Sacituzumab govitecan plus platinum-based chemotherapy mediates significant antitumor effects in triple-negative breast, urinary bladder, and small-cell lung carcinomas

Sacituzumab govitecan (SG) is an antibody-drug conjugate composed of an anti-Trop-2-directed antibody conjugated with the topoisomerase I inhibitory drug, SN-38, via a proprietary hydrolysable linker. SG has received United States Food and Drug Administration (FDA) approval to treat metastatic triple-negative breast cancer (TNBC), unresectable locally advanced or metastatic hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative breast cancer, and accelerated approval for metastatic urothelial cancer. We investigated the utility of combining SG with platinum-based chemotherapeutics in TNBC, urinary bladder carcinoma (UBC), and small-cell lung carcinoma (SCLC). SG plus carboplatin or cisplatin produced additive growth-inhibitory effects in vitro that trended towards synergy. Immunoblot analysis of cell lysates suggests perturbation of the cell-cycle and a shift towards pro-apoptotic signaling evidenced by an increased Bax to Bcl-2 ratio and down-regulation of two anti-apoptotic proteins, Mcl-1 and survivin. Significant antitumor effects were observed with SG plus carboplatin in mice bearing TNBC or SCLC tumors compared to all controls (P < 0.0062 and P < 0.0017, respectively) and with SG plus cisplatin in UBC and SCLC tumor-bearing animals (P < 0.0362 and P < 0.0001, respectively). These combinations were well tolerated by the animals. Combining SG with platinum-based chemotherapeutics demonstrates the benefit in these indications and warrants further clinical investigation.

Anti-CEA Pretargeted Immuno-PET Shows Higher Sensitivity Than DOPA PET/CT in Detecting Relapsing Metastatic Medullary Thyroid Carcinoma: Post Hoc Analysis of the iPET-MTC Study

Pretargeting parameters for the use of anti-carcinoembryonic antigen (CEA) bispecific monoclonal antibody TF2 and the ⁶⁸Ga-labeled IMP288 peptide for immuno-PET have been optimized in a first-in-humans study performed on medullary thyroid carcinoma (MTC) patients (the iPET-MTC study). The aim of this post hoc analysis was to determine the sensitivity of immuno-PET in relapsing MTC patients, in comparison with conventional imaging and ¹⁸F-l-dihydroxyphenylalanine (¹⁸F-DOPA) PET/CT. Methods: Twenty-five studies were analyzed in 22 patients. All patients underwent immuno-PET 1 and 2 h after ⁶⁸Ga-IMP288 injection pretargeted by TF2, in addition to neck, thoracic, abdominal, and pelvic CT; bone and liver MRI; and ¹⁸F-DOPA PET/CT. The gold standard was histology or confirmation by one other imaging method or by imaging follow-up. Results: In total, 190 lesions were confirmed by the gold standard: 89 in lymph nodes, 14 in lungs, 46 in liver, 37 in bone, and 4 in other sites (subcutaneous tissue, heart, brain, and pancreas). The number of abnormal foci detected by immuno-PET was 210. Among these, 174 (83%) were confirmed as true-positive by the gold standard. Immuno-PET showed a higher overall sensitivity (92%) than ¹⁸F-DOPA PET/CT (65%). Regarding metastatic sites, immuno-PET had a higher sensitivity than CT, ¹⁸F-DOPA PET/CT, or MRI for lymph nodes (98% vs. 83% for CT and 70% for ¹⁸F-DOPA PET/CT), liver (98% vs. 87% for CT, 65% for ¹⁸F-DOPA PET/CT, and 89% for MRI), and bone (92% vs. 64% for ¹⁸F-DOPA PET/CT and 86% for MRI), whereas sensitivity was lower for lung metastases (29% vs. 100% for CT and 14% for ¹⁸F-DOPA PET/CT). Tumor SUV_max at 60 min ranged from 1.2 to 59.0, with intra- and interpatient variability. Conclusion: This post hoc study demonstrates that anti-carcinoembryonic antigen immuno-PET is an effective procedure for detecting metastatic MTC lesions. Immuno-PET showed a higher overall sensitivity than ¹⁸F-DOPA PET/CT for disclosing metastases, except for the lung, where CT remains the most effective examination.

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.

Predictive biomarkers for sacituzumab govitecan efficacy in Trop-2-expressing triple-negative breast cancer

Sacituzumab govitecan (SG) is an antibody-drug conjugate composed of a humanized anti-Trop-2 IgG antibody conjugated via a hydrolysable linker to SN-38, the topoisomerase I-inhibitory active component of irinotecan. We investigated whether Trop-2-expression and homologous recombination repair (HRR) of SN-38-mediated double-strand DNA (dsDNA) breaks play a role in the sensitivity of triple-negative breast cancer (TNBC) to SG. Activation of HRR pathways, as evidenced by Rad51 expression, was assessed in SG-sensitive cell lines with low and moderate Trop-2-expression (SK-MES-1 squamous cell lung carcinoma and HCC1806 TNBC, respectively), compared to a low Trop-2-expressing, less SG-sensitive TNBC cell line (MDA-MB-231). Further, two Trop-2-transfectants of MDA-MB-231, C13 and C39 (4- and 25-fold higher Trop-2, respectively), were treated in mice with SG to determine whether increasing Trop-2 expression improves SG efficacy. SG mediated >2-fold increase in Rad51 in MDA-MB-231 but had no effect in SK-MES-1 or HCC1806, resulting in lower levels of dsDNA breaks in MDA-MB-231. SG and saline produced similar effects in parental MDA-MB-231 tumor-bearing mice (median survival time (MST) = 21d and 19.5d, respectively). However, in mice bearing higher Trop-2-expressing C13 and C39 tumors after Trop-2 transfection, SG provided a significant survival benefit, even compared to irinotecan (MST = 97d vs. 35d for C13, and 81d vs. 28d for C39, respectively; P < 0.0007). These results suggest that SG could provide better clinical benefit than irinotecan in patients with HRR-proficient tumors expressing high levels of Trop-2, as well as to patients with HRR-deficient tumors expressing low/moderate levels of Trop-2.

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.

