Sacituzumab govitecan, a Trop-2-directed antibody-drug conjugate, for patients with epithelial cancer: final safety and efficacy results from the phase I/II IMMU-132-01 basket trial

BACKGROUND

Sacituzumab govitecan (SG), a trophoblast cell surface antigen-2 (Trop-2)-directed antibody-drug conjugate, has demonstrated antitumor efficacy and acceptable tolerability in a phase I/II multicenter trial (NCT01631552) in patients with advanced epithelial cancers. This report summarizes the safety data from the overall safety population (OSP) and efficacy data, including additional disease cohorts not published previously.

PATIENTS AND METHODS

Patients with refractory metastatic epithelial cancers received intravenous SG (8, 10, 12, or 18 mg/kg) on days 1 and 8 of 21-day cycles until disease progression or unacceptable toxicity. Endpoints for the OSP included safety and pharmacokinetic parameters with investigator-evaluated objective response rate (ORR per RECIST 1.1), duration of response, clinical benefit rate, progression-free survival, and overall survival evaluated for cohorts (n > 10 patients) of small-cell lung, colorectal, esophageal, endometrial, pancreatic ductal adenocarcinoma, and castrate-resistant prostate cancer.

RESULTS

In the OSP (n = 495, median age 61 years, 68% female; UGT1A1∗28 homozygous, n = 46; 9.3%), 41 (8.3%) permanently discontinued treatment due to adverse events (AEs). Most common treatment-related AEs were nausea (62.6%), diarrhea (56.2%), fatigue (48.3%), alopecia (40.4%), and neutropenia (57.8%). Most common treatment-related serious AEs (n = 75; 15.2%) were febrile neutropenia (4.0%) and diarrhea (2.8%). Grade ≥3 neutropenia and febrile neutropenia occurred in 42.4% and 5.3% of patients, respectively. Neutropenia (all grades) was numerically more frequent in UGT1A1∗28 homozygotes (28/46; 60.9%) than heterozygotes (69/180; 38.3%) or UGT1A1∗1 wild type (59/177; 33.3%). There was one treatment-related death due to an AE of aspiration pneumonia. Partial responses were seen in endometrial cancer (4/18, 22.2% ORR) and small-cell lung cancer (11/62, 17.7% ORR), and one castrate-resistant prostate cancer patient had a complete response (n = 1/11; 9.1% ORR).

CONCLUSIONS

SG demonstrated a toxicity profile consistent with previous published reports. Efficacy was seen in several cancer cohorts, which validates Trop-2 as a broad target in solid tumors.

Sacituzumab govitecan in previously treated hormone receptor-positive/HER2-negative metastatic breast cancer: final results from a phase I/II, single-arm, basket trial

BACKGROUND

Trophoblast cell-surface antigen-2 (Trop-2) is expressed in epithelial cancers, including hormone receptor-positive (HR+) metastatic breast cancer (mBC). Sacituzumab govitecan (SG; Trodelvy®) is an antibody-drug conjugate composed of a humanized anti-Trop-2 monoclonal antibody coupled to SN-38 at a high drug-to-antibody ratio via a unique hydrolyzable linker that delivers SN-38 intracellularly and in the tumor microenvironment. SG was granted accelerated FDA approval for metastatic triple-negative BC treatment in April 2020.

PATIENTS AND METHODS

We analyzed a prespecified subpopulation of patients with HR+/human epidermal growth factor receptor 2-negative (HER2-) HR+/HER2- mBC from the phase I/II, single-arm trial (NCT01631552), who received intravenous SG (10 mg/kg) and whose disease progressed on endocrine-based therapy and at least one prior chemotherapy for mBC. End points included objective response rate (ORR; RECIST version 1.1) assessed locally, duration of response (DOR), clinical benefit rate, progression-free survival (PFS), overall survival (OS), and safety.

RESULTS

Fifty-four women were enrolled between 13 February 2015 and 1 June 2017. Median (range) age was 54 (33-79) years and all received at least two prior lines of therapy for mBC. At data cut-off (1 March 2019), 12 patients were still alive. Key grade ≥3 treatment-related toxicities included neutropenia (50.0%), anemia (11.1%), and diarrhea (7.4%). Two patients discontinued treatment due to treatment-related adverse events. No treatment-related deaths occurred. At a median follow-up of 11.5 months, the ORR was 31.5% [95% confidence interval (CI), 19.5%-45.6%; 17 partial responses]; median DOR was 8.7 months (95% CI 3.7-12.7), median PFS was 5.5 months (95% CI 3.6-7.6), and median OS was 12 months (95% CI 9.0-18.2).

CONCLUSIONS

SG shows encouraging activity in patients with pretreated HR+/HER2- mBC and a predictable, manageable safety profile. Further evaluation in a randomized phase III trial (TROPiCS-02) is ongoing (NCT03901339).

TRIAL REGISTRATION

ClinicalTrials.gov NCT01631552; https://clinicaltrials.gov/ct2/show/NCT01631552.

Abstract P2-11-01: Safety and efficacy of sacituzumab govitecan (anti-Trop-2-SN-38 antibody-drug conjugate) as ≥3rd-line therapeutic option for treatment-refractory HER2-negative metastatic breast cancer (HER2Neg mBC)

Background: Sacituzumab govitecan is an antibody-drug conjugate consisting of SN-38, the active metabolite of irinotecan, conjugated to a humanized mAb targeting Trop-2 (trophoblastic antigen-2), which is highly expressed in many epithelial cancers. A phase I/II basket trial (NCT01631552) investigated its activity in patients (pts) with advanced epithelial cancers. Herein, we summarize pooled safety and efficacy findings in 162 pts with HER2-negative metastatic breast cancer (mBC) accrued between 7/2013 and 6/2017 who received at least 2 prior therapies for metastatic disease and were treated with sacituzumab govitecan at the 10 mg/kg dose level.

Methods: Patients with triple-negative (N=108) and patients with hormone-receptor positive (N=54) mBC received 10 mg/kg sacituzumab govitecan on days 1 & 8 of a 21-day cycle continued until progression or unacceptable toxicity. All pts had measurable disease by CT or MRI. Efficacy was assessed locally by RECIST 1.1 including overall response rate (ORR) and Kaplan-Meier estimates of duration of response (DOR), progression-free survival (PFS) and overall survival (OS). Adverse events (AE) were evaluated according to CTCAE v4.0

Results: The patient cohort (161 female /1 male; median age 55 yrs, range 31-80) received a median of 4 prior therapies for metastatic disease (range 2-17), with prior chemotherapy agents in the metastatic setting including taxane (68%), capecitabine (60%), platinum (59%), gemcitabine (44%), eribulin (41%), and anthracycline (38%). 77 pts have died, with 57 in long-term follow-up and 28 still on treatment at data cutoff. The median number of administered sacituzumab govitecan doses was 14 (range 1-88). Treatment was generally well tolerated. 29% of pts had dose reductions, 3% discontinued treatment due to drug-related AEs, and there were no treatment-related deaths. Based on currently available AE data, grade ≥ 3 toxicity included neutropenia (43%), anemia (9.5%), diarrhea (7.0%) and febrile neutropenia (6.3%). For the TNBC subgroup, with a median follow-up of 9.3 months, the ORR was 33% (3 CRs + 33 PRs /108) with a median DOR of 8.3 months (95% CI: 4.8 – 11.6). For the ER+ subgroup, with a median follow-up of 10.0 months, the ORR was 31% (17 PRs/54) with a median DOR of 7.4 months (95% CI: 4.4 – 18.3). The combined HER2Neg ORR was 33% (3 CRs+50 PRs/162), with a median DOR of 8.3 months (95% CI: 4.9 - 10.8), PFS of 5.6 months (95% CI: 5.1 – 6.9) and OS of 13.0 months (95% CI: 11.5 - 15.0). The ORR was comparable for pts ≤ 50 yrs. old [32.2% (19/59)] vs. > 50 yrs old [33.0% (34/103)] and little different for pts with 2 prior therapies [35.4% (17/48)] vs. >2 prior therapies [31.6% (36/114)].

Conclusions: Monotherapy with sacituzumab govitecan was well tolerated with a manageable safety profile, and achieved a 30+% objective response rate among heavily pre-treated patients with HER2-negative metastatic breast cancer regardless of ER status.

Citation Format: Kalinsky K, Isakoff SJ, Tolaney SM, Juric D, Mayer IA, Vahdat LT, Diamond JR, O'Shaughnessy J, Moroose RL, Santin AD, Shah NC, Abramson V, Goldenberg DM, Sharkey RM, Washkowitz SA, Wegener WA, Iannone R, Bardia A. Safety and efficacy of sacituzumab govitecan (anti-Trop-2-SN-38 antibody-drug conjugate) as ≥3rd-line therapeutic option for treatment-refractory HER2-negative metastatic breast cancer (HER2Neg mBC) [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P2-11-01.

Abstract P1-12-01: Withdrawn

This abstract was withdrawn by the authors.

Abstract P4-22-15: Sacituzumab govitecan (IMMU-132), an anti-Trop-2-SN-38 antibody-drug conjugate (ADC) for the treatment of relapsed/refractory, metastatic triple-negative breast cancer (mTNBC): Updated results

Background. mTNBC has an aggressive course with limited effective therapy options and a median progression-free survival (PFS) of 2-4 months (mos) with standard therapy. Sacituzumab govitecan (IMMU-132) is an ADC targeting Trop-2, an antigen present in many epithelial cancers, including TNBC, and delivering SN-38, a topoisomerase I inhibitor as its therapeutic moiety. IMMU-132 was awarded Breakthrough Therapy designation by FDA based on its previously reported activity in relapsed/refractory mTNBC patients. Here we present updated results from the mTNBC cohort of an ongoing phase I/II study (ClinicalTrials.gov, NCT01631552).

Methods. mTNBC patients (pts) received IMMU-132 10 mg/kg on days 1 and 8 every 21 days. Trop-2 expression was not required for enrollment, but available tumor specimens underwent immunohistological (IHC) testing. Efficacy was assessed locally by RECIST 1.1; ORR, PFS and overall survival (OS) were determined for all pts. Pharmacokinetic parameters were estimated in select pts with adequate blood sampling. Immunogenicity to IMMU-132 was examined in all pts.

Results. We previously reported preliminary efficacy results in 51 mTNBC patients. Here we present data on 69 patients with data cutoff June 5, 2016. Median age was 56 years (31-81) and a median of 5 prior therapies (range 1-12), with 66 evaluable for response; ORR was 29% (19/66) 2 confirmed complete (CR) and 17 confirmed partial responses (PR). The median intention-to-treat PFS is 5.6 mos (95% CI, 3.6-7.1 mos) and median OS is 14.3 mos (95% CI, 10.5-18.8 mos). PRs included 2 pts whose tumors did not respond to anti-PD-L1 therapy. The duration of response in the 19 confirmed responders (8 continuing therapy) is 11.5 mos (95% CI = 7.6 to 12.7). The clinical benefit rate (CR+PR+SD>6 mos) for the 66 assessable patients is currently 45.5%. The majority (88%) of archival tumor specimens were moderately (2+) to strongly (3+) positive by IHC for Trop-2, precluding using Trop-2 expression as a selection criterion. Among current adverse events, grade >3 drug-related toxicities included neutropenia (35%), leukopenia (16%), anemia (13%), vomiting (9%), diarrhea (10%), and febrile neutropenia (4%). Clearance kinetics in 8 pts showed IMMU-132 and IgG had a terminal half-life of 15.3 ± 2.7 h and 86.5 ± 40.5 h, respectively, with area under the curve for free SN-38 (unbound) only 3% of the total amount of SN-38 (e.g., IgG bound). Thus, most SN-38 remains bound to the conjugate, and is released at a rate predicted from in vitro serum stability studies. No pt developed anti-IMMU-132 antibodies.

