Wonderful! Engineered prosthetics that target "glutamine addiction" in cancer cells so that healthy cells are not harmed

background

The rapid growth of tumor cells requires a lot of energy, a lot of substrate for the synthesis of proteins and nucleic acids
.
Since glutamine can act as an energy source through the tricarboxylic acid (TCA) cycle and provide carbon and nitrogen as precursors for amino acid, lipid and nucleotide synthesis and maintenance of redox balance, tumor cells have a higher glutamine consumption rate than normal tissues, so it has great therapeutic potential
to completely block the utilization of glutamine in cancer cells.

6-Diazo-5-oxo- L-norleucine (DON) has a high structural similarity to glutamine, not only selectively blocking multiple reactions using glutamine, leading to tumor cell starvation, but also enhancing the cytotoxic effects of T cells in the tumor microenvironment, showing good efficacy in 31 (66%) of 47 patients treated with DON for 2 weeks or more in one of the first clinical studies using DON
。 Unfortunately, broad metabolic inhibitors such as DON exhibit toxicity in healthy gastrointestinal (GI) tissues that are highly dependent on glutamine, and clinical development of DON has been abandoned due to its dose-limiting toxicity to normal tissues, particularly gastrointestinal tissues (e.
g.
, mucositis, diarrhea, and gastric bleeding).

Prodrug refers to a compound
in which the drug has been chemically modified, obtained in vitro inactive or less active, and has been enzymatically hydrolyzed or non-enzymatically transformed in the body to release the active drug and exert its medicinal effect.

Research highlights

Researchers at Johns Hopkins University School of Medicine have cleverly engineered DON to better target cancer cells without harming healthy tissue
.
Their experimental report was published Nov.
16 in
the journal Science Advances.

The researchers used a discrete chemical approach to design DON's tumor-targeted precursor drug, DRP-104, using two "precursor groups" that can be cleaved by enzymes rich in tumors (but not in gastrointestinal tissue) — adding acetylated tryptophan to the amine group and isopropyl ester
to the DON carboxylic acid.
DRP-104 is inactive against glutamine enzymes, including GLS-1, nor is the deesterified metabolite M1 of DRP-104 (see figure below).

Although DRP-104 is completely unstable in wild-type WT C57BL/6 mouse plasma (0% remaining at 60 min), it shows good stability in C57BL/6/CES1-/-mouse and human plasma (90% remaining >at 60 min
).
It is important to note that such interspecific metabolic differences are not uncommon
in precursor drug development.
Carboxylesterase 1 (CES1) is known to be very abundant in rodent plasma, but not in higher species, especially human plasma
.
C57BL/6/CES1-/-Mice are produced by inactivating the CES1 gene, with undetectable CES activity in their plasma but normal activity in tissue, making these mice better preclinical models
for mimicking human metabolism.
Assessing DRP-104 stability in mouse intestinal tissue homogenate and human small intestinal S9 tissue showed that DRP-104 was completely hydrolyzed to the charged and inactive intermediate metabolite M1 within 60 minutes in both intestinal stromals with less than 10%
DON release.

Experiments on DRP-104 administered in C57BL/6/CES1-/-tumor-bearing mouse model showed that DRP-104 in tumors in mice was activated into DON with anti-tumor activity, and the dose of DON was 6 times higher than in plasma and 11 times higher than in gastrointestinal tissue, respectively, showing complete tumor regression without gastrointestinal side effects
.
DRP-104 also enhances the efficacy of anti-PD-1 immunotherapy, which is CD8⁺ T cell-dependent
.
Most notably, mice cured with DRP-104 monotherapy were able to completely resist tumor re-attack, suggesting that glutamine antagonist therapy triggered immune memory
.
Based on these promising preclinical data, DRP-104 is currently undergoing clinical trials (NCT04471415) for the treatment of advanced solid tumors
as a monotherapy and in combination with immunotherapy.

"Our goal is to engineer an existing anti-cancer drug, DON, which shows strong efficacy but is too toxic, especially for the gut, to be clinically developed
.
" For this, we use a precursor drug approach
.
Our approach is unique in that we utilize a novel chemical design to create a prodrug that is simultaneously biologically activated in cancer cells but biologically inactivated
in healthy tissues such as the gut.
Dr.
Barbara Slusher, the study's author, is a professor of neurology, pharmacology and molecular sciences, psychiatry, neuroscience, medicine and oncology at the Johns Hopkins University School of Medicine and director of the Johns Hopkins Drug Discovery Program, M.
S.

The newly modified prodrug takes advantage of a common property of cancer cells: a strong appetite for glutamine — fast-growing cancer cells use large amounts of glutamine, a phenomenon known as "glutamine addiction," but other healthy cells that rotate quickly, such as those in the gut, also rely on glutamine
.

Co-author Rana Rais, Ph.
D.
, Associate Professor of Neurology and Pharmacology, said: "DRP-104 is a tumor-targeted prodrug for the glutamine-mimicking drug DON (6-diazo-5-oxo-l-norleucine), which inhibits a variety of glutamine-utilizing enzymes
in cancer cells.
" Slusher, Rais and their team's chemical modifications to DON allowed the development of this promising drug to resume.

"We added a chemical group called promoieties to DON and inactivated DON until it reaches the tumor, where the promoter group is cut off by enzymes that are abundant in the tumor but not in the gut," said Slusher, a member of
the Kimmel Cancer Center and Cancer Immunotherapy Institute at Johns Hopkins University.
"This particular prodrug design allows DON to target the intended destination – the tumor, with less
impact on healthy cells elsewhere.
"

In the new study, the researchers injected the original DON drug and the enhanced DRP-104 drug into mice implanted with tumors
.
In mice treated with DRP-104, the researchers found that the drug activity in tumors was 11 times
higher than in the gastrointestinal tract (intestine).
Both drugs completely wiped out the tumor, but DON was more intestinally toxic to mice than DRP-104
.

Slusher and study co-authors Rana Rais, Pavel Majer and Jonathan Powell co-founded a biotechnology company, Dracen Pharmaceuticals, which licenses the new precursor for clinical development
.
DRP-104 is undergoing Phase I/II clinical trials across the United States, including Johns Hopkins University Gimir Cancer Center, for patients with
advanced solid tumors.
Slusher said her Johns Hopkins Drug Discovery Lab is also actively looking for other drugs
that have failed in clinical trials due to toxicity issues.
They hope to apply this prodrug design to
drugs that treat other diseases.