The presence of a concomitant bulky tumor can decrease the uptake and therapeutic efficacy of radiolabeled antibodies in small tumors.

We describe the effects that a concomitant large tumor mass can exert on the therapeutic efficacy of radioimmunotherapy against small tumors, using the nude mouse/GW-39 human colonic cancer model. The tumor uptake 7 days p.i. of i.v.-injected 131I-labeled anti-CEA MAb (NP-4) and anti-CSAp MAb (Mu-9) in small (less than 0.2 g) s.c. GW-39 tumors was approximately 3-fold lower in animals with a concomitant large (greater than 1.0 g) GW-39 tumor than in the absence of a large tumor. An inverse correlation between the mass of the tumor burden and the 131I levels in the blood was observed, indicating that a large tumor mass may act as a sink for the injected radiolabeled antibody. Increasing antibody protein dose did not reverse the reduced uptake in the small s.c. tumors. The therapeutic efficacy of a single 0.25-mCi injection of 131I-labeled anti-CSAp MAb Mu-9 towards intrapulmonary GW-39 metastases was tested in nude mice bearing either small or large GW-39 s.c. tumors. Over 80% of the animals with small s.c. GW-39 tumors survived 18 weeks after tumor transplantation, whereas less than 20% of the animals bearing large s.c. tumors survived past 13 weeks. Dosimetric calculations, based on biodistribution data over time, indicated that the presence of a large s.c. tumor mass may have decreased the radiation dose to the intrapulmonary tumors almost two-fold. However, the radiation dose to the blood was also decreased in the animals with the large tumor burden. Therefore, the animals with larger tumor burden may also have been able to sustain higher doses of the radioantibody. The presence of a large tumor mass can thus affect the biodistribution and therapeutic efficacy of radioiodinated antibodies. We suggest that bulky tumors can adsorb a considerable amount of the injected dose, thereby reducing the total amount of MAb available for binding to the smaller tumors.     

Anti-oxidant vitamins reduce normal tissue toxicity induced by radio-immunotherapy

Our purpose was to determine whether the administration of anti-oxidant vitamins could reduce dose-limiting toxicity from radio-immunotherapy (RAIT) and thereby allow higher escalation of RAIT doses. Lipophilic vitamins A and E were administered i.p. and hydrophilic vitamin C was administered i.m. for 14 days (3 days pre-RAIT through 11 days post-RAIT) alone or with bone marrow transplantation (BMT) to either BALB/c mice for toxicity studies or to nude mice bearing s.c. GW-39 human colonic cancer xenografts for therapy studies. The maximal tolerated dose (MTD) of RAIT ((131)I-MN14 anti-CEA IgG) that results in no lethality was determined for mice that did not receive vitamins or BMT and those that did receive one or both interventions. Body weight, peripheral white blood cell (pWBC) and platelet (PLT) counts and tumor growth were also measured. Administration of vitamins (equivalent of 3.5 IU/day vitamin A, 0.107 IU/day vitamin E and 4.0 mg/day ascorbic acid) to mice along with BMT increased the MTD by 42% and reduced body weight loss associated with RAIT. Vitamins also reduced the magnitude of RAIT-induced myelosuppression. As early as day 7 after RAIT, vitamins increased WBC counts following both a 400 microCi and a 500 microCi dose. On day 14 after the 400 microCi dose of RAIT (day 7 post-BMT), the additive effect of BMT and vitamin could be detected. Tumor growth was not adversely affected by vitamin administration.     

Targeted therapy of athymic mice bearing GW-39 human colonic cancer micrometastases with 131I-labeled monoclonal antibodies.

