Target Profiling of an Iridium(III)-Based Immunogenic Cell Death Inducer Unveils the Engagement of Unfolded Protein Response Regulator BiP

Abstract

Clinical chemotherapeutic drugs have occasionally been observed to induce antitumor immune responses beyond the direct cytotoxicity. Such effects are coined as immunogenic cell death (ICD), representing a “second hit” from the host immune system to tumor cells. Although chemo-immunotherapy is highly promising, ICD inducers remain sparse with vague drug–target mechanisms. Here, we report an endoplasmic reticulum stress-inducing cyclometalated Ir­(III)–bisNHC complex (1a) as a new ICD inducer, and based on this compound, a clickable photoaffinity probe was designed for target identification, which unveiled the engagement of the master regulator protein BiP (binding immunoglobulin protein)/GRP78 of the unfolded protein response pathway. This has been confirmed by a series of cellular and biochemical studies including fluorescence microscopy, cellular thermal shift assay, enzymatic assays, and so forth, showing the capability of 1a for BiP destabilization. Notably, besides 1a, the previously reported ICD inducers including KP1339, mitoxantrone, and oxaliplatin were also found to engage BiP interaction, suggesting the important role of BiP in eliciting anticancer immunity. We believe that the ICD-related target information in this work will help to understand the mode of action of ICD that is beneficial to designing new ICD agents with high specificity and improved efficacy.

Towards Understanding the Molecular Mechanisms of Immunogenic Cell Death

“…The discovery of BiP engagement offers a promising targeting strategy as this protein is an upstream master regulator, dominating the on/off states of all the UPR ER branches. BiP is also found overexpressed in about one‐third of cancer types, rendering it a potential anticancer target [40] . To keep ER homeostasis upon excessive protein synthesis in cancer cells might explain such higher demand for BiP proteins.…”

“…BiP is also found overexpressed in about one-third of cancer types, rendering it a potential anticancer target. [40] To keep ER homeostasis upon excessive protein synthesis in cancer cells might explain such higher demand for BiP proteins. The remaining question lies in the specific role of BiP during the ICD-favored ER stress responses.…”

“…Albeit these findings showed BiP may play key roles in ICD, evidence for the direct drug‐target interaction lacks. Our group performed target profiling of an iridium‐based ICD inducer (compound 1 a ) using clickable photoaffinity approaches, discovering the engagement of BiP [40] . 1 a was then proved to destabilize BiP both in living cells and solution with purified proteins.…”

“…Our group performed target profiling of an iridium-based ICD inducer (compound 1 a) using clickable photoaffinity approaches, discovering the engagement of BiP. [40] 1 a was then proved to destabilize BiP both in living cells and solution with purified proteins. Moreover, other ICD agents, including oxaliplatin, mitoxantrone, and KP1339, exhibit BiPinhibiting activity in varied ways.…”

Efficient thermally activated delayed fluorescent emitter based on a spiro-type benzo[b]acridine donor and a benzophenone acceptor

“…[1][2][3][4][5][6] TADF can achieve a nearly 100% internal quantum efficiency (IQE) without using metal atoms through the reverse intersystem crossing (rISC) process owing to the small splitting energy (DE ST ) between the lowest triplet excited state (T 1 ) and the lowest singlet excited state (S 1 ). [7][8][9][10][11][12][13][14][15][16][17] To achieve a small DE ST , conventional TADF emitters generally need a near-vertical twist angle between the electron acceptor (A) and electron donor (D). The twisted structure gives the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) a large degree of separation, thus resulting in a small electron exchange energy.…”