PRMT5 Inhibition in MTAP-Deleted Mesothelioma

PRMT5 Inhibition in MTAP-Deleted Mesothelioma
At a Glance
Drug class	PRMT5 (arginine methyltransferase) inhibitors
FDA status	Investigational — none approved
Biomarker	Homozygous MTAP deletion (9p21 loss)
Mechanism	Synthetic lethality via MTA-cooperative PRMT5 blockade
Agents in trials	Navlimetostat (MRTX1719 / BMS-986504), TNG462
Efficacy data	None reported — all trials pre-readout
MTAP loss in mesothelioma	Roughly half of pleural cases (via 9p21 co-deletion)

Executive Summary

PRMT5 inhibition is an emerging, biomarker-directed treatment strategy being studied in mesothelioma tumors that have lost the MTAP gene. It is built on a principle called synthetic lethality: when a tumor deletes MTAP — which happens in roughly half of pleural mesotheliomas as part of a larger chromosomal loss — those cancer cells become unusually dependent on a related enzyme, PRMT5 (protein arginine methyltransferase 5). A drug that blocks PRMT5 can, in principle, kill the MTAP-deleted tumor cells while largely sparing normal cells that still have MTAP.

As of mid-2026, no PRMT5 inhibitor is approved by the U.S. Food and Drug Administration (FDA) for mesothelioma or any other cancer, and no efficacy or response-rate data have been reported for these drugs in mesothelioma. Every agent in this class remains experimental and available only through clinical trials. This page describes an early-stage research direction, not an available treatment.

Three trials anchor the current mesothelioma landscape: MRTX1719 (also known as BMS-986504, and since given the international nonproprietary name navlimetostat), a first-in-human phase 1 basket study in MTAP-deleted solid tumors that includes mesothelioma (NCT05245500, Recruiting as of August 2026); TNG462, a phase 1/2 study of a selective PRMT5 inhibitor alone and with pembrolizumab in MTAP-deleted tumors (NCT05732831, Recruiting as of September 2026); and SELECTmeso, a UK mesothelioma-specific phase 2 platform trial whose first arm (SELECTmeso1) tests navlimetostat (BMS-986504) in MTAP-deficient relapsed mesothelioma (NCT07602946). ClinicalTrials.gov still lists SELECTmeso1 as Not yet recruiting as of its last update (verified May 2026), but the trial site reported in June 2026 that recruitment had opened at Leicester Royal Infirmary — a status change the registry entry had still not caught up to as of September 2026. Because all three are phase 1, phase 1/2, or not-yet-open, they are designed to establish safety, dosing, and preliminary activity — not to prove that PRMT5 inhibition extends survival. At the IASLC 2026 World Conference on Lung Cancer (WCLC) in Seoul (September 12–15, 2026), SELECTmeso1's Chief Investigator, Professor Dean Fennell, presented trial-in-progress data — trial status and design, not efficacy results — in a poster session, underscoring that the trial remains in its early enrollment phase. Patients interested in this approach should discuss molecular testing and trial eligibility with their oncology care team.

At-a-Glance

PRMT5 inhibition in MTAP-deleted mesothelioma at a glance:

• Investigational only — no PRMT5 inhibitor is FDA-approved for mesothelioma or any cancer as of mid-2026; all are trial-access only.
• The target — tumors that have deleted MTAP (methylthioadenosine phosphorylase) become dependent on PRMT5, creating a synthetic-lethal vulnerability.
• How it works — MTAP loss lets its substrate MTA (methylthioadenosine) build up; MTA partially inhibits PRMT5, so an added PRMT5 inhibitor tips MTAP-deleted cells over the edge.
• How common — MTAP is co-deleted with CDKN2A in the 9p21 region, which is lost in the majority of pleural mesotheliomas, placing MTAP loss in roughly half of cases.
• Navlimetostat (MRTX1719 / BMS-986504) — phase 1 basket trial in MTAP-deleted solid tumors including mesothelioma (NCT05245500), status Recruiting.
• TNG462 — phase 1/2 trial, single-agent and with pembrolizumab, in MTAP-deleted tumors (NCT05732831), status Recruiting.
• SELECTmeso1 — mesothelioma-specific phase 2 arm testing BMS-986504 in MTAP-deficient relapsed disease (NCT07602946); ClinicalTrials.gov still shows Not yet recruiting, but Leicester Royal Infirmary reported recruitment underway as of June 2026.
• No efficacy data — no response rates or survival results have been published for any PRMT5 inhibitor in mesothelioma; all trials are pre-readout.
• WCLC 2026 update — at the IASLC World Conference on Lung Cancer in Seoul (September 2026), SELECTmeso1 Chief Investigator Professor Dean Fennell presented trial-in-progress data on navlimetostat in MTAP-deleted mesothelioma; the presentation described trial design and status, not results.
• A somatic target — MTAP deletion is a change acquired by the tumor, not an inherited trait and not an alternative cause of the disease.
• How to access — these drugs are available only in clinical trials; eligibility is checked at trial centers and on ClinicalTrials.gov.

