m6A-associated lncRNAs and their prognostic values
The expression profiles of 24 common m6A genes and 14,056 lncRNAs were obtained by analysing 178 pancreatic adenocarcinoma samples from TCGA. Through the Pearson test, we screened 129 m6A-associated lncRNAs (Fig1A), which were used to derive 17 m6A-associated lncRNAs with prognostic value via co-expression analysis and univariate Cox regression analysis, the results of which are shown in the following figure (Fig1B).
TCGA cohort-based m6A-associated lncRNA model construction
To eliminate covariate collinearity and avoid overfitting of the prognostic model, LASSO regression analysis was performed for the 17 differentially expressed m6A-associated lncRNAs with prognostic value, revealing three lncRNAs that could be further analysed using multivariate Cox regression. Ultimately, m6A-lncRNAs were used to determine the prognosis of patients with pancreatic adenocarcinoma based on the expression values of three lncRNAs (AC092171.5, MEG9, and AC002091.1)(Fig1E). The genes showing high expression levels were AC092171.5 [hazard ratio (HR) = 0.439, 95% confidence interval (CI) = 0.197–0.976)], MEG9 (HR = 0.309, 95% CI = 0.114–0.838), AC002091.1 (HR = 0.522, 95% CI = 0.288–0.954). The Cox coefficients of the three lncRNAs were used for modelling to calculate the prognostic risk scores for each patient in TCGA cohort as follows: -(1.20237572230772 × expression level of AC092171.5) - (0.975350163451454 × expression level of MEG9) - (1.49408312354077 × expression level of AC002091.1). Multivariate Cox regression analysis,Cox univariate analysis and c-index curve showed that the risk scores were significantly associated with survival and independent of clinical parameters(Figure2A, B, C). Subsequently, all patients were divided into high- and low-risk groups based on the median risk scores(Fig3A, B). In the high-risk subgroup, the expression levels of AC092171.5, MEG9, and AC002091.1 were lower Compared to low-risk group(Fig3E). According to the survival curves, the overall survival rate was lower in the high-risk subgroup than in the low-risk subgroup. The ROC curves showed AUC values of 0.710, 0.745, and 0.838 at 1, 3, and 5 years, respectively(Fig3D). Therefore, the time-dependent ROC curves validated the prognostic value of the risk score.
Validation of test group-based m6A-lncRNA model
To validate the prediction reliability of the training group m6A-lncRNA, the 88 samples in the test group were divided into high- and low-risk subgroups based on their median risk scores, which were calculated as described for the training group cohort(Fig4A, B). In the risk curve, the survival rate of the high-risk gene group was lower than that of the low-risk gene group(Fig4C). In the heat map, the expression of risk genes was similar to that in the training group(Fig4E). In the survival curve, the survival time of the high-risk gene group was significantly shorter than that of the low-risk gene group. The AUC values at 1, 3, and 5 years in the time-dependent ROC curve were 0.688, 0.746, and 0.919, respectively.(Fig4D)
Tumour mutation load analysis
The tumour mutation burden (TMB) indices of high- and low-risk genes were calculated separately; as shown in the violin plot (Fig5A), the TMB of differed for high- and low-risk genes (P < 0.05), with a higher TMB in the high-risk group. The waterfall plot shows the top 30 mutation frequencies. In the high-risk group (Fig5B), mutations were detected in 61 of 70 samples; KRAS (71%), TP53 (64%), and SMAD4 (23%) showed the highest mutation frequencies. In the low-risk group (Fig5C), mutations were detected in 49 of 71 samples, with KRAS (41%), TP53 (45%), and SMAD4 (15%) showing the highest mutation frequencies. As shown in the figure (Fig5D), the survival rate of patients with a high TMB was lower than that of patients with a low TMB. Additionally, the mutation frequency of high-risk genes was greater than that of genes in the low-risk group, and the survival rate of the high-TMB+high-risk gene group was lowest, followed by the low-TMB+high-risk gene, high-TMB+low-risk gene, and low-TMB+low-risk gene groups (Fig5E).
Differences in immune function
We observed significant differences in immune-related functions between the high- and low-risk groups (Fig6A). As a practical tool for assessing anti-tumour immunity, HLA was significantly lower in the high-risk subgroup, indirectly indicating weaker HLA function in this subgroup; TypeII IFN Reponse was lower in the high-risk group than in the low-risk group. In addition, Cytolytic activity, Inflammation-promoting, T cell co-inhibition, Check-point, and T cell co-stimulation showed lower expression in the high-risk group than in the low-risk group. As shown in the figure (Fig6B), the two groups were significantly different (P < 0.001), with higher TIDE scores in the high-risk than in the low-risk, indicating that the low-risk group has lower immune evasion potential and that immunotherapy has lower efficacy in the high-risk group.
Screening for potential drugs
Screening revealed eight potential therapeutic drugs which showed different sensitivities between high- and low-risk groups (P < 0.05): For ABT.888, ATRA, AP.24534, AG.014699, ABT.263, and axitinib, the IC50 in the low-risk group was less than that in the high-risk group (Fig7A-E), indicating that patients in the low-risk group were more sensitive to the drugs. For A.443654 and A.770041, the IC50 in the low-risk group was lower than that in the high-risk group, indicating that patients in the high-risk group are more sensitive to these drugs (Fig7F-J).