Atebimetinib Combinations with Anti-PD1 Cured 50% of Mice in a RAS-Mutant Colorectal Cancer Model and Nearly Doubled Survival in a RAS-Mutant Lung Cancer Model; New Data Presented at SITC 2026

- Durable complete regressions observed in 50% of mice in a RAS-mutant colorectal cancer model treated with Atebimetinib plus anti-PD-1, with no regrowth even after dosing stopped -

- Median survival extended by 1.8-fold with atebimetinib plus anti-PD-1 and chemotherapy versus anti-PD-1 plus chemotherapy alone in a RAS-mutant lung cancer model -

- Pulsatile MEK inhibition reversed MAPK-driven immune suppression by lowering suppressive myeloid cells and regulatory T-cells, and expanding NK cells, while avoiding T-cell signaling attenuation associated with continuous MAPK inhibition -

- Phase 2 clinical trial of atebimetinib in combination with anti-PD-1 and platinum-doublet chemotherapy in first-line RAS-mutant NSCLC is expected to dose the first patient by year-end -

NEW YORK, Nov. 06, 2026 (GLOBE NEWSWIRE) -- Immuneering Corporation (Nasdaq: IMRX), a late-stage clinical oncology company focused on keeping cancer patients alive and helping them thrive, today announced compelling preclinical data demonstrating that atebimetinib, the Company’s novel Deep Cyclic Inhibitor of MEK, enhanced the activity of PD-1 checkpoint blockade in RAS-mutant colorectal and lung cancer models, including a 50% durable complete regression rate in a colorectal model and a 1.8-fold median survival improvement with a triple combination in a lung model. The data are being presented at the Society for Immunotherapy of Cancer (SITC) 41st Annual Meeting, taking place November 4-8, 2026, in Phoenix, Arizona.

“Curing 50% of mice in one tumor model and nearly doubling median overall survival in another are both incredibly exciting. These data add to the body of preclinical evidence that combining a pulsatile inhibitor of MEK with immunotherapy may lead to enhanced activity,” said Ben Zeskind, Ph.D., Co-Founder and Chief Executive Officer of Immuneering. “The ultimate test of this hypothesis will be to show it in patients, and it starts very soon: we expect to dose the first patient by the end of the year in our Phase 2 clinical trial of atebimetinib in combination with anti-PD-1 and chemotherapy in first-line RAS-mutant NSCLC patients.”

In the CT-26 syngeneic mouse model of colorectal cancer, both the 75 mg/kg and 125 mg/kg atebimetinib plus anti-PD-1 groups achieved complete tumor regression in 6 of 12 mice (50%) per group, with no regrowth even after treatment discontinuation. Vehicle-treated animals had median survival of 21 days, while anti-PD-1 alone resulted in median survival of 29 days and atebimetinib monotherapy extended median survival dose-dependently from 28 to 41.5 days. In contrast, median survival was not reached in the atebimetinib plus anti-PD-1 combination groups, which outperformed the single-agent arms (P<0.0001 versus vehicle for nearly all combinations).

In the LL2 syngeneic lung cancer model, a PD-1-cold model unresponsive to anti-PD-1 monotherapy, atebimetinib demonstrated enhanced antitumor activity in combination with anti-PD-1 and platinum-doublet chemotherapy. At 125 mg/kg BID, atebimetinib plus anti-PD-1, carboplatin and pemetrexed extended median survival to 25 days, compared with 14 days for anti-PD-1 plus chemotherapy alone, representing a 1.8-fold improvement. All 12 mice receiving the triple combination were alive at Day 18, compared with none of the 12 mice receiving anti-PD-1 plus chemotherapy alone. These data support further clinical investigation of this combination in first-line RAS-mutant non-small cell lung cancer (NSCLC).

