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Purpose: Evaluate the efficacy of an SN-38-anti-Trop-2 antibody–drug conjugate (ADC) against several human solid tumor types, and to assess its tolerability in mice and monkeys, the latter with tissue cross-reactivity to hRS7 similar to humans.Experimental Design: Two SN-38 derivatives, CL2-SN-38 and CL2A-SN-38, were conjugated to the anti-Trop-2–humanized antibody, hRS7. The immunoconjugates were characterized in vitro for stability, binding, and cytotoxicity. Efficacy was tested in five different human solid tumor-xenograft models that expressed Trop-2 antigen. Toxicity was assessed in mice and in Cynomolgus monkeys.Results: The hRS7 conjugates of the two SN-38 derivatives were equivalent in drug substitution (∼6), cell binding (Kd ∼ 1.2 nmol/L), cytotoxicity (IC50 ∼ 2.2 nmol/L), and serum stability in vitro (t/½ ∼ 20 hours). Exposure of cells to the ADC demonstrated signaling pathways leading to PARP cleavage, but differences versus free SN-38 in p53 and p21 upregulation were noted. Significant antitumor effects were produced by hRS7-SN-38 at nontoxic doses in mice bearing Calu-3 (P ≤ 0.05), Capan-1 (P P P Conclusions: The anti-Trop-2 hRS7-CL2A-SN-38 ADC provides significant and specific antitumor effects against a range of human solid tumor types. It is well tolerated in monkeys, with tissue Trop-2 expression similar to humans, at clinically relevant doses, and warrants clinical investigation. Clin Cancer Res; 17(10); 3157–69. ©2011 AACR.

Supplementary Figures S1-S2; Supplementary Materials and Methods; Supplementary Tables S1-S2.

