Preparation, characterization, and biological evaluation of a streptavidin-chimeric t84.66 conjugate for antibody pretargeting.

In order to develop a new system for the antibody pretargeting of carcinoembryonic antigen (CEA)-positive cancers, a streptavidin (SA) conjugate of the monoclonal antibody (mAb) chimeric, T84.66, was synthesized and characterized. Antibody disulfide bonds were reduced with 1,4-dithiothreitol, and the resulting thiols were reacted with succinimidyl 4-(N-maleimidomethyl)cyclohexane-1-carboxylate-derivatized streptavidin (SMCC-SA). The desired SA-cT84.66 conjugate was purified by iminobiotin affinity chromatography and size-exclusion high-performance liquid chromatography (HPLC). The molecular weight of the SA-cT84.66 conjugate (210 kDa) and immounoreactivity (100%) were confirmed by size-exclusion HPLC, and the conjugate bound three equivalents of (111)In-DOTA-biotin. SA-cT84.66-pretargeted (111)In-DOTA-biotin was evaluated in nude mice bearing LS174T human colon carcinoma xenografts. Tumor uptake of (111)In-DOTA-biotin peaked at 3.32% injected dose per gram after 15 minutes. Clearance from blood and normal organs was extremely rapid, and tumor-to-blood ratios were >20:1 after 24 hours. The specific tumor targeting and rapid whole-body clearance of SA-cT84.66-pretargeted (111)In-DOTA-biotin indicated that this system is promising for the imaging and therapy of CEA-positive cancers.

Therapeutic efficacy of a 177Lu-labeled DOTA conjugated alpha-melanocyte-stimulating hormone peptide in a murine melanoma-bearing mouse model.

UNLABELLED: The aim of this study was to examine the therapeutic efficacy of (177)Lu-DOTA-Re(Arg(11))CCMSH in the B16/F1 murine melanoma-bearing mouse model. METHODS: (177)Lu-DOTA-Re(Arg(11))CCMSH was prepared in 0.5 M NH(4)OAc at a pH of 5.4. Two (2) treatment groups of 10 melanoma-bearing C57 mice were administrated with 2 x 18.5 MBq and 1 x 37.0 MBq of (177)Lu-DOTA-Re(Arg(11))CCMSH through the tail vein, respectively. One (1) group of 10 melanoma-bearing C57 mice was injected with saline placebos as untreated melanoma-bearing controls. RESULTS: In contrast to the untreated melanoma-bearing control group, (177)Lu-DOTA-Re(Arg(11))CCMSH administration yielded rapid and lasting therapeutic effects in the treatment groups. (177)Lu-DOTA-Re(Arg(11))CCMSH treatment decreased the tumor growth rate and significantly (p > 0.05) prolonged the survival time of melanoma-bearing C57 mice. Treatment with 2 x 18.5 MBq or 1 x 37.0 MBq of (177)Lu-DOTA-Re(Arg(11))CCMSH significantly extended the mean survival of tumor-bearing mice from 13.3 to 15.1 and 16.2 days, respectively. (177)Lu-DOTA-Re(Arg(11))CCMSH treatment produced no observed acute renal toxicity. CONCLUSIONS: The therapy study results revealed that (177)Lu-DOTA-Re(Arg(11))CCMSH yielded quantitative therapeutic effects in B16/F1 melanoma-bearing mice and appeared to be a promising radiolabeled peptide for the targeted radionuclide therapy of melanoma.

Preparation and biological evaluation of 111In-, 177Lu- and 90Y-labeled DOTA analogues conjugated to B72.3.

Three 1,4,7,10-tetraazacyclododecane-N,N',N",N"'-tetraacetic acid (DOTA) analogues were evaluated for relative in vivo stability when radiolabeled with (111)In, (90)Y and (177)Lu and conjugated to the monoclonal antibody B72.3. The DOTA analogues evaluated were "NHS-DOTA" [N-hydroxysuccinimdyl (NHS) group activating one carboxylate], "Arm-DOTA" (also known as MeO-DOTA; with a p-NCS, o-MeO-benzyl moiety on the methylene group of one acetic acid arm) and "Back-DOTA" (with a p-NCS-benzyl moiety on a backbone methylene group of the macrocycle). The B72.3 was conjugated to the DOTA analogues to increase the retention time of the radioloabeled conjugates in vivo in mice. The serum stability of the various radiometalated DOTA conjugates showed them to have good stability out to 168 h (all >95% except (111)In-NHS-DOTA-B72.3, which was 91% stable). Hydroxyapatite stability for the (111)In and (177)Lu DOTA-conjugates was >95% at 168 h, while the (90)Y DOTA-conjugates were somewhat less stable (between 90% and 95% at 168 h). The biodistribution studies of the radiometalated DOTA-conjugates showed that no significant differences were observed for the (111)In and (177)Lu analogues; however, the (90)Y analogues showed lower stabilities, as evidenced by their increased bone uptake relative to the other two [2-20% injected dose per gram (% ID/g) for (90)Y and 2-8% ID/g for (111)In and (177)Lu]. The lower stability of the (90)Y analogues could be due to the higher beta energy of (90)Y and/or to the larger ionic radius of Y(3+). Based on the bone uptake observed, the (177)Lu-NHS-DOTA-B72.3 had slightly lower stability than the (177)Lu-Arm-DOTA-B72.3 and (177)Lu-Back-DOTA-B72.3, but not significantly at all time points. For (90)Y, the analogue showing the lowest stability based on bone uptake was (90)Y-Arm-DOTA-B72.3, perhaps because of the metal's larger ionic radius and potential steric interactions minimizing effective complexation. The (111)In analogues all showed similar biological distributions at the various time points. This study suggests that care must be taken when evaluating (90)Y-labeled antibodies and in using NHS-DOTA-antibody conjugates with (177)Lu. All evaluations should be extended to time points relevant to the half-life of the radiometal and the therapy applications.

