New agents in the treatment of acute lymphocytic leukaemia

Advanced targeted therapies in cancer: Drug nanocarriers, the future of chemotherapy

Cancer is the second worldwide cause of death, exceeded only by cardiovascular diseases. It is characterized by uncontrolled cell proliferation and an absence of cell death that, except for hematological cancers, generates an abnormal cell mass or tumor. This primary tumor grows thanks to new vascularization and, in time, acquires metastatic potential and spreads to other body sites, which causes metastasis and finally death. Cancer is caused by damage or mutations in the genetic material of the cells due to environmental or inherited factors. While surgery and radiotherapy are the primary treatment used for local and non-metastatic cancers, anti-cancer drugs (chemotherapy, hormone and biological therapies) are the choice currently used in metastatic cancers. Chemotherapy is based on the inhibition of the division of rapidly growing cells, which is a characteristic of the cancerous cells, but unfortunately, it also affects normal cells with fast proliferation rates, such as the hair follicles, bone marrow and gastrointestinal tract cells, generating the characteristic side effects of chemotherapy. The indiscriminate destruction of normal cells, the toxicity of conventional chemotherapeutic drugs, as well as the development of multidrug resistance, support the need to find new effective targeted treatments based on the changes in the molecular biology of the tumor cells. These novel targeted therapies, of increasing interest as evidenced by FDA-approved targeted cancer drugs in recent years, block biologic transduction pathways and/or specific cancer proteins to induce the death of cancer cells by means of apoptosis and stimulation of the immune system, or specifically deliver chemotherapeutic agents to cancer cells, minimizing the undesirable side effects. Although targeted therapies can be achieved directly by altering specific cell signaling by means of monoclonal antibodies or small molecules inhibitors, this review focuses on indirect targeted approaches that mainly deliver chemotherapeutic agents to molecular targets overexpressed on the surface of tumor cells. In particular, we offer a detailed description of different cytotoxic drug carriers, such as liposomes, carbon nanotubes, dendrimers, polymeric micelles, polymeric conjugates and polymeric nanoparticles, in passive and active targeted cancer therapy, by enhancing the permeability and retention or by the functionalization of the surface of the carriers, respectively, emphasizing those that have received FDA approval or are part of the most important clinical studies up to date. These drug carriers not only transport the chemotherapeutic agents to tumors, avoiding normal tissues and reducing toxicity in the rest of the body, but also protect cytotoxic drugs from degradation, increase the half-life, payload and solubility of cytotoxic agents and reduce renal clearance. Despite the many advantages of all the anticancer drug carriers analyzed, only a few of them have reached the FDA approval, in particular, two polymer-protein conjugates, five liposomal formulations and one polymeric nanoparticle are available in the market, in contrast to the sixteen FDA approval of monoclonal antibodies. However, there are numerous clinical trials in progress of polymer-protein and polymer-drug conjugates, liposomal formulations, including immunoliposomes, polymeric micelles and polymeric nanoparticles. Regarding carbon nanotubes or dendrimers, there are no FDA approvals or clinical trials in process up to date due to their unresolved toxicity. Moreover, we analyze in detail the more promising and advanced preclinical studies of the particular case of polymeric nanoparticles as carriers of different cytotoxic agents to active and passive tumor targeting published in the last 5 years, since they have a huge potential in cancer therapy, being one of the most widely studied nano-platforms in this field in the last years. The interest that these formulations have recently achieved is stressed by the fact that 90% of the papers based on cancer therapeutics with polymeric nanoparticles have been published in the last 6 years (PubMed search).

BCL-2 dependence and ABT-737 sensitivity in acute lymphoblastic leukemia

Cancer cells acquire disruptions in normal signal transduction pathways and homeostatic mechanisms that would trigger apoptosis in normal cells. These abnormalities include genomic instability, oncogene activation, and growth factor independent proliferation. Therefore, cancer cells likely require a block in apoptosis in order to survive. Overexpression of the antiapoptotic protein BCL-2 provides a block in apoptosis that is frequently observed in cancer cells. We have developed methods for the detection and analysis of BCL-2 dependence and here apply them to acute lymphoblastic leukemia (ALL). BH3 profiling, a mitochondrial assay that classifies blocks in the intrinsic apoptotic pathway, indicated a dependence on BCL-2 of both ALL cell lines and primary samples. This dependence predicted that BCL-2 would be complexed with select pro-death BH3 family proteins, a prediction confirmed by the isolation of BCL-2 complexes with BIM. Furthermore, the BH3 profiling and protein analysis predicted that ALL cell lines and primary cells would be sensitive to ABT-737 as a single agent. Finally, BH3 profiling and protein studies accurately predicted a relative degree of sensitivity to BCL-2 antagonism in cell lines. The ALL cells studied exhibit BCL-2 dependence, supporting clinical trials of BCL-2 antagonists in ALL as single agents or combination therapies.

