Molecular surveillance of chronic myeloid leukemia patients in the imatinib era - evaluation of response and resistance

Bone marrow aspirate and biopsy: a pathologist's perspective. II. interpretation of the bone marrow aspirate and biopsy

Bone marrow examination has become increasingly important for the diagnosis and treatment of hematologic and other illnesses. Morphologic evaluation of the bone marrow aspirate and biopsy has recently been supplemented by increasingly sophisticated ancillary assays, including immunocytochemistry, cytogenetic analysis, flow cytometry, and molecular assays. With our rapidly expanding knowledge of the clinical and biologic diversity of leukemia and other hematologic neoplasms, and an increasing variety of therapeutic options, the bone marrow examination has became more critical for therapeutic monitoring and planning optimal therapy. Sensitive molecular techniques, in vitro drug sensitivity testing, and a number of other special assays are available to provide valuable data to assist these endeavors. Fortunately, improvements in bone marrow aspirate and needle technology has made the procurement of adequate specimens more reliable and efficient, while the use of conscious sedation has improved patient comfort. The procurement of bone marrow specimens was reviewed in the first part of this series. This paper specifically addresses the diagnostic interpretation of bone marrow specimens and the use of ancillary techniques.

Rituximab Induces Effective Clearance of Minimal Residual Disease in Molecular Relapses of Mantle Cell Lymphoma

Molecular remission (MR) is associated with improved outcome in mantle cell lymphoma (MCL). If MR is not achieved, patients are at high risk of relapse. We retrospectively describe the molecular and clinical follow-ups of 4 patients with molecular relapses (M-rels) who were treated with rituximab. The 4 patients received rituximab-supplemented, high-dose sequential chemotherapy and autologous stem cell transplantation as induction treatment and achieved clinical remission and MR. M-rel was defined as polymerase chain reaction (PCR) positivity in 2 consecutive samples in the absence of clinical relapse. M-rels occurred at 3, 6, 39, and 52 months and were always confirmed by direct sequencing of the clonal rearrangement. Minimal residual disease was monitored by qualitative and real-time quantitative PCR. All patients received 4 courses of rituximab, with 2 additional infusions if PCR positivity remained. After 4-6 courses of rituximab, all patients re-entered MR. No clinical relapses were recorded at 3, 6, 18, and 62 months from treatment, although 1 patient had a second M-rel that was sensitive to rituximab. Our results indicate that rituximab is active against residual MCL cells and suggest that molecularly tailored maintenance therapy needs to be investigated in clinical trials.

Activity of dual SRC-ABL inhibitors highlights the role of BCR/ABL kinase dynamics in drug resistance

Mutation in the ABL kinase domain is the principal mechanism of imatinib resistance in patients with chronic myelogenous leukemia. Many mutations favor active kinase conformations that preclude imatinib binding. Because the active forms of ABL and SRC resemble one another, we tested two dual SRC-ABL kinase inhibitors, AP23464 and PD166326, against 58 imatinib-resistant (IM(R)) BCR/ABL kinase variants. Both compounds potently inhibit most IM(R) variants, and in vitro drug selection demonstrates that active (AP23464) and open (PD166326) conformation-specific compounds are less susceptible to resistance than imatinib. Combinations of inhibitors suppressed essentially all resistance mutations, with the notable exception of T315I. Guided by mutagenesis studies and molecular modeling, we designed a series of AP23464 analogues to target T315I. The analogue AP23846 inhibited both native and T315I variants of BCR/ABL with submicromolar potency but showed nonspecific cellular toxicity. Our data illustrate how conformational dynamics of the ABL kinase accounts for the activity of dual SRC-ABL inhibitors against IM(R)-mutants and provides a rationale for combining conformation specific inhibitors to suppress resistance.