Conclusion The Trop-2-targeting ADC, IMMU-132, delivering cytotoxic doses of SN-38, shows high objective and durable tumor responses with manageable toxicity in heavily-pretreated pts with mTNBC in this updated cohort, supporting further development in this population with an unmet medical need.

Citation Format: Bardia A, Diamond JR, Mayer IA, Isakoff SJ, Abramson V, Starodub AN, O'Shaughnessy J, Kalinsky K, Moroose R, Shah N, Juric D, Shapiro GI, Guarino M, Ocean AJ, Messersmith WA, Berlin JD, Wegener WA, Sharkey RM, Goldenberg DM, Vahdat LT. Sacituzumab govitecan (IMMU-132), an anti-Trop-2-SN-38 antibody-drug conjugate (ADC) for the treatment of relapsed/refractory, metastatic triple-negative breast cancer (mTNBC): Updated results [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P4-22-15.

Abstract PD3-06: Safety and efficacy of anti-Trop-2 antibody drug conjugate, sacituzumab govitecan (IMMU-132), in heavily pretreated patients with TNBC

Background: Triple-negative breast cancer (TNBC) comprises about 15% of all breast cancer types, and has a particularly aggressive course. Following first-line therapy, the median PFS is <3 months, and OS is <10 months. Therefore, new treatment strategies are needed. Since Trop-2 is expressed in >90% of TNBC, as measured by IHC, we conducted a trial to evaluate the safety and efficacy of a humanized anti-Trop-2 monoclonal antibody conjugated to a high concentration of SN-38, a camptothecin that is a topoisomerase I inhibitor and the active metabolite of the prodrug irinotecan, with 2-3 logs higher potency than the prodrug.

Methods: After establishing the optimal repeated dose in a Phase I trial (ClinicalTrials.gov, NCT01631552) involving many different solid cancer types, an expanded Phase II was undertaken in a number of cancers, including TNBC. Patients received 8 or 10 mg/kg IMMU-132 i.v. on days 1 and 8 of 21-day repeated cycles. Assessments of safety and response by RECIST1.1 were made weekly and bimonthly, respectively. Tumor biopsies (archival, at baseline prior to treatment, and at disease progression) were obtained when safe and feasible.

Results: As of May 10, 2015, 58 patients with TNBC, with a median of 4 prior therapies (range, 1-11), were treated with IMMU-132. Grade 3-4 toxicities included neutropenia (26%), febrile neutropenia (2%), diarrhea (2%), anemia (4%), and fatigue (4%). No patient developed antibodies to SN-38 or the antibody, and no patient discontinued therapy due to toxicity. Tumor responses were defined as ORR (CR+PR) in 31% of 49 evaluated patients, including 2 with CR, and a clinical benefit ratio (CR+PR+SD>6 mo) of 49% (63% with SD>4 mo; 23 patients continuing treatment after 1st assessment). The current median progression-free survival is 7.3 months with 44% maturity in 50 patients treated at the 8 or 10 mg/kg dose level. Overall survival data are still not mature 20 months after enrollment of first patient. Clinical efficacy correlated to biomarker studies, including Trop-2 expression (target of antibody), topoisomerase-1 expression (target of SN-38), and homologous recombinant deficiency (HRD) assay (marker of DNA repair), is being studied. Immunohistochemistry results in archival specimens currently show 97% positivity of Trop-2 among 34 specimens evaluated, with 79% having high intensity (2+/3+) staining.

Conclusions: The Trop-2-targeting IMMU-132, delivering cytotoxic doses of the topoisomerase I inhibitor, SN-38, shows manageable toxicity, and encouraging anti-tumor activity in relapsed/refractory patients with TNBC. This ADC appears to have a high therapeutic index in heavily pretreated patients.

Citation Format: Bardia A, Diamond JR, Mayer IA, Starodub AN, Moroose RL, Isakoff SJ, Ocean AJ, Guarino MJ, Berlin JD, Messersmith WA, Thomas SS, O'Shaughnessy JA, Kalinsky K, Maurer M, Chang JC, Forero A, Traina T, Gucalp A, Wilhelm F, Wegener WA, Maliakal P, Sharkey RM, Goldenberg DM, Vahdat LT. Safety and efficacy of anti-Trop-2 antibody drug conjugate, sacituzumab govitecan (IMMU-132), in heavily pretreated patients with TNBC. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr PD3-06.

Abstract P6-15-02: Synthetic lethality in TNBC mediated by an anti-Trop-2 antibody-drug conjugate, sacituzumab govitecan (IMMU-132), when combined with paclitaxel or the PARP inhibitor, olaparib

Background: In current clinical trials (ClinicalTrials.gov, NCT01631552), triple-negative breast cancer (TNBC) patients treated with IMMU-132, which is composed of the active metabolite of irinotecan, SN-38, conjugated to an anti-Trop-2 antibody, shows manageable toxicity and very encouraging responses in relapsed/refractory cases. Synthetic lethality is a concept in which a cell harboring one out of two possible gene or protein defects is viable, while a cell containing both defects is nonviable. BRCA1/2 mutations are linked to deficiencies in DNA repair and are associated with TNBC. Other repair mechanisms involve poly(adenosine diphosphoribose) polymerase (PARP), which can be used by cancer cells to overcome loss of BRACA1/2. Treatment of TNBC cells with either IMMU-132 or paclitaxel results in cleavage and deactivation of PARP, whereas the small molecule olaparib directly inhibits PARP. Therefore, the rationale of combining IMMU-132 with either paclitaxel or olaparib to effectively knock-out PARP activity was investigated in TNBC xenografts to ascertain if these combinations will result in synthetic lethality.

Methods: Mice bearing human TNBC xenografts (MDA-MB-468 or HCC1806) were treated with 15 mg/kg paclitaxel weekly for 5 weeks. IMMU-132 was administered either at 10 mg/kg or 12.5 mg/kg on days 1, 8, 22, and 29. In vitro, various human TNBC cell lines were incubated with either a constant amount of IMMU-132 in combination with various amounts of olaparib or constant olaparib with varying amounts of IMMU-132. A combination index number was calculated to determine whether the interaction was synergistic, additive, or antagonistic. Mice bearing TNBC tumors were treated with olaparib (50 mg/kg, qdx5d, for 4 wks), or IMMU-132 (10 mg/kg, 2xwkly x 4 wks), or the combination of both.

Results: Mice bearing MDA-MB-468 tumors treated with the combination of IMMU-132 and paclitaxel exhibited superior anti-tumor effects with >11-fold shrinkage of tumors in comparison to 1.4-fold shrinkage in the IMMU-132 group alone (P=0.0003) or 11.4-fold increase in tumor size in those mice treated with paclitaxel alone (P<0.0001). In the more aggressive HCC1806, the combination improved median survival from 17.5 and 17 days for paclitaxel and IMMU-132, respectively, to 38 days for those in the combination group (P<0.0015). IMMU-132 and olaparib demonstrated synergy in all TNBC cell lines tested in vitro. In an ongoing experiment, this same combination is proving to be superior to single agent therapy in mice bearing MDA-MB-468 tumors (P<0.0032). In all studies, the combination of IMMU-132 with either paclitaxel or olaparib was well tolerated, with no observable toxicities. DNA breaks as determined by TUNEL staining of excised xenografts are being assessed.

Conclusions: Targeting the PARP DNA repair pathway in BRCA1/2 mutant TNBC tumors by combining IMMU-132 therapy with either paclitaxel or olaparib achieved synthetic lethality in this disease model with no observable toxicity. These data provide the rationale for the clinical evaluation of IMMU-132 in combination with other chemotherapeutics that likewise target DNA-repair mechanisms in patients with TNBC.

Citation Format: Goldenberg DM, Cardillo TM, Govindan SV, Zalath M, Arrojo R, Sharkey RM. Synthetic lethality in TNBC mediated by an anti-Trop-2 antibody-drug conjugate, sacituzumab govitecan (IMMU-132), when combined with paclitaxel or the PARP inhibitor, olaparib. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P6-15-02.

Anti-CEA antibody fragments labeled with [(18)F]AlF for PET imaging of CEA-expressing tumors

A facile and rapid method to label peptides with (18)F based on chelation of [(18)F]AlF has been developed recently. Since this method requires heating to 100 °C, it cannot be used to label heat-sensitive proteins. Here, we used a two-step procedure to prepare (18)F-labeled heat-labile proteins using the [(18)F]AlF method based on hot maleimide conjugation. 1,4,7-Triazacyclononae-1,4-diacetate (NODA) containing a methyl phenylacetic acid group (MPA) functionalized with N-(2-aminoethyl)maleimide (EM) was used as a ligand which was labeled with [(18)F]AlF and then conjugated to the humanized anti-CEA antibody derivatives hMN-14-Fab', hMN-14-(scFv)2 (diabody), and a Dock-and-Lock engineered dimeric fragment hMN-14 Fab-AD2 at room temperature. The in vivo tumor targeting characteristics of the (18)F-labeled antibody derivatives were determined by PET imaging of mice with s.c. xenografts. NODA-MPAEM was radiolabeled with [(18)F]AlF at a specific activity of 29-39 MBq/nmol and a labeling efficiency of 94 ± 2%. The labeling efficiencies of the maleimide conjugation ranged from 70% to 77%, resulting in [(18)F]AlF-labeled hMN14-Fab', hMN14-Fab-AD2, or hMN14-diabody with a specific activity of 15-17 MBq/nmol. The radiolabeled conjugates were purified by gel filtration. For biodistribution and microPET imaging, antibody fragments were injected intravenously into BALB/c nude mice with s.c. CEA-expressing LS174T xenografts (right flank) and CEA-negative SK-RC-52 xenografts (left flank). All [(18)F]AlF-labeled conjugates showed specific uptake in the LS174T xenografts with a maximal tumor uptake of 4.73% ID/g at 4 h after injection. Uptake in CEA-negative SK-RC-52 xenografts was significantly lower. Tumors were clearly visualized on microPET images. Using a [(18)F]AlF-labeled maleimide functionalized chelator, antibody fragments could be radiofluorinated within 4 h at high specific activity. Here, we translated this method to preclinical PET imaging studies and showed feasibility of [(18)F]AlF-fluorinated hMN-14-Fab', [(18)F]AlF-hMN-14-Fab-AD2, and [(18)F]AlF-hMN-14-diabody for microPET imaging of CEA-expressing colonic cancer.

Effect of combination radioimmunotherapy (RAIT) and chemoimmunotherapy on therapeutic response and toxicity in xenograft models of human pancreatic carcinoma: First experimental studies

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Background: Preclinical and early clinical data with RAIT involving a 90Y-labeled antibody to a pancreatic mucin antigen (hPAM4, clivatuzumab tetraxetan) have shown promising therapeutic activity in combination with gemcitabine. Selective targeting of therapeutic drugs using antibody-drug conjugates (ADC) might be useful in pancreatic cancer therapy.

Methods: ADCs composed of SN-38 coupled to an internalizing anti-TROP-2 antibody, an antigen found on many epithelial cancers, or to the non-internalizing anti-mucin humanized IgG, were prepared (6 SN-38/IgG). Nude mice bearing s.c. Capan-1 or BxPC3 xenografts (∼0.35 cm3) were given multiple ADC doses (twice weekly, 4 weeks) or appropriate controls of a non-targeting IgG-SN-38 conjugate or irinotecan. Other groups of animals were treated with the ADC conjugates and RAIT, using RAIT at 60% and 100% of its MTD. The endpoint was time to progress to 3.0 cm3 (TTP), with animals monitored up to 22 weeks.