The therapeutic potential of radiolabeled antibodies is usually evaluated in experimental animal models bearing s.c. xenografts. We have established a micrometastatic model of the GW-39 human colonic carcinoma in the nude mouse lung (J. Natl. Cancer Inst., 83: 627-632, 1991) and presented preliminary findings on the efficacy of a 131I-anticarcinoembryonic antigen (CEA) antibody in this model. We now extend our observations on the use of radioiodinated labeled monoclonal antibodies (MAbs) to treat multiple small tumor nodules. Biodistribution and dosimetry analysis was performed for intact and F(ab')2 of NP-4 anti-CEA IgG, Mu-9 anti-colon-specific antigen IgG, isotype-matched irrelevant anti-AFP IgG, and intact MAb 34A anti-lung endothelial IgG antibody. Comparisons were made for rad dose delivered to small s.c. tumors, normal lung, lung with tumor nodules, and isolated tumor nodules. Survival curves were generated for tumor-bearing animals treated 1, 7, or 14 days after tumor cell implantation with these antibodies using the maximal tolerated dose for intact antibodies (275 microCi) and for F(ab')2 fragments (1.2 mCi). The studies established the following observations: (a) in contrast to previous results in a bulky tumor model in hamsters, intact antibodies are more therapeutic than MAb fragments for both NP-4 and Mu-9; (b) tumor nodule size, even on the microscopic level, affects therapeutic outcome; antibodies were more effective when administered 7 days postimplantation (mean nodule diameter, 150 microns) compared with treatment 14 days postimplantation (mean nodule diameter, 750 microns); (c) administration of radioiodinated Mu-9 was exquisitely effective on single avascular tumor cells that had seeded in lung; irrelevant antibody was minimally radiotoxic; (d) as in the bulky disease model, the anti-colon-specific antigen p antibody delivers a higher rad dose than the anti-CEA antibody and is significantly more therapeutic in the micrometastasis model; (e) a higher affinity anti-CEA antibody (MN-14) recognizing the same epitope on CEA as NP-4 was equally therapeutic; (f) the use of MAb directed against the lung endothelium was not as therapeutic as a tumor-associated antibody; and (g) all tumor-associated antibodies were more efficacious than administration of the maximal tolerated dose of 5-fluorouracil and leucovorin in this human tumor-xenograft model. These results provide further support for the use of radioimmunotherapy in the handling of minimal disease, probably as part of an adjuvant treatment regimen.     

Experimental studies on the role of antibody fragments in cancer radio-immunotherapy: Influence of radiation dose and dose rate on toxicity and anti-tumor efficacy

Whereas bivalent fragments have been widely used for radio-immunotherapy, no systematic study has been published on the therapeutic performance of monovalent conjugates in vivo. The aim of our study was, therefore, to determine the therapeutic performance of ¹³¹I-labeled Fab as compared to bivalent conjugates and to analyze factors that influence dose-limiting organ toxicity and anti-tumor efficacy. The maximum tolerated doses (MTDs) and dose-limiting organ toxicities of the ¹³¹I-labeled anti-CEA antibody MN-14 [IgG, F(ab′)₂ and Fab] were determined in nude mice bearing s.c. human colon cancer xenografts. Mice were treated with or without bone marrow transplantation (BMT) or inhibition of the renal accretion of antibody fragments by D-lysine or combinations thereof. Toxicity and tumor growth were monitored. Radiation dosimetry was calculated from biodistribution data. With all 3 ¹³¹I-labeled immunoconjugates [IgG, F(ab′)₂ and Fab], the red marrow was the only dose-limiting organ; MTDs were 260 μCi for IgG, 1,200 μCi for F(ab′)₂ and 3 mCi for Fab, corresponding to blood doses of 17 Gy, 9 Gy and 4 Gy, respectively. However, initial dose rates were 10 times higher with Fab as compared to IgG and 3 times higher as compared to F(ab′)₂. The MTD of all 3 immunoconjugates was increased by BMT by approximately 30%. In accordance with renal doses below 10 Gy, no signs of nephrotoxicity were observed. Despite lower absorbed tumor doses, at equitoxic dosing, Fab fragments were more effective at controlling tumor growth than the respective bivalent fragment or IgG, probably due to higher intratumoral dose rates. Our data indicate that the improved anti-tumor effectiveness of antibody fragments as compared to IgG and the higher myelotoxicity at comparably lower red marrow doses are most likely due to the higher initial dose rates observed with antibody fragments. Int. J. Cancer 77:787–795, 1998. © 1998 Wiley-Liss, Inc.     

Quantitative and qualitative effects of experimental radioimmunotherapy on tumor vascular permeability

Localization of radiolabeled antibodies in the perivascular space of tumors resulted in morphological changes in blood vessel structure and physiological changes in tumor vessel function. Vessel diameter decreased by day 14 and was associated with a significant decline in vascular volume (VV). Upon recovery of VV, the basement membrane surrounding the endothelium had thickened. Tumor vascular permeability (VP) decreased within 7 days of treatment and remained suppressed throughout the 42-day observation period of our study. The decline in VP, which could be visualized by fluorescent microscopy of FITC-dextran extravasation, was dose-related and could be quantified at doses as low as 800 cGy. The radioantibody-induced 50–80% decline in tumor VP was observed in 3 human colonic xenografts (GW-39, LS174T and MOSER). Decreases in VP have been observed for proteins ranging in size from 20 to 150 kDa. Similar effects on VP were noted when low protein doses (10–30 μg), which resulted in heterogeneous antibody distribution, were used or with high protein doses (400–750 μg), which resulted in more uniform penetration of antibody. If ¹⁸⁸Re or ⁹⁰Y, radiometals with higher β-energy and longer path lengths, were substituted for ¹³¹I, a similar decrease in VP was observed. The radioimmunotherapy (RAIT)-induced decrease in tumor VP resulted in a 90% decline in accretion of a second dose of radioantibody. The 10% of the second dose that was taken up by the tumor targeted many already non-viable tumor regions and some, but not all, viable tumor cell clusters. © 1995 Wiley-Liss, Inc.     

