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[Radiosensitizer: hypoxic cell radiosensitizer]
1Dept. of Radiation Oncology, School of Medicine, Tokai University.
Abstract:
There is a world-wide demand for a clinically usable sensitizer for radio-resistant hypoxic cells. After unsuccessful clinical trials of misonidazole, many efforts have been made to develop new sensitizers. In the U.S., Brown and others reported a new drug named SR-2508 (ethanidazole), which is now in phase II and III clinical trials. In Japan, many drugs were synthesized and tested with the screening systems using EMT6 and SCCVII tumor. Since the failure with misonidazole is due to its neurotoxicity, two methods have been applied to find new sensitizers. The first one is to increase the sensitizing effects and the other is to decrease the neurotoxicity. KU-2285 is fluorinated nitroimidazole, and it has a higher sensitizing effect than misonidazole or SR-2508. Its sensitizing effect is 1.65 at 200 mg/kg, and the LD50 value is 2.3 g/kg. Hoping for less neurotoxicity, RK-28, RP-170 and KIH-801 were synthesized. RP-170 demonstrated less toxicity than Miso, and KIH-801 demonstrated an unexpectedly high sensitizing effect especially is in vivo experiments. Although RK-28 has a low LD50 value, it shows rapid clearance rate from serum and is supposed to have less cumulative neurotoxicity. KU-2285, RK-28, RP-170 and KIH-801 all await further clinical trials.
Insights
Researchers are developing new sensitizers to treat radio-resistant hypoxic cells, aiming to improve efficacy and reduce neurotoxicity. Promising candidates like KU-2285 and KIH-801 show enhanced effects and lower toxicity in preclinical studies.
Area of Science:
- Oncology
- Radiotherapy
- Pharmacology
Background:
- Hypoxic cells present a significant challenge in radiotherapy, leading to radioresistance.
- Misonidazole, a previously used sensitizer, demonstrated clinical limitations due to neurotoxicity.
- Development of novel hypoxic cell sensitizers is crucial for improving cancer treatment outcomes.
Purpose of the Study:
- To synthesize and evaluate novel hypoxic cell sensitizers with enhanced efficacy and reduced neurotoxicity.
- To screen potential drug candidates using established tumor models like EMT6 and SCCVII.
- To identify compounds that overcome the limitations of existing sensitizers such as misonidazole.
Main Methods:
- Synthesis and screening of novel nitroimidazole derivatives.
- Evaluation of sensitizing effects in vitro and in vivo using tumor models.
- Assessment of toxicity profiles, including LD50 values and neurotoxicity.
- Pharmacokinetic studies to assess drug clearance rates.
Main Results:
- KU-2285, a fluorinated nitroimidazole, exhibited a higher sensitizing effect (1.65 at 200 mg/kg) than misonidazole and SR-2508, with an LD50 of 2.3 g/kg.
- RK-28, RP-170, and KIH-801 were synthesized with the goal of reduced neurotoxicity.
- RP-170 showed decreased toxicity compared to misonidazole.
- KIH-801 demonstrated significant in vivo sensitizing effects.
- RK-28 exhibited rapid serum clearance, suggesting potentially lower cumulative neurotoxicity.
Conclusions:
- Novel hypoxic cell sensitizers, including KU-2285, RK-28, RP-170, and KIH-801, demonstrate promising preclinical efficacy and improved toxicity profiles.
- These compounds represent potential advancements over existing treatments for radio-resistant hypoxic tumors.
- Further clinical trials are warranted to establish the safety and effectiveness of these new sensitizers in cancer patients.