SEQUENCE LISTING

The instant application contains a Sequence Listing which has been submitted electronically in ASCII format and is hereby incorporated by reference in its entirety. Said ASCII copy, created on Jan. 25, 2022, is named Sequence_Listing.txt and is 13 kilobytes in size.

TECHNICAL FIELD

The present invention relates to a peptide and use of that peptide. Specifically, the present invention relates to a peptide having a high degree of accumulation in cancer cells or cancer tissue in the digestive system, a nucleic acid that encodes the peptide, a peptide-drug conjugate containing the peptide, a pharmaceutical composition containing the peptide-drug conjugate, a labeled peptide containing the peptide, an imaging composition containing the labeled peptide, and a vector, a peptide-drug conjugate expression vector and a labeled peptide expression vector each having the above nucleic acid. Priority is claimed on Japanese Patent Application No. 2018-088811, filed May 2, 2018, the content of which is incorporated herein by reference.

BACKGROUND ART

Pancreatic cancer (invasive pancreatic ductal adenocarcinoma) has a mean survival time of about 6 months following diagnosis, and is among the most intractable malignancies. According to demographic statistics published by the Ministry of Health, Labor and Welfare, annual deaths due to pancreatic cancer continue to increase each year, and the 2016 statistics record 33,475 deaths. Further, deaths due to pancreatic cancer represent 9% of all cancer deaths, the fourth highest percentage following lung cancer, colon cancer and stomach cancer. According to an investigative report on nationwide pancreatic cancer registrations (2007), the number of resectable cases of pancreatic cancer represented approximately 40% of all cases, with the three-year survival rate for the resectable cases being a low 23.2%.

One reason for the difficulty in treating pancreatic cancer is that subjective symptoms are limited, making early detection difficult, and in the majority of cases, at the time of detection the cancer has already reached an advanced state, meaning surgical intervention is either impossible or limited to palliative operations. Further, other reasons that make treatment difficult include the fact that the tissue construct of invasive pancreatic ductal adenocarcinoma is a hard cancer (scirrhous carcinoma) that is accompanied by severe background fibrosis, the fact that pancreatic cancer cells themselves have a growth capacity and are biologically highly aggressive with high drug resistance, and the fact that pancreatic cancer has a propensity to readily invade or metastasize from an early stage. The characteristic stroma in pancreatic cancer with severe fibrosis act as a barrier that inhibits effective penetration of anticancer drugs to the cancer cells, which in combination with the various issues outlined above, means there are currently no effective anticancer drugs capable of significantly improving this type of situation, leaving future development the current hope.

Incidentally, among trends in the pharmaceutical field for the utilization of peptides as biomaterials, cell membrane-permeable (bioabsorbable) peptides such as Tat, Penetratin and poly-arginin are attracting much attention. However, these peptides are absorbed extensively and non-selectively, with no distinction between normal cells or normal tissue and tumor cells or tumor tissue. Accordingly, application of these peptides to medical treatment DDS (drug delivery system) tools for patient malignant tumors including solid carcinomas, which requires target-selective drug delivery, is problematic due to the severe side-effects. In particular, cell membrane-permeable (bioabsorbable) peptides such as Tat that have been widely used in experimental systems around the world are known to cause accumulation in the liver (for example, see non-Patent Document 1).

In contrast, cyclic RGD is the only medicated peptide. Cyclic RGD targets the αvβ3 integrin that has been reported to be expressed highly in new blood vessels or vascular endothelial cells that constitute existing blood vessels (and in some tumor cells), acts through vascular hyperpermeability, and is expected to offer a drug transport effect by enhancement of an EPR (enhanced permeability and retention) effect (a substance diffusion effect via blood vessels). Accordingly, cyclic RGD is not used alone, but is rather used simultaneously in combination with another drug as an imaging agent or DDS agent (for example, see Patent Document 1). However, the permeability and action of cyclic RGD relative to cancer cells themselves is extremely poor, with the cyclic RGD system effectively offering mainly a drug diffusion effect via the blood vessels that is largely dependent on the structure (development and distribution of blood vessels) of the tumor tissue. For these reasons, a satisfactory effect cannot be expected in those cases where an anticancer treatment based on direct elimination of the cancer cells themselves is being targeted.

In order to address the types of issues outlined above, the inventors of the present invention have been developing peptides which act directly on pancreatic cancer cells or pancreatic cancer tissue, and act directly on (are incorporated into) tumors via highly shifted absorption (for example, see Patent Document 2).

Generally, oligopeptides composed of several to about 20 amino acids are known to be prone to rapid degradation, metabolism and excretion in vivo as a result of a large variety of proteases that exist within human blood plasma and cells, with elimination from the administered body typically occurring within a period of several minutes to several tens of minutes, and this ready decomposability is a significant problem when peptides are used in vivo as practical drugs. In actuality, although the peptide disclosed in Patent Document 2 exhibits a high degree of accumulation in pancreatic cancer cells or pancreatic cancer tissue, degradation of the constituent amino acids starts within several minutes of administration in the presence of blood plasma, with complete denaturation occurring within about 20 minutes, and therefore from a practicality viewpoint, there remains room for improvement from the perspective of in vivo degradation resistance.