Colonic tumor CEA, CSAp and MUC-1 expression following radioimmunotherapy or chemotherapy.

Understanding the changes in tumor biology following cytotoxic therapy may lead to a better understanding of the properties of surviving tumor cell populations and to an improved ability to target and treat these cells. This report addressed the time-dependent dynamic alterations in the expression of three tumor-associated antigens: carcinoembryonic antigen (CEA), colon-specific antigen (CSAp) and mucin-1 (MUC-1) following chemotherapy with 5-fluorouracil (5-FU) or radioimmunotherapy (RAIT; (131)I-labeled anti-CEA IgG) in human colonic tumor xenografts. Immunoassay results show that CEA and MUC-1 expression all increase rapidly after either 5-FU or RAIT. GW-39 tumors show a 2.7-fold increase in CEA expression after a maximum tolerated dose of RAIT, being highest after 21 days, while LS174T and HT-29 tumors maximally increase expression 8.3- and 2.6-fold on day 7 after RAIT, respectively. The change in LS174T is short-term, whereas the change in HT-29 is maintained for at least 4 weeks. Serum CEA levels in these tumor- bearing mice also increase in parallel to the changes observed in tumor. MUC-1 increases 2.5-fold by day 5-7 following RAIT in LS174T tumors and 6-fold by day 14 following RAIT in GW-39 tumors, with a corresponding increase in serum MUC-1. Dramatic increases in CSAp after RAIT were also demonstrated in GW-39 tissue by immunohistochemistry. Thus, these data indicate that the response of tumor cells to low-dose-rate radiation from RAIT or to chemotherapy is associated with an increase of CEA, MUC-1 and CSAp.     

Enhanced clearance of radiolabeled murine monoclonal antibody by a syngeneic anti-idiotype antibody in tumor-bearing nude mice.

A syngeneic anti-idiotype monoclonal antibody (MAb) (CM-11) directed against an anti-carcinoembryonic antigen (CEA) murine MAb (NP-4) was evaluated as a second antibody (SA) to promote the rapid clearance of radiolabeled NP-4 from the blood. Initial studies confirmed that CM-11 IgG removed 131I-NP-4 IgG from the blood as effectively as a polyclonal donkey anti-goat IgG removed 131I-goat IgG. However, use of an F(ab')2 in place of either the NP-4 or CM-11 IgG was not as effective in removing primary radiolabeled antibody, despite the formation of high-molecular-weight complexes. In accordance with previous results, the timing and dose of the SA injection was critical for optimizing tumor uptake and improving tumor/non-tumor ratios. In nude mice bearing GW-39 human colonic tumor xenografts, a delay in the injection of CM-11 by 48 hr after injection of radiolabeled NP-4 was optimal, since this allowed maximum tumor accretion. At a 200:1 CM-11:NP-4 ratio, tumor uptake was reduced, suggesting inhibition of NP-4 binding to CEA within the tumor. Despite optimizing tumor uptake by delaying SA injection and adjusting its dose, the percentage of 131I-NP-4 in the tumor decreased 2- to 3-fold within 2 days after CM-11 injection. A similar effect was seen for 111In-labeled NP-4 IgG with CM-11. Injection of excess unlabeled NP-4 given to block CM-11 shortly after its injection failed to curtail the loss of NP-4 from the tumor. Our results suggest that high blood levels of MAb are important for sustaining NP-4 in the tumor. Radiation-dose predictions derived from biodistribution studies indicate that a higher tumor dose may be delivered using the SA method than with either 131I-NP-4 IgG or F(ab')2 alone. Use of the SA method with 90Y-labeled NP-4 IgG, as modeled from biodistribution studies with 111In-NP-4 IgG, would likely be limited by liver toxicity.     

