Advances in immune checkpoint inhibitors therapy for small cell lung cancer

Mechanisms of immunotherapy resistance in small cell lung cancer

Small-cell lung cancer (SCLC) is an aggressive neuroendocrine tumor with a poor prognosis. Although the addition of immunotherapy to chemotherapy has modestly improved outcomes, most patients rapidly develop resistance. Resistance to immunotherapy can be broadly categorized into primary resistance and acquired resistance, as proposed by the Society for Immunotherapy of Cancer (SITC) consensus definition. Primary resistance occurs in the setting of failure to respond to immune checkpoint inhibitors (ICIs), while acquired resistance develops after initial response. The mechanisms of acquired and primary resistance to ICI are not well understood in SCLC, denoting an area of critical unmet need. Both intrinsic and extrinsic mechanisms play significant roles in immunotherapy resistance. Intrinsic mechanisms include defects in antigen presentation, mutations in key genes, reduced tumor immunogenicity, and epigenetic alterations. Extrinsic mechanisms involve the tumor microenvironment (TME), which is a complex interplay of both tumor- and immunosuppressive immune cells, vasculature, and microbiome. An understanding of these resistance mechanisms is crucial for developing novel therapeutic strategies to advance effective immunotherapy in patients with SCLC, a critical area of unmet need.

Immunotherapy for small cell lung cancer: the current state and future trajectories

Small cell lung cancer (SCLC) constitutes approximately 10% to 15% of all lung cancer diagnoses and represents a pressing global public health challenge due to its high mortality rates. The efficacy of conventional treatments for SCLC is suboptimal, characterized by limited anti-tumoral effects and frequent relapses. In this context, emerging research has pivoted towards immunotherapy combined with chemotherapy, a rapidly advancing field that has shown promise in ameliorating the clinical outcomes of SCLC patients. Through originally developed for non-small cell lung cancer (NSCLC), these therapies have extended new treatment avenues for SCLC. Currently, a nexus of emerging hot-spot treatments has demonstrated significant therapeutic efficacy. Based on the amalgamation of chemotherapy and immunotherapy, and the development of new immunotherapy agents, the treatment of SCLC has seen the hoping future. Progress has been achieved in enhancing the tumor immune microenvironment through the concomitant use of chemotherapy, immunotherapy, and tyrosine kinase inhibitors (TKI), as evinced by emerging clinical trial data. Moreover, a tripartite approach involving immunotherapy, targeted therapy, and chemotherapy appears auspicious for future clinical applications. Overcoming resistance to post-immunotherapy regimens remains an urgent area of exploration. Finally, bispecific antibodies, adoptive cell transfer (ACT), oncolytic virus, monotherapy, including Delta-like ligand 3 (DLL3) and T cell immunoreceptor with Ig and ITIM domains (TIGIT), as well as precision medicine, may present a prospective route towards achieving curative outcomes in SCLC. This review aims to synthesize extant literature and highlight future directions in SCLC treatment, acknowledging the persistent challenges in the field. Furthermore, the continual development of novel therapeutic agents and technologies renders the future of SCLC treatment increasingly optimistic.

Predictive Signatures for Responses to Checkpoint Blockade in Small-Cell Lung Cancer in Second-Line Therapy Do Not Predict Responses in First-Line Patients

Although immune checkpoint blockade (ICB) is currently approved for the treatment of extensive-stage small-cell lung cancer (SCLC) in combination with chemotherapy, relatively few patients have demonstrated durable clinical benefit (DCB) to these therapies. Biomarkers predicting responses are needed. Biopsies from 35 SCLC patients treated with ICB were subjected to transcriptomic analysis; gene signatures were assessed for associations with responses. Twenty-one patients were treated with ICB in the first-line setting in combination with platinum-based chemotherapy; fourteen patients were treated in the second-line setting with ICB alone. DCB after ICB in SCLC in the second-line setting (3 of 14 patients) was associated with statistically higher transcriptomic levels of genes associated with inflammation (p = 0.003), antigen presentation machinery (p = 0.03), interferon responses (p < 0.05), and increased CD8 T cells (p = 0.02). In contrast, these gene signatures were not significantly different in the first-line setting. Our data suggest that responses to ICB in SCLC in the second-line setting can be predicted by the baseline inflammatory state of the tumor; however, this strong association with inflammation was not seen in the first-line setting. We postulate that chemotherapy alters the immune milieu allowing a response to ICB. Other biomarkers will be needed to predict responses in first-line therapy patients.

ES-SCLC Patients with PD-L1+ CTCs and High Percentages of CD8+PD-1+T Cells in Circulation Benefit from Front-Line Immunotherapy Treatment

SCLC is an aggressive cancer type with high metastatic potential and bad prognosis. CTCs are a valuable source of tumor cells in blood circulation and are among the major contributors to metastasis. In this study we evaluated the number of CTCs that express PD-L1 in treatment-naïve ES-SCLC patients receiving ICI in a front-line setting. Moreover, we explored the percentages of different immune T-cell subsets in circulation to assess their potential role in predicting responses. A total of 43 patients were enrolled-6 of them with LS-SCLC, and 37 with ES-SCLC disease. In addition, PBMCs from 10 healthy donors were used as a control group. Different T-cell subtypes were examined through multicolor FACS analysis and patients' CTCs were detected using immunofluorescence staining. SCLC patients had higher percentages of PD-1-expressing CD3+CD4+ and CD3+CD8+ T-cells, as well as elevated PD-1 protein expression compared to healthy individuals. Additionally, in ES-SCLC patients, a positive correlation between CD3+CD8+PD-1+ T-cells and PD-L1+ CTCs was detected. Importantly, patients harboring higher numbers of CD3+CD8+PD-1+ T-cells together with PD-L1+CTCs had a survival advantage when receiving front-line immunotherapy. Thus, this study proposes, for first time possible, immune cell-CTCs interaction, as well as a potential novel clinical biomarker for ICI responses in ES-SCLC patients.

Advances in immune checkpoint inhibitors therapy for small cell lung cancer

BACKGROUND

As one of the most aggressive neuroendocrine tumors, small cell lung cancer (SCLC) has the most disappointing prognosis of all lung cancers. Although SCLC responds well to initial chemotherapy, the majority of patients experience disease recurrence within one year, and patient survival is poor. It is still necessary to explore the application of ICIs in SCLC since the beginning of the road to immunotherapy, which broke the 30-year treatment deadlock of SCLC.

METHODS

We searched PubMed, Web of Science, and Embase with search terms such as "SCLC", "ES-SCLC", "ICIs", and "ICBs", and categorized and summarized the relevant literature obtained, and we compiled the latest progress about the application of ICIs in SCLC.

RESULTS

We listed 14 clinical trials on ICIs, including 8 clinical trials on first-line SCLC treatment, 2 clinical trials on second-line SCLC treatment, 3 clinical trials on third-line SCLC treatment, and 1 clinical trial on SCLC maintenance treatment.

CONCLUSION

ICIs in combination with chemotherapy can improve OS in SCLC patients, but the extent to which SCLC patients can benefit from ICIs is limited, and ICIs' combination treatment strategies still need to be continuously explored.