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.

Clinical Utility of Radioimmunoscintigraphy of Non-Hodgkin's Lymphoma with Radiolabelled LL2 Monoclonal Antibody., Lymphoscan™: Preliminary Results

Aims and Background

Adequate clinical staging of non-Hodgkin's lymphoma patients is essential because only localized disease can be treated satisfactorily. Many imaging procedures are necessary to stage the disease accurately. The objective of this study was to evaluate the efficacy of an anti-lymphoma antibody in the Fab’ fragment form, labelled with 99mTc, to detect malignant lesions.

Methods

Radioimmunodetection (RAID) with 99mTc-labelled B-cell lymphoma monoclonal antibody IMMU-LL2-Fab’ (LymphoSCAN™; Immunomedics, Morris Plain, NJ, USA) was investigated in 10 patients (5 females and 5 males; age range, 20-72 years) with histologically proved non-Hodgkin's lymphoma. Of the 10 lymphomas, 7 were intermediate grade and 3 were low grade. Whole body images with multiple planar views were obtained at 30 min, 4-6 and 24 h after i.v. injection of 1 mg LL2-Fab’ labelled with 740-925 MBq of 99mTc. SPET of the chest or abdomen was performed in all patients 5-8 h after the immunoreagent injection.

Results

No adverse reactions were observed in any patient after Mab infusion, and no appreciable changes were seen in the blood counts, renal or liver function tests. A total of 18 of 21 (85.7%) lymphoma lesions were detected by RAID. All the tumor localizations were confirmed by clinical examination and with other imaging techniques, such as CT scan, MRI or gallium scan. In this series of patients no false-positive results were noted. As regards the biodistribution of the immunoreagent, no appreciable bone marrow activity was seen; splenic targeting was demonstrated in all patients; the tumor-to-non-tumor ratios ranged from 1.2 to 2.8 ad measured by the ROI technique; no difference in uptake was noted for different tumor grades. The images obtained 24 h after injection did not reveal new lesions, but areas of doubtful uptake were seen as positive focal areas in the delayed scan.

Conclusions

LymphoSCAN™ seems to be useful for detection, staging and follow-up of non-Hodgkin's lymphoma patients.

Abstract OT2-07-05: A phase III, randomized trial of sacituzumab govitecan (IMMU-132) vs treatment of physician choice (TPC) for metastatic triple-negative breast cancer (mTNBC)

Background: Metastatic TNBC has an aggressive course with limited therapy options and poor survival. Sacituzumab govitecan (IMMU-132) is a novel antibody drug conjugate consisting of SN-38, the active metabolite of the topoisomerase I inhibitor, irinotecan, conjugated to a humanized mAb targeting Trop-2, which is highly expressed in most epithelial cancers, including TNBC. We previously reported that patients (pts) with mTNBC treated with IMMU-132 after a median of 5 prior therapies from initial diagnosis achieved a 30% objective response rate (ORR), 8.9 mo median duration of response (DOR), and an acceptable safety profile with nausea, neutropenia, and diarrhea the most common toxicities (Bardia et al., JCO, 2017). IMMU-132 was awarded Breakthrough Designation by the FDA based on this data. Accordingly, we are enrolling additional patients with relapsed/refractory mTNBC with intention of seeking regulatory approval as a ≥3rd-line therapeutic option.

Trial design: An international, open-label, Phase III study in pts with refractory/relapsed mTNBC after ≥2 prior chemotherapies for advanced disease or >1 therapy for pts who progress within 12 months of adjuvant therapy (NCT02574455). Pts are randomized 1:1 to receive either IMMU-132 (10 mg/kg IV, days 1 and 8 every 21 days) or TPC from one of 4 prespecified single-agent regimens (capecitabine, eribulin, vinorelbine or gemcitabine). Pts continue treatment until progression requiring discontinuation or unacceptable toxicity. The primary endpoint is progression-free survival (PFS) and additional endpoints include overall survival (OS), ORR, DOR, safety and quality of life. Independent, blinded reads of scans will be performed.

Eligibility criteria: Adults >18 yrs old, with metastatic breast cancer, triple-negative by most recent biopsy, measurable disease by CT or MRI as per RECIST1.1, ECOG performance score 0 or 1, adequate safety laboratories. Refractory/relapsed after ≥2 prior standard chemotherapy regimens for advanced disease, or >1 therapy for pts who progress within 12 months of adjuvant therapy. Pts must have received taxane and be eligible by investigator to receive at least one of the TPC agents. Pts with treated, non-progressive brain metastases are eligible.

Specific aims: To compare IMMU-132 to TPC as measured by PFS, OS, ORR, DOR,QOL, adverse events, safety laboratories, incidence of dose delays and reductions, and treatment discontinuations due to toxicity.

Statistical methods: Assuming a median PFS of 3 mo. and OS of 10 mo. with TPC vs. 5 and 15 mo. with IMMU-132, respectively, a study size of 328 patients has >95% and >80% power to detect a statistically significant difference in PFS and OS, respectively, between the two treatment arms.

Present accrual and target accrual: Trial enrollment will begin prior to SABCS 2017 with approximately 328 patients expected to be enrolled over 18 months at approximately 100 institutions in North America, Europe and potentially elsewhere.

Contact: Immu132@Immunomedics.com

Citation Format: Bardia A, Rugo HS, Horne H, Wegener WA, Goldenberg DM, O'Shaughnessy J. A phase III, randomized trial of sacituzumab govitecan (IMMU-132) vs treatment of physician choice (TPC) for metastatic triple-negative breast cancer (mTNBC) [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr OT2-07-05.

