Therapeutic strategies to overcome KRAS (OFF) inhibitors resistance
, by Alessia Mira and Marie-Julie Nokin
Alessia Mira is a postdoctoral fellow in Chiara Ambrogio’s lab, at the University of Torino (Italy). Her research centers on identifying the molecular mechanisms associated with resistance to RAS inhibitors in lung cancer focusing on drug tolerance and new therapeutic targets.
Marie-Julie Nokin is a former postdoctoral fellow of the Lab of David Santamaria and is now assistant professor at the University of Liege (Belgium). Her research focuses on identifying therapeutic vulnerabilities in drug persistent and resistant lung cancer.
Alessia Mira1 and Marie-Julie Nokin2
1: Department of Molecular Biotechnology and Health Sciences, Molecular Biotechnology Center, University of Torino, Torino, Italy.
2: Laboratory of Biology of Tumor and Development (LBTD), GIGA-Cancer, University of Liège, Liège, Belgium.
RMC-4998, a tri-complex inhibitor that selectively targets the active GTP-bound state of KRAS G12C (KRAS ON), is a potential therapeutic strategy to re-sensitize resistant cancer cells to KRAS OFF inhibition (sotorasib, adagrasib).
In the realm of driver oncogenes, KRAS has historically been considered ‘undruggable’ due to a lack of actionable binding sites within the mutant isoforms. Nevertheless, crucial advancements in drug design have recently led to the generation and clinical use of inhibitors that specifically target mutant KRAS in its inactive form ¬–KRAS(OFF) inhibitors sotorasib and adagrasib (1,2). However, the initial enthusiasm towards these new drugs rapidly diminished upon evidence of fast-emerging clinical resistance that highlighted the limitations of these therapies (3,4). While primary and acquired resistance have been identified, the full spectrum of mutations that drive tumor resistance remains largely unexplored, and the heterogeneity observed in patients suggests that we have just reached the tip of the iceberg. Additionally, non-genetic factors may explain the relapse in patients without detectable mutations. Preclinical studies had predicted that reactivation of MAPK signaling, marked by increased KRAS G12C-GTP loading or activation of wild-type RAS (KRAS, NRAS, HRAS), could serve as a complementary resistance mechanism (5–8). Recently, Araujo et al. described a transcriptional program supporting RAS inhibitor tolerance in vitro, and noted the presence of mucinous histological traits in KRAS G12C-mutant Non-Small Cell Lung Cancer (NSCLC) patients with poor responses to KRAS G12C inhibitors (9), supporting the notion that adaptive mechanisms of resistance are common/putative features occurring in the clinic and not a mere artifact of preclinical models, in accordance with our findings.
In this work, we demonstrated the existence of adaptive resistance to KRAS inhibitors in patients, and we explored potential new therapeutic strategies to overcome the reactivation of RAS signaling (10). Our study uncovered both acquired mutations—proven irrelevant for tumor recurrence—and adaptive mechanisms leading to increased wild-type KRAS-GTP loading. This signal adaptation contributed to resistance against KRAS(OFF) inhibitors, providing additional important evidence in support of RAS signaling reactivation as a mediator of resistance in patients. The concept of adaptive resistance as a potential driver of disease relapse was further validated through whole transcriptome sequencing of a series of paired patient samples taken before and after developing resistance to KRAS inhibitors. These samples lacked any obvious genomic resistance mechanisms, but we identified transcriptomic markers associated with resistance to KRAS inhibitors. Consistently, our KRAS(OFF)-resistant Patient-Derived Orthoxenograft (PDOX) cells exhibited a general increase in both wild-type and mutant KRAS expression, along with an increase in the active GTP-bound fraction, likely influencing both forms of KRAS. Notably, this adaptive mechanism developed quickly under the selective pressure of KRAS(OFF) inhibitor treatment, as the resistant cells reverted to a basal state shortly after the drug was withdrawn in vitro.
How this adaptation is brought about in molecular terms and whether, in different tumors, mechanistically distinct adaptive responses converge on the reactivation of MAPK to restore cancer homeostatic signaling remain unclear. It is also unknown whether this putative KRAS signaling sweet-spot shows inter-tumor quantitative differences and if a similar concept could be applied to other downstream signaling effectors (11).
Nevertheless, by using the preclinical tool compound RMC-4998—a newly identified tri-complex inhibitor that specifically targets the active GTP-bound form of KRAS G12C—either alone or in combination with KRAS G12C(OFF) inhibitors, we show that targeting KRAS G12C(ON) is a promising therapeutic approach to restore sensitivity to KRAS inhibition in resistant lung adenocarcinoma (LUAD) and to overcome adaptive resistance. Our study provides a proof-of-concept for the efficacy of targeting the active (ON) state of KRAS, suggesting a new direction for developing treatments against KRAS-driven cancers. This therapeutic approach is currently undergoing clinical evaluation in patients carrying tumors that harbor KRAS G12C mutations (RMC-6291, Phase 1/1b NCT05462717). Considering the role of wild-type KRAS in this context, we can envision that newly developed panRAS inhibitors (12), such as RMC-6236 (NCT05379985), could achieve enhanced disease control.
Overall, our work adds crucial evidence that resistance to KRAS G12C inhibitors is extremely heterogeneous, involving both acquired and adaptive mechanisms leading to MAPK reactivation. By characterizing the specific dynamics that drive these different types of resistance, more precise treatment strategies for KRAS-mutant patients can be developed.