The 2011 Gordon Wilson Lecture: overcoming resistance to targeted cancer drugs

During the past decade, molecularly targeted drugs have had a transformative impact on the treatment of several cancer types. Although the clinical benefits of these drugs are impressive, their effects are generally short-lived due to the acquisition of resistance. Unlike most cytotoxic agents, for which resistance mechanisms have remained obscure despite decades of clinical use, an understanding of the molecular basis of resistance to most targeted agents has emerged quickly. This rapid progress has been possible due to advances in molecular technologies that allow genome-wide profiling of patient samples. One important and consistent theme is that resistance is almost invariably associated with restoration of the signaling pathway inhibited by the targeted agent. Here I review examples from three diseases--chronic myeloid leukemia, prostate cancer, and lung cancer--that illustrate these points and reveal how insights into resistance mechanisms can rapidly accelerate the development of second-generation targeted therapies or combination regimens to improve patient outcome.

[Analysis of relationship between bcr-abl transcription level detected by real-time quantitative polymerase chain reaction and clinical status of CML patients]

This study was aimed to investigate the bcr-abl transcription level and its relationship with the clinical status of patients so as to provide some bases for predicting patient status according to absolute value of bcr-abl transcript. The bcr-abl/abl values (%) of bone marrow samples from 30 newly diagnosed CML patients at the baseline bcr-abl/abl value obtained in CML patients with bcr-abl positive were defined, then 161 bone marrow samples from 82 patients were detected at virions time points, and the bcr-abl/abl value of each sample was compared with baseline value and its relationship with clinical status of patient at same time point was investigated. The results showed that bcr-abl/abl values (%) of 30 patients showed positive skew distribution and a large variation with mean 13.5631 (1.0206 - 98.3159) and mathematical mean of 21.1491 (95% CI: 12.3532 - 29.9450). For strict standard, the baseline value of bcr-abl/abl (%) was set as 1, the lower limit of these values. In the detected results of 161 samples, there were 33 samples' values above the baseline value, in which resistance/relapse/progression (R/R/P) 13 (39.4%, 13/33), no remission (NR) 17 (51.5%, 17/33) and complete hematologic remission (CHR) 3 (9.1%, 3/33) were observed. the values of 26 samples decreased by 0 - 1 order of magnitude (0.1 < or = bcr-abl/abl % < 1), in which R/R/P 6 (23.1%, 6/26), NR 7 (26.9%, 7/26), CHR 7 (26.9%, 7/26) and cytogenetic remission (CyR) 6 (23.1%, 6/26) were observed, the values of 19 samples decreased by 1 - 2 order of magnitude (0.01 < or = bcr-abl/abl % < 0.1), in which NR 2 (10.5%, 2/19), CHR 3 (15.8%, 3/19) and CyR 14 (73.7%, 14/19) were determined. 7 samples decreased by 2 - 3 order of magnitude (0.001 < or = bcr-abl/abl % < 0.01) in which major CyR (MCyR) 2 (28.6%, 2/7) and complete CyR (CCyR) 5 (71.4%, 5/7) were determined, the values of 76 samples decreased by 3 or more order of magnitude (bcr-abl/abl % < 0.001), and all these were CCyR. In conclusion, the using decrease degree of one time point-detected value compared to the baseline could well assess the patient clinical status. The bcr-abl/abl % < 0.01 can reliably reflect CyR obtained by patients at the time point, and bcr-abl/abl % < 0.001 can reflect CCyR obtained by patients. However, exact judgments of patient status relies on dynamic and serial monitoring.

[Chronic myeloid leukemia in the 21st century: biology and treatment]

Chronic Myeloid Leukaemia (CML) is a clonal disease, originated at the level of Hematopoietic Stem Cells (HSC) and characterized by the presence of the Philadelphia (Ph) chromosome and its oncogenic product p210(BcrAbl). Such a protein has been shown to be essential for malignant transformation, since it is capable of altering cell adhesion, proliferation and apoptosis. Historically, CML has been treated by using different approaches: arsenic (in the early days), a variety of chemical agents (busulfan, hydroxyurea, cytarabine), cytokines (IFN-alpha, IFNalpha-PEG), hematopoietic cell transplant (HCT), and more recently drugs generated by design (imatinib, nilotinib, dasatinib). All these molecules exert specific effects on HSC and lead to a variety of clinical and biological responses. In this article, we present an overview about hematopoiesis in CML and its implications in the treatment of this disease.

