Identification of subtypes of KEAP1/NFE2L2-mutant lung adenocarcinoma
As previously stated in the Methods section, we integrated five data subtypes and clustered 89 KEAP1/NFE2L2-mutant lung adenocarcinoma patients into two subgroups (P1 and P2 groups, Fig. 1A). Similarly, two subtypes were identified in 20 lung adenocarcinoma cell lines harboring KEAP1/NFE2L2-mutations (C1 and C2 groups, Fig. 1C). Clustering with two classes in both patients and cell line samples showed the highest silhouette values (silhouette = 0.93 and 0.83, Fig. 1B and 1D).
Clinicopathological differences of the KEAP1/NFE2L2-mutant subtypes
A significant difference was found in the smoking status of patients in P1, P2 and wild-type groups (P = 0.033, Table 1). The P2 group consisted of the highest proportions of current smokers and reformed smokers for ≤ 15 years, while P1 groups consisted of more reformed smokers ≥ 15 years (Table 1). No significant difference of pathological stage was found among patients with P1, P2 and KEAP1/NFE2L2 wild-type lung adenocarcinoma (P = 0.233, Table 1). Mutant samples contained a significantly higher proportion of female patients (P = 0.003, Table 1). Survival analysis showed no significant difference in the overall survival between subgroups of KEAP/NFE2L2-mutant and wild-type lung adenocarcinoma (P = 0.212, Fig. 2A). However, the P2-mutant subgroup was associated with a significantly worse survival than the P1 subgroup (P = 0.020, Fig. 2B).
Table 1
Baseline characteristics of wild type and KEAP1/NFE2L2 mutant subgroups of lung adenocarcinoma samples in TCGA
| Wild type | Mutant P1 group | Mutant P2 group | P-value |
Age | 65.3 ± 9.9 | 67.6 ± 7.1 | 64.3 ± 11.2 | |
Gender | | | | 0.003 |
Female | 234 (57.2) | 12 (46.2) | 22 (34.9) | |
Male | 175 (42.8) | 14 (53.8) | 41 (65.1) | |
Pathological Stage | | | | 0.233* |
Stage I | 226 (55.3) | 14 (53.8) | 30 (47.6) | |
Stage II | 99 (24.2) | 5 (19.2) | 17 (27.0) | |
Stage III | 67 (16.4) | 5 (19.2) | 9 (14.3) | |
Stage IV | 15 (3.7) | 2 (7.7) | 7 (11.1) | |
Unknown | 2 (0.5) | 0 (0) | 0 (0) | |
Smoking Status | | | | 0.033* |
Non-smoker | 66 (16.1) | 1 (3.8) | 5 (7.9) | |
Current smoker | 96 (23.5) | 5 (19.2) | 16 (25.4) | |
Reformed smoker (> 15 years) | 105 (25.7) | 12 (46.2) | 11 (17.5) | |
Reformed smoker (≤ 15 years) | 127 (31.1) | 8 (30.8) | 28 (44.4) | |
Unknown | 15 (3.7) | 0 (0) | 3 (4.8) | |
* Samples with unknown information were removed when comparisons were conducted among groups. |
Basic biological features of KEAP1/NFE2L2-mutant subtypes
GSEA was performed in KEAP1/NFE2L2-mutant subtypes in both patients and cell line cohorts. As shown in Fig. 3A and 3B, P2 and C2 subtypes were both enriched in pathways, such as KRAS signaling, IL2/STAT5 signaling, apoptosis, and interferon alpha and gamma response. GSEA showed similarities between P2 and C2 subtypes, validating the integration and clustering to some degree.
Moreover, both P2 and C2 subtypes were associated with regulations of immune-related pathways, such as activations of T cells and macrophages (Supplement Fig. 1A an 1B). The results revealed that P2 and C2 subgroups displayed active immune pathways compared with P1 and C1 subgroups.
The P2 subgroup was found associated with higher proportions of TP53 (P < 0.001), PCLO (P = 0.011), NF1 (P = 0.029) and PTPRT (P = 0.040) mutations, while the P1 subgroup may have more patients with STK11 (P = 0.008) mutation (Supplement Table 1). However, we did not validate the mutational associations in lung adenocarcinoma cell lines owing to the small sample size.
