anti-CD22 Conjugate Research Articles

Strategies and Advancement in Antibody-Drug Conjugate Optimization for Targeted Cancer Therapeutics.

Antibody-drug conjugates utilize the antibody as a delivery vehicle for highly potent cytotoxic molecules with specificity for tumor-associated antigens for cancer therapy. Critical parameters that govern successful antibody-drug conjugate development for clinical use include the selection of the tumor target antigen, the antibody against the target, the cytotoxic molecule, the linker bridging the cytotoxic molecule and the antibody, and the conjugation chemistry used for the attachment of the cytotoxic molecule to the antibody. Advancements in these core antibody-drug conjugate technology are reflected by recent approval of Adectris® (anti-CD30-drug conjugate) and Kadcyla® (anti-HER2 drug conjugate). The potential approval of an anti-CD22 conjugate and promising new clinical data for anti-CD19 and anti-CD33 conjugates are additional advancements. Enrichment of antibody-drug conjugates with newly developed potent cytotoxic molecules and linkers are also in the pipeline for various tumor targets. However, the complexity of antibody-drug conjugate components, conjugation methods, and off-target toxicities still pose challenges for the strategic design of antibody-drug conjugates to achieve their fullest therapeutic potential. This review will discuss the emergence of clinical antibody-drug conjugates, current trends in optimization strategies, and recent study results for antibody-drug conjugates that have incorporated the latest optimization strategies. Future challenges and perspectives toward making antibody-drug conjugates more amendable for broader disease indications are also discussed.

Abstract 2526: Optimal cleavable linker for antibody-SN-38 conjugates for cancer therapy: Impact of linker's stability on efficacy

Abstract We reported therapeutic results of antibody (MAb) conjugates of the topo I inhibitor, SN-38, in human tumor xenografts in nude mice. These involved SN-38 derivatives, CL2-SN-38 (maleimido-[x]-Phe-Lys-PABOCO-20-O-SN-38) and its ‘Phe’-deleted variant, CL2A-SN-38. Conjugates of these derivatives showed similar serum stabilities and equivalent therapeutic efficacies. A more stably linked, cathepsin-B sensitive, derivative, CL2E-SN-38 (maleimido-[x]-Phe-Lys-PABOCO-N(Me)-(CH2)2-N(Me)-CO-10-O-SN-38) was prepared to determine the relative advantage of CL2E vs. CL2A linkers for MAb-SN-38 conjugates using MAbs with a spectrum of internalizing rates in hematological and solid tumor cell lines. Initial studies found these linkers differed in the drug-release rate from the MAb conjugates in human serum, with half-lives (t½) of ∼ 1 day for CL2A- and >10 days for CL2E-conjugates. The t½ for cathepsin-B cleavage at the lysosomal pH (pH 5) for CL2A- and CL2E-SN-38 derivatives were 10 h and 0.5 h, respectively; the CL2A linker cleavage rate at this pH was the same with or without the enzyme, indicating a pH-mediated, but cathepsin-B insensitive, drug release. The release of SN-38 from CL2E-SN-38, requiring both the cathepsin-B cleavage and an intramolecular cyclization, proceeded with an overall t½ of 10 h at pH 5, very similar to that for CL2A-SN-38, suggesting that the corresponding MAb conjugates would liberate free SN-38 at a similar rate in the lysosome. For a slowly internalizing anti-CEACAM5 MAb, hMN-14 (labetuzumab), SN-38 conjugate with the CL2A linker was superior to that with CL2E in the LS174T colonic tumor cell line and xenograft model. With a more rapidly internalizing anti-TROP-2 MAb, hRS7, IC50s for CL2A- and CL2E-SN-38 conjugates were 9 nM and 132 nM, and 20 nM and 242 nM, in the pancreatic tumor cell line, Capan-1, and the lung adenocarcinoma cell line, Calu-3, respectively. CL2A-SN-38 and CL2E-SN-38 conjugates of the fast internalizing anti-CD22 MAb, hLL2 (epratuzumab), exhibited EC50 values of 3.2 nM and 135.8 nM, respectively, in the Raji lymphoma cell line. With an anti-CD74 MAb, hLL1 (milatuzumab), which internalizes exceptionally quickly with rapid CD74 re-cycling, CL2A- and CL2E-SN-38 conjugates showed IC50 values of 5 nM and 34 nM, respectively, in the CD74-positive melanoma cell line, A-375. The IC50 for free SN-38 ranged from 0.5 nM to 7 nM in these cell lines. While specific antitumor effects against human tumor xenografts were found using CL2A-SN-38 conjugates, specificity could not be shown in a 4-day in vitro MTS assay, most likely because of the 1-day half-life for drug release. However, with hLL1-CL2E-SN-38 conjugate in the A-375 cell line, specificity was established vs. non-targeting anti-CD22 conjugate, hLL2-CL2E-SN-38. The significance of these findings will be presented, together with the data from ongoing therapy studies in xenograft models. 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 2526. doi:1538-7445.AM2012-2526

Epratuzumab–SN-38: A New Antibody–Drug Conjugate for the Therapy of Hematologic Malignancies