Abstract P1-12-01: Withdrawn

This abstract was withdrawn by the authors.

Immunization with HIV-1 envelope T20-encoding DNA vaccines elicits cross-clade neutralizing antibody responses

Background: Genetic immunization is expected to induce the expression of antigens in a native form. The encoded peptide epitopes are presented on endogenous MHC molecules, mimicking antigen presentation during a viral infection. We have explored the potential of enfuvirtide (T20), a short HIV peptide with antiviral properties, to enhance immune response to HIV antigens. To generate an expression vector, the T20 sequence was cloned into a conventional plasmid, the novel minicircle construct, and a replicon plasmid. In addition, 3 conventional plasmids that express the envelope of HIV-1 subtypes A, B and C and contain T20 in their gp41 sequences were also tested. Results: All combinations induced HIV-specific antibodies and cellular responses. The addition of T20 as a peptide and as an expression cassette in the 3 DNA vectors enhanced antibody responses. The highest anti-HIV-1 Env titers were obtained by the replicon T20 construct. This demonstrates that besides its known antiviral activity, T20 promotes immune responses. We also confirm that the combination of slightly divergent antigens improves immune responses. Conclusions: The antiretroviral T20 HIV-1 sequence can be used as an immunogen to elicit binding and neutralizing antibodies against HIV-1. These, or similarly modified gp41 genes/peptides, can be used as priming or boosting components for induction of broadly neutralizing anti-HIV antibodies. Future comparative studies will reveal the optimal mode of T20 administration.

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 P2-04-17: Directing NK cells to Trop-2-expressing breast and other cancers, with chimeric antigen receptors

Adoptive immunotherapy with chimeric antigen receptor (CAR)-engineered T or NK cells is in active clinical and preclinical development, with recent interest increasingly focused on advancing the availability of off-the-shelf allogeneic clonal NK cell lines capable of targeting tumors with appropriately designed CARs. Among the human NK cell lines established, the IL-2-dependent NK-92 is the most studied and has been transduced with human IL-2 to generate NK-92MI, which exhibits cytotoxicity similar to NK-92, and is independent of IL-2 for its cytotoxicity, viability and proliferation. We report the assembly of E1.BB.3z-92MI, a novel CAR-NK for potential therapy of diverse Trop-2-expressing breast, lung, bladder, ovarian, and other cancers. The Trop-2-specific CAR, referred to as hRS7-CAR, consists of the CD8α signal peptide, the VK and VH of hRS7 (a humanized anti-human Trop-2 mAb used in the antibody-drug conjugate, IMMU-132), the hinge region and transmembrane domain of CD8α, the intracellular domains (ICD) of 4-1BB, and the ICD of CD3ξ. The construct of hRS7-CAR is introduced into NK-92MI either by electroporation of the mRNA synthesized in vitro, or by inoculation with the lentiviral particles harvested from the 48-h supernatants of Lenti-X 293T cells transduced with pLVX-puro-hRS7-CAR.

The presence of hRS7-CAR in E1.BB.3z-92MI was probed by Western blot using an HRP conjugate of a rat anti-id antibody against hRS7, which detected a distinct band of about 50 kDa from the cell lysates of NK-92MI transfected with hRS7-CAR mRNA, but not from the mock-transfected NK-92MI. As the calculated molecular weight of hRS7-CAR is about 51 kDa, these results support that hRS7-CAR is produced in NK-92MI cells transfected with hRS7-CAR mRNA. Additional evidence by flow cytometry shows about 41% of NK-92MI cells transfected with hRS7-CAR mRNA are alive at the time of analysis and 25% of this subpopulation expresses hRS7. The cytotoxicity of E1.BB.3z-92MI was evaluated against the Trop-2-expressing, human breast cancer cell line, HCC1806, in 96-well plates (4,500 cells/well) at 3 different effector-to-target (E/T) ratios (1:1, 2:1, or 4:1). As shown in the Table, the results of the MTS assay indicate that NK-92MI cells transfected with hRS7-CAR mRNA significantly killed more HCC1806 cells at the E/T ratio of 2:1 or 4:1, in comparison to mock-transfected NK-92MI. Another study performed by flow cytometry using dye-labeled HCC1806 at the E/T ratio of 3:1 indicates that the specific lysis of HCC1806 cells by NK-92MI cells transfected with hRS7-CAR mRNA was about 2-fold higher than that observed for mock-transfected NK-92MI. Finally, the initial results obtained for NK-92MI cells transduced with the lentiviral pLVX-puro-hRS7-CAR show about 70% viability and greater than 30-fold higher MFI in the live population than the control transduced with pLVX-puro or not transduced. Together, these results demonstrate the feasibility of developing E1.BB.3z-92MI as a novel CAR-NK for targeting Trop-2-expressing cancers, including breast cancer.

Table. Cytotoxicity of Trop-2-targeting NKcellsE/TViability (mean ± SD)Mock vs. hRS7-CAR MockhRS7-CARΔP-value1:188.5 ± 9.980.3 ± 11.18.20.392:189.9 ± 10.667.4 ± 4.422.50.0274:184.8 ± 4.072.4± 2.512.40.010

Citation Format: Chang C-H, Liu D, Goldenberg DM. Directing NK cells to Trop-2-expressing breast and other cancers, with chimeric antigen receptors [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 P2-04-17.

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.

