The emergence of trophoblast cell-surface antigen 2 (TROP-2) as a novel cancer target

TROP-2 is a glycoprotein first described as a surface marker of trophoblast cells, but subsequently shown to be increased in many solid cancers, with lower expression in certain normal tissues. It regulates cancer growth, invasion and spread by several signaling pathways, and has a role in stem cell biology and other diseases. This review summarizes TROP-2's properties, especially in cancer, and particularly its role as a target for antibody-drug conjugates (ADC) or immunotherapy. When the irinotecan metabolite, SN-38, is conjugated to a humanized anti-TROP-2 antibody (sacituzumab govitecan), it shows potent broad anticancer activity in human cancer xenografts and in patients with advanced triple-negative breast, non-small cell and small-cell lung, as well as urothelial cancers.

Sensitivity of pretargeted immunoPET using 68Ga-peptide to detect colonic carcinoma liver metastases in a murine xenograft model: Comparison with 18FDG PET-CT

PURPOSE

The aim of this study was to compare the performances pretargeted immunoPET 68Ga-PETimaging (68Ga-pPET) with anti carcino-embryonic antigen (CEA) and anti-histamine-succinyl-glycine (HSG) recombinant humanized bispecific monoclonal antibody (TF2) and 68Ga-labeled HSG peptide (IMP288) to conventional 18FDG-PET in an orthotopic murine model of liver metastases of human colonic cancer.

METHODS

Hepatic tumor burden following intra-portal injection of luciferase-transfected LS174T cells in nude mice was confirmed using bioluminescence. One group of animals was injected intravenously with TF2 and with 68Ga-IMP288 24 hours later (n=8). Another group received 18FDG (n=8), and a third had both imaging modalities (n=7). PET acquisitions started 1 hour after injection of the radioconjugate. Biodistributions in tumors and normal tissues were assessed one hour after imaging.

RESULTS

Tumor/organ ratios were significantly higher with 68Ga-pPET compared to 18FDG-PET (P<0.05) with both imaging and biodistribution data. 68Ga-pPET sensitivity for tumor detection was 67% vs. 31% with 18FDG PET (P=0.049). For tumors less than 200 mg, the sensitivity was 44% with 68Ga-pPET vs. 0% for 18FDG PET (P=0.031). A strong correlation was demonstrated between tumor uptakes measured on PET images and biodistribution analyses (r2=0.85).

CONCLUSION

68Ga-pPET was more sensitive than 18FDG-PET for the detection of human colonic liver metastases in an orthotopic murine xenograft model. Improved tumor/organ ratios support the use of pretargeting method for imaging and therapy of CEA-expressing tumors.

Sacituzumab Govitecan (IMMU-132) in treatment-resistant uterine serous carcinoma: A case report

Background

Uterine serous carcinoma (USC) is a biologically aggressive variant of uterine cancer. Effective treatment options for recurrent, chemotherapy-resistant USC are extremely limited.

Case

We describe a 74-year-old woman with recurrent and widespread treatment-resistant disease, who experienced a dramatic response to sacituzumab govitecan, a novel antibody-drug conjugate (ADC) targeting human trophoblast-cell-surface antigen (TROP-2), after failing multiple chemotherapy and immunotherapy. The impressive clinical response (66% reduction of target lesions by RECIST 1.1 with a duration response of over 10 months) was confirmed with serial CT scans in the absence of significant adverse events.

Conclusion

Sacituzumab govitecan may present a new treatment option for recurrent USC patients harboring Trop-2+ tumors resistant to chemotherapy. Clinical trials with sacituzumab govitecan are warranted.

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Uterine serous carcinoma (USC) is a rare but aggressive variant of uterine cancer.

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Sacituzumab-govitecan (IMMU-132) is an antibody-drug conjugate targeting TROP-2.

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IMMU-132 may represent a new treatment option for USC overexpressing TROP-2.

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.

Efficacy of Epratuzumab, an Anti-CD22 Monoclonal IgG Antibody, in Systemic Lupus Erythematosus Patients With Associated Sjögren's Syndrome: Post Hoc Analyses From the EMBODY Trials

OBJECTIVE

EMBODY 1 (ClinicalTrials.gov identifier: NCT01262365) and EMBODY 2 (ClinicalTrials.gov identifier: NCT01261793) investigated the efficacy and safety of epratuzumab, a CD22-targeted humanized monoclonal IgG antibody, in patients with systemic lupus erythematosus (SLE). The studies showed no significant difference from placebo in primary or secondary clinical outcome measures but did demonstrate B cell-specific immunologic activity. The aim of this post hoc analysis was to determine whether epratuzumab had a different clinical efficacy profile in SLE patients with versus those without an associated diagnosis of Sjögren's syndrome (SS).

METHODS

The efficacy and safety of epratuzumab were compared between 2 patient subpopulations randomized in EMBODY 1 and 2: SLE patients with and those without a diagnosis of associated SS. British Isles Lupus Assessment Group (BILAG) total score, BILAG-based Combined Lupus Assessment (BICLA) clinical response to treatment, biologic markers (including B cells, IgG, IgM, and IgA), and safety were assessed.

