Sacituzumab govitecan (IMMU-132), an anti-Trop-2-SN-38 antibody-drug conjugate for the treatment of diverse epithelial cancers: Safety and pharmacokinetics.

BACKGROUND: Sacituzumab govitecan (IMMU-132), an antitrophoblastic cell-surface antigen (anti-Trop-2) humanized antibody-SN-38 conjugate, had encouraging efficacy in the phase 1 clinical trial. This report further examines the pharmacokinetics and safety of multiple cycles of IMMU-132 at doses of 8 or 10 mg/kg in patients with diverse advanced epithelial cancers. METHODS: Patients who had multiple prior therapies received IMMU-132 on days 1 and 8 of 21-day treatment cycles. Trop-2 staining of archived tumor specimens, clearance of IMMU-132 and its constituents (ie, immunoglobulin G [IgG], SN-38 [a camptothecin, the active component of irinotecan], and glucuronidated SN-38 [SN-38G]), antibody responses, and uridine diphosphate glucuronosyltransferase 1A1 (UGT1A1) levels were determined. Safety was assessed according to Common Terminology Criteria for Adverse Events version 4.0, and responses were assessed using Response Evaluation Criteria in Solid Tumors, version 1.1. RESULTS: Patients with diverse metastatic cancers who received IMMU-132 at 8 mg/kg (n = 81) and 10 mg/kg (n = 97) were examined. Trop-2 was positive in 93% of the available specimens. IMMU-132 cleared with a half-life of approximately 11 to 14 hours, reflecting the release of SN-38 from the conjugate; IgG cleared more slowly (half-life, approximately 103-114 hours). Most SN-38 in the serum (>95%) was bound to IgG. SN-38G concentrations were lower than SN-38 concentrations. Dose-limiting neutropenia after the first cycle was not correlated with SN-38 in serum or with UGT1A1 genotype. No antibody responses were detected. Objective responses were observed in several indications, including metastatic triple-negative breast cancer, confirming that 10 mg/kg produced an encouraging overall response. CONCLUSIONS: Sacituzumab govitecan has a predictable pharmacokinetic profile and manageable toxicity at doses of 8 and 10 mg/kg. With objective responses and a good therapeutic index at 10 mg/kg, this dose was chosen for future development. Cancer 2017;123:3843-3854. © 2017 American Cancer Society.

Sacituzumab Govitecan (IMMU-132), an Anti-Trop-2/SN-38 Antibody-Drug Conjugate: Characterization and Efficacy in Pancreatic, Gastric, and Other Cancers.

Sacituzumab govitecan (IMMU-132) is an antibody-drug conjugate (ADC) made from a humanized anti-Trop-2 monoclonal antibody (hRS7) conjugated with the active metabolite of irinotecan, SN-38. In addition to its further characterization, as the clinical utility of IMMU-132 expands to an ever-widening range of Trop-2-expressing solid tumor types, its efficacy in new disease models needs to be explored in a nonclinical setting. Unlike most ADCs that use ultratoxic drugs and stable linkers, IMMU-132 uses a moderately toxic drug with a moderately stable carbonate bond between SN-38 and the linker. Flow cytometry and immunohistochemistry disclosed that Trop-2 is expressed in a wide range of tumor types, including gastric, pancreatic, triple-negative breast (TNBC), colonic, prostate, and lung. While cell-binding experiments reveal no significant differences between IMMU-132 and parental hRS7 antibody, surface plasmon resonance analysis using a Trop-2 CM5 chip shows a significant binding advantage for IMMU-132 over hRS7. The conjugate retained binding to the neonatal receptor, but it lost greater than 60% of the antibody-dependent cell-mediated cytotoxicity activity compared to that of hRS7. Exposure of tumor cells to either free SN-38 or IMMU-132 demonstrated the same signaling pathways, with pJNK1/2 and p21(WAF1/Cip1) upregulation followed by cleavage of caspases 9, 7, and 3, ultimately leading to poly-ADP-ribose polymerase cleavage and double-stranded DNA breaks. Pharmacokinetics of the intact ADC in mice reveals a mean residence time (MRT) of 15.4 h, while the carrier hRS7 antibody cleared at a similar rate as that of the unconjugated antibody (MRT ∼ 300 h). IMMU-132 treatment of mice bearing human gastric cancer xenografts (17.5 mg/kg; twice weekly × 4 weeks) resulted in significant antitumor effects compared to that of mice treated with a nonspecific control. Clinically relevant dosing schemes of IMMU-132 administered either every other week, weekly, or twice weekly in mice bearing human pancreatic or gastric cancer xenografts demonstrate similar, significant antitumor effects in both models. Current Phase I/II clinical trials ( ClinicalTrials.gov , NCT01631552) confirm anticancer activity of IMMU-132 in cancers expressing Trop-2, including gastric and pancreatic cancer patients.