Results: ADCs alone were each able to inhibit tumor growth significantly compared to untreated animals. The specificity of the effect was a dose-dependent and related to antigen saturation at higher doses. When ADC was combined with RAIT, TTP improved significantly and more animals were tumor-free. An effective ADC dose could be combined even with RAIT given at its MTD, achieving enhanced efficacy with minimal additional toxicity. ADC + RAIT treatments were best when RAIT was given 1-2 weeks before, the same day, or within 1 week after the ADC treatment, but delaying RAIT for 2 weeks after ADC treatment reduced efficacy. The same anti-pancreatic mucin antibody, hPAM4, could be used in the combination treatment both as RAIT and as an ADC without losing effectiveness.

Conclusions: These studies show the feasibility of using ADC for the treatment of pancreatic cancer, and for combining antibody drug- and radionuclide-targeted therapeutics for improved efficacy with minimal toxicity. Supported in part from NCI grant R01 CA115755.

[Table: see text]

Multicenter study of radiosensitizing gemcitabine combined with fractionated radioimmunotherapy for repeated treatment cycles in advanced pancreatic cancer

4620

Background: In a phase I study, a single dose of 90Y-labeled anti-mucin humanized antibody, hPAM4 (90Y-hPAM4), led to several transient reductions or stabilization of lesions in advanced pancreatic cancer, with bone marrow toxicity limiting the maximum tolerated dose to 20 mCi/m2. Preclinical studies showed gemcitabine enhanced radioimmunotherapy, so a phase Ib study was undertaken to evaluate repeated treatment cycles of 90Y-hPAM4 plus gemcitabine. Methods: Patients (pts) with previously untreated, locally advanced or metastatic, pancreatic cancer were treated in 4-week cycles (200 mg/m2 gemcitabine once-weekly; 111In-hPAM4 the 1st wk for imaging, biodistribution, and dosimetry; 90Y-hPAM4 once-weekly the last 3 wks), which could be repeated in the absence of progression or unacceptable toxicity. The 90Y-dose was escalated by patient cohort following a 3+3 design, with tumor responses assessed by CT and FDG/PET imaging, and by CA19.9 serum levels. Results: Eight pts (3F/5M, 56–72 years old, 7 with metastatic disease) have now been treated at the first 2 dose levels (6.5 and 9.0 mCi/m2 90Y-hPAM4 x 3) with hematologic toxicity all transient Grade 1–2 (NCI CTC v3). 111In-hPAM4 imaging showed normal biodistribution, evidence of tumor targeting and acceptable dosimetry estimates to normal organs per treatment cycle. Two pts had tumor responses to initial treatment with significant decreases in FDG metabolic activity on PET imaging, regression of lesion sizes on CT, and CA19.9 decreases. Both pts continue in excellent performance status now at 9 and 11 months after study entry, after receiving a total of 3 and 4 treatment cycles, respectively, without additional toxicity. A 3rd pt with a stable response by PET and CT 4 weeks after initial treatment and decreases in CA19.9 levels is now undergoing a 2nd treatment cycle. Four other pts had early progression of disease by or before post-treatment week-4 evaluation, and the remaining pt is still being evaluated. Conclusions: Dose escalation is continuing after fractionated radioimmunotherapy with 90Y-hPAM4 plus low-dose gemcitabine demonstrated therapeutic activity at the first two 90Y dose levels, with minimal hematologic toxicity, even after 4 treatment cycles.

[Table: see text]

Novel radiolabeled antibody conjugates

This article reviews the development of radioimmunoconjugates as a new class of cancer therapeutics. Numerous conjugates involving different antigen targets, antibody forms, radionuclides and methods of radiochemistry have been studied in the half-century since radioactive antibodies were first used in model systems to selectively target radiation to tumors. Whereas directly conjugated antibodies, fragments and subfragments have shown promise preclinically, the same approaches have not gained success in patients except in radiosensitive hematological neoplasms, or in settings involving minimal or locoregional disease. The separation of tumor targeting from the delivery of the therapeutic radionuclide in a multistep process called pretargeting has the potential to overcome many of the limitations of conventional, or one-step, radioimmunotherapy, with initial preclinical and clinical data showing increased sensitivity, specificity and higher radiation doses delivered. Our particular focus in pretargeting is the use of bispecific, trimeric (three Fab's) constructs made by a new antibody engineering method termed 'dock-and-lock.

Advances in cancer therapy with radiolabeled monoclonal antibodies

Two radiolabeled antibody products for the treatment of non-Hodgkin's lymphoma have been approved, thus indicating that cancer radioimmunotherapy (RAIT) has finally come of age as a new therapeutic modality, exemplifying the collaboration of multiple disciplines, including immunology, radiochemistry, radiation medicine, medical oncology, and nuclear medicine. Clinical trials are showing usefulness in other hematological neoplasms, but the treatment of solid tumors remains the major challenge, since the doses shown to be effective in hematological tumors are insufficient in the more common epithelial cancers. Nevertheless, use of RAIT in locoregional applications and in the treatment of minimal residual disease have shown promising

RESULTS

There is also optimism that pretargeting procedures, including new molecular constructs and targets, will improve the delivery of radioactivity to tumors with less hematologic toxicity, and thus may become the next generation of RAIT.

Evaluation of a novel MUC1 biomarker/target antigen for pancreatic cancer

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Background: Pancreatic cancer provides a major challenge in terms of diagnosis and treatment. We have developed an anti-MUC1 MAb, PAM4, which identifies an epitope that is more restricted to MUC1-expressed by pancreatic cancer than MUC1 from other forms of cancer. PAM4 has been studied for in vitro and in vivo detection and therapy of pancreatic cancer. Methods: The in vitro immunoassay consists of PAM4 as the capture reagent and an IgG fraction derived from a polyclonal, anti-MUC1 antiserum as the probe. For in vivo detection and therapy, PAM4 is either directly radiolabeled or used in a 2-step pretargeting protocol. Results: The PAM4-based immunoassay provided high sensitivity (77%) and specificity (95%), with a value ≥ 10.2 units/ml indicating a high likelihood of pancreatic cancer, as compared to normal and benign disease groups and non-pancreatic cancers. A direct pairwise comparison of the PAM4 and CA19–9 immunoassays for discrimination of pancreatic cancer and pancreatitis demonstrated a superior performance of the PAM4-immunoassay (P<0.003). Initial clinical studies with directly labeled 131I-PAM4 provided positive imaging in 8/10 patients, with one negative patient having only pancreatitis, and the other negative patient having a tumor that was MUC1-negative. A Phase I, dose-escalation study of 90Y-humanized PAM4 administered as a single dose to patients with advanced pancreatic cancer is in progress (Immunomedics, Inc), and has already achieved doses of 20 mCi/m2. Finally, pretargeting involving a bispecific MAb with one arm being PAM4 targeting MUC1 and the other arm capturing a hapten peptide carrying a radionuclide is under preclinical evaluation. This second generation targeting system has shown higher tumor/nontumor ratios and improved imaging (111In) as compared to directly radiolabeled PAM4. Conclusions: These results suggest that the PAM4-reactive MUC1 epitope may prove useful as a selective biomarker/target antigen for diagnosis, detection, imaging, and therapy of pancreatic cancer. (Supported in part by grants CA96924and CA98488 from the NIH).

[Table: see text]

Improved therapy of non-Hodgkin's lymphoma xenografts using radionuclides pretargeted with a new anti-CD20 bispecific antibody

A comparison of the therapeutic efficacy of a new bispecific monoclonal antibody (bsMAb)-pretargeting system vs the conventional direct targeting modality was undertaken. A bsMAb was made by coupling the Fab' of a humanized anti-CD20 antibody to the Fab' of a murine antibody directed against the peptide histamine-succinyl-glycine (HSG). The tumor targeting of the bsMAb was separated from the subsequent delivery of the radionuclide-bearing HSG peptide conjugated with (111)In or (90)Y. Nude mice bearing s.c. Ramos human B-cell lymphomas were injected with the bsMAb and then, 48 h later, (111)In/(90)Y-HSG peptide was given. At 3 h postinjection, tumor/blood ratios for pretargeted (111)In-HSG-peptide were similar to that observed with the directly conjugated (111)In-anti-CD20 IgG at its highest level on day 7, but by day 1, tumor/blood ratios were about 10-fold higher than the IgG. Tumors progressed rapidly in animals given 800 microCi of (90)Y-HSG peptide alone, whereas 5/10 animals in the group pretargeted by the anti-CD20 bsMAb were tumor-free 18 weeks later. The antitumor response in animals administered the pretargeted (90)Y-HSG peptide was also significantly superior to treatment with the directly radiolabeled (90)Y-anti-CD20 IgG, whether given as a single injection (P<0.007) or as a divided dose (P=0.016). This bsMAb-pretargeting procedure significantly improves the therapeutic response of targeted radionuclides in non-Hodgkin's lymphoma, warranting further development of this method of radioimmunotherapy.

Pretargeting for cancer radioimmunotherapy with bispecific antibodies: role of the bispecific antibody's valency for the tumor target antigen

The use of a divalent effector molecule improves bispecific antibody (bsMAb) pretargeting by enabling the cross-linking of monovalently bound bsMAb on the cell surface, thereby increasing the functional affinity of a bsMAb. In this work, it was determined if a bsMAb with divalency for the primary target antigen would improve bsMAb pretargeting of a divalent hapten. The pretargeting of a (99m)Tc-labeled divalent DTPA-peptide, IMP-192, using a bsMAb prepared by chemically coupling two Fab' fragments, one with monovalent specificity to the primary target antigen, carcinoembryonic antigen (CEA), and to indium-loaded DTPA [DTPA(In)], was compared to two other bsMAbs, both with divalency to CEA. One conjugate used the whole anti-CEA IgG, while the other used the anti-CEA F(ab')(2) fragment to make bsMAbs that had divalency to CEA, but with different molecular weights to affect their pharmacokinetic behavior. The rate of bsMAb blood clearance was a function of molecular weight (IgG x Fab' < F(ab')(2) x Fab' < Fab' x Fab' conjugate). The IgG x Fab' bsMAb conjugate had the highest uptake and longest retention in the tumor. However, when used for pretargeting, the F(ab')(2) x Fab' conjugate allowed for superior tumor accretion of the (99m)Tc-IMP-192 peptide, because its more rapid clearance from the blood enabled early intervention with the radiolabeled peptide when tumor uptake of the bsMAb was at its peak. Excellent peptide targeting was also seen with the Fab' x Fab' conjugate, albeit tumor uptake was lower than with the F(ab')(2) x Fab' conjugate. Because the IgG x Fab' bsMAb cleared from the blood so slowly, when the peptide was given at the time of its maximum tumor accretion, the peptide was captured predominantly by the bsMAb in the blood. Several strategies were explored to reduce the IgG x Fab' bsMAb remaining in the blood to take advantage of its 3-4-fold higher tumor accretion than the other bsMAb conjugates. A number of agents were tested, including those that could clear the bsMAb from the blood (e.g., galactosylated or nongalactosylated anti-id antibody) and those that could block the anti-DTPA(In) binding arm [e.g., DTPA(In), divalent-DTPA(In) peptide, and DTPA coupled to bovine serum albumin (BSA) or IgG]. When clearing agents were given 65 h after the IgG x Fab' conjugate (time of maximum tumor accretion for this bsMAb), (99m)Tc-IMP-192 levels in the blood were significantly reduced, but a majority of the peptide localized in the liver. Increasing the interval between the clearing agent and the time the peptide was given to allow for further processing of the bsMAb-clearing agent complex did not improve targeting. At the dose and level of substitution tested, galacosylated BSA-DTPA(In) was cleared too quickly to be an effective blocking agent, but BSA- and IgG-DTPA(In) conjugates were able to reduce the uptake of the (99m)Tc-IMP-192 in the blood and liver. Tumor/nontumor ratios compared favorably for the radiolabeled peptide using the IgG x Fab'/blocking agent combination and the F(ab')(2) x Fab' (no clearing/blocking agent), and peptide uptake 3 h after the blocking agent even exceeded that of the F(ab')(2) x Fab'. However, this higher level of peptide in the tumor was not sustained over 24 h, and actually decreased to levels lower than that seen with the F(ab')(2) x Fab' by this time. These results demonstrate that divalency of a bsMAb to its primary target antigen can lead to higher tumor accretion by a pretargeted divalent peptide, but that the pharmacokinetic behavior of the bsMAb also needs to be optimized to allow for its clearance from the blood. Otherwise, blocking agents will need to be developed to reduce unwanted peptide uptake in normal tissues.