Mutations in the kinase binding domain of BTK at position C481 are associated with resistance to BTK inhibitor (BTKi) therapy in chronic lymphocytic leukemia (CLL). Nearly half of patients manifesting clinical progression with these alterations exhibit a subclonal burden of resistance. Intriguingly, measured BTKC481 variant allelic fractions (VAF) are commonly lower than 10% [Ahn et al, Blood 2017]. This raises the important question of how BTKC481-mutated (MUT) and wildtype (WT) cells differ in their response to therapeutic challenge, and how low-burden MUT subclones facilitate escape from therapy. While the admixture of MUT and WT cells within the same individual presents an opportunity to directly study the downstream effects of subclonal resistance mutations, these cells cannot be separated through sorting. To overcome this limitation, we utilized Genotyping of Transcriptomes (GoT)-a strategy to jointly capture genotyping of a locus of interest together with whole transcriptomes at the single cell level (Fig. 1A). Importantly, GoT eliminates patient-specific and technical confounders, enabling direct linkage of BTK genotypes to transcriptional phenotypes. We applied GoT to 64,099 CD19+ cells across a cohort of seven patients with clinically progressive CLL found to have low-burden BTKC481 subclones (Fig. 1B). Samples were obtained at the time of progression and were screened for mutations in PLCG2. We genotyped 33.3% of cells, consistent with 34.0% of cells expressing BTK in whole transcriptome data. Clustering of the gene expression profiles showed that MUT and WT clones did not segregate by genotype in most (6/7) patients (Fig. 1C), implying a large degree of transcriptional similarity between MUT and WT cells, and further highlighting the need for multi-omics single-cell sequencing to directly link genotype to phenotype in this context. We note that the single exception with distinct genotypic clustering (CLL06, Fig. 1D) was driven by co-occurring large chromosomal aberrations within the MUT cells, including del(8p), which is associated with BTKi resistance [Burger et al, Nat Comm 2016]. CLL cells are known to cycle between the peripheral blood and protective microenvironmental niches, which is a process modulated by BTKi. We applied CXCR4/CD5 expression as a read out to these migration patterns [Chen et al, Leukemia 2016], and observed that MUT cells were comparatively enriched in CXCR4lowCD5hi CLL, which is associated with recent emigration from the stromal niche and increased BCR signaling (Fig. 1E). Conversely, WT cells were the majority of CXCR4hiCD5low CLL, which is associated with a resting peripheral cellular state and BCR downregulation, suggesting WT quiescence with limited stromal support. To explore the phenotypic changes associated with BTK mutations, we first measured the activity of reported BTKi response expression signatures. WT cells showed higher mean response scores compared to MUT (Fig. 1F), demonstrating that the WT cells preserve BTKi responsiveness. To unbiasedly interrogate transcriptional differences, we applied a set of 336 predefined gene modules representing B-cell cellular functions and processes. Enriched modules in MUT cells implicated restoration of B-cell receptor (BCR) signaling and recovery of CLL cell identity (NF-kB, IRF4, CD40, Fig. 1G), a finding also supported by de novo differential gene expression analysis (Fig. 1H), and gene set enrichment of differentially expressed genes (Fig. 1I). In contrast, WT cells showed increases in modules related to quiescence, hypoxia, cellular stress (HIF-1α, XBP1) and terminal B-cell development (Blimp-1). Intriguingly, changes in gene targets associated with restoration of NOTCH1 and IL4 activity were also observed. As these pathways are impaired in patients responding to BTKi and implicated in resistance [Del Papa et al, CCR 2019; Chen et al, ASH 2019], their re-emergence may reflect a cytoprotective strategy. In summary, we utilized multi-omics single-cell sequencing to identify the distinct transcriptional programs of admixed MUT and WT cells in subclonal BTKC481 progression. MUT cells showed robust escape from BTKi inhibition via increased immune receptor signaling and restoration of CLL cell identity program, while WT cells demonstrated a signature of hypoxia and stress response, with NOTCH1 and IL4 activation implicated as mechanisms of clonal persistence. Disclosures Trisal: Celgene: Current Employment, Current equity holder in publicly-traded company. Gandhi:Celgene: Current Employment, Current equity holder in publicly-traded company. Wiestner:Pharmacyclics LLC, an AbbVie Company, Acerta, Merck, Nurix, Verastem, and Genmab: Research Funding; NIH: Patents & Royalties: NIH. Allan:Acerta, Genentech, Abbvie, Sunesis, Ascentage, Pharmacyclics, Janssen, AstraZeneca, BeiGene: Consultancy; Celgene, Genentech, Janssen, TG Therapeutics: Research Funding; Abbvie, Janssen, AstraZeneca, Pharmacyclics: Honoraria. Furman:Genentech: Consultancy; Beigene: Consultancy; AstraZeneca: Consultancy, Research Funding; Acerta: Consultancy; Verastem: Consultancy; Pharmacyclics: Consultancy; TG Therapeutics: Consultancy, Research Funding; Incyte: Consultancy; Janssen: Consultancy, Speakers Bureau; Oncotarget: Consultancy; Loxo Oncology: Consultancy; Abbvie: Consultancy; Sunesis: Consultancy. Landau:Bristol Myers Squibb: Research Funding; Illumina: Research Funding.

International audience; Chemotherapy plus rituximab has been the mainstay of treatment for follicular lymphoma (FL) for two decades but is associated with immunosuppression and relapse. In phase 2 studies, lenalidomide combined with rituximab (R 2 ) has shown clinical synergy in front-line and relapsed/refractory FL. Here, we show that lenalidomide reactivated dysfunctional T and Natural Killer (NK) cells ex vivo from FL patients by enhancing proliferative capacity and T-helper cell type 1 (Th1) cytokine release. In combination with rituximab, lenalidomide improved antibody-dependent cellular cytotoxicity in sensitive and chemo-resistant FL cells, via a cereblon-dependent mechanism. While single-agent lenalidomide and rituximab increased formation of lytic NK cell immunological synapses with primary FL tumour cells, the combination was superior and correlated with enhanced cytotoxicity. Immunophenotyping of FL patient samples from a phase 3 trial revealed that R 2 treatment increased circulating T- and NK-cell counts, while R-chemotherapy was associated with reduced cell numbers. Finally, using an in vitro model of myeloid differentiation, we demonstrated that lenalidomide caused a reversible arrest in neutrophil maturation that was distinct from a cytotoxic chemotherapeutic agent, which may help explain the lower rates of neutropenia observed with R 2 versus R-chemotherapy. Taken together, we believe these data support a paradigm shift in the treatment of FL – moving from combination immunochemotherapy to chemotherapy-free immunotherapy. © 2019 The Authors. British Journal of Haematology published by British Society for Haematology and John Wiley and Sons Ltd.

