Selective tumor sensitization to taxanes with the mAb-drug conjugate cBR96-doxorubicin

Abstract

The chimeric monoclonal antibody cBR96 conjugated to doxorubicin (cBR96-Dox) is selectively internalized by a wide variety of human carcinomas expressing an extended form of Lewis Y antigen (Le y ). Endocytosis is followed by cleavage and release of free doxorubicin from the endocytic vesicles and subsequent cytotoxicity. Combination studies with standard anti-cancer agents, undertaken to further increase the potency of this targeted therapy, identified significant synergistic anti-tumor activity of cBR96-Dox and either of the taxanes paclitaxel or docetaxel. Treatment with cBR96-Dox 24 hr prior to paclitaxel resulted in a steady increase in the percentage of G 2 tumor cells and corresponding increase in sensitivity to taxanes. Cell cycle analysis indicated the cBR96-delivered doxorubicin was most effective against S-phase cells, yet cells exposed to even subtoxic levels progressed to and arrested in G 2 , at a point of high sensitivity to the antitubulin agent paclitaxel. The synergy obtained by staged combination of cBR96-Dox and paclitaxel in vitro was reflected in significant anti-tumor efficacy in vivo against xenograft models of human lung and breast tumors that could not be achieved by either agent alone. The staged combination elicited significant or complete regressions of established human Le y -positive tumor xenografts using significantly reduced drug levels. Taken together, these data demonstrate a mechanistic approach to the selective elimination of Le ypositive tumors by using targeted doxorubicin followed by taxane treatment. © 2001 Wiley-Liss, Inc. Key words: doxorubicin; paclitaxel; immunoconjugate; antitumortargeting; antibody-mediatedMonoclonal antibodies (mAbs) directing drugs or toxins to tumor-specific antigens have held the promise of selective tumor cell elimination with reduced collateral damage to normal tissue. 1,2 In addition to mAb accessory functions that mobilize natural killer and complement-mediated cytotoxicity (antibody-dependent cellmediated cytotoxicity [ADCC] and complement-dependent cytotoxicity [CDC]) responses against the tumor, internalizing mAbs can direct delivery of cytotoxics to the tumor. Despite these qualities, and despite demonstrated efficacy in hematologic disease, 3 mAb-directed therapy as a single agent has not shown great success in eliminating established solid carcinomas in the clinic. The reasons for this shortcoming include the fact that most tumor antigens are preferentially expressed by, but not restricted to, tumor cells; thus, dose-limiting toxicity is still seen in normal tissues expressing significant levels of the antigen. Second, most solid tumors not amenable to surgical removal represent significant and well-established masses. The effectiveness of mAb-based therapeutics relative to small molecules in this setting may be reduced by poor tumor vascularization and increased internal pressure of the tumor compared with surrounding tissue, which reduces the ability of large molecules such as mAbs to penetrate a large tumor mass. 4 -6 Interestingl...

Efficient Elimination of B-Lineage Lymphomas by Anti-CD20–Auristatin Conjugates

“…Dox appended to other internalizing mAbs can produce a potent G 2 arrest in antigenpositive cells (37). However, treatment with rituximab or rituximab-vcDox at 5 g/mL showed no significant perturbation in cell cycle position or DNA fragmentation compared with untreated control cells, suggesting the free drug was not delivered to the cell interior.…”

Antibody-Targeted Chemotherapy with the Calicheamicin Conjugate hu3S193- N -Acetyl γ Calicheamicin Dimethyl Hydrazide Targets Lewisy and Eliminates Lewisy-Positive Human Carcinoma Cells and Xenografts

“…The Le y antigen is cytophysiologically different from CD33 and CD22 in a sense that internalization of Le y depends on the internalization of the glycoprotein or glycosphingolipid that carries the antigen. Hence, although Le y internalization has been reported for various cell types (22,24), it is difficult to imagine that different cell types would have similar internalization rates for Le y . A different internalization rate could also explain why two cell lines with comparable sensitivity to CalichDMH and expression of Le y (e.g., LNCaP and LOVO; Table 2) still have different sensitivity to hu3S193-Calich-DMH.…”

“…However, because Le y is located on the epithelial surface of these tissues, the antigen should have restricted accessibility to administered antibodies (23). In addition, the fact that Le yϪ antibody complexes can be internalized by tumor cells (22,24) further underscores the feasibility of using this TAA as a target for antibody-targeted chemotherapy. To target Le y , an antibody with exclusive specificity to the antigen is ideally required.…”

A randomized, multicenter study to determine the safety and efficacy of the immunoconjugate SGN-15 plus docetaxel for the treatment of non-small cell lung carcinoma

“…suggest that the maximum effect in terms of tumor cell killing is achieved if SGN-15 precedes docetaxel application by 24 h [13]. Additional preclinical work using a nude mouse xenograft model (unpublished data, Seattle Genetics, Inc.) showed that administration of SGN-15 48 h before docetaxel administration led to increased clinical response compared to either concomitant administration of the drugs or administration of docetaxel prior to SGN-15.…”

“…Following exposure to doxorubicin, cells arrest in G2 [12] and are then sensitized to G2/M acting drugs such as taxanes. In vitro studies [13] and animal models [14] confirm that the combination of SGN-15 plus a taxane is more effective than either drug alone in several tumor types. Phases I and II studies in subjects with epithelial malignancies, including metastatic breast and colorectal carcinomas, confirm that the combination of SGN-15 and docetaxel is safe and clinically active [15][16][17][18] We now report the results of a randomized Phase II, multicenter study designed to determine the safety and efficacy of SGN-15 and docetaxel in patients with NSCLC.…”