Phase I Study of Ad5-hGCC (Human Guanylyl Cyclase C)-PADRE in Stage I/II Colon Cancer

There is an unmet need for improved therapeutic paradigms in colorectal cancer, the 3rd leading cause of cancer and 2nd leading cause of cancer mortality worldwide. This need is underscored by the populations in jeopardy, including the ~100 million people in the US over 50 y that have a 1:8 risk associated with a disease-specific mortality of 50%. Mortality reflects metastatic disease: ~50% of patients initially present with regional or distant metastases, while ~20% present with occult metastases. Beyond the general population risk, there is an established stage-specific difference in outcomes in pN0 (node negative) African Americans with colorectal cancer, who exhibit ~40% excess mortality attributable to race. Reductions in mortality have been hampered by the absence of effective chemo-, radio-, and immuno- therapeutic approaches to metastatic disease. In that context, immunotherapy has been disappointing, in part, reflecting the absence of antigens that are tumor-specific, immunogenic, and universally associated with neoplasia. Moreover, the gap in survival between African Americans and Caucasians specifically reflects the inability to identify those with occult metastases who are at increased risk for developing recurrent disease.

This study advances an emerging paradigm in colorectal cancer cell detection and eradication, employing GCC as a molecular marker and immunological target. GCC is a protein whose expression is normally restricted to intestinal epithelial cells, but universally expressed by metastatic colorectal tumors. We have clinically validated the detection of occult metastases in lymph nodes by quantifying GCC mRNA (messenger RNA) by reverse transcriptase (RT)-PCR (qRT-PCR). This study revealed that occult metastases were the most powerful independent predictors of survival in pN0 patients. Further, there is a disproportionate burden of occult disease in African American, compared to Caucasian, patients. This new molecular staging platform provides a unique opportunity to identify occult metastases underlying racial disparities in disease recurrence, which could be prevented by tumor-targeted immunotherapy.

In the absence of ideal tumor antigens, immunotherapy has been directed to tissue-specific proteins. Barriers to employing self-antigens include tolerance, which limits anti-tumor immunity, and autoimmunity. The present study advances an emerging paradigm exploiting immunological compartmentalization of mucosally-restricted antigens to generate systemic antitumor immunity without autoimmunity. Asymmetry in immunological cross-talk between compartments, wherein systemic T and B cell responses rarely extend to mucosae, suggest that proteins normally expressed in mucosae, but which are expressed systemically by tumors, may serve as vaccine targets for metastases. Advantages of these cancer mucosa antigens include unique systemic immunoreactivity profiles supporting highly effective durable antitumor immunity in the context of absent immunological cross-talk between compartments restricting autoimmunity. Here, this paradigm will be advanced employing the tumor marker GCC, which induces immune responses that oppose metastatic colorectal cancer in preclinical models, without autoimmunity. This study will define the safety and immunological efficacy of adenoviral GCC vaccine in African American and Caucasian pN0 colon cancer patients with excess recurrence risk reflecting occult lymph node metastases identified by GCC qRT-PCR. This study will be the first step in translating GCC into a vaccine for the secondary prevention of metastases in African American and Caucasian colorectal cancer patients.