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.

Purpose: Evaluate the efficacy of an SN-38-anti-Trop-2 antibody–drug conjugate (ADC) against several human solid tumor types, and to assess its tolerability in mice and monkeys, the latter with tissue cross-reactivity to hRS7 similar to humans. Experimental Design: Two SN-38 derivatives, CL2-SN-38 and CL2A-SN-38, were conjugated to the anti-Trop-2–humanized antibody, hRS7. The immunoconjugates were characterized in vitro for stability, binding, and cytotoxicity. Efficacy was tested in five different human solid tumor-xenograft models that expressed Trop-2 antigen. Toxicity was assessed in mice and in Cynomolgus monkeys. Results: The hRS7 conjugates of the two SN-38 derivatives were equivalent in drug substitution (∼6), cell binding (Kd ∼ 1.2 nmol/L), cytotoxicity (IC50 ∼ 2.2 nmol/L), and serum stability in vitro (t/½ ∼ 20 hours). Exposure of cells to the ADC demonstrated signaling pathways leading to PARP cleavage, but differences versus free SN-38 in p53 and p21 upregulation were noted. Significant antitumor effects were produced by hRS7-SN-38 at nontoxic doses in mice bearing Calu-3 (P ≤ 0.05), Capan-1 (P Conclusions: The anti-Trop-2 hRS7-CL2A-SN-38 ADC provides significant and specific antitumor effects against a range of human solid tumor types. It is well tolerated in monkeys, with tissue Trop-2 expression similar to humans, at clinically relevant doses, and warrants clinical investigation. Clin Cancer Res; 17(10); 3157–69. ©2011 AACR.

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.

Background Advanced or metastatic renal cell carcinoma (RCC) has a poor prognosis, because it is relatively resistant to conventional chemotherapy or radiotherapy. Treatments with human interferon-α2b alone or in combination with mammalian target of rapamycin (mTOR) inhibitors have led to only a modest improvement in clinical outcome. One observation made with mTOR inhibitors is that carcinomas can overcome these inhibitory effects by activating the insulin-like growth factor-I (IGF-I) signaling pathway. Clinically, there is an association of IGF-I receptor (IGF-IR) expression in RCC and poor long-term patient survival. We have developed a humanized anti-IGF-IR monoclonal antibody, hR1, which binds to RCC, resulting in effective down-regulation of IGF-IR and moderate inhibition of cell proliferation in vitro. In this work, we evaluate the anti-tumor activity of two novel IGF-1R-targeting agents against renal cell carcinoma given alone or in combination with an mTOR inhibitor. Methods hR1 was linked by the DOCK-AND-LOCK™ (DNL™) method to four Fabs of hR1, generating Hex-hR1, or to four molecules of interferon-α2b, generating 1R-2b. Eight human RCC cell lines were screened for IGF-1R expression and sensitivity to treatment with hR1 in vitro. Synergy with an mTOR inhibitor, temsirolimus, was tested in a cell line (ACHN) with low sensitivity to hR1. Results Hex-hR1 induced the down-regulation of IGF-IR at 10-fold lower concentrations compared to the parental hR1. Sensitivity to growth inhibition mediated by hR1 and Hex-hR1 treatments correlated with IGF-1R expression (higher expression was more sensitive). The potency of 1R-2b to inhibit the in vitro growth of RCC was also demonstrated in two human cell lines, ACHN and 786-O, with EC50–values of 63 and 48 pM, respectively. When combined with temsirolimus, a synergistic growth-inhibition with hR1, Hex-hR1, and 1R-2b was observed in ACHN cells at concentrations as low as 10 nM for hR1, 1 nM for Hex-hR1, and 2.6 nM for 1R-2b. Conclusions Both Hex-hR1 and 1R-2b proved to be more potent than parental hR1 in inhibiting growth of RCC in vitro. Synergy was achieved when each of the three hR1-based agents was combined with temsirolimus, suggesting a new approach for treating RCC.

