Holmium-166 Chitosan in Radiopharmaceutical Cancer Treatment

Milican, a radiopharmaceutical drug consisting of Holmium-166 Chitosan, offers a targeted therapy option for hepatocellular carcinoma and has potential applications in other medical conditions. Launched in South Korea in August 2001, it utilises Chitosan—a substance derived from crab shell chitin—and the radionuclide Holmium-166 for brachytherapy. Chitosan’s unique property of solidifying at pH levels below 7.0, common near tumour cells, facilitates the local retention of the radionuclide, enhancing its therapeutic efficacy. While initially approved for hepatocellular carcinoma, its use has been explored in treating prostate cancer, rheumatoid arthritis, glioblastoma, and skin cancer through different formulations.


Introduction to Holmium-166 Chitosan

Holmium-166 Chitosan, marketed as Milican, is a pioneering radiopharmaceutical treatment developed for hepatocellular carcinoma, with its first marketing authorisation granted in South Korea in August 2001. The drug’s foundation lies in its two principal components: Chitosan and 166Ho. Chitosan is a biological substance extracted from crab shell chitin, known for its gel-like state at slightly acidic pH levels, which transitions to a solid (foam) form when the pH drops below 7.0. This characteristic is crucial for the drug’s effectiveness, as the lower pH conditions prevalent around tumour cells enable Chitosan to solidify, thus localising the 166Ho radionuclide near the cancer cells for targeted therapy.

Mechanism of Action of Holmium-166 Chitosan

The therapeutic mechanism of 166Ho-Chitosan centres on brachytherapy, a type of radiation therapy wherein a radiation source is placed close to or within the tumour. The key to its effectiveness is the ability of Chitosan to become solid under acidic conditions near tumour sites, thereby physically retaining the 166Ho radionuclide in proximity to the cancer cells. This close presence allows the beta electrons (^β–) emitted by 166Ho to exert their cytotoxic effects directly on the tumour cells, minimising damage to surrounding healthy tissue.

Clinical Applications and Explorations

Initially authorised for the treatment of hepatocellular carcinoma, the applications of Holmium-166 Chitosan have broadened to include other medical conditions:

  • Hepatocellular Carcinoma: Milican’s primary indication is leveraging the localised radiation effect of 166Ho to target liver cancer cells efficiently.
  • Prostate Cancer: Research has explored its utility in treating prostate cancer, another potential area benefitting from localised radiation therapy.
  • Rheumatoid Arthritis: Although explored as a treatment option, its development for rheumatoid arthritis was discontinued in 2005 due to unspecified reasons.
  • Glioblastoma: The characteristics of Holmium-166 Chitosan suggest the potential for treating glioblastoma, a highly aggressive brain tumour, though further research is needed.
  • Skin Cancer: Innovations in formulation, such as a patch containing Holmium-166 Chitosan, have been investigated for the non-invasive treatment of skin cancer.

Conclusion

Holmium-166 Chitosan (Milican) represents a significant advancement in the field of radiopharmaceutical therapy, especially for hepatocellular carcinoma. Its innovative use of Chitosan’s pH-responsive solidification property to localise radiation therapy directly at tumour sites embodies a novel approach to cancer treatment. While its primary use remains in treating liver cancer, the exploration of its application to other cancers and diseases highlights the potential versatility and impact of this therapeutic modality. The continued research and development in expanding its indications could further cement its role in oncology and beyond.

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Tags: Brachytherapy, Cancer, Targeted Radionuclide Therapy
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