Sacituzumab govitecan (SG) in patients (pts) with previously treated metastatic endometrial cancer (mEC): results from a phase I/II study

6081

Background: Unselected pts with EC who progressed on prior chemotherapy have a poor prognosis with limited treatment options. SG is a novel antibody-drug conjugate that targets Trop-2, a cell surface glycoprotein highly expressed in many epithelial tumors. It is conjugated to deliver SN-38, the active metabolite of irinotecan, via a proprietary hydrolyzable linker. Preclinical studies show SG has activity against chemotherapy-resistant EC and significant bystander effect against EC with heterogenous Trop-2 expression (Perrone E. Mol Oncol. 2019). Methods: The phase I/II basket study (NCT01631552) evaluated pts unselected for Trop-2 with advanced solid tumors who received intravenous SG (days 1 and 8 of 21-day cycles), until progression or unacceptable toxicity. CT/MRI scans were obtained at 8-week intervals for response assessment by RECIST 1.1. We report results for mEC pts who progressed after ≥1 prior systemic therapy and were treated with SG 10 mg/kg. Endpoints include safety, objective response rate (ORR), clinical benefit rate (CBR), duration of response (DOR), progression-free survival (PFS), and overall survival (OS). Results: 18 mEC pts (all women; 17 white and 1 black; median age 69 years [range, 41–76]) had a median 3.5 (range 2–6) prior lines of therapy. All pts received prior treatment with platinum therapies. At a median follow-up of 12.7 months, the ORR (95% CI) was 22.2% (6.4–47.6), with 4 partial responses. CBR (95% CI) was 44.4% (21.5–69.2), with 8 of 18 pts having either an objective response or stable disease ≥6 months. The DOR of responders ranged from 9.1 to 26.6 months, with 2 of 4 responders having a duration of ≥18 months. Median PFS (95% CI) was 3.2 months (1.9–9.4), and median OS (95% CI) was 11.9 months (4.7–not calculable). Key grade ≥3 TRAEs in the overall basket study safety population (n=495) included neutropenia (28%), neutrophil count decrease (14%), anemia (10%), diarrhea (8%), fatigue (6%), and febrile neutropenia (5%). A similar safety profile was seen in the mEC cohort. Conclusions: Median OS in unselected pts with mEC who progressed on prior platinum therapy is ~10 months with an ORR of ~10%. SG monotherapy showed clinical activity in pts with relapsed/refractory mEC, consistent with previous preclinical findings, and support further clinical investigation (NCT04251416). The phase II TROPiCS-03 (NCT03964727) study in pts with metastatic solid tumors selected based on elevated Trop-2 expression by a validated IHC assay will also provide further insights. Clinical trial information: NCT01631552.

Sacituzumab govitecan, a novel, third-generation, antibody-drug conjugate (ADC) for cancer therapy

INTRODUCTION

We describe a new, third-generation of antibody-drug conjugates (ADCs) having a high drug payload against topoisomerase I, important for DNA function, and targeting selective tumor antigens, predominantly TROP-2.

AREAS COVERED

The historical development of ADCs is reviewed before presenting the current line of improved, third-generation ADCs targeting topoisomerase I, thus affecting DNA and causing double-stranded DNA breaks. Emphasis is given to explaining why sacituzumab govitecan represents a paradigm change in ADCs by achieving a high therapeutic index due to its novel target, TROP-2, an internalizing antigen/antibody, proprietary linker chemistry, and high drug payload, resulting in a high tumor concentration of the drug given in repeated doses with acceptable tolerability, particularly evidencing a lower percentage of 'late' diarrhea than its prodrug, irinotecan. PubMed was used for the primary search conducted.

EXPERT OPINION

The properties and clinical results of third-generation ADCs, based on sacituzumab govitecan, are discussed, including prospects for future applications, particularly combination therapies with PARP inhibitors and immune checkpoint inhibitors. Since one topoisomerase I ADC has just received regulatory approval for HER2⁺ breast cancer, and sacituzumab govitecan is under FDA review for accelerated approval in the therapy of triple-negative breast cancer, the prospects for these novel ADCs are discussed.

Initial Clinical Results of a Novel Immuno-PET Theranostic Probe in Human Epidermal Growth Factor Receptor 2-Negative Breast Cancer

This prospective study evaluated the imaging performance of a novel pretargeting immunologic PET (immuno-PET) method in patients with human epidermal growth factor receptor 2 (HER2)-negative, carcinoembryonic antigen (CEA)-positive metastatic breast cancer, compared with CT, bone MRI, and ¹⁸F-FDG PET. Methods: Twenty-three patients underwent whole-body immuno-PET after injection of 150 MBq of ⁶⁸Ga-IMP288, a histamine-succinyl-glycine peptide given after initial targeting of a trivalent anti-CEA, bispecific, antipeptide antibody. The gold standards were histology and imaging follow-up. Tumor SUVs (SUV_max and SUV_mean) were measured, and tumor burden was analyzed using total tumor volume and total lesion activity. Results: The total lesion sensitivity of immuno-PET and ¹⁸F-FDG PET were 94.7% (1,116/1,178) and 89.6% (1,056/1,178), respectively. Immuno-PET had a somewhat higher sensitivity than CT or ¹⁸F-FDG PET in lymph nodes (92.4% vs. 69.7% and 89.4%, respectively) and liver metastases (97.3% vs. 92.1% and 94.8%, respectively), whereas sensitivity was lower for lung metastases (48.3% vs. 100% and 75.9%, respectively). Immuno-PET showed higher sensitivity than MRI or ¹⁸F-FDG PET for bone lesions (95.8% vs. 90.7% and 89.3%, respectively). In contrast to ¹⁸F-FDG PET, immuno-PET disclosed brain metastases. Despite equivalent tumor SUV_max, SUV_mean, and total tumor volume, total lesion activity was significantly higher with immuno-PET than with ¹⁸F-FDG PET (P = 0.009). Conclusion: Immuno-PET using anti-CEA/anti-IMP288 bispecific antibody, followed by ⁶⁸Ga-IMP288, is a potentially sensitive theranostic imaging method for HER2-negative, CEA-positive metastatic breast cancer patients and warrants further research.

Correction: Trop-2 is a novel target for solid cancer therapy with sacituzumab govitecan (IMMU-132), an antibody-drug conjugate (ADC)

[This corrects the article DOI: 10.18632/oncotarget.4318.].