Key Facts

Measure	Finding (Source)
Drug class	Protein arginine methyltransferase 5 (PRMT5) inhibitors — investigational
Biomarker required	Homozygous (bi-allelic) deletion of methylthioadenosine phosphorylase (MTAP)
Mechanism	Synthetic lethality — MTAP loss raises methylthioadenosine (MTA), which partially inhibits PRMT5 and creates dependence on it
MTAP / CDKN2A loss in pleural mesothelioma	CDKN2A homozygous deletion in up to 74% of cases; MTAP co-deleted in the majority
MTAP / CDKN2A loss in peritoneal mesothelioma	CDKN2A homozygous deletion in ~35% of cases; MTAP co-deleted in every deleted case
Lead agent (basket)	Navlimetostat (MRTX1719 / BMS-986504) — phase 1, Bristol-Myers Squibb (NCT05245500), Recruiting
Second agent	TNG462 — phase 1/2, Tango Therapeutics (NCT05732831), Recruiting
Mesothelioma-specific trial	SELECTmeso1 — phase 2, University of Southampton with BMS (NCT07602946); registry status Not yet recruiting, though Leicester Royal Infirmary reported recruitment open as of June 2026
Efficacy in mesothelioma	None reported — no response-rate or survival data published
FDA status	No PRMT5 inhibitor approved for any cancer as of mid-2026
Latest conference update	Trial-in-progress poster on navlimetostat in MTAP-deleted mesothelioma presented by Prof. Dean Fennell at IASLC WCLC 2026, Seoul (September 12–15, 2026); design/status only, no efficacy data

What Is PRMT5 Synthetic Lethality?

Synthetic lethality is a strategy that turns a cancer's own genetic loss into a weakness. Two genes are "synthetic lethal" when a cell can survive losing either one alone, but dies if it loses both. In MTAP-deleted mesothelioma, the tumor has already lost one of the pair — MTAP (methylthioadenosine phosphorylase) — so a drug that removes the function of its partner, PRMT5 (protein arginine methyltransferase 5), can in principle kill the tumor cells while sparing normal cells that still carry MTAP. In the 2016 laboratory studies that defined this relationship, PRMT5 inhibitors showed a modest preferential impairment of cell viability in MTAP-deleted cancer cell lines compared with MTAP-intact counterparts; no clinical efficacy has been demonstrated in mesothelioma patients.

The connection between the two genes runs through metabolism. MTAP normally breaks down a small molecule called MTA (methylthioadenosine). When MTAP is deleted, MTA accumulates inside the cell — and MTA happens to be a partial inhibitor of PRMT5. So MTAP-deleted tumor cells already run their PRMT5 at reduced capacity, leaving them with little reserve. Adding a PRMT5 inhibitor pushes PRMT5 activity below the level the cell needs to survive, an effect that is far weaker in normal, MTAP-intact cells. This mechanism was first defined in 2016 by two independent research teams, and it has since driven the design of a newer generation of "MTA-cooperative" PRMT5 inhibitors engineered to act preferentially in the MTA-rich environment of MTAP-deleted tumors.

It is important to be precise about what this is. MTAP deletion is a somatic event — a change acquired by the tumor cells themselves as part of a larger chromosomal loss — not an inherited trait and not an alternative explanation for how mesothelioma develops. Asbestos exposure remains the established cause of the disease; the MTAP loss that these drugs exploit arises within the tumor after it has formed, and it represents a treatment opportunity rather than a cause. For more on the molecular changes found in mesothelioma tumors, see Mesothelioma Molecular and Genetic Testing and the BAP1 gene mutation page.

How Common Is MTAP Deletion in Mesothelioma?

MTAP loss is common in mesothelioma because of where the gene sits. MTAP lies on chromosome 9p21, immediately next to the tumor-suppressor gene CDKN2A (which encodes the p16 protein). CDKN2A deletion is one of the most frequent genetic events in mesothelioma, and because MTAP is its close neighbor, MTAP is usually swept away in the same deletion — a "passenger" loss that rides along with the "driver."

