Abstract 4288: Molecular imaging of tumor-associated cathepsins: implication for rapid detection of human nonmelanoma skin cancer
Authors: Walker Ethan , Mann Margaret , Blum Galia , Bogyo Matthew , Basilion James P. 
Published: May 2015

Of the non-melanoma skin cancers, 75% are basal cell carcinomas (BCC) and rest is squamous cell carcinomas (SCC). They are the most common cancers in humans, and their incidence may soon surpass that of all other cancers. Four million people will be diagnosed with BCC/SCC this year in the US with the overall workload of diagnosis and management increasing by 50% by 2030. Mohs micrographic surgery (MMS), which examines all margins of the entire resected sample, is the treatment of choice for BCC/SCC. However, ¾ of skin cancer lesions are too large for their entire margins to be practically assessed for cancer using MMS. Therefore, 75% of BCC/SCC patients will undergo traditional surgery. Non-MMS assesses ∼1% of the margin with the results being available days after surgery. Thus, there exists an unmet clinical need to more completely assess surgical margins to increase cure rates and minimize removal of normal tissue. Here we test a quenched near infrared fluorescent contrast agent, GB119, to rapidly and globally detect cancer in skin samples. We first characterized the feasibility of ex vivo applied GB119, to penetrate human skin tissue and “find” BCC/SCC in skin cancer samples obtained from debulking MMS. Detection of the cancer was measured by increased fluorescence resulting from specific activation and de-quenching of GB119 as it encounters active cathepsin associated with BCC/SCC. Excised skin samples were pre-imaged and then, using an applicator pad, GB119 was topically applied onto the samples containing BCC (n=12) or SCC (n=3). Activation GB119 was measured (Maestro, PerkinElmer) and fluorescent “hot spots” on the surface of samples were marked with pathology ink followed by snap freezing for histology and IHC. 13 of 15 skin samples produced robust fluorescence spots that were marked with ink. Two samples did not produce any signal greater than pre-imaging auto-fluorescence. H/E staining of marked skin samples confirmed presence of ink nearby “nests” of cancerous tissue. The two samples that did not activate GB119 were determined by histology to be cancer free. Since it was not possible to detected GB119 fluorescence after H/E staining we developed an IHC assay to visualize the presence of activated de-quenched GB119 and used it to pathologically correlate GB119 activation with cancer. Using an anti-Cy5 antibody (Sigma) our immunoassay detected de-quenched GB119 and could be used to detect activated GB119 in tissue. Using this assay we detected low levels of GB119 activation in normal skin and cancer free samples from patients with BCC/SCC. In contrast, high levels of GB119 activation were found within “nests” of cancerous tissue for BCC/SCC samples. These data confirm the feasibility of topically applying GB119 to excised skin samples to rapidly detect the presence of cancer within the margins of the samples. If successful this technology could potentially impact MMS-like precision to non-MMS surgical techniques.

Citation Format: Ethan Walker, Margaret Mann, Galia Blum, Matthew Bogyo, James P. Basilion. Molecular imaging of tumor-associated cathepsins: implication for rapid detection of human nonmelanoma skin cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4288. doi:10.1158/1538-7445.AM2014-4288