Localization of pancreatic cancer with radiolabeled monoclonal antibody PAM4

Experimental animal studies were performed with (111)In-labeled PAM4 anti-MUC1 antibody along with (111)In-labeled control antibody. Tumor uptake of radiolabeled PAM4 was significantly higher than for the control antibody at all time points. When normalized to a blood dose of 1500 cGy as an estimate of myelotoxicity, (90)Y-labeled PAM4 would provide 5344 cGy to the tumor, whereas an equitoxic dose of (90)Y-labeled control antibody would provide only 862 cGy to the tumor. In addition to the animal studies, five patients with proven pancreatic cancer were administered either (131)I-PAM4 IgG (n=2) or 99mTc-PAM4 Fab' (n=3). Tumor targeting was observed in four out of five patients. By immunohistochemistry, PAM4 was non-reactive with tumor from the one patient not targeted. Dosimetry from the patients given (131)I-PAM4 predicted that tumors would receive 10-20 cGy/mCi with tumor/red marrow dose ratios ranging from 3 to 10. Based upon these results, we have established a phase-I (111)In-labeled PAM4 imaging and (90)Y-labeled PAM4 therapy trial.

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.

Experimental pretargeting studies of cancer with a humanized anti-CEA x murine anti-[In-DTPA] bispecific antibody construct and a (99m)Tc-/(188)Re-labeled peptide

The aim of this study was to localize (99m)Tc and (188)Re radionuclides to tumors, using a bispecific antibody (bsMAb) in a two-step approach where the radionuclides are attached to novel peptides incorporating moieties recognized by one arm of the bsMAb. A chemically cross-linked human/murine bsMAb, hMN-14 x 734 (Fab' x Fab'), anti-carcinoembryonic antigen [CEA] x anti-indium-DTPA was prepared as a prelude to constructing a fully humanized bsMAb for future clinical application. N,N'-o-Phenylenedimaleimide was used to cross-link the Fab' fragments of the two antibodies at their hinge regions. This construct was shown to be >92% pure and fully reactive with CEA and a divalent (indium)DTPA-peptide. For pretargeting purposes, a peptide, IMP-192 [Ac-Lys(In-DTPA)-Tyr-Lys(In-DTPA)-Lys(TscG-Cys-)-NH(2) ¿TscG = 3-thiosemicarbazonylglyoxyl¿], with two indium-DTPAs and a chelate for selectively binding (99m)Tc or (188)Re, was synthesized. IMP-192 was formulated in a "single dose" kit and later radiolabeled with (99m)Tc (94-99%) at up to 1836 Ci/mmol and with (188)Re (97%) at 459-945 Ci/mmol of peptide. [(99m)Tc]IMP-192 was shown to be stable by extensive in vitro and in vivo testing and had no specific uptake in the tumor with minimal renal uptake. The biodistribution of the hMN-14 x murine 734 bsMAb was compared alone and in a pretargeting setting to a fully murine anti-CEA (F6) x 734 bsMAb that was reported previously [Gautherot, E., Bouhou, J., LeDoussal, J.-M., Manetti, C., Martin, M., Rouvier, E., and Barbet, J. (1997) Therapy for colon carcinoma xenografts with bispecific antibody-targeted, iodine-131-labeled bivalent hapten. Cancer 80 (Suppl.), 2618-2623]. Both bsMAbs maintained their integrity and dual binding specificity in vivo, but the hMN-14 x m734 was cleared more rapidly from the blood. This coincided with an increased uptake of the hMN-14 x m734 bsMAb in the liver and spleen, suggesting an active reticuloendothelial cell recognition mechanism of this mixed species construct in naive mice. Animals bearing GW-39 human colonic cancer xenografts were injected with bsMAb (15 microg) and after allowing 24 or 72 h for the bsMAb constructs to clear from the blood (hMN-14 and murine F6 x 734, respectively), [(188)Re]IMP-192 (7 microCi) or [(99m)Tc]IMP-192 (10 microCi) was injected at a bsMAb:peptide ratio of 10:1. Tumor uptake of [(99m)Tc] or [(188)Re]IMP-192 was 12.6 +/- 5.2 and 16.9 +/- 5.5% ID/g at 3 h postinjection, respectively. Tumor/nontumor ratios were between 5.6 and 23 to 1 for every major organ, indicating that early imaging with (99m)Tc will be possible. Radiation absorbed doses showed a 4.8-, 7.2-, and a 12.6 to 1.0 tumor to blood, kidney, and liver ratios when (188)Re was used. Although this new bsMAb pretargeting approach requires further optimization, it already shows very promising targeting results for both radioimmunodetection and radioimmunotherapy of colorectal cancer.

Initial experience with high-dose radioimmunotherapy of metastatic medullary thyroid cancer using 131I-MN-14 F(ab)2 anti-carcinoembryonic antigen MAb and AHSCR

This phase I study was initiated to determine the toxicity and therapeutic potential of high-dose 131I-MN-14 F(ab)2 anti-carcinoembryonic antigen monoclonal antibody (MAb) combined with autologous hematopoietic stem cell rescue (AHSCR) in patients with rapidly progressing metastatic medullary thyroid cancer.

METHODS

Twelve patients were entered into the study. Dose escalation was based on prescribed radiation doses to critical organs (i.e., kidney, lung, and liver). Starting doses were 900 cGy to the kidney and no more than 1200 cGy to the lung and liver, with dose increments of 300 cGy until the maximum tolerable dose is determined. Tumor targeting was assessed by external scintigraphy, toxicity was assessed according to the common toxicity criteria of the National Cancer Institute, and therapy responses were assessed by CT, serum carcinoembryonic antigen, and calcitonin.

RESULTS

One patient received 9.95 GBq 131I-MN-14 F(ab)2, for an initial dose of 656 cGy to critical organs, 8 received 900 cGy (8.69-17.98 GBq), and 3 received 1200 cGy (15.17-17.69 GBq). The MAb scans of all patients showed positive findings. Autologous hematopoietic stem cells were given to all patients 1-2 wk after therapy, when the total body radiation exposure was less than 5.2 x 10(-7) C/kg/h. Dose-limiting toxicity, defined as grade 3 or 4 nonhematologic toxicity, was not seen in the patient who received the 656-cGy dose, and only 1 of the 8 patients treated at the 900-cGy dose level had grade 3 toxicity, which was gastrointestinal and reversible. No dose-limiting toxicity was seen in the 3 patients treated at the 1200-cGy dose level. Except for the instance of grade 3 gastrointestinal toxicity, nonhematologic toxicity was relatively mild, with only grade 1 or 2 toxicity observed in 9 patients. No renal toxicity was seen. Of the 12 patients, 1 had partial remission for 1 y, another had a minor response for 3 mo, and 10 had stabilization of disease lasting between 1 and 16 months.

CONCLUSION

The results show the safety of administering high myeloablative doses of 131I-MN-14 F(ab)2 with AHSCR in patients with metastatic medullary thyroid cancer. The antitumor responses in patients with aggressive, rapidly progressing disease are encouraging and warrant further research to optimize the effectiveness of this new treatment.

Radioimmunotherapy of small volume disease of colorectal cancer metastatic to the liver: preclinical evaluation in comparison to standard chemotherapy and initial results of a phase I clinical study

At the time of surgery, occult metastases (micrometastases) are present in more than 50% of colorectal cancer patients, and the liver is the most frequent site of apparent metastatic disease. Frequently, adjuvant chemotherapy is unable to prevent tumor recurrence. Thus, novel therapeutic strategies are warranted. The aim of this study was to establish a model of human colon cancer metastatic to the liver of nude mice, to assess, in this setting, the therapeutic efficacy of radioimmunotherapy (RAIT) compared to standard chemotherapy and to evaluate, in a Phase I/II trial, the toxicity and therapeutic efficacy of RAIT in colorectal cancer patients with small volume disease metastatic to the liver. Multiple liver metastases of the human colon cancer cell line GW-39 were induced by intrasplenic injection of a 10% tumor cell suspension. Whereas controls were left untreated, therapy was initiated on day 10 or 20 after tumor inoculation with the 131I-labeled, low affinity anticarcinoembryonic antigen (anti-CEA) monoclonal antibody (MAb), F023C5 (Ka = 10(7) liters/mol), or the high-affinity anti-CEA MAb, MN-14 (Ka = 10(9) liters/mol), or chemotherapy (5-fluorouracil/leucovorin (folinic acid) versus irinotecan) at their respective maximum tolerated doses (MTDs). Twelve colorectal cancer patients with small volume disease metastatic to the liver (all lesions < or = 2.5 cm) were entered into a mCi/m2-based Phase I dose escalation study with 131I-labeled humanized version of MN-14, hMN-14. The patients were given single injections, starting at 50 mCi/m2 and escalating in 10-mCi/m2 increments. The MTD was defined as the dose level at which < or = 1 of 6 patients develop grade 4 myelotoxicity. In the mice, untreated controls died from rapidly progressing hepatic metastases at 6-8 weeks after tumor inoculation. The life span of mice treated with 5-fluorouracil/leucovorin was prolonged for only 1-3 weeks, whereas irinotecan led to a 5-8-week prolongation. In contrast, at their respective MTDs, the 131I-labeled low-affinity anti-CEA MAb, F023C5, led to a 20% permanent cure rate, and the high affinity MAb, MN-14, led to an 80% permanent cure rate, when therapy was initiated at 10 days after tumor inoculation. In the 20-day-old tumor stage, although it prolonged life, 131I-F023C5 was unable to achieve cures, whereas 131I-MN-14 was still successful in 20%. Histologically, no remaining viable tumor cells could be demonstrated in these animals surviving > 6 months. In patients, the MTD was reached at 60 mCi/m2 of hMN-14 (at 70 mCi/m2, two of three grade 4 myelotoxicities). Of 11 assessable patients, 2 had partial remissions (corresponding to an objective response rate of 18%), and 5 (45%) had minor/mixed responses or experienced stabilization of previously rapidly progressing disease. These data suggest that in small volume disease, RAIT may be superior to conventional chemotherapy. Antibodies of higher affinity seem to be clearly superior. The clinical response rates in patients with small volume disease are encouraging, being comparable to the response rates of conventional chemotherapeutic regimens but with fewer side effects. Ongoing studies will show whether treatment at the MTD will further improve therapeutic results.

