Nanodelivery of MRI contrast agent enhances sensitivity of detection of lung cancer metastases

Abstract

Rationale and objectives: Early detection of lung cancer can be problematic. Although current imaging methods can identify lung cancers, they are limited in the size of detectable nodules. There is also lack of evidence that these methods can correctly classify nodules <7 mm as malignant because lung cancer can be mimicked in appearance by benign lesions that lower specificity. Therefore, there is a need for enhanced sensitivity/specificity of detection for small lung cancers.

Materials and methods: We have developed a nanosized ( approximately 100 nm) immunoliposome complex for delivery of molecular medicines to tumors. In this complex, an anti-transferrin receptor single-chain antibody fragment (TfRscFv) decorates the surface of a cationic liposome encapsulating the payload. We have previously shown that this systemically administered complex (scL) selectively targets, and efficiently delivers its payload into, tumor cells. We have also encapsulated the magnetic resonance imaging (MRI) contrast agent gadopentetate dimeglumine ("gad-d") within this complex, resulting in increased resolution and image intensity in a mouse model of primary cancer. Here we examine the ability of the scL-gad-d complex to increase the sensitivity of detection of lung metastases.

Results: These MRI studies show that the scL-gad-d nanocomplex is able to improve detection, and increase enhancement of, small lung cancers (400 microm and as small as 100 microm) compared to that of uncomplexed gad-d.

Conclusions: Because of its tumor targeting specificity, deliver of an MRI contrast agent via this nanocomplex has potential for use as an agent that can identify small lung cancers, thus improving early detection and possibly increasing survival.

Figure 1. Metastases to lung in the RenCa lung metastasis model

In this composite figure/chart, we compare the image of the same mouse imaged with both free gad-d and scL-gad-d. A-The base views show the respective pre-contrast images. PI = pixel intensity of the lower left lung nodule. B-This is graphically shown in the Chart that shows the enhancement from the precontrast images. The scL-gad-d complex shows greater enhancement than free gad-d in this metastasis. Arrows indicate the nodule measured and the enhancing pleural metastases.

Figure 2. Detection of 4 pixel RenCa nodules

A- Pixel Intensity of upper nodule with free gad-d was 1857, while that with scL-gad-d complex was 2848. This upper nodule does not show on base (pre-contrast image) with free gad-d and either does not show or is hidden in atelectasis on base for complex. The lower nodule is not visible except with complex. Its intensity is 2938. The region of the nodule measures 1121 with free gad-d, but the nodule itself cannot be identified. B-This chart demonstrates the increase in peak pixel intensity in the region including the small (approximately 4 pixel—400 micron) upper lung nodule shown in A

Figure 3. Histograms corresponding to the RenCa nodules in Figure 2

A-These histograms of the region of the nodule display the spread of pixel intensities (x-axis) vs the number of pixels of that value (y-axis). The maximum y-axis for these images is 2 pixels. The histogram charts provide both the mean and standard deviation levels. B- Standard gad-d: Two profiles, one pixel apart, through the center of the upper nodule after enhancement with gad-d. C- scL-gad-d. Two profiles, one pixel apart, through the center of the upper nodule after enhancement with scL-gad-d.

Figure 4. Detection of 1–2 pixel RenCa lung metastases

A-Three lung nodules are identified on the post contrast scL-gad-d images. The two smaller nodules (N1 and N2) measure 1–2 pixels (approximately 100–200 microns) in size. They measure about 700 microns apart. They are just barely visible on the pre-contrast images. The Arrows indicate the lung nodules. B- Chart showing the change in pixel value of the three small nodules identified in Figure 4A.

Figure 5. Nodule 1 from Figure 4A, pre and post contrast with scL-gad-d

A- Histogram of pre and post- contrast with scL-gad-d. B-Profile through Nodule 1

Figure 6. Data for Nodules 2 and 3 from Figure 4A post contrast with scL-gad-d with histogram and profile through the center of the nodule

A-Histogram and profile for Nodule 2. B-Histogram and profile for Nodule 3.

Figure 7. Histology section (H&E stain) of the lungs from the mouse described above (Figure 4A)

MR images were used to guide the sectioning of the lungs. Arrows point to the two small metastases, each less than 100 microns in size.

Figure 8. Comparison of MR image enhancement between targeted and unliganded complex

In this composite figure/chart, we compare the image of the same mouse imaged with both scL-gad-d and unliganded gad-d (L-gad-d). A-The base view and post-contrast image after i.v. injection of the unliganded L-gad-d. B- The base view and post-contrast image after i.v. injection of the targeted scL-gad-d. C- A graph of the enhancement over baseline values with both agents.