Epratuzumab for systemic lupus erythematosus

Epratuzumab (EMab, UCB, Immunomedics) is a humanized monoclonal antibody targeting CD22 that is being studied in clinical trials for patients with a variety of rheumatic and hematologic conditions, including systemic lupus erythematosus (SLE). An overview of its mechanism of action is followed by a summary of completed lupus studies, and a preview of studies in progress. The agent clearly has anti-inflammatory activity and is a potentially useful agent in the management of autoimmune disorders.

CD84 is a survival receptor for CLL cells

Chronic lymphocytic leukemia (CLL) is characterized by the accumulation of CD5+ B lymphocytes in peripheral blood, lymphoid organs and bone marrow. The main feature of the disease is accumulation of the malignant cells due to decreased apoptosis. CD84 belongs to the signaling lymphocyte activating molecule family of immunoreceptors, and has an unknown function in CLL cells. Here, we show that the expression of CD84 is significantly elevated from the early stages of the disease, and is regulated by macrophage migration inhibitory factor and its receptor, CD74. Activation of cell surface CD84 initiates a signaling cascade that enhances CLL cell survival. Both downmodulation of CD84 expression and its immune-mediated blockade induce cell death in vitro and in vivo. In addition, analysis of samples derived from an on-going clinical trial, in which human subjects were treated with humanized anti-CD74 (milatuzumab), shows a decrease in CD84 messenger RNA and protein levels in milatuzumab-treated cells. This downregulation was correlated with reduction of Bcl-2 and Mcl-1 expression. Thus, our data show that overexpression of CD84 in CLL is an important survival mechanism that appears to be an early event in the pathogenesis of the disease. These findings suggest novel therapeutic strategies based on the blockade of this CD84-dependent survival pathway.

P3-02-02: Novel Ranpirnase-Based ImmunoRNases Display Potent Cytotoxicity in Diverse Human Breast Cancer Cell Lines

Ranpirnase (Rap) is an amphibian ribonuclease originally isolated from the oocytes of Rana pipiens. Rap shows anti-tumor activity in diverse cancers and its potency can be enhanced by chemically linking or recombinantly fusing Rap to a tumor-targeting antibody, as demonstrated for CD22- or CD74-expresing hematological malignancies, as well as a variety of Trop-2-expressing cell lines derived from breast, cervical, lung, pancreatic, and prostate cancers. The Dock-and-Lock (DNL) platform enables the design and generation of targetable therapeutics that are multivalent, multispecific, and multifunctional. Here, we report the successful application of the DNL method to generate a novel class of Rap-based immunoRNases, each of which features a pair of dimeric Rap molecules covalently tethered to a select monoclonal antibody at the carboxyl termini of the heavy chains. Two such constructs, designated E1-Rap and 22-Rap, were developed with hRS7 (humanized anti-Trop-2) and epratuzumab (humanized anti-CD22), respectively, purified to near homogeneity, and evaluated in a panel of human breast cancer lines, including the basal-like, triple-negative subtype (MDA-MB-468, MDA-MB-231, BT20, HCC1806, and HCC1395), the luminal B, HER2−negative subtype (MCF-7), and the HER2−positive subtype (SKBR3), all except HCC1395 expressing high to moderate levels of Trop-2, and none expressing CD22. As demonstrated by flow cytometry, E1-Rap and hRS7 bound equivalently to MDA-MB-468, indicating the affinity of E1-Rap for Trop-2 is not compromised. Surprisingly, 22-Rap, but not epratuzumab, also bound substantially to MDA-MB-468, albeit to a lesser extent than E1-Rap. We thus postulate that the four highly basic Rap molecules in the DNL conjugate may confer a spatial configuration to largely enhance their interaction with negatively-charged cell surface proteins, such as heparan sulfate proteoglycans. Whereas the individual DNL component (IgG or Rap) alone or in combination showed negligible in vitro cytotoxicity in all seven breast cancer cell lines examined, E1-Rap exhibited EC50 values of 1 nM or less in MDA-MB-468 (0.03 nM), MCF-7 (0.1 nM), BT20 (0.18 nM), HCC1806 (0.19 nM), and SKBR3 (1.29 nM). In comparison, the potency of 22-Rap was at least 10-fold lower than E1-Rap in MDA-MB-468, BT20 and HCC1806, with an EC50 of ∼2 nM. Neither E1-Rap nor 22-Rap was very effective in inhibiting the proliferation of the more aggressive MDA-MB-231, with an EC50 above 50 nM. In the Trop-2-negative HCC1395, the dose-response curves obtained for E1-Rap and 22-Rap were nearly identical (EC50 ∼100 nM), as they should be if the cytotoxicity was mediated mainly through the Rap component. The results of Immunofluorescence microscopy showed E1-Rap was effectively internalized and localized in the cytosol. Thus, these ImmunoRNases are potentially new cancer therapeutics for breast and other solid tumors.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P3-02-02.

Pretargeted radioimmunotherapy in the treatment of metastatic medullary thyroid cancer

Medullary thyroid carcinoma (mtc) is a rare cancer (less than 8% of all thyroid cancers) that occurs both as a familial and as a sporadic disease [...]

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

206

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]

Activity of fractionated radioimmunotherapy with clivatuzumab tetraxetan combined with low-dose gemcitabine (Gem) in advanced pancreatic cancer (APC)

240

Background: The90Y-labeled anti-mucin humanized mAb, clivatuzumab tetraxetan (90Y-hPAM4), is in clinical development in APC. A phase I/II trial of 90Y-hPAM4 with low-dose radiosensitizing Gem has now concluded 90Y-dose escalation.

