RTx-303, an Orally Bioavailable Polθ Polymerase Inhibitor That Potentiates PARP Inhibitors in BRCA Mutant Tumors

Gurushankar Chandramouly; William Fried; John Gordon; Douglas Ralph; Channita Keuk; Sangeeta Kumari; Mercy Ramanjulu; William Auerbacher; Leonid Minakhin; Taylor Tredinnick; Bernadette Tiberi; George Morton; Robert Betsch; Kathy Q. Cai; Umeshkumar M. Vekariya; Mrityunjay Tyagi; Tomasz Skorski; Sergey Karakashev; Neil Johnson; Wayne E. Childers; Xiaojiang S. Chen; Richard T. Pomerantz

doi:10.1021/acs.jmedchem.5c00551

RTx-303, an Orally Bioavailable Polθ Polymerase Inhibitor That Potentiates PARP Inhibitors in BRCA Mutant Tumors

Gurushankar Chandramouly
, William Fried
, John Gordon
, Douglas Ralph
, Channita Keuk
, Sangeeta Kumari
, Mercy Ramanjulu
, William Auerbacher
, Leonid Minakhin
, Taylor Tredinnick
, Bernadette Tiberi
, George Morton
, Robert Betsch
, Kathy Q. Cai
, Umeshkumar M. Vekariya
, Mrityunjay Tyagi
, Tomasz Skorski
, Sergey Karakashev
, Neil Johnson
, Wayne E. Childers

Xiaojiang S. Chen, Richard T. Pomerantz

Thomas Jefferson University
University of Southern California
Temple University
Pennsylvania Biotechnology Center
Fox Chase Cancer Center

Research output: Contribution to journal › Article › peer-review

3 Scopus citations

Abstract

DNA polymerase θ (Polθ) is a polymerase-helicase fusion protein that is synthetically lethal with homologous recombination (HR) factors, such as BRCA1/2, and confers resistance to PARP inhibitors (PARPi) and other genotoxic cancer therapies. Previously developed Polθ polymerase (Polθ-pol) inhibitors (Polθi) exhibited limited pharmacological activity and metabolic stability, warranting the development of a Polθi with improved drug-like properties. Here, we developed RTx-303, a selective allosteric small-molecule Polθ-pol inhibitor that exhibits 5.1 nM IC 50, 88% oral bioavailability, and a prolonged half-life along with its equipotent metabolite. X-ray crystallography highlights the development of a solvent-exposed side-chain that is essential for the optimal drug-like properties of RTx-303. Notably, RTx-303 exhibits significantly higher cellular potency than previously developed Polθ-pol inhibitors and strongly potentiates PARPi in BRCA1/2 mutant cells and patient-derived xenograft models. The superior potency, robust pharmacological activity, and high tolerability of RTx-303 warrant further development as a Polθ-pol inhibitor drug candidate.

Original language	English
Pages (from-to)	22196-22215
Number of pages	20
Journal	Journal of Medicinal Chemistry
Volume	68
Issue number	21
Early online date	Oct 22 2025
DOIs	https://doi.org/10.1021/acs.jmedchem.5c00551 https://doi.org/10.1021/acs.jmedchem.5c00551
State	Published - Nov 13 2025

UN SDGs

This output contributes to the following UN Sustainable Development Goals (SDGs)

SDG 3 Good Health and Well-being

Keywords

Administration, Oral
Animals
Antineoplastic Agents/pharmacology
BRCA1 Protein/genetics
BRCA2 Protein/genetics
Biological Availability
Cell Line, Tumor
Crystallography, X-Ray
DNA Polymerase theta
DNA-Directed DNA Polymerase/metabolism
Enzyme Inhibitors/pharmacology
Female
Humans
Mice
Mutation
Poly(ADP-ribose) Polymerase Inhibitors/pharmacology
Rats
Structure-Activity Relationship
Xenograft Model Antitumor Assays

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Chandramouly, G., Fried, W., Gordon, J., Ralph, D., Keuk, C., Kumari, S., Ramanjulu, M., Auerbacher, W., Minakhin, L., Tredinnick, T., Tiberi, B., Morton, G., Betsch, R., Cai, K. Q., Vekariya, U. M., Tyagi, M., Skorski, T., Karakashev, S., Johnson, N., ... Pomerantz, R. T. (2025). RTx-303, an Orally Bioavailable Polθ Polymerase Inhibitor That Potentiates PARP Inhibitors in BRCA Mutant Tumors. Journal of Medicinal Chemistry, 68(21), 22196-22215. https://doi.org/10.1021/acs.jmedchem.5c00551, https://doi.org/10.1021/acs.jmedchem.5c00551

