Inhibition of a complement regulator in vivo enhances antibody therapy in a model of mammary adenocarcinoma

Abstract

Key words: complement, Crry, inhibitor, antibody therapyComplement effector systems involved in an immune response to tumor cells can include the amplification of an inflammatory response, recruitment of immune effector cells, opsonization of tumor cells that result in complement-dependent cell-mediated cytotoxicity (CDCC) and enhanced antibody-dependent cell-mediated cytoxicity (ADCC), and direct complement mediated lysis. Normal and tumor cells are protected from complement by the expression of membrane bound complement regulatory proteins, and these proteins are upregulated on some cancers. 1-5 Regulators of complement activation are decay accelerating factor (DAF), membrane cofactor proteins (MCP) and, in rodents only, Crry. Rodent Crry is a structural and functional analog of DAF and MCP. These proteins act early in the pathway and limit C3 deposition/opsonization. CD59 regulates the terminal pathway of complement and controls formation of the cytolytic membrane attack complex (MAC).Many in vitro studies have shown that blocking the function of membrane-bound complement regulatory proteins sensitizes normally resistant tumor cells to antibody-mediated complement deposition and lysis (reviewed in references 6 -8). Complement regulatory proteins expressed on tumor cells have also been shown to enhance tumorigenesis in rodent models. 9 -11 These results have lead to the hypothesis that inhibiting the function of complement regulatory proteins expressed on tumor cells will enhance antibody immunotherapy. However, complement regulatory proteins are widely expressed on normal cells, and targeting inhibitory molecules to complement regulators expressed on tumor cells in vivo is a technical challenge. As a consequence, the effect of inhibiting complement regulatory proteins on tumor cells has not been investigated in a therapeutic protocol in vivo.In the short term, untargeted inhibitors of complement regulatory proteins may not pose serious health concerns in the absence of a specific complement activation signal (e.g., a specific antibody), but a "sink" effect would certainly be a barrier to effectiveness. One approach for targeting and inhibiting complement regulators on tumor cells that has been evaluated in vitro is the use of bispecific antibodies. Bispecific antibodies that recognize both a tumor-associated antigen and a complement regulatory protein (function blocking) have been shown to selectively target and enhance complement sensitivity of tumor cells in vitro. [12][13][14] Nevertheless, the development of bispecific antibodies with relevant specificities for in vivo and clinical testing needs to be preceded by animal testing to show that the concept can be translated into effective cancer therapy. We have investigated whether inhibiting a complement regulatory protein on tumor cells in vivo represents a viable strategy with regard to effect on antibody and complement dependent immune response and therapeutic outcome. For our feasibility study, we use a cancer model consisting of the Crrypositive 13762...

Complement-Mediated Mechanisms in Anti-GD2 Monoclonal Antibody Therapy of Murine Metastatic Cancer

“…A previous proofof-principle study showed that the endogenous expression of Crry on a rat tumor cell line provided protection from mAb-mediated therapy. In this previous study, anti-rat Crry mAb was administered to immune-deficient mice challenged with rat tumor cells, thus allowing for tumor-specific targeting of rat Crry (49).…”

CD46 and Oncologic Interactions: Friendly Fire against Cancer

“…Several strategies have been employed to target the overexpression of complement regulators and thereby improve the therapeutic outcome [34]. These include small interfering RNAs [35][36][37], neutralizing (blocking) mAbs to complement inhibitors [38,39], bispecific antibodies [40][41][42][43] and a targeted complement activator (CR2-Fc) [30,44].…”

Targeted complement inhibition by C3d recognition ameliorates tissue injury without apparent increase in susceptibility to infection

“…The complement-inhibitory activity of CR2-Crry and Crry-Ig was compared by measurement of the sensitivity of antibody-sensitized CHO cells to lysis by rat serum ( Figure 1B). Mouse Crry is functionally active against rat serum (45), and rat serum was used for functional comparison of activities because isolated mouse serum has poor lytic activity in vitro (46,47). CR2-Crry and Crry-Ig caused 50% inhibition of lysis at concentrations of 12 nM (0.84 μg/ml) and 40 nM (6.4 μg/ml), respectively, an approximately 3.5-fold difference.…”