PRIOR ART LITERATURE

Patent Documents

Patent Document 1: Japanese Patent (Granted) Publication No. 5721140Patent Document 2: International Patent Publication No. 2017/086090

Non-Patent Document

Non-Patent Document 1: Vives E., et al., A Truncated HIV-1 Tat Protein Basic Domain Rapidly Translocates through the Plasma Membrane and Accumulates in the Cell Nucleus, J. Biol. Chem., 272, 16010-16017, 1997.

DISCLOSURE OF INVENTION

Problems to be Solved by the Invention

The present invention has been developed in light of the above serious current issues associated with practical application in the medical field, and provides a novel peptide having a high degree of accumulation in cancer cells or cancer tissue in the digestive system including pancreatic cancer, and also having excellent degradation resistance in vivo, and also provides a nucleic acid that encodes the peptide, a peptide-drug conjugate containing the peptide, a pharmaceutical composition containing the peptide-drug conjugate, a labeled peptide containing the peptide, an imaging composition containing the labeled peptide, and a vector, a peptide-drug conjugate expression vector and a labeled peptide expression vector each containing the above nucleic acid.

Means for Solving the Problems

As a result of intensive research aimed at achieving the objects described above, the inventors of the present invention discovered that a novel peptide having an optimized amino acid sequence and an optimized peptide design based on that amino acid sequence maintained a high degree of accumulation not only in pancreatic cancer cells or pancreatic cancer tissue, but also in cancer cells or cancer tissue of the digestive system, while also having outstanding degradation resistance and persistence of action in vivo, and they were thus able to complete the present invention.

In other words, the present invention includes the following aspects.

A peptide according to a first aspect of the present invention is composed of an amino acid sequence represented by general formula (I) shown below, and has a high degree of accumulation in cancer cells or cancer tissue in the digestive system.
[Formula 1]
X11—(Y11—X12)n11(I)
(In general formula (I), X11is a peptide residue composed of an amino acid sequence of (a) or (b) below:

(a) an amino acid sequence represented by any of SEQ ID NOs: 1 to 3,

(b) an amino acid sequence including a sequence in which one or two amino acids have been deleted, substituted or added in an amino acid sequence represented by any of SEQ ID NOs: 1 to 3;

Y11is a peptide linker composed of an amino acid residue of at least 1 but not more than 10 amino acids, wherein each amino acid residue is independently a glycine residue, a proline residue, a serine residue, a cysteine residue or a lysine residue;

X12is either a peptide residue composed of an amino acid sequence of (a) or (b) above, or a retro-inverso peptide residue thereof. Further, n11 represents an integer of at least 1 but not more than 9.)

In the peptide according to the first aspect described above, Y11may be a peptide linker of at least 1 but not more than 10 amino acids, wherein each amino acid residue is independently a glycine residue, a cysteine residue or a lysine residue.

In the peptide according to the first aspect described above, n11 may be an integer of at least 1 but not more than 4.

In the peptide according to the first aspect described above, X11and X12may be peptide residues composed of the same amino acid sequence, or X12may be a retro-inverso peptide residue of X11.

The peptide according to the first aspect described above may be composed of an amino acid sequence represented by any of SEQ ID NOs: 15 to 31.

A nucleic acid according to a second aspect of the present invention encodes the peptide according to the first aspect described above.

A peptide-drug-conjugate according to a third aspect of the present invention comprises the peptide according to the first aspect described above and a biologically active substance.

A pharmaceutical composition according to a fourth aspect of the present invention comprises the peptide-drug-conjugate according to the third aspect described above.

The pharmaceutical composition according to the fourth aspect may be used for treatment of cancer of the digestive system.

The pharmaceutical composition according to the fourth aspect may be used for pancreatic cancer treatment.

The above biologically active substance may be an anticancer drug.

A labeled peptide according to a fifth aspect of the present invention comprises the peptide according to the first aspect described above and a labeling substance.

The labeling substance may be a stable isotope, a radioisotope, or a fluorescent substance.

An imaging composition according to a sixth aspect of the present invention comprises the labeled peptide according to the fifth aspect described above.

The imaging composition according to the sixth aspect may be used for cancer of the digestive system.

The imaging composition according to the sixth aspect may be used for pancreatic cancer diagnosis.

A vector according to a seventh aspect of the present invention has the nucleic acid according to the second aspect described above.

A peptide-drug-conjugate expression vector according to an eighth aspect of the present invention has the nucleic acid according to the second aspect described above and a nucleic acid that encodes a biologically active substance.

A labeled peptide expression vector according to a ninth aspect of the present invention has the nucleic acid according to the second aspect described above and a nucleic acid that encodes a labeling substance.

Effects of the Invention

The peptide of the aspect described above has a high degree of accumulation in cancer cells or cancer tissue in the digestive system (and particularly in pancreatic cancer cells or pancreatic cancer tissue), and exhibits excellent in vivo degradation resistance.