@article{37dbb3f168fb4f1f93a854d5912f8c2f,

title = "RTx-303, an Orally Bioavailable Polθ Polymerase Inhibitor That Potentiates PARP Inhibitors in BRCA Mutant Tumors",

abstract = "DNA polymerase θ (Polθ) is a polymerase-helicase fusion protein that is synthetically lethal with homologous recombination (HR) factors, such as BRCA1/2, and confers resistance to PARP inhibitors (PARPi) and other genotoxic cancer therapies. Previously developed Polθ polymerase (Polθ-pol) inhibitors (Polθi) exhibited limited pharmacological activity and metabolic stability, warranting the development of a Polθi with improved drug-like properties. Here, we developed RTx-303, a selective allosteric small-molecule Polθ-pol inhibitor that exhibits 5.1 nM IC 50, 88\% oral bioavailability, and a prolonged half-life along with its equipotent metabolite. X-ray crystallography highlights the development of a solvent-exposed side-chain that is essential for the optimal drug-like properties of RTx-303. Notably, RTx-303 exhibits significantly higher cellular potency than previously developed Polθ-pol inhibitors and strongly potentiates PARPi in BRCA1/2 mutant cells and patient-derived xenograft models. The superior potency, robust pharmacological activity, and high tolerability of RTx-303 warrant further development as a Polθ-pol inhibitor drug candidate. ",

keywords = "Administration, Oral, Animals, Antineoplastic Agents/pharmacology, BRCA1 Protein/genetics, BRCA2 Protein/genetics, Biological Availability, Cell Line, Tumor, Crystallography, X-Ray, DNA Polymerase theta, DNA-Directed DNA Polymerase/metabolism, Enzyme Inhibitors/pharmacology, Female, Humans, Mice, Mutation, Poly(ADP-ribose) Polymerase Inhibitors/pharmacology, Rats, Structure-Activity Relationship, Xenograft Model Antitumor Assays",

author = "Gurushankar Chandramouly and William Fried and John Gordon and Douglas Ralph and Channita Keuk and Sangeeta Kumari and Mercy Ramanjulu and William Auerbacher and Leonid Minakhin and Taylor Tredinnick and Bernadette Tiberi and George Morton and Robert Betsch and Cai, \{Kathy Q.\} and Vekariya, \{Umeshkumar M.\} and Mrityunjay Tyagi and Tomasz Skorski and Sergey Karakashev and Neil Johnson and Childers, \{Wayne E.\} and Chen, \{Xiaojiang S.\} and Pomerantz, \{Richard T.\}",

note = "Publisher Copyright: {\textcopyright} 2025 The Authors. Published by American Chemical Society",

year = "2025",

month = nov,

day = "13",

doi = "10.1021/acs.jmedchem.5c00551",

language = "English",

volume = "68",

pages = "22196--22215",

journal = "Journal of Medicinal Chemistry",

issn = "0022-2623",

publisher = "American Chemical Society",

number = "21",

}

Chandramouly, G, Fried, W, Gordon, J, Ralph, D, Keuk, C, Kumari, S, Ramanjulu, M, Auerbacher, W, Minakhin, L, Tredinnick, T, Tiberi, B, Morton, G, Betsch, R, Cai, KQ, Vekariya, UM, Tyagi, M, Skorski, T , Karakashev, S , Johnson, N, Childers, WE, Chen, XS & Pomerantz, RT 2025, 'RTx-303, an Orally Bioavailable Polθ Polymerase Inhibitor That Potentiates PARP Inhibitors in BRCA Mutant Tumors', Journal of Medicinal Chemistry, vol. 68, no. 21, pp. 22196-22215. https://doi.org/10.1021/acs.jmedchem.5c00551, https://doi.org/10.1021/acs.jmedchem.5c00551

TY - JOUR

T1 - RTx-303, an Orally Bioavailable Polθ Polymerase Inhibitor That Potentiates PARP Inhibitors in BRCA Mutant Tumors

AU - Chandramouly, Gurushankar

AU - Fried, William

AU - Gordon, John

AU - Ralph, Douglas

AU - Keuk, Channita

AU - Kumari, Sangeeta

AU - Ramanjulu, Mercy

AU - Auerbacher, William

AU - Minakhin, Leonid

AU - Tredinnick, Taylor

AU - Tiberi, Bernadette

AU - Morton, George

AU - Betsch, Robert

AU - Cai, Kathy Q.

