Nanoscale photodynamic therapy (PDT) is an appealing antitumor modality for which apoptosis is the major mechanism of toxicity induction. It was postulated that the highly reactive singlet oxygen in PDT could deplete glutathione (GSH) and activate ferroptosis, the extent to which could be further manipulated by a redox-responsive nanocarrier. To validate this, a disulfide-bearing imidazole ligand coordinated with zinc to form an all-active metal organic framework (MOF) nanocarrier where a photosensitizer (chlorin e6/Ce6) was encapsulated. Regardless of light irradiation, the Ce6-loaded nanocarrier caused the depletion of intracellular GSH via the disulfide–thiol exchange reaction in a murine mammary carcinoma cell line (4T1). The GSH depletion further caused the inactivation of glutathione peroxide 4 (GPX4) and the enhancement of cytotoxicity that was alleviated by ferroptosis inhibitors. The superior in vivo antitumor efficacy of the all-active nanocarrier was corroborated in a 4T1 tumor-bearing mice model regarding tumor growth suppression and animal survival rate. The coadministration of an iron chelator weakened the antitumor potency of the nanocarrier due to ferroptosis inhibition, which was supported by the fact of tumor growth upsurge and the recovered GPX4 activity. The current work highlights the contribution of ferroptotic machinery to antitumor PDT via an activatable, adaptable, all-active MOF nanocarrier.

Voltage-gated K + (Kv) channels couple the movement of a voltage sensor to the channel gate(s) via a helical intracellular region, the S4-S5 linker. A number of studies link voltage sensitivity to interactions of S4 charges with membrane phospholipids in the outer leaflet of the bilayer. Although the phospholipid phosphatidylinositol-4,5-bisphosphate (PIP 2 ) in the inner membrane leaflet has emerged as a universal activator of ion channels, no such role has been established for mammalian Kv channels. Here we show that PIP 2 depletion induced two kinetically distinct effects on Kv channels: an increase in voltage sensitivity and a concomitant decrease in current amplitude. These effects are reversible, exhibiting distinct molecular determinants and sensitivities to PIP 2 . Gating current measurements revealed that PIP 2 constrains the movement of the sensor through interactions with the S4-S5 linker. Thus, PIP 2 controls both the movement of the voltage sensor and the stability of the open pore through interactions with the linker that connects them.voltage-gated channels | lipids | channel modulation | open probability V oltage-gated K + (Kv) channels are tetrameric integral membrane proteins critical to membrane excitability that respond rapidly to changes in membrane potential to control membrane permeability to potassium ions. Upon membrane depolarization, a voltage sensor in each subunit undergoes a transition from a resting to an activated state followed by a concerted transition leading to the opening of the pore (1-4). The voltage-sensing domain [i.e., the S1-S4 transmembrane (TM) helices] of Kv channel subunits harbors within its S4 helix several positively charged residues that respond directly to changes in membrane voltage (5-7). The movement of these charges can be monitored by the gating current they produce, and the opening of the pore is monitored by the ionic current that follows. The S4-S5 linker couples the movement of the voltage sensor to the opening of the pore.X-ray structures of Kv channels have shown that the S1-S4 voltage-sensing domains are exposed to lipids when embedded in a membrane (8,9). A number of studies have suggested that, after depolarization, interactions of the S4 charges with lipids in the outer leaflet of the membrane are important in the stabilization of the sensor in the activated state (10-12).Phosphatidylinositol-4,5-bisphosphate (PIP 2 ), a phospholipid that affects the activity of many types of ion channels (13, 14), acts as a docking platform for the N-terminal domain of fastinactivating Kv channels (15). Activation of Ciona intestinalis voltage-sensitive phosphatase (Ci-VSP), which contains a voltage-sensing domain (S1-S4) coupled to a cytoplasmic phosphatase domain rather than a TM pore, shows a dependence on membrane depolarization similar to that of voltage-gated channels (16). PIP 2 modulates the motions of the Ci-VSP voltagesensor domain and its coupling to the phosphatase domain by interacting with the linker that connects the voltage sensor and phosphatase...

Ferroptosis is an iron-dependent cell death pathway that can eradicate certain apoptosis-insensitive cancer cells. The ferroptosis-inducing molecules are tailored lipid peroxides whose efficacy is compromised in hypoxic solid tumor and lack of tumor selectivity. It has been demonstrated that ascorbate (Asc) in pharmacological concentrations can selectively kill cancer cells via accumulating hydrogen peroxide (H 2 O 2 ) only in tumor extracellular fluids. It was hypothesized that Asc-induced, selective enrichment of H 2 O 2 in tumor coupled with Fe 3+ codelivery could simultaneously address the above two problems via boosting the levels of hydroxyl radicals and oxygen in the tumor site to ease peroxidation initiation and propagation, respectively. The aim of this work was to synergize the action of Asc with lipid-coated calcium phosphate (CaP) hybrid nanocarrier that can concurrently load polar Fe 3+ and nonpolar RSL3, a ferroptosis inducer with the mechanism of inhibiting lipid peroxide repair enzyme (GPX4). The hybrid nanocarriers showed accelerated cargo release at acidic conditions (pH 5.0). The combinational approach (Asc plus nanocarrier) produced significantly elevated levels of hydroxyl radicals, lipid peroxides, and depleted glutathione under hypoxia, which was accompanied with the strong cytotoxicity (IC 50 = 1.2 ± 0.2 μM) in the model 4 T1 cells. In the 4 T1 tumor-bearing xenograft mouse model, the intravenous nanocarrier delivery plus intraperitoneal Asc administration resulted in a superior antitumor performance in terms of tumor suppression, which did not produce supplementary adverse effects to the healthy organs. This work provides a novel approach to enhance the potency of ferroptotic nanomedicine against solid tumors without inducing additional side effects.