Methods: Pts with untreated, inoperable, stage 3-4 APC received 200 mg/m2 Gem once-weekly x 4 with 90Y-hPAM4 on wks 2-4, and with 90Y escalated in cohorts by 3+3 design. Tumor responses were assessed by CT, FDG/PET and serum CA19.9, with cycles repeated until progression or unacceptable toxicity.

Results: Of 42 pts (40-87 yrs, ECOG PS 0-1, 36 stage 4), 4 withdrew early while 38 received weekly x 3 90Y doses of 6.5 (N=4), 9 (N=12), 12 (N=17) and 15 (N=5) mCi/m2. Treatment was well-tolerated with few non-hematologic side-effects, including 13 pts retreated with 1-3 additional cycles. CTCv3 grade 3-4 plts or ANC developed in 21/38 (55%) pts after cycle 1 and all (100%) retreated pts after last cycle. Escalation reached limits on radiation doses to the marrow, but hematologic suppression was reversible without major infections or bleeding events, except for 3 pts after repeated cycles, one with extensive marrow tumor infiltration. By CT, the overall disease control rate was 55%, including 6 pts (16%) with partial responses (PRs) by RECIST criteria and 15 pts (39%) with stabilization as best response. After cycle 1, 43% (10/23) improved by PET studies (negative or >25% reduced uptake), and 36% (9/25) with elevated CA19.9 levels had >50 decreases. With 26% (10/38) of pts still in follow-up, 55% (21/38) have now achieved survival of ≥ 6 months [18% (7/38) ≥ 1 yr]. Treatment outcome may increase with 90Y dose, since pts treated at 3 x ≥12 mCi/m2 vs ≤9 mCi/m2 had 19% vs 6% PRs by CT, 47% vs 22% CA19.9 decreases, 63% vs 25% PET improvement, and 64% vs. 44% survival ≥ 6 months. Anecdotally, PS and pain level improved, which needs validation. Updated survival will be presented at the meeting.

Conclusions: Fractionated 90Y-hPAM4 plus low-dose Gem showed encouraging therapeutic activity with manageable hematological toxicity. The 12-mCi/m2 dose level was selected for continued dose exploration now underway, involving standard Gem doses and adding maintenance Gem.

[Table: see text]

Dose-escalation trial of milatuzumab (humanized anti-CD74 monoclonal antibody) in multiple myeloma

8593

Background: CD74 (HLA-DR-associated invariant chain) is highly expressed in multiple myeloma (MM), rapidly internalized, and a promising target for immunotherapy. Methods: A multicenter dose-escalation study was initiated in patients (pts) with relapsed/refractory MM who had failed at least 2 standard therapies. Pts received milatuzumab IV twice-weekly for 4 wks, with doses escalated by a 3+3 cohort design. Pts were evaluated over 12 wks, with responding pts continuing follow-up. AEs and safety laboratories were evaluated by NCI CTC v3 grades, with any treatment-related Grade 3–4 events considered dose-limiting toxicity (DLT). Responses were classified by EBMT criteria, with PK and immunogenicity evaluated by serum milatuzumab levels and human anti-milatuzumab antibody (HAHA) titers, respectively. Results: Twenty-one pts (12M/9F, median age 63) have now received 1.5 (n=8), 4.0 (n=9) or 8.0 mg/kg (n=4) doses twice weekly. They had MM for 0.9–16.8 years (median 5.4), predominantly IgG subtype, were heavily pretreated (4 median prior treatments), and were Durie-Salmon stage II (n=13) or III (n=8). After increasing premedications and slowing administration, infusions were well tolerated (Grade 1–2). There was 1 DLT (infusion reaction) and 3 SAEs (bact. meningitis, confusion/hypercalcemia, fever post demerol) at 1.5 mg/kg, 1 DLT (unexplained anemia) and 2 SAEs (cord compression, epistaxis/thrombocytopenia), at 4.0 mg/kg, but no DLTs or SAEs at 8.0 mg/kg. There has been no pattern of other AEs nor effects on routine laboratories, including serum chemistries, CBC, serum immunoglobulins, B- or T-cells, and no cases of HAHA. At current doses, milatuzumab is rapidly cleared from serum, with little accumulation and low trough levels across infusions. There have been no objective responses so far, but 4 pts have had stable disease by EBMT criteria for at least 3 months post-treatment, occurring with a possible trend towards higher milatuzumab serum levels than pts with earlier disease progression. Conclusions: Milatuzumab doses up to 8.0 mg/kg may be given safely twice-weekly for 4 weeks. In spite of rapid clearance, several patients have had disease stabilization at 4.0 and 8.0 mg/kg doses, which is encouraging. Accrual of the next cohort receiving 16.0 mg/kg is ongoing.

[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]