[Angiogenesis in different clinical phases of chronic myeloid leukemia]

Angiogensis plays the crucial role in growth and dissemination of neoplastic diseases, both for solid tumors and hematopoietic malignancies. Development of the abundant neoplastic vasculature results from an imbalance between pro- and antiangiogenic regulatory mechanisms. The investigation was focused on expression of the main regulatory angiogeneic factors in different phases of chronic myeloid leukemia (CML) and on influence of leukemic cells on the human umbilical vein endothelial cells proliferation. The groups of 29 patients with CML and of 14 healthy controls were enrolled to the study. The expression of vascular endothelial growth factor (VEGF), basic fibroblast growth factor, interleukin-8, angiopoetin-1, platelet factor-4, extracellular matrix metalloproteinases (MMP) -2 and -9 as well as tissue inhibitors of metalloproteinases was determined in peripheral blood and bone marrow mononuclear cells with the use of quantitative real-time PCR method and additionally the concentration of VEGF with the flow cytofluorometry. We evaluated the phosphorylation of endothelial mitogen activated protein kinase in human umbilical vein endothelial cells after incubation in CML cells conditioned media, applying Western blot technique. We determined an influence of the leukemic cells on the endothelial cells proliferation with the colorimetric metabolic MTT test. We showed, that in peripheral blood and bone marrow mononuclear cells in CML patients most of the studied factors were increased at the time of CML diagnosis and became lower in remission. In newly diagnosed CML patients an expression of VEGF, MMP-2 and MMP-9 was particularly elevated. In remission, the levels of VEGF and metalloproteinases, specifically MMP-9, were decreased. If failed to achieve remission, the patients presented the elevated expression of most of the investigated angiogenic factors. In the acceleration or blast crisis phase angiopoetin, VEGF and MMP-2 levels were particularly high. We noticed the markedly enhanced human umbilical vein endothelium proliferation after an incubation in CML cells conditioned media, both in the test of mitogen activated protein kinase phosphorylation in endothelial cells and in the metabolic test for the proliferation intensity of endothelium. The differences of an angiogeneic potential found between clinical phases of CML, and the ability of leukemic cells to stimulate endothelial proliferation, point at the significance of neovascularisation in CML pathogenesis. Further studies are necessary to delineate the possibility of the use of angiogenic inhibitors in the treatment of this malignancy.

Primary myelodysplastic syndrome in Jordan: a single-centre experience

OBJECTIVE

Study of the disease patterns and clinical evaluation of myelodysplastic syndrome (MDS).

SUBJECTS AND METHODS

A retrospective analysis was carried out on 85 patients, with MDS who were followed up over a period of 23 years at Jordan University Hospital, Amman, Jordan. Cases were analyzed according to the French, American and British Classification.

RESULTS

Of the 85 patients, 42 (49.4%) were females and 43 (50%) males; mean age was 59 +/- 19 years (range 18-88). Most subtypes found in patients were refractory anemia (RA) in 27 (31.8%) and RA with excess blasts (RAEB) in 28 (32.9%). Adverse prognostic indicators were RAEB subtype and requirement for blood transfusion.

CONCLUSION

Our findings showed that MDSs appeared at a younger age and tended to be of the aggressive subtype. Chronic myelomonocytic leukemia subtype seemed to appear dominantly in men.

Secondary pulmonary alveolar proteinosis in a patient with chronic myeloid leukemia in the accelerated phase

Pulmonary alveolar proteinosis (PAP) is a rare respiratory disease the character of which is accumulation of protein consisting of surfactant in alveolar spaces. PAP sometimes complicates with hematological malignancies, especially myeloid leukemia. As one of the cause of PAP, impairment of alveolar macrophage is considered. We experienced a case of PAP with chronic myeloid leukemia (CML). 41 years old woman having CML for nine years developed PAP, and was treated by bronchoalveolar lavage and imatinib. She died of respiratory failure in the end, but BAL fluid had been becoming gradually crystalline after induction of imatinib. We consider that we should try to treat to improve respiratory status not only PAP but also hematological disease.

Rho-signaling pathways in chronic myelogenous leukemia

Chronic myelogenous leukemia (CML) is a hematological malignancy that is characteristic by as expansion of myeloid cells and their premature release into the circulation. The molecular cause of CML is the fusion oncoprotein Bcr-Abl whose constitutive tyrosine-kinase (TK) activity maintains enhanced signaling through multiple signal transduction pathways and confers proliferative and survival advantage to CML cells. These effects can be largely suppressed by TK inhibitor Imatinib mesylate, currently the leading drug in CML treatment. However, Bcr-Abl contains also additional functional domains, in particular a DBL homology (DH) domain with guanine-exchange function (GEF) which can activate small GTPases of Rho family and a Src-homology3 (SH3) domain which recruits other proteins with GEF activity. Bcr-Abl affects among others the RhoA/ROCK/LIM/cofilin pathway that regulates the actin cytoskeleton assembly and thereby the cellular adhesion and migration. This review deals in detail with the known points of interference between Bcr-Abl and Rho kinase pathways and with the effects of Imatinib mesylate on Rho signaling and cell adhesion to the extracellular matrix (ECM) components. The potential protein targets related to Bcr-Abl non-kinase activity are discussed.

