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In a first-in-human, Phase I trial, researchers at The University of Texas MD Anderson Cancer Center discovered that ATR inhibitor RP-3500 was safe and well tolerated with promising clinical benefit. Principal investigator Timothy A. Yap, Ph.D., associate professor of Investigational Cancer Therapeutics, today presented initial data from the trial at the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics.
The trial is the largest biomarker-selected study to test an ATR inhibitor as a single agent in cancers harboring synthetic lethal genomic alterations in DNA damage repair (DDR) pathways. Yap and his team observed preliminary antitumor efficacy in patients with advanced solid tumors — including ovarian, prostate and breast cancers — that were resistant, refractory or intolerant to standard therapy, including BRCA1 and BRCA2 mutated cancer patients who had previously received PARP inhibitor treatment. The potent and highly selective RP-3500 achieved meaningful clinical benefit across a variety of gene alterations in 34 of 69 evaluable patients (49%), including 12 patients with objective tumor responses, 14 patients with RECIST-defined stable disease for at least 16 weeks, and eight patients with early significant decreases in tumor markers and tumor shrinkage.
“Not only did RP-3500 demonstrate a favorable and differentiated safety profile, but our initial data also showed promising and distinct early efficacy,” Yap said. “Although this Phase I study has only had approximately nine months of dosing at efficacious doses of 100mg or more of RP-3500, we are encouraged by what we have observed so far in this hard-to-treat advanced cancer patient population.”
Various conditions of DNA damage, specifically breaks in the DNA double strand and replication stress, activate a complex network of DDR mechanisms. One of the key mediators of the DDR signaling pathway is the protein kinase ATR, which is activated in response to DNA replication stress — making it a promising therapeutic target in cancers with a range of DDR defects.
Based on a genome-wide CRISPR-based screening platform, 17 biomarkers for sensitivity to RP-3500 — including ATM, BRCA1/2 and other alterations — were identified for prospective patient selection for this trial.
“We were keen to give every patient the best chance of responding by only enrolling those who had at least one of these pre-identified actionable predictive biomarkers of response to RP-3500,” Yap said.
The study enrolled a total of 101 patients with heavily pre-treated advanced solid tumors carrying synthetic lethal genomic alterations that researchers predicted for ATR inhibitor sensitivity. The primary endpoints of the study were safety and tolerability, as well as recommended phase 2 dose (RP2D) and optimal schedule. Other endpoints included pharmacokinetics, pharmacodynamics and preliminary antitumor activity.
Patients were treated on different doses and schedules of RP-3500. Treatment emergent adverse events of all grades most commonly included grade 1-2 anemia, fatigue and decreased appetite. Grade 3 anemia was observed in 21.8% of all patients treated. No grade 4 or worse anemia was reported during the trial.
After assessing the adverse events, pharmacokinetic, pharmacodynamic and antitumor activity, the researchers determined the RP2D of RP-3500 to be 160mg once daily for three days, followed by four days off.
Early analysis of antitumor activity shows promising clinical activity across a spectrum of tumor types and genetic alterations, including ATM or CDK12-mutated castration-resistant prostate cancer, PARP inhibitor-resistant ovarian cancer with BRCA1 or RAD51C mutations, BRCA1-mutated ER+ breast cancer, BRCA1 mutated head and neck squamous cell carcinomas and BRCA2 mutated melanoma.
While the study is ongoing, Yap is encouraged by the initial data and will soon open enrollment to the TRESR Phase II expansion cohorts.
“Our promising early clinical data of this potent and highly selective ATR inhibitor offer a clear direction for further development of RP-3500,” Yap said. “We will continue to assess RP-3500 in patients with defined molecular alterations and also in novel rational combinations.”
The trial was supported by Repare Therapeutics through its strategic collaboration with MD Anderson. A full list of co-authors and their disclosured can be found here.
The University of Texas MD Anderson Cancer Center and the Rare Cancer Research Foundation today announced the launch of a collaboration designed to accelerate the development of new treatments for rare cancers by empowering all patients in the United States to contribute tumor samples directly to MD Anderson for translational research efforts.
This initiative is designed to overcome a major obstacle that has long prevented significant progress in rare cancer research — the lack of available samples. The Rare Cancer Research Foundation will use its Pattern.org online engagement platform to enable patients to donate tumor biopsies and surgical samples for research purposes.
With these samples, MD Anderson researchers will perform comprehensive analyses and will work to develop laboratory models that can be used to pursue new therapeutic strategies for rare cancers. New discoveries then can be used to design and launch clinical trials to evaluate these strategies for patients in need.
“The development of new rare cancer treatments is often stymied not by hard scientific questions but rather by the lack of patient models and datasets necessary to conduct research,” explained Mark Laabs, founder and chairman of the Rare Cancer Research Foundation. “We are delighted that this collaboration will empower patients nationwide to contribute their samples and medical information to cutting-edge work at MD Anderson and to accelerate the development of new treatments for rare cancers.”
