Small cell lung cancer, accounting for approximately 15% of all lung cancers, represents one of the most challenging malignancies in oncology. Characterized by rapid growth, early metastasis, and near-universal recurrence after initial treatment, SCLC has a five-year survival rate of less than 7%. Despite decades of research, therapeutic advances have lagged behind those in non-small cell lung cancer and many other cancer types.

The molecular landscape of SCLC is dominated by near-universal inactivation of TP53 and RB1 tumor suppressor genes. However, these alterations, while defining the disease, do not immediately suggest therapeutic targets. The identification of actionable drivers in SCLC has proven elusive, with targeted therapies showing limited efficacy to date. This therapeutic drought underscores the need for deeper understanding of SCLC biology.

Alternative splicing, the process by which different mRNA isoforms are generated from a single gene, represents an important layer of gene regulation that is frequently dysregulated in cancer. Splicing variants can alter protein function, localization, and interactions, contributing to malignant phenotypes. The systematic characterization of splicing variants in SCLC has been limited, leaving a gap in understanding of this disease feature.

Focal adhesion kinase (FAK), a non-receptor tyrosine kinase involved in cell adhesion, migration, and survival signaling, has been implicated in multiple cancer types. FAK overexpression and activation correlate with poor prognosis in various malignancies. However, the role of FAK splicing variants in cancer, and specifically in SCLC, has not been well characterized.

This study identified novel FAK splicing variants that are preferentially expressed in SCLC compared to normal lung tissue and non-small cell lung cancer. These variants result from alternative exon inclusion or exclusion, generating FAK proteins with altered functional properties. The splicing variants showed enhanced kinase activity and distinct subcellular localization patterns compared to canonical FAK.

Functional studies demonstrated that the FAK splicing variants promote SCLC cell proliferation, migration, and invasion. Knockdown of the variants impaired tumor growth in vitro and in vivo, while overexpression enhanced malignant phenotypes. These effects were mediated through activation of downstream signaling pathways including PI3K/AKT, MAPK, and STAT3.

Importantly, the FAK splicing variants were found to confer resistance to chemotherapy and radiation, the mainstay treatments for SCLC. Cells expressing high levels of the variants showed reduced apoptosis following treatment, while variant knockdown sensitized cells to therapy. This finding suggests that FAK splicing variants contribute to treatment resistance, a hallmark feature of SCLC.

Therapeutic targeting of FAK splicing variants was explored using small molecule FAK inhibitors. Treatment with these agents effectively inhibited variant kinase activity and sensitized SCLC cells to chemotherapy. Combination approaches pairing FAK inhibitors with standard chemotherapy showed synergistic effects in preclinical models, supporting further investigation of this strategy.

The clinical implications of these findings are significant. First, FAK splicing variant expression could serve as a biomarker to identify patients likely to benefit from FAK-targeted therapy. Second, FAK inhibitors, several of which are in clinical development, could be repurposed for SCLC treatment. Third, understanding splicing regulation in SCLC could reveal additional therapeutic targets.

Several questions remain for future investigation. The mechanisms driving altered splicing in SCLC are not fully understood and may involve mutations or altered expression of splicing factors. The relationship between FAK splicing variants and other molecular features of SCLC, such as neuroendocrine differentiation, warrants exploration. Clinical trials will be needed to validate the therapeutic potential of FAK inhibition in SCLC.
DOI
10.1007/s11684-026-1215-1