New dual CDK approach tackles drug-resistant breast cancer

A new study from researchers at The University of Texas MD Anderson Cancer Center has demonstrated that simultaneously targeting two key cell cycle regulators can produce durable anti-tumour effects across multiple breast cancer subtypes, including hard-to-treat forms of the disease. The study combined a selective cyclin-dependent kinase 2 (CDK2) inhibitor with existing cyclin-dependent kinase 4/6 (CDK4/6) inhibitors, which researchers believe could significantly improve outcomes for patients whose cancers no longer respond to standard therapies.

Tackling resistance in breast cancer

CDK4/6 inhibitors combined with endocrine therapy are the established first-line treatment for hormone receptor-positive, HER2-negative metastatic breast cancer. While initially effective, resistance almost always develops. In triple-negative breast cancer, an aggressive subtype with few targeted options, the benefit of CDK4/6 inhibitors has been uncertain.

To address both problems, researchers, led by postdoctoral fellow Dr Linjie Luo, MD and Dr Khandan Keyomarsi, explored whether blocking an additional pathway could prevent cancer cells from escaping treatment. Their work focused on combining the selective CDK2 inhibitor BLU-222 with CDK4/6 inhibitors.

Across every preclinical model tested, including treatment-resistant hormone receptor-positive disease and aggressive triple-negative breast cancer, the combination produced strong and lasting anti-tumour effects. The researchers report that this synergy occurred without exception, highlighting the broad translational potential of the strategy.

“This is an important and highly consistent finding,” Keyomarsi said. “Across all resistant HR-positive models and all TNBC models we tested, the combination of BLU-222 with CDK4/6 inhibitors consistently outperformed standard-of-care therapies, producing durable tumour regression and prolonged survival.”

Why target CDK2?

Cancer cells depend on CDKs to divide and replicate their DNA. While CDK4/6 inhibitors disrupt part of this process, many cancers adapt by shifting their reliance to CDK2, allowing growth to continue despite treatment.

The study demonstrates that inhibiting CDK2 closes this escape route. Although CDK2 has long been recognised as an important cancer driver, earlier inhibitors caused unacceptable toxicity. Newer and more selective drugs such as BLU-222 have now made CDK2 inhibition a viable therapeutic option.

How the combination works

BLU-222, either alone or alongside CDK4/6 inhibitors, was shown to activate the cancer cells’ natural braking system by increasing levels of the proteins p21 and p27. These proteins normally restrain cell division but are often suppressed in resistant tumours.

By restoring p21 and p27, the treatment blocked both CDK2 and CDK4 activity, effectively halting cancer cell proliferation. When researchers removed p21 or p27 using CRISPR gene editing, the powerful synergy disappeared, confirming that these proteins are essential to the treatment’s effect.

Further analysis using RNA sequencing revealed that the combination therapy triggered cellular senescence, a permanent shutdown of tumour growth and activated interferon signalling, which may help stimulate immune responses and explain the durability of tumour regression.

Implications for future treatment

The findings come as several next-generation CDK2 inhibitors are entering clinical development. According to Keyomarsi, the study provides a clear framework for how these drugs could be used in patients with resistant disease.

“Our data demonstrates that targeting CDK2 is not just additive – it fundamentally restores control over the cell cycle in resistant tumours. Therefore, this study provides a clear blueprint for how these drugs should be used clinically,” Keyomarsi said. “This is significant because there is an urgent unmet clinical need for patients with CDK4/6 inhibitor-resistant HR-positive breast cancer and for those with triple-negative disease.”