Around ten years ago, Brazilian husband and wife scientists, Renata Pasqualini and Wadih Arap, began investing heavily in a line of research against cancer, with the potential, at least, to generate drugs with a high degree of specificity that are lethal only to tumor cells. The idea of the molecular biologist and the researcher-physician, who jointly headed up a laboratory in the prestigious MD Anderson Cancer Center at the University of Texas, in Houston, was to explore a vascular characteristic of tumors (and of other health problems) to design more selective treatments and diagnostic ways. Cancer generates blood vessels that have a unique chemical signature, a type of peculiar molecular postcode that is different from that found in healthy cells of this same tissue, and that appear at the wrong time in the wrong place. If it is possible, therefore, to map out the chemical address of each type of tumor and develop mailman-proteins capable of taking an explosive package only to vessels that feed the undesired cells, the possibility of constructing drugs based on the peculiarities of the vascular system can be tested in practice.
Renata and Wadih recently published two articles in important scientific journals in which they report results they recently obtained with this approach. Although it was not a study on cancer, the couple’s central area of operation, one of the pieces of work received extensive coverage in the press worldwide because it signaled a possible new way of combating one of the epidemics most associated with modern life: obesity. In the November 9 edition of Science Translational Medicine (STM), the researchers reported that a group of 10 obese rhesus monkeys had lost on average 11% of their weight after being submitted over a four-week period to treatment with a drug called adipotide. Apparently, the candidate remedy caused no particular adverse effects in the primates. “This is a potentially important discovery, given that the occurrence of unpleasant side effects limits the use of approved drugs that reduce the absorption of fat in the intestines,” says Renata.
The second study came out on November 15 in the printed version of the journal Proceedings of the National Academy of Sciences (PNAS). It is an article with a lesser degree of appeal to the general public, but essential to the task of building a map with the molecular postcode of the blood vessels that irrigate each type of tissue in the human body, a challenge that Renata and Wadih’s group have been focusing on over the last few years. The work consisted of identifying four molecular postcodes from the biopsy of the tissue of three patients with cancer. Two vascular addresses are common to the tissues of several organs; one leads specifically to cancer metastases of the prostate and is found in bone marrow, and the other is linked to the cells of white adipose tissue, the technical name of the dangerous type of fat that accumulates around the stomach and below the skin. “This study is part of the work of our laboratory to show that blood vessels are more than just a ubiquitous and uniform ‘plumbing’ in the service of the circulatory system,” Wadih says. “We’re going to use these new ‘vascular addresses’ to develop drugs against cancer and obesity, or new methodologies for directing drugs and reducing side effects,” comments Fernanda Staquicini, a Brazilian researcher at MD Anderson and the first author of the work in the PNAS. Besides the scientist couple and Fernanda, four other Brazilians signed the article.
Designed by the Brazilians, the drug tested on the monkeys is formed by joining two molecules. The first is a fragment of a protein, technically called peptide, which is specifically linked to the prohibitin receiver, a chemical postcode found on the surface of the blood vessel cells of fatty tissue. The second is a spiral-shaped, corkscrew-like structure called KLAKLAK, which penetrates the blood vessel cells and selectively causes the death of these structures that irrigate the adipose tissue. KLAKLAK attacks the mitochondria, the power plant of cells. Without vessels to supply them with nutrients, the fat cells themselves die. Returning to the mail analogy, one molecule plays the role of mailman, and of finding the desired address, and the other is the letter bomb itself.
The results of the work with adipotide in obese rhesus monkeys were encouraging and confirm the data obtained in a similar study carried out with rodents in 2004. In addition to the primates having lost a little more than a tenth of their body weight, magnetic resonance images showed that there was a reduction of 27% in the feared abdominal fat after using the drug for just 28 days. Insulin-resistance, a diabetes risk factor, was reduced by 50% in the animals. No behavioral changes were seen in the monkeys, which continued interacting with those treating them, and there were no signs of nausea or food-aversion. “The main side effects were in the kidneys,” says Renata. “But they depend on the dose of the drug used, were already forecast and are reversible.” When they stop taking adipotide, its positive and negative effects disappear. The drug caused no alteration in weight in thin monkeys, indicating that the compound only attacks the blood vessels of adipose tissue.
