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Small molecule modulators of cyclin-dependent kinases for cancer therapy
1Oral and Pharyngeal Cancer Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, Maryland 20892-4340, USA.
Abstract:
The majority of human malignancies have aberrancies in the Retinoblastoma (Rb) pathway. Loss in Rb function results from the phosphorylation and inactivation of Rb by the cyclin-dependent kinases (cdks), main regulators of cell cycle progression. Thus, modulators of cdks may have a role in the treatment of human malignancies. Flavopiridol, the first cdk modulator tested in clinical trials, demonstrates interesting preclinical features: cell cycle block, induction of apoptosis, promotion of differentiation, inhibition of angiogenic processes and modulation of transcriptional events. Initial clinical trials with infusional flavopiridol demonstrated activity in some patients with lymphomas and renal, colon gastric carcinomas. Main side effects were diarrhea and hypotension. Phase 2 trials with infusional flavopiridol, other schedules and combination with standard chemotherapies are ongoing. The second cdk modulator tested in clinical trials, UCN-01, is a PKC inhibitor that can also modulate cdk activity. Similar to flavopiridol, UCN-01 blocks cell cycle progression and promotes apoptosis. Moreover, UCN-01 may abrogate checkpoints induced by genotoxic stress due to inhibition of chk1 kinase. The first clinical trial of UCN-01 demonstrated very prolonged half-life (approximately 600 h), due to high binding affinity of UCN-01 to the human alpha-1-acid glycoprotein. Main side effects were headaches, vomiting, hypoxemia and hyperglycemia. Clinical activity was observed in some patients with melanoma and lymphoma. Trials of shorter infusions of UCN-01 or in combination with standard chemotherapeutic agents are ongoing. Although several important basic and clinical questions remain unanswered, development of cdk modulators is a reasonable strategy for cancer therapy.
Insights
Cyclin-dependent kinase (cdk) modulators like flavopiridol and UCN-01 show promise in cancer treatment by affecting cell cycle progression and apoptosis. Ongoing trials explore their efficacy and safety in various human malignancies.
Area of Science:
- Oncology
- Molecular Biology
- Pharmacology
Background:
- Aberrations in the Retinoblastoma (Rb) pathway are common in human malignancies.
- Cyclin-dependent kinases (cdks) regulate cell cycle progression and are key targets due to their role in Rb pathway inactivation.
Purpose of the Study:
- To review the preclinical and clinical development of cdk modulators as a cancer therapy strategy.
- To highlight the mechanisms of action, clinical activity, and side effects of flavopiridol and UCN-01.
Main Methods:
- Review of preclinical data and clinical trial results for flavopiridol and UCN-01.
- Analysis of drug mechanisms, including cell cycle arrest, apoptosis induction, and checkpoint abrogation.
Main Results:
- Flavopiridol demonstrated preclinical activity and initial clinical efficacy in lymphomas and carcinomas, with diarrhea and hypotension as main side effects.
- UCN-01, a PKC inhibitor with cdk modulating activity, showed clinical activity in melanoma and lymphoma, characterized by a prolonged half-life and side effects including headache and vomiting.
- Both agents induce cell cycle arrest and apoptosis; UCN-01 also abrogates genotoxic stress checkpoints.
Conclusions:
- Cdk modulators represent a rational therapeutic strategy for human malignancies.
- Further clinical trials are ongoing to optimize schedules and combinations for improved efficacy and safety.