RESULTS

A total of 1,584 patients were randomized in the EMBODY 1 and EMBODY 2 trials; 113 patients were anti-SSA positive and had a diagnosis of associated SS, and 1,375 patients (86.8%) had no diagnosis of associated SS (918 patients were randomized to receive epratuzumab and 457 to receive placebo). For patients with associated SS, but not those without associated SS, a higher proportion of patients receiving epratuzumab achieved a BICLA response and a reduction from baseline in BILAG total score. B cell reduction was faster in patients with associated SS. The sensitivity of B cells to epratuzumab as measured by the mean concentration producing 50% of the maximum B cell count depletion was lower for patients with associated SS (9.5 μg/ml) versus the total EMBODY population (87.1 μg/ml). No difference in the frequency of adverse events in those receiving placebo was reported.

CONCLUSION

Patients with SLE and associated SS treated with epratuzumab showed improvement in SLE disease activity, which was associated with bioactivity, such as decreases in B cell number and IgM level.

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 &gt;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 &gt;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 &gt;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 &gt;95% and &gt;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.

IMMU-140, a Novel SN-38 Antibody-Drug Conjugate Targeting HLA-DR, Mediates Dual Cytotoxic Effects in Hematologic Cancers and Malignant Melanoma

HLA-DR is a member of the MHC class II antigen family expressed on hematologic and solid tumors. Antibodies directed against HLA-DR have demonstrated some clinical success, but toxicities limited development. IMMU-140 is an anti-HLA-DR antibody-drug conjugate composed of the active metabolite of irinotecan, SN-38, conjugated to a humanized anti-HLA-DR IgG₄ antibody (IMMU-114); the IgG₄ naked antibody is devoid of immune functions. Our aim was to determine if SN-38, the metabolite of a drug not commonly used in hematopoietic cancers, would be effective and safe when targeted to HLA-DR-expressing tumors. IMMU-140 had dual-therapeutic mechanisms, as evidenced by its retention of nonoverlapping anti-HLA-DR nonclassical apoptotic signaling and classical apoptosis mediated by its SN-38 payload. In seven human disease models [acute lymphocytic leukemia (ALL), chronic lymphocytic leukemia (CLL), multiple myeloma (MM), acute myeloid leukemia (AML), diffuse large B-cell lymphoma (DLBCL), Hodgkin lymphoma (HL), and melanoma], IMMU-140 provided significant therapeutic efficacy compared with controls, in vitro, in 3D spheroid models, and in vivo Except for MM and HL, IMMU-140 imparted significantly improved antitumor effects compared with parental IMMU-114. Even in intractable AML and ALL, where IMMU-114 only had modest antitumor effects, IMMU-140 therapy mediated >80% improvement in survival. Therapy was well tolerated, as demonstrated by no marked loss in body weight. Combined with doxorubicin, IMMU-140 produced significantly greater antitumor effects in HL than with monotherapy and without any added toxicity. The dual-therapeutic action of IMMU-140 resulted in promising therapeutic activity in a range of hematopoietic tumors and melanoma, and therefore warrants clinical development. Mol Cancer Ther; 17(1); 150-60. ©2017 AACR.

Selective and Concentrated Accretion of SN-38 with a CEACAM5-Targeting Antibody-Drug Conjugate (ADC), Labetuzumab Govitecan (IMMU-130)

Labetuzumab govitecan (IMMU-130), an antibody-drug conjugate (ADC) with an average of 7.6 SN-38/IgG, was evaluated for its potential to enhance delivery of SN-38 to human colonic tumor xenografts. Mice bearing LS174T or GW-39 human colonic tumor xenografts were injected with irinotecan or IMMU-130 (SN-38 equivalents ∼500 or ∼16 μg, respectively). Serum and homogenates of tumors, liver, and small intestine were extracted, and SN-38, SN-38G (glucuronidated SN-38), and irinotecan concentrations determined by reversed-phase HPLC. Irinotecan cleared quickly from serum, with only 1% to 2% injected dose/mL after 5 minutes; overall, approximately 20% was converted to SN-38 and SN-38G. At 1 hour with IMMU-130, 45% to 63% injected dose/mL of the SN-38 was in the serum, with >90% bound to the ADC over 3 days, and with low levels of SN-38G. Total SN-38 levels decreased more quickly than the IgG, confirming a gradual SN-38 release from the ADC. AUC analysis found that SN-38 levels were approximately 11- and 16-fold higher in LS174T and GW-39 tumors, respectively, in IMMU-130-treated animals. This delivery advantage is amplified >30-fold when normalized to SN-38 equivalents injected for each product. Levels of SN-38 and SN-38G were appreciably lower in the liver and small intestinal contents in animals given IMMU-130. On the basis of the SN-38 equivalents administered, IMMU-130 potentially delivers >300-fold more SN-38 to CEA-producing tumors compared with irinotecan, while also reducing levels of SN-38 and SN-38G in normal tissues. These observations are consistent with preclinical and clinical data showing efficacy and improved safety. Mol Cancer Ther; 17(1); 196-203. ©2017 AACR.