Detection of early-stage pancreatic carcinoma

4613

Background: Invasive pancreatic carcinoma is a virtually lethal disease, mostly because of the failure to detect it at a sufficiently early timepoint for successful treatment. Our laboratory has identified a unique biomarker detected by MAb PAM4 that shows high specificity for a mucin glycoprotein expressed by pancreatic carcinoma (PC). While identified in almost 90% of PC and its precursor lesions, the antigen is not detectable in normal pancreas. We are investigating this biomarker for the early detection of PC. Methods: Both immunohistochemical (IHC) and enzyme immunoassay (EIA) were employed for detection and/or quantitation of PAM4-mucin in tissue and sera, respectively. Results: We have extended our prior IHC results with precursor lesions (Clin Cancer Res 2007;13:7380–7); PAM4 gave an intense, diffuse labeling pattern in 81% of mucinous cystic neoplasms (MCN), with an additional 11% showing a focal pattern (n=27). Thus, a total of 92% of MCN showed evidence of PAM4-antigen expression. Of interest, a difference in the labeling pattern was observed in association with the grade of dysplasia, providing easy identification of MCN with high- grade dysplasia. We previously reported use of an EIA for quantitation of PAM4-antigen in sera. The assay demonstrated a sensitivity and specificity of 77% and 95%, respectively, for identification of PC (J Clin Oncol, 2006;24:252–8). We have now confirmed these results in a set of serum specimens (n= 49 PC, 13 normal) for which staging information was available. Overall specificity and sensitivity were 82% and 85%, respectively, calculated by ROC curve analysis (AUC=0.878±0.045; 95% CI=0.769–0.947). Although only a small number of specimens were from patients with stage I disease (n=12), 92% of these were above the cutoff value for positive response. A correlation was observed for average concentration of antigen in the circulation with stage of disease (R2=0.988). Conclusions: IHC and EIA results indicate that PAM4 identifies a biomarker for PC that is present at the earliest stages of neoplastic transformation, thus warranting controlled analyses of larger specimen numbers. (Supported in part by USPHS grant CA096924 from the NIH.)

[Table: see text]

Subcutaneous injections of low doses of veltuzumab (humanized anti-CD20 antibody): Objective responses in B-cell malignancies

8530

Background: Low IV doses of veltuzumab, a second-generation anti-CD20 monoclonal antibody with structure-function differences from chimeric rituximab, have shown clinical activity, thus justifying subcutaneous (SC) injections. Methods: A phase I/II study was initiated in patients (pts) with previously untreated or relapsed CD20+ indolent NHL or CLL who received 4 SC injections of veltuzumab 2 weeks apart at dose levels of 80, 160, or 320 mg. Efficacy was assessed by CT-based IWG (NHL) or hematology-based NCI/IWCLL (CLL) criteria 4 and 12 weeks later, with responding pts continuing follow-up. Other evaluations included AEs, safety laboratories, B-cell blood levels (CD19), serum veltuzumab levels, and human anti-veltuzumab antibody (HAHA) titers. Results: Nineteen pts (8M/11F, median age 63), including 14 NHL pts (11 follicular, 3 other indolent NHL; 5 treatment naive) most with stage III or IV disease (11/14) and 5 CLL pts (4 treatment naïve) all with Rai stage II or III disease, have now received SC veltuzumab at 80 mg (3 NHL, 3 CLL), 160 mg (9 NHL, 2 CLL) or 320 mg (2 NHL) dose levels. Pre-treatment with antihistamines or steroids has not been required, and SC veltuzumab was well tolerated with only mild, transient injection site reactions and tenderness. To date, all HAHA results have been negative. In NHL pts, SC veltuzumab demonstrates good bio-availability, with a slow release pattern over several days and depletion of circulating B cells starting after 1st injection. Initial response information is currently available for 10 pts. For 7 NHL pts, 4 weeks after treatment with 80 or 160 mg doses, 2 pts had partial responses, 3 pts showed stable disease, and 2 pts had disease progression. For 3 CLL pts who received 80 mg doses, serum veltuzumab levels were lower, but all pts still achieved 65–75% decreases in circulating leukemic cells over the course of treatment. Conclusions: SC administration of veltuzumab is well tolerated, achieves slow but efficient delivery into the blood, and is pharmacologically active. The low doses currently evaluated in B-cell malignancies show evidence of therapeutic activity, achieving objective responses in NHL and notable reductions in circulating leukemic cells in CLL.

[Table: see text]

Differential effects of epratuzumab on peripheral blood B cells of patients with systemic lupus erythematosus versus normal controls

OBJECTIVE

B lymphocytes have been implicated in the pathogenesis of lupus and other autoimmune diseases, resulting in the introduction of B cell-directed therapies. Epratuzumab, a humanised anti-CD22 monoclonal antibody, is currently in clinical trials, although its effects on patients' B cells are not completely understood.

METHODS

This study analysed the in vivo effect of epratuzumab on peripheral B cell subsets in 12 patients with systemic lupus erythematosus, and also addressed the in vitro effects of the drug by analysing anti-immunoglobulin-induced proliferation of isolated B cells obtained from the peripheral blood of 11 additional patients with lupus and seven normal subjects.

RESULTS

Upon treatment, a pronounced reduction of CD27(-) B cells and CD22 surface expression on CD27(-) B cells was observed, suggesting that these cells, which mainly comprise naïve and transitional B cells, are preferentially targeted by epratuzumab in vivo. The results of in vitro studies indicate additional regulatory effects of the drug by reducing the enhanced activation and proliferation of anti-immunoglobulin-stimulated lupus B cells after co-incubation with CD40L or CpG. Epratuzumab inhibited the proliferation of B cells from patients with systemic lupus erythematosus but not normal B cells under all culture conditions.

CONCLUSIONS

Epratuzumab preferentially modulates the exaggerated activation and proliferation of B cells from patients with lupus in contrast to normal subjects, thus suggesting that epratuzumab might offer a new therapeutic option for patients with systemic lupus erythematosus, as enhanced B cell activation is a hallmark of this disease.