Rare cancers are defined as those with fewer than 40,000 new cases diagnosed annually in the U.S. Taken together, rare cancers represent roughly 25% of all cancer cases and are the leading cause of cancer-related deaths. The Rare Cancer Research Foundation is committed to advancing research for these cancer types through strategic investments and innovative collaborations. MD Anderson is a world leader in the diagnosis and treatment of these cancers; more than 5,000 patients with the rarest diagnoses seek treatment at the institution each year.
“Our collaboration with the Rare Cancer Research Foundation allows rare cancer patients having surgery anywhere in the U.S. to join in the research effort by contributing excess tumor tissue, giving them the opportunity to truly make an impact on the entire community of these patients,” said Andy Futreal, Ph.D., chair of Genomic Medicine at MD Anderson. “Each piece of data or model generated is a potentially transformative tool that can advance our understanding and bring us closer to effective new therapies.”
MD Anderson established its Rare Tumor Initiative in 2019 to comprehensively characterize rare tumors throughout the course of each patients’ care. In 2021, the institution launched a translational research platform with the Broad Institute of MIT and Harvard, designed to create a catalog of rare cancer models and to provide a data resource for researchers in the field. The current collaboration will integrate with these efforts to further accelerate the pace of research and generate much-needed therapeutic insights.
Research efforts at MD Anderson will be led by Futreal and Timothy Heffernan, Ph.D., executive director of Translational Research to AdvanCe Therapeutics and Innovation in ONcology (TRACTION) platform. The work will focus on comprehensive molecular and functional characterization of donated tumor samples, with the potential to generate laboratory cell lines to enable further study. The initiative aims to fully characterize more than 60 rare cancer samples and develop 20 laboratory models. These data and models will be made available to the research community, allowing scientists worldwide to contribute breakthroughs to the field.
Researchers from The University of Texas MD Anderson Cancer Center have discovered that grouping epidermal growth factor receptor (EGFR) mutations by structure and function provides an accurate framework to match patients with non-small cell lung cancer (NSCLC) to the right drugs. The findings, published today in Nature, identify four subgroups of mutations and introduce a new strategy for testing tyrosine kinase inhibitors (TKIs), as well as instant clinical opportunities for approved targeted therapies.
“More than 70 different EGFR mutations have been identified in patients, but drugs have only been approved for a handful of them. One of the immediate implications of our research is the discovery that therapies we already have may work for many of these mutations. For some mutations, older drugs may actually work better, and for other mutations, newer drugs work better,” said John Heymach, M.D., Ph.D., chair of Thoracic/Head & Neck Medical Oncology and senior author of the study. “Right now, in the absence of guidance, clinicians often use the newest treatment for all EGFR mutations. This model can help us pick better therapies for patients immediately and hopefully develop better drugs for specific subgroups of mutations.”
First-, second- and third-generation TKIs use different mechanisms to target the EGFR protein. Heymach and his team found that drugs work better for certain subgroups based on how the mutations within a given group functionally impact the drug-binding pocket on the protein.
The four EGFR-mutant NSCLC subgroups identified by the team are:
- Classical-like mutations, with little to no impact on drug binding
- T790M-like mutations, which contain at least one mutation in the hydrophobic cleft and often are acquired after resistance to a first-generation targeted therapy
- Exon 20 loop insertion mutations, characterized by insertions of additional amino acids in the loop after the C-terminal end of the αC-helix in exon 20
- P-loop αC-helix compression (PACC) mutations on the interior surface of the ATP binding pocket or C-terminal end of the αC-helix
The current approach to testing new drugs in EGFR-mutant NSCLC is
based on exon number, which indicates where the mutation occurs within
a linear portion of the DNA. Grouping mutations by exon has produced
mostly heterogeneous results in clinical studies and laboratory
models, which the authors note seems to indicate a poor correlation
between exon number and drug sensitivity or resistance.
“Within a given exon, mutations vary widely. We organized mutations based on how they impact the EGFR structure and drug binding instead, which allows for testing a drug across a whole group of mutations that are structurally similar at the same time,” Heymach said. “We believe this could become the new standard approach for classifying and describing mutations and then pairing them with the right drug.”
Big data reveals diversity in atypical mutations
Mutations in the EGFR protein are present in about 15% of NSCLCs in North America and about 30 to 40% in Asia. Overall, more than 70 different types of EGFR mutations exist. “Classical” mutations tend to respond well to FDA-approved targeted therapies, but effective therapies and guidelines for the remaining “atypical” mutations have been lacking.
For this study, the researchers analyzed data from 16,175 patients with EGFR-mutant NSCLC from five different patient databases. Primary and co-occurring mutations were recorded for 11,619 patients. Of those, 67.1% had classical EGFR mutations, 30.8% had atypical EGFR mutations and 2.2% had both.