Comparison of therapeutic efficacy and host toxicity of two different 131I-labelled antibodies and their fragments in the GW-39 colonic cancer xenograft model

The in vivo uptake, therapeutic potential, and host toxicity were evaluated for both the intact IgG and F(ab')2 fragment of 2 murine monoclonal antibodies (MAbs) directed against either carcino-embryonic antigen (CEA), called NP-4, or colon-specific antigen-p (CSAp), called Mu-9, in the GW-39 human colorectal carcinoma grown in the hamster cheek pouch. Mu-9 IgG and F(ab')2 were retained longer by the tumor than was the NP-4 IgG or F(ab')2, respectively. Localization of the two antibodies by micro-autoradiography revealed two distinct patterns. Mu-9 was seen densely around whole acini of tumor cells, whereas NP-4 was found around each individual cell, albeit less densely. The anti-tumor effects of 131I-labelled Mu-9 and NP-4 IgG were equal, but the therapeutic effectiveness of Mu-9 F(ab')2 was significantly higher than NP-4 F(ab')2, as measured by change in tumor size. A dose-dependent increase in host toxicity, as measured by change in body weight and change in peripheral white blood cells (p-WBCs), was observed with 0.5 to 3.0 mCi doses of 131I-IgG regardless of the MAb used. A 10-22% loss in body weight lasting 3-7 weeks and a 50-80% loss in pWBCs lasting 6-8 weeks were observed in these animals. In contrast, 3 x 2 mCi doses of 131I-NP-4 or Mu-9 F(ab')2 given at 3-day intervals, a schedule which was equally therapeutic to a single 2-mCi dose of 131I-IgG, resulted in only a 9% loss in body weight and a 50% loss in pWBCs that lasted only 1 week. This was followed by a complete recovery over the next 2-3 weeks. These data suggest that multiple doses of F(ab')2 can be as tumoricidal as a single dose of an intact MAb IgG, but significantly less toxic to the host.     

Optimizing the use of combined radioimmunotherapy and hypoxic cytotoxin therapy as a function of tumor hypoxia.

Combined radioimmunotherapy (RAIT) and hypoxic cytotoxin therapy (SR4233 or NLCQ-1) have been evaluated with both modalities administered on the same day with only moderate improvement compared with the effects of RAIT alone. In a series of studies using oxygen electrodes, immunohistochemistry and radiotracers, we have demonstrated that RAIT induces a prolonged state of hypoxia in most tumors, without affecting the pO(2) levels in normal tissues. Using serial microelectrode measurements through subcutaneous (s.c.) GW-39 human colonic xenografts, we established that the median pO(2) was unrelated to the initial size of the tumor, over a range of sizes from 1.0 to 4.0 cm. Fourteen days after mice were given a 240-microCi dose of (131)I-MN-14 anti-carcinoembryonic antigen immunoglobulin G, their median pO(2) declined from 26.1 +/- 9.6 mmHg to 9.8 +/- 3.9 mmHg (p < 0.001). Using the radiotracer (3)H-MISO that accumulates in hypoxic regions, uptake in GW-39, LoVo and LS174T s.c. human colonic tumors increased 3.0- to 4.2-fold from day 14 through day 28 post-RAIT, but uptake of (3)H-MISO in CALU-3 tumors remained unchanged after RAIT. Normal tissue (liver, kidney, lung) uptake of (3)H-MISO did not exhibit significant changes. The increase in tumor hypoxia was also demonstrated visually using anti-PIMO staining of tumor sections. We postulated that sequential delivery of the 2 therapeutic agents, with the hypoxic cytotoxin given 2 weeks after RAIT when tumor pO(2) levels were at their nadir, would improve the therapeutic response above either modality alone or above the 2 agents delivered on the same day. Tumor growth was compared in mice given either RAIT or cytotoxin alone, the combined treatment on the same day or with the cytotoxin delivered 14 days after RAIT. Tumor size on day 35 for RAIT-treated and SR4233-treated GW-39 were 3.56 +/- 0.40 and 7.98 +/- 2.50 cm(3). When RAIT + SR4233 were delivered on the same day, tumor size dropped to 2.78 +/- 0.80 cm(3). If RAIT was given on day 0 and SR4233 on day 14, size further declined further to 1.74 +/- 0.32 cm(3) (p < 0.05 compared with same day delivery). For LS174T, tumor size on day 28 for RAIT-treated and SR4233-treated tumors were 1.14 +/- 0.36 cm(3) and 3.65 +/- 0.78 cm(3), respectively. When RAIT + SR4233 were delivered on the same day, size was 0.51 +/- 0.174 cm(3). If RAIT was dosed on day 0 and SR4233 was given on day 14, tumor size was 0.13 +/- 0.07 cm(3) (p < 0.05). Similar results were obtained for LoVo, but not for CALU-3 tumors. Another hypoxic cytotoxin, NLCQ-1, was also more efficacious 2 weeks after RAIT, compared with same-day dosing. Thus, information on tumor hypoxia after radioantibody therapy could be important for ascertaining a window of opportunity when the surviving tumor regions are most responsive to hypoxic cytotoxins.     

