ALBERT

Description: Pts with CML resistant to im have few therapeutic options. A growing body of evidence suggests that treatment outcomes can be improved with increased potency of BCR-ABL inhibition. Escalating the dose of im to 800mg/day (d) can overcome some cases of im-resistance, but tolerability and durability of response are significant issues. Dasatinib (SPRYCEL®, formerly BMS-354825) is a novel, oral, multi-targeted kinase inhibitor of BCR-ABL, SRC, and other kinases that is approximately 300 times more potent than im in vitro. Dasatinib has been shown to be effective and safe in pts with CML resistant or intolerant to im, leading to recent FDA approval. START-R is an international trial of dasatinib 70mg twice daily (BID) and im 800mg/d in pts with CP-CML resistant to prior im 400–600mg/d. Crossover was allowed upon confirmed progression or intolerance despite dose reduction (grade 3/4 non-hematologic toxicity). Dasatinib dose escalation to 90mg BID was allowed for inadequate response at 12 wks, and dose reduction to 50 or 40mg BID for toxicity. Dose reduction of im to 600mg/d was allowed for patients who had not previously received that dose. Major cytogenetic response (MCyR) rate at 12 weeks was the primary endpoint. From Feb–Nov 2005, 150 pts were randomized (2:1), 101 to dasatinib, 49 to im. MCyR to prior im had been seen in 28% of dasatinib and 29% of im pts. With a minimum follow-up of 10 mo, complete hematologic response (CHR) rate was 92% (93 dasatinib pts) vs 82% (40 im pts), and MCyR rate was 48% dasatinib vs 33% im. Of importance, the primary difference was the complete cytogenetic response (CCyR) rate of 35% (35/101) dasatinib vs 16% (8/49) im, suggesting that dasatinib can achieve deeper responses in this patient population. Of pts with no prior CyR to im, 44% (17/39) achieved a MCyR with dasatinib vs 7% (1/15) with higher dose im. MCyR rates of 40% to dasatinib and 20% to im were achieved in pts with baseline im-resistant BCR-ABL mutations, with 47% of dasatinib pts vs 0 im pts with difficult-to-treat P-loop mutations achieving a MCyR. Pts with no prior CyR to im were able to achieve MCyR with dasatinib, but dose escalation of im was not effective. 23% dasatinib pts vs 80% im pts had treatment failure (TF, defined as progression, lack of response, crossover for intolerance, or off treatment). Median time to TF was not reached for dasatinib, and was 3.5 mo (95% CI: 3.3-3.8) for im. 61 pts discontinued the initially assigned treatment, of whom 50 (12 dasatinib; 38 im) crossed over after progression, no response, or intolerance. Of 45 post-crossover pts (38 dasatinib; 7 im), 17 (45%) dasatinib pts achieved MCyR, but no (0%) im pts with 800mg/d achieved MCyR after crossover following dasatinib. Grade 3/4 non-hematologic toxicity was minimal in both arms. All grades of superficial edema and fluid retention were more common with im than dasatinib (41% im vs 15% dasatinib; and 43% im vs 28% dasatinib respectively), whereas pleural effusion was 13% (3% grade 3/4) dasatinib vs 0 im. Cytopenia was more frequent and severe with dasatinib. This is the first clinical trial in pts with CML to include both im and dasatinib arms. Based on nearly 1 year of follow-up, dasatinib clearly appears to be more effective in achieving MCyR than high-dose im in pts who fail 400–600mg/d im. An update with molecular response data and detailed mutational analysis will be presented.

Description: The majority of patients with chronic phase (CP) CML treated with imatinib achieve a CCR, which is associated with a high progression-free survival (PFS). Nevertheless, BCR-ABL mutations have been observed in patients in ongoing CCR. We previously reported that virtually all patients with mutations develop evidence of resistance. The current analysis of 211 patients with CP CML aimed to determine the incidence of mutations in those who achieve CCR, assess whether the incidence varies with increasing duration of CCR, and evaluate the rate of loss of response in those who do develop mutations. BCR-ABL levels measured by quantitative RT-PCR at 1–6 month intervals were used to guide the frequency of mutation analysis. All patients were screened for mutations at least 6 monthly. Of the 211 patients, 159 (75%) achieved CCR after a median of 3 months (25th to 75th percentile 3–6 months), and were then followed for a median of 12 months after achieving CCR (25th to 75th percentile 6–28 months). Twelve patients lost CCR and this was associated with the development of a mutation in 8 (67%). The median time to loss of CCR was 3 months after the mutation was detected (range 1–10 months). Three of these 12 patients proceeded to transplant, and 9 received an increased imatinib dose (4 maintaining a major cytogenetic response (MCR); 3 re-establishing CCR). Only 1 of the 12 lost a complete hematologic response (CHR) (patient had 2 mutations) and none have progressed to blast crisis (BC) with a median follow-up of 9 months (range 6–38 months) including 3 patients with P-loop mutations, which have been associated with a poorer prognosis. As well as the 8 patients who lost CCR after a mutation was detected, mutations were detected in 3 patients who have maintained CCR; 2 had an increased imatinib dose. The detection of a mutation was associated with a rise in the BCR-ABL level in all patients with mutations. Of the 159 patients in CCR, mutations were detected in 11 of 25 (44%) with a 〉2-fold rise in BCR-ABL whereas none of 131 patients with stable or decreasing BCR-ABL had a mutation detected (P

