The molecular evolution of acquired resistance to targeted EGFR blockade in colorectal cancers

Abstract

Colorectal tumors that are wild-type (WT) for KRAS are often sensitive to EGFR blockade, but almost always develop resistance within several months of initiating therapy1,2. The mechanisms underlying this acquired resistance to anti-EGFR antibodies are largely unknown. This situation stands in marked contrast to that of small molecule targeted agents, such as inhibitors of ABL, EGFR, BRAF, and MEK, in which mutations in the genes encoding the protein targets render the tumors resistant to the effects of the drugs3–6. The simplest hypothesis to account for the development of resistance to EGFR blockade are that rare cells with KRAS mutations pre-exist at low levels in tumors with ostensibly WT KRAS genes. Though this hypothesis would seem readily testable, there is no evidence in pre-clinical models to support it, nor is there data from patients. To test this hypothesis, we determined whether mutant KRAS DNA could be detected in the circulation of 28 patients receiving monotherapy with panitumumab, a therapeutic anti-EGFR antibody. We found that nine of 24 (38%) patients whose tumors were initially KRAS WT developed detectable mutations in KRAS in their sera, three of which developed multiple different KRAS mutations. The appearance of these mutations was very consistent, generally occurring between five to six months following treatment. Mathematical modeling indicated that the mutations were present in expanded subclones prior to the initiation of panitumumab. These results suggest that the emergence of KRAS mutations is a mediator of acquired resistance to EGFR blockade and that these mutations can be detected in a non-invasive manner. Moreover, they explain why solid tumors develop resistance to targeted therapies in a highly reproducible fashion.

Detection of KRAS Mutations in Plasma DNA Using a fully Automated Rapid Detection System in Colorectal Cancer Patients

“…KRAS mutations were frequently detected in systemic metastatic cancers, and these were newly detected after acquired resistance to anti-EGFR antibody. Recently, mutation analysis using peripheral blood-socalled liquid biopsy-has been applied to colorectal cancer [9,10,[23][24][25]. In most published reports, quantitative PCR and BEAMing were used for detection with plasma DNA.…”

“…In addition, we confirmed that KRAS mutations were newly detected after acquired resistance to anti-EGFR antibody contained in chemotherapy, as other papers have reported. Since the first report of a patient with acquired resistance to cetuximab having newly detected KRAS mutation in cancer tissue, several papers have demonstrated acquired KRAS mutations, including mutations detected in plasma [8,10,11]. The mechanism of appearance of KRAS mutations after acquired resistance to anti-EGFR antibody has been assumed to be clonal selection from a minor population of pre-existing mutations or novel spontaneous mutations, but this mechanism has not been clarified.…”

“…In addition to the relationship with primary resistance, these mutations were also detected in patients who acquired resistance to anti-EGFR antibodies [8][9][10][11]. Mechanisms of acquired resistance to anti-EGFR antibodies include activation of an alternative pathway, such as MET/HGF or EGFR, or activation of RAS/RAF/MAPK mediated through the appearance of KRAS mutations [12][13][14].…”

PCR digitale en micro-compartiments

“…Trois échantillons plasmatiques contenant un allèle KRas muté présentaient une discordance avec le profil de mutations de la tumeur du patient [20]. Des mutations de l'oncogène KRas indétectables dans les tissus tumoraux avaient également pu être mises en évidence à partir de sérum par dPCR BEAMing [30], illustrant la capacité des techniques de dPCR à reflé-ter l'hétérogénéité clonale de la tumeur. DOSSIER TECHNIQUE REVUES cellules tumorales à des molécules inhibitrices de l'EGFR (gefitinib et erlotinib, deux inhibiteurs sélectifs de la tyrosine kinase de EGFR), alors que la mutation T790M est identifiée comme une mutation secondaire de résistance à ces mêmes molécules.…”

Targeted therapies in cancer and mechanisms of resistance

“…Thus, from the beginning, the tumor contains cells harboring genetic lesions that can sustain resistance to targeted therapies. As mentioned by Dr. Vogelstein in a recent paper, "resistance is a fait accompli and the time to recurrence is simply the interval required for the subclone to repopulate the lesion" [8]. The presence of genetic heterogeneity in the primary tumor may also explain the common finding of patients presenting, at relapse, different metastases, each bearing a diverse genetic alteration responsible for drug resistance.…”