Radioimmunotherapy of experimental pancreatic cancer with 131I-labeled monoclonal antibody PAM4

We examined the therapeutic efficacy of ¹³¹I-labeled murine monoclonal antibody (MAb) PAM4 against human pancreatic cancers carried as xenografts in athymic nude mice. Animals bearing the CaPanI tumor (0.2 cm³) were either untreated or were given, ¹³¹I-labeled nonspecific Ag8 antibody. By week 7 mean tumor size had grown 16.5 ± 8.4-fold and 4.2 ± 2.5-fold for the untreated and ¹³¹I-Ag8-treated animals, respectively. In contrast, animals administered ¹³¹I-PAM4 exhibited marked regression of tumors to an average of 15% of initial tumor volume. Since most pancreatic cancer patients present with large tumor burdens, the limitation of ¹³¹I-PAM4 treatment with respect to initial tumor size was investigated in animals bearing tumors of approximately 0.5 cm³, 1.0 cm³ and 2.0 cm³. Significant extension of survival time (>3-fold increase) was noted for both the 0.5 cm³ and 1.0 cm^{3 131}I-PAM4-treated groups, compared to their respective untreated controls. Even in the group bearing large 2.0-cm³ tumors, survival was increased 2-fold over the control group. To further improve anti-tumor effects in large tumors, 2 injections of ¹³¹I-PAM4 were administered at a 4-week interval to animals bearing tumors of approximately 1.0 cm³. Significant extended survival was noted for the group receiving 2 doses when compared to the group receiving only 1 dose. Int. J. Cancer 71:660-667, 1997. © 1997 Wiley-Liss, Inc.     

Preclinical Therapy of Breast Cancer with a Radioiodinated Humanized Anti-EGP-1 Monoclonal Antibody: Advantage of a Residualizing Iodine Radiolabel

BACKGROUND: A humanized monoclonal antibody (MAb), hRS7, labeled with 131I-IMP-R4, was evaluated for the preclinical radioimmunotherapy (RAIT) of breast cancer. 131I-IMP-R4 is an improved residualizing form of 131I that overcomes the short tumor residence time associated with conventionally radioiodinated MAbs. RS7, an internalizing MAb, recognizes epithelial glycoprotein-1, which is highly expressed in the carcinomas of breast, lung, ovary, and prostate. METHODS: A humanized version of RS7 was generated by CDR-grafting and transfection. In vivo experiments were carried out in nude mice bearing subcutaneous MDA-MB-468 human breast cancer xenografts. Therapy experiments were performed using established tumors with mean tumor volume (MTV) of 0.3 cm3, and single administrations, at approximately 70% of the estimated maximum tolerated doses (MTD), of the residualizing 131I-IMP-R4-hRS7 and 131I-hRS7 prepared by the conventional chloramine-T method [131I-hRS7 (CT)]. Therapeutic specificity was determined by comparison with untreated and non-specific MAb controls. RESULTS: hRS7 was functionally very similar to murine and chimeric RS7. A biodistribution study using 125I-IMP-R4-hRS7 and 131I-hRS7 (CT) indicated a dosimetric advantage for the former. The MTVs 8 weeks post-treatment were 20, 163, and 280% of the starting MTVs of 131I-IMP-R4-hRS7-treated, 131I-hRS7 (CT)-treated, and untreated groups, respectively. Complete remissions were seen in 5 of 11 [and 6 of 8] mice treated with 131I-IMP-R4-hRS7, and in 1 of 11 mice treated with 131I-hRS7(CT). 131I-IMP-R4-hRS7 was significantly more efficacious than 131I-hRS7 (CT) [ P = 0.01 for AUC] and the control 131I-IMP-R4-MAb. CONCLUSION: 131I-IMP-R4-hRS7 is a promising new agent for RAIT, providing significant therapeutic advantage in comparison to the conventionally 131I-labeled antibody.     

Cure of metastatic human colonic cancer in mice with radiolabeled monoclonal antibody fragments.

