Comparison of the biodistribution and the efficacy of monoclonal antibody 323/A3 labeled with either 131I or 186Re in human ovarian cancer xenografts

Effect of a radiolabel biochemical nature on tumor-targeting properties of EpCAM-binding engineered scaffold protein DARPin Ec1

Radionuclide-based imaging of molecular therapeutic targets might facilitate stratifying patients for specific biotherapeutics. New type of imaging probes, based on designed ankyrin repeat proteins (DARPins), have demonstrated excellent contrast of imaging of human epidermal growth factor type 2 (HER2) expression in preclinical models. We hypothesized that labeling approaches, which result in lipophilic radiometabolites (non-residualizing labels), would provide the best imaging contrast for DARPins that internalize slowly after binding to cancer cells. The hypothesis was tested using DARPin Ec1 that binds to epithelial cell adhesion molecule (EpCAM). EpCAM is a promising therapeutic target. Ec1 was labeled with ¹²⁵I using two methods to obtain the non-residualizing labels, while residualizing labels were obtained by labeling it with ^99mTc. All labeled Ec1 variants preserved target specificity and picomolar binding affinity to EpCAM-expressing pancreatic adenocarcinoma BxPC-3 cells. In murine models, all the variants provided similar tumor uptake. However, ¹²⁵I-PIB-H₆-Ec1 had noticeably lower retention in normal tissues, which provided appreciably higher tumor-to-organ ratios. Furthermore, ¹²⁵I-PIB-H₆-Ec1 demonstrated the highest imaging contrast in preclinical models than any other EpCAM-imaging agent tested so far. In conclusion, DARPin Ec1 in combination with a non-residualizing label is a promising probe for imaging EpCAM expression a few hours after injection.

Chemotherapeutic Efficacy of Implantable Antineoplastic-Treatment Protocols in an Optimal Mouse Model for Human Ovarian Carcinoma Cell Targeting

The present study aimed to design and develop a nanocomposite drug delivery system employing an antineoplastic-loaded antibody functionalized nanomicelle encapsulated within a Chitosan⁻Poly(vinylpyrrolidone)⁻Poly(N-isopropylacrylamide) (C⁻P⁻N) hydrogel to form an in situ forming implant (ISFI), responsive to temperature and pH for cancer cell-targeting following intraperitoneal implantation. The optimum nanomicelle formulation was surface-functionalized with anti-MUC 16 (antibody) for the targeted delivery of methotrexate to human ovarian carcinoma (NIH:OVCAR-5) cells in Athymic nude mice that expressed MUC16, as a preferential form of intraperitoneal ovarian cancer (OC) chemotherapy. The cross-linked interpenetrating C⁻P⁻N hydrogel was synthesized for the preparation of an in situ-forming implant (ISFI). Subsequently, the ISFI was fabricated by encapsulating a nanocomposite comprising of anti-MUC16 (antibody) functionalized methotrexate (MTX)-loaded poly(N-isopropylacrylamide)-b-poly(aspartic acid) (PNIPAAm-b-PASP) nanomicelles (AF(MTX)NM's) within the cross-linked C⁻P⁻N hydrogel. This strategy enabled specificity and increased the residence time of the nanomicelles at tumor sites over a period exceeding one month, enhancing uptake of drugs and preventing recurrence and chemo-resistance. Chemotherapeutic efficacy was tested on the optimal ovarian tumor-bearing Athymic nude mouse model and the results demonstrated tumor regression including reduction in mouse weight and tumor size, as well as a significant (p < 0.05) reduction in mucin 16 levels in plasma and ascitic fluid, and improved survival of mice after treatment with the experimental anti-MUC16/CA125 antibody-bound nanotherapeutic implant drug delivery system (ISFI) (p < 0.05). The study also concluded that ISFI could potentially be considered an important immuno-chemotherapeutic agent that could be employed in human clinical trials of advanced, and/or recurring, metastatic epithelial ovarian cancer (EOC). The development of this ISFI may circumvent the treatment flaws experienced with conventional systemic therapies, effectively manage recurrent disease and ultimately prolong disease-free intervals in ovarian cancer patients.