It is interesting to note that the work with fat monkeys has direct implications on the central line of research of the Brazilian couple. “Obesity is a major risk factor for the development of cancer and has more or less the same weight as smoking,” says Wadih. “From any angle, obese patients with cancer react worse to surgery and radiotherapy or chemotherapy. But like smoking, obesity is potentially reversible.” The next step will be to test adipotide in obese individuals with prostate cancer, a clinical experiment that is being prepared by the MD Anderson Cancer Center team. Patients are going to receive the drug every day for four weeks and it will be checked if the loss of body mass and reduction in risks associated with obesity also lead to benefits for controlling the tumor.
For Lício Velloso, a doctor from the State University of Campinas (Unicamp), who is a specialist in obesity studies, Renata and Wadih’s scientific article, which shows the effects of the adipotide drug in overweight rhesus monkeys, is a very good and interesting piece of work. “Though extremely promising for the treatment of obesity, this type of approach (not necessarily this drug) must be submitted to important scrutiny to investigate the destination of the fat,” says Velloso. “If there’s a reduction in the mass of the adipose tissue it’s important to know where the flow of lipids (fats) that should be stored in that tissue is being diverted to,” says Velloso.
According to the researcher from Unicamp, there is a possibility that these lipids are lodging in the liver, increasing the risk of hepatic steatosis, cirrhosis and cancer in the organ. A second hypothesis is that the fat has migrated to the artery walls, where it could cause a blockage of the circulatory system and perhaps unleash a heart attack or stroke. Individuals affected by the disease called lipodystrophy, caused by a spontaneous mutation in a gene, have no adipose tissue. However, the STM study showed no increase in the storage of lipids in the liver or in the artery walls. The adipotide drug did not have this negative effect. Renata and Wadih add that they examined the circulation, feces and more than 40 tissues of the monkeys that received the drug and found no fat accumulation.
More than 130 patents
Renata and Wadih are cautious when asked if the methodology of hunting down vascular postcodes to use them as targets for new therapies can lead to a cure for cancer or even obesity. “We don’t know when we’ll have all the replies,” ponders the molecular biologist. “Developing drugs is complex and time-consuming.” To discover the most efficient peptides to take the deadly KLAKLAK to the blood vessel cells to be attacked, the researchers use a technique called phage display. In general terms, the method consists of injecting billions of particles of a virus that only attacks bacteria, (the phages), into an organism. In its genome, each virus carries different strands of DNA that code particular peptides. The affinity between these peptides and proteins of the vessels of each type of tissue determines the distribution of the phages in the organism. DNA sequencing of the phages then enables the identification of the peptides that are only linked to certain tissues, such as the vessels of fatty tissue or of tumors. “With the more modern techniques of genomics, we can sequence the DNA of phages found in various tissues on a large scale and discover more peptides of interest to us,” comments Emmanuel Dias-Neto, head of the Laboratory of Medical Genomics of the A.C. Camargo Hospital in São Paulo, who also took part in the work in the PNAS.
Various groups around the world are using the peptides obtained by the Brazilian couple. In Italy, Angelo Corti, from the San Raffaele del Monte Tabor Foundation in Milan, did studies on animals with the NGR peptide as a transporter of the TNF molecule, which damages the blood vessels of tumors. Now, the drug is being tested in patients by Molmed. There are also similar studies in Germany. At the University of São Paulo, biochemist Ricardo Giordano, who spent 10 years at MD Anderson, is testing a drug in rodents against a sight deficiency known as retinopathy of prematurity, based on a peptide formulated in Texas (see article in Pesquisa FAPESP issue 173, July 2010).
Renata, Wadih and the MD Anderson center have more than 130 patents relating to molecules discovered by their innovative approach, including that of adipotide, already licensed by Ablaris, a company with which the researchers have business relations. When 99% of the patents requested in the United States since 1946 are counted, Renata’s is among the 400 most important names on the list. Shortly, a new study should be published by the couple with a peptide that was tested on patients with prostate cancer. “We’ve already found hundreds of vascular postcodes and every day we discover more,” says Renata.
STAQUICINI, F.I. et al. Vascular ligand-receptor mapping by direct combinatorial selection in cancer patients. PNAS. v. 108, n. 46, p. 18.637-42. 15 Nov. 2011.
BARNHART, K.F. et al. A peptidomimetic targeting white fat causes weight loss and improved insulin resistance in obese monkeys. Science Translational Medicine. v. 3, n. 108, p. 108-12. 9 Nov. 2011.