There is currently no method to cure patients with disseminated colorectal cancer, which is the third leading cancer killer in the Western World. This report shows that the GW-39 intrapulmonary micrometastatic human colonic cancer model in nude mice can be cured with radiolabeled antibodies against carcinoembryonic antigen, and that this approach of radioimmunotherapy is superior to conventional chemotherapy with 5-fluorouracil and leucovorin (5-FU/LV). Monovalent Fab fragments labeled with 131I are superior to intact IgG when survival was evaluated 3, 7, and 14 days after implantation, leading to cures in up to 90% of the mice. Histological results provide support for the differences in therapeutic efficacy observed. Microautoradiography was used to evaluate the intratumoral distribution of each form of antibody. The enhanced tumor control by Fab compared with IgG could be explained in part by the homogeneity of radioantibody distribution of Fab. Biodistribution analysis and initial dose rate calculations for all three forms of antibody also help explain the ability of 131I-labeled Fab to provide better tumor growth control than seen with 131I-labeled IgG. Thus, radioimmunotherapy may be a new modality to treat metastatic disease, particularly when using small antibody fragments.     

Representation of epitopes on colon-specific antigen-p defined by monoclonal antibodies

Colon-specific antigen-p (CSAp) is a large molecular-sized protein restricted to normal and neoplastic gastrointestinal tissues and to some mucinous ovarian tumors. Murine monoclonal antibodies (MAbs) were raised against CSAp that was affinity purified with goat polyclonal antibodies from GW-39 human colonic carcinoma xenografts or against the CSAp-producing colon cancer cell line SW-948. Two of the MAbs, designated Mu-2 and Mu-4, recognized a CSAp determinant containing sialic acid, and this epitope was also expressed on bovine submaxillary mucin (BSM). Blocking experiments demonstrated that the Mu-2 and Mu-4 MAbs recognized different determinants. A third MAb, Mu-3, did not cross-react with BSM, but unlike Mu-2 and Mu-4, it did react with human saliva. Reactivity of Mu-3 with saliva did not correlate with major blood group and Lewis-related secretory blood group substances in saliva. This reactivity was not related to sialylated Lewis activity. The fourth antibody, Mu-1, appeared to react with a conformational determinant since its epitope was destroyed by heat treatment or thiol reduction. Enzyme immunoassays have demonstrated that all four epitopes may be expressed on one molecular species.     

Therapeutic efficacy and dose-limiting toxicity of auger-electron vs. beta emitters in radioimmunotherapy with internalizing antibodies: Evaluation of 125I- vs. 131I-labeled CO17-1A in a human colorectal cancer model

Recent clinical results suggest that higher anti-tumor efficacy may be achieved with internalizing monoclonal antibodies (MAbs) at lower toxicity when labeled with Auger-electron, as compared to conventional β-emitters. The aim of our study was to compare the toxicity and anti-tumor efficacy of the ¹²⁵I-labeled internalizing MAb, CO17-1A, with its ¹³¹I-labeled form in a human colon cancer model in nude mice. Biodistribution studies were performed in nude mice bearing s.c. human colon cancer xenografts. For therapy, the mice were injected either with unlabeled ¹²⁵I- or ¹³¹I-labeled CO17-1A at equitoxic doses. Control groups were left untreated, were given a radiolabeled isotype-matched irrelevant antibody or a tumor-specific, but noninternalizing antibody. The maximum tolerated activities (MTD) of ¹³¹I- and ¹²⁵I-CO17-1A without artificial support were 300 μCi and 3 mCi, respectively. Myelotoxicity was dose-limiting; bone marrow transplantation allowed for an increase of the MTD to 400 μCi of ¹³¹I-17-1A, whereas the MTD of ¹²⁵I-17-1A with bone marrow support had not been reached at 5 mCi. Whereas no significant therapeutic effects were seen with unlabeled CO17-1A, tumor growth was retarded with ¹³¹I-CO17-1A. With the ¹²⁵I-label, however, therapeutic results were clearly superior. In contrast, no significant difference was observed in the therapeutic efficacy of the ¹³¹I- vs. ¹²⁵I-labeled, noninternalizing antibodies. Our data indicate a superiority of Auger-electron emitters, such as ¹²⁵I, as compared to therapy with conventional β-emitters with internalizing antibodies. The lower toxicity of Auger emitters may be due to the short path length of their low-energy electrons, which can reach the nuclear DNA only if the antibody is internalized (as is the case in antigen-expressing tumor tissue, but not in the stem cells of the red marrow). Int. J. Cancer 76:738–748, 1998.© 1998 Wiley-Liss, Inc.     

