Novel Antibody-Drug Conjugates Targeting Adam9-Expressing Solid Tumors Demonstrate Potent Preclinical Activity

ADAM9, also known as MDC9 or meltrin-γ, is a member of the ADAM (a disintegrin and metalloproteinase) family of proteases, which have been implicated in cytokine and growth factor shedding, and cell migration. Dysregulation of ADAM9 has been implicated in tumor progression and metastasis, as well as pathological neovascularization. ADAM9 overexpression has been shown to correlate with poor prognosis in prostate, renal, and pancreatic cancers. Using an immunization approach in which antibodies were raised to fetal progenitor and stem-like cancer cell lines followed by screening on tumor and normal tissues, we identified ADAM9 as a promising cell surface tumor target. FFPE-IHC expression analysis revealed that ADAM9 is overexpressed in multiple solid tumor indications relative to corresponding normal tissues. The overexpression of ADAM9 in tumors coupled with its restricted expression in normal tissues make ADAM9 an attractive target for antibody-drug conjugate (ADC) therapy. Here, we describe two ADCs both of which are based on a high affinity anti-ADAM9 antibody to selectively target ADAM9-expressing tumors. The first ADC utilizes the maytansine-derived microtubule disruptor, DM4, linked via a hindered disulfide hydrophilic linker (sulfo-SPDB). The second ADC exploits an ultra-potent DNA alkylating payload, DGN549, which is conjugated to two engineered cysteines via a peptide linker. Both conjugates bound with similar subnanomolar affinity to ADAM9-expressing cells. In vitro cytotoxicity studies showed that anti-ADAM9 ADCs can kill a broad panel of ADAM9-positve tumor cell lines, including lung, pancreatic, renal, prostate, and colon tumor cell lines. In particular, the anti-ADAM9-DGN549 conjugate was extremely potent with IC50 values ranging from 0.1 to 65 pM and was at least 2 logs more active than a non-targeting conjugate. Surprisingly, efficient in vitro cytotoxicity was observed at ADAM9 expression levels as low as a few thousand cell surface receptors per cell. Consistent with their in vitro activity, both anti-ADAM9 ADCs displayed compelling anti-tumor activity in xenograft models. In a CaLu3 non-small cell lung cancer xenograft model, anti-ADAM9-DM4 induced tumor growth delay at a single 1.25 mg Ab/kg dose. In the same model, a single intravenous dose of 0.25 mg Ab/kg of the anti-ADAM9-DGN549 produced durable complete remissions in 8/8 mice. A non-targeting DGN549 ADC was inactive even when dosed at 10 times that of the anti-ADAM9 ADC, demonstrating that targeted delivery of DGN549 through ADAM9 binding is required for activity. These data demonstrate that anti-ADAM9 ADCs exhibit antitumor activity against a broad panel of ADAM9-positive malignancies and cause durable remissions in preclinical models at doses expected to be clinically achievable. Anti-ADAM9 ADCs represent a promising therapeutic strategy to target a wide range of ADAM9-expressing tumors. Citation Format: Stuart W. Hicks, Nicholas C. Yoder, Deryk Loo, Asli Muvaffak, Yinghui Zhou, Megan E. Fuller, Molly A. McShea, Marian Themeles, Katherine H. Mucciarone, Juniper A. Scribner, Bhaswati Barat, Thomas Sun, James Tamura, Francine Z. Chen, Kerry A. Donahue, Tom Chittenden. Novel antibody-drug conjugates targeting ADAM9-expressing solid tumors demonstrate potent preclinical activity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 37. doi:10.1158/1538-7445.AM2017-37