Abstract
Photoimmunotherapy (PIT) using an antibody conjugated to a near infrared dye IR700 is achieving significant success in target-specific elimination of cells. Fibroblast activation protein alpha (FAP-α) is an important target in cancer because of its expression by cancer associated fibroblasts (CAFs) as well as by some cancer cells. CAFs that express FAP-α have protumorigenic and immune suppressive functions. Using immunohistochemistry of human breast cancer tissue microarrays, we identified an increase of FAP-α+ CAFs in invasive breast cancer tissue compared to adjacent normal tissue. We found FAP-α expression increased in fibroblasts co-cultured with cancer cells. In proof-of-principle studies, we engineered human FAP-α overexpressing MDA-MB-231 and HT-1080 cancer cells and murine FAP-α overexpressing NIH-3T3 fibroblasts to evaluate several anti-FAP-α antibodies and selected AF3715 based on its high binding-affinity with both human and mouse FAP-α. After conjugation of AF3715 with the phthalocyanine dye IR700, the resultant antibody conjugate, FAP-α-IR700, was evaluated in cells and tumors for its specificity and effectiveness in eliminating FAP-α expressing cell populations with PIT. FAP-α-IR700-PIT resulted in effective FAP-α-specific cell killing in the engineered cancer cells and in two patient-derived CAFs in a dose-dependent manner. Following an intravenous injection, FAP-α-IR700 retention was three-fold higher than IgG-IR700 in FAP-α overexpressing tumors, and two-fold higher compared to wild-type tumors. FAP-α-IR700-PIT resulted in significant growth inhibition of tumors derived from FAP-α overexpressing human cancer cells. A reduction of endogenous FAP-α+ murine CAFs was identified at 7 days after FAP-α-IR700-PIT. FAP-α-targeted NIR-PIT presents a promising strategy to eliminate FAP-α+ CAFs.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
Competing interests: No competing interests declared
Data Availability: All data generated or analysed during this study are included in the manuscript and supporting file; Source Data files have been provided for Figures 1-7. N/A
Ethics: Human Subjects: No Animal Subjects: Yes Ethics Statement: All the animal care and in vivo procedures were conducted in accordance with the regulations of the Institutional Animal Care and Use Committee of The Johns Hopkins University. The protocols (MO17M02, MO18M138 and MO20M04) were approved by the Institutional Animal Care and Use Committee of The Johns Hopkins University.
Financial Support: This work was supported by NIH R35 CA209960, R01 CA82337, P41 EB024495, P30 CA006973, ZIA BC011513 and a grant from the Emerson Collective Cancer Research Fund.
Conflict of Interest Disclosures: The authors have no conflict of interest to disclose