Improving the therapeutic index in cancer therapy by using antibody-drug conjugates designed with a moderately cytotoxic drug.

The antibody-drug conjugate (ADC), IMMU-130, of the moderately cytotoxic topoisomerase I inhibitor, SN-38, and the CEACAM5-targeted humanized antibody (mAb), labetuzumab, was evaluated in model systems of human colon carcinoma and in phase I clinical trials of heavily pretreated patients with metastatic colorectal cancer. The conjugate, designed with a near-homogeneous drug substitution of 7-8 SN-38/mAb and with a linker that released 50% of the drug in ∼20 h, showed significant antitumor effects compared to a nontargeted ADC in human tumor xenografts, which could be augmented in combination with bevacizumab. The advantage of fractionated dosing was demonstrated, with potential implications for the clinical dosing schedule. Biodistribution comparing IMMU-130 with labetuzumab showed that the conjugate cleared somewhat faster from the blood, but this did not affect tumor uptake and retention. The use of an ultrastable linker in the conjugate design abrogated antitumor effects. A tolerability study in rabbits showed a high safety margin, with no-observed-adverse-effect level (NOAEL) corresponding to a cumulative human-equivalent protein dose of 40-60 mg/kg. The preclinical findings appear to be corroborated in two phase I clinical trials, with high tolerability and evidence of antitumor activity, including objective responses. The impact of the ADC design on the utility of IMMU-130, tailored to a poorly internalizing target, is discussed.

Improving Intracellular Delivery of an Antibody-Drug Conjugate Targeting Carcinoembryonic Antigen Increases Efficacy at Clinically Relevant Doses In Vivo.

Solid tumor antibody-drug conjugates (ADC) have experienced more clinical success in the last 5 years than the previous 18-year span since the first ADC approval in 2000. While recent advances in protein engineering, linker design, and payload variations have played a role in this success, high expression and readily internalized targets have also been crucial to solid tumor therapy. However, these factors are also paradoxically connected to poor tissue penetration and lower efficacy. Previous work shows that potent ADCs can benefit from slower internalization under subsaturating doses to improve tissue penetration and increase tumor response. In contrast, faster internalization is predicted to increase efficacy under higher, tumor saturating doses. In this work, the intracellular delivery of SN-38 conjugated to an anti-carcinoembryonic antigen (anti-CEA) antibody (Ab) is increased by coadministering a noncompeting (cross-linking) anti-CEA Ab to improve efficacy in a colorectal carcinoma animal model. The SN-38 payload enables broad tumor saturation with clinically-tolerable doses, and under these saturating conditions, using a second CEA receptor cross-linking Ab yields faster internalization, which increases tumor killing efficacy. Our spheroid results show indirect bystander killing can also occur, but the more efficient direct cell killing from targeted intracellular payload release drives a greater tumor response. These results provide a strategy to increase therapeutic effectiveness with improved intracellular delivery under tumor saturating doses with the potential to expand the ADC target repertoire.

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.

Antibody-Drug Conjugate Sacituzumab Govitecan Drives Efficient Tissue Penetration and Rapid Intracellular Drug Release.