Presentation Details:
Title: “Cyclic disruption of the mitogen-activated protein kinase (MAPK) pathway by the pulsatile MEK inhibitor, Atebimetinib, enhances PD-1 checkpoint blockade in RAS mutant tumors.”
Abstract: #377
Presenting Author: Amy E. Axel, Immuneering Corporation
Presentation: Friday, November 6, 2026

Following presentation, the poster will be available on the publications section of Immuneering’s website at https://immuneering.com/publications.

About Immuneering Corporation
Immuneering is a late-stage clinical oncology company dedicated to keeping cancer patients alive and helping them thrive, with an initial focus on patients with RAS, RAF, and other MAPK-driven cancers. The Company is developing an entirely new category of cancer medicines, Deep Cyclic Inhibitors, designed to improve overall survival by three mechanisms: shrinking tumors durably with less resistance, preserving body mass by countering cachexia, and minimizing side effects to maximize performance status and combinability. Immuneering’s lead product candidate, atebimetinib, is an oral, once-daily Deep Cyclic Inhibitor of MEK, designed to improve survival across many cancer indications. The Company is conducting a global randomized pivotal trial, MAPKeeper 301, evaluating atebimetinib in combination with chemotherapy in first-line pancreatic cancer patients. The Company’s development pipeline also includes additional combination opportunities and preclinical stage programs. For more information, please visit www.immuneering.com.

Forward-Looking Statements
This press release contains forward-looking statements, including within the meaning of the Private Securities Litigation Reform Act of 1995. All statements contained in this press release that do not relate to matters of historical fact should be considered forward-looking statements, including, without limitation, statements regarding: the treatment potential of atebimetinib, alone or in combination with other agents to treat cancer, including anti-PD-1 therapy and platinum-doublet chemotherapy; the timing, design and initiation of the Phase 2 study of atebimetinib in combination with anti-PD-1 therapy and chemotherapy; the translation of preclinical efficacy and immune profiling findings to patients, including that combining a pulsatile inhibitor of MEK with an immunotherapy may lead to enhanced activity.

These forward-looking statements are based on management’s current expectations. These statements are neither promises nor guarantees, but involve known and unknown risks, uncertainties and other important factors that may cause our actual results, performance or achievements to be materially different from any future results, performance or achievements expressed or implied by the forward-looking statements, including, but not limited to, the following: we are a late-stage clinical oncology company with a limited operating history and have not completed any registrational clinical trials; we have incurred significant losses, are not currently profitable and may never become profitable; limitations on our cash runway and potential increases in expenditures; our need for additional funding; our unproven approach to therapeutic intervention; our ability to address regulatory questions and changing regulatory standards, and the uncertainties relating to regulatory filings, reviews and approvals; the lengthy, expensive, and uncertain process of clinical drug development, including the uncertainty of whether positive preclinical or early clinical efficacy and safety results are confirmed in later-stage trials, potential delays in activation of trial sites or enrollment of trial participants, or failure to obtain regulatory approvals; our reliance on third parties and collaborators to conduct our clinical trials, manufacture our product candidates, and develop and commercialize our product candidates, if approved; failure to compete successfully against other drug companies; protection of our proprietary technology and the confidentiality of our trade secrets; potential lawsuits for, or claims of, infringement of third-party intellectual property or challenges to the ownership of our intellectual property; our patents being found invalid or unenforceable; costs and resources of operating as a public company; and unfavorable or no analyst research or reports.

These and other important factors discussed under the caption “Risk Factors” in our Quarterly Report on Form 10-Q for the period ended September 30, 2026, and our other reports filed with the U.S. Securities and Exchange Commission, could cause actual results to differ materially from those indicated by the forward-looking statements made in this press release. Any such forward-looking statements represent management's estimates as of the date of this press release. While we may elect to update such forward-looking statements at some point in the future, except as required by law, we disclaim any obligation to do so, even if subsequent events cause our views to change. These forward-looking statements should not be relied upon as representing our views as of any date subsequent to the date of this press release.

Investor Contact:
Laurence Watts
New Street Investor Relations
laurence@newstreetir.com

Media Contact:
David Caouette
dcaouette@immuneering.com