Eradication of large colon tumor xenografts by targeted delivery of maytansinoids.

The maytansinoid drug DM1 is 100- to 1000-fold more cytotoxic than anticancer drugs that are currently in clinical use. The immunoconjugate C242-DM1 was prepared by conjugating DM1 to the monoclonal antibody C242, which recognizes a mucin-type glycoprotein expressed to various extents by human colorectal cancers. C242-DM1 was found to be highly cytotoxic toward cultured colon cancer cells in an antigen-specific manner and showed remarkable antitumor efficacy in vivo. C242-DM1 cured mice bearing subcutaneous COLO 205 human colon tumor xenografts (tumor size at time of treatment 65-130 mm3), at doses that showed very little toxicity and were well below the maximum tolerated dose. C242-DM1 could even effect complete regressions or cures in animals with large (260- to 500-mm3) COLO 205 tumor xenografts. Further, C242-DM1 induced complete regressions of subcutaneous LoVo and HT-29 colon tumor xenografts that express the target antigen in a heterogeneous manner. C242-DM1 represents a new generation of immunoconjugates that may yet fulfill the promise of effective cancer therapy through antibody targeting of cytotoxic agents.

Enhancement of the selectivity and antitumor efficacy of a CC-1065 analogue through immunoconjugate formation.

Bis-indolyl-(seco)-1,2,9a-tetrahydrocyclopropa[c]benz[e]indol-4-on e compounds are synthetic analogues of CC-1065 that are highly cytotoxic toward a broad spectrum of tumor cell lines. One of these compounds, called DC1, was conjugated to antibodies via novel cleavable disulfide linkers. Conjugates of DC1 with murine mAbs anti-B4 and N901 directed against tumor-associated antigens CD19 and CD56, respectively, proved to be extremely potent and antigen selective in killing target cells in culture. DC1 conjugates with humanized versions of anti-B4 and N901 antibodies were also constructed and demonstrated to be as cytotoxic and selective as the respective murine antibody conjugates. The anti-B4-DC1 conjugate showed antitumor efficacy in an aggressive metastatic human B-cell lymphoma survival model in SCID mice and completely cured animals hearing large tumors. Anti-B4-DC1 was considerably more effective in this tumor model than doxorubicin, cyclophosphamide, etoposide, or vincristine at their maximum tolerated doses.