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The concept of an impermeable blood-brain barrier is less relevant once brain metastases are established. The barrier becomes highly permeable, or 'leaky,' allowing even large molecules like antibody-drug conjugates (ADCs) to penetrate the CNS. This suggests that any therapy systemically active in the periphery has potential CNS activity.
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Beyond overall response rates, a critical area of excitement for new ADCs in lung cancer is their potential to treat brain metastases. Early data showing hints of intracranial efficacy is a significant point of interest, as this addresses a common and difficult-to-treat site of disease progression, offering a potential advantage over other therapies.
Unlike many traditional chemotherapies, new antibody-drug conjugates (ADCs) like IDXD are demonstrating high objective response rates (over 45%) within the brain. This intracranial efficacy is a major advance for small cell lung cancer (SCLC) patients, who frequently develop hard-to-treat brain metastases, potentially reducing reliance on immediate whole-brain radiation.
Unlike the standard chemotherapy regimen TCHP, the newer drug T-DXd can cross the blood-brain barrier. This is a crucial advantage for high-risk HER2-positive breast cancer patients, as it offers the potential to prevent brain metastases, a common and devastating site of recurrence for this cancer subtype.
The B7H3-targeted antibody-drug conjugate (ADC) ifanatumab deruxtecan shows a high intracranial response rate in SCLC, numerically even better than its systemic response rate. This suggests excellent CNS penetration, offering a promising strategy for managing brain metastases, a common and difficult challenge in SCLC.
The antibody-drug conjugate ifinatamab deruxtecan (I-O-DXd) demonstrates remarkable CNS activity. In SCLC patients with brain metastases who have not had prior radiation, the intracranial response rates are even better than the impressive systemic responses, addressing a critical unmet need for this disease.
The historical difficulty of delivering biologics to the brain is being addressed by novel "brain shuttle" technologies. These platforms, which facilitate transport across the blood-brain barrier, are enabling new enzyme replacement therapies and even AAV-delivered biologics for CNS diseases like leukodystrophies.
The success of the IDH inhibitor vorasidenib in glioma was driven by its specific design for blood-brain barrier (BBB) penetration. This contrasts with its predecessor, which failed in brain tumors due to poor CNS penetration, highlighting that BBB is a critical design consideration for neuro-oncology drugs.
Unlike the intact blood-brain barrier, the blood-tumor barrier within brain metastases is permeable. This "leakiness" allows large molecules like the ADC trastuzumab deruxtecan (TDXD) to enter and deliver its payload, providing a mechanism for its high CNS efficacy.
While zongertinib demonstrates high systemic efficacy with a 77% response rate, its efficacy in the central nervous system (CNS) is significantly lower at 44%. This gap highlights a critical challenge for patients with brain metastases and underscores the need for combination therapies or next-generation drugs with better CNS penetration.
With efficacy and toxicity profiles being nearly identical between the first approved KRAS G12C inhibitors, intracranial activity becomes a key differentiator for clinicians, especially since a third of these lung cancer patients develop brain metastases. Adagrasib's demonstrated CNS activity gives it a slight advantage.