Chemoradionuclide therapy with 186re-labeled liposomal doxorubicin: toxicity, dosimetry, and therapeutic response

This study was performed to determine the maximum tolerated dose (MTD) and therapeutic effects of rhenium-186 ((186)Re)-labeled liposomal doxorubicin (Doxil), investigate associated toxicities, and calculate radiation absorbed dose in head and neck tumor xenografts and normal organs. Doxil and control polyethylene glycol (PEG)-liposomes were labeled using (186)Re-N,N-bis(2-mercaptoethyl)-N',N'-diethylethylenediamine (BMEDA) method. Tumor-bearing rats received either no therapy (n=6), intravenous Doxil (n=4), or escalating radioactivity of (186)Re-Doxil (185-925 MBq/kg) or (186)Re-PEG-liposomes (1110-1665 MBq/kg) and were monitored for 28 days. Based on body weight loss and systemic toxicity, MTD for (186)Re-Doxil and (186)Re-PEG-liposomes were established at injected radioactivity/body weight of 740 and 1480 MBq/kg, respectively. (186)Re-injected radioactivity/body weight for therapy studies was determined to be 555 MBq/kg for (186)Re-Doxil and 1295 MBq/kg for (186)Re-PEG-liposomes. All groups recovered from their body weight loss, leucopenia, and thrombocytopenia by 28 days postinjection. Normalized radiation absorbed dose to tumor was significantly higher for (186)Re-Doxil (0.299±0.109 Gy/MBq) compared with (186)Re-PEG-liposomes (0.096±0.120 Gy/MBq) (p<0.05). In a separate therapy study, tumor volumes were significantly smaller for (186)Re-Doxil (555 MBq/kg) compared with (186)Re-PEG-liposomes (1295 MBq/kg) (p<0.01) at 42 days postinjection. In conclusion, combination chemoradionuclide therapy with (186)Re-Doxil has promising potential, because good tumor control was achieved with limited associated toxicity.

Radiolabeling of MAG3-morpholino oligomers with 188Re at high labeling efficiency and specific radioactivity for tumor pretargeting

We are investigating a novel pretargeting approach involving an initial IV injection of antitumor antibody conjugated with a phosphorodiamidate morpholino oligomer (MORF, a DNA analog) and the subsequent IV injection of the radiolabeled complement oligomer (cMORF). In this paper, the cMORF was labeled with (188)Re using MAG(3) as chelator for therapeutic applications. Since (c)MORFs are unstable in acidic condition, an optimal labeling pH was first selected and the other labeling factors were then examined. A labeling efficiency of greater than 90% can be achieved even at a concentration of MAG(3)-cMORF as low as 0.8 microM. The labeled cMORF is stable and capable of hybridizing to its complement.

Synergistic effects of combined therapy using paclitaxel and [90Y-DOTA]776.1 on growth of OVCAR-3 ovarian carcinoma xenografts

OBJECTIVE

776.1 is a monoclonal antibody prepared against the human ovarian cancer antigen CA 125 that demonstrates preferential binding to the cell-associated form of the antigen and has shown promising results as an yttrium-90-labeled antibody in pre-clinical studies examining the effects on tumor growth in a murine xenograft model of human ovarian cancer. The purpose of the present study was to examine the effects of combined therapy with [90Y-DOTA]776.1 and paclitaxel compared with monotherapy with either agent on the growth of OVCAR-3 xenografts in nude mice.

METHODS

Mice bearing OVCAR-3 xenografts were treated with paclitaxel alone, 50 microCi or 150 microCi [90Y-DOTA]776.1 alone, or a combination of both treatments. Control groups were included which consisted of a nonspecific antibody, MOPC-21, labeled to a similar degree, administered as monotherapy or in combination with paclitaxel. The effects of administration of radioimmunotherapy prior to or following chemotherapy were also examined.

RESULTS

Treatment with paclitaxel and [90Y-DOTA]776.1 had a synergistic anti-tumor effect on the growth of OVCAR-3 xenografts. Synergy was only observed when a tumor-specific antibody was used in radioimmunotherapy. While no difference in tumor growth was observed with order of dosing, reduced toxicity was seen when paclitaxel was administered prior to radioimmunotherapy.