Pharmacokinetics, dosimetry, and initial therapeutic results with 131I- and (111)In-/90Y-labeled humanized LL2 anti-CD22 monoclonal antibody in patients with relapsed, refractory non-Hodgkin's lymphoma

The pharmacokinetics, dosimetry, and immunogenicity of 131I- and (111)In-/90Y-humanized LL2 (hLL2) anti-CD22 monoclonal antibodies were determined in patients with recurrent non-Hodgkin's lymphoma. Fourteen patients received tracer doses of 131I-hLL2 followed 1 week later by therapeutic doses intended to deliver 50-100 cGy to the bone marrow. Another eight patients received (111)In-hLL2 followed by therapy with 90Y-hLL2 also delivering 50 or 100 cGy to the bone marrow. The blood T(1/2) (hours) for the tracer infusions of 131I-hLL2 was 44.2 +/- 10.9 (mean +/- SD) compared with 54.2 +/- 25.0 for the therapy infusions, whereas the values were 70.7 +/- 17.6 for (111)In-hLL2 and 65.8 +/- 15.0 for 90Y-hLL2. The estimated average radiation dose from 131I-hLL2 in tumors >3 cm was 2.4 +/- 1.9 cGy/mCi and was only 0.9-, 1.0-, 1.1-, and 1.0-fold that of the bone marrow, lung, liver, and kidney, respectively. In contrast, the estimated average radiation dose from 90Y-hLL2 in tumors >3 cm was 21.5 +/- 10.0 cGy/mCi and was 3.7-, 2.5-, 1.8-, and 2.5-fold that of the bone marrow, lung, liver, and kidney, respectively. No evidence of significant anti-hLL2 antibodies was seen in any of the patients. Myelosuppression was the only dose-limiting toxicity and was greater in patients who had prior high-dose chemotherapy. Objective tumor responses were seen in 2 of 13 and 2 of 7 patients given 131I-hLL2 or 90Y-hLL2, respectively. In conclusion, 90Y-hLL2 results in a more favorable tumor dosimetry compared with 131I-hLL2. This finding, combined with the initial anti-tumor effects observed, encourage further studies of this agent in therapeutic trials.

Prediction of hematologic toxicity after radioimmunotherapy with (131)I-labeled anticarcinoembryonic antigen monoclonal antibodies

This study was undertaken to determine the factors affecting myelotoxicity after radioimmunotherapy (RAIT) with 131I-labeled anticarcinoembryonic antigen (anti-CEA) monoclonal antibodies (MAbs).

METHODS

Ninety-nine patients who received 131I-labeled MN-14 or NP-4 anti-CEA MAbs for the treatment of CEA-producing cancers were assessed for platelet and white blood cell (WBC) toxicity based on the common Radiation Therapy Oncology Group (RTOG) criteria. Univariate and multivariate regression analyses were used to identify the statistically significant factors affecting toxicity among the following variables: red marrow dose, baseline platelet and WBC counts, bone or marrow (or both) metastases, prior chemo- or radiotherapy, timing of prior chemo- or radiotherapy in relation to RAIT, type and number of prior chemotherapeutic regimens, age, sex, antibody form and cancer type.

RESULTS

Red marrow dose, baseline platelet or WBC counts and multiple bone or marrow (or both) metastases were the only significant factors affecting hematologic toxicity according to both univariate and multivariate analyses, whereas chemotherapy, 3-6 mo before RAIT, was significant according to multivariate analysis. In this retrospective study, the multivariate regression equations using these four variables provided an exact fit for postRAIT platelet toxicity grade (PltGr) and WBC toxicity grade (WBCGr) in 40% and 46%, respectively, of the 99 patients included in the analysis. Moreover, severe (grade 3 or 4) PltGr and WBCGr could be classified accurately in all cases, whereas nonsevere (grade 0, 1, or 2) PltGr and WBCGr could be classified accurately in all but 6 of 13 cases of grade 2 toxicity, in which a severe toxicity grade was estimated using the regression equations.

CONCLUSION

Red marrow dose, baseline blood counts, multiple bone or marrow (or both) metastases and recent chemotherapy are the most important factors related to hematologic toxicity after RAIT. This study provides a simple model for predicting myelotoxicity with reasonable accuracy in most patients. In addition, the identification of bone or marrow (or both) metastases and recent chemotherapy as significant factors for myelotoxicity may be important in the future design of clinical trials.

Low- versus high-dose radioimmunotherapy with humanized anti-CD22 or chimeric anti-CD20 antibodies in a broad spectrum of B cell-associated malignancies

Both CD22 and CD20 have been used successfully as target molecules for radioimmunotherapy (RAIT) of low-grade B cell non-Hodgkin's lymphoma. Because both CD20 and CD22 are highly expressed relatively early in the course of B cell maturation, and because its expression is maintained up to relatively mature stages, we studied the potential of the humanized anti-CD22 antibody, hLL2, as well as of the chimeric anti-CD20 (chCD20) antibody, rituximab (IDEC-C2B8), for low- or high-dose (myeloablative) RAIT of a broad range of B cell-associated hematological malignancies. A total of 10 patients with chemorefractory malignant neoplasms of B cell origin were studied with diagnostic (n = 5) and/or potentially therapeutic doses (n = 9) of hLL2 (n = 4; 0.5 mg/kg, 8-315 mCi of 131I) or chCD20 (n = 5; 2.5 mg/kg, 15-495 mCi of 131I). The diagnostic doses were given to establish the patients' eligibility for RAIT and to estimate the individual radiation dosimetry. One patient suffered of Waldenström's macroglobulinemia, eight patients had low- (n = 4), intermediate- (n = 2) or high- (n = 2) grade non-Hodgkin's lymphoma, and one patient had a chemorefractory acute lymphatic leukemia, after having failed five heterologous bone marrow or stem cell transplantations. Three of these 10 patients were scheduled for treatment with conventional (30-63 mCi, cumulated doses of up to 90 mCi of 131I) and 7 with potentially myeloablative (225-495 mCi of 131I) activities of 131I-labeled hLL2 or chCD20 (0.5 and 2.5 mg/kg, respectively); homologous (n = 6) or heterologous (n = 1) stem cell support was provided in these cases. Good tumor targeting was observed in all diagnostic as well as posttherapeutic scans of all patients. In myeloablative therapies, the therapeutic activities were calculated based on the diagnostic radiation dosimetry, aiming at lung and kidney doses < or = 20 Gy. Stem cells were reinfused when the whole-body activity retention fell below 20 mCi. In eight assessable patients, five had complete remissions, two experienced partial remissions (corresponding to an overall response rate of 87%), and one (low-dose) patient had progressive disease despite therapy. In the five assessable, actually stem-cell grafted patients, the complete response rate was 100%. Both CD20 and CD22 seem to be suitable target molecules for high-dose RAIT in a broad spectrum of hematological malignancies of B cell origin with a broad range of maturation stages (from acute lymphatic leukemia to Waldenström's macroglobulinemia). The better therapeutic outcome of patients undergoing high-dose, myeloablative RAIT favors this treatment concept over conventional, low-dose regimens.

Studies on the red marrow dosimetry in radioimmunotherapy: an experimental investigation of factors influencing the radiation-induced myelotoxicity in therapy with beta-, Auger/conversion electron-, or alpha-emitters

Usually, the red marrow (RM) is the first dose-limiting organ in radioimmunotherapy. However, several studies have obtained only poor correlations between the marrow doses and the resulting toxicities. Furthermore, RM doses are mostly not determined directly but are derived from blood doses by assuming a ratio that is, over time for the respective conjugates, more or less constant between blood and marrow activities. The aim of this study was to determine, in a mouse model, this RM:blood activity ratio for various immunoconjugates, to investigate whether there may be differences between complete IgG and its fragments with various labels ((125/131)I versus (111)In, (88/90)Y, or 213Bi), and to analyze, in more detail, factors other than just total dose, such as dose rate or relative biological effectiveness factors, that may influence the resulting myelotoxicity. The maximum tolerated activities (MTAs) and doses (MTDs) of several murine, chimeric, and humanized immunoconjugates as complete IgG or fragments (F(ab)2 and Fab), labeled with beta(-)-emitters (such as 131I or 90Y), Auger electron-emitters (such as 125I or (111)In), or alpha-emitters (such as 213Bi) were determined in nude mice. Blood counts were monitored at weekly intervals; bone marrow transplantation was performed to support the assumption of the RM as dose-limiting. The radiation dosimetry was derived from biodistribution data of the various conjugates, accounting for cross-organ radiation; besides the major organs, the activities in the blood and bone marrow (and bone) were determined over time. Whereas no significant differences were found for the RM:blood ratios between various IgG subtypes, different radiolabels or various time points, differences were found between IgG and bi- or monovalent fragments: typically, the RM:blood ratios were approximately 0.4 for IgG, 0.8 for F(ab')2, and 1.0 for Fab'. Nevertheless, at the respective MTAs, the RM doses differed significantly between the three conjugates: e.g., with 131I-labeled conjugates, the maximum tolerated activities were 260 microCi for IgG, 1200 microCi for F(ab)2, and 3 mCi for Fab, corresponding to blood doses of 17, 9, and 4 Gy, respectively. However, initial dose rates were 10 times higher with Fab as compared to IgG, and still 3 times higher as compared to F(ab)2; interestingly, all three deliver approximately 4 Gy within the first 24 h. The MTDs of all three conjugates were increased by BMT by approximately 30%. Similar observations were made for 90Y-conjugates. Higher RM doses were tolerated with Auger-emitters than with conventional beta(-)-emitters, whereas the MTDs were similar between alpha- and beta(-)-emitters. In accordance to dose rates never exceeding those occurring at the single injection MTA, two subsequent injections of two doses of 80% of the single shot MTA of 131I- or 90Y-labeled Fab' and two doses of 100% of the single shot MTA of 213Bi-labeled Fab' were tolerated without increased lethality, if administered 24-48 h apart. In contrast, reinjection of bivalent conjugates was not possible within 6 weeks. These data suggest that the RM:blood activity ratios differ between IgG and fragments, although there is no anatomical or physiological explanation for this phenomenon at this point. In contrast to the current opinion, indication for a strong influence of the dose rate (or dose per unit time), not only total dose, on the resulting toxicity is provided, whereas the influence of high-linear energy transfer (alpha and Auger/conversion electrons) versus low-linear energy transfer (beta and gamma) type radiation seems to be much lower than expected from previous in vitro data. The lower myelotoxicity of Auger-emitters is probably due to the short path length of their low-energy electrons, which cannot reach the nuclear DNA if the antibody is not internalized into the stem cells of the RM.

The effects of domain deletion, glycosylation, and long IgG3 hinge on the biodistribution and serum stability properties of a humanized IgG1 immunoglobulin, hLL2, and its fragments

Antibody (Ab) fragments are preferred agents for imaging applications because of their rapid clearance from the blood, thereby providing high tumor:blood ratios within a few hours. Several preclinical studies have also suggested that Ab fragments might be preferred for therapeutic applications over an intact IgG. The purpose of this project was to develop engineered Ab fragments using a humanized anti-carcinoembryonic antigen and anti-CD22 Ab as the parent. Three types of variants were prepared: a deltaCH2 (deletion mutant missing the CH2), a gamma3 F(ab')2 containing the human IgG3 hinge, and three glycosylated variants. The gamma3 F(ab')2 and glycosylated variants were developed because of the potential for site-specific linkage to the Ab in its divalent or monovalent fragment. The gamma3 F(ab')2 variant contains 10 cysteine residues that could be used for direct coupling using thiol chemistry, whereas the glycosylated variants have N-linked glycosylation sites engineered in the CH1 domain (two variants) as well as the VK domain (one variant). All of these variants were successfully prepared and shown to react with the target antigen. All Abs could be purified to a single peak by size-exclusion HPLC, but the deltaCH2 variant showed two distinct peaks, which were believed to be both the divalent and monovalent forms of this fragment. The two CH1 glycosylated variants showed differences in the extent of glycosylation. Modeling studies suggest that one variant would be better suited for site-specific coupling than the other because the carbohydrate chain is extended further away from the antigen-binding site. The Abs were radioiodinated to determine their pharmacokinetic behavior in mice. All of the humanized Ab divalent fragments cleared nearly 20 times faster from the blood than the murine parent F(ab')2 over a 24-h period. The glycosylated fragments showed some added stability compared to the other fragments over 4 h, but by 24 h, they had cleared to the same extent. Size-exclusion high-performance liquid chromatography of blood samples indicated that the humanized Ab fragments were quickly degraded in the blood. Thus, there is an inherent instability of the divalent fragments from these humanized IgG1 constructs that may affect their utility in imaging or therapy applications.