低剂量131I标记的抗癌胚抗原抗体C50联合5-FU对结直肠癌裸鼠移植瘤生长的影响

背景与目的:癌胚抗原 (CEA)在结直肠癌组织中表达率高达 90%以上,本研究拟探讨低剂量 131I标记的抗 CEA单抗 C50( 131I- C50)及低剂量 131I- C50联合 5-氟尿嘧啶( 5- FU)对人结直肠癌移植瘤生长的影响.方法:建立表达 CEA的人 LoVo结直肠癌裸鼠移植瘤模型.接种第 9天,分别采用 5- FU、2775kBq 131I- C50及 5- FU联合 131I- C50尾静脉注射治疗荷瘤裸鼠.尾静脉给药后第 7天,每组各随机处死 2只荷瘤裸鼠,观察肿瘤细胞超微结构改变及组织病理学改变.计算各组裸鼠肿瘤体积、群体倍增时间及抑瘤率,比较接种第 30天的肿瘤体积.结果:对照组、5- FU组、131I- C50治疗组和 131I- C50联合 5- FU组接种第 30天肿瘤体积分别为 (9 765.19± 792.21)mm3、(6 533.75± 601.14)mm3、(5 413.57± 415.46)mm3和 (3 865.23± 263.57)mm3,四组之间差异均有显著性( P< 0.001);四组肿瘤群体倍增时间依次延长,分别为 3.07、3.09、3.18和 3.14天;后三组抑瘤率依次增大,分别为 30.97%、42.33%和 59.04%.结论:低剂量 131I- C50可抑制结直肠癌裸鼠移植瘤的生长,低剂量 131I- C50联合 5- FU可以增强抑制肿瘤生长的效果.     

Quantitative whole-body autoradiography of radiolabeled antibody distribution in a xenografted human cancer model

Quantitative whole-body autoradiography (WBAR) was used to study the biodistribution of goat anti-carcinoembryonic antigen and normal goat IgG, each labeled with 125I, in hamsters bearing the carcinoembryonic antigen-producing GW-39 human colonic carcinoma xenograft. Comparisons between computer-assisted videodensitometric profiles of WBARs and tissue radioactivity counts were made at 1, 3, and 7 days following administration of the radiolabeled IgGs. The results indicated that maximal tumor accretion of the radiolabeled antibody and normal IgG occurred within 1-3 days, with a marked selective accretion of antibody in the tumor being evidenced at 3-7 days because of clearance of normal IgG. Radioactivity derived from antibody IgG showed 6.5 to 118.7 times that found in other tissues, as measured by videodensitometry, whereas organ radioactivity counting revealed ratios of only 6.7 to 29.6. Specificity of tumor-cell accretion of the radiolabeled antibody was confirmed by microscopic autoradiography, showing intense labeling of the proliferating perimeters of GW-39 tumors. WBAR was found to have a resolution of 0.10 to 0.25 mm in 100-g hamsters, which appears to be greater than the resolving power of external body imaging by gamma camera scintigraphy. These studies suggest the use of WBAR and microautoradiography to complement external imaging methods for the analysis of antibody distribution and localization in cancer radioimmunodetection models.     

Physiological factors influencing radioantibody uptake: a study of four human colonic carcinomas.

We evaluated the accretion of 131I-labeled NP-4 anticarcinoembryonic antigen (CEA) into 4 size-matched human colonic carcinomas grown s.c. in nude mice. Antibody uptake for LS174T and GW-39 tumors was relatively high (19 to 23% ID/g on day 3), whereas moderate uptake was seen in the Moser tumor (7.5% on day 3) and low uptake was detected in the GS-2 tumor (1.8% on day 3). Blood clearance of radioantibody was twice as fast in mice with GS-2 tumors than in mice with GW-39, LS174T or Moser tumors. Seven physiological parameters that might influence radioantibody accretion were evaluated in order to better understand the differences in observed tumor targeting: vascular volume, blood flow rate, vascular permeability, tumor antigen content, serum antigen content and complexation of radioantibody, intratumoral antigen distribution, and intracellular antigen distribution. Although marked variability in vascular physiology, antigen content and antibody complexation of the 4 tumors grown in the same host and site existed, it was insufficient to explain the differences in antibody uptake. However, intra-tumoral distribution of antigen, and sub-cellular accessibility of antigen for radioantibody were important considerations. GS-2 tumors are well differentiated and have polarized cells. CEA in GS-2 is largely inaccessible to radioantibody; most of the antigen is located in the lumen of the glands or on the apical surface of gland cells and most of the antibody distributes to the stromal region on the basolateral surface. The low antibody targeting in GS-2 could therefore be explained by restricted intra-tumor accessibility of antibody. Scatchard analysis of NP-4 binding to Moser cells under non-internalizing and internalizing conditions revealed that 90% of the antigen is found within the cell, unavailable to bind with the NP-4 antibody, which is slow to internalize. In contrast, CEA in LS174T cells was almost entirely accessible. The reduced antibody targeting to Moser xenografts might therefore, be explained by restricted antibody accessibility at the cellular level.     