Antibody-drug conjugates (ADC) are a rapidly growing class of targeted cancer treatments, but the field has experienced significant challenges from their complex design. This study examined the multiscale distribution of sacituzumab govitecan (SG; Trodelvy), a recently clinically approved ADC, to clarify the mechanism(s) of efficacy given its unique design strategy. We employed a multiscale quantitative pharmacokinetic approach, including near-infrared fluorescence imaging, single-cell flow cytometry measurements, payload distribution via γH2AX pharmacodynamic staining, and a novel dual-labeled fluorescent technique to track the ADC and payload in a high trophoblast cell-surface antigen 2 expression xenograft model of gastric cancer (NCI-N87). We found that rapid release of the SN-38 payload from the hydrolysable linker inside cells imparts more DNA damage in vitro and in vivo than an ADC with a more stable enzyme cleavable linker. With SG, little to no extracellular payload release in the tumor was observed using a dual-labeled fluorescence technique, although bystander effects were detected. The high dosing regimen allowed the clinical dose to reach the majority of cancer cells, which has been linked to improved efficacy. In addition, the impact of multiple doses (day 1 and day 8) of a 21-day cycle was found to further improve tissue penetration despite not changing tumor uptake [percent injected dose per gram (%ID/g)] of the ADC. These results show increased ADC efficacy with SG can be attributed to efficient tumor penetration and intracellular linker cleavage after ADC internalization. This quantitative approach to study multiscale delivery can be used to inform the design of next-generation ADCs and prodrugs for other targets.

New antibody conjugates in cancer therapy.

Targeting of radiation, drugs, and protein toxins to cancers selectively with monoclonal antibodies (MAbs) has been a topic of considerable interest and an area of continued development. Radioimmunotherapy (RAIT) of lymphoma using directly labeled MAbs is of current interest after approval of two radiolabeled anti-CD20 MAbs, as illustrated with the near 100% overall response rate obtained in a recent clinical trial using an investigational radiolabeled anti-CD22 MAb, 90Y-epratuzumab. The advantage of pretargeted RAIT over directly labeled MAbs is continuing to be validated in preclinical models of lymphoma and solid tumors. Importantly, the advantages of combining RAIT with radiation sensitizers, with immunotherapy, or a drug conjugate targeting a different antigen are being studied clinically and preclinically. The area of drug-conjugated antibodies is progressing with encouraging data published for the trastuzumab-DM1 conjugate in a phase I clinical trial in HER2-positive breast cancer. The Dock-and-Lock platform technology has contributed to the design and the evaluation of complex antibody-cytokine and antibody-toxin conjugates. This review describes the advances made in these areas, with illustrations taken from advances made in the authors' institutions.

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.].

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.

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.

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

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

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 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.

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.

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.

Advantage of a residualizing iodine radiolabel in the therapy of a colon cancer xenograft targeted with an anticarcinoembryonic antigen monoclonal antibody.

PURPOSE: A disadvantage of conventionally radioiodinated monoclonal antibodies (mAb) for cancer therapy is the short retention time of the radionuclide within target cells. To address this issue, we recently developed a method in which radioiodine is introduced onto antibodies using an adduct consisting of a nonmetabolizable peptide attached to the aminopolycarboxylate diethylenetriaminepentaacetic acid, designated IMP-R4. This adduct causes the radioiodine to become trapped in lysosomes following antibody catabolism. Clinical-scale production of 131I-IMP-R4-labeled antibodies is possible using a recently developed facile method. EXPERIMENTAL DESIGN: The properties of 131I-IMP-R4-labeled anticarcinoembryonic antigen (CEA) humanized mAb hMN-14 were compared with the directly radioiodinated hMN-14 (131I-hMN-14) in CEA-expressing human colon cancer cell lines, LoVo and LS174T, and in nude mice bearing established LoVo tumor xenografts. RESULTS: 125I-IMP-R4-hMN-14 retention in the cell lines was significantly increased (61.5% after 3 days) compared with 125I-hMN-14. In vivo, a significant improvement in tumor accretion of radiolabel was obtained using 131I-IMP-R4-hMN-14, which led to a marked improvement in therapeutic efficacy. Eight weeks post-treatment, mean tumor volumes were 0.16 +/- 0.19 and 1.99 +/- 1.35 cm3 in mice treated with 131I-IMP-R4-hMN-14 and 131I-hMN-14, respectively, with complete remissions observed in 27% of mice treated with 131I-IMP-R4-hMN-14 and none using 131I-hMN-14. CONCLUSION: 131I-IMP-R4-hMN-14 provides a significant therapeutic advantage in comparison to the conventionally 131I-labeled antibody. The ability of this labeling method to lend itself to clinical-scale labeling, the broad applicability of a humanized anti-CEA mAb for CEA-expressing cancers, and the clinical benefits of radioimmunotherapy with anti-CEA mAb shown recently for small-volume and minimal residual disease combine to make 131I-IMP-R4-hMN-14 a promising new agent for radioimmunotherapy.

Anti-CD74 antibody-doxorubicin conjugate, IMMU-110, in a human multiple myeloma xenograft and in monkeys.

