Covalent targeting of oncogenic KRas G12C

My doctoral dissertation focuses on the covalent and noncovalent targeting of oncogenic Ras with modified peptidomimetics, which are based on the secondary and tertiary structures of proteins. However, the development of minimal protein mimics that engage intracellular targets with high affinity remains a major challenge since mimicry of a portion of the binding interface is often associated with the loss of critical binding interactions. Covalent targeting provides an attractive approach to overcome the loss of non-covalent contacts but carries the inherent risk of dominating non-covalent contacts and increasing the likelihood of non-selective binding. I first developed and validated a viable, electrophilic peptide scaffold targeting the oncogenic G12C Ras mutant. We explored several carbon-based Michael acceptors as reactive warheads for my proteolytically stable helix mimic. The designed lead peptide modulates nucleotide exchange, inhibits activation of the Ras-mediated signaling cascade, and is selectively toxic towards mutant G12C Ras cancer cells.

Publication reference: Yoo, D.Y. et al., J Am Chem Soc, 2020, 15(6), 1604-1612.

Macropinocytosis as a therapeutic route for larger peptidomimetics

Inspired by the results from both previous works, I then investigated the cellular penetration of different classes of conformationally stabilized peptides in multiple Ras mutant cancer cell lines and found an exploitable therapeutic route unique to larger molecules. Efficient uptake of various conformationally defined peptide constructs (i.e. linear peptides, peptide macrocyles, stabilized helices, beta-hairpin peptides, and crosslinked helix dimers) directly correlated with the macropinocytic activity of each cell line: high uptake of compounds was observed in cells with mutations in certain signaling pathways. Our findings expand the current understanding of cellular uptake in cancer cells by designed peptidomimetics and suggest that cancer cells with specific mutations are suitable mediums for the study of biological pathways and potential future therapeutics.

Publication reference: Hong, S.H.*, Yoo, D.Y.* et al., Proc Natl Acad Sci, 2021, 118(18), 1-11.

Increased osseointegration effect of BMP-2 on dental implants

My master’s thesis work specifically revolved around the increased osseointegration effects with the application of recombinant human BMP-2 (rhBMP-2) onto plasma-sprayed hydroxyapatite (PSCaP) and textured titanium dental implant surfaces in a sheep iliac model. After 3 and 6 weeks post-operatively, the implanted samples were retrieved and subjected to bone-to-implant contact (BIC) and bone area fraction occupancy (BAFO) evaluation. When rhBMP-2 was applied to the PSCaP surface, significant increases in BIC and BAFO were observed after only 3 weeks in vivo. In contrast, the direct adsorption of rhBMP-2 onto an unmodified titanium implant surface did not as effectively improve the bone response in either histomorphometric category. In addition to my thesis work, I handled everything from modified titanium implants (i.e. plasma-treatment, chemical deposition, surface treatments including laser alterations, etc.), synthetic graft materials (i.e. calcium phosphate, Nanogen, BioOss), to hydroxyapatite-tricalcium phosphate (HA-TCP) scaffolds in rabbit, dog, pig, sheep, monkey, and even human models.

Publication reference: Yoo, D. et al., J Biomed Mat Res A, 2013, 102(6), 1921-1927.

High-throughput in vivo small molecule screen for beta cell regeneration in transgenic zebrafish

My primary project at the time revolved around a high-throughput in vivo small molecule screen for beta cell regeneration, proliferation, and neogenesis. We screened multiple chemical compound collections, ranging from the NIH Clinical Collections, Sigma Lopac, Kume, Nuclear Receptor Ligand, and Bioactive Lipid libraries. From a few dozen positively classified compounds, we identified five compounds that doubled the number of beta cells after 2 days of treatment: 5′-N-ethylcarbox-amidoadenosine (NECA, a nonspecific adenosine agonist for GPCR signaling), A-134974 (an adenosine kinase inhibitor blocking adenosine degradation), Cilostamide (a PDE3 inhibitor), and Zardaverine (a PDE3 and PDE4 inhibitor). The majority of these compounds affected the adenosine signaling pathway and were predicted to enhance the pathway’s signaling output. The zebrafish model has been successfully employed in large-scale chemical screens for identification of relevant signaling pathways in different biological contexts. With the validation of these compounds in a diabetes mouse model, the next step is to develop these findings towards novel therapies for diabetes.

Publication reference: Andersson, O. et al., Cell Metabolism, 2012, 15(6), 885-894.

Biologically functional cationic phospholipid-gold nanoplasmonic carriers

My undergraduate research focused on the refinement of the original CTAB-coated gold nanorod designs to biologically functional cationic phospholipid-gold plasmonic carriers (bioGNPs) with properly tuned aspect ratios, concentration of bound RNA, increased transfection capability, and minimal cytotoxicity. Working with these multi-functional nanotubes, I determined the transfection efficiency, accuracy, and cytotoxicity against conventional nanorods targeting the ERBB2 (HER2/neu) receptor on both BT474 and MCF-7 breast carcinoma populations. Since they also retain their unique optical properties under physiological conditions, we expect bioGNPs to play important roles in gene and drug delivery, imaging, and therapeutics.

Publication reference: Lee, S.E. et al., J Am Chem Soc, 2009, 131(39), 14066-14074.