Management of acute lymphoblastic leukemia in older patients

Although the median age for adults with acute lymphoblastic leukemia (ALL) is older than 60 years, relatively few of these patients have been enrolled on prospective clinical trials. The presence of coexisting medical disorders and unfavorable cytogenetic and biologic disease characteristics within this population presents considerable challenges for successful treatment using conventional chemotherapy programs. Selected patients have achieved remission and long-term survival following intensive chemotherapy. Philadelphia (Ph) chromosome (BCR/ABL)-positive ALL is particularly common among older patients. The availability of specific tyrosine kinase inhibitors is changing the prognosis for this challenging subset.

Phase II study of sphingosomal vincristine in patients with recurrent or refractory adult acute lymphocytic leukemia

BACKGROUND

Outcomes with salvage therapy for patients with recurrent or refractory acute lymphocytic leukemia (ALL) are poor, with complete response (CR) rates reported to be 20-30% and a median survival ranging from 2-6 months. New agents are needed to reduce the recurrence rate after frontline chemotherapy. Vincristine is an important component of ALL therapy. In animal models, the encapsulation of vincristine into sphingomyelin liposomes or "sphingosomes" for injection (SV) has improved efficacy compared with conventional vincristine.

METHODS

A Phase II clinical trial of single-agent SV given at a dose of 2.0 mg/m2 every 2 weeks was conducted in patients with recurrent or refractory ALL. Approximately half of the 16 patients who received SV had a first CR duration of less than 1 year, 19% had failed standard induction chemotherapy, and 50% had Philadelphia chromosome-positive disease. SV was the first salvage attempt in 69% of the patients.

RESULTS

The overall response rate in the 14 evaluable patients was 14% (1 CR and 1 partial response). Five patients (36%) had transient reductions in bone marrow leukemia infiltrate with subsequent regrowth of the leukemia between SV infusions. Toxicity with limited treatment (median number of doses was two; range, one to five doses) was minimal with expected peripheral neuropathy.

CONCLUSIONS

Further study of SV in patients with ALL is warranted. A Phase I-II clinical trial of weekly SV with pulse dexamethasone currently is ongoing.

Acute Lymphoblastic Leukemia: Older Patients and Newer Drugs

Although the median age for adults with acute lymphoblastic leukemia (ALL) is older than 60 years, relatively few of these patients have been enrolled on prospective clinical trials. The presence of coexisting medical disorders and unfavorable cytogenetic and biological characteristics within this population presents considerable challenges for successful treatment using conventional chemotherapy programs. Selected patients have achieved remission and long-term survival following intensive chemotherapy. Preliminary data using several new agents that have shown promise for patients with ALL are described.

Acute Lymphoblastic Leukaemia in Elderly Patients

Acute lymphoblastic leukaemia (ALL) is a rare disease in the elderly. The prevalence of ALL in patients >60 years of age is reported to be between 16% and 31% of all adult cases. The biology of ALL in older patients seems to be significantly different from that in younger patients and may, at least in part, explain poor treatment outcome. Immunophenotyping and cytogenetic characteristics are among the most important biological differences in comparison with younger adults. The frequency of pre B-cell ALL and common ALL is higher and T-cell ALL subtype is under-represented in elderly populations compared with younger patients. The frequency of the Philadelphia chromosome also seems to increase with age and adversely influences complete remission rate and survival. Few reports on the effectiveness and toxicity of therapeutic programmes concerning exclusively older patients with ALL have been published so far and only some of them were prospective studies. In some of the studies age-adapted approaches have been applied in which protocols processed earlier for younger patients have been adopted for older patients. In such modified protocols chemotherapy was usually less aggressive, especially if it was given for patients with comorbidities and poor performance status. Consequently, in several studies elderly patients received suboptimal treatment. Death during induction chemotherapy was observed in 7-42% of the patients in particular reports. The overall response rate varied from 12% to 85%. The median overall survival (OS) durations in patients who received a curative approach ranged from 3 to 14 months and from 1 to 14 months in patients treated palliatively. Poor performance status, comorbidities and high early mortality during intensive chemotherapy are the main reasons for poor treatment results and short OS time. New therapeutic approaches are necessary to improve the outcome in this age group of patients with ALL.