase enzymatic activity, overcoming this deficiency in existing tools. However, the chemistry of the probe synthesis required installation of electron-withdrawing fluorine atoms on the fluorophore to facilitate activation by heparanase, a design strategy that excludes the use of many common imaging reporters. To accommodate a wider variety of imaging modalities for heparanase detection, we experimented with the addition of a collapsible linker with suitable electronegativity that can be easily tuned. Our results show that a tetra-fluorinated benzyl alcohol linker enables heparanase activation of a probe bearing any reporter, giving comparable results to our original fluorinated coumarin probe. This disaccharide-linker scaffold holds potential for accessing a broader scope of heparanase imaging probes for laboratory and clinical applications of this burgeoning biomarker. Citation Format: Kelton Schleyer, Jun Liu, Zhishen Wang, Hua Guo, Lina Cui. Expanding the library of small molecule imaging probes for heparanase [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2925.

  PublisherDOI

• Molecular probes for selective detection of cysteine cathepsins

  Organic & Biomolecular Chemistry · 2021 · 18 citations

  1st authorCorresponding
  • Chemistry
  • Biochemistry
  • Computational biology

  Cysteine cathepsins are proteases critical in physiopathological processes and show potential as targets or biomarkers for diseases and medical conditions. The 11 members of the cathepsin family are redundant in some cases but remarkably independent of others, demanding the development of both pan-cathepsin targeting tools as well as probes that are selective for specific cathepsins with little off-target activity. This review addresses the diverse design strategies that have been employed to accomplish this tailored selectivity among cysteine cathepsin targets and the imaging modalities incorporated. The power of these diverse tools is contextualized by briefly highlighting the nature of a few prominent cysteine cathepsins, their involvement in select diseases, and the application of cathepsin imaging probes in research spanning basic biochemical studies to clinical applications.

  PublisherOA PDFDOI

• Abstract 328: Selective fluorogenic probe for rapid detection of cathepsin L activity

  Cancer Research · 2021-07-01 · 1 citations

  article1st authorCorresponding

  Abstract Cathepsin L (CTL) is a cysteine protease that demonstrates upregulated activity and altered trafficking in various cancers. Its upregulation in many cancers correlates positively with tumor grade while its excessive secretion makes elevated serum levels a possible biomarker for aggressive cancer types. The overlapping substrate specificity of cathepsin family members makes selective detection of activity from a single cathepsin difficult, and CTL activity is particularly difficult to parse from its close homologue CTV and the ubiquitous CTB. This complicates clinical sample assays for CTL activity, which generally rely on simple fluorescent probes lacking specificity for CTL over other cathepsins. We have developed a fluorogenic probe, CTLAP, that is rapidly activated by CTL and displays good selectivity over CTB and CTV, the closest competing analytes for CTL. The novel chemical structure of CTLAP facilitates markedly higher signal generation and improved selectivity for CTL when compared to Z-FR-AMC, the commercial probe commonly used to detect CTL activity in mixed samples. Optimum selectivity for CTL is achieved within 10 min of incubation, suggesting that CTLAP is amenable for rapid detection of CTL, even in the presence of competing cathepsins. Citation Format: Kelton A. Schleyer, Ben Fetrow, Peter Fatland, Jun Liu, Maya Chaaban, Biwu Ma, Lina Cui. Selective fluorogenic probe for rapid detection of cathepsin L activity [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 328.

  PublisherDOI

• A self-immolative linker for heparanase activatable probes

  bioRxiv (Cold Spring Harbor Laboratory) · 2021-06-15

  preprintOpen access1st author

  Abstract Substrate-based probes utilize known substrate specificity parameters to create a probe that can be activated by a target enzyme. In developing probes for heparanase, an endo-ß-glucuronidase, we previously reported that small, inactive substrate-based probes could be electronically tuned by incorporating electron-withdrawing atoms on the aromatic aglycone fluorophore, ortho - to the cleaved glycosidic bond. However, the installation of electron-withdrawing groups directly onto established fluorophores or other reporters complicates the synthesis of new heparanase probes. In this work we report a new design strategy to expand the toolkit of heparanase imaging probes, in which the installation of an electronically tuned benzyl alcohol linker restored the activity of a previously inactive heparanase probe using 4-methylumbelliferone as the fluorescent reporter, suggesting such a linker can provide a scaffold for facile development of activatable heparanase probes bearing a variety of imaging moieties.

  PublisherOA PDFDOI

• Dual‐Mechanism Quenched Fluorogenic Probe Provides Selective and Rapid Detection of Cathepsin L Activity**

  ChemMedChem · 2020-12-10 · 2 citations

  articleOpen access1st author

  Abstract Cathepsin L (CTL) is a cysteine protease demonstrating upregulated activity in many disease states. Overlapping substrate specificity makes selective detection of CTL activity difficult to parse from that of its close homologue CTV and the ubiquitous CTB. Current probes of CTL activity have limited applications due to either poor contrast or extra assay steps required to achieve selectivity. We have developed a fluorogenic probe, CTLAP, that displays good selectivity for CTL over CTB and CTV while exhibiting low background fluorescence attributed to dual quenching mechanisms. CTLAP achieves optimum CTL selectivity in the first 10 min of incubation, thus suggesting that it is amenable for rapid detection of CTL, even in the presence of competing cathepsins.

  PublisherOA PDFDOI

Frequent coauthors

• Lina Cui

  University of Florida

  128 shared

• Chao Cui

  Northwest A&F University

  74 shared

• Xiaowei Ma

  66 shared

• Jun Liu

  University of Florida Health Science Center

  57 shared

• Brandon Burnside

  University of New Mexico

  28 shared

• John K. Grey

  28 shared

• Benjamin D. Datko

  New Mexico Cancer Center

  28 shared

• Peter Zannes Fatland

  21 shared

Labs

• Center for Natural Products, Drug Discovery and Development (CNPD3)PI

  Director Associate Director for Drug Design Associate Director for Synthetic Biology Assistant Director Core Directors/Core Leaders Microbial Genomics and Synthetic Biology: Yousong Ding, Ph.D. (Core Director), Manyun Chen, Ph.D., M.S. (Core Leader) Molecular Diversity and Screening: Ranjala Ratnayake, Ph.D. (Core Leader) AI-Based and Structure-Base Structure Based Drug Design & Optimization: Gustavo Seabra, Ph.D. (Core Leader)

Education

• Ph.D. Pharmaceutical Sciences - Medicinal Chemistry, Medicinal Chemistry

  University of Florida

  2021

• M.S. Chemistry, Chemistry and Chemical Biology

  The University of New Mexico

  2018

• B.S. Chemistry, Chemistry and Biochemistry

  Harding University

  2014