SCLC, a highly lethal type of cancer, is primarily characterized by early invasion and an extreme sensitivity to primary chemotherapy. While it initially responds well to treatment, nearly all patients eventually develop resistance, resulting in the progression of the disease. In this study, we have unveiled two distinct groups based on the expression of 7 genes related to sialylation (Sialylation-Related Genes – SRGs), which also possess prognostic value. These two groups exhibit contrasting patterns in terms of immune infiltration and SRG expression. Analysis reveals that cluster A demonstrates a higher presence of immune cells and longer survival time. Furthermore, we have discovered two clusters of DEGs (Differentially Expressed Genes) related to sialylation that are also strongly correlated with immune activation. Lastly, we have developed a scoring system, known as SS (Sialylation Score), which allows for individualized prognosis and precise treatment guidance for patients with SCLC.
In recent years, the field of cancer treatment has witnessed a remarkable diversification of strategies. One such advancement is the development of immune checkpoint inhibitors (ICIs), which have shown unprecedented progress in targeting and eliminating cancer cells by harnessing the power of the body’s own immune system to enhance anti-tumor immunity[23]. In recent years, immune checkpoint inhibitors (ICIs) targeting programmed death-1 (PD-1), programmed death-1 ligand (PD-L1), and cytotoxic T lymphocyte antigen-4 (CTLA-4) have been developed to block the immune regulatory checkpoints present on tumor cells and immune cells. This strategy has shown significant efficacy in the treatment of non-small cell lung cancer (NSCLC), leading to the approval of certain ICIs for clinical use [24, 25]. Although the use of ICIs has improved the survival status of SCLC patients, it is only a subset of patients benefits from immunotherapy[4, 26–28]. High tumor mutational burden (TMB) may correlate with immunotherapy response in SCLC[29]. There is increasing recognition that discrete molecular subtypes of SCLC exist in preclinical models of the disease that may differ in their response to different therapies, providing new perspectives for the treatment of SCLC[30]. In our analysis, patients with high and low sialylation scores showed significant differences in immune cell infiltration and immune checkpoint gene expression, suggesting that identification of the distinct subtypes of sialylation may help us identify patients with SCLC who may benefit from treatment with ICIs.
According to a recent investigation, the sialoglycan-siglec axis emerges as a novel immune checkpoint with potential for regulating innate and adaptive immune responses against cancerous growths[31]. In advanced solid tumors, molecules that block siglecs, such as antibodies against siglec-15, are considered promising for normalising the immune system[32, 33]. In addition, other investigators have shown that local removal of sialic acids in the tumor microenvironment leads to increased infiltration of NK and infiltration of NK and cytotoxic T cells, while reducing suppressive myeloid cells[34]. Siglec-9 has also been found on effector memory T-cell subsets in the tumor microenvironment, suggesting that sialic acid removal may affect T-cell function[35]. Zhou et al. have developed a sialylation lncRNA-based signature for predicting immune landscape and chemotherapeutic response to guide the prognosis for patients with colorectal cancer[9]. We have successfully developed a sialylation scoring system for the identification of patients who may benefit from immunotherapy as a basis for further studies, implying that sialylation-related genes were potential targets for SCLC therapy.
Despite the new insights, the present study has several limitations. Firstly, it is essential to conduct further independent cohorts focusing on immunotherapy to strengthen the robustness and consistency of the SS prognosis. Secondly, it is crucial to conduct additional in vivo and in vitro experiments to validate the function of regulatory molecules responsible for sialylation in SCLC. Lastly, given that this study mostly relied on retrospective data sourced from online databases, prospective double-blind trials involving large sample sizes and multi-centers are needed for future validation and confirmation.
In summary, this study extensively examined the relationship between sialylation and ICI in SCLC. Diving into the various subtypes of sialylation will enhance understanding of SCLC’s diversity. By creating a quantification process for sialylation patterns, the SS has the potential to serve as a robust biomarker for evaluating prognosis and predicting immunotherapy responses. This research’s outcomes have paved the way forward for determining sialylation immunophenotypes, prognostic forecasting, and providing personalized immunotherapy in SCLC.