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.

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

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

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

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

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

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

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

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

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

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

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

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

Phase I study of dasatinib in combination with capecitabine, oxaliplatin, and bevacizumab followed by an expanded cohort in previously untreated metastatic colorectal cancer

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Background: SRC is a non-receptor tyrosine kinase involved in normal and tumor cell signaling functions including cell proliferation, angiogenesis and survival. Dasatinib (D) is a potent inhibitor of SRC kinase activity. Preclinical data suggests the addition of D to standard chemotherapy agents for colon cancer may increase anti-tumor activity. We evaluated D in combination with capecitabine (C), oxaliplatin (O) and bevacizumab (B) in a phase I dose escalation study followed by an expanded cohort in 1st line colorectal.

Methods: For dose escalation, eligible patients had advanced solid tumors with adequate organ and bone marrow function and no increased risk for class-related toxicities. B and O were given intravenously, and C and D were orally administered; cycle length was 21 days. C was dosed at 850 mg/m2 on days 1-14; O was dosed at 130 mg/m2 and B was dosed at 7.5 mg/kg on day one of each cycle. D was dosed at 50 mg twice daily in cohort one and 70 mg once daily in cohort -1. Dose limiting toxicity (DLT) was assessed in cycle 1.

Results: Dose escalation is complete with 10 subjects evaluable for toxicity and 11 subjects evaluable for efficacy. Two DLTs were observed out of 5 evaluable subjects in cohort one. Six evaluable subjects were enrolled in the -1 cohort with 1 DLT. Possible grade ≥ 3 treatment-related adverse events (AEs) included neutropenia, febrile neutropenia, anorexia, diarrhea, fatigue, anemia, hypophosphatemia, hyponatremia and grade 5 GI-perforation. One non-treatment related death was due to disease progression. D-related nausea and fatigue were responsive to low dose oral steroids; fluid retention was responsive to diuretics. Of 10 subjects evaluable for efficacy, 1 subject had a partial response (PR), 2 had a minor response (MR), and 4 had stable disease (SD). Four subjects had disease control (PR, MR, or SD) ≥ 6 months.

Conclusions: D in combination with C, O and B is well-tolerated with a toxicity profile similar to standard C, O and B.The recommended phase II dose is C at 850 mg/m2 on days 1-14, O at 130 mg/m2 and B at 7.5 mg/kg on day one of each cycle, and D at 70 mg once daily. Enrollment in the expanded cohort of 1st line colorectal is ongoing.

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Dual inhibition of αV integrins and Src kinase activity in colon cancer cells

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Background: Integrins are commonly upregulated in tumor cells and are important regulators of invasion and metastasis. Integrin signaling is initiated upon engagement of ECM and requires Src as well as various other proteins including ILK, FAK, and paxillin. Methods: Presence of αv integrins on CRC cell lines was established by flow cytometry. CNTO 95 (10μg/ml, a monoclonal anti-αv integrin antibody; Ortho Biotech), and dasatinib (<200nM; BMS, src small molecule inhibitor) were used to study the effects of combined integrin and src inhibition on proliferation and serum-induced migration of colon cancer cell lines in vitro. Downstream signaling changes were assessed by immunoblotting for phosphorylated forms of src, FAK (Y397, Y576/577 and Y925), paxillin, GSK3β and AKT (S473) in HT29, HCT116 and RKO. Results: Proliferation was inhibited by dasatinib in HT29, HCT116, DLD1 and HCT15 in a dose-dependent manner, while RKO and SW48 were resistant. Combining CNTO 95 with dasatinib further inhibited proliferation in all dasatinib-sensitive cells, yet resistant cells were unaffected. Migration was blocked by both CNTO 95 and dasatinib in all cell lines, and combining the two drugs produced augmented effect. Src activation and src- dependent FAK phosphorylation at sites 576 and 925 were blocked by dasatinib; CNTO 95 had little effect alone, but potentiated the effect of dasatinib. Paxillin phosphorylation was modestly blocked by both compounds, but the combination produced significantly augmented inhibition in the three cell lines tested. The phosphorylation status of AKT and GSK-3β, which are downstream of ILK, was inhibited by both drugs as single agents. The combination of dasatinib and CNTO 95 produced further inhibition. Conclusions: Dual inhibition of Src by dasatinib and αv integrins by CNTO 95 produced additive to synergistic inhibition of proliferation in dasatinib sensitive CRC cell lines, and inhibition of migration in all cell lines tested. Decreased phospho-paxillin levels may be responsible for the pronounced inhibition of migration observed after dual treatment with dasatinib and CNTO 95 in these CRC cell lines. These data support the rationale for combined Src/integrin inhibition in colon cancer, and further suggest approaches to patient selection strategies.

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