Antibody-drug conjugates targeting TROP-2 and incorporating SN-38: A case study of anti-TROP-2 sacituzumab govitecan

Antibody-drug conjugates (ADCs) that exploit the active metabolite SN-38, which is derived from the popular anticancer drug, irinotecan (a camptothecin that inhibits the nuclear topoisomerase I enzyme, inducing double-stranded DNA breaks during the mitotic S-phase of affected cells), represent a substantial advance in the ADC field. SN-38 has been conjugated to a humanized antibody against trophoblast cell surface antigen 2 (TROP-2), which is involved in cancer signaling pathways and has increased expression by many cancer cell types, yielding the ADC sacituzumab govitecan. By conjugating a higher number of SN-38 molecules to the immunoglobulin (drug-to-antibody ratio = 7-8:1), and giving higher (10 mg/kg) and repeated therapy cycles (Days 1 and 8 of 21-day cycles), enhanced drug uptake by the targeted cancer cells is achieved. Based on a unique conjugation method, the lactone ring of the SN-38 molecule is stabilized and the molecule is protected from glucuronidation, a process that contributes to the untoward late diarrhea experienced with irinotecan. Finally, while the ADC is internalized, the use of a moderately stable linker permits release of SN-38 in an acidic environment of the tumor cell and its microenvironment, contributing to a bystander effect on neighboring cancer cells. Here, we discuss the development of sacituzumab govitecan and clinical results obtained using it for the management of patients with advanced, refractive breast, lung, and urinary bladder cancers. Sacituzumab govitecan, which is undergoing accelerated approval review by the US Food and Drug Administration while also being studied in Phase 3 clinical studies, was granted Breakthrough Therapy status from the FDA for advanced, refractory, metastatic triple-negative breast cancer patients.

Sacituzumab Govitecan-hziy in Refractory Metastatic Triple-Negative Breast Cancer

BACKGROUND

Standard chemotherapy is associated with low response rates and short progression-free survival among patients with pretreated metastatic triple-negative breast cancer. Sacituzumab govitecan-hziy is an antibody-drug conjugate that combines a humanized monoclonal antibody, which targets the human trophoblast cell-surface antigen 2 (Trop-2), with SN-38, which is conjugated to the antibody by a cleavable linker. Sacituzumab govitecan-hziy enables delivery of high concentrations of SN-38 to tumors.

METHODS

We conducted a phase 1/2 single-group, multicenter trial involving patients with advanced epithelial cancers who received sacituzumab govitecan-hziy intravenously on days 1 and 8 of each 21-day cycle until disease progression or unacceptable toxic effects. A total of 108 patients received sacituzumab govitecan-hziy at a dose of 10 mg per kilogram of body weight after receiving at least two previous anticancer therapies for metastatic triple-negative breast cancer. The end points included safety; the objective response rate (according to Response Evaluation Criteria in Solid Tumors, version 1.1), which was assessed locally; the duration of response; the clinical benefit rate (defined as a complete or partial response or stable disease for at least 6 months); progression-free survival; and overall survival. Post hoc analyses determined the response rate and duration, which were assessed by blinded independent central review.

RESULTS

The 108 patients with triple-negative breast cancer had received a median of 3 previous therapies (range, 2 to 10). Four deaths occurred during treatment; 3 patients (2.8%) discontinued treatment because of adverse events. Grade 3 or 4 adverse events (in ≥10% of the patients) included anemia and neutropenia; 10 patients (9.3%) had febrile neutropenia. The response rate (3 complete and 33 partial responses) was 33.3% (95% confidence interval [CI], 24.6 to 43.1), and the median duration of response was 7.7 months (95% CI, 4.9 to 10.8); as assessed by independent central review, these values were 34.3% and 9.1 months, respectively. The clinical benefit rate was 45.4%. Median progression-free survival was 5.5 months (95% CI, 4.1 to 6.3), and overall survival was 13.0 months (95% CI, 11.2 to 13.7).

CONCLUSIONS

Sacituzumab govitecan-hziy was associated with durable objective responses in patients with heavily pretreated metastatic triple-negative breast cancer. Myelotoxic effects were the main adverse reactions. (Funded by Immunomedics; IMMU-132-01 ClinicalTrials.gov number, 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. &gt; 50 yrs old [33.0% (34/103)] and little different for pts with 2 prior therapies [35.4% (17/48)] vs. &gt;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.

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.

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.

•

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

•

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

•

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

Abstract P1-12-01: Withdrawn

This abstract was withdrawn by the authors.

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.

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.

Therapy for chemopretreated metastatic urothelial cancer (mUC) with the antibody-drug conjugate (ADC) sacituzumab govitecan (IMMU-132)

327

Background: Patients (pts) with mUC pre-treated with platinum-containing chemotherapy have limited therapeutic options, with checkpoint-inhibitor immunotherapy (IO) responses in a minority of pts. We present an interim update of the safety and activity of sacituzumab govitecan (IMMU-132), an anti-Trop-2-SN-38 ADC, as therapy for chemotherapy-pretreated mUC pts (ClinicalTrials.gov, NCT01631552). Methods: We enrolled 32 pts with mUC and ECOG PS 0-1 who failed ≥ 1 prior standard therapy (median=3; range, 1-5). IMMU-132 was administered at 8 or 10 mg/kg on days 1 and 8 every 21 days, continued until disease progression (PD) or unacceptable toxicity. Response-evaluable pts received ≥ 2 doses, and had ≥ 1 post-baseline response assessment. Results: Twenty-five pts [median age 68 yrs (range: 50-91), 24 males] are currently assessable for safety and response; 23 had prior platinum-containing therapy; 46% had >2 prior therapies; 4 also had IO agents. Sites of metastases included liver (N=4; 16%), lungs (N=7; 28%), bone (N=4; 16%), and lymph nodes (N=16; 64%). Pts received a median of 7 cycles (range, 2-23) of IMMU-132. ORR was 36% (9/25) [1 complete (CR) and 8 partial responses (PR)]; 44% (11/25) had stable disease (SD). Further, pts with 1 line of prior chemotherapy had an ORR of 53.8% (7/13), and 16.7% for those with 2 to 5 prior therapy lines. Median PFS for all patients is 7.2 mos (95% CI, 4.9-10.7); median survival is not reached yet. Of the 4 pts with progression after prior IO, there were 1 PR and 2 SDs with IMMU-132. Duration of response for CR/PR pts is currently 5.1 mos (95% CI, 4.1-12.9) and 10/11 pts (5 with ≥ 20% tumor reduction) had stable disease > 4 mos. Grade 4 neutropenia (16%) lasted < 7 days, and non-hematological grade 3 AEs included fatigue (12%) and hypophosphatemia (8%). No treatment-related deaths were observed. Analysis of Trop-2 expression revealed 1+ to 3+ positive staining in 95% of 19 archival patient specimens. Conclusions: With an ORR of 36% and a median PFS of 7.2 months in a heavily pretreated population, these interim results suggest that IMMU-132 is a promising agent as 2nd line or later therapy for platinum- or IO- pretreated mUC pts. Clinical trial information: NCT01631552.

