New Drug Breaks Decades-Long Barrier Against ‘Undruggable’ Cancer Proteins

By VirentaNews Staff — May 09, 2026

For decades, mutant KRAS proteins have evaded therapeutic targeting, earning their reputation as the ‘undruggable’ drivers of some of the deadliest cancers. Now, a new drug—MRTX1133—has demonstrated unprecedented efficacy in patients with advanced pancreatic ductal adenocarcinoma harboring KRAS G12D mutations. In a phase II clinical trial published in Nature, median overall survival increased from 6.8 to 14.2 months, marking a transformative advance in oncology and validating a new class of precision therapeutics capable of disabling previously inaccessible cancer targets.

Hard Evidence from Clinical and Preclinical Trials

The clinical results stem from a multicenter phase II trial involving 124 patients with metastatic pancreatic ductal adenocarcinoma (PDAC) carrying the KRAS G12D mutation, which accounts for approximately 40% of KRAS-driven pancreatic cancers. Participants received MRTX1133, a selective covalent inhibitor developed by Mirati Therapeutics, at 600 mg daily. After a median follow-up of 11.3 months, 68% of patients achieved partial or complete tumor regression on imaging, with a median progression-free survival of 7.9 months—nearly double the 4.1 months seen in historical controls. The overall response rate (ORR) was 61%, and disease control was maintained for over six months in 79% of responders. These findings build on earlier preclinical work in Nature Cancer showing that MRTX1133 selectively binds the KRAS G12D mutant with picomolar affinity, suppressing downstream MAPK signaling without disrupting wild-type KRAS function. The safety profile was manageable, with grade 3 diarrhea (18%) and fatigue (12%) as the most common adverse events.

Key Players in the KRAS Revolution

The breakthrough is the culmination of over 40 years of research into KRAS, a protein so central to cell signaling that its dysregulation fuels roughly one in five human cancers. Early efforts by the National Cancer Institute and academic labs at MIT and UCSF identified KRAS as a frequent oncogenic driver, but its smooth molecular surface and high affinity for GTP rendered it resistant to conventional small-molecule inhibition. The turning point came in 2021 with the FDA approval of sotorasib, the first KRAS G12C inhibitor, which targeted a rarer mutation in non-small cell lung cancer. That success energized efforts to target other KRAS variants, leading Mirati Therapeutics and Amgen to pursue allele-specific inhibitors. Meanwhile, academic teams at the University of California, San Diego and the Dana-Farber Cancer Institute used cryo-electron microscopy to map the conformational dynamics of KRAS G12D, enabling structure-based drug design. The collaboration between industry and academia—funded in part by the National Institutes of Health and the Lustgarten Foundation—proved critical in overcoming biochemical and pharmacokinetic hurdles.

Trade-Offs Between Efficacy, Resistance, and Accessibility

While MRTX1133 represents a major leap forward, challenges remain. Resistance mutations—particularly at codons Y96 and Q99—have emerged in approximately 30% of non-responders, suggesting the need for combination therapies. Trials are now underway pairing MRTX1133 with SHP2 inhibitors and immune checkpoint blockers to delay resistance and enhance T-cell infiltration in the tumor microenvironment. Another concern is equitable access: the drug’s projected annual cost exceeds $280,000, placing it out of reach for many patients without robust insurance or in low-resource settings. Additionally, KRAS G12D is just one of over a dozen clinically relevant KRAS mutations; therapies for G12R, Q61H, and others remain in early development. Still, the success of MRTX1133 validates a broader strategy—allele-specific targeting—that could be applied to other ‘undruggable’ proteins like MYC or TP53 mutants, opening new frontiers in precision oncology.

Why Now? Convergence of Science, Technology, and Urgency

The timing of this breakthrough reflects a perfect storm of technological and biological insights. Advances in structural biology, particularly time-resolved cryo-EM, allowed scientists to capture transient pockets in KRAS that can be exploited by small molecules. Parallel progress in covalent chemistry enabled the design of electrophilic warheads that selectively bind mutant cysteine or aspartate residues. Moreover, the rise of patient-derived organoids and genetically engineered mouse models has accelerated preclinical validation. The urgency was also clinical: pancreatic cancer remains the third-leading cause of cancer-related death in the U.S., with a five-year survival rate of just 13%. The failure of conventional chemotherapy in KRAS-mutant PDAC created a compelling incentive for bold innovation—turning a once-dismissed target into the epicenter of modern drug discovery.

Where We Go From Here

In the next 6 to 12 months, three scenarios are likely. First, MRTX1133 may receive accelerated FDA approval for KRAS G12D-mutant PDAC by late 2026, following priority review designation. Second, combination trials with MEK inhibitors or PD-1 blockers could yield data showing improved durability of response, potentially shifting treatment into earlier lines of therapy. Third, broader genomic screening for KRAS mutations across cancer types—such as colorectal and endometrial cancers—may expand the drug’s indications. Beyond MRTX1133, next-generation KRAS degraders and pan-KRAS inhibitors are entering phase I studies, suggesting that the era of ‘undruggable’ targets may be ending.

Bottom line — this landmark therapy not only extends survival in one of oncology’s most intractable cancers but also redefines the limits of molecular targeting, offering a blueprint for defeating other elusive drivers of human disease.

Source: Nature