One of the key databases to provide detailed molecular and outcome information for the study was the Genomic Marker-Guided Therapy Initiative (GEMINI), a big data project of the Lung Cancer Moon Shot®, part of MD Anderson’s Moon Shots Program®, a collaborative effort designed to accelerate the development of scientific discoveries into clinical advances that save patients’ lives.
For both classical and atypical EGFR mutations, the team analyzed the time to treatment failure (TTF), an indication of how quickly a cancer becomes resistant to therapy. The researchers found a shorter TTF and lower overall survival for patients with atypical mutations regardless of treatment type. Patients with classical mutations treated with first- and third-generation TKIs had a longer TTF.
The researchers then created a panel of 76 cell lines with EGFR mutations and screened those cell lines against 18 EGFR inhibitors, which revealed the four distinct subgroups. Comparing the correlation to drug sensitivity by subgroup, versus exons, showed that the structure-based subgroups were more predictive than exon-based groups. The subgroup approach was further validated by machine learning to analyze data by classification and regression trees.
Classical-like mutations were sensitive to all classes of TKIs, particularly third-generation TKIs. Exon 20 loop insertion mutations remained the most heterogeneous subgroup, with certain mutations responding best to second-generation TKIs. T790M-like mutations were sensitive to ALK and PKC inhibitors, with some mutations retaining sensitivity to third-generation TKIs. PACC mutations were most sensitive to second-generation TKIs.
“Proteins aren't linear, so grouping mutations by exon didn’t seem an intuitive approach to me when I started thinking about how to match the right drug to the right mutation seen in patients,” said Jacqulyne Robichaux, Ph.D., assistant professor of Thoracic/Head & Neck Medical Oncology Research and lead author of the study. “Proteins are three dimensional, and this led us to investigate if there were areas of the proteins that correlate with drug sensitivity when mutated, which is what we found. These subgroups share properties in their structure that directly relate to their function and retrospectively predicted patient outcomes better than the traditional approach.”
Further emphasis on the role of next-generation sequencing and future studies
The study also highlights the importance of biomarker testing for all patients with a new diagnosis or recurrence of NSCLC. Current next-generation sequencing methods have the ability to detect the full spectrum of known oncogenic driver EGFR mutations, virtually all of which fall into one of the four structure-based subgroups. The authors note that this is especially important for rare mutations, which are more difficult to study through a traditional clinical trial approach based on individual mutations. Future prospective studies will help refine and inform the subgroup framework.
“This is an important advance for patients because, right now, there is no FDA-approved targeted therapy for the majority of EGFR mutations, leaving clinicians in the dark as to what drug to use for which mutation,” Heymach said. “Now, based on the structural group in which the mutation falls, we can better match the best drug for a given mutation. Going forward, this may also help focus drug development efforts, by testing drugs against an entire group of mutations that are structurally similar, rather than against individual mutations.”
This research was funded by the Lung Cancer Moon Shot and the National Cancer Institute (NCI) MD Anderson Cancer Center Support Grant (P30 CA016672). Additional research support was provided by the National Institutes of Health and NCI (R01CA247975, R01CA234183, R01CA190628, Lung SPORE P50 CA070907-20, 1U54CA224065-01), the Cancer Prevention and Research Institute of Texas (CPRIT-IIRA RP200150), the David Bruton, Jr. Chair, Rexanna’s Foundation for Fighting Lung Cancer, the Hallman Fund, generous donors to the Stading Fund for EGFR Resistance Research, the Gil and Dody Weaver Foundation, the Hanlon Fund, generous donors to the Richardson Family Fund, Spectrum Pharmaceuticals (SP) and the American Society of Clinical Oncology (CDA-57112).
The University of Texas MD Anderson Cancer Center has an institutional financial conflict of interest with Spectrum related to this research. Dr. Heymach also has a financial interest with Spectrum. Due to these financial interests and Dr. Heymach’s role as an Institutional Decision Maker under our policies, MD Anderson has implemented an Institutional Conflict of Interest Management and Monitoring Plan (Plan) to manage and monitor the conflict of interest with respect to MD Anderson’ s conduct of this research. MD Anderson, including Heymach and Robichaux, have filed a patent for the use of poziotinib and licensed the technology to SP. MD Anderson, including Heymach and Robichaux have a pending patent submitted for treatment of EGFR TKI resistant NSCLC and another for the classification of EGFR mutations.
Heymach and Robichaux report research support from Spectrum Pharmaceuticals, Takeda and Enliven Therapeutics. Heymach also receives grant or research support from AstraZeneca (AZ) and GlaxoSmithKline (GSK) and has served on advisory committees for AZ, Boehringer Ingelheim, Bristol Myers Squibb, Catalyst, EMD Serono, Foundation Medicine, Hengrui Therapeutics, Genentech, GSK, Guardant Health, Lilly, Merck, Novartis, Pfizer, Roche, Sanofi, Seagen (formerly Seattle Genetics), SP and Takeda, and serves as scientific advisor for Rexanna’s Foundation for Fighting Lung Cancer and the EGFR Resisters. A full list of co-authors and their disclosures can be found in the paper.