Phase I/II Trial of Labetuzumab Govitecan (Anti-CEACAM5/SN-38 Antibody-Drug Conjugate) in Patients With Refractory or Relapsing Metastatic Colorectal Cancer

Purpose The objectives were to evaluate dosing schedules of labetuzumab govitecan, an antibody-drug conjugate targeting carcinoembryonic antigen-related cell adhesion molecule 5 (CEACAM5) for tumor delivery of 7-ethyl-10-hydroxycamptothecin (SN-38), in an expanded phase II trial of patients with relapsed or refractory metastatic colorectal cancer. Patients and Methods Eligible patients with at least one prior irinotecan-containing therapy received labetuzumab govitecan once weekly at 8 and 10 mg/kg, or two times per week at 4 and 6 mg/km on weeks 1 and 2 of 3-week repeated cycles. End points were safety, response, pharmacokinetics, and immunogenicity. Results Eighty-six patients who had undergone a median of five prior therapies (range, one to 13) were each enrolled into one of the four cohorts. On the basis of Response Evaluation Criteria in Solid Tumors 1.1, 38% of these patients had a tumor as well as plasma carcinoembryonic antigen reduction from baseline after labetuzumab govitecan treatment; one patient achieved a partial response with a sustained response spanning > 2 years, whereas 42 patients had stable disease as the best overall response. Median progression-free survival and overall survival were 3.6 and 6.9 months, respectively. The major toxicities (grade ≥ 3) among all cohorts were neutropenia (16%), leukopenia (11%), anemia (9%), and diarrhea (7%). The antibody-drug conjugate's mean half-life was 16.5 hours for the four cohorts. Anti-drug/anti-antibody antibodies were not detected. The two once-weekly dose schedules, showing comparable toxicity and efficacy, were chosen for further study. Conclusion Monotherapy with labetuzumab govitecan demonstrated a manageable safety profile and therapeutic activity in heavily pretreated patients with metastatic colorectal cancer, all with prior irinotecan therapy. Further studies of labetuzumab govitecan treatment alone or in combination with other therapies in earlier settings are indicated.

Combination Therapy with Bispecific Antibodies and PD-1 Blockade Enhances the Antitumor Potency of T Cells

The DOCK-AND-LOCK (DNL) method is a platform technology that combines recombinant engineering and site-specific conjugation to create multispecific, multivalent antibodies of defined composition with retained bioactivity. We have applied DNL to generate a novel class of trivalent bispecific antibodies (bsAb), each comprising an anti-CD3 scFv covalently conjugated to a stabilized dimer of different antitumor Fabs. Here, we report the further characterization of two such constructs, (E1)-3s and (14)-3s, which activate T cells and target Trop-2- and CEACAM5-expressing cancer cells, respectively. (E1)-3s and (14)-3s, in the presence of human T cells, killed target cells grown as monolayers at subnanomolar concentrations, with a similar potency observed for drug-resistant cells. Antitumor efficacy was demonstrated for (E1)-3s coadministered with human peripheral blood mononuclear cells (PBMC) in NOD/SCID mice harboring xenografts of MDA-MB-231, a triple-negative breast cancer line constitutively expressing Trop-2 and PD-L1. Growth inhibition was observed following treatment with (E1)-3s or (14)-3s combined with human PBMC in 3D spheroids generated from target cell lines to mimic the in vivo behavior and microenvironment of these tumors. Moreover, addition of an antagonistic anti-PD-1 antibody increased cell death in 3D spheroids and extended survival of MDA-MB-231-bearing mice. These preclinical results emphasize the potential of combining T-cell-redirecting bsAbs with antagonists or agonists that mitigate T-cell inhibition within the tumor microenvironment to improve immunotherapy of solid cancers in patients. They also support the use of 3D spheroids as a predictive alternative to in vivo models for evaluating T-cell functions. Cancer Res; 77(19); 5384-94. ©2017 AACR.

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.

Therapy of Small Cell Lung Cancer (SCLC) with a Topoisomerase-I-inhibiting Antibody-Drug Conjugate (ADC) Targeting Trop-2, Sacituzumab Govitecan

Purpose: We evaluated a Trop-2-targeting antibody conjugated with SN-38 in metastatic small cell lung cancer (mSCLC) patients.Experimental Design: Sacituzumab govitecan was studied in patients with pretreated (median, 2; range, 1-7) mSCLC who received either 8 or 10 mg/kg i.v. on days 1 and 8 of 21-day cycles. The primary endpoints were safety and objective response rate (ORR); duration of response, progression-free survival (PFS), and overall survival (OS) were secondary endpoints.Results: Sixty percent of patients showed tumor shrinkage from baseline CTs. On an intention-to-treat basis (N = 50), the ORR was 14% (17% for the 10-mg/kg group); the median response duration, 5.7 months; the clinical benefit rate (CBR ≥4 months), 34%; median PFS, 3.7 months; and median OS, 7.5 months. There was a suggested improvement in PR, CBR, and PFS with sacituzumab govitecan in second-line patients who were sensitive to first-line therapy, but no difference between first-line chemosensitive versus chemoresistant patients in the overall population. There was a statistically significant higher OS in those patients who received prior topotecan versus no topotecan therapy in a small subgroup. Grade ≥3 adverse events included neutropenia (34%), fatigue (13%), diarrhea (9%), and anemia (6%). Trop-2 tumor staining was not required for patient selection. No antibodies to the drug conjugate or its components were detected on serial blood collections.Conclusions: Sacituzumab govitecan appears to have a safe and effective therapeutic profile in heavily pretreated mSCLC patients, including those who are chemosensitive or chemoresistant to first-line chemotherapy. Additional studies as a monotherapy or combination therapy are warranted. Clin Cancer Res; 23(19); 5711-9. ©2017 AACR.

