ANTI-HUMAN CCR9 THERAPEUTIC ANTIBODIES

ANTI-HUMAN CCR9 THERAPEUTIC ANTIBODIES[1][2]

Cancer treatment is expanding from non-specific cytotoxic chemotherapies to targeted therapies. Many tumor cells over-express functional chemokine receptors, undetectable on their normal counterparts. Interaction of chemokines with their chemokine receptors, expressed in the surface of tumor cells, promote cell survival, proliferation, adhesion and/or migration. Being also able to promote metastasis formation on tissues or organs where the corresponding chemokines are secreted. Chemokine receptors expressed on the surface of cancer cells and their ligands have been considered suitable therapeutic targets for anti-tumor drugs. Recent achievements in the use of monoclonal antibodies (mAbs) targeting a variety of molecules for the treatment of different tumor types have contributed to move the efforts onto targeting chemokines and their receptors towards generating specific antibodies for therapeutic purposes (1).

We have reported the generation and characterization of 91R [3], a mouse anti-human CCR9 mAb, which is able to reduce on an 85% the size of a human T lymphoblastic cell tumor growing in vivo as a xenotransplant on mice (Figure 1). Tumor size reduction was concomitant with an increased apoptotic tumor cell fraction and tumor necrotic areas, as well as decreased fraction of proliferating cells and tumor vascularization. 91R is able to kill tumor target cells in vitro through CDC and ADCC, although the in vivo mechanism(s) of action of this mAb remain unknown (2). These results suggest that CCR9-expressing tumors, such as acute and chronic T cell lineage leukemia (3), prostate cancer (4), breast cancer (5) and melanomas (6), can potentially be targeted with this mAb.

Figure 1. Leukemia xenograft growth is reduced in mice treated with 91R mAb. For xenograft analyses, MOLT-4 cells were inoculated s.c. in Rag2^–/– mice on day 0 (d0). Experimental groups received four i.p. doses of 91R or irrelevant IgG2b mAb (first and second, 4 mg/kg; third and fourth, 2 mg/kg). Tumor growth was measured with a caliper every three days. After mice were sacrificed, tumors were removed and weighed. (A) Antibody administration schedule on days 1, 7, 14 and 21 for mice bearing tumor cells injected in on both flanks. (B) Tumor growth kinetics. Tumor volume was measured at times indicated and calculated as V = [axial diameter length, mm] x [(rotational diameter, mm)2/2] (6 mice/group). (C) Tumor weight (%) relative to IgG2b treatment on d56. Mean ± SEM (n = 6 mice/group). (D) Images of tumors from IgG2b- and 91R-treated mice at the time of sacrifice (day 56). Bar = 1 cm. (This figure is modified from (2) and is shown with permission from Dr. L. Kremer).

Please note that in the representative experiment shown in Figure 1. The largest of the 91R-treated tumors is smaller than the smallest of the IgG2b isotype-treated tumors, suggesting that mAb 91R, an antibody against the human chemokine receptor CCR9 could be used as therapeutic antibody for the treatment of human tumors.

We are currently analyzing the in vivo mechanism(s) of action, the effectiveness of these antibodies inhibiting the growth of primary human tumors as xenografts in immunocompromised mice, as well as the effect of the growth of these cell lines and primary tumors implanted as orthotropic tumors in lymphoid organs. These data will allow us to ascertain the effectiveness of 91R as a therapeutic anti-tumor antibody