Radioimmunoimaging of human small cell lung carcinoma xenografts in nude mice receiving several monoclonal antibodies

Small cell carcinoma of the lung is a highly lethal disease, killing nearly all patients afflicted with it. Although it metastasizes early and widely, it is exquisitely radiosensitive, and transient responses to this form of therapy are often dramatic. We have recently developed several monoclonal antibodies (MAb) reactive with antigens associated with this tumor. Scintigraphic and dual-label evaluations of their localization in nude mice bearing small cell carcinoma xenografts (derived from the human small cell carcinoma cell line NCI H69) were undertaken as a preliminary step in the eventual evaluation of their therapeutic potential. Anti-small cell MAb UM-MS1, 2, and 3, were labeled with 131I with the Iodobead method. Labeling efficiencies ranged from 68% to 88%. A control MAb, 225.28S (antimelanoma), was labeled with 125I by the same method. Although the labeled anti-small cell antibodies bound 20-40 times more to NCI H69 cells than did the antimelanoma control antibody, their total immunoreactive fraction was relatively low. Separate groups of nude mice bearing NCI H69-derived tumors were studied for imaging and localization with each 131I-labeled MAb. Successful imaging was achieved with two of the MAb; the quality of the images ranged from moderate to excellent. However, much of the localization to the tumors was due to nonspecific factors, as evidenced by the considerable tumor accretion of the control antibody.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of animal host and tumor implantation site on radio-antibody uptake in the GW-39 human colonic cancer xenograft

The magnitude and kinetics of tumor uptake of a monoclonal antibody (MAb) directed against carcinoembryonic antigen (CEA) in the GW-39 human colorectal cancer xenograft differ according to the animal used (nude mouse or hamster) and the site of implantation of the tumor within the animal (cheek pouch, leg muscle, subcutaneous or liver). Several physiological factors have been evaluated in an attempt to explain these differences in radio-antibody accumulation. The following observations have been made: (1) The animal host with the slower blood clearance of radio-antibody and the higher non-tumor tissue uptake has the higher tumor uptake; (2) the xenografts with a higher blood-flow rate, vascular volume and/or vascular permeability have a higher specific radio-antibody targeting; (3) the smaller, more viable tumors take up more radio-antibody per gram than the larger tumors; and (4) tumors with higher specific antigen content accrete more radio-antibody. These results are discussed in terms of the feasibility of clinical tumor imaging and therapy with radiolabelled antibodies.     

Carcinoembryonic antigen as a target for radioimmunotherapy of human medullary thyroid carcinoma: antibody processing, targeting, and experimental therapy with 131I and 90Y labeled MAbs

The poor prognosis of patients with advanced medullary thyroid carcinoma (MTC) has prompted a search for new treatment modalities. In this report we explore the characteristics of carcinoembyronic antigen (CEA) as a target for radioimmunotherapy (RAIT) of MTC, with respect to antibody processing, targeting, and experimental therapy. In vitro studies showed a high level of CEA expression on the cell surface of the MTC cell line TT. MAbs bound to the cell were predominantly retained for several days, although there was also a significant level of internalization and catabolism. Immunohistology of frozen sections of tumor xenografts demonstrated that approximately half of the cells were darkly stained, however, some cells expressed little or no CEA. In biodistribution studies in nude mice bearing TT tumors, the mean percent injected dose per gram of tumor observed at three days post injection (time of maximum uptake) of 125I-MN-14 was 19.7%. When the MAb was labeled with 88Y, a residualizing label, a much higher accretion, 50.5%, was observed at the time of maximum uptake (7 days). Significant anti-tumor effects were seen at the maximum tolerated doses of 131I- and 90Y-MN-14, compared with relatively rapid tumor growth in untreated animals or those treated with the same dose of control MAbs. Importantly, it was observed that 90Y-MN-14 yielded significantly improved therapeutic efficacy in comparison to 131I-MN-14, which may have important implications for design and conduct of future clinical trials for the treatment of MTC.