Description: Imatinib mesylate (IM) has dramatically changed the treatment approach for patients with chronic myeloid leukemia (CML). However, ~20% of chronic phase (CP) patients are initially resistant to IM, and among patients who achieve a complete cytogenetic response (CCyR), a small minority relapse back into CP or progress to advanced disease. Abl tyrosine kinase domain mutations are the major cause of secondary resistance. Oligonucleotide microarray analysis was used to study gene expression patterns associated with primary IM resistance and relapse after initial successful response to IM. Samples included total RNA from diagnostic samples of 25 CML CP patients within 6 months of diagnosis and at the time of failure (7 patients); total RNA from 18 patients who relapsed after initial CCyR with documented Abl point mutations (12 CP and 6 BC); and 10 myeloid progenitor samples (sorted by CD34 and CD38 status) from an IM naïve and IM resistant (R) patient, both in blast crisis. Results: For primary IM resistance, analysis of paired samples before and after treatment revealed that primary failure was associated with the differential expression of genes associated with RNA post-transcriptional modification, protein synthesis, cellular growth and proliferation, and cell death. Two genes with the highest differential expression included the apotosis resistance genes API5 and TRAF5. TRAF5 was also increased in patients who relapsed after initial CCyR, while API5 showed significantly increased expression in sorted CD34+ cells from an IMR patient. In secondary resistance patients, a set of drug transporters including ABCA2, ABCA3, MDR1, and ABCC3 had increased expression and hOCT1 decreased expression relative to 42 IM naïve CP patients. In vitro experiments compared K562 resistant (R) and sensitive (S) cell lines over time exposed to IM. The K562 IMR cell line showed a 1.5 log higher expression of ABCG2 and a 1 log higher expression of TRAF5 compared to the K562 IMS cells. However, sequential clinical samples of 16 IM non-responders vs. 14 CCyR patients showed no change in ABCG2 expression, possibly because ABCG2 is expressed only in early progenitor cells, not differentiated cells. The importance of using CD34+ cells was demonstrated in 7 array studies comparing gene expression in CD34+ selected cells from an IMR patient compared to an IM naïve patient. IM resistance was associated with increased expression of genes associated with cell cycle, DNA recombination and repair, and proliferation. Genes associated with apoptosis resistance included increased expression of API5, survivin, and decreased expression of BAK1. Protein serine/threonine and tyrosine kinases associated with cell proliferation/survival and tumor progression with increased expression in the IMR patient included: AURKB, AKT3, BUB1B, CDC2, CHEK1, MAPK9, STK6, TTK, and WEE1. Conclusion: Gene expression studies suggest that primary resistance to IM therapy is associated with resistance to apoptosis; relapse on IM is associated with activation of drug transporter genes and genes associated with disease progression; in studying disease response and resistance, primitive hematopoetic cells are critical for analysis.

Description: The dose of 400mg per day of imatinib is currently considered standard therapy for patients with newly diagnosed chronic myeloid leukemia (CML) in chronic phase (CP). The IRIS trial demonstrated superior response rates in imatinib treated patients compared to interferon alfa, and evaluated molecular response up to 24 months of imatinib therapy in patients who achieved a complete cytogenetic response (CCR). Those patients with a major molecular response (MMR, ≥3 log reduction of BCR-ABL) by 12 months had 100% progression free survival at 24 months. However, very few patients had undetectable BCR-ABL levels. In the current study, we monitored the molecular response for a median of 42 months (25th to 75th percentile 39–45 months) in all patients enrolled in the IRIS trial in Australia and New Zealand who commenced imatinib as their first-line therapy (n=28 patients). We aimed to determine if the BCR-ABL levels continued to decrease and whether additional patients achieve a MMR with a longer follow up. BCR-ABL transcript levels were monitored by real-time quantitative PCR at 3 to 6 month intervals. A CCR (approximately equivalent to a greater than 2-log reduction of BCR-ABL) was achieved in 24 of the 28 patients (85%). The table demonstrates that while the frequency of achieving a MMR increased between 12 and 42 months, most of the improvement occurred between 12 and 24 months. Conversely, from 24 to 42 months the number of patients achieving a ≥4-log reduction increased significantly (P