Among kidney cancer types, approximately 90% are renal cell carcinomas (RCC). Advanced or metastatic RCC, which presents in about one third of the patients, has a poor prognosis as it is resistant to conventional chemotherapy or radiotherapy. Treatments with human interferon-α2b (IFN-γ2b) alone or in combination with mammalian target of rapamycin (mTOR) inhibitors have led to only modest improvements in clinical outcomes. One observation made with mTOR inhibitors is that cancer cells can overcome the effects of the inhibitor by activating the insulin-like growth factor-I (IGF-I) signaling pathways. Clinically, there is an association of IGF-I receptor (IGF-IR) expression in RCC and poor long-term patient survival, particularly among patients with high-grade tumors. We have developed a humanized anti-IGF-IR monoclonal antibody, hR1, which binds to multiple tumor types, including RCC, resulting in effective down-regulation of IGF-IR and moderate inhibition of cell proliferation in vitro. To enhance the anti-tumor activity of hR1, we applied the Dock-and-Lock (DNL) platform technology to generate 1R-2b, comprising a conjugate of hR1 IgG with two dimers of interferon-α2b, and Hex-hR1, comprising 6 Fab fragments of hR1 tethered onto a common Fc. There was no loss in cell binding for both 1R-2b and Hex-hR1 when compared to parental hR1 as determined by flow cytometry. Units of activity for 1R-2b as measured by a luciferase reporter gene fused to a promoter containing the interferon-stimulated response element (iLite kit), yielded a specific activity of 3750 U/pmole versus 180 U/pmole and 3255 U/pmole for two different forms of peginterferon alpha-2a (60 and 31 kDa), respectively. An in vitro cytotoxicity assay with1R-2b demonstrated growth inhibition of two different RCC cell lines, 786-0 and ACHN with EC50-values of 0.049 and 0.062 pmole/mL, respectively. In terms of receptor down-regulation, Hex-hR1 could effectively down-regulate IGF-IR at concentrations 10-fold lower than parental hR1 IgG. In soft-agar growth assays, all three agents (hR1, Hex-hR1 and 1R-2b) could significantly inhibit colony formation of 786-0 and ACHN (P Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4402. doi:1538-7445.AM2012-4402

Background Combination therapy using two different monoclonal antibodies to achieve improved efficacy without increased toxicity is being pursued in various preclinical and clinical studies but, in principle, could be accomplished with a single bispecific antibody (bsAb). We note the elevated expression of the type-I insulin-like growth factor receptor (IGF-1R) and the trophoblast cell-surface marker (Trop-2) in diverse epithelial tumors, including breast cancers, and the increasing evidence of their correlation with poor survival. Therefore, we chose to explore the potential of 1R-(E1)-(E1), the bispecific HexAb constructed from hR1 (humanized anti-IGF-1R) and hRS7 (humanized anti-Trop-2) for treating breast cancers. Methods: 1R-(E1)-(E1) was generated by the Dock-and-Lock (DNL) method to comprise a full IgG of hR1 linked to two stabilized dimers of hRS7 Fab, and evaluated in three HER2−negative breast cancer cell lines: the non-evasive MCF-7, the moderately invasive MDA-MB-468, and the highly invasive MDA-MB-231. The in vitro characterizations of 1R-(E1)-(E1) included flow cytometry to determine cell binding, soft agar assay to evaluate the effect on anchorage-independent growth, and BD matrigel chambers to assess invasion properties. Statistical differences (P values) between two populations were determined by Student's t-test. Results: All three cell lines were found to express both IGF-1R and Trop-2, with MCF-7 and MDA-MB-468 notably higher in IGF-1R and Trop-2, respectively. As expected, 1R-(E1)-(E1) bound to all three cell lines. At 50 μg/mL, 1R-(E1)-(E1) reduced the invasion of MDA-MB-468 to less than 10% of the untreated control, whereas under the same conditions, MDA-MB-231 appeared to be resistant, while the parental antibodies showed no effects. The ability of 1R-(E1)-(E1) to inhibit anchorage-independent growth was demonstrated at 200 nM in MDA-MB-231, with a statistically significant difference (P Conclusions: These promising results warrant further evaluation of 1R-(E1)-(E1) in other breast cancer cell lines, as well as the exploration of new bispecific HexAbs that comprise different antibodies capable of targeting other solid cancers. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P3-02-01.

