SPECT tracks colorectal tumor-sniping chemoradiotherapy
A treatment strategy for colon cancer combining molecular imaging, a radioimmunotherapy that seeks colon-specific anatomy and concomitant chemotherapy is being bundled as chemoradiotherapy to take out more metastatic disease, according to a study published online Feb. 20 in the Journal of Nuclear Medicine.
The agent is comprised of the therapeutic radionuclide I-131 conjugated with a humanized antibody called huA33, which hunts down the A33 antigen in intestinal epithelium expressed in the vast majority of colon cancers—perhaps more than 95 percent of them, but not usually in healthy organs and tissues.
A team of researchers including Rebecca A. Herbertson, from the Ludwig Institute for Cancer Research in Melbourne, Australia, evaluated the investigational compound as a supplement to chemotherapy by combining it with the drug capecitabine for patients being treated for metastatic colorectal cancer.
“This study demonstrated that targeted chemoradiation in the form of I-131 huA33 combined with capecitabine can be administered safely and effectively to patients with metastatic [colorectal cancer],” wrote Herbertson et al.
A cohort of 19 patients was involved in this phase I prospective and outpatient study. At first patients were given a “scout” dose of I-131 huA33 and then a single therapy infusion was administered one week following as chemotherapy with capecitabine began. Patient dose was escalated for a total of five intensities. Weekly follow-ups culminated in a 12th-week final assessment of therapeutic response. An analysis of I-131 huA33 biodistribution revealed “excellent” targeting of the known sites of metastases and normal tissue uptake was not found.
The agent was well tolerated with some toxicity in the form of hyperbilirubinemia, myelosuppression and gastrointestinal symptoms. Ultimately one patient went on to reveal partial response to therapy and 10 patients remained stable.
“Biodistribution, pharmacokinetic, and tumor-targeting properties remained favorable with this combination treatment, and the clinical benefit [of partial response and stable disease] seen in 11 of 18 (61 percent) evaluable patients and long median overall survival (28.7 months) suggest potential synergy and improved efficacy through the addition of capecitabine to I-131 huA33 radioimmunotherapy,” wrote the authors.
More studies will need to be conducted to validate these results for broader clinical use.