Abstract: Oxaliplatin is a cornerstone platinum-based chemotherapeutic agent widely utilized in the treatment of various malignancies, particularly colorectal and gastric cancers. While its classical mechanism of action involves the formation of cytotoxic DNA crosslinks, recent research has illuminated its profound immunomodulatory capabilities. Oxaliplatin is now recognized as a potent inducer of immunogenic cell death (ICD), a specialized form of regulated cell death that stimulates robust innate and adaptive antitumor immune responses through the emission of damage-associated molecular patterns (DAMPs). This literature review synthesizes current knowledge on oxaliplatin, focusing on its pharmacological activity, molecular mechanisms driving ICD, and structure-activity relationships. Furthermore, it addresses the current clinical limitations of oxaliplatin, such as peripheral neuropathy and drug resistance, and explores future perspectives, including the development of novel Pt(IV) prodrugs, nanomedicine delivery systems, and synergistic combination therapies with immune checkpoint inhibitors to overcome immunosuppressive tumor microenvironments.
1. Introduction
Cisplatin, the first platinum-based anti-cancer therapy, paved the way for the development of subsequent platinum compounds, including carboplatin and oxaliplatin, designed to increase cytotoxicity and reduce side effects [5]. Oxaliplatin is a clinically effective tumoricidal platinum salt that has become a standard-of-care cornerstone in chemotherapy regimens for several carcinomas, most notably colorectal cancer (CRC) and gastric cancer [1][2][4]. Historically, the primary mode of action attributed to oxaliplatin was the induction of DNA damage [2]. However, contemporary immuno-oncology has revealed that the efficacy of oxaliplatin is not solely dependent on direct cytotoxicity but is heavily reliant on an intact host immune system and the induction of immunogenic cell death (ICD) [2][3]. Unlike cisplatin, which generally fails to induce pre-apoptotic calreticulin exposure, oxaliplatin is classified as a bona fide ICD inducer, making it a highly attractive candidate for combination with modern immunotherapies [1][3][4].
2. Pharmacological Activity
The pharmacological activity of oxaliplatin is dual-faceted, encompassing both direct genotoxic effects and indirect immunomodulatory functions. Upon entering the cell, oxaliplatin generates intra- and interstrand DNA adducts by crosslinking with specific base sequences, which leads to severe cellular stress and apoptosis [2][5]. Beyond DNA damage, oxaliplatin actively reverses the immunosuppressive tumor microenvironment (TME). It enriches the TME by promoting the infiltration of innate and adaptive immune cells, including CD8+ T cells, natural killer (NK) cells, and dendritic cells (DCs), while simultaneously depleting immunosuppressive populations such as tumor-associated macrophages (TAMs) and myeloid-derived suppressor cells (MDSCs) [1].
Interestingly, the full pharmacological efficacy of oxaliplatin is also dependent on the host's microbiota. Disruption of the microbiota with broad-spectrum antibiotics reduces oxaliplatin's cytotoxicity and the production of reactive oxygen species (ROS) by tumor-infiltrating myeloid cells, which are necessary for its antitumor effect [2]. Specific immunogenic ileal-residing bacteria, such as Bacteroides fragilis, have been shown to foster the immunostimulatory anticancer effects of oxaliplatin regimens [2].
3. Molecular Mechanism of Action
The hallmark of oxaliplatin's molecular mechanism in the context of immuno-oncology is its ability to trigger Immunogenic Cell Death (ICD). Oxaliplatin is classified as a Type I ICD inducer, meaning it primarily targets intracellular organelles (excluding the endoplasmic reticulum initially) and initiates signaling via subsequent ER stress responses [1]. This ER stress is critical for the spatiotemporal emission of damage-associated molecular patterns (DAMPs) from dying cancer cells [1][3].
Oxaliplatin induces three key links of the ICD pathway:
- Calreticulin (CRT) Exposure: ER stress causes the translocation of CRT to the cell surface, where it acts as a potent "eat me" signal by interacting with the low-density lipoprotein receptor-related protein 1 (LRP1) on DCs and macrophages, promoting the phagocytosis of tumor cells [1][3][4].
- ATP Release: Apoptotic cells actively or passively release ATP into the extracellular space, which functions as a short-range "find me" signal to recruit DCs and macrophages to the tumor site and acts as an inflammasome activator [1][3][4].