Antibody drug conjugates (ADCs) of the topoisomerase I inhibitor, SN-38, that allowed for a slow release of SN-38 from the ADC over time, were prepared using anti-CEACAM5 MAb, labetuzumab (hMN-14), anti-TROP-2 MAb, hRS7, and other MAbs by thiol-maleimide conjugation chemistry. These were shown previously to have significant anti-tumor activity in human cancer-xenograft models at cumulative doses frequently ≤ 100 mg/kg (≤ 8 mg/kg human equivalent dose; HED) without toxicity. To determine tolerability and dose-limiting toxicity, hRS7-SN-38 was examined in Swiss-Webster (S-W) mice and Cynomolgus monkeys (CMs), and labetuzumab-SN-38 was evaluated in New Zealand White rabbits. CMs do not express CEACAM5, but similarity in tissue cross-reactivity of hRS7 renders toxicity evaluation of hRS7-SN-38 conjugates in CM feasible. Male S-W mice (n = 14; ∼ 40 g) were administered i.p with 0 (control), 250, 500, or 750 mg/kg (0, 4, 8, and 12 mg/kg SN-38 equivalents) of hRS7-SN-38 on days 1 and 4. Half of the animals were necropsied 7 d, and the remainder 15 d, after the last dose. Blood counts, serum chemistry, and histopathology were performed. This ADC was also administered to CMs (3 M + 3 F/group), via i.v. infusion, at 0, 60, or 120 mg/kg (0, 0.96 and 1.92 mg/kg SN-38 equivalents, respectively) on days 1 and 4. Two males and 2 females from each group were euthanized and necropsied day 11, while the remaining animals were terminated on day 32. Blood counts and chemistries were collected pre-study and periodically through termination. The labetuzumab-SN-38 conjugate was examined in rabbits (n = 6-10) at 0, 30, 60, and 90 mg/kg, administered on days 1 and 4. Mice experienced no hematopoietic toxicity, and only transient weight loss of Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3619. doi:10.1158/1538-7445.AM2011-3619

Rap, a single-chain ribonuclease originally isolated from the oocytes of Rana pipiens, exhibits cytostatic and cytotoxic effects on a variety of tumor cell lines in vitro, as well as antitumor activity in vivo. Rap enters cells via receptor-mediated endocytosis and selectively degrades tRNA, resulting in inhibition of protein synthesis and induction of apoptosis. Rap was reported to exhibit reversible dose-limiting renal toxicity and no immunogenicity in cancer patients. The Dock-and-Lock (DNL) method was applied to generate a novel class of immunotoxins, each of which contains 4 copies of Rap site-specifically linked to an IgG (MAb-Rap). We combined Rap-DDD2, a dimeric fusion protein comprising Rap and a dimerization and docking domain (DDD), with several IgG-AD2 modules, which comprise two anchor domain (AD) peptides fused to the carboxyl termini of the heavy chains. The DNL method allowed the rapid synthesis of 22-Rap, 20-Rap, C2-Rap and 74-Rap, which target B-cell lymphoma via CD22 (epratuzumab), CD20 (veltuzumab), HLA-DR (MAb hL243) and CD74 (milatuzumab), respectively. The parental MAbs/antigens vary with respect to internalization rate, antigen density and cytotoxicity. A non-targeting control construct, 14-Rap, was derived from a MAb to CEACAM5 (hMN-14), which is not expressed on NHL. The Rap-DDD2 module was expressed in E. coli as inclusion bodies, which were purified by immobilized metal affinity chromatography and efficiently refolded. The IgG-AD2 modules were expressed in myeloma cells and purified from the culture supernatant using Protein A affinity chromatography. MAb-Rap was prepared by mixing the IgG-AD2 modules with the Rap-DDD2 module under mild redox conditions and purified to near homogeneity in a single step using Protein A affinity chromatography. SE-HPLC, RP-HPLC and SDS-PAGE analyses showed that preparations of each MAb-Rap are nearly homogeneous and consistent with a covalent structure of ∼230 kDa, indicative of an IgG and 4 Rap groups. Results of in vitro cytotoxicity assays using several NHL lines demonstrated that each NHL-targeting MAb-Rap was highly cytotoxic, resulting in nearly 100% cell killing at ≥1 nM. In comparison, 14-Rap at 30 nM resulted in only modest (10-40%) inhibition of proliferation for most of the cell lines tested. Interestingly, 14-Rap was considerably more potent than recombinant Rap in some cell lines, suggesting that the multiple copies of Rap may facilitate internalization of MAb-Rap. We are currently investigating the significance of internalization rate and antigen density. The DNL method provides a modular approach to efficiently tether multiple cytotoxins onto a targeting antibody, resulting in novel immunotoxins that are expected to show higher in vivo potency due to improved pharmacokinetics and targeting specificity. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5345.