PURPOSE: IMMU-110 is a drug immunoconjugate composed of doxorubicin conjugated to the humanized anti-CD74 monoclonal antibody, hLL1, at a doxorubicin/monoclonal antibody ratio of approximately 8:1 (mol/mol). CD74 is a rapidly internalizing molecule associated with HLA-DR, which has high expression by several tumor types. Here, we describe safety evaluations of IMMU-110 in mice and monkeys as well as efficacy studies in a xenograft model of the human multiple myeloma cell line, MC/CAR. EXPERIMENTAL DESIGN: In vitro binding of IMMU-110 was determined by a cell-based ELISA and cytotoxicity of IMMU-110 assayed with a tetrazolium assay. Pharmacokinetics and biodistribution of radiolabeled IMMU-110 were examined in tumor-free BALB/c mice, and the therapeutic effectiveness was evaluated in severe combined immunodeficient mice bearing MC/CAR cells. Acute toxicity of IMMU-110 was studied in CD74-positive cynomolgus monkeys (Macaca fascicularis). RESULTS: In vitro, IMMU-110 specifically binds to CD74 and is cytotoxic against MC/CAR cells. In vivo, IMMU-110 displayed a pharmacokinetic and biodistribution profile identical to that of unconjugated hLL1 monoclonal antibody, except for higher kidney uptake. Treatment with a single dose of IMMU-110 as low as 50 microg antibody/mouse (or 1.4 microg doxorubicin/mouse), 5 days postinjection of the multiple myeloma cells, resulted in cure of most mice. In mice, no host toxicity of IMMU-110 was observed at the highest protein dose tested (125 mg/kg). In cynomolgus monkeys, bone marrow toxicity was observed at 30 and 90 mg/kg doses. CONCLUSIONS: The excellent safety and efficacy profile of IMMU-110 supports clinical testing of this immunoconjugate in the treatment of CD74-positive B-cell malignancies.

Improved iodine radiolabels for monoclonal antibody therapy.

A major disadvantage of (131)iodine (I)-labeled monoclonal antibodies (MAbs) for radioimmunotherapy has been the rapid diffusion of iodotyrosine from target cells after internalization and catabolism of the radioiodinated MAbs. We recently reported that a radioiodinated, diethylenetriaminepentaacetic acid-appended peptide, designated immunomedics' residualizing peptide 1 (IMP-R1), was a residualizing iodine label that overcame many of the limitations that had impeded the development of residualizing iodine for clinical use. To determine the factors governing the therapeutic index of the labeled MAb, as well as the factors required for production of radioiodinated MAb in high yield and with high specific activity, variations in the peptide structure of IMP-R1 were evaluated. A series of radioiodinated, diethylenetriaminepentaacetic acid-appended peptide moieties (IMP-R1 through IMP-R8) that differed in overall hydrophilicity and charge were compared. Radioiodinations of the peptides followed by conjugations to disulfide-reduced RS7 (an anti-epithelial glycoprotein-1 MAb) furnished radioimmunoconjugates in good overall incorporations, with immunoreactivities comparable to that of directly radioiodinated RS7. Specific activities of up to 8 mCi/mg and yields > 80% have been achieved. In vitro processing experiments showed marked increases in radioiodine retention with all of the adducts; radioiodine retention at 45 h was up to 86% greater in cells than with directly iodinated RS7. Each of the (125)I-peptide-RS7 conjugates was compared with (131)I-RS7 (labeled by the chloramine-T method) in paired-label biodistribution studies in nude mice bearing human lung tumor xenografts. All of the residualizing substrates exhibited significantly enhanced retention in tumor in comparison to directly radioiodinated RS7, but the nontarget uptakes differed significantly among the residualizing labels. The best labels were IMP-R4 and IMP-R8, showing superior tumor-to-non-tumor ratios by virtue of high tumor uptake and retention and low normal organ uptake, as well as superior radiochemical properties. The therapeutic efficacy of (131)I-IMP-R4-RS7 was compared with that of conventionally (131)I-labeled RS7 and (90)yttrium-RS7 in the nude mice lung cancer model. The therapeutic efficacy of (131)I-IMP-R4-RS7 and (90)yttrium-RS7 were equivalent, and both agents yielded significantly improved control of tumor growth compared with conventional (131)I-labeled RS7.

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.