We previously found that slowly internalizing antibodies conjugated with SN-38 could be used successfully when prepared with a linker that allows approximately 50% of the IgG-bound SN-38 to dissociate in serum every 24 hours. In this study, the efficacy of SN-38 conjugates prepared with epratuzumab (rapidly internalizing) and veltuzumab (slowly internalizing), humanized anti-CD22 and anti-CD20 IgG, respectively, was examined for the treatment of B-cell malignancies. Both antibody-drug conjugates had similar nanomolar activity against a variety of human lymphoma/leukemia cell lines, but slow release of SN-38 compromised potency discrimination in vitro even against an irrelevant conjugate. When SN-38 was stably linked to the anti-CD22 conjugate, its potency was reduced 40- to 55-fold. Therefore, further studies were conducted only with the less stable, slowly dissociating linker. In vivo, similar antitumor activity was found between CD22 and CD20 antibody-drug conjugate in mice-bearing Ramos xenografts, even though Ramos expressed 15-fold more CD20 than CD22, suggesting that the internalization of the epratuzumab-SN-38 conjugate (Emab-SN-38) enhanced its activity. Emab-SN-38 was more efficacious than a nonbinding, irrelevant IgG-SN-38 conjugate in vivo, eliminating a majority of well-established Ramos xenografts at nontoxic doses. In vitro and in vivo studies showed that Emab-SN-38 could be combined with unconjugated veltuzumab for a more effective treatment. Thus, Emab-SN-38 is active in lymphoma and leukemia at doses well below toxic levels and therefore represents a new promising agent with therapeutic potential alone or combined with anti-CD20 antibody therapy.

Abstract 2578: Efficacy of anti-CD22 antibody drug-conjugates in Ramos and Raji tumor xenograft models

Abstract CD22 is a well-validated target for immunotherapy on B cell tumors. CD22 is a B lymphoid lineage-specific differentiation antigen, and its cell surface expression coincides with IgD expression in human. CD22 expression is upregulated on mature B cells, and is lost upon terminal differentiation to plasma cells. CD22 is also highly expressed on B cell tumors including non-Hodgkin's lymphoma (NHL) and acute lymphocytic leukemia (ALL). Antibodies to CD22 rapidly internalize, making it an ideal target for an antibody drug conjugate (ADC) therapeutic approach. Human antibodies to CD22 have been generated. The antibodies bind B cells with high affinity and are rapidly internalized upon binding. Anti-CD22 conjugates linked to highly potent synthetic DNA minor-groove binding alkylating (MGBA) agents have been prepared and tested in vivo for the treatment of established Ramos and Raji subcutaneous tumor xenografts. Anti-tumor efficacy of the anti-CD22 conjugate was highly specific in comparison with the isotype control conjugate. The anti-CD22 conjugate at a single dose of 0.3 µmole/kg resulted in regression of established subcutaneous tumors with less than 5% body weight loss and no clinical signs of toxicity. The anti-CD22 conjugate at a single dose of 0.1 µmole/kg was more efficacious than Rituximab treatment on Ramos tumors. The anti-CD22 conjugate also had better tumor growth inhibition than an anti-CD19 conjugate. In summary, anti-CD22-ADCs have been prepared which show superior in vivo efficacy to Rituximab and to anti-CD19-ADCs. 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 2578.

Non-Clinical Pharmacology of Anti-CD22 Antibody Drug Conjugates.

CD22 is a B-cell specific antigen expressed on both normal and malignant cells. It is internalized rapidly upon binding to its antibody, making it an ideal target for immunotoxin therapy. Anti-CD22 is a humanized monoclonal antibody that recognizes human and cynomolgus monkey CD22 but not the rodent CD22. When conjugated with mitotic inhibitors such as DM1 (a maytansinoid) or monomethylauristatin F (MMAF) as anti-CD22-MCC-DM1 or anti-CD22-MC-MMAF, the conjugates have been shown to regress tumors completely after a single IV bolus in a variety of xenograft mouse models. Pharmacokinetics (PK), pharmacodynamics (PD), efficacy and safety studies were conducted to explore the non-clinical pharmacology of the two anti-CD22 conjugates (ADC). Dose response of anti-tumor activity, characterized in the Bjab-Luc xenograft model, yielded an ED50 of ∼1 mg/kg for MC-MMAF. MCC-DM1 was about 2-fold less potent compared to MC-MMAF in this model. Anti-CD22 antibody demonstrated very limited antibody dependent cell mediated cytotoxicity and no complement dependent cytotoxicity in vitro. Antigen-independent pharmacokinetics were assessed in mouse (single IV bolus, 0.5 or 5 mg/kg) and rat (single IV bolus, 10 mg/kg), while the effect of target mediated disposition was studied in cynomolgus monkey (two IV bolus with three weeks apart, vehicle, 10, 20 or 30 mg/kg). Conjugation with DM1 or MMAF appeared to have minimal impact on the PK of anti-CD22 when the PK of naked anti-CD22 was compared with the total antibody PK profile in all three species. Pharmacokinetic parameters of both total antibody and ADCs were generally dose proportional at the dose range studied. Free DM1 in plasma increased with dose, while free MMAF was not detected. Safety and PD were also characterized in the cynomolgus monkey. Both ADCs were well tolerated up to 30 mg/kg through out the entire study period (42 days). For PD, B-cell depletion was analyzed via FACS. Substantial decreases of CD20+ B-cells were observed in peripheral blood at all dose levels. In tissues, reduction of CD20+ B-cells was observed in spleen, bone marrow and in the lymph nodes, although to a lesser extent. No anti-drug antibodies were detected in the cynomolgus monkey at the doses tested. Based on the preclinical data, human efficacious dose and therapeutic window were estimated to be ∼2–5 mg/kg and 5–10, respectively. In summary, both ADCs exhibit an encouraging nonclinical efficacy, pharmacokinetic, pharmacodynamic, and safety profile that supports clinical development for the potential treatment of NHL.