Background: IFN-α2 is indicated for the therapy of hairy cell leukemia, chronic myelogenous leukemia, follicular lymphoma, and malignant melanoma. As is the case for most cytokines, the pharmacokinetic (PK) properties of IFN-α2 are critical for dosing and efficacy. In vivo, the protein is quickly degraded, diffuses widely throughout the body, and has a rapid rate of renal clearance. Pegylation of IFN-α2 significantly increases the serum half-life and reduces renal clearance, thus enhancing its efficacy. However, established pegylation of IFN-α2 results in a mixture of positional isomers and reduced in vitro activity, as known for PEGASYS (Roche) and PEG-INTRON (Schering-Plough). Methods: To improve the PK properties and the potency, the DNL method (Rossi et al. Proc. Natl. Acad. Sci. USA, 2006,103:6841) was used to generate novel agents having two copies of IFN-α2b conjugated to polyethylene glycol (PEG). Results: A fusion protein (DDD2-IFN-α2b) composed of IFN-α2b with a dimerization-and-docking domain (DDD2) and a six-His tag was expressed both in myeloma cells and in E. coli. Two PEG-based modules, each composed of a fluorescent molecule, an anchor domain (AD) and either a 20-kDa PEG (IMP362) or a 30-kDa PEG (IMP413), were synthesized. Combining DDD2-IFN-α2b and IMP362 or IMP413 under redox conditions resulted in the desirable DNL conjugates consisting of two copies of IFN-α2b and one PEG linked site-specifically via the DDD and AD interaction. The cytotoxic activity of DDD2-IFN-α2b on Daudi lymphoma cells was similar to that of commercially available recombinant IFN-α2 (rhIFN-α2). The purity and identity of the two DNL conjugates (α2b-413 and α2b-362) were demonstrated by SDS-PAGE, immunoblotting, and fluorescence imaging. Both also showed potent cytotoxic activity on Daudi cells in vitro and superior PK properties to PEG-INTRON. For example, the mean blood residence times for α2b-362 (10.3 h) and α2b-413 (21.7 h) were significantly longer than those of rhIFN-α2 (0.7 h) and PEG-INTRON (5.1 h). Initial studies in mice bearing Daudi xenografts showed a significant therapeutic advantage over PEG-INTRON for both α2b-362 and α2b-413. Animals given 14,000 IU of PEG-INTRON had a median survival (MS) of 32 days compared to 21 days for saline control, whereas those receiving α2b-362 at 14,000 IU, 7,000 IU and 3,500 IU resulted in MS of 45, 41 and 32 days, respectively. More remarkably, α2b-413 was the most effective, achieving MS of 46, >53, and >53 days with 3,500 IU, 7,000 IU and 14,000 IU, respectively, all statistically significant improvements (P< 0.0028) compared to PEG-INTRON given at each equivalent activity. Conclusions: The DNL method provides a novel pegylation strategy for generating a dimeric IFN-α2b that is linked site-specifically to a single PEG at the predetermined location. Since the resulting conjugates exhibit improved PK and efficacy in a Burkitt lymphoma model, they may represent a new class of interferons for use in cancer and infectious disease therapy.