Abstract 4081: Superior SN-38 pharmacodynamic and tumor-accretion profiles of labetuzumab govitecan (IMMU-130) versus irinotecan in experimental human colonic cancer models

BACKGROUND: IMMU-130 is an antibody-drug conjugate (ADC) undergoing clinical investigation in patients with metastatic colorectal cancer (ClinicalTrials.gov, NCT01605318). It is composed of a humanized anti-CEACAM5 IgG conjugated via a cleavable linker to SN-38, a topoisomerase-I inhibitor and active form of irinotecan. We investigated the potential advantage of IMMU-130 versus irinotecan for SN-38 delivery in nude mice bearing CEA-expressing human colonic tumor xenografts (LS174T or GW-39).

METHODS: Mice were injected with irinotecan (~ 900 µg; SN-38 equivalents = ~500 µg) or 1.0 mg of IMMU-130 (16 µg SN-38 equivalents). Irinotecan-treated animals were necropsied 5 min, 1, 2, 6-8 h post-injection, while IMMU-130-treated animals were evaluated at 1, 6, 24, 48-72 h. Serum and homogenates of tumors, liver, and small intestinal contents were extracted, and SN-38, SN-38G, and irinotecan concentrations were determined by reversed-phase HPLC. For IMMU-130-treated specimens, SN-38 concentrations were assessed in the extracted samples (Free SN-38), as well as in acid-hydrolyzed samples to determine Total SN-38 (Free + bound). IgG was measured by ELISA.

RESULTS: Irinotecan cleared quickly from serum, with [SN-38]averaging ~900 ng/mL to 200 ng/mL from 5 min to 6 h. SN-38G and SN-38 levels were similar. With IMMU-130, Free SN-38 was detected in serum over the entire monitoring period, but levels were only a small fraction of the Total SN-38 (~10%). Importantly, Free SN-38G was very low, being detected only within the first 6 h. Total SN-38 levels dropped more quickly than the IgG, confirming in vitro studies showing gradual SN-38 release from the ADC. In tumors, for irinotecan-treated animals, SN-38 peaked at 5 min, representing ≤0.2%/g of the SN-38 equivalent given. In IMMU-130-treated animals, no Free SN-38 was detected in tumors, but levels of Total SN-38 peaked at 6 h, with ~5%/g of the injected SN-38 dose present at that time, and were sustained longer than SN-38 delivered by irinotecan. Area under the curve analysis found SN-38 levels were ~10- and 17-fold higher in LS174T and GW-39 tumors, respectively, from IMMU-130-dosed versus irinotecan-dosed animals. This delivery advantage is amplified &gt; 30-fold when normalized to SN-38 equivalents injected for each product, illustrating the improved bioavailability with IMMU-130-targeted SN-38. Levels of SN-38 and SN-38G were appreciably lower in the liver and small intestinal contents, which likely explains the lower incidence of severe diarrhea reported in patients given IMMU-130.

CONCLUSION: IMMU-130 delivers &gt;300-fold more SN-38 to CEA-producing tumors compared to irinotecan, while also reducing levels of potentially harmful SN-38 and SN-38G in normal tissues. These observations are consistent with preclinical data showing improved efficacy and safety.

Citation Format: Thomas M. Cardillo, Robert M. Sharkey, Serengulam V. Govindan, Jennifer Donnel, Maria Zalath, David M. Goldenberg. Superior SN-38 pharmacodynamic and tumor-accretion profiles of labetuzumab govitecan (IMMU-130) versus irinotecan in experimental human colonic cancer models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4081. doi:10.1158/1538-7445.AM2017-4081

Abstract CT155: Phase 2 study of sacituzumab govitecan (IMMU-132), an anti-Trop-2/SN-38 antibody-drug conjugate (ADC), in patients with pretreated metastatic small-cell lung cancer (mSCLC)

Introduction: Sacituzumab govitecan (IMMU-132) is an antibody-drug conjugate (ADC) delivering SN-38, a topoisomerase-1 inhibitor, to mSCLC cells expressing Trop-2. We are studying the safety/tolerability and efficacy of IMMU-132 in patients with relapsed/refractory mSCLC who had received a platinum-containing first-line regimen.

