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SSTR2-based reporters for assessing gene transfer into non-small cell lung cancer: evaluation using an intrathoracic
1Department of Experimental Diagnostic Imaging, University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA.
Abstract:
The most common cause of cancer-related deaths in North America is lung cancer, 85% of which is non-small cell lung cancer (NSCLC). Gene therapy is a promising approach, but has been hindered by lack of methods for localizing and quantifying gene expression in vivo. Human somatostatin receptor subtype-2 (SSTR2)-based reporters can be used to follow gene expression in vivo using ligands with greater affinity for this subtype. NSCLCs can express SSTR subtypes, which may interfere with SSTR2-based reporters. We assessed whether a SSTR2-based reporter can serve as a reporter of gene transfer into NSCLCs. SSTR subtype expression was assessed in NSCLC cell lines A549, H460, and H1299 using RT-PCR. After infection with an adenovirus containing hemagglutinin-A-tagged-SSTR2 (Ad-HA-SSTR2) or control insert, expression was assessed by immunologic techniques and binding to clinically-approved (111)In-octreotide. In vivo, after magnetic resonance (MR) imaging, intrathoracic H460 tumors were injected with Ad-HA-SSTR2 or control virus (n = 6 mice/group) under ultrasound guidance. Intravenous injection of (111)In-octreotide 2 days later was followed by planar and single-photon emission computed tomography (SPECT) imaging. Biodistribution into tumors was assessed in vivo using anatomic MR and functional gamma-camera images and ex vivo using excised organs/tumors. In human lung tumor samples (n = 70), SSTR2 expression was assessed using immunohistochemistry. All three NSCLC cell lines expressed different SSTR subtypes, but none expressed SSTR2. Upon Ad-HA-SSTR2 infection, HA-SSTR2 expression was seen in all three cell lines using antibodies targeting the HA domain or (111)In-octreotide targeting the receptor domain (p < 0.05). Intrathoracic tumors infected with Ad-HA-SSTR2 were clearly visible by gamma-camera imaging; expression was quantified by both in vivo and ex vivo biodistribution analysis and demonstrated greater uptake in tumors infected with Ad-HA-SSTR2 compared with control virus (p < 0.05). Immunohistochemistry found that 78% of NSCLCs are negative for and 13% have low levels of SSTR2 expression. It is concluded that SSTR2-based reporters can serve as reporters of gene transfer into NSCLCs.
Insights
This study shows that somatostatin receptor subtype-2 (SSTR2)-based reporters can effectively track gene transfer in non-small cell lung cancer (NSCLC). This advance aids in localizing and quantifying gene expression for potential lung cancer gene therapies.
Area of Science:
- Oncology
- Molecular Imaging
- Gene Therapy
Background:
- Non-small cell lung cancer (NSCLC) is a leading cause of cancer death.
- Gene therapy for NSCLC is promising but lacks methods for in vivo gene expression tracking.
- Somatostatin receptor subtype-2 (SSTR2)-based reporters offer potential for in vivo tracking.
Purpose of the Study:
- To assess if an SSTR2-based reporter can indicate gene transfer into NSCLCs.
- To evaluate SSTR subtype expression in NSCLC cell lines and human tumors.
- To validate the use of SSTR2 reporters for monitoring gene delivery in NSCLC models.
Main Methods:
- RT-PCR to assess SSTR subtype expression in NSCLC cell lines (A549, H460, H1299).
- Adenovirus-mediated delivery of hemagglutinin-tagged SSTR2 (Ad-HA-SSTR2) to cell lines and mouse models.
- In vivo and ex vivo imaging (SPECT, gamma-camera, MR) and biodistribution studies using (111)In-octreotide.
- Immunohistochemistry to assess SSTR2 expression in human NSCLC samples.
Main Results:
- NSCLC cell lines expressed various SSTR subtypes but not SSTR2.
- Ad-HA-SSTR2 infection led to detectable HA-SSTR2 expression in all cell lines.
- Tumors infected with Ad-HA-SSTR2 showed significantly higher (111)In-octreotide uptake.
- 78% of human NSCLC samples lacked SSTR2 expression, with 13% showing low levels.
Conclusions:
- SSTR2-based reporters are effective for reporting gene transfer into NSCLCs.
- The lack of endogenous SSTR2 in most NSCLCs minimizes interference with reporter systems.
- This approach facilitates in vivo monitoring of gene therapy delivery in NSCLC.
