Multifunctional nanosystems sequentially regulating intratumor Fenton chemistry by remodeling the tumor microenvironment to reinforce chemodynamic therapy

The particularity of the tumor microenvironment (TME) significantly limits the efficiency of chemodynamic therapy (CDT). Although various measures have been taken to improve the efficiency of CDT, how to organically integrate them into one nanosystem to achieve efficient synergy for CDT according to predetermined procedures is still an urgent problem to be solved. This work reported a multifunctional nanosystem, TP_I@PP_CAI, which comprised the inner triphenylphosphine modified D-α-Tocopheryl polyethylene glycol 1000 succinate (TPGS-PPh₃) micelles loading iron-oxide nanoparticles (IONs), and the outer poly (dopamine-co-protocatechuic acid) (PDA-PA, PP) coating modified with carbonic anhydrase IX inhibitor (CAI). TP_I@PP_CAI remodeled TME by sequential function adjustment to make it suitable for the efficient Fenton reactions: CAI first inhibited the overexpressed CA IX to result in intracellular acidification, which combined with near-infrared light (NIR) irradiation to accelerate the PP coating degradation, thereby promoting the exposure and disintegration of the inner micellar structure to release TPGS-PPh₃ and IONs. The TPGS-PPh₃ further elevated the intracellular ROS basal level by targeting and interfering with the mitochondrial function. Therefore, the TME was transformed into an acidic microenvironment with high ROS levels, which vigorously promoted the Fenton reaction mediated by IONs with the aid of photothermal effect induced by PP coating via NIR irradiation, ultimately earning high-efficiency CDT on xenograft MDA-MB-231 tumor-bearing mice. This study improved the efficiency of Fenton reaction in biological systems through the practical design of nanostructures and provided a novel thought for ROS-mediated therapy.

Myrtenal-induced V-ATPase inhibition - A toxicity mechanism behind tumor cell death and suppressed migration and invasion in melanoma

BACKGROUND

Metastatic tumor cells have acidic extracellular pH and differential electrochemical H⁺ gradients generated across their cell membranes by V-type H⁺-ATPases. This study shows that inhibition of the V-ATPases by the plant-derived monoterpene Myrtenal results in tumor cell death and decreased metastatic dissemination in mice.

METHODS

The Myrtenal anticancer toxicity was evaluated in vitro using murine (B16F0 and B16F10) and human (SkMel-5) melanoma cell lines, and in in vivo mouse metastatic dissemination model. Proton flux and extracellular acidification were directly evaluated at the surface of living cells using a non-invasive selective ion electrode approach.

RESULTS

The inhibition of V-ATPases by 100 μM Myrtenal disrupted the electrochemical H⁺ gradient across the cell membranes, strongly induced cell death (4-5 fold), and decreased tumor cells migration and invasion in vitro. Myrtenal (15 mg/kg) also significantly reduced metastasis induced by B16F10 in vivo, further reinforcing that V-ATPase is a molecular target to halt the progression of cancers.

CONCLUSIONS

These data revealed the therapeutic potential of Myrtenal as inhibitor of melanoma progression proposing a mechanism of action by which once inhibited by this monoterpene the proton pumps fail to activate cancer-related differential electrochemical gradients and H⁺ fluxes across the tumor cell membranes, disrupting pH signatures inherent in tumor progression, resulting in reprogrammed cell death and metastasis inhibition.

GENERAL SIGNIFICANCE

The work represents a new mechanistic strategy for contention of melanoma, the most aggressive and deadly form of cutaneous neoplasm, and highlights Myrtenal, other related monoterpenes and derivatives as promising proton pump inhibitors with high chemotherapeutic potential.

Mechanism of antineoplastic activity of lonidamine

Lonidamine (LND) was initially introduced as an antispermatogenic agent. It was later found to have anticancer activity sensitizing tumors to chemo-, radio-, and photodynamic-therapy and hyperthermia. Although the mechanism of action remained unclear, LND treatment has been known to target metabolic pathways in cancer cells. It has been reported to alter the bioenergetics of tumor cells by inhibiting glycolysis and mitochondrial respiration, while indirect evidence suggested that it also inhibited l-lactic acid efflux from cells mediated by members of the proton-linked monocarboxylate transporter (MCT) family and also pyruvate uptake into the mitochondria by the mitochondrial pyruvate carrier (MPC). Recent studies have demonstrated that LND potently inhibits MPC activity in isolated rat liver mitochondria (K_i 2.5μM) and cooperatively inhibits l-lactate transport by MCT1, MCT2 and MCT4 expressed in Xenopus laevis oocytes with K_0.5 and Hill coefficient values of 36-40μM and 1.65-1.85, respectively. In rat heart mitochondria LND inhibited the MPC with similar potency and uncoupled oxidation of pyruvate was inhibited more effectively (IC₅₀~7μM) than other substrates including glutamate (IC₅₀~20μM). LND inhibits the succinate-ubiquinone reductase activity of respiratory Complex II without fully blocking succinate dehydrogenase activity. LND also induces cellular reactive oxygen species through Complex II and has been reported to promote cell death by suppression of the pentose phosphate pathway, which resulted in inhibition of NADPH and glutathione generation. We conclude that MPC inhibition is the most sensitive anti-tumour target for LND, with additional inhibitory effects on MCT-mediated l-lactic acid efflux, Complex II and glutamine/glutamate oxidation.

Inhibition of carbonic anhydrase IX as a novel anticancer mechanism

Carbonic anhydrases (CA, EC 4.2.1.1) catalyze the interconversion bewteen carbon dioxide and bicarbonate with generation of protons. The carbonic anhydrase isozyme IX (CA IX) is highly overexpresed in hypoxic tumors and shows very restricted expression in normal tissues. CA IX is a dimeric protein possessing very high catalytic activity for the hydration of carbon dioxide to protons and bicarbonate. Its quaternary structure is unique among members of this family of enzymes, allowing for structure-based drug design campaigns of selective inhibitors. Inhibition of CA IX with sulfonamide and/or coumarin inhibitors was recently shown to lead to a potent retardation for the growth of both primary tumors and metastases. Some fluorescent sulfonamides were shown to accumulate only in hypoxic tumor cells overexpressing CA IX, and might be used as diagnostic tools for imaging of hypoxic cancers. Sulfonamide inhibitors were also more effective in inhibiting the growth of the primary tumors when associated with irrdiation. CA IX is thus both a diagnostic and therapeutic validated target for the management of hypoxic tumors normally non-responsive to classical chemio- and radiotherapy.