# Peptides That Block RAS-p21 Protein-Induced Cell Transformation
## 3 Anti-RAS-p21 Peptides from Expression Libraries
### Small Molecules Freeze Oncogenic RAS-p21 in an Inactive GDP Bound State
The structure of AMG510 bound to G12C-RAS-p21-GDP is shown in Figure 7. In this figure, the unusual groove involving the switch 2 domain including its \(\alpha\)2 helix is shown, and unique to this groove, the \(\alpha\)3 helix. This drug appears to synergize with other anti-cancer agents such as carboplatin, MAPK inhibitors and with immunotherapeutic agents, particularly anti-PD-1 [36]. In this latter case, combination therapy with AMG-510 and anti-PD1 caused dramatic survival rates in CT-26 mice with G12C-RAS-p21 over treatment with either agent alone. In addition, tumors in mice treated with AMG-510 showed a large increase in T cell infiltration, primarily CD8 positive T cells, and seem to have created an inflammatory anti-tumor environment [34; 36]. The importance to the overall anti-tumor effect of AMG-510 of a positive anti-tumor immune environment has been shown in recent studies showing that AMG-510 induces only transient tumor regression in immune-deficient nude mice [36]. Figure 6: [PERSON] et al. Chemical structures of three poly aromatic ring molecules, AMG500 (**A**), MRTX849 (**B**) and MRTX 1139 (**C**) that insert into a groove formed by the switch 2 domain, its \(\alpha\)2 helix and its \(\alpha\)3 helix. The first two compounds, (**A**,**B**), bind uniquely to G12C-K-RAS-p21-GDP, the third, (**C**), binds to G12D-K-RAS-p21-GDP. Of prime importance, as noted above, AMG-510 has received FDA approval for treating G12C-RAS-p21-induced human tumors. At present, the treatment of four patients with NSCCL resulted in 34 and 67% remission in two of the patients and stable disease in the other two patients. A follow-up scan of the second responder patient after 18 weeks of treatment revealed a complete resolution of target emissions. These findings suggest that AMG-510 is a major advance in treating ras-induced human tumors. However, further studies indicate that human colorectal carcinomas (CRC) with G12C-RAS-p21 mutations do not respond as favorably [36]. Furthermore, a number of mechanisms that result in anti-tumor drug resistance have been identified including the possibility of double mutations in the G12C-RAS-p21 protein that appear to close off the switch 2 pocket, disenabling drug binding. These include mutations at Tyr 96 (Y96D) in the \(\alpha\)-3 helix and R68S, H95D or H95Q or H95R (each presumably disenabling the histidine 95 \"swing\" opening up the switch 2 pocket in G12C-RAS-p21-GDP) [36]. Another drug,  
Figure 7: Ribbon representation of the X-ray structure of AMG510 bound to G12C-RAS-p21-GDP from Ref. [36]. Coordinates were obtained from the Protein Data Base (PDB) identity number 7 RPZ and rotated to give a clear view of the binding pocket occupied by AMG510. The color scheme for critical domains is the same as for Figure 5. G12C-RAS-p21 uniquely has a groove formed by the switch 2 domain, consisting of residues 55–76 (colored blue except for its \(\alpha\)2 helix that is colored red) and its \(\alpha\)3 helix (residues 89–103, colored yellow). The orientation of this complex is similar to that of the KD2-G12D-RAS-p21-GppNHp complex shown in Figure 5. As in Figure 5, the nucleotide (here, GDP) is oriented horizontally such that the guanine ring is on the far right in the middle of the figure, and a \(\beta\)-phosphate oxygen binds to the magnesium ion (green sphere in the middle of the figure). The AMG510 molecule can be seen in the lower left of the protein inserted into a groove between the yellow \(\alpha\)3 helix and the blue switch 2 loop region above it in the figure. Just above Leu 80 (“Leu” in the middle of the figure), there is a red projection that is the carbonyl oxygen of the acryl moiety of the drug that is positioned to react with the-SH group of Cys 12 labeled in the figure. In contrast to Figure 5, the switch 1 domain is seen to be well-defined and can be identified by the labeled residue positions Asp 33, Thr 35 and Leu 36. Unlike the positioning of switch 1 residues on the surface of the protein in Figure 5, the switch 1 residues of G12C-RAS-p21-GDP are not as exposed.