The numbers vary by mesothelioma type but are consistently high. In pleural mesothelioma — the most common form — homozygous deletion of CDKN2A has been reported in up to 74% of cases, with MTAP co-deleted in the majority of those tumors; loss of the 9p21 region encompassing MTAP is found in the majority of pleural mesotheliomas overall. In peritoneal mesothelioma, CDKN2A homozygous deletion is somewhat less frequent — about 35% in one tissue-microarray series — but in that study MTAP was co-deleted in every CDKN2A-deleted case. Taken together, these figures place MTAP loss in roughly half of pleural mesotheliomas, making it one of the more common precision-oncology biomarkers in the disease. That prevalence is central to the interest in PRMT5 inhibition: a synthetic-lethal target is only useful if enough patients carry the underlying deletion, and in mesothelioma, many do. Loss of MTAP by immunohistochemistry is also increasingly used as an inexpensive diagnostic surrogate for 9p21 deletion.

Which PRMT5 Inhibitors Are Being Tested in Mesothelioma?

Three clinical programs define the current mesothelioma landscape for PRMT5 inhibition. All are early-phase, and none has reported efficacy results in mesothelioma.

MRTX1719 / BMS-986504 (Bristol-Myers Squibb) is a first-in-human phase 1 study in patients whose advanced solid tumors carry a homozygous MTAP deletion (NCT05245500). Mesothelioma is one of the eligible tumor types, alongside non-small-cell lung cancer, pancreatic cancer, and others, and the trial's status is Recruiting (verified August 2026), with an enrollment target of 336 patients. The drug is an MTA-cooperative PRMT5 inhibitor; MRTX1719 and BMS-986504 are two names for the same molecule, which moved into the Bristol-Myers Squibb portfolio and has since been assigned the international nonproprietary name (INN) navlimetostat — confirmed by the ClinicalTrials.gov registry record below, which lists all three names as synonyms for the same intervention. As a phase 1 basket study, its primary goals are safety, tolerability, dose-finding, and pharmacology rather than a definitive efficacy readout.

A related but distinct MTA-cooperative PRMT5 inhibitor, AMG 193 (anvumetostat, Amgen), is not being tested in mesothelioma but illustrates how this drug class is performing elsewhere in the clinic. A first-in-human phase 1 dose-exploration study in 80 patients with MTAP-deleted solid tumors, published in Annals of Oncology in December 2024, reported an objective response rate of 21.4% (95% CI 10.3%–36.8%) among 42 efficacy-assessable patients at active, tolerable doses, with responses across eight tumor types including non-small-cell lung cancer, pancreatic adenocarcinoma, and biliary tract cancer, and a favorable safety profile without clinically significant myelosuppression. No mesothelioma patients were reported among the responders in this dataset, but the result is relevant context: it is the first peer-reviewed clinical confirmation that an MTA-cooperative PRMT5 inhibitor produces objective tumor responses in MTAP-deleted disease, the same mechanism navlimetostat is built on.

TNG462 (Tango Therapeutics) is a phase 1/2 study of an orally administered selective PRMT5 inhibitor in patients with confirmed MTAP-deleted advanced or metastatic solid tumors (NCT05732831). It is testing the drug both as a single agent and in combination with the immunotherapy pembrolizumab, with a planned enrollment of 225 patients, and its status is Recruiting (verified September 2026). The phase 1 portion escalates the dose; the phase 2 portion is designed to enroll expansion arms in specific MTAP-deleted tumor types at the recommended dose.

SELECTmeso (University of Southampton, with Bristol-Myers Squibb) is the only mesothelioma-specific trial of the three (NCT07602946). It is a molecularly stratified, multi-arm phase 2 platform trial for patients with relapsed malignant mesothelioma, and its first candidate-specific arm, SELECTmeso1, will test BMS-986504 in patients whose tumors are MTAP-deficient. ClinicalTrials.gov's status field for the trial still reads Not yet recruiting as of its last update (May 2026), but the trial site, Leicester Royal Infirmary, announced in June 2026 that the study had opened there with first patients recruited — a change the registry entry has not yet caught up to. The listed enrollment is 30 patients, and the primary measure is disease-control rate at 12 weeks by RECIST 1.1 — an endpoint designed to detect early signals of activity, not to establish a survival benefit. Because SELECTmeso is built as a platform, additional treatment arms for other biomarkers can be added over time.

