P1.14-08 - Activity of Poziotinib and Other 2nd-Gen Quinazoline EGFR TKIs in Atypical Exon18 and Acquired Osimertinib Resistance Mutants 09:45 - 09:45 | Presenting Author(s): Jacqulyne Ponville Robichaux | Author(s): Xiuning Le, Yasir Elamin, Monique Nilsson, Limei Hu, Junqin He, Fahao Zhang, Alissa Poteete, Huiying Sun, Waree Rinsurongkawong, Jason B Cross, John Victor Heymach
Background
In EGFR, exon 18 encodes for the P-loop (L718-V726), and mutations in this region (G719S/A, L718Q/V, G724S) are known to reduce sensitivity to osimertinib and first-generation EGFR TKIs. Osimertinib resistance is associated with a number of acquired mutations in exons 19 and 20 (S784F, L747S, C797S and L792H). We investigated the frequency and drug sensitivity of these and other osimertinib-resistant EGFR mutations Method
We generated ~50 different Ba/F3 cell line models expressing classical and/or atypical EGFR mutations (exons 18-21) and evaluated the transforming ability and sensitivity to 14 EGFR TKIs including non-covalent (first-generation), afatinib, dacomitinib, and poziotinib (quinazoline and covalent, second-generation), and covalent T790M-specific (third-generation) inhibitors. Impact of atypical mutations was analyzed by in silico modeling. Result
We found 3.6% (N=32/895) of EGFR-mutant patients had atypical, exon 18, P-loop mutations in the MD Anderson GEMINI database. Modeling of classical EGFR mutations revealed osimertinib has distinct interactions between the solvent front of osimertinib and residues within the P-loop of EGFR, whereas second-generation quinazoline TKIs, such as poziotinib, extend into the pocket, near T790, lacking these interactions. Mutations in the P-loop were predicted to shift osimertinib out of alignment with V726 and F723, causing resistance to osimertinib but not quinazoline-based TKIs. Atypical exon 18 mutations (G719S/A, L718Q/V, G724S) had IC50values of 113.6nM, 1.6nM, and 137.5nM for first-, second-, and third-generation TKIs, respectively. Second-generation TKIs inhibited G719S/A-T790M mutations at concentrations 2-fold lower than third-generation TKIs (IC50 = 23.4nM and 46nM). Osimertinib-resistance mutations (L747S, S784F, C797S, L792H) co-occurring with classical sensitizing mutations (L858R or ex19del) had IC50values of 56.8nM, 1.4nM, and 996nM to first, second and third-generation inhibitors. Of the second-generation TKIs tested, poziotinib was the most potent for atypical exon 18 P-loop mutations; G719S/A-T790M mutations; and classical mutants with acquired osimertinib-resistance mutations (IC50= 0.4nM, 3.2nM, 0.8nM). Conclusion
Exon 18 atypical P-loop mutations and osimertinib-resistance mutations demonstrated high sensitivity to second-generation quinazoline TKIs, compared to first- and third-generation inhibitors. Mutations in the P-loop of EGFR confer resistance to third-generation TKIs by destabilizing solvent front interactions of the molecule, and osimertinib-resistance mutations interfere with covalent binding at C797. Second-generation TKIs, especially poziotinib, are potent inhibitors of these mutations because they have increased hydrophobic interactions at the back of the drug binding cleft that are retained without covalent binding. Together, these data indicate that poziotinib and other second-generation TKIs may be useful for the treatment of NSCLC patients with atypical P-loop and selected osimertinib-resistant EGFR mutations. https://library.iaslc.org/conference-program?product_id=15&author=&category=Targeted%20Therapy&date=2019-09-08&session_type=&session=&presentation=P1.14-08&keyword=&cme=undefined&;