AU - Vekariya, Umeshkumar M.

AU - Tyagi, Mrityunjay

AU - Skorski, Tomasz

AU - Karakashev, Sergey

AU - Johnson, Neil

AU - Childers, Wayne E.

AU - Chen, Xiaojiang S.

AU - Pomerantz, Richard T.

PY - 2025/11/13

Y1 - 2025/11/13

N2 - DNA polymerase θ (Polθ) is a polymerase-helicase fusion protein that is synthetically lethal with homologous recombination (HR) factors, such as BRCA1/2, and confers resistance to PARP inhibitors (PARPi) and other genotoxic cancer therapies. Previously developed Polθ polymerase (Polθ-pol) inhibitors (Polθi) exhibited limited pharmacological activity and metabolic stability, warranting the development of a Polθi with improved drug-like properties. Here, we developed RTx-303, a selective allosteric small-molecule Polθ-pol inhibitor that exhibits 5.1 nM IC 50, 88% oral bioavailability, and a prolonged half-life along with its equipotent metabolite. X-ray crystallography highlights the development of a solvent-exposed side-chain that is essential for the optimal drug-like properties of RTx-303. Notably, RTx-303 exhibits significantly higher cellular potency than previously developed Polθ-pol inhibitors and strongly potentiates PARPi in BRCA1/2 mutant cells and patient-derived xenograft models. The superior potency, robust pharmacological activity, and high tolerability of RTx-303 warrant further development as a Polθ-pol inhibitor drug candidate.

AB - DNA polymerase θ (Polθ) is a polymerase-helicase fusion protein that is synthetically lethal with homologous recombination (HR) factors, such as BRCA1/2, and confers resistance to PARP inhibitors (PARPi) and other genotoxic cancer therapies. Previously developed Polθ polymerase (Polθ-pol) inhibitors (Polθi) exhibited limited pharmacological activity and metabolic stability, warranting the development of a Polθi with improved drug-like properties. Here, we developed RTx-303, a selective allosteric small-molecule Polθ-pol inhibitor that exhibits 5.1 nM IC 50, 88% oral bioavailability, and a prolonged half-life along with its equipotent metabolite. X-ray crystallography highlights the development of a solvent-exposed side-chain that is essential for the optimal drug-like properties of RTx-303. Notably, RTx-303 exhibits significantly higher cellular potency than previously developed Polθ-pol inhibitors and strongly potentiates PARPi in BRCA1/2 mutant cells and patient-derived xenograft models. The superior potency, robust pharmacological activity, and high tolerability of RTx-303 warrant further development as a Polθ-pol inhibitor drug candidate.

KW - Administration, Oral

KW - Animals

KW - Antineoplastic Agents/pharmacology

KW - BRCA1 Protein/genetics

KW - BRCA2 Protein/genetics

KW - Biological Availability

KW - Cell Line, Tumor

KW - Crystallography, X-Ray

KW - DNA Polymerase theta

KW - DNA-Directed DNA Polymerase/metabolism

KW - Enzyme Inhibitors/pharmacology

KW - Female

KW - Humans

KW - Mice

KW - Mutation

KW - Poly(ADP-ribose) Polymerase Inhibitors/pharmacology

KW - Rats

KW - Structure-Activity Relationship

KW - Xenograft Model Antitumor Assays

UR - https://www.scopus.com/pages/publications/105021427014

U2 - 10.1021/acs.jmedchem.5c00551

DO - 10.1021/acs.jmedchem.5c00551

M3 - Article

C2 - 41124685

SN - 0022-2623

VL - 68

SP - 22196

EP - 22215

JO - Journal of Medicinal Chemistry

JF - Journal of Medicinal Chemistry

IS - 21

ER -

RTx-303, an Orally Bioavailable Polθ Polymerase Inhibitor That Potentiates PARP Inhibitors in BRCA Mutant Tumors

Abstract

UN SDGs

Keywords

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