At the IASLC 2026 World Conference on Lung Cancer (WCLC) in Seoul, South Korea (September 12–15, 2026), Professor Fennell gave a video interview describing a "new, quite exciting therapy for mesothelioma targeting MTAP deleted mesotheliomas," noting the team was "presenting some data in the poster format as a trial in progress" to test "whether through synthetic lethality we can actively target this disease." The interview itself does not name SELECTmeso1 or navlimetostat; the identification here rests on the institutional announcement above — same Chief Investigator, same mechanism, same disease — not on the WCLC interview. The interview did not disclose response rates, survival data, or any other efficacy readout — consistent with a trial that, as of the conference, had only recently begun enrolling patients. This is a status update, not a results announcement.

The SELECTmeso1 arm's investigational drug has also changed since the trial was first approved. The original 2024 ethics-approval summary for SELECTmeso1 described the study drug as brigimadlin (BI 907828), a different investigational agent, with a planned enrollment of 26 patients beginning in winter 2024. The trial as it is registered and open today instead tests BMS-986504 — also known as navlimetostat — the PRMT5 inhibitor described above, with a target enrollment of 30 patients. This reflects a protocol amendment that changed the study drug, not two names for the same molecule.

Across all three programs, the common thread is that PRMT5 inhibition in mesothelioma is at the stage of testing whether the approach is safe and active — not demonstrating that it works.

Why Is This an Emerging Target, Not a Treatment Yet?

The case for PRMT5 inhibition in mesothelioma rests, so far, on laboratory science and trial design rather than on patient outcomes. The synthetic-lethal relationship between MTAP and PRMT5 is well established in cell-line and preclinical work, where PRMT5 inhibitors have shown preferential activity against MTAP-deleted cancer cells compared with MTAP-intact cells. But preclinical rationale is not the same as clinical benefit. No PRMT5 inhibitor has reported a response rate, progression-free survival, or overall survival result in mesothelioma, and every relevant trial is phase 1, phase 1/2, or not yet open.

There are also open questions the trials are designed to answer. Early PRMT5 inhibitors were not selective for MTAP-deleted cells and caused broad toxicity; the newer MTA-cooperative agents are meant to widen that therapeutic window, but whether they do so in patients — and at what cost in side effects — is still being determined. The problem is documented in the earlier drugs directly: GSK3326595 (pemrametostat) and JNJ-64619178 (onametostat), two first-generation PRMT5 inhibitors that block the enzyme regardless of a tumor's MTAP status, each showed only modest single-agent clinical activity and ran into dose-limiting hematologic toxicity — chiefly thrombocytopenia — before reaching consistently effective doses. Navlimetostat, AMG 193, and TNG462 are all designed to bind PRMT5 preferentially in the MTA-rich environment created by MTAP loss, which is the mechanistic bet behind why this second generation might succeed where the first did not. Combination strategies, such as TNG462 with pembrolizumab, add further variables. Until phase 2 and eventually randomized data mature, PRMT5 inhibition should be understood as a scientifically grounded investigational direction, not an established option.

For patients, the practical takeaway is straightforward: this is a target worth knowing about and, for those with MTAP-deleted tumors, potentially worth exploring through a clinical trial — but it is not a therapy that can be prescribed today. How emerging targeted approaches fit into the broader treatment sequence is covered in latest treatment advances for mesothelioma, and a related investigational target is described on the TEAD inhibitors page.

How Do Patients Access These Trials?

Because no PRMT5 inhibitor is FDA-approved, the only way to receive one is through a clinical trial. Eligibility begins with a tumor's molecular profile: these trials require documented homozygous MTAP deletion (detected by next-generation sequencing) or loss of MTAP protein (detected by immunohistochemistry), so molecular testing of the tumor is the essential first step. The pages on molecular and genetic testing and mesothelioma biomarkers explain how this testing works and where it fits in the diagnostic process.

PRMT5 inhibitor trials generally focus on patients whose disease has progressed after standard therapy, which places these drugs in the later-line setting where new options are most needed. The most reliable, up-to-date source for open trials, locations, and eligibility criteria is the U.S. National Library of Medicine's registry at ClinicalTrials.gov, which lists each study by its NCT number. Patients interested in a trial should start by discussing it with their treating oncologist, who can assess whether a trial is medically appropriate and coordinate referral to a participating center. A specialized mesothelioma center is often the best point of entry, because these centers are more likely to be trial sites and to have the molecular-testing infrastructure that trials require. General guidance is available on the mesothelioma clinical trials page.