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&gt;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 &gt;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.

Synthetic Lethality Exploitation by an Anti-Trop-2-SN-38 Antibody-Drug Conjugate, IMMU-132, Plus PARP Inhibitors in BRCA1/2-wild-type Triple-Negative Breast Cancer

Purpose: Both PARP inhibitors (PARPi) and sacituzumab govitecan (IMMU-132) are currently under clinical evaluation in triple-negative breast cancer (TNBC). We sought to investigate the combined DNA-damaging effects of the topoisomerase I (Topo I)-inhibitory activity of IMMU-132 with PARPi disruption of DNA repair in TNBC.Experimental Design:In vitro, human TNBC cell lines were incubated with IMMU-132 and various PARPi (olaparib, rucaparib, or talazoparib) to determine the effect on growth, double-stranded DNA (dsDNA) breaks, and cell-cycle arrest. Mice bearing BRCA1/2-mutated or -wild-type human TNBC tumor xenografts were treated with the combination of IMMU-132 and PARPi (olaparib or talazoparib). Study survival endpoint was tumor progression to >1.0 cm³ and tolerability assessed by hematologic changes.Results: Combining IMMU-132 in TNBC with all three different PARPi results in synergistic growth inhibition, increased dsDNA breaks, and accumulation of cells in the S-phase of the cell cycle, regardless of BRCA1/2 status. A combination of IMMU-132 plus olaparib or talazoparib produces significantly improved antitumor effects and delay in time-to-tumor progression compared with monotherapy in mice bearing BRCA1/2-mutated HCC1806 TNBC tumors. Furthermore, in mice bearing BRCA1/2-wild-type tumors (MDA-MB-468 or MDA-MB-231), the combination of IMMU-132 plus olaparib imparts a significant antitumor effect and survival benefit above that achieved with monotherapy. Most importantly, this combination was well tolerated, with no substantial changes in hematologic parameters.Conclusions: These data demonstrate the added benefit of combining Topo I inhibition mediated by IMMU-132 with synthetic lethality provided by PARPi in TNBC, regardless of BRCA1/2 status, thus supporting the rationale for such a combination clinically. Clin Cancer Res; 23(13); 3405-15. ©2017 AACR.

Abstract 584: Significant enhancement of efficacy of an anti-Trop-2 antibody-drug conjugate, sacituzumab govitecan (IMMU-132), in experimental triple-negative breast cancer (TNBC) when combined with microtubule or PARP inhibitors

Purpose: In current clinical trials (ClinicalTrials.gov, NCT01631552), TNBC patients treated with IMMU-132, which is composed of the active metabolite of irinotecan, SN-38, conjugated to an anti-Trop-2 antibody (drug:Ab ratio = 7.6), shows manageable toxicity and encouraging responses in relapsed/refractory cases. Preclinical studies were performed to determine the utility of combinations of IMMU-132 with either a poly(adenosine diphosphoribose) polymerase (PARP) inhibitor (olaparib) or microtubule inhibitors (paclitaxel or eribulin mesylate) in mice bearing BRCA1/2 defective (HCC1806)and wild-type (MDA-MB-468) TNBC tumor xenografts.

Procedures: In vitro, human TNBC cell lines were incubated with IMMU-132 and olaparib to determine a combination index number and whether the interaction was synergistic, as well as incubating with SN-38 or IMMU-132 ± olaparib with analysis by western blot or flow cytometry (FACS) for double-stranded DNA breaks, as evidenced by increases in phosphorylated histone H2AX (p-H2AX). In vivo, mice bearing MDA-MB-468 or HCC1806 tumors were treated with either paclitaxel (qwklyx5wks) or eribulin mesylate (wks 1, 2, 4, & 5) alone or in combination with IMMU-132 (wks 1, 2, 4, & 5). Additionally, mice bearing TNBC tumors were treated with olaparib (qdx5d) plus IMMU-132 (qwkly) for 4 wks. Study survival endpoint was tumor progression to &gt;1.0 cm3.

Results: Treatment with IMMU-132 plus paclitaxel in HCC1806 or MDA-MB-468 tumor-bearing mice significantly inhibited tumor growth compared to monotherapy (P&lt;0.0195 and &lt;0.0328, respectively). IMMU-132 plus eribulin mesylate also resulted in significant tumor regressions when compared to all other treatments in these two disease models (P&lt;0.0007 and &lt;0.0432, respectively). In vitro, olaparib combined with SN-38 or IMMU-132 increased p-H2AX levels. Cytotoxicity assays revealed this interaction to be synergistic in both BRCA1/2 defective and wild-typeTNBC cell lines. In vivo, IMMU-132 plus olaparib had significant anti-tumor effects in both HCC1806 and MDA-MB-468 tumor-bearing mice when compared to single-agent responses (P&lt;0.0017 and &lt;0.004, respectively). In all studies, the combination of IMMU-132 with either microtubule inhibitors or olaparib was well tolerated, with no observable toxicities (e.g., weight loss).

Conclusions: Combining IMMU-132 with a PARP inhibitor achieves synergistic growth inhibition in TNBC, regardless of BRCA1/2 status. The combination of IMMU-132 therapy with either microtubule or PARP inhibitors results in significant anti-tumor effects in TNBC disease models with no observable toxicity. These data provide the rationale for the clinical evaluation of IMMU-132 in combination with these chemotherapeutics in TNBC patients.

