Bladder cancer (BCa) remains a significant cause of cancer-related morbidity and mortality globally (Bray et al., 2024). For patients with advanced or metastatic disease, platinum-based combination chemotherapy, with cisplatin as the cornerstone drug, is the first-line standard of care (von der Maase et al., 2000). While a subset of patients responds favorably, the majority develops innate or acquired drug resistance, leading to disease progression and poor survival outcomes (Lenis et al., 2020). This clinical challenge has driven extensive research into the molecular mechanisms underpinning cisplatin resistance. Prior studies have focused on genomic alterations and cellular processes like reduced drug influx, increased drug efflux, and enhanced detoxification (Gosland et al., 1996). However, these mechanisms do not fully account for the rapid and adaptive nature of drug resistance, suggesting the involvement of more dynamic regulatory layers.

The gap in understanding anticancer drug resistance is increasingly being addressed by the field of epigenetics. Epigenetic dysregulation provides a versatile and plastic framework for cancer cells to adapt to therapeutic stress without requiring permanent genetic mutations (Dawson and Kouzarides, 2012). Key mechanisms include aberrant DNA methylation that silences tumor suppressor genes (Li et al., 2023), and post-translational modifications (PTMs) of histones—such as acetylation (Xie et al., 2024), methylation (Lee et al., 2020), and lactylation (Li et al., 2024a)—that alter chromatin accessibility and gene expression programs. These changes can promote a drug-resistant state by upregulating DNA damage repair pathways, enhancing anti-apoptotic signals, and inducing a drug-tolerant persister phenotype (Li et al., 2023). The reversible nature of these epigenetic marks makes them particularly attractive therapeutic targets, as their modulation offers a strategy to “re-sensitize” tumor cells to conventional chemotherapy.

Among the various epigenetic targets, histone deacetylases (HDACs) have been particularly promising. HDACs remove acetyl groups from lysine residues, leading to chromatin condensation and transcription repression (Pinkerneil et al., 2017; Zhang et al., 2024a). Their overexpression in cancers is associated with poor prognosis and therapy resistance (Hai et al., 2022; Singh et al., 2022). Entinostat, a U.S. Food and Drug Administration (FDA)-approved class I-selective HDAC inhibitor, has shown a potent anti-tumor activity (Baretti et al., 2024; Ny et al., 2021; Roussos Torres et al., 2024; Xu et al., 2023) and a synergistic efficacy with cisplatin in various solid tumors (Huang et al., 2018; Schelch et al., 2023; Solta et al., 2023). While this synergy suggested a strategy to overcome drug resistance, the precise molecular cascade initiated by HDAC inhibition remained a central question.

The precise regulation of gene expression is profoundly influenced by histone PTMs (Zaib et al., 2022). While the roles of canonical modifications such as acetylation (Gallinari et al., 2007; Gil et al., 2017; Miziak et al., 2024) and methylation (McCabe et al., 2017; Song et al., 2016) have been extensively studied in cancer, a series of novel modifications driven by cellular metabolites have recently been discovered, significantly expanding the scope of epigenetics(Cao et al., 2024a). Among these, histone Kla has emerged as a mechanism that directly links cellular metabolism to the epigenome (Yu et al., 2024; Zhang et al., 2024b). Histone Kla entails the covalent attachment of lactate to lysine residues on histones (e.g., H3K9, H3K18, H4K12), a process distinct from, yet functionally analogous to, acetylation (Zhang et al., 2019). Crucially, the substrate for this modification—lactate—is directly derived from glycolysis. This positions histone lactylation as a real-time sensor of cellular metabolic state, particularly in cancer cells with a pronounced Warburg effect. Within this context, accumulated lactate is not merely a metabolic byproduct but is transformed into an active epigenetic signal. Through Kla, it directly initiates programs related to metabolic remodeling (Chen et al., 2024; Lu et al., 2024), immune responses (De Leo et al., 2024; Li et al., 2024b), and cell fate determination (Li et al., 2020; Rho et al., 2023). Given that the efficacy of cisplatin can be modulated by the metabolic and epigenetic landscape of cancer cells (Govoni et al., 2021), we hypothesized that targeting the histone Kla pathway could represent a novel therapeutic avenue to enhance cisplatin sensitivity in bladder cancer.

Dehydrogenase/reductase member 2 (DHRS2) is a poorly characterized member of the short-chain dehydrogenase/reductase superfamily. It functions as a tumor suppressor in certain cancers, potentially involved in retinoic acid metabolism and the cellular response to oxidative stress. The role of DHRS2 in BCa and chemotherapy response has not been explored (Li et al., 2021). Aldo-keto reductase family 1 member C3 (AKR1C3) (Li et al., 2024c, Penning, 2019) is a multifunctional enzyme that confers cisplatin resistance through several mechanisms: it protects cells against oxidative stress-induced apoptosis (Pan et al., 2022), and functions as a key androgen-synthesizing enzyme, converting weak androgens into more potent ligands for the androgen receptor (AR) (Detlefsen et al., 2023; Himura et al., 2024). AR signaling has been increasingly implicated in promoting BCa progression and chemoresistance (Chen et al., 2023; Chen et al., 2020; Elahi Najafi et al., 2023; Teramoto et al., 2021). The regulatory connection between DHRS2 and AKR1C3 had not been established.

Through an integrated approach employing BCa cell lines, xenograft models, and multi-omics analyses, we elucidated a novel epigenetic pathway underpinning the synergy of cisplatin and Entinostat. Our results demonstrate that Entinostat counteracts drug resistance by promoting H3K18la-mediated upregulation of DHRS2, which suppresses the expression of AKR1C3, a key enzyme in androgen synthesis. We validated the clinical relevance of this DHRS2–AKR1C3 axis, linking it to chemotherapy response and revealing a specific survival benefit for male patients, thus uncovering a critical sex-specific dimension in BCa treatment. These findings not only elucidate a new mechanism of action for HDAC inhibitors but also identify a novel predictive biomarker and a potential therapeutic target for overcoming cisplatin resistance.