In vitro and in vivo evaluation of 177Lu- and 90Y-labeled E. coli heat-stable enterotoxin for specific targeting of uroguanylin receptors on human colon cancers.

The human E. coli heat-stable enterotoxin (ST(h), amino acid sequence N1SSNYCCELCCNPACTGCY19) binds specifically to the guanylate cyclase C (GC-C) receptor, which is present in high density on the apical surface of normal intestinal epithelial cells as well as on the surface of human colon cancer cells. Analogs of ST(h) are currently being used as vectors targeting human colon cancers. Previous studies in our laboratory have focused on development of 111Indium-labeled ST(h) analogs for in vivo imaging applications. Here, we extend the scope of this work to include targeting of the therapeutic radionuclides 90Y and 177Lu. The peptide DOTA-F19-ST(h)(1-19) was synthesized using conventional Fmoc-based solid-phase techniques and refolded in dilute aqueous solution. The peptide was purified by RP-HPLC and characterized by MALDI-TOF MS and in vitro receptor binding assay. The DOTA-conjugate was metallated with nonradioactive Lu(III)Cl3 and Y(III)Cl3, and IC50 values of 2.6+/-0.1 and 4.2+/-0.9 nM were determined for the Lu- and Y-labeled peptides, respectively. 177Lu(III)Cl3 and 90Y(III)Cl3 labeling yielded tracer preparations that were inseparable by C18 RP-HPLC, indicating that putative differences between Lu-, Y- and In coordination spheres are not observed in the context of labeled ST(h) peptides. In vivo biodistribution studies of the 177Lu-labeled peptide in severe combined immunodeficient (SCID) mice bearing T-84 human cancer tumor xenografts showed rapid clearance from the bloodstream, with >90 %ID in the urine at 1 h pi. Localization of the tracer within tumor xenografts was 1.86+/-0.91 %ID/g at 1 h pi, a value higher than for all other tissues with the exception of kidney (2.74+/-0.24 %ID/g). At 24 h pi, >98 %ID was excreted into the urine, and 0.35+/-0.23 %ID/g remained in tumor, again higher than in all other tissues except kidney (0.91+/-0.46 %ID/g). Biodistribution results at 24 h pi for the 90Y-labeled peptide mirrored those for the 177Lu analog, in agreement with the identical behavior of the labeled analogs by C18 RP-HPLC. These results demonstrate the ability of 177Lu- and 90Y-labeled ST(h) molecules to specifically target GC-C receptors expressed on T-84 human colon cancer cells.

Evaluation of combined (177)Lu-DOTA-8-AOC-BBN (7-14)NH(2) GRP receptor-targeted radiotherapy and chemotherapy in PC-3 human prostate tumor cell xenografted SCID mice.

The focus of this study was to evaluate the therapeutic benefit of combined gastrin-releasing peptide (GRP) receptor-targeted radiotherapy (TRT) with chemotherapy, using the PC-3 xenograft severe combined immunodeficiency (SCID) mouse model. (177)Lu-DOTA-8-AOC-BBN(7-14)NH(2) is a radiotherapeutic peptide that specifically targets the gastrin-releasing peptide receptor overexpressed on primary and metastatic prostate cancer. The chemotherapeutic agents, docetaxel and estramustine, were administered as single agents or in combination with the receptor-targeted radiotherapeutic agent. Combination receptor TRT/chemotherapy studies were begun 21 days postxenografting and were conducted as multiple-dose trials. The GRP receptor TRT agent was administered every 14 days, and single and combination chemotherapy dose regimens were given weekly. Tumor size, body weight, and body condition score were evaluated twice-weekly and a hematology profile once-weekly. Therapy study tumor volumes were evaluated by way of a repeated measures analysis of variance (ANOVA). Tumor volume measurements at 12 days postdose administration demonstrated a statistically significant (two-tailed P-value <0.05) tumor growth suppression in all experimental groups receiving GRP receptor-targeted radiotherapy, when compared to the control group. The two combined GRP receptor TRT/chemotherapy treatment groups demonstrated the greatest tumor growth suppression of all treatment groups. In comparing the two combined GRP receptor TRT/chemotherapy groups to the GRP receptor TRT alone group, a statistically significant difference was demonstrated for the combined groups by day 30, postdose administration. These data demonstrate that GRP receptor-targeted radiation therapy, using (177)Lu-DOTA-8-AOC-BBN(7-14)NH(2), used either alone or in combination with conventional chemotherapy, can suppress the growth of androgen- independent prostate cancer (AIPC).