Preclinical and clinical evaluation of epratuzumab (anti-CD22 IgG) in B-cell malignancies

The vast majority of non-Hodgkin's lymphomas are of B-cell phenotype. Development of unlabeled or radiolabeled therapeutic monoclonal antibodies against the cell surface antigen, CD20, has revolutionized the treatment of these malignancies. It is clear that antibodies targeting other B-cell-specific molecules, such as CD22, also offer potential therapeutic benefit. Epratuzumab is a humanized anti-CD22 monoclonal, which has undergone preclinical and phase I/II clinical evaluation in patients with indolent or aggressive lymphoma. Data suggest that this agent is well tolerated, and can induce tumor regressions. Trials are currently evaluating its safety and activity in combination with rituximab (chimeric anti-CD20) and standard chemotherapy are ongoing. Initial results suggest that these regimens have acceptable toxicity, and that epratuzumab warrants further evaluation as an adjunct to standard lymphoma treatment regimens.

First clinical experience with 90Y-radiolabeled humanized anti-MUC1 antibody (hPAM4) in patients with advanced pancreatic cancer: A phase I study

15034

Background: The humanized antibody, hPAM4, specifically targets an epitope in the mucin glycoprotein MUC1 expressed in most pancreatic cancers, but not normal pancreas or most other normal tissues. This study evaluated the dose-limiting toxicity (DLT), maximum tolerated dose (MTD), pharmacokinetics (PK), dosimetry and preliminary efficacy of 90Y-DOTA-hPAM4 administered as a single dose to patients (pts) with pancreatic adenocarcinoma. Methods: Pts with locally advanced disease and progression on 1 prior therapy (TX) or metastatic disease with 0–1 prior TX’s were eligible if they were ≥ 4 wks beyond prior TX, had adequate hematology/chemistries, with measurable disease, but no lesion >10 cm. Pts initially received 111In-hPAM4 followed by 7 days of serum samples and imaging for PK, biodistribution and organ radiation dose analysis. Pts then received a single infusion of 90Y-hPAM4 with the 90Y dose escalated in cohorts of 3–6 pts (5-mCi/m2 increments) until 2 evaluable pts/cohort encountered DLT. Treatment toxicity was evaluated by NCI CTC v. 3 criteria and tumor response by CT-based RECIST criteria. Results: Fifteen pts (8F/7M; median age 60; 11 metastatic/4 locally advanced;13 with, 2 without prior TX) received 90Y-hPAM4 at a dose level of 15 mCi/m2 (n=4), 20 mCi/m2 (n=7), and 25 mCi/m2 (n=4). Pre-therapy 111In-hPAM imaging showed acceptable biodistribution and organ radiation dosimetry in all pts. Four wks after treatment, 1 pt at 15 mCi/m2 and 2 pts at 20 mCi/m2 had CT responses, with 32–51% shrinkage of their pancreatic mass, while 3 other pts at various dose levels had stable target lesions by CT. All pts showed disease progression at or after wk 8. The only significant drug-related toxicity was hematologic, with >1 DLT (>7 day grade 4 thrombocytopenia and/or neutropenia) encountered at the 25 mCi/m2 level. Conclusions: For 90Y-hPAM administered once as a single agent, hematologic toxicity was dose-limiting, the MTD was established at 20 mCi/m2, and CT demonstrated several transient reductions or stabilization of index lesions. Based on this Phase I experience, combined/sequential treatment with chemotherapy and fractionated radioimmunotherapy is being considered for future trials.

No significant financial relationships to disclose.

Safety and efficacy of repeated anti-CEA radioimmunotherapy (RAIT) with 131I-labetuzumab post salvage resection of colorectal liver metastases

14507

Background: As shown recently (JCO 2005; 23:6763–70), a single application of RAIT improved both, median overall survival (OS), and 5-year survival rates of colorectal cancer (CRC) patients (pts) post salvage resection of liver metastases (LM) compared to controls without RAIT (P=0.004). In an ongoing phase II trial we are evaluating the safety and efficacy of repeated RAIT at doses of 2x 40–50 mCi/m2 (3 mos apart) post salvage resection of LM. Methods: To date, 26 pts (8x f, 18x m; age: 63 ± 9 ys) who underwent surgery for CRC-LM have received the first dose of 131I-labetuzumab (Immunomedics, In., NJ, USA), a humanized monoclonal antibody against CEA, within 2 months of LM surgery. Three months after the first RAIT, a second infusion of 40–50 mCi/m2 has been applied to all pts after completion of standardized re-staging procedures. Results: The primary tumor sites were 17 colonic and 9 rectal cancers; primary tumor stages were 5x UICC-II, 7x UICC-III, 14x UICC-IV. 13 pts received adjuvant therapy. In 11 pts preoperative chemotherapy (FOLFOX or FOLFIRI) was given to achieve resectability of bilobular LM. After resection of LM (y)mTNM tumor stages were 1x mTNM-I, 6x mTNM-II, 6x mTNM-III and 4x mTNM-IV, respectively. After first RAIT, hematologic Grade 3 and 4, toxicity (WBC/platelet count) occurred in 8/14 and 5/3 pts, respectively. No cumulative toxicity was seen after repeated RAIT, with complete bone marrow recovery observed in all cases so far. To date, all pts are alive. Of the total, 17 pts received RAIT with adjuvant intention (as classified by FDG-PET and CT scans at pre-RAIT re-staging). In these, DFS was 70% post salvage resection of LM during ongoing follow-up of 15 months (median; range: 4–23 mos). As of Dec. 20, 2006, cancer recurrence was detected in 5/17 pts (3x pulmonary, 1x intrahepatic, 1x both) and in 4 pts R0-resection of distant metastases was done. 1 patient with pulmonary and intrahepatic relapses receives polychemotherapy with palliative intention. The pts‘ compliance to repeated RAIT has been 100%. Conclusion: RAIT re-treatment to date appears to be safe, feasible, and well accepted. Extended follow-up of the encouraging survival data will be presented.

