Clayton Staheli

Introduction: Cutaneous melanomas comprise 5% of all cutaneous malignancies, however, they cause most skin related cancer deaths, roughly 55,500 deaths yearly due to metastasis and visceral involvement.^1,2 Two mutations cause most melanomas, a BRAF protein mutation and an NRAS protein mutation. BRAF-mutant driven melanomas are the more common of these two types and clinically have received more attention. As such, therapeutic intervention for these has become very effective. NRAS mutations, however, are mutually exclusive from BRAF mutations and therapeutic interventions for this type of melanoma are in dire need.^1,3 The NRAS signaling pathway contains many potential targets of inhibition including the mutant NRAS protein itself, downstream RAF proteins, or a novel NRAS activator, STK19.^4-6 Methods: At the level of NRAS inhibition, researchers investigated pan-RAS inhibitors, particularly a computationally derived molecule, Molecule 3144. Isothermal titration calorimetry, microscale electrophoresis and NMR were used to investigate binding affinity across a broad spectrum of RAS mutant proteins. Subsequently, western blot was used to determine effectiveness in prevention of tumorigenesis.⁴ At the level of downstream Raf inactivation, the drug belvarafenib is currently being tested in phase I trials as a Raf dimer inhibitor. X-ray crystallography and cellular thermal shift assays were used to characterize the binding action of belvarafenib while ongoing phase I trial is underway to determine clinical applicability of the drug.⁵ Lastly, at the level of upstream activator inhibition, several gene knockouts were researched to determine novel candidates as NRAS activators. Among these knockouts was STK19. Mass spectroscopy was used to characterize the mechanism of activation of NRAS via STK19 and a computationally designed drug, ZT-12-037-01, was used in cell cultures to determine its effects on tumorigenesis.⁶ Results: Molecule 3144 was shown to bind a conserved pocket, P2, of KRAS, NRAS and HRAS. Furthermore, molecule 3144 prevented tumorigenesis in rat xenographs due to its decrease in MEK/ERK activation.⁴ Downstream, belvarafenib has significantly improved mean progression free survival rate of participants with a p-value of 0.0285.⁵ Upstream, STK19 phosphorylates serine residue 89 of NRAS. ZT-12-037-01 showed decreased colony formation, proliferation, and tumor growth in NRAS-mutant colonies.⁶ Conclusion: As mentioned, intervention for NRAS-mutant melanoma is not sufficient, however, these groundbreaking studies suggest that there is great potential. Further research and exploitation of one or multiple of the inhibition points of the NRAS-mutant pathway may be necessary to bring about proper therapeutic intervention that could aid in healing from this devastating disease.

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2. Schadendorf D, van Akkooi ACJ, Berking C, et al. Melanoma. Lancet. Sep 15 2018;392(10151):971-984. doi:10.1016/s0140-6736(18)31559-9
3. Randic T, Kozar I, Margue C, Utikal J, Kreis S. NRAS mutant melanoma: Towards better therapies. Cancer Treat Rev. Sep 2021;99:102238. doi:10.1016/j.ctrv.2021.102238
4. Welsch ME, Kaplan A, Chambers JM, et al. Multivalent Small-Molecule Pan-RAS Inhibitors. Cell. Feb 23 2017;168(5):878-889.e29. doi:10.1016/j.cell.2017.02.006
5. Yen I, Shanahan F, Lee J, et al. ARAF mutations confer resistance to the RAF inhibitor belvarafenib in melanoma. Nature. Jun 2021;594(7863):418-423. doi:10.1038/s41586-021-03515-1
6. Yin C, Zhu B, Zhang T, et al. Pharmacological Targeting of STK19 Inhibits Oncogenic NRAS-Driven Melanomagenesis. Cell. Feb 21 2019;176(5):1113-1127.e16. doi:10.1016/j.cell.2019.01.002