Experimental Procedure: Patients received 8 or 10 mg/kg IV IMMU-132 on days 1 and 8 of repeated 21-day cycles. Objective tumor response (ORR) was determined by RECISTv1.1 in patients receiving at least one treatment cycle, and progression-free survival (PFS) and overall survival (OS) in all patients by Kaplan-Meier methods. (ClinicalTrials.gov, NCT01631552)

Summary of New Unpublished Data: A total of 53 patients (23/30 M/F, median 63 years old) with 1-7 (median 2) prior lines of therapy were enrolled between November, 2013 and June, 2016. Immunohistochemistry of evaluable archival tumor specimens for Trop-2 expression (N=26) showed 92% positivity (61% moderately to strongly positive). They received up to 32 treatment cycles (median 5); the most frequent Grade &gt;3 adverse events were neutropenia (34%), fatigue (13%) and diarrhea (9%). Four patients did not complete one cycle of treatment. In the other 49 patients (14 at 8 mg/kg, 35 at 10 mg/kg), there were 7 confirmed PRs and 21 SDs as best response. The resulting ORR rate was 14% (7/49), with a median duration and time-to-progression of a response of 4.0 and 7.6 mos, respectively, and the clinical benefit rate (PR+SD &gt;4 mos) was 35% (17/49). The ORR rate was similar in pts who were sensitive (&gt;3 mos response) or resistant (&lt;3 mos) to 1st-line therapy [13% (3/23) vs 15% (4/26), respectively]. In 2nd-line setting, IMMU-132 had a confirmed ORR rate of 14% (3/21), and a clinical benefit rate of 38% (8/21). This compares well to recent results with topotecan having an ORR of 13-16% in 2nd-line. Comparing dose levels, ORR was 17% (6/35) with 10 mg/kg vs 7% (1/14) with 8 mg/kg, with little difference in toxicity. Median PFS and OS in all 53 patients was 3.7 mos (95% CI, 2.0 - 4.3) and 7.0 mos (95% CI, 5.5 - 8.3), respectively, and included 6 long-term survivors (12.7 - 25.4 months). No antibody response to the ADC or antibody was detected despite multiple therapy cycles.

Conclusion: These interim results demonstrate encouraging activity in patients with late-stage mSCLC having a high expression of Trop-2. Even after failing 1st-line platinum chemotherapy or 2nd-line topotecan therapy, IMMU-132 showed promising activity, and has a manageable toxicity profile. IMMU-132 given at 10 mg/kg on day 1 and 8 of a 3-week cycle was selected for further clinical evaluation in this population.

Citation Format: Jhanelle E. Gray, Rebecca S. Heist, Alexander N. Starodub, D. Ross Camidge, Ebenezer Kio, Gregory Masters, W. Thomas Purcell, Michael J. Guarino, Jamal Misleh, Charles J. Schneider, Bryan J. Schneider, Allyson J. Ocean, Tirrell Johnson, Leena Gandhi, Kevin Kalinsky, Serengulam V. Govindan, Pius Maliakal, Boyd Mudenda, William A. Wegener, Robert M. Sharkey, David M. Goldenberg. Phase 2 study of sacituzumab govitecan (IMMU-132), an anti-Trop-2/SN-38 antibody-drug conjugate (ADC), in patients with pretreated metastatic small-cell lung cancer (mSCLC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr CT155. doi:10.1158/1538-7445.AM2017-CT155

Abstract 3734: Pharmacokinetics of sacituzumab govitecan (IMMU-132), an antibody-drug conjugate (ADC) targeting Trop-2, in patients with diverse advanced solid tumors

BACKGROUND: Sacituzumab govitecan (IMMU-132), an ADC targeting Trop-2, an antigen present in many solid tumors, uses SN-38, a topoisomerase I inhibitor that has nanomolar potency derived from irinotecan (IRI), and a pH sensitive linker that releases SN-38 gradually (in vitro, 50% released per 1 day in serum). Clinical studies in patients (pts) with diverse solid tumors have shown manageable toxicity (dose-limiting neutropenia, diarrhea but lower incidence than IRI) and encouraging efficacy.

METHODS: Conjugate and IgG were monitored in pts given 8 (N = 24) or 10 mg/kg (N = 29) by ELISA. SN-38 and glucuronidated SN-38 (SN-38G) were measured by reversed-phase HPLC. SN-38 and SN-38G levels are expressed as the amount of drug dissociated from the conjugate (i.e., Free SN-38) and the amount bound to the IgG (Total SN-38). UGT1A1 status was determined in baseline blood sample from 146 pts.

RESULTS: IMMU-132 cleared with a half-life of 11.7-18.9 h, depending on the assay, while the IgG half-life was 4-5 days, which agrees with in vitro drug-release data. Levels of Free SN-38 at 30 min or 1 d after injection were &lt;2% and ~ 5% of Total SN-38, respectively, indicating most SN-38 in serum is bound to the conjugate. Free SN-38 clears with a half-life of ~20 h, which is consistent with SN-38 clearance in IRI therapy. No correlation was found between Free SN-38 in serum at 30 min and the incidence of severe neutropenia. Total and Free levels of SN-38G were similar, supporting in vitro results indicating that SN-38 is not glucuronidated while bound to the IgG. Free SN-38G levels were lower than Free SN-38 (SN-38G/SN-38 AUC ratio = 0.52), explaining the lower incidence of severe diarrhea. PK parameters for 8 and 10 mg/kg group were similar; no major differences in toxicity. UGT1A1 status showed 43% and 44% with *1*1 and *1*28 haplotype, respectively, and 13% with *28*28 haplotype, which is associated with higher risk of severe neutropenia and diarrhea for IRI therapy. With IMMU-132, 58% of the *28*28 pts had severe neutropenia compared to ~40% of the *1*1 and *1*28 pts, and 16% of the *28*28 pts had grade 3 diarrhea compared to 5-8% of the *1*1 and *1*28. In 3 of 4 cancer indications, objective response rate and clinical benefit ratio favored the 10 mg/kg group.