Phase I/II trial of (131)I-MN-14F(ab)2 anti-carcinoembryonic antigen monoclonal antibody in the treatment of patients with metastatic medullary thyroid carcinoma

BACKGROUND

Monoclonal antibodies (MAbs) against carcinoembryonic antigen (CEA) have been recognized as targeting agents for medullary thyroid carcinoma (MTC). This Phase I/II study was initiated to determine the safety, maximum tolerated dose (MTD), and therapeutic potential of (131)I-MN-14 F(ab)2 anti-CEA MAb for patients with metastatic MTC.

METHODS

Fifteen patients were enrolled in this study. Dose escalation was based on estimates of radiation dose to the bone marrow, and the radioactive dose given was determined by a pretherapy diagnostic study in which 8 mCi (0.6-20 mg) of (131)I-MN-14 F(ab)2 was administered 1 week prior to therapy.

RESULTS

Three patients received an initial dose of 140 centigray (cGy) to bone marrow, 11 received 180 cGy, and 1 received 220 cGy. Myelosuppression was the only significant treatment-related dose-limiting toxicity (DLT), and the MTD appeared to be 180 cGy to the bone marrow. Human antimouse antibodies (HAMA) developed in 8 patients 2-6 weeks after therapy. Seven patients had a median of 55% reduction of tumor markers. One patient showed a dramatic improvement in the mass effect on the airways caused by 3 tumor lesions in the neck, with a 45% reduction of overall tumor burden. The disease has continued to be radiologically stable in 11 of 12 assessable patients for periods ranging from 3+ to 26+ months.

CONCLUSIONS

Therapy with (131)I-MN-14 F(ab)2 is well tolerated and shows evidence of biochemical and radiologic antitumor activity. HAMA development suggests that humanized MAbs will be required in trials with repeated dose schedules. Further dose escalation, alone or in combination with other therapy modalities, is indicated for future trials, preferably with humanized anti-CEA MAbs.

In vivo stability and metabolism of 99Tcm-labelled anti-CD4 monoclonal antibodies and Fab' fragments

In a comparative study, the in vivo metabolic profile of 99Tcm-anti-CD4 monoclonal antibodies (MAb) and Fab' fragments (direct thiol-reduction method) was investigated in rats with adjuvant arthritis. Plasma samples were obtained 1, 4 and 15 h following intravenous injection and urine was collected over 15 h. The composition of the radiolabelled molecules was analysed by gel filtration chromatography. The profile of the complete MAb was as follows. (1) Serum: a predominant peak of 150 kDa (complete MAb; approximately 80%); three minor peaks of 125, 100 and 50 kDa (presumably H2L1, H2 and H1 chains; 14%); and two small peaks of approximately 1500 and 300 Da (presumably 99Tcm-glutathione and Cys-99Tcm-Cys; 5%). (2) Urine: minor peaks of 125, 100 and 50 kDa (15%), major peaks of 1500 and 300 Da (50%), and an additional 25-kDa peak (30%). The profile of the Fab' was as follows. (1) Serum: three minor peaks of 150 kDa [conceivably F(ab')2 plus soluble-CD4], 110 kDa [F(ab')2] and 95 kDa (Fab' plus soluble-CD4; together 30%); a predominant peak of 55 kDa (Fab'; 61%); and two minor peaks of 1500 and 300 Da (8%). (2) Urine: predominantly a 55 kDa (16%) and 1500 and 300 Da peaks (74%). Also, the anti-CD4 Fab' showed higher urine excretion and lower plasma levels than the complete anti-CD4 MAb, but still more favourable tissue-to-blood ratios following scintigraphy of the arthritic joints. Thus, the complex metabolic profile of the anti-CD4 Fab' does not appear to interfere with specific targeting of the inflamed synovial membrane.

90Yttrium-labeled complementarity-determining-region-grafted monoclonal antibodies for radioimmunotherapy: radiolabeling and animal biodistribution studies

90Yttrium-labeled monoclonal antibodies (mAbs) are likely to be important to radioimmunotherapy (RAIT) of a variety of cancers. The goal of this study was to select and evaluate a form of [90Y]mAb suitable for RAIT and determine conditions for high-yield, reproducible radiolabelings. 90Y-Labelings, at 2-40 mCi levels, of cdr-grafted versions of anti-B-cell lymphoma (hLL2) and anti-CEA (hIMMU-14) mAbs were optimized to >90% incorporations using the macrocyclic chelator DOTA as the metal carrier. In in vitro challenge assays, the stability of mAbs labeled with [90Y]DOTA was better than that of the corresponding [90Y]benzyl-DTPA conjugates. The retention of [90Y]DOTA-hLL2 on Raji tumor cells in vitro was similar to that of the same mAb labeled with [90Y]benzyl-DTPA and was about twice as much as with [125I]hLL2, indicating residualization of metalated mAb. Both [90Y]hLL2 conjugates, prepared using DOTA and Bz-DTPA, had similar maximum tolerated doses of 125 muCi in BALB/c mice and showed no discernible chelator-induced immune responses. Animal biodistribution studies in nude mice bearing Ramos human B-cell lymphoma xenografts revealed similar tumor and tissue uptake over a 10 day period, with the exception of bone uptake which was up to 50% lower for [88Y]DOTA-hLL2 compared to [88Y]Bz-DTPA-hLL2 at time points beyond 24 h. With [90Y]DOTA-hLL2 fragments, in vivo animal tumor dosimetries were inferior to those for the IgG, and kidney uptake was relatively high even with D-lysine administration. The ability of [111In]DOTA-hLL2 to accurately predict [90Y]DOTA-hLL2 biodistribution was established. These preclinical findings demonstrate that [90Y]DOTA-(CDR-grafted) mAbs are suitable for examination in clinical RAIT.

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 (131)I-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 (131)I-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 (131)I-labeled immunoconjugates [IgG, F(ab')2 and Fab], the red marrow was the only dose-limiting organ; MTDs were 260 microCi for IgG, 1,200 microCi 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.

Myelosuppressive changes from single or repeated doses of radioantibody therapy: effect of bone marrow transplantation, cytokines, and hematopoietic suppression

Myelosuppression is the dose-limiting side effect of most forms of radioimmunotherapy (RAIT). Long-term leukopenia (4-8 weeks) has been documented from a single maximum tolerated dose (MTD) in experimental mice. Several methods for alleviating RAIT-induced marrow toxicity have been evaluated preclinically, including cytokine intervention, bone marrow transplantation (BMT), and hemoregulatory peptide administration. To improve the therapeutic potential of RAIT, multiple doses of radioantibody must be delivered. Maximizing the frequency of radioantibody administration is desirable. However, little is known about the myelotoxic effects of multiple cycles of RAIT. In the studies presented here we compared the magnitude of myelosuppression, the time of nadir, and the duration of toxicity associated with one or two MTDs of 1-131-MN-14 anti-carcinoembryonic antigen immunoglobulin G (250 microCi) administered to BALB/c mice 49 days apart, the shortest interval possible without producing lethality. Studies were conducted with radioantibody alone or with cytokines (interleukin-1/granulocyte-macrophage colony-stimulating factor), BMT, or Hp5b to determine whether bone marrow became more "brittle" after the first dose. Profiles of myelosuppression and recovery were monitored weekly for 7 weeks after each dose in both granulocyte and lymphocyte populations. The results demonstrated that granulocyte suppression was greater and of longer duration after the second dose of RAIT administered alone, with cytokines, or with BMT, but less severe with Hp5b. For example, in the RAIT + BMT treatment, the second dose resulted in an 87% loss of granulocytes, whereas a 30% loss occurred after the first dose. The nadir of toxicity lasted until days 21 to 28 after the second dose and until day 14 after the first dose. Lymphocyte suppression was of greater duration after the second cycle of RAIT alone or RAIT with BMT, plateauing at <50% of untreated levels between days 28 and 49, but was of shorter duration when RAIT was given with cytokines or Hp5b. The results are discussed in terms of 1) the radiosensitivity of each subpopulation, 2) the effects on progenitors and on stromal cells, 3) the benefits of increasing dose frequency vs. increasing dose intensity, and 4) the possibility of using preclinical data to optimize the frequency of dosing in patient trials.

Carbohydrates engineered at antibody constant domains can be used for site-specific conjugation of drugs and chelates

To improve the efficiency of site-specific conjugation of chelates and drugs to antibodies, and to minimize the incidence of immunoreactivity perturbation to the resultant immunoconjugates, Asn-linked oligosaccharide moieties were designed and engineered into the constant domains of a humanized anti-CD22 monoclonal antibody, hLL2. From 10 potential glycosylation mutants, two CH1 domain glycosylation sites, HCN1 and HCN5, were identified that were positioned favorably for glycosylation. The carbohydrate (CHO) chains attached at these sites were differentially processed so that HCN5-CHOs were physically larger than HCN1-CHOs. Although both the CH1-appended CHOs, and the LL2 Vkappa-appended CHOs conjugated efficiently with small chelates, the HCN5-CHOs, due to the structural and positional superiority, appear to be a better conjugation site for large drug complexes, such as 18 kDa doxorubicin (DOX)-dextran.

Rapid blood clearance of mouse IgG2a and human IgG1 in many nude and nu/+ mouse strains is due to low IgG2a serum concentrations

We reported previously that the blood clearance of injected mouse IgG2a was extremely rapid in many strains of nude and nu/+ mice. In an attempt to determine the cause of this phenomenon, the levels of endogenous IgG2a in the blood of these mice was assayed. It was found that the serum level of IgG2a was extremely low in many of these mice, below 50 microg/ml, which is 20-100 times lower than the expected normal value. Great heterogeneity between individual mice was observed in their blood level of IgG2a, and there was an excellent correlation between low blood IgG2a levels and rapid clearance of injected IgG2a. Thus, the blood IgG2a levels are so low that a novel, previously undescribed effect occurs, namely the rapid clearance of small amounts of injected IgG2a. The clearance is due primarily to binding sites in the spleen and liver. The low level of endogenous IgG2a is not due to the lack of a thymus, since it occurs in nu/+ as well as nude mice, but can probably be attributed to the very clean environment in which these mice are raised. In assays of sera from approximately 50 mouse strains, low IgG2a levels were found in all nude colonies and also in some normal mouse strains. Some nude mice displayed relatively normal IgG2a clearance rates despite having low levels of endogenous IgG2a. In repeated bleedings of individual mice, IgG2a levels were found to fluctuate greatly. A similar clearance effect was observed with a human IgG1 Ab injected into mice. This rapid clearance of injected IgG, of certain subclasses, represents a practical problem for many experiments in which antibodies are used for diagnosis or therapy, and several methods of circumventing the problem are discussed.

Pharmacokinetics, dosimetry and toxicity of rhenium-188-labeled anti-carcinoembryonic antigen monoclonal antibody, MN-14, in gastrointestinal cancer

The biodistribution, pharmacokinetics and dosimetry of 188Re-labeled MN-14, an IgG anti-carcinoembryonic antigen monoclonal antibody (MAb), were assessed in patients in advanced gastrointestinal cancer. In addition, the dose-limiting toxicity (DLT) and maximum tolerated dose of fractionated doses of this agent were determined.

