Background PT-112 is a novel platinum-pyrophosphate conjugate1 under clinical development for cancer therapy.2-5 Besides mediating cytostatic and cytotoxic effects in numerous human and mouse cancer cells, PT-112 elicits various danger signals that are linked to immunogenic cell death (ICD), such as calreticulin exposure, as well as ATP and HMGB1 secretion.3,6,7 Accordingly, mouse cancer cells succumbing to PT-112 in vitro efficiently protect immunocompetent, tumor-naïve mice from challenge with living cancer cells of the same type.6,7 Moreover, PT-112 synergizes with PD-1 or PD-L1 blockade to control mouse tumors developing in immunologically competent hosts.6,7 In some tumor models, robust type I interferon (IFN) signaling is required for ICD8-10 However, the role of type I IFN signaling in the immunogenicity of PT-112 remains unclear.
Methods We used wild-type, mitochondrial DNA (mtDNA) depleted (rho0), as well as Casp2-/- and Casp3-/- mouse TS/A cells.11 ELISA, flow cytometry and immunofluorescence microscopy were employed to monitor type I IFN levels, reactive oxygen species (ROS) generation, mitochondrial polarization, cell death, and cytosolic dsDNA accumulation driven by PT-112 and underlying regulatory mechanisms.
Results In cultured TS/A cells, PT-112 induced mitochondrial dysfunction, as demonstrated by ROS generation and mitochondrial hyperpolarization, as well as cytosolic accumulation of dsDNA that was abrogated in rho0 TS/A cells. Type I IFN secretion by wild-type TS/A responding to PT-112 was not observed. Both Casp2 and Casp3 deletion provided TS/A cells with some protection from PT-112-driven ROS generation and mitochondrial hyperpolarization, but only Casp3 deletion afforded robust protection against the acute cytotoxicity of PT-112. Importantly, both Casp2 and Casp3 deletion augmented cytosolic dsDNA accumulation driven by PT-112.
Conclusions PT-112 causes pronounced mitochondrial dysfunction in cancer cells coupled with cytosolic mtDNA accumulation, which generally leads to type I IFN secretion.8 PT-112-driven caspase activation, however, possibly prevents mtDNA-driven type I IFN secretion, likely reflecting CGAS cleavage by active CASP312 and/or the rapid CASP3-dependent transition of dying cancer cells into metabolically inert corpses.13,14 In line with this possibility, both Casp2-/- and Casp3-/- TS/A cells exhibited increased cytosolic mtDNA accumulation upon PT-112 treatment. As PT-112 is a potent inducer of ICD in vaccination assays6,7 CASP3 activation elicited during the cytotoxic response to PT-112 may not influence the ability of PT-112 to drive prophylactic anticancer immunity in tumor-naïve hosts. Additional studies with established tumor models are needed to clarify the impact of caspases on the immunogenicity of PT-112 in clinically relevant settings.
Ames T, Slusher B, Wozniak K, et al. Findings across pre-clinical models in the development of PT-112, a novel investigational platinum-pyrophosphate anti-cancer agent. European Journal of Cancer 2016;69:S153.
Ames TD, Sharik ME, Rather GM, et al. Translational research of PT-112, a clinical agent in advanced phase I development: evident bone tropism, synergy In vitro with bortezomib and lenalidomide , and potent efficacy in the Vk*MYC mouse model of multiple myeloma. Blood 2017;130(Supplement 1):1797–1797.
Buque A, Rodriguez-Ruiz ME, Fucikova J, Galluzzi L. Apoptotic caspases cut down the immunogenicity of radiation. Oncoimmunology 2019;8(11):e1655364.
De Giovanni C, Nicoletti G, Landuzzi L, Palladini A, Lollini PL, Nanni P. Bioprofiling TS/A. Murine mammary cancer for a functional precision experimental model. Cancers (Basel). 2019;11(12).
Karp DD, Camidge DR, Bryce AH, Jimeno J, Infante JR. A phase I study of PT-112 in advanced solid tumors. Journal of Clinical Oncology. 2017;35(15_suppl):2519–2519.
Karp DD, Camidge DR, Infante JR, Ames TD, Jimeno JM, Bryce AH. PT-112: A well-tolerated novel immunogenic cell death (ICD) inducer with activity in advanced solid tumors. Annals of Oncology. 2018;29(suppl_8).
Karp DD, Camidge DR, Infante JR, et al. Phase I study of PT-112, a novel pyrophosphate-platinum immunogenic cell death inducer, in advanced solid tumours. EClinicalMedicine 2022;49:101430.
Ning X, Wang Y, Jing M, et al. Apoptotic caspases suppress type I interferon production via the cleavage of cGAS, MAVS, and IRF3. Mol Cell 2019;74(1):19–31 e17.
Rodriguez-Ruiz ME, Buque A, Hensler M, et al. Apoptotic caspases inhibit abscopal responses to radiation and identify a new prognostic biomarker for breast cancer patients. Oncoimmunology 2019;8(11):e1655964.
Sistigu A, Yamazaki T, Vacchelli E, et al. Cancer cell-autonomous contribution of type I interferon signaling to the efficacy of chemotherapy. Nat Med 2014;20(11):1301–1309.
Yamazaki T, Ames TD, Galluzzi L. Abstract B199: Potent induction of immunogenic cell death by PT-112. Cancer Immunology Research 2019;7(2 Supplement):B199.
Yamazaki T, Buque A, Ames TD, Galluzzi L. PT-112 induces immunogenic cell death and synergizes with immune checkpoint blockers in mouse tumor models. Oncoimmunology 2020;9(1):1721810.
Yamazaki T, Kirchmair A, Sato A, et al. Mitochondrial DNA drives abscopal responses to radiation that are inhibited by autophagy. Nat Immunol. 2020;21(10):1160–1171.
Zitvogel L, Galluzzi L, Kepp O, Smyth MJ, Kroemer G. Type I interferons in anticancer immunity. Nat Rev Immunol 2015;15(7):405–414.
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