Dihydrotanshinone I inhibits PHGDH to suppress serine synthesis and remodel TME in NSCLC.

BACKGROUND

The strategy of limiting the availability of tumor cell phosphoglycerate dehydrogenase (PHGDH) has become a potential treatment for cancer. Modulation of the tumor-derived serine synthesis pathway to reprogram the tumor microenvironment represents a viable approach to optimize the efficacy of anti-tumor immunotherapy. However, currently no reliable PHGDH inhibitors of natural product origin have been approved for clinical use, and the precise pharmacological mechanisms underlying their biological activity have not yet been fully elucidated.

PURPOSE: This study aims to identify PHGDH inhibitors from natural products and elucidate the underlying anti-tumor pharmacological mechanisms.

METHODS

Multiple public databases were utilized to analyze the correlation between PHGDH and human non-small cell lung cancer (NSCLC) in this study. We took advantage of a natural compound library to perform the compound screening of PHGDH inhibitors. The binding capacity of DHT I to PHGDH was examined using molecular docking simulations, cellular thermal shift assay (CETSA), drug affinity responsive target stability (DARTS), and microscale thermophoresis (MST). Co-immunoprecipitation and western blotting assays were employed to investigate the regulatory effect of DHT I on PRMT1-mediated monomethylation of PHGDH. The roles of DHT I in PHGDH-mediated serine synthesis pathway in the lung cancer cells were determined through metabolomics analysis. Western blotting analysis was performed to examine the regulatory impact of DHT I on histone H3 lysine 4 methylation (H3K4me). Quantitative real-time PCR (qRT-PCR) and enzyme-linked immunosorbent assay (ELISA) were utilized to determine the effects of DHT I on the transcriptional and secretory levels of IL-10 and TGF-β. Co-culture assays of tumor cells and bone marrow-derived macrophages (BMDMs) were performed to investigate DHT I-mediated polarization of macrophages. Single-cell RNA sequencing (scRNA-seq) analysis was performed to elucidate the molecular mechanisms underlying DHT I-mediated suppression of lung cancer progression in a murine model. Combined administration of DHT I and anti-PD-1 was employed to evaluate the therapeutic efficacy of this combinatorial regimen for anti-tumor immunotherapy.

RESULTS

Elevated PHGDH expression and enzymatic activity were closely correlated with poor clinical prognosis in patients with NSCLC. DHT I was identified as a novel PHGDH inhibitor with therapeutic potential for NSCLC. DHT I bound to PHGDH at the Arg236 residue, which abrogated PRMT1-mediated methylation of PHGDH and consequently induced its functional inactivation. It also demonstrated that DHT I-mediated PHGDH inhibition reprograms the serine synthesis pathway in lung cancer cells, thereby reducing intracellular L‑serine and S-Adenosylmethionine (SAM) levels. DHT I downregulates H3K4me expression and suppresses the transcription of IL-10 and TGF-β, thereby modulating macrophage polarization in the tumor microenvironment. Furthermore, scRNA-seq analysis revealed that DHT-I-mediated reprogramming of tumor metabolism and alterations of the macrophage signature reversed the tumor immunosuppressive microenvironment, thereby potentiating the efficacy of anti-PD-1-based immunotherapy.

CONCLUSION

Collectively, our findings demonstrate that DHT I is a potent PHGDH inhibitor with the potential for further optimization as a candidate agent for combination with immunotherapy to suppress the progression of NSCLC.