Preclinical evaluation of light-activatable, bispecific anti-human CD3 antibody conjugates as anti-ovarian cancer therapeutics.

The administration of anti-CD3 antibodies, either unmodified or in bispecific formats, has been shown to kill tumors. However, their activity needs to be carefully controlled. We have approached this problem by inhibiting their anti-CD3 activity until it is required. Folated anti-human CD3 antibody bispecific conjugates were therefore synthesised in which the folate portion of the conjugates remained free to bind to folate receptor (FR) expressing cancer cells, whilst their anti-CD3 activity was reversibly inhibited. On irradiation with UV-A light, the T-cell binding activity of the anti-CD3 antibody can be restored only when and where it is required, i.e., adjacent to a tumor. Conjugate bound to FR expressed on normal tissues in other parts of the body remains inactive. This report describes the preclinical in vivo testing of these conjugates in transgenic mice whose T-cells express human CD3 molecules. When the 'cloaked' conjugates were reactivated in the region of the primary tumor, both primary tumor growth and liver metastasis were markedly reduced. That the deliberate targeting of T-cell activity locally to the primary tumor also resulted in reduced distant metastatic growth was a key finding. Light-activatable bispecific antibody conjugates similar to those described here offer a means to control T-cell targeting with a much higher degree of specificity to tumors because they minimize potentially dangerous and unwanted side effects in non-illuminated areas. The addition of light-specific targeting to the inherent tumor specific targeting of therapeutic antibody conjugates could result in the development of safer treatments for patients.

The construction and in vitro testing of photo-activatable cancer targeting folated anti-CD3 conjugates.

The construction and in vitro testing of a photo-activatable anti-tumour immuno-regulatory antibody is described. In this 'cloaked' folated anti-CD3 antibody conjugate, the folate portion of the conjugate is free to bind to folate receptor expressing cancer cells, whilst the anti-CD3 activity is effectively rendered inert by a coating of photo-labile 2-nitrobenzyl groups. On irradiation with UV-A light the activity of the anti-CD3 antibody is restored, not only when it is required, but more importantly, only where it is required. The conjugate can then attract killer T-cells to the surface of the tumour cells and kill them. Unirradiated normal tissues, to which the conjugate has been targeted by specific and non-specific binding, remain unharmed. We believe that these 'photo-switchable' conjugates could be used to markedly improve the targeting of the immune response to folate receptor (FR) expressing ovarian and breast cancers whilst minimising the side effects in the rest of the body.