Intravesical Bacillus Calmette-Guérin therapy for murine bladder tumors: initiation of the response by fibronectin-mediated attachment of Bacillus Calmette-Guérin.

Intravesical Bacillus Calmette-Guérin (BCG) is considered to be one of the most effective treatments for superficial bladder cancer. Although the mechanisms by which BCG inhibits tumor growth are not known, previous studies have shown that systemic immunization to BCG and the local expression of the immune response in the bladder are associated with a favorable response to BCG therapy. We have investigated the conditions required for the initiation of an immunological response after the intravesical instillation of BCG. Initial histological studies showed that BCG attached to the bladder wall only in areas where the urothelium was damaged by electrocautery and suggested that attachment was associated with the fibrin clot. Quantitative studies verified the histological observations. Minimal BCG attachment (mean less than 10(2) colony forming units) was observed in normal bladders in contrast with a mean of 1.42 X 10(4) colony forming units/bladder in bladders damaged by electrocautery (10 separate experiments). BCG attachment to the bladder wall was durable since organisms were observed in bladders 48 h after instillation. To investigate the proteins to which BCG attached, we tested the binding of BCG to extracellular matrix and inflammatory proteins which comprise a significant portion of the fibrin clot. BCG bound in vitro to coverslips coated in vivo with extracellular matrix proteins but did not bind to control albumin-coated coverslips. BCG also bound to coverslips coated with purified plasma fibronectin but not to coverslips coated with other purified extracellular matrix proteins including laminin, fibrinogen, and type IV collagen. BCG attachment to coverslips coated with either extracellular matrix proteins or purified fibronectin was inhibited by antibodies specific for fibronectin. Moreover, BCG attachment to cauterized bladders in vivo was inhibited by antifibronectin antibodies. These results demonstrate that fibronectin mediates the attachment of BCG to surfaces and suggest that it is the primary component mediating attachment within the bladder. Moreover, the data suggest that the BCG-fibronectin interaction may be a requisite first step for the initiation of the antitumor activity in intravesical BCG for bladder cancer.