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.

Inclusion Criteria:

- Male and Female African American or Caucasian subjects older than 18 years of age.
Race will be defined by the subject.

- Stage I or stage II (pN0) colon cancer within 3 years of surgery

- Competent immune system, defined by the ability to make a delayed type
hypersensitivity (DTH) reaction to at least one of the following: candida, mumps,
tetanus or trichophyton

- Adequate renal, liver, and bone marrow functions:

Serum creatinine ≤ 2.0 mg/dl, Hemoglobin ≥ 10.0 g/dl WBC (white blood cells) ≥ 3,000 /mm3,
platelet count ≥ 100,000/mm3, total bilirubin ≤2.0 mg/ml, and albumin ≥ 3.0 g/dl

- Lymph node specimens available for quantification of occult metastases

- Minimum of 2 months and maximum of 36 months since surgery

- No clinical or laboratory evidence of local or systemic recurrence at entry to the
study

- Expected survival of at least 6 months

- Karnofsky performance status ≥ 80 (ECOG 0 or 1)

- Willingness and ability to understand and give informed consent and follow the
procedures described in the protocol

Exclusion Criteria:

- Failure to meet any of the inclusion criteria above

- Rectal cancer

- Prior chemotherapy/radiotherapy/immunotherapy/experimental medications for colon
cancer

- Prior splenectomy

- Concurrent use of systemic steroids or immunosuppressive drugs (Note: topical or
inhaled aerosol steroid therapies are not contraindicated for participation in the
study)

- HIV-positive by ELISA, confirmed by Western blot

- Active autoimmune diseases that the Investigator considers would interfere with an
immunologic response (e.g., systemic lupus erythematosus, multiple sclerosis or
ankylosing spondylitis)

- Other malignancy within 5 years except curatively treated non-melanomatous skin
cancer and curatively treated carcinoma in situ of the uterine cervix, or early stage
(stage A or B1) prostate cancer

- Medically-proven inflammatory bowel disease

- Has at the time of enrollment, serious infection or other serious medical condition
that implies a survival of less than six months

- Pregnancy or lactation (serum B-human chorionic gonadotropin test must be negative in
fertile women at screening visit). Subjects will be asked to use contraception during
conduct of the study.

- Past medical history of serious reaction to adenovirus vaccine

- Mental handicap

- Chronic diarrhea >6 times per day