METHODS

Eleven patients were administered radioactive doses of directly labeled 188Re-MN-14 IgG, ranging from 20.5 mCi to 161.0 mCi (2.0 mg-4.9 mg). Ten of these patients received two or three MAb infusions, given 3-4 days apart, delivering total doses of 30 mCi/m2-80 mCi/m2. External scintigraphy was used to evaluate the MAb biodistribution, and quantitative external scintigraphic methods were used to determine the organ and tumor radiation doses.

RESULTS

The biodistribution studies showed enhanced 188Re-MN-14 uptake in the liver, spleen and kidneys, compared to that of 131I-MN-14. The biological T(1/2) values for 188Re-MN-14 in the blood and whole body (in hours) were 8.2 +/- 4.1 (n = 7) and 107.8 +/- 104.2 (n = 9), respectively (mean +/- s.d.). The radiation absorbed doses (cGy/mCi) delivered to the total body, red marrow, lungs, liver, spleen and kidneys were 0.5 +/- 0.05, 3.6 +/- 1.6, 2.0 +/- 0.8, 5.9 +/- 2.5, 7.1 +/- 1.9 and 8.5 +/- 2.8, respectively. Red marrow suppression was the only DLT observed. The maximum tolerated dose of fractionated doses of 188Re-MN-14 was estimated to be 60 mCi/m2.

CONCLUSION

Despite its relatively increased renal and hepatic uptake, red marrow suppression is the only DLT of 188Re-MN-14. The feasibility of administering relatively high doses of 188Re on a completely outpatient basis may make this agent a preferred candidate for radioimmunotherapy.

Changes in tumor vascular permeability in response to experimental radioimmunotherapy: a comparative study of 11 xenografts

Single and fractionated doses of radioimmunotherapy (RAIT) and standard chemotherapy (0.6 mg 5-FU/day and 0.36 leucovorin/day on days 1-5) result in decreases in vascular permeability (VP) in the GW-39 human colonic xenograft. The effect of a single dose of RAIT (MN-14 anticarcinoembryonic antigen, Mu-9 anticolon-specific antigen, PAM-4 anti-MUC-1, RS-7 and RS-11 antiepithelial glycoprotein labeled with 131I) has also been evaluated in 10 other tumors. Fourteen days after a fixed 1,500-cGy dose of RAIT, 3 colonic tumors (LS174T, HT-29 and MOSER) all exhibited decreases in VP (58, 75 and 70%, respectively). Two colonic (LoVo and GS-7) and 1 breast tumor (MDA-468) did not exhibit any change in VP, and 1 lung (CALU-3), 1 cervical (ME-180), 1 pancreatic (CaPan-1) and 1 breast cancer line (ZR-75) exhibited increases in tumor VP (214, 289, 170 and 139%, respectively). The differences in VP response to RAIT do not appear to be related to the type of tumor, the size of tumor or the antigen being targeted by RAIT. The differences in tumor VP response to RAIT are discussed in terms of the ability to achieve significant tumor accretion of a second dose of radioantibody on a multiple-dosing regimen. We have begun to investigate the mechanism(s) which regulate the varying responses of tumor VP to RAIT by assessing the role that nitric oxide plays. Administration of arginine, a substrate for nitric oxide synthase, results in increases in both baseline and RAIT-modified VP in GW-39 and ME-180 tumors.

Overcoming the nephrotoxicity of radiometal-labeled immunoconjugates: improved cancer therapy administered to a nude mouse model in relation to the internal radiation dosimetry

BACKGROUND

Elevated renal uptake and extended retention of radiolabeled antibody fragments and peptides is a problem in the therapeutic application of such agents. However, cationic amino acids have been shown to reduce renal accretion. The aims of the current study were to evaluate whether this methodology would benefit therapy with yttrium 90 (90Y)-labeled antibody fragments (Fab, F(ab)2), to establish the relationship between radiation dosimetry and observed biologic effects, and to compare the antitumor efficacy of antibody fragments with that of whole immunoglobulin (Ig)G.

METHODS

The maximum tolerated dose (MTD) and the dose-limiting organ toxicity of 90Y-labeled anti-carcinoembryonic antigen (CEA) MN-14 monoclonal antibodies (Fab, F(ab)2, and IgG) were determined in nude mice bearing GW-39 human colon carcinoma xenografts. The mice were treated with or without kidney protection by administration of D-lysine, with or without bone marrow transplantation (BMT), or with combinations of each. Toxicity and tumor growth were monitored at weekly intervals after radioimmunotherapy. Dosimetry was calculated from biodistribution studies using 88Y-labeled antibody. Three different dosimetric models were examined: 1) taking solely self-to-self doses into account, using S factors for 90Y in spheroids from 0.1 to 1 g; 2) correcting for cross-organ radiation; and 3) using actual mouse anatomy as represented by nuclear magnetic resonance imaging with a three-dimensional internal dosimetry package (3D-ID).

RESULTS

The kidney was the first dose-limiting organ with the use of Fab fragments. Acute radiation nephritis occurred at injected activities > or = 325 microCi, and chronic nephrosis at doses > or = 250 microCi. Activities of 200 microCi were tolerated by 100% of the animals (i.e., the MTD). Application of lysine decreased the renal dose by approximately fivefold, facilitating a 25% increase in the MTD (to 250 microCi), because myelotoxicity became dose-limiting despite red marrow doses of less than 5 gray (Gy). By using BMT and lysine, the MTD could be doubled from 200 to 400 microCi, where no biochemical or histologic evidence of renal damage was observed (kidney dose, < or = 40 Gy). With injected activities of > or = 325 microCi without kidney protection, and with a hepatic self-to-self dose of only 4 Gy, rising liver enzymes were observed, which could be explained only by cross-organ radiation from radioactivity in the kidneys (in the immediate neighborhood of the right kidney up to > or = 150 Gy). The MTD of F(ab)2 fragments could be elevated only by a combination of BMT and lysine. With IgG, the bone marrow alone was dose-limiting. Tumor dosimetry correlated well with antitumor effects; Fab was more effective than F(ab)2, which was consistent with its more favorable dosimetry, and it may also be more effective than IgG due to its higher dose rate and more homogenous distribution. Dosimetry Model 1 was insufficient for predicting biologic effects. Model 2 seemed to be more accurate, accounting for interorgan crossfire. However, Model 3 showed an additional substantial contribution to the red bone marrow dose due to crossfire from the abdominal organs.

CONCLUSIONS

These data show that radiation nephrotoxicity is an important effect of cancer therapy with radiometal-conjugated antibody fragments or peptides. However, this effect can be overcome successfully with the application of cationic amino acids, which substantially increase the anti-tumor efficacy of radiometal-labeled immunoconjugates. For understanding the biologic effects (e.g., liver toxicity) of 90Y in a mouse model, accounting for cross-organ radiation is essential. Further studies with radiometal-conjugated monoclonal antibody fragments and peptides are necessary to determine the MTD, dose-limiting organs, antitumor effectiveness, and nephroprotective effects of cationic amino acids in humans.

Factors influencing hematologic toxicity of radioimmunotherapy with 131I-labeled anti-carcinoembryonic antigen antibodies

BACKGROUND

Several investigators have reported a considerable variability in the observed hematologic toxicity after radioimmunotherapy (RAIT) with monoclonal antibodies (MoAb) given at similar amounts of radioactivity based on body surface area and/or similar radiation absorbed doses given to the red marrow. The authors investigated various factors potentially affecting hematologic toxicity after RAIT with 131I-labeled anti-carcinoembryonic antigen (CEA) MoAb to identify the statistically significant factors from those commonly perceived clinically to substantially contribute to this toxicity.

METHODS

Ninety-nine patients who received 131I-labeled anti-CEA MoAb for the treatment of CEA-producing cancers were assessed for platelet and white blood cell toxicity based on the common Radiation Therapy Oncology Group criteria. Multivariate regression analysis was used to identify the statistically significant factors affecting toxicity among the following variables: red marrow dose, baseline platelet and white blood cell counts, bone and/or marrow metastases, prior chemotherapy or radiotherapy, timing of prior chemotherapy or radiotherapy in relationship to RAIT, type and number of prior chemotherapeutic regimens, age, sex, antibody form, and cancer type.

RESULTS AND CONCLUSIONS

Red marrow dose, baseline platelet or white blood cell counts, multiple bone and/or marrow metastases, and chemotherapy 3-6 months before RAIT were the only four significant factors affecting hematologic toxicity according to multivariate analysis. The identification of bone and/or marrow metastases and recent chemotherapy as significant factors for hematologic toxicity could be important in the design of future clinical trials.

Defining the optimal spacing between repeat radioantibody doses in experimental models: is there an accurate measurement for hematopoietic recovery?

BACKGROUND

Single doses of radioantibody are effective at treating single cells or small clusters of cancer cells. However, large tumor masses require either multiple doses of radioantibody or a multimodal approach to therapy using two or more therapeutic agents. Timing of the second dose in a multiple cycle scheme or the second treatment in a multimodal protocol will depend on recovery from toxicity associated with the first treatment.

METHODS

BALB/c mice were dosed with a maximal tolerated dose (MTD) of I-131-MN-14 anti-carcinoembryonic antigen immunoglobulin G (IgG) (250 microCi) or F(ab')2 (1.2 mCi). Mice were redosed with the MTD at one of four time points, either Day 28, 35, 42, or 49 after IgG or Day 14, 21, 28, or 35 after F(ab')2. Survival was monitored to determine the earliest time to redose without lethality. Several studies were then performed to identify an accurate measure of true myelorecovery. Mice were bled retroorbitally on the day of the first dose and at weekly intervals thereafter. Total peripheral white blood cell counts, granulocyte counts, and lymphocyte counts were determined for each animal. GR-1hi expression (percentage of positive cells) and mean channel florescence were determined by FACScan analysis of a blood sample incubated with fluorescein isothiocyanate-anti-mouse Ly-6G (GR-1). In other studies, two mice were killed weekly from a group treated with a single MTD of radioantibody. The weights of their spleens and thymus glands were determined. At that time, femoral marrow was collected from these animals and plated in Methocult M3430 methylcellulose medium (Stemcell Technologies, Vancouver, Canada), and total colony-forming cells in culture were determined. Another population of mice was used to assess normal tissue metabolic activity following radioantibody therapy by quantitating the 4-hour utilization of I-125-dUrd.

RESULTS

The ability to redose mice with a second MTD of 1-131-IgG or F(ab')2 required 49 days and 35 days, respectively. Granulocyte and lymphocyte counts did not accurately predict myelorecovery from the first dose. Hematopoietic tissue weight, tissue metabolic activity, and marrow colony forming cells all suggested that redosing was possible 1-2 weeks before it could actually be done without lethality. Percent of cells expressing GR-1hi (>60%) and absolute numbers of GR-1hi cells (>1400 cells/mm3) suggested myelorecovery in most animals. A greater degree of accuracy was achieved when trends in GR-1hi expression were noted over 2 or more weeks (i.e., the absolute amount of GR-1hi had to exceed levels in untreated mice, as evidence that the hyperproliferative phase of recovery was complete).

CONCLUSIONS

The only approach that accurately predicted the ability to retreat with myelosuppressive therapy without risk of lethality was an increase in GR-1hi-positive cells above untreated levels. Other approaches are currently being investigated, including the expression of proliferation antigens (e.g., proliferating cell nuclear antigen and Ki-67) in both murine and human samples and differentiation antigens (CD33 and CD34) in humans.