Chronic myeloid leukaemia at the University Hospital of the West Indies: a 17-year review

OBJECTIVE

To determine the presenting features and evolution of patients diagnosed with chronic myeloid leukaemia between 1983 and 1999 at the University Hospital of the West Indies.

METHODS

Forty-one records were retrospectively analyzed for the patients' demographics, reasons for referral, clinical features, laboratory investigations and the time to blast transformation and death.

RESULTS

Seventy-one per cent were males and 29% were females. The male to female ratio was 2.4:1. The median age at presentation was 37 years (range 14-81 years). Seventy-eight per cent of the patients presented in the chronic phase. Weight loss and splenomegaly were the most frequent presenting features being seen in 54 and 83 per cent respectively. The median survival was 36 months.

CONCLUSION

In this study, the clinical features and evolution were comparable to existing data. Improved accrual and routine Philadelphia chromosome testing would provide a more accurate reflection of the status of CML in our population.

Therapy options in imatinib failures

Chronic myelogenous leukemia (CML) is defined by the presence of the constitutively active tyrosine kinase breakpoint cluster region/Abelson (Bcr-Abl), which activates numerous signal transduction pathways leading to uncontrolled cell proliferation. The development of the Bcr-Abl-targeted imatinib represents a paradigm shift in the treatment of CML, because treatment with imatinib resulted in significantly better patient outcome, response rates, and overall survival compared with previous standards. Despite this advance, not all patients benefit from imatinib because of resistance and intolerance. Resistance to imatinib can develop from a number of mechanisms that can be defined as Bcr-Abl-dependent (e.g., most commonly resulting from point mutations in the Abl kinase domain) and Bcr-Abl-independent mechanisms (including the constitutive activation of downstream signaling molecules, e.g., Src family kinases), which could result in the activation of the pathway regardless of Bcr-Abl inhibition. Clearly, new treatment approaches are required for patients resistant to or intolerant of imatinib, which can be dose escalated in patients who demonstrate resistance. This does not result in long-term responses. Hematopoietic stem cell transplantation is limited by the availability of matched donors and the potential for morbidity. Dasatinib, a dual Bcr-Abl/Src kinase inhibitor, has shown efficacy against all imatinib-resistant Bcr-Abl mutations except for T315I. A large trial program showed that dasatinib is effective in patients previously exposed to imatinib and has a manageable safety profile in all phases of CML and Philadelphia chromosome-positive acute lymphoblastic leukemia, resulting in its approval. Nilotinib, an analogue of imatinib, also has demonstrated activity in a similar patient population. These agents and less clinically advanced strategies are discussed in this review.

Neurological complications of chronic myeloid leukaemia: any cure?

OBJECTIVE

To attempt to explain the non-reversal, contrary to the widely held view, of the neurological deficits complicating chronic myeloid leukaemia.

METHOD

Using patients' case folders and haematological malignancy register all cases of chronic myeloid leukaemia seen in Jos University Teaching Hospital between July 1995 and June 2005 were retrospectively studied. All the available literature on the subject was also reviewed.

RESULTS

Thirty-three cases of chronic myeloid leukaemia were seen within the study period. Five (15.15%) of them had one or more sensori-neural defects. Of the five, two (40%) patients presented with bilateral hearing impairment, each beginning with the left ear; one (20%) presented with left ear hearing loss; one (20%) came with severe left ear tinnitus; one (20%) presented with complete bilateral hearing and bilateral visual losses. Fundoscopy showed leukaemic deposits on the retina. Other causes of blindness and deafness, e.g. trauma and foreign body in the ear respectively, were excluded.

CONCLUSION

While the complications due to hyperleucocytosis-induced stasis recover following the conventional treatment, those due to other pathogenetic mechanisms such as leukaemic deposits do not return to their pre-morbid states following disease control despite the use of the currently available treatment protocols. For future research, more still needs to be done to elicit other uncommon pathogenetic mechanisms underlying these complications with a view to finding specific treatment measures for worrisome chronic myeloid leukaemia-related sensori-neural deficits.