CONCLUSION: IMMU-132 cleared as predicted from in vitro serum stability data, with no difference between the 8 and 10 mg/kg groups. Current data show neutropenia did not correlate with Free SN-38 levels in serum at 30 min, and low SN-38G levels support the lower incidence of severe diarrhea. While pts with the *28*28 haplotype had a somewhat higher incidence of severe neutropenia or diarrhea than *1*1 and *1*28 pts, the overall incidence of each is small, suggesting toxicity management rather than screening is appropriate. With no major difference in safety and PK, but improved responses with 10 mg/kg, 10 mg/kg is selected for future clinical studies.

Citation Format: Robert M. Sharkey, Allyson J. Ocean, Alexander N. Starodub, Aditya Bardia, Michael Guarino, Wells A. Messersmith, Jordan D. Berlin, Vincent J. Picozzi, Rebecca Moroose, William A. Wegener, Pius Maliakal, Serengulam V. Govindan, David M. Goldenberg. Pharmacokinetics of sacituzumab govitecan (IMMU-132), an antibody-drug conjugate (ADC) targeting Trop-2, in patients with diverse advanced solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3734. doi:10.1158/1538-7445.AM2017-3734

Abstract 3193: Treatment of high Trop-2-expressing triple-negative breast cancer (TNBC) with sacituzumab govitecan (IMMU-132) overcomes homologous recombination repair (HRR) rescue mediated by Rad51

Purpose: IMMU-132 is an antibody-drug conjugate composed of a humanized anti-Trop-2 IgG conjugated via a cleavable linker to SN-38, a topoisomerase I inhibitor and active component of irinotecan. It is currently under clinical investigation in a range of solid tumors (NCT01631552). We investigated the hypothesis that IMMU-132, through its targeting of Trop-2 in solid tumors, will be superior to irinotecan in overcoming Rad51-mediated HRR repair of DNA breaks in TNBC tumors with high Trop-2 expression.

Methods: Rad51 and DNA-breaks (γ-H2A.X) were determined by Western blot. Cells with different Trop-2 levels were exposed to IMMU-132 for 24 h (25 - 100 nM SN-38 equivalents), including squamous cell lung carcinoma (SK-MES-1; ~30,000 Trop-2/cell) and TNBC (HCC1806, ~90,000 Trop-2/cell and MDA-MB-231, ~30,000 Trop-2/cell). Also, two Trop-2-transfectants of MDA-MB-231, designated C13 and C39 (4- and 25-fold higher Trop-2 levels, respectively), were likewise exposed to IMMU-132. Mice bearing MDA-MB-231, C13, or C39 tumors were treated with irinotecan (MTD, 40 mg/kg; q2dx5) or IMMU-132 (0.5 mg; 9 μg SN-38 equivalent, twice wkly x 4). Tumors were measured and mice weighed twice weekly. Study survival endpoint was tumor progression to &gt;1.0 cm3.

Results: SK-MES-1 and HCC1806 are sensitive to IMMU-132 therapy whereas MDA-MB-231 is resistant. IMMU-132 mediated a &gt;2-fold increase in Rad51 levels in MDA-MB-231 cells, but had no effect in SK-MES-1 or HCC1806. At 25 nM IMMU-132, there were lower levels of DNA breaks detected in MDA-MB-231 relative to SK-MES-1 and HCC1806 (2-fold increase in MDA-MB-231 vs. &gt;3-fold). At higher concentrations of IMMU-132 (100 nM), all 3 cell lines demonstrated similar levels of DNA breaks (~5-fold above background), suggesting that higher levels of SN-38 can overcome Rad51-mediated repair. Both the C13 and C39 clones had a similar response as parental MDA-MB-231 upon IMMU-132 exposure. Mice bearing MDA-MB-231, C13, or C39 tumors treated with irinotecan demonstrated significant improvements in median survival times (MST) compared to saline (P&lt;0.0009). As expected, IMMU-132 was no different than saline in mice bearing MDA-MB-231 tumors (MST=21d and 19.5d, respectively). However, in mice bearing high Trop-2 C13 and C39 tumors, IMMU-132 provided a significant survival benefit compared to irinotecan-treated mice (MST&gt;70d vs. 35d, respectively for C13 and &gt;70d vs. 28d for C39; P&lt;0.0007), supporting the hypothesis that IMMU-132 is able to deliver more SN-38 to tumors with high Trop-2 than can be achieved by irinotecan, and can thus overcome Rad51-mediated HRR.

Conclusion: IMMU-132, with its unique SN-38-delivery platform, has the potential to provide clinical benefit both to chemo-sensitive solid tumors with low Trop-2 expression, as well as to chemo-resistant tumors with high Trop-2 expression.

