Fox and colleagues tested the toxicity and tolerance of this drug when given in 28-day cycles to patients 2 to 19 years old with malignant solid tumors to determine the appropriate dose of cediranib for this age group. Patients who participated in this phase I study had not responded to or recurred after conventional therapy.
Among the 13 patients enrolled, once daily dosing of 12 mg/m2 of cediranib was tolerable. Thus far, three patients have experienced partial shrinkage of their tumor while receiving the antiangiogenic agent. Side effects in children were similar to those seen in adults on cediranib: dose-limiting toxicities were diarrhea, nausea, vomiting, lethargy and high blood pressure.
"This outcome is encouraging and provides evidence that cediranib should be further studied in future clinical trials in young patients with these and other sarcomas to determine the activity of this new agent," Fox said. "Hopefully, newer classes of anti-cancer drugs currently being developed will have fewer acute and long-term side effects than the chemotherapy that we currently use to treat childhood cancers."
The researchers are currently evaluating the effects with 17 mg/m2 of cediranib and proposed to the Children's Oncology Group that a phase II study be conducted in selected childhood solid tumors.
# A114. Preclinical evaluation of the PARP inhibitor olaparib in homologous recombination deficient (HRD) MRE11 mutant microsatellite instable (MSI) colorectal cancer
The investigational cancer therapy olaparib demonstrated activity against colorectal cancer cells, which suggests that microsatellite instable colorectal cancer represents a potential patient population that could benefit from treatment with this agent.
Researchers have already evaluated the use of the oral poly (adenosine diphosphate [ADP]-ribose) polymerase (PARP) inhibitor olaparib and its antitumor activity pre-clinically and in patients with breast and ovarian cancer that contain a specific DNA repair defect in the form of BRCA1 and BRCA2 mutations. These gene mutations are associated with hereditary breast and ovarian cancer and play a major role in the repair of DNA by the homologous recombination repair pathway. PARPs also play a major role in DNA repair, by working in an alternative pathway.
Olaparib exploits the "Achilles' heel" of homologous recombination deficient cancers by blocking another DNA repair pathway in these already compromised cancer cells, therefore leading to an overload of DNA damage and resulting in tumor cell death. The activity of one such homologous recombination gene, MRE11, is lost as a consequence of microsatellite instability in colorectal cancer cells.
"DNA damage is occurring all the time in our cells and a number of mechanisms have evolved to repair this damage that include the PARP and the homologous recombination repair pathways," said Mark O'Connor, Ph.D., chief scientist at KuDOS Pharmaceuticals Ltd., United Kingdom.
The aim of this study was to determine if microsatellite instability and MRE11 status correlated with sensitivity to olaparib. Olaparib is an oral anti-cancer drug in early development for the treatment of certain types of breast and ovarian cancer.
The researchers found the majority of colorectal cancer cell lines sensitive to olaparib correlated with microsatellite instability status and had MRE11 mutations. Furthermore, all olaparib-sensitive colorectal cancer cell lines were homologous recombination deficient.
"These results reinforce the idea that PARP inhibition might have broader clinical utility than in BRCA-deficient tumors alone," said O'Connor. "They support the idea of using targeted cancer therapies in defined molecular genetic backgrounds that exploit specific DNA repair deficiencies in the cancer to be treated."
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