Citation Format: Thomas M. Cardillo, Serengulam V. Govindan, Maria Zalath, Ali Mostafa, Roberto Arrojo, Robert M. Sharkey, David M. Goldenberg. Significant enhancement of efficacy of an anti-Trop-2 antibody-drug conjugate, sacituzumab govitecan (IMMU-132), in experimental triple-negative breast cancer (TNBC) when combined with microtubule or PARP inhibitors. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 584.

Abstract 587: Superior anti-tumor effects of an anti-HLA-DR IgG4 antibody, IMMU-114, in chronic and acute lymphocytic leukemia (CLL and ALL): Comparison to anti-CD20 therapy, chemotherapy, or combined with kinase inhibitors

Purpose: IMMU-114 is a humanized anti-HLA-DR IgG4 monoclonal antibody currently under investigation for non-Hodgkin's lymphoma and CLL (ClinicalTrials.gov, NCT01728207). This study was undertaken to continue preclinical evaluations in CLL and ALL models, comparing IMMU-114 efficacy to anti-CD20 or doxorubicin therapy, respectively, as well in combination with Bruton's tyrosine kinase (Btk) or phosphoinositide-3-kinase (PI3K) inhibitors in CLL.

Procedures: The human CLL cell line, JVM-3, was grown s.c. in SCID mice. Once tumors reached ∼0.2 cm3, they were divided into treatment groups of either IMMU-114 or rituximab (200, 100, or 50 μg, twice weekly for 4 weeks). Study survival endpoint was tumor progression to &gt;1.0 cm3. In vitro, JMV-3 was treated with various concentrations of either a Btk inhibitor (ibrutinib) or PI3K inhibitor (idelalisib) in the presence of a constant amount of IMMU-114. IC50-values were determined, data were normalized, and isobolograms generated for each inhibitor to determine overall effect. For ALL, MN-60 cells were injected i.v. into SCID mice. After 5 days, animals received IMMU-114 (50 or 25 μg, 2 x weekly for 4 weeks) or doxorubicin (3×20 μg qdx3d induction phase, followed by a 60μg bolus injection maintenance phase on week 3). Disease progression was declared upon the onset of hind-limb paralysis.

Results: Mice with JVM-3 tumors had a median survival time (MST) of 14 days for saline controls, while therapy with rituximab significantly improved survival (P&lt;0.0102); the MST was only 19 days for the two highest doses. In contrast, mice treated with IMMU-114 had a MST ≥42 days for all three doses tested (P&lt;0.0001), providing an overall superior tumor growth control over rituximab (P&lt;0.0116). In vitro, an additive effect was observed in JVM-3 when IMMU-114 was combined with either ibrutinib or idelalisib. In the ALL disseminated MN-60 disease model, mice were refractory to the doxorubicin treatment, succumbing to disease at the same rate as saline controls (MST = 23 and 21 days, respectively). Importantly, IMMU-114, at both the 50 and 25 μg doses, provided a significant survival benefit compared to both saline control and doxorubicin-treated animals (MST&gt;39 days, P&lt;0.0001). IMMU-114 therapy was well tolerated in all these studies, as evidenced by no significant loss in weight.

Conclusions: In a preclinical model of human CLL, IMMU-114 was superior to anti-CD20 therapy using rituximab, and had an additive effect when combined with Btk or PI3K inhibitors. IMMU-114 also achieved a significant survival benefit in the doxorubicin-refractive MN-60 ALL model. These data demonstrate IMMU-114's overall activity in diverse hematopoietic cancers and show the need for continued clinical and preclinical evaluation.

Citation Format: Thomas M. Cardillo, Maria Zalath, Roberto Arrojo, Robert M. Sharkey, David M. Goldenberg. Superior anti-tumor effects of an anti-HLA-DR IgG4 antibody, IMMU-114, in chronic and acute lymphocytic leukemia (CLL and ALL): Comparison to anti-CD20 therapy, chemotherapy, or combined with kinase inhibitors. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 587.

Abstract CT064: Treatment for metastatic platinum-resistant urothelial cancer (PRUC) with an anti-Trop-2-SN-38 antibody-drug conjugate (ADC), sacituzumab govitecan (IMMU-132): phase I/II clinical experience

Background. Patients (pts) with PRUC have an aggressive disease with limited therapeutic options. Sacituzumab govitecan (IMMU-132) is an ADC comprised of SN-38, the active metabolite of the topoisomerase inhibitor, irinotecan, conjugated to an anti-Trop-2 humanized mAb. In vitro and in vivo preclinical data show that this is a unique ADC, with a high drug:antibody ratio of 7.6. It is capable of delivering up to 136-fold more SN-38 than its parent drug, irinotecan, in a human cancer xenograft. The ADC and mAb are immunotherapeutic in vitro (ADCC). Expression of Trop-2 is elevated in most epithelial cancers (&gt;80%), including UC. The efficacy and safety of this new ADC is examined in PRUC pts.

Methods. A Phase I/II clinical trial (ClinicalTrials.gov, NCT01631552) is enrolling PRUC pts. IMMU-132 is administered on days 1 and 8 of 21-day treatment cycles. Treatment is continued based on tolerance or until progression, with safety and response assessments (RECIST 1.1) made every week and every 8 weeks, respectively.

Results. Fifteen PRUC pts were enrolled by 11/10/15 and 14 are evaluable [median age 68 yrs, 93% M, 71% with ECOG 1, 71% with visceral metastases], with a median of 2 (range, 1-5) prior chemotherapies. IMMU-132 doses given were 8 mg/kg (N = 3), 10 mg/kg (N = 10), or 12 mg/kg (N = 1).

Six patients have confirmed partial response, providing an objective tumor response rate of 46% in 13 patients assessable by RECIST 1.1. The clinical benefit ratio (PR+SD &gt; 4 months) is 57%. The current median progression-free survival (PFS) is 8.1 months with 50% maturity (# events divided by # patients), and median overall survival (OS) is 10.8 months, with 79% patients still alive.

Among collected adverse events so far among 15 UC pts enrolled before 8/31/15, grade 3+ drug-related toxicities above 5% incidence (single events) are neutropenia (9%), diarrhea (9%) and staphylococcal bacteremia (9%). No patient developed antibodies (by ELISA) to the antibody or drug.