No significant financial relationships to disclose.

Chemoimmunotherapy reinduction with epratuzumab in children with ALL with marrow relapse: A Children's Oncology Group (COG) pilot study (ADVL04P2)

9513

Background: CD22, a 135kd protein restricted to B-cells, is expressed in > 90% of childhood B-precursor acute lymphoblastic leukemia (ALL). We conducted a feasibility/phase 2 study of epratuzumab, a humanized monoclonal antibody against CD22, with reinduction chemotherapy in children with relapsed CD22+ ALL. Methods: The feasibility portion (n=12) of the study is reported here. Patients with first or later ALL marrow relapse at any time following diagnosis, ± extramedullary disease, with = 25% blasts expressing CD22 and a presenting white blood cell count (WBC) of = 50,000/μl, were eligible. Therapy consisted of a 14-day single agent phase (epratuzumab 360 mg/m2 /dose IV twice weekly × 4 doses), followed by 4 weekly doses of epratuzumab in combination with standard reinduction chemotherapy (vincristine, prednisone, PEG-asparaginase, doxorubicin). Remission induction rates and minimal residual disease (MRD) by flow cytometry were determined at the end of this 6-week period. PK studies were performed by ELISA based immunoassay (prior + 30 minutes after infusions). Results: 12 evaluable patients, median age 10 years (range 3 - 18), were accrued. 9 pts were in 1st (n=5 early; n=4 late), and 3 pts in 2nd or later marrow relapse. The mean (±SD) trough epratuzumab concentration increased from 69±23 to 232±74 μg/ml during the initial 14 days. Surface CD22 was not detected by flow cytometry on peripheral blood leukemic blasts within 24 hours of drug administration in all but one patient, indicating effective targeting of leukemic cells by epratuzumab. The most frequent toxicities were grade 1–2 infusion reactions (n=9). Two dose limiting toxicities occurred: one patient had a Grade 4 seizure of unclear etiology and one patient had asymptomatic Grade 3 ALT elevation. 9 patients achieved a complete remission following chemoimmunotherapy, of whom 7 were MRD-negative. Conclusions: Treatment with epratuzumab plus standard reinduction chemotherapy is feasible and well tolerated in children with relapsed ALL, producing favorable early responses in the majority of patients. The phase II portion of the study is ongoing.

[Table: see text]

Low doses of humanized anti-CD20 antibody, IMMU-106 (hA20), in refractory or recurrent NHL: Phase I/II results

8032

Background: An open-label, multicenter study has shown that the humanized anti-CD20 antibody, IMMU-106 (hA20), which has framework regions of epratuzumab, has a good safety and efficacy profile in NHL pts when administered once-weekly × 4 at different doses. The trial is now focused on confirming the efficacy of lower doses (80–120 mg/m2/wk × 4). Methods: A total of 68 pts (35 male, 33 female; age 34–84) received hA20 at 750 (N=3), 375 (N=27), 200 (N=11), 120 (N=21), or 80 mg/m2 (N=6). They had follicular (FL, N=47) or other (N=21) B-cell NHL, were predominantly stage III/IV (N=47) at study entry, and had received 1–8 prior treatments (median, 2), including 1 (N=40) or more (N=21) rituximab regimens (without progression within 6 months). Results: Sixty- six pts completed all 4 infusions; 1 pt progressed during treatment and withdrew, while another pt with hives and chills after prior rituximab discontinued treatment after a similar episode at 1st infusion. hA20 was generally well tolerated, with shorter infusion times (typically 2 h initially and 1 h subsequently) at lower doses. Drug-related adverse events were transient, Grade 1–2, most occurring only at 1st infusion, and there was no evidence of HAHA in 54 pts now evaluated. Mean antibody serum levels increased with dose and infusions; serum clearance at 375 mg/m2 appears similar to rituximab. Currently, 48 pts with at least 12 wks follow-up were evaluated by Cheson criteria: 32 FL pts had 15 (47%) OR's with 7 (22%) CR/CRu's, even after 2–4 prior rituximab-regimens, and 17 non-FL pts had 6 (38%) OR's, with 1 CRu in a marginal zone NHL pt. At a median follow-up of 11 mo., 9/21 pts with ORs are continuing responses, including 4 long-lived responses (15–20 mo). The evaluated pts include 17 pts at 120 mg/m2 who had 5 (29%) ORs with 3 (17%) CR/CRu's. Responses at 80 mg/m2 remain to be evaluated, but B-cell depletion occurs after the 1st infusion even at this low dose. Conclusions: hA20 appears well-tolerated, with no evidence of significant adverse events other than minor infusion reactions, even at short infusion times. B-cell depletion and responses have occurred at all doses evaluated, with no clear-cut evidence of a dose-response. As such, the study is continuing to confirm the efficacy of lower doses.

No significant financial relationships to disclose.

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.