Rho GTPases and regulation of hematopoietic stem cell localization

Bone marrow engraftment in the context of hematopoietic stem cell and progenitor (HSC/P) transplantation is based on the ability of intravenously administered cells to lodge in the medullary cavity and be retained in the appropriate marrow space, a process referred to as homing. It is likely that homing is a multistep process, encompassing a sequence of highly regulated events that mimic the migration of leukocytes to inflammatory sites. In leukocyte biology, this process includes an initial phase of tethering and rolling of cells to the endothelium via E- and P-selectins, firm adhesion to the vessel wall via integrins that appear to be activated in an "inside-out" fashion, transendothelial migration, and chemotaxis through the extracellular matrix (ECM) to the inflammatory nidus. For HSC/P, the cells appear to migrate to the endosteal space of the bone marrow. A second phase of engraftment involves the subsequent interaction of specific HSC/P surface receptors, such as alpha(4)beta(1) integrin receptors with vascular cell-cell adhesion molecule-1 and fibronectin in the ECM, and interactions with growth factors that are soluble, membrane, or matrix bound. We have utilized knockout and conditional knockout mouse lines generated by gene targeting to study the role of Rac1 and Rac2 in blood cell development and function. We have determined that Rac is activated via stimulation of CXCR4 by SDF-1, by adhesion via beta(1) integrins, and via stimulation of c-kit by the stem cell factor-all of which involved in stem cell engraftment. Thus Rac proteins are key molecular switches of HSC/P engraftment and marrow retention. We have defined Rac proteins as key regulators of HSC/P cell function and delineated key unique and overlapping functions of these two highly related GTPases in a variety of primary hematopoietic cell lineages in vitro and in vivo. Further, we have begun to define the mechanisms by which each GTPase leads to specific functions in these cells. These studies have led to important new understanding of stem cell bone marrow retention and trafficking in the peripheral circulation and to the development of a novel small molecule inhibitor that can modulate stem cell functions, including adhesion, mobilization, and proliferation. This chapter describes the biochemical footprint of stem cell engraftment and marrow retention related to Rho GTPases. In addition, it reviews abnormalities of Rho GTPases implicated in human immunohematopoietic diseases and in leukemia/lymphoma.

Chronic myeloid leukaemia

Chronic myeloid leukaemia (CML) was the first neoplastic disease for which knowledge of the genotype led to a rationally designed therapy. As a result of its well known pathophysiology, straightforward diagnosis, well established prognostic factors, and treatment for the cause of disease, CML has been studied to an extent that far exceeds that expected from its frequency, and serves as a model disease for other cancers. Imatinib, an inhibitor of BCR-ABL tyrosine kinase, has revolutionised treatment of this disease, and is now recommended as standard treatment for chronic-phase CML. Interferon alfa is an acceptable alternative treatment in the early chronic phase for patients who do not tolerate imatinib. If imatinib treatment fails, allogeneic stem-cell transplantation, a dose increase of imatinib, or new drugs are recommended. Up to 87% of patients achieve complete cytogenetic remission, therefore we provide guidance for monitoring disease status. Many trials of new drugs and combination therapies that include imatinib are underway.

Concise review: Telomere biology in normal and leukemic hematopoietic stem cells

The measurement of telomere length can give an insight into the replicative history of the cells in question. Much of the observed telomere loss occurs at the stem and progenitor cell level, even though these populations express the enzyme telomerase. Telomerase-transfected hematopoietic stem cells (HSC), although able to maintain telomere length, are still limited in terms of ability to undergo sequential transplantation, and other factors require to be addressed to achieve optimal levels of stem cell expansion. Unchecked telomere loss by HSC, meanwhile, would appear to play a significant role in the pathogenesis of bone marrow failure, as observed in the condition dyskeratosis congenita. This heterogeneous inherited condition appears to exhibit telomerase dysfunction as a common final pathogenic mechanism. Although less well-established for acquired marrow failure syndromes, mutations in key telomerase components have been described. The identification of the leukemic stem cell (LSC), along with the desire to target this population with anti-leukemia therapy, demands that telomerase biology be fully understood in this cell compartment. Future studies using primary selected LSC-rich samples are required. A better understanding of telomerase regulation in this population may allow effective targeting of the telomerase enzyme complex using small molecule inhibitors or additional novel approaches. Disclosure of potential conflicts of interest is found at the end of this article.

Modulating autophagy for therapeutic benefit

Autophagy is an ancient cell survival pathway that allows cells to recoup ATP and essential building blocks for biosynthesis when they are starved of nutrients or when they are exposed to hypoxia, which are hallmarks of the tumor microenvironment. This pathway involves the formation of double-membraned vesicles, coined autophagosomes, which envelop bulk cellular material and/or organelles and that subsequently fuse with lysosomes that degrade their cargo. Autophagy has been suggested to play important roles in chemoresistance of cancer to some therapeutic agents, which typically induce an apoptotic response. For example, the histone deacetylase inhibitor SAHA induces both apoptosis and autophagy, suggesting that agents that disrupt the autophagy pathway might augment its efficacy as a therapeutic agent. We tested this notion in a model of Imatinib-refractory chronic myelogenous leukemia (CML) and in imatinib-resistant primary CML cells from patients bearing mutations in Bcr-Abl, including the T315I mutation that causes resistance to currently utilized tyrosine kinase inhibitors and translates into a very poor clinical prognosis. Agents that disrupt autophagy were shown to synergize with SAHA in provoking apoptotic death of these refractory tumors. These findings support the use of agents that disrupt the autophagy pathway in settings of chemorefractory malignancies.