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Lurasidone is an antipsychotic drug clinically used for the treatment of schizophrenia and bipolar disorder. During a mechanism‐based forced degradation study of lurasidone, two novel degradation products were observed under free radical‐mediated oxidative (via AIBN) and solution photolytic conditions. The structures of the two novel degradants were identified through an approach combining HPLC, LC‐MSn (n = 1, 2), preparative HPLC purification and NMR spectroscopy. The degradant formed under the free radical‐mediated condition is an oxidative degradant with half of the piperazine ring cleaved to form two formamides; a mechanism is proposed for the formation of the novel N,N′‐diformyl degradant, which should be readily applicable to other drugs that contain a piperazine moiety that is widely present in drug molecules. The degradant observed under the solution photolytic condition is identified as the photo‐induced isomer of lurasidone with the benzisothiazole ring altered into a benzothiazole ring.

Background and Aims: Purines are building blocks for the cellular genome, and excessive purine nucleotides are seen in tumors. However, how purine metabolism is dysregulated in tumors, and impacting tumorigenesis remains elusive. Approach and Results: Transcriptomic and metabolomic analyses of purine biosynthesis and purine degradation pathways were performed in the tumor and associated nontumor liver tissues obtained from 62 patients with HCC, one of the most lethal cancers worldwide. We found that most genes in purine synthesis are upregulated, while genes in purine degradation are inhibited in HCC tumors. High purine anabolism is associated with unique somatic mutational signatures linked to patient prognosis. Mechanistically, we discover that increasing purine anabolism promotes epitranscriptomic dysregulation of DNA damage repairing (DDR) machinery through upregulating RNA N6-methyladenosine (m6A) modification. High purine anabolic HCC is sensitive to DDR-targeting agents but not to standard HCC treatments, correlating with the clinical outcomes in 5 independent HCC cohorts containing 724 patients. We further showed that high purine anabolism determines the sensitivity to DDR-targeting agents in 5 HCC cell lines in vitro and in vivo. Conclusions: Our results reveal a central role of purine anabolism in regulating DDR, which could be therapeutically exploited in HCC.

Introduction Purines are building blocks for genomics and the abundance of purine nucleotides is controlled by purine synthesis and purine degradation. Imbalance of purine nucleotide pool in tumors has been shown, but how synthesis and degradation of purine integrates in tumors has not been well characterized. Hepatocellular carcinoma (HCC) is the most common liver cancer with a high mortality rate and limited treatments. Aberrant purine metabolism was observed in HCC, but the functional status of global purine metabolism in HCC and how that drive HCC fitness and therapeutic response remain unclear. Method HCC-specific purine metabolic changes were identified from the transcriptomic and metabolic data of tumor and paired non-tumor liver tissues obtained from 62 HCC patients from Thailand (discovery cohort) and validated in an additional 672 HCC with different race/ethnicities and etiologies. Correlation analysis of purine metabolic alteration and tumor-associated genomic, transcriptome and metabolome were conducted. The impacts of purine metabolism on HCC survival and therapeutic vulnerability were investigated. Biological functions of purine metabolic alterations were assessed in vitro and in vivo on multiple HCC cell lines. Results Using multi-omics integrative analyses, we found a tumor-specific activation of purine anabolism, induced by upregulation of purine de novo biosynthesis and inhibition of purine degradation, in HCC. A high purine anabolic status was associated with dysregulation of the DNA damage repairing (DDR) machinery in HCC, accompanied by unique somatic mutational signatures linked to patient prognosis. By examining drug responses to 180 molecular targeted agents in HCC cells, we found that increasing purine anabolism induced a therapeutic vulnerability of HCC to DDR targeting agents. Mechanistically, we found that excessive purine metabolites induced N6-methyladenosine (m6A) modification on DTL, a DDB1 cullin4 associated factor, thereby delaying the degradation of DTL mRNA transcriptomic remodeling of the DDR machinery and tumor fitness. Experimentally, we demonstrated that suppressing purine anabolism or exposing to DDR targeting agent, such as berzosertib, inhibited the growth of HCCs with high purine anabolism in vitro and in vivo. Conclusion Our study suggests that targeting purine anabolism or DDR may represent as attractive strategies in patients with high purine anabolic HCCs, and purine anabolic status could be a valuable biomarker to allocate systemic treatments for patients with advanced HCC. Citation Format: Man-Hsin Hung, Ching Wen Chang, Kathy Cheng Wang, Jittiporn Chaisaingmongkol, Mathuros Ruchirawat, Tim F. Greten, Xin Wei Wang. Activation of purine anabolism creates a therapeutic vulnerability in hepatocellular carcinoma via m6A-mediated epitranscriptomic regulation. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3683.