Research Progress on Resistance Mechanisms and Counterstrategies of KRAS G12C Inhibitors

1. Introduction

The KRAS gene is one of the most commonly mutated oncogenes in cancer. Due to its protein structure lacking ideal drug-binding pockets and its extremely high affinity for GTP, KRAS mutations have long been considered "undruggable" targets. This dilemma was only broken with the advent of covalent inhibitors targeting the KRAS G12C mutant subtype. The first KRAS G12C inhibitor (sotorasib) was approved for locally advanced or metastatic KRAS G12C-mutated non-small cell lung cancer, marking a new era in RAS-targeted therapy. However, as clinical use deepens, drug resistance has gradually emerged, potentially limiting the long-term efficacy of such drugs. A thorough understanding of the resistance mechanisms to KRAS G12C inhibitors and the exploration of counterstrategies are of great significance for maximizing their therapeutic value.

2. Resistance Mechanisms of KRAS G12C Inhibitors

Resistance to KRAS G12C inhibitors can be divided into two categories: intrinsic resistance and acquired resistance. Intrinsic resistance refers to pre-existing resistance mechanisms before drug treatment, typically manifested as low tumor dependency on the KRAS signaling pathway. Acquired resistance occurs in patients who initially respond to treatment, where tumors escape drug effects through genetic mutations or signaling pathway remodeling under therapeutic pressure. Current studies, through paired liquid and tissue biopsy analyses, have revealed multiple acquired resistance mechanisms.

(1) Secondary KRAS Mutations and Other RAS Family Mutations

A study of 43 patients treated with KRAS G12C inhibitors found that 27 cases developed treatment-related genetic mutations, with several cases detecting secondary RAS mutations. Secondary KRAS mutations include G12D, G12V, G12F, and Y96D, among others, with some patients also exhibiting increased KRAS copy numbers. Additionally, NRAS mutations such as Q61L and G13V have been detected. These mutations allow tumor cells to maintain downstream signaling through activation of other RAS family members even when KRAS G12C is inhibited.

(2) Activation of Bypass Signaling Pathways

Beyond secondary mutations in RAS genes themselves, activation of bypass signaling pathways is another important acquired resistance mechanism. Studies show that patients progressing after KRAS G12C inhibitor treatment exhibit MET amplification, NRAS activating mutations, BRAF mutations, MAP2K1 mutations, and oncogenic fusion events involving RET, ALK, and FGFR3. These alterations bypass the inhibited KRAS G12C by activating downstream or parallel signaling pathways. Furthermore, loss-of-function mutations in tumor suppressor genes such as NF1 and PTEN also contribute to resistance.

(3) Histologic Transformation

In some lung adenocarcinoma patients, histologic transformation to squamous cell carcinoma has been observed, suggesting tumor cells evade targeted drug inhibition by altering histologic phenotypes. This phenotypic plasticity adds a new dimension to resistance mechanism research.

3. Combination Therapy Strategies to Overcome Resistance

Given the difficulty of single-agent KRAS G12C inhibitors addressing complex resistance mechanisms, combination therapy has become a primary direction in clinical exploration. Rational drug combinations based on resistance mechanisms may delay resistance onset and reverse established resistance.

(1) Rationale for Combining with Immune Checkpoint Inhibitors

KRAS-mutant lung cancers are often associated with smoking history and exhibit high tumor mutational burden (TMB), a positive predictor of immune checkpoint inhibitor efficacy. Meanwhile, KRAS signaling is thought to contribute to an immunosuppressive tumor microenvironment, and KRAS inhibition may temporarily relieve this state, creating favorable conditions for T-cell activation. Preclinical studies show that combining PD-1 inhibitors with KRAS G12C inhibitors enhances CD8-positive T-cell infiltration and synergistically inhibits tumor growth.

(2) Clinical Evidence for Combination Therapy

A Phase Ib study evaluated the safety and efficacy of combining KRAS G12C inhibitors with PD-(L)1 inhibitors in advanced KRAS G12C-mutated NSCLC. The study enrolled 58 patients previously untreated with KRAS G12C inhibitors, exploring concurrent and sequential dosing models. Results showed that the concurrent dosing group had significantly higher treatment-related adverse events, particularly elevated liver enzymes, with ≥Grade 3 adverse events exceeding 75%. In contrast, the sequential dosing group (KRAS G12C inhibitor monotherapy followed by PD-(L)1 inhibitor combination) had lower overall adverse events and hepatotoxicity rates, with better tolerability. Efficacy-wise, the overall objective response rate (ORR) was 29%, disease control rate (DCR) was 83%, and median duration of response reached 17.9 months. This study suggests that combining immune checkpoint inhibitors has synergistic antitumor potential, but optimizing dosing sequence and schedules is critical for toxicity control.

4. Application Prospects of Targeted Protein Degradation in Overcoming Resistance

With the rapid development of targeted protein degradation technologies (e.g., PROTAC), strategies inducing KRAS G12C protein degradation offer new avenues to overcome resistance. Unlike traditional occupancy-driven inhibitors, protein degraders recruit target proteins to E3 ubiquitin ligase complexes (e.g., CRBN, VHL), enabling ubiquitination and proteasomal degradation, thereby completely eliminating KRAS G12C's oncogenic function.

Among research tools, the Human KRAS G12C & CRBN Binding Assay Kit (GDP-loaded) can evaluate interactions between KRAS G12C protein and E3 ligase ligand-target protein chimeras. Based on the conformational features of KRAS G12C protein in its GDP-bound state, this kit mimics the process of targeted degraders recruiting CRBN ligase, providing a standardized detection platform for screening and optimizing KRAS G12C degraders. By quantitatively assessing KRAS G12C-CRBN binding activity, it effectively evaluates candidate degradation molecules' targeting efficiency and synergy, offering experimental support for developing novel resistance-overcoming strategies.