Immunological features of the KEAP1/NFE2L2-mutant subtypes
The tumor-infiltrating lymphocyte fractions were compared according to Saltz et al stratified by the mutation status [28]. Compared with the wild-type samples, lung adenocarcinoma harboring KEAP1/NFE2L2 had a significantly lower lymphocyte fractions (P = 0.001, Fig. 4A). Subgroup analyses revealed that the P2 group exhibited significantly higher lymphocyte fractions compared with the P1 group (P < 0.001, Fig. 4A). We also observed that significant differences of ESTIMATE scores exist among three groups, in which P1 was linked to the lowest score (Fig. 4B, 4C and 4D). Based on TIMER, a significant decrease was found in the infiltrating levels of CD4 + T cells (P < 0.001), CD8 + T cells (P = 0.011), B cells (P < 0.001), neutrophils (P < 0.001), dendritic cells (P < 0.001), and macrophages (P = 0.008) in the mutant subgroup. (Fig. 3B). Moreover, the P1 subgroup was associated with reduced infiltrations of B cells (P = 0.017), CD4 + T cells (P = 0.001), neutrophils (P = 0.002) and dendritic cells (P = 0.006) (Fig. 4E). Furthermore, P2 subtype was associated with higher number of immunogenic mutations than P1 group (Fig. 4F).
Smoking-related genomic features of the KEAP1/NFE2L2-mutant subtypes of lung adenocarcinoma
First, the methylation levels were compared across mutant subgroups. 84,700 and 64,204 differentially hypermethylated probes were found in the P1 and P2 groups, respectively (Fig. 5A). Meanwhile, 8,981 hypermethylated probes were found in the C1 group, while 5,933 hypermethylated probes were found in the C2 group (Fig. 5B). Next, unique smoking-related probes were extracted according to Vaz et al [31]. Both P2 and C2 groups displayed a similar trend of hypermethylation compared with the P1 and C1 groups (Fig. 5C-D). The results suggested that smoking-related epigenomic alterations might play essential roles in KEAP1/NFE2L2-mutant subgroups. The epigenomic similarities also confirmed a potential resemblance between patient and cell line mutant subsets.
Second, we assessed the somatic mutational patterns of all lung adenocarcinoma patients and obtained four distinctive signatures (Supplement Fig. 2A). Among them, signature 2 subgroup (W2) was highly similar to Signature 4 and 29 of thirty known somatic mutational signatures in the COSMIC database, which were closely associated with smoking and tobacco chewing (coefficient of cosine similarity = 0.805 and 0.740). Then, we compared the normalized activities of the identified W2 mutational signature between KEAP1/NFE2L2-mutant subgroups. We found that P2 subset had significantly higher activities of W2 signature than P1 subset (Supplement Fig. 2B, P = 0.004), which further indicated possible different roles of smoking in the mutant subgroups.
Screening for compounds with potential sensitivity to the KEAP1/NFE2L2-mutant subtypes
After characterizing the clinical and biological features of the mutant subtypes, possible cancer-associated drugs which were sensitive to each subtype were explored. More than 400 drugs or compounds were tested on KEAP1/NFE2L2-mutant or wild-type lung adenocarcinoma cell lines in GDSC. This study aimed to target cancer-associated drugs or compounds with potential specific sensitivity to C1 or C2. 38 drugs, which were potentially sensitive to the C2 KEAP1/NFE2L2-mutant subtype, were discovered (Supplement Table 2). Although the criteria were adjusted, only one C1-specific compound was identified (Supplement Table 2).
C2-specific drugs were found to be mainly composed of the following types. First, inhibitors of the PI3K/Akt signaling pathways, such as afuresertib, AZD8186 and AMG-319 might be sensitive to the C2 KEAP1/NFE2L2-mutant subgroup compared with the C1 and wild-type groups (Fig. 6 and Supplement Table 2). Second, inhibitors of IGF1R signaling, such as BMS-536924, linsitinib and NVP-ADW742, showed better efficacy in the C2 subset (Fig. 6 and Supplement Table 2). Moreover, drugs that target Wnt and MAPK/Erk signaling pathways were more toxic to the C2 group (Fig. 6 and Supplement Table 2). In addition, chemotherapy drugs, such as docetaxel, epothilone B and vinorelbine were found to preferentially kill the cells in the C2 subgroup (Fig. 6 and Supplement Table 2). Nevertheless, only one compound (EHT-1864) was found that might be sensitive to the C1 subset compared with C2 and wild-type cell lines (Fig. 6 and Supplement Table 2). The selected compound, EHT-1864, is an inhibitor of Rac1, Rac2 and Rac3 and mediated the reorganization of actin cytoskeleton.