Conclusion. Compared to historical response rates of &lt; 20% in this clinical setting, PFS of 2-4 mos, and OS of 4-9 mos for pts with PRUC, the early efficacy seen in this study to date combined with the toxicity profile encourage further study of IMMU-132 at the 10 mg/kg dosing level.

Citation Format: Scott T. Tagawa, Bishoy Faltas, Elaine Lam, Wells A. Messersmith, Philip Saylor, Aditya Bardia, Julio J. Hajdenberg, Alicia K. Morgans, Jordan D. Berlin, Emerson Lim, Kevin Kalinsky, Pius Maliakal, Robert M. Sharkey, Francois Wilhelm, David M. Goldenberg, Allyson J. Ocean. Treatment for metastatic platinum-resistant urothelial cancer (PRUC) with an anti-Trop-2-SN-38 antibody-drug conjugate (ADC), sacituzumab govitecan (IMMU-132): phase I/II clinical experience. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr CT064.

Therapy of relapsed/refractory metastatic triple-negative breast cancer (mTNBC) with an anti-Trop-2-SN-38 antibody-drug conjugate (ADC), sacituzumab govitecan (IMMU-132): Phase II results

LBA509

Notice of Retraction: “Therapy of relapsed/refractory metastatic triple-negative breast cancer (mTNBC) with an anti-Trop-2-SN-38 antibody-drug conjugate (ADC), sacituzumab govitecan (IMMU-132): Phase II results.” ASCO's Confidentiality Policy requires that abstracts be considered confidential and embargoed from the time of submission until the findings have been publicly released in conjunction with the ASCO Annual Meeting. Abstract LBA509, published in the 2016 ASCO Annual Meeting Proceedings Part II, violated this policy and was retracted from publication and presentation at the 2016 ASCO Annual Meeting.

Immuno-PET Using Anticarcinoembryonic Antigen Bispecific Antibody and 68Ga-Labeled Peptide in Metastatic Medullary Thyroid Carcinoma: Clinical Optimization of the Pretargeting Parameters in a First-in-Human Trial

Earlier clinical studies reported a high sensitivity of pretargeted immunoscintigraphy using murine or chimeric anticarcinoembryonic antigen (CEA) bispecific antibody (BsMAb) and peptides labeled with ¹¹¹In or ¹³¹I in medullary thyroid carcinoma (MTC). Preclinical studies showed that new-generation humanized recombinant anti-CEA × antihistamine-succinyl-glycine (HSG) trivalent BsMAb TF2 and radiolabeled HSG peptide (IMP288) present good features for PET. This study aimed at optimizing molar doses and pretargeting interval of TF2 and ⁶⁸Ga-labeled IMP288 for immuno-PET in relapsed MTC patients with calcitonin serum levels greater than 150 pg/mL.

METHODS

Five cohorts (C1-C5) of 3 patients received variable molar doses of TF2 and approximately 150 MBq of ⁶⁸Ga-IMP288 after different pretargeting time intervals (C1: 120 nmol TF2, 6 nmol IMP288, 24 h; C2: 120 nmol TF2, 6 nmol IMP288, 30 h; C3: 120 nmol TF2, 6 nmol IMP288, 42 h; C4: 120 nmol TF2, 3 nmol IMP288, 30 h; and C5: 60 nmol TF2, 3 nmol IMP288, 30 h). TF2 and ⁶⁸Ga-IMP288 pharmacokinetics were monitored. Whole-body PET was recorded 60 and 120 min after ⁶⁸Ga-IMP288 injection. Tumor maximal SUV (T-SUV_max) and T-SUV_max-to-mediastinum blood-pool (MBP) SUV_mean ratios (T/MBP) were determined.

RESULTS

In C1, T-SUV_max and T/MBP ranged from 4.09 to 8.93 and 1.39 to 3.72 at 60 min and 5.14 to 11.25 and 2.73 to 5.38 at 120 min, respectively. Because of the high MBP, the delay was increased to 30 h in C2, increasing T-SUV_max and T/MBP. Further increasing the delay to 42 h in C3 decreased T-SUV_max and T/MBP, showing that 30 h was the most favorable delay. In C4, the TF2-to-peptide mole ratio was increased to 40 (delay 30 h), resulting in high T-SUV_max but with higher MBP than in C2. In C5, the molar dose of TF2 was reduced, resulting in lower imaging performance. Pharmacokinetics demonstrated a fast TF2 clearance and a clear relationship between blood activity clearance and the ratio between the molar amount of injected peptide to the molar amount of circulating TF2 at the time of peptide injection.

CONCLUSION

High tumor uptake and contrast can be obtained with pretargeted anti-CEA immuno-PET in relapsed MTC patients, especially using optimized pretargeting parameters: a BsMAb-to-peptide mole ratio of 20 and 30 h pretargeting delay.

Prospects and progress of antibody-drug conjugates in solid tumor therapies

INTRODUCTION

Antibody-drug conjugates (ADCs) for targeted chemotherapy have evolved in the past 2-3 decades to become a validated clinical cancer therapy modality. While considerable strides have been made in treating hematological tumors, challenges remain in the more difficult-to-treat solid cancers.

AREAS COVERED

The current model for a successful ADC uses a highly potent cytotoxic drug as the payload, with stringent linker requirements and limited substitutions. In solid tumor treatment, a number of ADCs have not progressed beyond Phase I clinical trials, indicating a need to optimize additional factors governing translational success. In this regard, insights from mathematical modeling provide a number of pointers relevant to target antigen and antibody selection. Together with the choice of targets, these can be expected to complement the gains made in ADC design towards the generation of better therapeutics.

EXPERT OPINION

While highly potent microtubule inhibitors continue to dominate the current ADC landscape, there are promising data with other drugs, linkers, and targets that suggest a more flexible model for a successful ADC is evolving. Such changes will undoubtedly lead to the consideration of new targets and constructs to overcome some of the unique natural barriers that impede the delivery of cytotoxic agents in solid tumor.

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 &lt;3 months, and OS is &lt;10 months. Therefore, new treatment strategies are needed. Since Trop-2 is expressed in &gt;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&gt;6 mo) of 49% (63% with SD&gt;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 &gt;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&lt;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&lt;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&lt;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.

