Usefulness of combined treatment with continuous administration of tirapazamine and mild temperature hyperthermia inγ-ray irradiation in terms of local tumour response and lung metastatic potential

Targeting Hypoxia: Hypoxia-Activated Prodrugs in Cancer Therapy

Hypoxia is an important characteristic of most solid malignancies, and is closely related to tumor prognosis and therapeutic resistance. Hypoxia is one of the most important factors associated with resistance to conventional radiotherapy and chemotherapy. Therapies targeting tumor hypoxia have attracted considerable attention. Hypoxia-activated prodrugs (HAPs) are bioreductive drugs that are selectively activated under hypoxic conditions and that can accurately target the hypoxic regions of solid tumors. Both single-agent and combined use with other drugs have shown promising antitumor effects. In this review, we discuss the mechanism of action and the current preclinical and clinical progress of several of the most widely used HAPs, summarize their existing problems and shortcomings, and discuss future research prospects.

An attempt to improve the therapeutic effect of boron neutron capture therapy using commonly employed 10B-carriers based on analytical studies on the correlation among quiescent tumor cell characteristics, tumor heterogeneity and cancer stemness

Based on our previously published reports concerning the response of quiescent (Q) tumor cell populations to boron neutron capture therapy (BNCT), the heterogeneous microdistribution of 10B in tumors, which is influenced by the tumor microenvironment and the characteristics of the 10B delivery carriers, has been shown to limit the therapeutic effect of BNCT on local tumors. It was also clarified that the characteristics of 10B-carriers for BNCT and the type of combined treatment in BNCT can also affect the potential for distant lung metastases from treated local tumors. We reviewed the findings concerning the response of Q tumor cell populations to BNCT, mainly focusing on reports we have published so far, and we identified the mode of BNCT that currently offers the best therapeutic gain from the viewpoint of both controlling local tumor and suppressing the potential for distant lung metastasis. In addition, based on the finding that oxygenated Q tumor cells showed a large capacity to recover from DNA damage after cancer therapy, the interrelationship among the characteristics in Q tumor cell populations, tumor heterogeneity and cancer stemness was also discussed.

Therapeutic potential of using the vascular disrupting agent OXi4503 to enhance mild temperature thermoradiation

PURPOSE

The response of tissues to radiation with mild temperature hyperthermia is dependent on the interval between the two modalities. This study investigated the effect that the vascular disrupting agent OXi4503 had on this time-interval interaction.

METHODS

The normal right rear foot of female CDF1 mice or foot-implanted C3H mammary carcinomas were locally irradiated (230 kV X-rays) and heated (41.5 °C for 60 min) by foot immersion in a water bath. OXi4503 (50 mg/kg) was injected intraperitoneally 1.5 h before irradiating. Irradiation was performed either in the middle of the heating period (simultaneous treatment) or at 1 or 4 h prior to starting the heating (sequential treatments). Response was the percentage of mice showing local tumour control at 90 days or skin moist desquamation between days 11-23. From the radiation dose response curves the dose producing tumour control (TCD(50)) or moist desquamation (MDD50) in 50% of mice was calculated.

RESULTS

The TCD(50) and MDD50 values for radiation alone were 54 Gy and 29 Gy, respectively. Simultaneously heating the tissues enhanced radiation response, the respective TCD(50) and MDD50 values being significantly (chi-square test, p < 0.05) reduced to 33 Gy and 14 Gy. A smaller enhancement was obtained with a sequential treatment in both tissues. OXi4503 enhanced the radiation response of tumour and skin. Combined with radiation and heat, the only effect was in tumours where OXi4503 prevented the decrease in sensitisation seen with the sequential treatment.

CONCLUSION

Combining OXi4503 with a sequential radiation and heat treatment resulted in a 1.4-fold therapeutic gain.