Grant Zeng, CFA
CytRx Reports Positive Phase II Preliminary Results
On June 13, 2011, CytRx Corporation (CYTR) announced preliminary positive results from its ENABLE Phase II proof-of-concept trial of bafetinib for the treatment of B-cell chronic lymphocytic leukemia (B-CLL).
As a reminder, in May 2010, CytRx initiated a Phase II proof-of-concept clinical trial (ENABLE) with bafetinib as a second line treatment for B-CLL due to the potent and specific inhibitory properties of bafetinib against Lyn and Fyn kinases, which are overexpressed in B-CLL cancers.
In this clinical trial, high-risk B-CLL patients who have failed treatment with first-line agents will self-administer oral doses of bafetinib twice daily. The bafetinib dose used in this trial is based on the highest dose that was best tolerated in the Phase I study. Patients will be monitored for clinical response, time to disease progression and cancer progression-free survival. Total of 30 patients will be enrolled. The dose of bafetinib may be escalated to 360 mg twice daily if relatively few side effects are observed at the 240 mg twice daily dose. The endpoint of this Phase II trial is objective response rate (30% ORR is target). MD Anderson is the primary US site.
Of the 16 patients enrolled in the ENABLE Phase II clinical trial, 11 patients were evaluable for tumor response (patients who have received both baseline and follow-up tumor assessments). At the time of evaluation, the median duration of treatment for all patients was two months, and five of these 11 patients had received three to five months of bafetinib therapy; five patients either did not receive baseline or follow-up assessments. The median number of prior therapies for the full group is three, with a range between one and five prior therapies, and nine of 12 patients demonstrated unfavorable cytogenetics (del 17p; 13). This subgroup of patients typically has fast disease progression and shorter median overall survival.
All 11 evaluable patients demonstrated ≥50% elevation in their lymphocyte counts during the first two months of treatment, similar to other kinase inhibitors being tested in B-CLL patients. Six demonstrated >50% shrinkage in their lymph nodes and/or spleen, two patients had stable disease and three patients had progressive disease at their initial assessments. Lymph node softening also was noted in these patients. Only one grade 3 or 4 adverse event (grade 3 elevated liver enzymes) was noted, which resolved when bafetinib administration was ceased. Grade 1 and 2 adverse events included elevated liver enzymes with normal bilirubin, fatigue and gastrointestinal symptoms.
The initial results are encouraging. The Phase II study demonstrated that bafetinib is clinically active in a group of patients with relapsed B-CLL who have failed several other treatments for their cancer. Based on this indication of clinical activity and the low incidence of adverse events, additional patients enrolled in the ENABLE Phase II clinical trial will receive bafetinib as a single agent at a higher dose. This increased dosage could increase the potential for greater efficacy.
B-CLL is the most common form of leukemia in adults in Western countries. More than 17,000 new cases of B-CLL are reported in the United States alone each year; however up to an estimated 40% of cases may not be reported due to under-diagnosis and lack of placement in cancer registries. Virtually all patients are older than 55 years at presentation, with an average age of 70 years. Patients in the high-risk B-CLL classification have a median overall survival period of one to five years.
We have an Outperform rating on CytRx with a twelve-month price target of $1.80.
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