Citation Format: Thomas M. Cardillo, Ali A. Mostafa, Diane L. Rossi, Donglin Liu, Chien-Hsing Chang, Robert M. Sharkey, David M. Goldenberg. Treatment of high Trop-2-expressing triple-negative breast cancer (TNBC) with sacituzumab govitecan (IMMU-132) overcomes homologous recombination repair (HRR) rescue mediated by Rad51 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3193. doi:10.1158/1538-7445.AM2017-3193

Therapy of Advanced Non-Small-Cell Lung Cancer With an SN-38-Anti-Trop-2 Drug Conjugate, Sacituzumab Govitecan

Purpose Trop-2, expressed in most solid cancers, may be a target for antibody-drug conjugates (ADCs) in non-small-cell lung cancer (NSCLC). We studied sacituzumab govitecan (IMMU-132), a Trop-2 ADC, for the targeting of SN-38. Patients and Methods We evaluated IMMU-132 in a single-arm multicenter trial in patients with pretreated metastatic NSCLC who received either 8 or 10 mg/kg on days 1 and 8 of 21-day cycles. The primary end points were safety and objective response rate (ORR). Progression-free survival and overall survival were secondary end points. Results Fifty-four patients were treated. In the response-assessable study population (n = 47), which had a median of three prior therapies (range, two to seven), the ORR was 19%; median response duration, 6.0 months (95% CI, 4.8 to 8.3 months); and clinical benefit rate (complete response + partial response + stable disease ≥ 4 months), 43%. ORR in the intention-to-treat (ITT) population was 17% (nine of 54). Responses occurred with a median onset of 3.8 months, including patients who had relapsed or progressed after immune checkpoint inhibitor therapy. Median ITT progression-free survival was 5.2 months (95% CI, 3.2 to 7.1 months) and median ITT overall survival, 9.5 months (95% CI, 5.9 to 16.7 months). Grade 3 or higher adverse events included neutropenia (28%), diarrhea (7%), nausea (7%), fatigue (6%), and febrile neutropenia (4%). One patient developed a transient immune response, despite patients receiving a median of 10 doses. More than 90% of 26 assessable archival tumor specimens were highly positive (2+, 3+) for Trop-2 by immunohistochemistry, which suggests that Trop-2 is not a predictive biomarker for response. Conclusion IMMU-132 was well-tolerated and induced durable responses in heavily pretreated patients with metastatic NSCLC. This ADC should be studied further in this disease and in other patients with Trop-2-expressing tumors.

Efficacy and Safety of Anti-Trop-2 Antibody Drug Conjugate Sacituzumab Govitecan (IMMU-132) in Heavily Pretreated Patients With Metastatic Triple-Negative Breast Cancer

Purpose Trop-2, expressed in most triple-negative breast cancers (TNBCs), may be a potential target for antibody-drug conjugates. Sacituzumab govitecan, an antibody-drug conjugate, targets Trop-2 for the selective delivery of SN-38, the active metabolite of irinotecan. Patients and Methods We evaluated sacituzumab govitecan in a single-arm, multicenter trial in patients with relapsed/refractory metastatic TNBC who received a 10 mg/kg starting dose on days 1 and 8 of 21-day repeated cycles. The primary end points were safety and objective response rate; secondary end points were progression-free survival and overall survival. Results In 69 patients who received a median of five prior therapies (range, one to 12) since diagnosis, the confirmed objective response rate was 30% (partial response, n = 19; complete response, n = 2), the median response duration was 8.9 (95% CI, 6.1 to 11.3) months, and the clinical benefit rate (complete response + partial response + stable disease ≥ 6 months) was 46%. These responses occurred early, with a median onset of 1.9 months. Median progression-free survival was 6.0 (95% CI, 5.0 to 7.3) months, and median overall survival was 16.6 (95% CI, 11.1 to 20.6) months. Grade ≥ 3 adverse events included neutropenia (39%), leukopenia (16%), anemia (14%), and diarrhea (13%); the incidence of febrile neutropenia was 7%. The majority of archival tumor specimens (88%) were moderately to strongly positive for Trop-2 by immunohistochemistry. No neutralizing antibodies to the ADC or antibody were detected, despite repeated cycles developed. Conclusion Sacituzumab govitecan was well tolerated and induced early and durable responses in heavily pretreated patients with metastatic TNBC. As a therapeutic target and predictive biomarker, Trop-2 warrants further research.

