188Re labelled anti-EGFr humanized monoclonal antibody h-R3 for radioimmunotherapy of glyomas

Full text: Locally administered monoclonal antibodies labelled with radioisotopes like 90Y, 131I, 186Re, 212Bi, 211At, 177Lu and others, constitute a viable and promising alternative for management different kind of malignancies. The development of 188W/188Re generator has given the possibility of having a radionuclide showing satisfactory features for radioimmunotherapy (Eβ=2.12 MeV, Eγ=155 keV, T1/2=16.9 h and easy to make labelling approaches, similar to used for 99mTc). Neuroepithelial-derived tumours have an overexpression of the EGF receptor with regard to adjacent normal tissue. It could be related with the autocrine stimulation of the neoplasm by EGF and TGFα. Humanized monoclonal antibody h-R3 has shown high affinity for this EGF receptor, blocking the binding of EGF to it receptor and inducing apoptosis. Thus, it could be a good candidate for radioimmunotherapy of neuroepithelial malignancies. The aim of the present work was to label monoclonal antibody h-R3 with 188Re, to assess it an animal model and evaluate its internal dosimetry in patients with grade III-IV glyomas. Direct labelling method was employed, using 2-mercaptoethanol as a reducing agent. The amount of sodium glucoheptonate, ascorbic acid and stannous fluoride were varied to achieve optimum labelling yield. 188Re-labeling yield was proportional to the volume of stannous glucoheptonate solution added to the formulation. Radiochemical purity of 188Re-h-R3 was 98.0±0.4%. Challenge against 300-fold molar excess of L-cysteine was made to assess the stability of the tracer. There was not found significant difference between stability of 188Re-h- R3 and 99mTc-h-R3 against cysteine challenge up to 24 h. Animal biodistribution study was performed at 3 and 24 h after intravenous administration of 188Re-h-R3 through tale vein of Male Wistar rats. The results were compared with those attained using 99mTc-h-R3 as a control. Biodistribution study showed high radiopharmaceutical uptake in kidneys and small intestine. Urinary excretion was similar for the antibody labelled with 188Re as well as 99mTc. A Phase I dose escalation trial was performed by administering into the post-operative cavity through an indwelling catheter a single dose 188Re-h-R3. The study was reviewed and approved by the ethics Committees of the all involved institutions. Five patients with partial tumour resections have been included. Immunihistochemical study of tumours showed an overexpression of EGFr. SPECT and planar images as well as multiple blood and urine samples were collected up to 24 h after administration of 3 mg of MAb labelled with 10 or 15 mCi of 188Re. Biodistribution was computed from scintigraphic images and the absorbed dose were estimated using the MIRD methodology at organ and voxel level. Data processing and statistical analyses were performed using the SPSS and Microcal Origin v6.0 software packages. The effective half-life of the 188Re-h-R3 in the tumoural bed were ranged 7,3-14,4 h (mean value 8,4±2,8 h). The liver, kidneys and urinary bladder showed the highest uptakes of the compound leaving the tumoural bed. The mean absorbed dose in the tumour ranged 13,9 Gy- 68,4 Gy and the maximum doses were ranged 26,9 Gy-136,2 Gy. The maximum absorbed dose for liver, kidneys and urinary bladder was lower than 2 Gy in all patients. Transitory acute side effects following treatment were headache, seizures, and worsening of pre-existing neurological symptoms. Two patients developed stable disease during 3 months, 2 patients with multiform glyoblastoma are practically asymptomatic and in complete remission after one year of treatment. The other patient with glyoblastoma multiform is not yet evaluable after one month of treatment. Proposed procedure allowed the stable efficient labelling of h-R3 with 188Re. Preliminary results of this study strongly suggest that loco-regional radioimmunotherapy of high grade glyoma using the anti-EGFr humanized monoclonal antibody h-R3 labelled with 188Re may be safe and constitute a promising therapeutic approach for these patients. (author)