CONCLUSION

The combination of radioimmunotherapy using an anti-CA 125 monoclonal antibody and chemotherapy with paclitaxel was shown to be effective in an in vivo model of ovarian cancer and may hold promise as a treatment regimen for patients with ovarian cancer.

Indium-111-bleomycin complex in squamous cell cancer xenograft tumors of nude mice

INTRODUCTION

Labeling of bleomycin with Auger-emitter Indium-111 increases cytotoxicity in squamous cell cancer (SCC) cell lines, as we have reported earlier. In this study, we investigated whether (111)In- BLMC is toxic and effective in vivo among SCC-xenografted mice. The influence of (111)InBLMC on the squamous cell carcinoma cell cycle stimulated interest.

MATERIALS AND METHODS

In an animal experiment, 10 SCC-xenografted mice were used, two for demonstrating targeting in gamma-camera images, eight for intraperitoneally receiving NaCl, BLM, or (111)InBLMC as therapy. After a 2-week follow-up, the tumors were analyzed for proliferation (mitoses, Ki-67). DNA flow cytometric analysis was carried out from tumor samples and three UT-SCC cell lines.

RESULTS

Tumors were observed on gamma-camera images in xenografted mice after a (111)InBLMC injection. The UT-SCC-19A-xenografted mouse had a T/non-T uptake of 7.54 at 4 hours after the injection. At the end of the therapeutic trial, the mice were alive. In spite of a small number of animals, our findings indicate that BLM and (111)InBLMC seem to be more effective than NaCl in reducing tumor size. The proliferative activity was strong in BLM and in (111)InBLMC groups, indicating regrowth of the tumors. In DNA analysis, the percentages of cells in the G2/M-phases increased after exposure to BLM and particularly to (111)InBLMC in all three cell lines.

CONCLUSIONS

The effect of BLM is preserved after the adding of Auger-emitter In-111. Tumor-seeking (111)InBLMC can be administered safely at tumor-decreasing concentrations in xenograft head and neck cancers. To demonstrate the antitumor effect of (111)InBLMC, the experiments should be extended to include a larger number of mice. BLM, and especially (111)InBLMC, seems to induce alteration in the cell cycle by producing a G2/M block. The verification of the result requires repeated in vitro experiments.

Long-Lived Positron Emitters Zirconium-89 and Iodine-124 for Scouting of Therapeutic Radioimmunoconjugates with PET

Antibody-PET imaging might be of value for the selection of radioimmunotherapy (RIT) candidates to confirm tumor targeting and to estimate radiation doses to tumor and normal tissues. One of the requirements to be set for such a scouting procedure is that the biodistributions of the diagnostic and therapeutic radioimmunoconjugates should be similar. In the present study we evaluated the potential of the positron emitters zirconium-89 ((89)Zr) and iodine-124 ((124)I) for this approach, as these radionuclides have a relatively long half-life that matches with the kinetics of MAbs in vivo (t(1/2) 3.27 and 4.18 days, respectively). After radiolabeling of the head and neck squamous cell carcinoma (HNSCC)-selective chimeric antibody (cMAb) U36, the biodistribution of two diagnostic (cMAb U36-N-sucDf-(89)Zr and cMAb U36-(124)I) and three therapeutic radioimmunoconjugates (cMAb U36-p-SCN-Bz-DOTA-(88)Y-with (88)Y being substitute for (90)Y, cMAb U36-(131)I, and cMAb U36-MAG3-(186)Re) was assessed in mice with HNSCC-xenografts, at 24, 48, and 72 hours after injection. Two patterns of biodistribution were observed, one pattern matching for (89)Zr- and (88)Y-labeled cMAb U36 and one pattern matching for (124)I-, (131)I-, and (186)Re-cMAb U36. The most remarkable differences between both patterns were observed for uptake in tumor and liver. Tumor uptake levels were 23.2 +/- 0.5 and 24.1 +/- 0.7%ID/g for the (89)Zr- and (88)Y-cMAb U36 and 16.0 +/- 0.8, 15.7 +/- 0.79 and 17.1 +/- 1.6%ID/g for (124)I-, (131)I-, and (186)Re-cMAb U36-conjugates, respectively, at 72 hours after injection. For liver these values were 6.9 +/- 0.8 ((89)Zr), 6.2 +/- 0.8 ((88)Y), 1.7 +/- 0.1 ((124)I), 1.6 +/- 0.1 ((131)I), and 2.3 +/- 0.1 ((186)Re), respectively. These preliminary data justify the further development of antibody-PET with (89)Zr-labeled MAbs for scouting of therapeutic doses of (90)Y-labeled MAbs. In such approach (124)I-labeled MAbs are most suitable for scouting of (131)I- and (186)Re-labeled MAbs.