A new method of constructing CD20/CD22 bispecfic antibody fusion proteins with improved direct lymphoma cytotoxicity compared to rituximab

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Background: Anti-CD20 and anti-CD22 monoclonal antibodies (MAbs) have been shown to have antitumor activity in non-Hodgkin’s lymphoma (NHL) patients. Since preclinical and clinical trials also suggested that combining CD20 and CD22 MAbs, which have different mechanisms of action, could improve antitumor activity without a commensurate increase in toxicity, we hypothesized that a therapeutic advantage may be achieved with bispecific MAbs that bind simultaneously to both CD20 and CD22. Methods: A new platform technology, termed the Dock and Lock method (DNL), was successfully applied to produce a trivalent bispecific antibody, named TF3, which comprises two recombinant Fab fragments of hA20 (humanized anti-CD20 MAb; IMMU-106) stably tethered to one recombinant Fab fragment of epratuzumab (humanized anti-CD22 MAb; IMMU-103) via the specific interaction between a dimerization-and-docking domain and an anchoring domain appended to hA20 and epratuzumab, respectively. The cytotoxicity of TF3 was evaluated by cell-based assays using NHL cell lines. Results: TF3 is stable in both human and mouse sera andexhibitsthe samebinding affinity as hA20 IgG or epratuzumab Fab by competitive ELISA. With a 3-day MTT assay, TF3 at 10 nM inhibited 50% and 60% growth of Daudi and Ramos cells, respectively. Further, the observed anti-proliferative activity increased synergistically to >90% in the presence of anti-IgM (0.1 μg/mL). Results from a cell counting assay also demonstrated the ability of TF3 at 1 μM to completely inhibit the growth of Daudi and the potency of TF3 at 1 nM was comparable to that of rituximab at 1 μM under the same experimental conditions, reflecting a 1000-fold enhancement. Conclusions: These findings, to be extended by ongoing in vivo studies, suggest that the new DNL platform technology for making bispecific antibody fusion proteins provided a CD20/CD22 binding protein that is significantly more potent than rituximab in an in vitro NHL direct cytotoxicity assay.

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Phase I/II results of a second-generation humanized anti-CD20 antibody, IMMU-106 (hA20), in NHL

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Background: The humanized anti-CD20 antibody, IMMU-106 (hA20), has similar murine CDRs to rituximab, but the remaining framework is identical to humanized anti-CD22 IgG1 antibody, epratuzumab, whose safety and short infusion times have been reported. Methods: An open-label, multicenter, phase I/II, dose escalation study was conducted in adult patients with recurrent NHL to establish the safety, tolerance, PK, and immunogenicity (HAHA) of hA20 administered weekly x 4. Thirty-four patients have now received hA20 at 120 (n = 7), 200 (n = 6), 375 (n = 18) or 750 mg/m2 (n = 3). These were predominantly stage III/IV patients (n = 27) with follicular lymphoma (N = 23) who received 1–7 prior treatments (median, 2), including 1 (N = 22) or more (N = 9) rituximab regimens (without progression within 6 months). Results: Thirty-three patients completed all 4 hA20 infusions. Median infusion times at 375 mg/m2 were 3.1 h for 1st infusion, 2.0–2.3 h for subsequent infusions, and were generally shorter at lower doses. Fourteen patients (14%) had transient events, predominantly grade 1–2 events at 1st infusion. Antibody levels increased with hA20 dose; at 375 mg/m2, mean serum half-lives after 1st and 4th infusions were 3.4 ± 1.7 and 12.3 ± 3.9 days, respectively. With median follow-up now 3–6 months, peripheral blood B-cell depletion persists, HAHA evaluations are negative, and 14/23 patients (61%) with response assessments have objective responses by Cheson criteria. All 6 CR/CRu’s (23%) were in follicular lymphoma, occurred at all dose levels even at 120 mg/m2 (including patients with 2–4 prior rituximab-containing regimens ), and with 5/6 continuing. Conclusions: The tolerability, relatively short infusion times, and CR/CRu’s in patients with follicular lymphoma who relapsed after rituximab-containing regimens is encouraging. This study is continuing to assess response durability and to determine the optimal hA20 dose for subsequent studies.

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Anti-CD74-doxorubicin immunoconjugate (IMMU-110) is cytotoxic in non-Hodgkin’s lymphoma (NHL) models and overcomes MDR

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Background: The internalizing LL1 anti-CD74 antibody is an optimal agent for delivering drugs, toxins, or radionuclides to CD74+ cancer cells. Here, we investigated the efficacy of IMMU-110 (Immunomedics, Inc.) in common follicular and aggressive types of NHL cells and in two disseminated non-Burkitt NHL models. Methods: CD74, MDR and MRP expression on NHL cell lines was determined by flow cytometry. In vitro cytotoxicity was assessed by cell cycle analysis of propidium iodide (PI)-stained cells and by measuring apoptotic cells using FITC-Annexin V and PI. In vivo therapy of a single 350-μg dose of IMMU-110 was evaluated in disseminated SUDHL4 and FSCCL. Results: Raji and Daudi Burkitt lines express similar amounts of CD74 (>93% positive cells and a MCF=35), yet a 3-day treatment with 0.8 μg/ml of IMMU-110 results is 18.4% of Raji and 67.9% of Daudi cells in Sub-Go. Aside from Daudi cells that respond with cells shifting into Sub-Go, most other NHL cell lines experience a G2/M block (44%-82% of cells) in response to a 3-day exposure to IMMU-110. Both MDR- and MDR+ NHL cells responded to IMMU-110. Kaplan Meier analysis showed a significant increase in survival of both SUDHL4 (MDR-/MRP-)- and FSCCL (MDR+/MRP+)-bearing SCID mice (P < 0.025) with 100% survival of treated mice vs. 38% survival of untreated mice at 70–77 days post cell implantation. Conclusions: IMMU-110 is cytotoxic in non-Burkitt and in Burkitt NHL cell lines. The magnitude of the cytotoxic response is not related to the amount of CD74 expressed on the cell surface. IMMU-110 is therapeutic in drug-sensitive (SUDHL4) and drug-resistant (FSCCL) NHL models, suggesting that antibody targeting can bypass the MDR drug efflux system that prevents free doxorubicin from being therapeutic.

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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).

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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.