Combining PD-1 blockade with T-cell redirecting bispecific antibodies for solid cancer therapy

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Background: Bispecific antibodies (bsAbs) for redirecting T cells to cancers have shown promise in both preclinical and clinical studies. However, clinical results have been disappointing in solid cancers. We have applied the DOCK-AND-LOCK method to generate a novel class of trivalent bsAbs, each comprising an anti-CD3 scFv covalently conjugated to a stabilized dimer of different anti-tumor Fabs. Herein we report the characterization of two such constructs, (E1)-3s and (14)-3s, which activate T cells and target Trop-2- and CEACAM5-expressing cancer cells, respectively. Methods: Human breast and colonic cancer cell lines were grown in monolayer cultures or as 3D spheroids for in vitro evaluation. NOD/SCID mice carrying xenografts of MDA-MB-231 (a TNBC line constitutively expressing Trop-2 and PD-L1) were used for in vivo studies. A human PD-1 antagonistic murine hybridoma antibody was subsequently converted to its chimeric form (IMMU-cPD-1). Human PBMCs, or T cells isolated from buffy coats by negative selection, were used as effector cells in cytotoxicity assays. The effect of IMMU-cPD-1 on cancer cells pretreated with IFN-γ to induce the expression of PD-L1 was compared with those not pretreated. Results: (E1)-3s and (14)-3s, in the presence of human T cells, killed target cells grown as monolayers at low picomolar concentrations, with similar potency observed for drug-resistant cells. The antitumor efficacy was demonstrated for (E1)-3s plus human PBMCs in NOD/SCID mice bearing MDA-MB-231, and for human PBMCs combined with (E1)-3s or (14)-3s in 3D spheroids generated from target cell lines to mimic the in vivo behavior and microenvironment of these tumors. Moreover, with the addition of IMMU-cPD-1, the benefit of PD-1 blockade was indicated by increased cell death in 3D spheroids and longer survival of MDA-MB-231-bearing mice. Conclusions: These results highlight the potency of (E1)-3s and (14)-3s as T-cell redirecting bsAbs, emphasize the potential of combining such bsAbs with immune checkpoint inhibitors to improve the therapeutic activity in the immunotherapy of solid cancers, and provide a basis for using 3D spheroids as an alternative to in vivo models for evaluating T-cell functions.

α- Versus β-Emitting Radionuclides for Pretargeted Radioimmunotherapy of Carcinoembryonic Antigen-Expressing Human Colon Cancer Xenografts

Pretargeted radioimmunotherapy (PRIT) with the β-emitting radionuclide ¹⁷⁷Lu is an attractive approach to treat carcinoembryonic antigen (CEA)-expressing tumors. The therapeutic efficacy of PRIT might be improved using α-emitting radionuclides such as ²¹³Bi. Herein, we report and compare the tumor-targeting properties and therapeutic efficacy of ²¹³Bi and ¹⁷⁷Lu for PRIT of CEA-expressing xenografts, using the bispecific monoclonal antibody TF2 (anti-CEA × anti-histamine-succinyl-glycine [HSG]) and the di-HSG-DOTA peptide IMP288. Methods: The in vitro binding characteristics of ²¹³Bi-IMP288 were compared with those of ¹⁷⁷Lu-IMP288. Tumor targeting of ²¹³Bi-IMP288 and ¹⁷⁷Lu-IMP288 was studied in mice bearing subcutaneous LS174T tumors that were pretargeted with TF2. Finally, the effect of ²¹³Bi-IMP288 (6, 12, or 17 MBq) and ¹⁷⁷Lu-IMP288 (60 MBq) on tumor growth and survival was assessed. Toxicity was determined by monitoring body weight, analyzing blood samples for hematologic and renal toxicity (hemoglobin, leukocytes, platelets, creatinine), and immunohistochemical analysis of the kidneys. Results: The in vitro binding characteristics of ²¹³Bi-IMP288 (dissociation constant, 0.45 ± 0.20 nM) to TF2-pretargeted LS174T cells were similar to those of ¹⁷⁷Lu-IMP288 (dissociation constant, 0.53 ± 0.12 nM). In vivo accumulation of ²¹³Bi-IMP288 in LS174T tumors was observed as early as 15 min after injection (9.2 ± 2.0 percentage injected dose [%ID]/g). ²¹³Bi-IMP288 cleared rapidly from the circulation; at 30 min after injection, the blood levels were 0.44 ± 0.28 %ID/g. Uptake in normal tissues was low, except for the kidneys, where uptake was 1.8 ± 1.1 %ID/g at 30 min after injection. The biodistribution of ²¹³Bi-IMP288 was comparable to that of ¹⁷⁷Lu-IMP288. Mice treated with a single dose of ²¹³Bi-IMP288 or ¹⁷⁷Lu-IMP288 showed significant inhibition of tumor growth. Median survival for the groups treated with phosphate-buffered saline, 6 MBq ²¹³Bi-IMP288, 12 MBq ²¹³Bi-IMP288, and 60 MBq ¹⁷⁷Lu-IMP288 was 22, 31, 45, and 42 d, respectively. Mice receiving 17 MBq ²¹³Bi-IMP288 showed significant weight loss, resulting in a median survival of only 24 d. No changes in hemoglobin, platelets, or leukocytes were observed in the treatment groups. However, immunohistochemical analysis of the kidneys of mice treated with 17 or 12 MBq ²¹³Bi-IMP288 showed signs of tubular damage, indicating nephrotoxicity. Conclusion: To our knowledge, this study shows for the first time that PRIT with TF2 and ²¹³Bi-IMP288 is feasible and at least as effective as ¹⁷⁷Lu-IMP288. However, at higher doses, kidney toxicity was observed. Future studies are warranted to determine the optimal dosing schedule to improve therapeutic efficacy while reducing renal toxicity.