Frequently Asked Questions

What is PRMT5 inhibition, in plain terms? It is an experimental treatment strategy for tumors that have deleted a gene called MTAP. Losing MTAP makes cancer cells unusually dependent on a related enzyme, PRMT5. A drug that blocks PRMT5 can therefore kill the MTAP-deleted tumor cells while largely sparing normal cells — an approach known as synthetic lethality. It is being tested in clinical trials and is not an approved treatment.

Is MTAP deletion tested for routinely in mesothelioma? Loss of the 9p21 region — which includes CDKN2A and MTAP — is already assessed in many mesothelioma cases, often as part of diagnosis, because CDKN2A/9p21 deletion is a well-established marker. MTAP status specifically can be checked by immunohistochemistry (an inexpensive stain) or next-generation sequencing, and it is becoming more common as PRMT5-targeted trials look for eligible patients. Ask your care team whether your tumor's MTAP status is known.

Are any of these trials open right now? As of mid-2026, the MRTX1719 / BMS-986504 basket study (NCT05245500) and the TNG462 study (NCT05732831) are listed as Recruiting. ClinicalTrials.gov still lists the mesothelioma-specific SELECTmeso1 arm (NCT07602946) as Not yet recruiting, but Leicester Royal Infirmary — the trial site — reported in June 2026 that recruitment had begun there, a change the registry entry has not yet caught up to. Trial statuses (and, in this case, the study drug itself) can change, so verify current status directly on ClinicalTrials.gov before assuming eligibility.

When might PRMT5 inhibition become an approved treatment? There is no timeline. No PRMT5 inhibitor has reported efficacy results in mesothelioma, and the current trials are designed to establish safety and preliminary activity, not to win approval. Approval would require successful later-phase trials showing clinical benefit, which have not yet been conducted in mesothelioma. This is an emerging research direction, not a near-term therapy.

What did Professor Fennell present at WCLC 2026? At the IASLC 2026 World Conference on Lung Cancer in Seoul (September 12–15, 2026), Professor Dean Fennell — SELECTmeso1's Chief Investigator — gave an interview describing "a new, quite exciting therapy for mesothelioma targeting MTAP deleted mesotheliomas" and said the trial is testing whether synthetic lethality can be used to target the disease. The interview itself did not name the drug or the trial; that identification (navlimetostat, SELECTmeso1) comes from the institutional announcement naming Fennell as Chief Investigator of the same trial. It was a trial-in-progress poster describing study design and status — no response-rate or survival data were disclosed.

Does MTAP deletion mean my mesothelioma was caused by genetics rather than asbestos? No. MTAP deletion is a somatic change — one the tumor acquires as it develops — not an inherited trait and not an alternative cause of the disease. Asbestos exposure remains the established cause of mesothelioma. MTAP loss is relevant only as a potential treatment target, not as an explanation of how the cancer began.

Quick Statistics

• 0 — PRMT5 inhibitors FDA-approved for mesothelioma (or any cancer) as of mid-2026.
• 3 — PRMT5-inhibitor trials relevant to mesothelioma: MRTX1719/BMS-986504, TNG462, SELECTmeso1.
• ~50% — approximate share of pleural mesotheliomas with MTAP loss, via 9p21 co-deletion.
• up to 74% — pleural mesotheliomas with homozygous CDKN2A deletion (MTAP co-deleted in the majority).
• ~35% — peritoneal mesotheliomas with CDKN2A deletion; MTAP co-deleted in every deleted case.
• 2016 — year the MTAP–PRMT5 synthetic-lethal relationship was first defined.
• 0 — efficacy or response-rate results reported for any PRMT5 inhibitor in mesothelioma.

External Links

• Danziger & De Llano — Mesothelioma Treatment Overview — plain-language guide to current and emerging mesothelioma treatment options
• Mesothelioma Lawyer Center — treatment, diagnosis, and clinical-trial background for patients and families
• Mesothelioma.net — patient resources on treatment, second opinions, and specialist centers
• ClinicalTrials.gov — MRTX1719 Study (NCT05245500) — official registry listing with locations and eligibility criteria

Related Pages

• Mesothelioma Molecular and Genetic Testing
• BAP1 Gene Mutation in Mesothelioma
• TEAD Inhibitors for Mesothelioma
• Mesothelin CAR-T Therapy for Mesothelioma
• Latest Treatment Advances for Mesothelioma
• Clinical Trials for Mesothelioma