The Second Act of Thalidomide: From Teratogen to the Foundation of Targeted Protein Degradation

Few drugs have undergone a clinical trajectory as extreme as thalidomide查看药品详情, from widespread use as a sedative to global withdrawal following catastrophic teratogenic effects, and then to a carefully controlled reintroduction as a cornerstone of modern multiple myeloma (搜索)搜索该疾病 therapy. Its scientific legacy now extends even further: the molecular target that explained both its toxicity and its therapeutic activity became the foundation for an entire new class of medicines built on targeted protein degradation.

The Thalidomide Disaster

Thalidomide查看药品详情 entered the market in 1957 as a non-barbiturate sedative promoted as relatively safe, and its antiemetic effects led to widespread use for nausea and vomiting during pregnancy. Its reproductive toxicity proved devastating. Exposure during a critical window of embryonic development could produce severe limb reduction defects along with abnormalities of the ears, eyes, and internal organs. More than 10,000 children worldwide are estimated to have been born with thalidomide-associated abnormalities, not counting miscarriages and stillbirths, which add to the true toll.

In 1961, independent observations by William McBride and Widukind Lenz linked prenatal thalidomide查看药品详情 exposure to severe congenital anomalies such as phocomelia and amelia, culminating in the drug's withdrawal from most major commercial markets beginning later that year. The disaster exposed a basic weakness in drug development at the time: a medication could appear well tolerated in adults while exposing the embryo to profound toxicity. The regulatory consequences extended far beyond thalidomide itself, strengthening requirements for evidence of safety and efficacy across the industry.

How Thalidomide Returned to Medicine

Thalidomide查看药品详情's return did not begin with cancer. In the 1960s, Israeli physician Jacob Sheskin observed rapid improvement of erythema nodosum leprosum (搜索)搜索该疾病 (ENL), a painful inflammatory complication of leprosy, after giving thalidomide to a patient. Subsequent work confirmed its anti-inflammatory and immunomodulatory activity, leading to its use for this indication under strict controls. By 1998, thalidomide gained FDA approval for ENL under stringent controls intended to prevent fetal exposure.

Its path toward multiple myeloma (搜索)搜索该疾病 came later, as investigators grew interested in the role of angiogenesis in cancer. Myeloma marrow was known to have increased microvascular density, and thalidomide查看药品详情 had shown antiangiogenic activity in experimental models. In 1999, Singhal and colleagues reported single-agent thalidomide activity in heavily pretreated patients with refractory multiple myeloma, with responses in roughly one-third of the study population—the first new drug in decades to show substantial single-agent activity in the disease. By 2006, the U.S. FDA approved thalidomide in combination with dexamethasone for newly diagnosed multiple myeloma patients, with subsequent approvals for the thalidomide derivatives lenalidomide查看药品详情 and pomalidomide查看药品详情 in 2006 and 2013, respectively.

Cereblon Solved Part of a Decades-Old Mystery

For decades, the molecular basis of thalidomide查看药品详情's effects remained unknown. In 2010, Ito and colleagues identified cereblon (CRBN) (搜索)搜索该靶点 as a direct molecular target of thalidomide. CRBN functions as the substrate receptor of the CRL4^CRBN E3 ubiquitin ligase complex, part of the cellular machinery that determines which proteins are tagged with ubiquitin and directed toward proteasomal degradation.

This gave thalidomide查看药品详情's developmental toxicity a molecular anchor, though subsequent work has shown the relationship is more complex than CRBN alone: the consequences of exposure depend on which proteins are recruited to the drug-modified CRBN complex. In 2011, Zhu and colleagues demonstrated that reducing CRBN expression made multiple myeloma (搜索)搜索该疾病 cells highly resistant to lenalidomide查看药品详情 and pomalidomide查看药品详情 while preserving sensitivity to unrelated agents such as bortezomib, dexamethasone, and melphalan—confirming that the antimyeloma activity of the drug class depended on CRBN.