Radioactive antibodies: a historical review of selective targeting and treatment of cancer

Radioactive antibodies have served as imaging and therapeutic agents for several decades, but recent developments raise enthusiasm that a new generation of cancer therapeutics and diverse molecular imaging agents for various cancers are more likely than ever before. This article traces the development of tumor-targeting antibodies labeled with diagnostic or therapeutic radionuclides, and describes the problems encountered and the clinical advances made. We also emphasize recent attempts to improve both molecular imaging and radioimmunotherapy with multistep pretargeting methods that separate the delivery of the tumor-binding, bispecific antibody given in the first step from the radionuclide carrier, which, in the second step, will localize to the "anti-carrier" binding arm of the pretargeted bispecific antibody.

Abstract C166: Combining an anti-Trop-2 antibody-SN-38 conjugate (sacituzumab govitecan) with microtubule inhibitors (paclitaxel and eribulin mesylate) or PARP inhibitor (olaparib) significantly improves therapeutic outcome in experimental triple-negative breast cancer (TNBC)

Purpose: Determine whether combining sacituzumab govitecan (IMMU-132), an anti-Trop-2/SN-38 antibody-drug conjugate, with microtubule inhibitors (paclitaxel or eribulin mesylate) or a poly(adenosine diphosphoribose) polymerase (PARP) inhibitor (olaparib) in mice bearing human TNBC xenografts improves anti-tumor effects.

Experimental Procedures: Mice bearing human TNBC xenografts (MDA-MB-468 or HCC1806; ∼0.3 cm3) were treated with the maximum tolerated dose of paclitaxel (15 mg/kg weekly x 5 wks) and IMMU-132 at either 10 mg/kg or 12.5 mg/kg on days 1, 8, 22, and 29. Mice bearing HCC1806 tumors (∼0.28 cm3) were treated for 2 cycles with IMMU-132 (12.5 mg/kg) and 0.5 mg/kg of eribulin mesylate (equivalent to human dose of 1.4 mg/m2) weekly for 2 weeks on a 21-day cycle. Studies examining PARP inhibition used mice bearing MDA-MB-468 tumors (∼0.32 cm3) treated with olaparib (50 mg/kg, qdx5d, x 4 wks; 33% of human dose equaling 800 mg daily) and IMMU-132 (10 mg/kg, twice weekly x 4 wks). The primary endpoint was the median survival time (MST), defined as the time for tumors to progress to 1.0 cm3.

Results: Mice with MDA-MB-468 tumors given the combination of IMMU-132 and paclitaxel exhibited superior anti-tumor effects, with &gt;11-fold tumor shrinkage, in comparison to 1.4-fold shrinkage in the IMMU-132 group alone (P = 0.0003; area under the curve, AUC) or 11.4-fold increase in tumor size in mice treated with paclitaxel alone (P&lt;0.0001; AUC). In the rapidly-progressing HCC1806 xenografts, the combination improved MST to 38 days from 17.5 and 17.0 days for paclitaxel and IMMU-132, respectively (P&lt;0.0015; log-rank). Mice treated with the combination of IMMU-132 plus eribulin mesylate exhibited a significantly greater anti-tumor response than all other monotherapy groups (P&lt;0.0432; paired t-test). This resulted in a significant survival benefit for the combination (MST = 23 days) when compared to eribulin or IMMU-132 monotherapy (MST = 18 and 14 days, respectively; P&lt;0.0044; log-rank). Likewise, combining IMMU-132 therapy with olaparib was superior to single agent therapy in mice bearing MDA-MB-468 tumors (P&lt;0.0032; AUC). All the IMMU-132 combination treatments were well-tolerated.

Conclusions: IMMU-132 is a humanized anti-Trop-2 antibody conjugated to SN-38, the active metabolite of irinotecan, a topoisomerase I inhibitor. Clinically, IMMU-132 has shown manageable toxicity and encouraging responses in patients with relapsed/refractory TNBC (ClinicalTrials.gov, NCT01631552). Since preclinical studies indicate IMMU-132 can be combined with two different microtubule-inhibitors or a PARP-inhibitor with significantly enhanced anti-tumor activity, these data provide a rationale for future clinical evaluation of IMMU-132 in combination with these and other chemotherapeutics that likewise target cell division through microtubule inhibition or DNA-repair mechanisms in patients with TNBC.

Citation Format: Thomas M. Cardillo, Serengulam V. Govindan, Maria Zalath, Roberto Arrojo, Robert M. Sharkey, David M. Goldenberg. Combining an anti-Trop-2 antibody-SN-38 conjugate (sacituzumab govitecan) with microtubule inhibitors (paclitaxel and eribulin mesylate) or PARP inhibitor (olaparib) significantly improves therapeutic outcome in experimental triple-negative breast cancer (TNBC). [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr C166.

Pharmacokinetics and Dosimetry Studies for Optimization of Pretargeted Radioimmunotherapy in CEA-Expressing Advanced Lung Cancer Patients

Objectives

A phase I pretargeted radioimmunotherapy trial (EudractCT 200800603096) was designed in patients with metastatic lung cancer expressing carcinoembryonic antigen (CEA) to optimize bispecific antibody and labeled peptide doses, as well as the delay between their injections.

Methods

Three cohorts of three patients received the anti-CEA × anti-histamine-succinyl-glycine (HSG)-humanized trivalent bispecific antibody (TF2) and the IMP288 bivalent HSG peptide. Patients underwent a pretherapeutic imaging session S1 (44 or 88 nmol/m² of TF2 followed by 4.4 nmol/m², 185 MBq, of ¹¹¹In-labeled IMP288) and, 1–2 weeks later, a therapy session S2 (240 or 480 nmol/m² of TF2 followed by 24 nmol/m², 1.1 GBq/m², of ¹⁷⁷Lu-labeled IMP288). The pretargeting delay was 24 or 48 h. The dose schedule was defined based on preclinical TF2 pharmacokinetic (PK) studies, on our previous clinical data using the previous anti-CEA-pretargeting system, and on clinical results observed in the first patients injected using the same system in Netherlands.

