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Although classical platinum drugs such as cisplatin, carboplatin and oxaliplatin play a vitally important role in cancer treatment, nonselective distribution of platinum drugs in normal and tumor cells can induce serious gastrointestinal reaction, nephrotoxicity, ototoxicity, neurotoxicity and cross resistance, limiting their applications. Over the past few years, a great number of platinum complexes of non-classical structures have been extensively investigated and evaluated in vitro and in vivo, some of them exhibiting considerable activity. In this review, platinum-based complexes with non-classical structures which have anticancer potential are described and several representative examples are discussed with their mechanism of action.

Triggering receptor expressed on myeloid cells‐2 (TREM2) is a key pro‐tumorigenic marker of tumor‐infiltrating macrophages, showing potent immunosuppressive activity in tumor microenvironment. A platinum(IV) complex OPA derived from oxaliplatin (OP) and artesunate (ART) exhibited direct cytotoxicity against human colon cancer cells and immunomodulatory activity to inhibit TREM2 on macrophages in vitro and vivo. Furthermore, OPA deterred the tumor growth in mouse models bearing MC38 colorectal tumor by reducing the number of CD206+ and CX3CR1+ immunosuppressive macrophages; it also promoted the expansion and infiltration of immunostimulatory dendritic, cytotoxic T, and natural killer cells. OPA is the first small‐molecular TREM2 inhibitor capable of relieving immunosuppressive tumor microenvironment and enhancing chemical anticancer efficiency of a platinum drug, thus showing typical characteristics of a chemoimmunotherapeutic agent.

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Activating cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway is a promising immunotherapeutic strategy for cancer treatment. Manganese(II) complexes MnPC and MnPVA (P = 1,10-phenanthroline, C = chlorine, VA =...