Viruses Created to Selectively Attack Tumor Cells

The image shows tumor cells infected by the virus, which expresses a fluorescent protein. Over the days (in the image fifth day), the virus multiplies, generating new virus that infect more cancer cells

It is an innovative approach that takes advantage of the different expression profiles of certain proteins between tumor and healthy cells that make the virus to only infect the first ones.

Scientists at the IDIBAPS Biomedical Research Institute and at the Institute for Research in Biomedicine (IRB Barcelona) lead a study in which they have designed a new strategy to get genetically modified viruses to selectively attack tumor cells without affecting healthy tissues. The study, published today by the journal Nature Communications, is part of Eneko Villanueva's work for his PhD and it is co-lead by Cristina Fillat, head of the Gene Therapy and Cancer Group at IDIBAPS, and Raúl Méndez, ICREA researcher at IRB Barcelona.

Conventional cancer treatment may cause undesirable side effects as a result of poor selectivity. To avoid them it is important that new therapies can efficiently remove cancer cells and preserve the healthy ones. One of the new approaches in cancer therapy is based on the development of oncolytic viruses, ie, viruses modified to only infect tumor cells. In recent years several studies have been focused on the development of viruses created by genetic engineering to maximize their anticancer effect but, as their potency increases, so does the associated toxicity. Limiting this effect on healthy cells is now the key for the application of this promising therapy.



An innovative and specific approach
In the study published in the journal Nature Communications, researchers from IDIBAPS and IRB Barcelona have developed an innovative approach to provide adenovirus with high specificity against tumor cells. "We have taken advantage of the different expression of a type of protein, CPEBs, in normal and tumor tissues," explains Raúl Méndez from IRB Barcelona.

CPEB is a family of four RNA binding proteins (the molecules that carry information from genes to synthesize proteins) that control the expression of hundreds of genes and maintain the functionality and the ability to repair tissues under normal conditions. When CPEBs become imbalanced, they change the expression of these genes in cells and contribute to the development of pathological processes such as cancer. "We have focused on the double imbalance of two of these proteins in healthy tissues and tumors: on the one hand we have CPEB4, which in previous studies we have shown that it is highly expressed in cancer cells and necessary for tumor growth; and, on the other hand, CPEB1, expressed in normal tissue and lost in cancer cells. We have taken advantage of this imbalance to make a virus that only attacks cells with high levels of CPEB4 and low CPEB1, that means that it only affects tumor cells, ignoring the healthy tissues," says Méndez.



"In this study we have worked with adenoviruses, a family of viruses that can cause infections of the respiratory tract, the urinary tract, conjunctivitis or gastroenteritis but which have features that make them very attractive to be used in the therapy against tumors," explains Cristina Fillat. To do this, it is necessary to modify the genome of these viruses. In the study researchers have inserted sequences that recognize CPEB proteins in key regions for the control of viral proteins. Their activity was checked in in vitro models of pancreatic cancer and control of tumor growth was observed in mouse models.

The onco-selective viruses created in this study were very sophisticated, being activated by CPEB4 but repressed by CPEB1. Thus, researchers achieved attenuated viral activity in normal cells, while in tumor cells the virus potency was maintained or even increased. "When the modified viruses entered into tumor cells they replicated their genome and, when going out, they destroyed the cell and released more particles of the virus with the potential to infect more cancer cells," says Fillat. She adds that, "this new approach is very interesting since it is a therapy selectively amplified in the tumor."



Since CPEB4 is overexpressed in several tumors, this oncoselective strategy may be valid for other solid tumors. Researchers are now trying to combine this treatment with therapies that are already being used in clinical practice, or that are in a very advanced stage of development, to find synergies that make them more effective.
Source: Materials provided by the Institute for Research in Biomedicine (IRB Barcelona)

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Speaking to our cells

Taking ultrasound to the molecular level

Ultrasound could be used to image cells and molecules deep inside the human body thanks to developments in protein engineering at Caltech in the US.

Gas vesicles – which can be engineered with proteins to improve ultrasound methods – can help detect specific cell types and create ‘multicolor’ images.

The researchers are said to have engineered protein-shelled nanostructures called gas vesicles – which reflect sound waves – to exhibit new properties useful for ultrasound technologies.

The modified gas vesicles were shown to give off more distinct signals, making them easier to image; target specific cell types; and help create color ultrasound images. In the future, they could be administered to a patient to visualize tissues of interest.



“It’s somewhat like engineering with molecular Legos,” said Mikhail Shapiro, an assistant professor of chemical engineering and senior author of a new paper about the research published in ACS Nano. “We can swap different protein ‘pieces’ on the surface of gas vesicles to alter their targeting properties and to visualize multiple molecules in different colors.”

“Today, ultrasound is mostly anatomical,” said Anupama Lakshmanan, a graduate student in Shapiro’s lab and lead author of the study. “We want to bring it down to the molecular and cellular level.”

Gas vesicles are naturally occurring in water-dwelling single-celled organisms, such as Anabaena flos-aquae, a species of cyanobacteria that forms filamentous clumps of multicell chains. The gas vesicles help the organism control how much they float and their exposure to sunlight at the water’s surface. From a previous study, Shapiro realized that the vesicles would readily reflect sound waves during ultrasound imaging, and demonstrated these using mice.



In the current research, Shapiro and his team set out to give gas vesicles new properties by engineering gas vesicle protein C, or GvpC, a protein naturally found on the surface of vesicles that prevents them from collapsing. The protein can be engineered to have different sizes, with longer versions of the protein producing stronger and stiffer nanostructures.

“The proteins are like the framing rods of an airplane fuselage. You use them to determine the mechanics of the structure,” Shapiro said in a statement.

In one experiment, the scientists removed the strengthening protein from gas vesicles and then administered the engineered vesicles to mice and performed ultrasound imaging. Compared to normal vesicles, the modified vesicles vibrated more in response to sound waves, and resonated with harmonic frequencies. According to Caltech, harmonics are not readily created in natural tissues, making the vesicles stand out in ultrasound images.

In another set of experiments, the researchers demonstrated how the gas vesicles could be made to target certain tissues in the body. They genetically engineered the vesicles to display various cellular targets, such as an amino acid sequence that recognizes proteins called ‘integrin’s’ that are overproduced in tumour cells.



The team is also said to have shown how multicolor ultrasound images might be created. Conventional ultrasound images appear black and white. Shapiro’s group created an approach for imaging three different types of gas vesicles as separate “colors” based on their differential ability to resist collapse under pressure. The vesicles themselves do not appear in different colors, but they can be assigned colors based on their different properties.

To demonstrate this, the team made three different versions of the vesicles with varying strengths of the GvpC protein. They then increased the ultrasound pressures, causing the variant populations to successively collapse. As each population collapsed, the overall ultrasound signal decreased in proportion to the amount of that variant in the sample, and this signal change was then mapped to a specific color. In the future, if each variant population targeted a specific cell type, researchers would be able to visualize the cells in multiple colors.



“You might be able to see tumour cells versus the immune cells attacking the tumour, and thus monitor the progress of a medical treatment,” said Shapiro.

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