Successful treatment of chronic adult T-cell leukemia with ubenimex

A mutation in aminopeptidase N (CD13) isolated from a patient suffering from leukemia leads to an arrest in the endoplasmic reticulum

Human aminopeptidase N (APN) is used as a routine marker for myelomonocytic cells in hematopoietic malignant disorders. Its gene and surface expressions are increased in cases of malignant transformation, inflammation, or T cell activation, whereas normal B and resting T cells lack detectable APN protein expression. In this study we elucidated the intracellular distribution, expression pattern, and enzymatic activity of a naturally occurring mutation in the coding region of the APN gene. At physiological temperatures the mutant protein is enzymatically inactive, persists as a mannose-rich polypeptide in the endoplasmic reticulum, and is ultimately degraded by an endoplasmic reticulum-associated degradation pathway. It shows in part the distinct behavior of a temperature-sensitive mutant with a permissive temperature of 32 degrees C, leading to correct sorting of the Golgi compartment accompanied by the acquisition of proper glycosylation but without reaching the cell-surface membrane and without regaining its enzymatic activity. Because the patient bearing this mutation suffered from leukemia, possible links to the pathogenesis of leukemia are discussed.

The human T-cell lymphoma/leukemia viruses

The primate T-cell lymphoma/leukemia viruses belong to an oncogenic genus of complex retroviruses. Members of this genus have been shown to be pathogenic in man. The human T-cell lymphoma/leukemia virus (HTLV) type I has been linked in the etiology of T-cell malignancies and "autoimmune-like" neurologic and rheumatic disorders; a related virus, HTLV-II, is becoming increasingly associated with similar disorders. Cell transformation is thought to be caused predominantly by the effects of the viral regulatory protein, Tax. An additional induced host cell molecule, adult T-cell lymphoma-derived factor, may contribute to cell immortalization. Like the DNA tumor viruses, HTLV activates transcription of cellular proto-oncogenes and inhibits cellular mechanisms of tumor suppression, cell cycle arrest, and apoptosis. However, individuals who are able to mount a strong cell-mediated immune response and limit viral entry into uninfected cells do not develop associated malignancies. Unfortunately, HTLV-induced malignancies are difficult to treat with conventional chemotherapy, and disease progression is often rapid with a median survival of less than 2 years. There are, however, some novel approaches that have yet to be fully tested that may have greater efficacy in the treatment of HTLV-induced diseases. In the future, better screening and detection methods, along with new vaccines and therapies, may contribute to the increased prevention and control of HTLV infection and its associated diseases.

Possible association between adult T-cell leukemia/lymphoma and acute myeloid leukemia

BACKGROUND

To the authors' knowledge, an association between adult T-cell leukemia/lymphoma (ATL) and acute myeloid leukemia (AML) has been reported only in four patients. The authors identified five additional patients with both neoplasms.

METHODS

A review of the clinical records of patients with AML, ATL, or lymphoid neoplasms other than ATL diagnosed between 1986 and 1995 was performed. Cytokine levels were assayed in selected patients. The authors searched for reports from other institutions using MEDLINE and the proceedings of two Japanese hematology societies.

RESULTS

ATL was diagnosed in 134 patients, whereas 180 had AML. Five patients with both neoplasms were identified (3.7% of ATL patients and 2.8% of AML patients). In seven of the nine patients (including four patients in the literature) with ATL and AML, the ATL was diagnosed prior to the AML, whereas in the remaining two patients both neoplasms were diagnosed simultaneously. Six of the nine cases were therapy-related (t)-AML, which developed after chemotherapy for ATL. Monoclonal integration of proviral human T-lymphotropic virus type 1 was detected in ATL cells but not in AML cells in the six patients examined. The plasma levels of macrophage colony-stimulating factor (M-CSF), granulocyte-colony stimulating factor, and granulocyte-macrophage-colony stimulating factor (GM-CSF) were elevated in 3, 1, and 1, respectively, of the 4 patients examined at AML onset who had active ATL. In one case, the levels of several cytokines, including GM-CSF and M-CSF, in the supernatant fluid of short term cultured ATL cells were elevated. Three patients with de novo ATL and AML received remission induction therapy, and two achieved a complete remission (CR) of both diseases. Among the four patients who received chemotherapy for t-AML, two achieved CR.

CONCLUSIONS

ATL patients also can develop AML, irrespective of treatment with chemotherapy for ATL. This association does not indicate exclusive chemoresistance of both neoplasms. Cytokines produced by ATL cells may support the growth of AML cells.

Characterization of the decline in alcohol consumption by aminopeptidase inhibition

Bestatin, an aminopeptidase inhibitor, prolongs the action of angiotensin and enkephalin. Previous studies have shown that bestatin can reduce alcohol intake in heterogeneous as well as genetically selected alcohol preferring 'P' rats, but more detailed studies of the characteristics of this effect have not yet been done. In experiment 1, daily injections of 10, 20 or 40 mg/kg bestatin for 12 days produced a uniform reduction in alcohol intake (approximately 40%) which did not recover following suspension of bestatin, but did recover following a 7 day period of morphine-stimulated alcohol drinking. In experiment 2, the lower end of the dose range was explored (2.5, 5, 10 mg/kg) and a dose-dependent effect was observed with a threshold dose of 5 mg/kg. Again, alcohol drinking did not recover following suspension of the 10 mg/kg dose of bestatin. Using a limited access procedure, bestatin reduced the intake of a preferred sodium chloride solution but not an avidly-consumed glucose solution indicating that while bestatin's effect was selective, it was not specific to alcohol. In the final experiment, the role of angiotensin and enkephalin was explored by pretreating animals with losartan (5, 10, 20 mg/kg), an angiotensin receptor blocker and naltrexone, (0.25, 0.5, 1 mg/kg) an opiate receptor blocker. Both agents produced significant but rather small attenuations in bestatin's effect suggesting that other factors are involved in its action. These findings further characterize the inhibitory effect of bestatin on alcohol intake in rodents. In addition, the novel finding of a carry-over inhibition of alcohol intake in the bestatin-free period adds further impetus to the recommendation that this drug, which has been safely used in humans, might be examined as a possible therapeutic agent for alcohol abuse.