Radioimmunotherapy with 186Re-labeled monoclonal antibody to treat liver metastases of colon cancer cells in nude mice

The efficacy of radioimmunotherapy (RIT) in the treatment of minimal disease has been previously shown, despite the limitation of beta-emitters suggested by a mathematical model. In the present study, the efficacy of RIT with an anti-colorectal cancer IgG1 A7 conjugated with 186Re was examined in a liver metastasis model established by intrasplenic inoculation of human colon cancer cells. In this model, small metastases of less than 1 mm in diameter can be observed 1 week after cell inoculation. Metastases attain a diameter of several millimeters at 2 weeks. 186Re-A7 accumulated exclusively in metastases, displaying a value of 24.1 +/- 8.7% ID/g 2 days after the injection. 186Re-A7 accumulation in liver metastases increased with decreasing size. RIT with 7 MBq 186Re-A7 at 2 weeks significantly suppressed the growth of metastases; weight of metastases 4 weeks after cell inoculation was 5.96 +/- 0.87 g in nontreated control mice and 1.25 +/- 0.75 g in mice receiving 186Re-A7 RIT (p < 0.0001). RIT at 1 week more effectively inhibited metastatic growth to 0.08 +/- 0.05 g (p < 0.002 vs. RIT at 2 weeks). RIT with a class-matched irrelevant MAb 186Re-HPMS-1 at 1 week after cell inoculation somewhat suppressed metastatic growth, 3.39 +/- 0.25 g at 4 weeks, as compared with the control; however, 186Re-HPMS-1 RIT was far less effective than 186Re-A7 RIT (p < 0.0001). These results support the use of RIT with 186Re-MAb in an adjuvant setting in cases involving minimal disease. Factors such as higher and homogeneous MAb accumulation in small nodules, better perfusion, and subsequent better oxygenation likely compensate for the loss of beta radiation outside small metastases.

Tumor targeting properties of monoclonal antibodies with different affinity for target antigen CD44V6 in nude mice bearing head-and-neck cancer xenografts

The CD44 protein family consists of isoforms with tissue-specific expression, which are encoded by standard exons and up to 9 alternatively spliced variant exons (v2-v10) of the same gene. The murine MAbs U36 and BIWA-1, directed against overlapping epitopes within the v6 region of CD44, have previously been shown to efficiently target HNSCC. We herein report on the construction of 1 chimeric (BIWA-2) and 2 humanized (BIWA-4 and BIWA-8) derivatives of BIWA-1. Together with U36 and BIWA-1, these new antibodies were evaluated for affinity to the antigen in vitro as well as for biodistribution and efficacy in RIT using nude mice bearing the HNSCC xenograft line HNX-OE. As determined by surface plasmon resonance, the MAbs bound to CD44v6 with an up to 46-fold difference in affinity (K(d) ranging from 1.1 x 10(-8) to 2.4 x 10(-10) M) with the following ranking: mMAb U36 < hMAb BIWA-4 < hMAb BIWA-8 < mMAb BIWA-1 approximately cMAb BIWA-2. To evaluate their in vivo tumor-targeting properties, 2 MAbs with identical murine or human isotype were labeled with either (131)I or (125)I and administered simultaneously (50 microg/10 microCi each) as pairs showing a stepwise decrease in the difference in affinity: U36 vs. BIWA-1 (35.0-fold difference), BIWA-4 vs. BIWA-2 (14.0-fold) and BIWA-4 vs. BIWA-8 (4.0-fold). Biodistribution was assessed at 1, 2, 3 or 4 and 7 days after injection. Remarkably, for all 3 MAb pairs tested, the lower-affinity MAb showed a higher degree and specificity of tumor localization. The difference in tumor localization was more pronounced when the difference in affinity was larger. For example, 3 days after injection, the lower-affinity mMAb U36 showed a 50% higher tumor uptake than the higher-affinity mMAb BIWA-1, while blood levels and uptake in organs were similar. After labeling with (186)Re (300 or 400 microCi), the same MAb pairs showed RIT efficacy consistent with the biodistribution data: (186)Re-U36 was more effective than (186)Re-BIWA-1, (186)Re-BIWA-4 was slightly more effective than (186)Re-BIWA-2 and (186)Re-BIWA-4 and (186)Re-BIWA-8 demonstrated similar efficacy. Based on these data, we conclude that antibodies with markedly lower affinity to a given target antigen (e.g., U36, BIWA-4) may show superior tumor targeting in comparison with higher-affinity versions of these antibodies.