Radiolanthanide-labeled monoclonal antibody CC49 for radioimmunotherapy of cancer: biological comparison of DOTA conjugates and 149Pm, 166Ho, and 177Lu.

The radiolanthanides 149Pm, 166Ho, and 177Lu have decay characteristics suitable for radioimmunotherapy (RIT) of cancer. N-Hydroxysulfosuccinimidyl DOTA (DOTA-OSSu) and methoxy-DOTA (MeO-DOTA) were conjugated to the anti-TAG-72 monoclonal antibody CC49 for radiolabeling with 149Pm, 166Ho, and 177Lu. While both DOTA conjugates could be labeled to high specific activity with 177Lu, MeO-DOTA afforded superior conjugate stability, radiolabeling, and radiochemical purity. Pilot biodistributions in nude mice bearing LS174T human colon carcinoma xenografts demonstrated that MeO-DOTA afforded higher tumor uptake and lower kidney retention of 177Lu than DOTA-OSSu. The in vitro stability of 149Pm-, 166Ho-, and 177Lu-MeO-DOTA-CC49 was evaluated using serum and hydroxyapatite assays. Serum stability of radiolanthanide-labeled MeO-DOTA-CC49 followed a trend based on the coordination energies of the radiometals, with 177Lu showing the highest stability after 96 to 168 h at 37 C. In contrast, MeO-DOTA-CC49 labeled with all three radiolanthanides was >92% stable to hydroxyapatite challenge for 168 h at 37 C. Comprehensive biodistributions of 149Pm-, 166Ho-, and 177Lu-MeO-DOTA-CC49 were obtained in LS174T-bearing nude mice. Maximum tumor uptakes were 100.0% ID/g for 149Pm at 96 h, 69.5% ID/g for 166Ho at 96 h, and 132.4% ID/g for 177Lu at 168 h. Normal organ uptakes were generally low, except in the liver, spleen, and kidney at early time points. By 96 to 168 h postinjection, nontarget organ uptake decreased to approximately 7% ID/g (kidney), 12% ID/g (spleen), and 20% ID/g (liver) for each radiolanthanide. When labeled with 149Pm, 166Ho, and 177Lu, MeO-DOTA-CC49 has potential for RIT of colorectal cancer and other carcinomas.

Melanoma therapy via peptide-targeted {alpha}-radiation.

PURPOSE: The therapeutic efficacy of a unique melanoma-targeting peptide conjugated with an in vivo generated alpha-particle-emitting radionuclide was evaluated in the B16/F1 mouse melanoma animal model. alpha-Radiation is densely ionizing, resulting in high concentrations of destructive radicals and irreparable DNA double-strand breaks. This high linear energy transfer overcomes radiation-resistant tumor cells and oxygen effects resulting in potentially high therapeutic indices in tumors such as melanoma. EXPERIMENTAL DESIGN: The melanoma targeting peptide, 1,4,7,10-tetraazacyclodecane-1,4,7,10-tetraacetic acid (DOTA)-Re(Arg(11))CCMSH, was radiolabeled with (212)Pb, the parent of (212)Bi, which decays via alpha and beta decay. Biodistribution and therapy studies were done in the B16/F1 melanoma-bearing C57 mouse flank tumor model. RESULTS: (212)Pb[DOTA]-Re(Arg(11))CCMSH exhibited rapid tumor uptake and extended retention coupled with rapid whole body disappearance. Radiation dose delivered to the tumor was estimated to be 61 cGy/muCi (212)Pb administered. Treatment of melanoma-bearing mice with 50, 100, and 200 muCi of (212)Pb[DOTA]-Re(Arg(11))CCMSH extended their mean survival to 22, 28, and 49.8 days, respectively, compared with the 14.6-day mean survival of the placebo control group. Forty-five percent of the mice receiving 200 muCi doses survived the study disease-free. CONCLUSIONS: Treatment of B16/F1 murine melanoma-bearing mice with (212)Pb[DOTA]-Re(Arg(11))CCMSH significantly decreased tumor growth rates resulting in extended mean survival times, and in many cases, complete remission of disease. (212)Pb-DOTA-Re(Arg(11))CCMSH seems to be a very promising radiopharmaceutical for targeted radionuclide therapy of melanoma.