- HMGB1 and Annexin A1 Release: In the late stages of ICD, changes in membrane permeability lead to the release of high-mobility group box 1 (HMGB1) and Annexin A1 (ANXA1). HMGB1 binds to Toll-like receptor 4 (TLR4) on DCs, significantly enhancing their proliferation and activation, while ANXA1 acts as a formyl peptide receptor 1 (FPR1) agonist [1][2][3][4].
Together, these DAMPs interact with pattern-recognition receptors (PRRs) on antigen-presenting cells, leading to enhanced presentation of tumor neoantigens and the robust activation of tumor-targeting cytotoxic T lymphocytes [1][3][4].
4. Structure-Activity Relationship (SAR)
The immunomodulatory and cytotoxic properties of oxaliplatin are closely tied to its chemical structure, particularly the trans-(1R,2R)-DACH (diaminocyclohexane) ligand. Research into substituting this ligand has yielded valuable SAR insights. For example, replacing the DACH ligand with cis-1,3-diaminocyclobutane results in a complex that maintains comparable cytotoxicity and ICD features to oxaliplatin but markedly increases macrophage phagocytosis, suggesting it may be a superior ICD inducer for antigen presentation [1]. Other structural isomers, such as cis-1,4-DACH and trans-1,2-diamino-4-cyclohexene (DACHEX), have demonstrated comparable or superior cytotoxicity against oxaliplatin-resistant CRC cell lines [1].
Furthermore, the development of Pt(IV) prodrugs has expanded the SAR landscape. The octahedral geometry of Pt(IV) complexes provides additional axial coordination sites that can be conjugated with bioactive molecules. Oxaliplatin-based Pt(IV) prodrugs have been synthesized incorporating payloads such as indoleamine 2,3-dioxygenase (IDO) inhibitors (e.g., 1-methyl-tryptophan, NLG919), COX-2 inhibitors (e.g., aspirin, flurbiprofen), and TREM2 inhibitors (e.g., artesunate). These dual-action complexes not only deliver the cytotoxic Pt(II) core upon intracellular reduction but also release immunomodulators that actively reverse the immunosuppressive TME [1].
5. Current Limitations
Despite its clinical success, oxaliplatin therapy is hindered by several significant limitations. The primary challenge is the lack of tumor selectivity, which leads to severe systemic side effects. The most prominent and dose-limiting toxicity associated with oxaliplatin is oxaliplatin-induced peripheral neuropathy (OIPN), alongside other issues like myelosuppression [1].
Additionally, the development of drug resistance remains a major hurdle. Resistance mechanisms are multifaceted and include alterations in drug entry, accumulation, and efflux; enhanced tolerance and repair of platinum-induced DNA damage; changes in cell survival pathways; and physical barriers within the TME, such as dense extracellular matrix and hypoxia [1][5].
Paradoxically, while oxaliplatin stimulates immunity via ICD, it can also trigger adaptive immune resistance. Oxaliplatin treatment has been shown to upregulate the expression of IDO—an enzyme that depletes tryptophan and produces immunosuppressive kynurenine—and increase the expression of immune checkpoint molecules like PD-L1 and PD-L2 on tumor and myeloid cells, which can impair T-cell cytotoxicity and promote immune escape [1].
6. Future Perspectives
The future of oxaliplatin and platinum-based drugs lies at the intersection of chemotherapy and immunotherapy. Because oxaliplatin can upregulate PD-L1 and induce ICD, there is a strong clinical rationale for combining it with immune checkpoint inhibitors (ICIs) targeting PD-1, PD-L1, or CTLA-4. Preclinical and clinical evidence suggests that oxaliplatin can sensitize immunologically "cold" tumors—such as mismatch repair-proficient/microsatellite stable (pMMR/MSS) colorectal cancers—to ICI therapy, leading to synergistic tumor regression and durable immune responses [1][3][4].
Advancements in drug delivery systems also hold great promise. The encapsulation of oxaliplatin or its Pt(IV) prodrugs into nanomedicines, liposomes, and polymeric micelles aims to exploit the enhanced permeability and retention (EPR) effect, improving tumor-specific accumulation while mitigating systemic toxicities like OIPN [1][3]. For instance, nanocarriers combining oxaliplatin with agents like all-trans-retinoic acid (ATRA) or IDO inhibitors have successfully reshaped the TME by reducing MDSCs and promoting CD8+ T cell infiltration in preclinical models [1][3].
Finally, ongoing clinical trials are heavily focused on immunomonitoring to identify predictive biomarkers (e.g., T cell profiling, circulating cytokines) that will help tailor oxaliplatin-based chemo-immunotherapy regimens, ensuring maximum immunostimulation and clinical benefit for cancer patients [3].