Experimental radioimmunotherapy with 186Re-MAG3-A7 anti-colorectal cancer monoclonal antibody: comparison with 131I-counterpart

A murine IgG1 against a Mr 45 kD tumor-associated glycoprotein in human colorectal cancer, A7, was radiolabeled with 186Re by a chelating method with a mercaptoacetyltriglycine (MAG3). Its specific activity was 119 MBq/mg, which would be high enough for a therapeutic purpose, and its immunoreactivity was preserved well as was 131I-A7 labeled by the chloramine-T method. Growth of human colon cancer xenografts, 9.14 +/- 0.44 mm in diameter, in nude mice was significantly suppressed by an intravenous dose of 4.48 MBq of 186Re-A7. The therapeutic outcome with 186Re-A7 was better than that with 4.63 MBq of 131I-A7. Toxicity of treatments assessed by body weight change was similar with both conjugates. These results are likely caused by the tumor size and more favorable physical properties of 186Re than those of 131I.

Combination radioimmunotherapy with local hyperthermia: increased delivery of radioimmunoconjugate by vascular effect and its retention by increased antigen expression in colon cancer xenografts

Hyperthermia (HT) may increase tumor targeting of a radiolabeled antibody by its effects on tumor vasculature and antigen expression. Expression of a 45-kDa glycoprotein antigen on LS180 colon cancer cells was 2.7-fold enhanced 2 days after heating at 43 degrees C for 1 h. Preferential tumor accumulation of 125I-A7 recognizing this antigen was doubled and the antitumor effect of 131I-A7 was significantly improved by HT. Hyperthermia also increased tumor uptake of an irrelevant antibody but its radioactivity was rapidly cleared. These results indicate that HT increased the initial delivery of an antibody to a tumor by its vascular effect, and radioactivity was retained in tumors by increased specific binding, resulting in a better radioimmunotherapy outcome.

[186Re]-labeled mouse and chimeric monoclonal antibody 323/A3: a comparison of the efficacy in experimental human ovarian cancer

We have investigated whether [186Re]-labeled chimeric monoclonal antibody 323/A3 (MAb c-323/A3) is as effective as [186Re]-labeled mouse 323/A3 (m-323/A3) in the growth inhibition of human ovarian cancer xenografts OVCAR-3 and FMa. [186Re] was conjugated to MAbs with the use of the chelate S-benzoylmercaptoacetyltriglycine (S-benzoyl-MAG3). The maximum number of metal-MAG3 groups that could be conjugated to one MAb molecule accepting a minimal initial increase of the blood clearance (15%) was 8.5 and 2.9 for c-323/A3 and m-323/A3, respectively. With these molar ratios the immunoreactivity of both MAbs was maintained. An inverse relationship was observed between the protein dose of c-323/A3 and its blood clearance. Both [186Re]-c-323/A3 and [186Re]-m-323/A3 were comparable in the inhibition of the tumor growth when higher protein doses were used. Together with the expected lower immunogenicity, our results imply that c-323/A3 is preferable for use in [186Re]-radioimmunotherapy in ovarian cancer patients.