Results

TF2 PK was represented by a two-compartment model in which the central compartment volume (Vc) was linearly dependent on the patient’s surface area. PK was remarkably similar, with a clearance of 0.33 ± 0.03 L/h/m². ¹¹¹In- and ¹⁷⁷Lu-IMP288 PK was also well represented by a two-compartment model. IMP288 PK was faster (clearance 1.4–3.3 L/h). The Vc was proportional to body surface area, and IMP288 clearance depended on the molar ratio of injected IMP288 to circulating TF2 at the time of IMP288 injection. Modeling of image quantification confirmed the dependence of IMP288 kinetics on circulating TF2, but tumor activity PK was variable. Organ-absorbed doses were not significantly different in the three cohorts, but the tumor dose was significantly higher with the higher molar doses of TF2 (p < 0.002). S1 imaging predicted absorbed doses calculated in S2.

Conclusion

The best dosing parameters corresponded to the shorter pretargeting delay and to the highest TF2 molar doses. S1 imaging session accurately predicted PK as well as absorbed doses of S2, thus potentially allowing for patient selection and dose optimization.

Trial Registration

ClinicalTrials.gov NCT01221675 (EudractCT 200800603096).

Sacituzumab Govitecan, a Novel Antibody--Drug Conjugate, in Patients With Metastatic Platinum-Resistant Urothelial Carcinoma

Patients with metastatic, platinum-resistant urothelial carcinoma (PRUC) have no Food and Drug Administration-approved therapies. The response rates to second-line chemotherapy have generally been < 20%, with a median overall survival of < 1 year. We report our experience with 6 heavily pretreated patients with advanced PRUC (ClinicalTrials.gov identifier NCT01631552) with the novel antibody-drug conjugate, sacituzumab govitecan (IMMU-132). This antibody-drug conjugate comprises the active metabolite of irinotecan, SN-38, conjugated to an anti-Trop-2 antibody. Trop-2 is widely expressed in ≤ 83% of urothelial carcinomas. Of the 6 patients, 3 had a clinically significant response (progression-free survival, 6.7 to 8.2 months; overall survival, 7.5+ to 11.4+ months). Sacituzumab govitecan was well tolerated. Because of these results, a phase II trial has been initiated. The present report highlights the promise of antibody-drug conjugates, such as sacituzumab govitecan, as a novel therapeutic strategy for the treatment of PRUC.

Pretargeted immunoPET of prostate cancer with an anti-TROP-2 x anti-HSG bispecific antibody in mice with PC3 xenografts

PURPOSE

Pretargeting with bispecific antibodies and radiolabeled hapten-peptides could be used to specifically target tumors with high target-to-background ratios. TF12 is a trivalent bispecific antibody that consists of two anti-TROP-2 Fab fragments and one anti-HSG (histamine-succinyl-glycine) Fab fragment. The TROP-2 antigen is expressed in many epithelial cancers, including prostate cancer (PC), and therefore, this bispecific antibody can be used for pretargeting of PC. In this study, the potential for pretargeted radioimmunoPET with TF12 and the (68)Ga-labeled di-HSG peptide IMP288 in mice with human PC xenografts was investigated using 2-deoxy-2-[(18)F]fluoro-D-glucose ([(18)F]FDG) as a reference.

PROCEDURES

The potential of pretargeted immunoPET with TF12 and the (68)Ga-labeled di-HSG hapten-peptide, IMP288, was studied in mice with subcutaneous PC3 tumors using [(18)F]FDG as a reference. Furthermore, the use of this pretargeting system for imaging PC lesions was evaluated in mice with intraperitoneally growing tumors with [(18)F]FDG as a reference.

RESULTS

[(68)Ga]lMP288 showed rapid accumulation in the TF12 pretargeted subcutaneous tumor (7.2 ± 1.1 % ID/g) with low uptake in the kidneys (1.8 ± 0.5 % ID/g) and high tumor-to-blood ratios (17.4 ± 11.2) at 1 h p.i. Accumulation of [(18)F]FDG in the s.c. tumors was significantly lower (3.4 ± 0.9 % ID/g, P = 0.008), with lower tumor-to-blood ratios (3.0 ± 1.9, P = 0.011). ImmunoPET/CT images clearly visualized both subcutaneous and intraperitoneal tumors as small as 5 mm(3) with low blood levels and kidney uptake as early as 1 h p.i.

CONCLUSION

Pretargeted immunoPET with TF12 in combination with a (68)Ga-labeled hapten-peptide is an efficient system for rapid, sensitive, and specific imaging of prostate cancer.

(90)Y-clivatuzumab tetraxetan with or without low-dose gemcitabine: A phase Ib study in patients with metastatic pancreatic cancer after two or more prior therapies

BACKGROUND

For patients with metastatic pancreatic adenocarcinoma, there are no approved or established treatments beyond the 2nd line. A Phase Ib study of fractionated radioimmunotherapy was undertaken in this setting, administering (90)Y-clivatuzumab tetraxetan (yttrium-90-radiolabelled humanised antibody targeting pancreatic adenocarcinoma mucin) with or without low radiosensitising doses of gemcitabine.

METHODS

Fifty-eight patients with three (2-7) median prior treatments were treated on Arm A (N=29, (90)Y-clivatuzumab tetraxetan, weekly 6.5 mCi/m(2)doses×3, plus gemcitabine, weekly 200 mg/m(2) doses×4 starting 1 week earlier) or Arm B (N=29, (90)Y-clivatuzumab tetraxetan alone, weekly 6.5 mCi/m(2)doses×3), repeating cycles after 4-week delays. Safety was the primary endpoint; efficacy was also evaluated.

RESULTS

Cytopaenias (predominantly transient thrombocytopenia) were the only significant toxicities. Fifty-three patients (27 Arm A, 26 Arm B, 91% overall) completed ⩾1 full treatment cycles, with 23 (12 Arm A, 11 Arm B; 40%) receiving multiple cycles, including seven (6 Arm A, 1 Arm B; 12%) given 3-9 cycles. Two patients in Arm A had partial responses by RECIST criteria. Kaplan-Meier overall survival (OS) appeared improved in Arm A versus B (hazard ratio [HR] 0.55, 95% CI: 0.29-0.86; P=0.017, log-rank) and the median OS for Arm A versus Arm B increased to 7.9 versus 3.4 months with multiple cycles (HR 0.32, P=0.004), including three patients in Arm A surviving >1 year.

CONCLUSIONS

Clinical studies of (90)Y-clivatuzumab tetraxetan combined with low-dose gemcitabine appear feasible in metastatic pancreatic cancer patients beyond 2nd line and a Phase III trial of this combination is now underway in this setting.