Usefulness of combined treatment with mild temperature hyperthermia and/or tirapazamine in the treatment of solid tumors: its independence of p53 status

Abstract

t has been shown that the p53 tumor suppressor gene serves a critical role in maintaining genomic stability during a cell cycle checkpoint in G1 and the G2/M transition, 1) and as an effector of DNA repair 2) and apoptosis.3) Wild-type p53 is needed to activate apoptosis in sensitive cells in response to DNA damage.4) These actions of p53 are potentially critical in determining the effectiveness of ionizing radiation and/or chemotherapeutic agents. Actually, mutations in the p53 tumor suppressor gene have been shown to have an impact on the clinical course of several human cancers: patients with cancers harboring p53 mutations often have a worse prognosis than those with tumors harboring wild-type p53.5) Thus, the genetic and functional status of the p53 gene is thought to be an important factor in guiding therapeutic strategies for cancer patients.Meanwhile, mild temperature hyperthermia (MTH) was reported to increase the tumor response to radiation by improving tumor oxygenation through an increase in tumor blood flow, 6) and tirapazamine (TPZ, SR-4233, WIN 59075, 3-amino-1,2,4-benzotriazine-1,4-dioxide), a well-known bioreductive agent, has highly selective cytotoxicity toward hypoxic cells in in vivo tumor systems.7) In addition, MTH was also shown to enhance the tumor response, especially of the intratumor quiescent (Q) cell population, to chemotherapy. 8) Based on these reports, we have already demonstrated that combined treatment with MTH and/or TPZ is a promising modality in radiotherapy or chemotherapy from the viewpoint of the killing effect on intratumor Q tumor cells in comparison with the total (proliferating (P)+Q) tumor cell population, using several tumor systems with wildtype p53 status. 9)Accordingly, to investigate the usefulness of MTH and/or TPZ in the treatment of solid tumors consisting of cells with a mutated p53 status, we analyzed the killing effects of several DNA-damaging cytocidal treatments combined with or without MTH and/or TPZ on intratumor Q and total cells, employing two different tumor cell lines identical in genetic background except for p53 status 10) and our method for detecting the intratumor Q cell response in terms of the micronucleus (MN) frequency and apoptosis frequency. 9) As DNA-damaging cytocidal treatments, γ-ray irradiation, TPZ administration, cisplatin (CDDP) injection and paclitaxel (TXL) treatment were employed. Materials and MethodsCells, tumors and mice. The human head and neck squamous cell carcinoma cell line SAS (provided by JCRB, Tokyo) was cultured at 37°C in Dulbecco's modified Eagle's medium (DMEM) containing 20 mM 2-[4-(2-hydroxyethyl)-1-piperazinyl]ethanesulfonic acid (HEPES) and 12.5% fetal bovine serum in a conventional humified 5% CO 2 incubator. SAS cells show the phenotype of wild-type p53 in radiation-and heat-induced signal transduction.11) Plasmids pC53-248, which contains an mp53 gene (codon 248, from Arg to Trp) producing a dominant negative mp53 protein, and pCMV-Neo-Bam, which contains a neo-resistance marker, were provided by B. Vogels...

Tumor-specific CD8-positive T cell-mediated antitumor immunity is implicated in the antitumor effect of local hyperthermia

“…However, in our LH models ( Figure 1) the actual temperature achieved in the tumor while inducing LH was not assessed due to tumor size, which reached approximately 150 mm 3 after 1 week following tumor inoculation. In several reports, LH was performed in the same way as in our study; within few minutes after initiating LH, the tumor reached a slightly lower temperature than the bath temperature within a few minutes after LH was started [28,29]. Therefore, we speculated that tumor temperature was slightly lower than 42 C in our model.…”

Usefulness of Hexamethylenetetramine as an Adjuvant to Radiation and Cisplatin in the Treatment of Solid Tumors: its Independency of p53 Status

“…In contrast, in Q cells, the values for SAS/neo were only slightly larger than those for SAS/mp53. According to the reported result concerning cytotoxicity of TPZ, 18) the employed doses of 65.6 millimole/kg of HMTA induced almost the same cytotoxicity to total tumor cell population of SAS/neo tumors in terms of cell survival and induced MN frequency as the dose of 40 mg/kg (= 0.224 millimole/kg) of TPZ when administered intraperitoneally to SAS/neo tumors. 19) Therefore, the employed doses of HMTA combined with γ-ray irradiation or cisplatin treatment in the subsequent experiments were determined to be 65.6 millimole/kg.…”

“…One hour after the intraperitoneal injection or after the 24hour continuous subcutaneous infusion of HMTA, γ-rays were delivered with a cobalt-60 γ-ray irradiator at a dose rate of approximately 2.5 Gy/min for detecting the radiosensitizing effect of HMTA. Based on the reported results concerning TPZ-induced cytotoxicity, 18) the employed doses of HMTA induced almost the same cytotoxicity to total tumor cell population in terms of cell survival and induced micronucleus (MN) frequency as the dose of 40 mg/kg (= 0.224 millimole/kg) of TPZ when administered intraperitoneally to SAS/neo tumors. Immediately after irradiation, implanted tumors were excised.…”