Enhancement of Hyperthermia-induced Apoptosis by Local Anesthetics on Human Histiocytic Lymphoma U937 Cells

Abstract

The combined effects of hyperthermia at 44°C and local anesthetics on apoptosis in human histiocytic lymphoma U937 cells were investigated. When the cells were exposed to hyperthermia for l0 min marginal DNA fragmentation and nuclear fragmentation were observed. In the presence of amide-type local anesthetics further enhancement was found depending on concentration. The order of the concentration required for maximum induction was the reverse order of the lipophilicity (prilocaine > lidocaine > bupivacaine). Western blotting revealed that in hyperthermia there was initial release of Ca 2؉ from the intracellular store site as indicated by increased expression of the type 1 inositol-1,4,5-trisphosphate receptor. The effectiveness of hyperthermia combined with radiotherapy in the treatment of various solid tumors has been demonstrated (1). Furthermore, recent clinical randomized trials of patients with brain tumors, recurrent or metastatic malignant melanoma, advanced breast carcinoma, locally advanced pelvic tumors, and malignant germ cell tumors clearly have indicated the advantages for patients treated with hyperthermia combined with radiotherapy (2-6) or chemotherapy (7) compared with radiotherapy alone. However, the uniform and precise delivery of heat to tumors still remains a challenge. In many circumstances the tumor cell killing is insufficient. Drugs that have been discussed as overcoming this difficulty are heat sensitizers. An ideal sensitizer would be nontoxic at normothermia but could become cytotoxic at hyperthermic temperatures.Local anesthetics belong to a class of clinically useful compounds that exert a pharmacological effect by blocking nerve impulse propagation. The involvement of cell membranes as the site for these drug actions has been widely accepted, and many reports showing modification of cell killing due to hyperthermia by LAs 1 have been published (e.g. potentiation by procaine in murine L5178Y lymphoma cells (8) and by lidocaine in murine FM3A mammary carcinoma cells (9), potentiation of survival of tumor-bearing mice after hyperthermia combined with lidocaine (10), enhancement of hyperthermia-induced tumor regression by lidocaine in murine tumor models (11, 12), and enhancement of cytotoxic effects of hyperthermia by dibucaine, tetracaine, and procaine in hepatoma tissue culture cells (13)). However, little is known about the modification and mechanism of apoptosis when hyperthermia is combined with LAs.Here we will present our recent findings that subtoxic levels of LAs enhanced hyperthermia-induced apoptosis via the Ca 2ϩ -and mitochondria-dependent pathways in human lymphoma U937 cells. Evidence for the cardinal roles of initial release of Ca 2ϩ from intracellular store sites due to hyperthermia and the subsequent increase of [Ca 2ϩ ] i and the additional activation of the mitochondrial caspase-dependent pathway in enhancement of apoptosis induced by the combination of hyperthermia and lidocaine will also be presented. In addition the potential usefulness of LAs as sensitizers o...

Proteasome Inhibition Potentiates the Cytotoxic Effects of Hyperthermia in HT-29 Colon Cancer Cells through Inhibition of Heat Shock Protein 27

“…In addition, sublethal hyperthermia may also lead to heat-induced cellular resistance by upregulating cell survival mechanism(s), thereby making tumor cells more resistant to subsequent therapies [8]. Therefore, the use of thermal sensitizing agents has been studied to increase tumor cell kill as well as decrease subsequent thermal tolerance by blocking cell survival pathways [3,4,5]. …”

“…While dependent on tumor cell type and conditions, the usual breakpoint temperature at which cells undergo significant cell death is 43°C for a minimum of 1 h. While appropriate for in vitro studies, achieving temperatures of 43°C or greater for a prolonged period has been associated with increased morbidity [2]. To this end, clinical investigators have studied agents to act as thermal sensitizers in an attempt to achieve the same tumor cell kill at lower temperatures [3,4,5]. An ideal sensitizer would be nontoxic to normal cells at normothermia, but cytotoxic to malignant cells at hyperthermic temperatures.…”

Lidocaine-induced apoptosis and necrosis in U937 cells depending on its dosage

“…Recently, Johnson et al showed that lidocaine at 18-37 mM induced mitochondrial injury followed by caspase activation in neuronal cells with inhibition of mitochondrial respiration. Arai et al (1) reported that enhancement of hyperthermia-induced apoptosis by lidocaine was associated with the ΔΨm reduction in U937 cells through the increased intracellular Ca 2+ concentration. It is uncertain at present whether the ΔΨm reduction in U937 cells is due to direct or indirect action by lidocaine.…”

Enhancement of apoptosis by nitric oxide released from α‐phenyl‐tert‐butyl nitrone under hyperthermic conditions

“…Recently, we found that hyperthermia-induced apoptosis in human lymphoma U937 cells is associated with the intracellular generation of superoxide (O 2 À ), rapid lipid peroxidation (LPO), and an increase in the intracellular Ca 2þ concentration ([Ca 2þ ] i ) (Li et al, 2001(Li et al, , 2003Arai et al, 2002;Yuki et al, 2003). In addition, hyperthermiainduced apoptosis was also enhanced in U937 cells by excess oxidative stress due to a temperature-dependent free radical generator (Li et al, 2001;Yuki et al, 2003) and a intracellular hydrogen peroxide generator, 6-formylpterin (Wada et al, 2005).…”