Ikaros and Aiolos Reveal the Mechanism

Landmark studies showed that lenalidomide查看药品详情 promotes CRBN-dependent ubiquitination and degradation of the lymphoid transcription factors IKZF1 (Ikaros) and IKZF3 (Aiolos), proteins central to plasma-cell biology and multiple myeloma (搜索)搜索该疾病 cell survival. Their loss suppresses the IRF4-MYC transcriptional program that supports myeloma-cell survival and explains the immunological effects associated with IMiDs.

This mechanism is now understood through the concept of a molecular glue—a small molecule that creates or stabilizes an interaction between proteins that would otherwise interact weakly or not at all. Thalidomide查看药品详情 derivatives bind CRBN and alter its recognition surface, allowing new substrates, or neosubstrates, to be recruited, ubiquitinated, and destroyed by the proteasome. As the source materials note, a relevant protein does not always need to be inhibited if the cell can instead be induced to eliminate it.

From IMiDs to CELMoDs

Cereblon E3 ligase modulators (CELMoDs), including iberdomide查看药品详情 and mezigdomide查看药品详情, retain the basic principle established by IMiDs but were designed for more potent and efficient degradation of Ikaros and Aiolos. This is particularly relevant as lenalidomide查看药品详情 and pomalidomide查看药品详情 are used earlier and for longer, with resistance becoming more common.

In August 2026, iberdomide查看药品详情 brought this approach into approved multiple myeloma (搜索)搜索该疾病 therapy when the FDA granted accelerated approval to Zenbexus in combination with daratumumab, hyaluronidase-fihj, and dexamethasone for adults with multiple myeloma after at least one prior line of therapy. In the primary efficacy population, minimal residual disease-negative complete response at any time was achieved in 41% of patients on iberdomide versus 21% on the comparator. Iberdomide carries a boxed warning for embryo-fetal toxicity and serious venous and arterial thromboembolism.

Mezigdomide查看药品详情, another oral cereblon modulator, has shown phase III activity in relapsed or refractory multiple myeloma (搜索)搜索该疾病. In SUCCESSOR-2, mezigdomide with carfilzomib and dexamethasone produced a median progression-free survival of 18.0 months versus 8.3 months with carfilzomib and dexamethasone alone. Mezigdomide remains investigational, but its New Drug Application is now under FDA review.

The Expansion into Programmable Protein Degradation

PROTACs use a different design: one end binds the target protein, the other recruits an E3 ligase, and a linker connects them, bringing the target into the ubiquitin-proteasome system for degradation. CRBN became one of the most widely used E3 ligases for this approach. In 2015, dBET1 used a thalidomide查看药品详情-derived CRBN recruiter to degrade BET proteins such as BRD4, an epigenetic regulator implicated in hematologic malignancies and several solid tumors.

A decade later, this strategy reached clinical practice. In May 2026, vepdegestrant查看药品详情 became the first FDA-approved PROTAC, for ESR1-mutated, ER-positive/HER2-negative advanced or metastatic breast cancer (搜索)搜索该疾病. Targeted degradation has become attractive for proteins historically labeled "undruggable," though it depends on suitable molecular recognition, productive geometry between target and ligase, cellular exposure, E3 ligase availability, and adequate selectivity.

The Unexpected Legacy of Thalidomide

Thalidomide查看药品详情's later therapeutic value does not diminish the consequences of its teratogenicity, and its scientific legacy remains complicated. When thalidomide entered medicine, its molecular target was unknown. In multiple myeloma (搜索)搜索该疾病, decades of research turned it from an empirically used drug into the starting point for an entire therapeutic lineage. CRBN-binding chemistry then became a building block for PROTACs directed at unrelated targets, and CELMoDs extended this lineage, most recently with the 2026 approval of iberdomide查看药品详情. As the source materials conclude, what began with thalidomide largely by accident, drug development is now trying to achieve on purpose.