Can occult metastases be treated by radioimmunotherapy?

BACKGROUND

Tumor lesions in the millimeter (mm) range may escape detection with nuclear medicine imaging methods (including single photon emission computed tomography [SPECT]) using radiolabeled monoclonal antibodies (MoAbs). We hypothesized that these lesions still could receive a potentially therapeutic radiation absorbed dose, and therefore should be treated, despite the lack of detection.

METHODS

To simulate this situation, 2-mm beads (0.004 mL) containing approximately 1.15 microCi of iodine-131 (131I) were used. The beads were placed centrally in a 1200-mL liver phantom containing approximately 3 mCi of 131I. The resultant activity concentration on the beads was approximately 288 microCi/mL compared with approximately 2.5 microCi/mL in the phantom, corresponding to a maximum tumor uptake of approximately 0.3% injected dose per gram (%ID/g) if 100 mCi of 131I-labeled immunoglobulin G were administered. The phantom, containing the beads, was imaged by both planar and SPECT techniques at hypothetical Day 1 (time of maximum tumor uptake) and at hypothetical Day 7 to examine the improved target-to-nontarget ratio over time. In addition to imaging the beads, the radiation absorbed dose to the simulated lesions from the beta component emissions of 131I was calculated using absorbed fractions based on Berger's point kernels.

RESULTS

Regardless of the conditions used, the beads could not be observed by either planar or SPECT imaging. However, the radiation-absorbed dose to the simulated lesion was calculated to be as high as approximately 6200 centigray (cGy), with an average dose rate of approximately 89.5 cGy/hour.

CONCLUSIONS

This simulation demonstrates that a relatively high absorbed dose and dose rate can be delivered to mm-sized lesions not observed by conventional nuclear imaging methods, and that these lesions should be considered for radioimmunotherapy with 1311 MoAbs. However, for micrometastases of <1 mm, other radionuclides with shorter path length beta particles than 131I, Auger electrons, or alpha particles should be considered.

Improved selection of patients for reoperation for medullary thyroid cancer by imaging with radiolabeled anticarcinoembryonic antigen antibodies

BACKGROUND

This study examined the utility of using radiolabeled anticarcinoembryonic antigen (CEA) monoclonal antibodies (MAbs) as a noninvasive imaging method to aid in the selection of patients for reoperation after operation for medullary thyroid carcinoma (MTC).

METHODS

Sixteen patients with persistent or recurrent hypercalcitoninemia since operation or MTC, but had negative or equivocal conventional imaging study results, were given 99mTc-, 123I-, or 131I-labeled NP-4 or MN-14 anti-CEA MAbs. Scintigraphic images were then performed to determine detection of tumor lesions.

RESULTS

The MAb scans were positive in 13 (81%) of the 16 patients studied. However, in only three of 13 patients was disease confined to the cervical or mediastinal nodes. In 10 patients, disease was additionally or solely found in distant organs such as liver (five patients), bone (four patients), and periaortic nodes (one patient). On the basis of our studies, only three of the 13 patients with positive scans would benefit from repeat neck exploration, another three would possibly benefit from neck or mediastinal exploration and hepatic resection, and the remaining seven patients would not benefit from any reoperation with curative intent.

CONCLUSIONS

MTC imaging with anti-CEA MAbs could be very useful in determining the ideal candidates for repeat neck exploration.

Prospects of radioimmunotherapy in epithelial ovarian cancer: results with iodine-131-labeled murine and humanized MN-14 anti-carcinoembryonic antigen monoclonal antibodies

OBJECTIVES

Epithelial ovarian cancer (EOC) is known to produce carcinoembryonic antigen (CEA), and the plasma CEA level is frequently elevated in patients with advanced stage and bulk of tumor. This study reports the results of a phase I therapy trial with intravenously administered 131I-MN-14 anti-CEA monoclonal antibody (MAb) in patients with EOC.

METHODS

Fourteen patients with advanced refractory EOC were given escalating intravenous doses (two received 30 mCi/m2, six 40 mCi/m2, and six 50 mCi/m2) of 131I-MN-14 IgG. All patients received a diagnostic study with 8 mCi (0.6 mg) of 131I-MN-14 IgG 1 week prior to their therapy infusion. Tumor targeting was assessed by external scintigraphy, toxicity according to the Radiation Therapy Oncology Group criteria, and therapy responses by CT and serum CA-125.

RESULTS

The MAb scan was positive in all 14 treated patients. Myelosuppression was the only observed treatment-related toxicity. Dose-limiting toxicity, defined as grade 4 leukopenia or thrombocytopenia of any duration, or grade 3 leukopenia or thrombocytopenia of > 2 weeks, was not seen at the 30 or 40 mCi/m2 dose levels. However, 2 of 6 patients treated at 50 mCi/m2 had a grade 4 thrombocytopenia or a grade 3 thrombocytopenia lasting 18 days. Of the 14 patients, 1 with diffuse peritoneal implants of < or = 2 cm had a complete clinical remission by CT and CA-125 for 8 months, following an initial partial remission for 10 months, both at the 40 mCi/m2 dose level. Another patient had a mixed response for 1 month.

CONCLUSION

MN-14 anti-CEA MAb is a suitable agent for tumor targeting and may have a therapeutic potential in patients with chemotherapy-refractive EOC, especially those with minimal disease.

Structure determination of N-linked oligosaccharides engineered at the CH1 domain of humanized LL2

Two humanized antibody mutants, hLL2HCN1 and hLL2HCN5, engineered with CH1 domain-appended carbohydrates (CHOs) were generated to facilitate site-specific conjugation of radionuclides and anti-cancer drugs to antibodies. Such site-specific conjugation may minimize the incidence of immunoreactivity perturbation as is often observed with random conjugation. Since the compositions and structures of CHOs are important in determining the chemistry, efficiency, and extent of conjugation, the sequences of the CH1-appended CHOs were determined by exoglycosidase digestions and fluorophore-assisted CHO electrophoresis (FACE). The CHO species attached at HCN1 and HCN5 sites in hLL2HCN1 and hLL2HCN5, respectively, were distinct from each other, heterogeneous, and extensively processed. All of these CHOs were core-fucosylated complex-type oligosaccharides and contained Gal (galactose) and GlcNAc (N-acetylglucosamine) residues in the outer branches. Some of the outer branches were composed of Gal alpha1-3Galbeta1-4GlcNAc structure, also known as alpha-galactosyl epitope. Most of the CHOs were sialylated. While all HCN1-CHOs were biantennary, the majority of HCN5-CHOs (>60%) were triantennary. The CH1-appended CHOs have favorable structural characteristics suitable for site-specific conjugation. For efficient conjugation of large drug complexes, hLL2HCN5 is preferable to hLL2HCN1 because the attached CHO is larger in size and more remotely positioned from the V region. The effects of the alpha-galactosyl epitope found in these CHOs on the immunological properties of the immunoconjugates as efficient cancer diagnostics and therapeutics are being studied.

Selection of radioimmunoconjugates for the therapy of well-established or micrometastatic colon carcinoma

In order to optimize radioimmunotherapy (RAIT) as a cancer-treatment modality, it is necessary to select the appropriate radionuclide and antibody carrier. We evaluated the therapeutic potential of a single cycle of Mu-9 anti-CSAp monoclonal antibody (MAb) labeled with 3 different radionuclides, 131I, 90Y and 188Re. Intact antibodies and bivalent fragments with different blood clearance kinetics, normal organ distribution and varying tumor accretion and retention are also evaluated. Efficacy of treatment for large and small tumor burden was assessed in nude mice bearing s.c. GW-39 human colonic-carcinoma xenografts or intrapulmonary micrometastatic GW-39 colonies at the maximal tolerated dose of each agent. The magnitude and duration of myelosuppression associated with each radioantibody was considered by monitoring peripheral blood counts, marrow colony-forming unit activity and hematopoietic tissue weight. Radiation-dose estimates were calculated based on the kinetics of antibody accretion and elimination from tumor and normal tissues, and the results were correlated with tumoricidal activity and dose-limiting toxicity results. These studies, therefore, represent a detailed analysis, in a well-defined experimental tumor system, of several parameters (antibody form, radioisotope, tumor size) influencing the overall outcome of RAIT using equitoxic doses. It was found that myelosuppression is the primary dose-limiting toxicity for all radioantibodies except 90Y-F(ab')2, even though the different agents showed varied organ distribution. In a single-cycle treatment schedule of Mu-9 MAb, the 131I-labeled IgG is the radioimmunoconjugate of choice for the treatment of s.c. and intrapulmonary growth of the GW-39 human colonic-carcinoma xenograft in nude mice.

Selection of radioimmunoconjugates for the therapy of well-established or micrometastatic colon carcinoma

In order to optimize radioimmunotherapy (RAIT) as a cancer-treatment modality, it is necessary to select the appropriate radionuclide and antibody carrier. We evaluated the therapeutic potential of a single cycle of Mu-9 anti-CSAp monoclonal antibody (MAb) labeled with 3 different radionuclides, 131I, 90Y and 188Re. Intact antibodies and bivalent fragments with different blood clearance kinetics, normal organ distribution and varying tumor accretion and retention are also evaluated. Efficacy of treatment for large and small tumor burden was assessed in nude mice bearing s.c. GW-39 human colonic-carcinoma xenografts or intrapulmonary micrometastatic GW-39 colonies at the maximal tolerated dose of each agent. The magnitude and duration of myelosuppression associated with each radioantibody was considered by monitoring peripheral blood counts, marrow colony-forming unit activity and hematopoietic tissue weight. Radiation-dose estimates were calculated based on the kinetics of antibody accretion and elimination from tumor and normal tissues, and the results were correlated with tumoricidal activity and dose-limiting toxicity results. These studies, therefore, represent a detailed analysis, in a well-defined experimental tumor system, of several parameters (antibody form, radioisotope, tumor size) influencing the overall outcome of RAIT using equitoxic doses. It was found that myelosuppression is the primary dose-limiting toxicity for all radioantibodies except 90Y-F(ab')2, even though the different agents showed varied organ distribution. In a single-cycle treatment schedule of Mu-9 MAb, the 131I-labeled IgG is the radioimmunoconjugate of choice for the treatment of s.c. and intrapulmonary growth of the GW-39 human colonic-carcinoma xenograft in nude mice.

Application of cytokine intervention for improved radio-antibody dose delivery

The goal of our studies was to determine whether administration of IL-1/GM-CSF to mice could reduce radio-antibody-induced myelosuppression and allow either dose escalation of radio-antibody using 131I, 90Y or 188Re conjugated to either intact antibody or bivalent fragments or more frequent dosing with 131I-IgG. Survival, peripheral blood counts, hematopoietic tissue weight and number of marrow CFCs were used to determine the ability to dose-intensify with a single dose or to reduce the spacing between doses. In this report, we show that in the absence of cytokines, 2 cycles of 131I-IgG spaced at 28, 35, 42 and 49 days resulted in 100%, 100%, 40% and 0% lethality, respectively. In contrast, cytokine intervention reduced lethality to 45%, 20%, 0% and 0% at the same time intervals between doses. Thus, the use of cytokines permits at least a 1 week earlier redosing of 131I-IgG. Cytokine intervention also has reduced the magnitude of myelosuppression, as measured by neutropenia and thrombocytopenia, thus permitting intensification of single doses of radio-iodinated intact antibodies, bivalent fragments and 90Y-IgG by at least 30%, 50% and 25%, respectively. However, cytokines were not effective at permitting dose escalation of either 90Y-F(ab')2 or 188Re-IgG. Further optimization of the dose schedule of cytokine administration needs to be explored for these 2 nuclide-antibody forms.