Polimorfismos genéticos y su influencia en la efectividad del tratamiento quimioterapéutico de pacientes leucémicos / Genetic polymorphisms and its influence in chemotherapeutic treatment of leukemic patients

En Chile la incidencia de leucemia es de 4.2/100.000 adultos al año. Dentro de ellas, 2,8/100.000 son leucemias agudas y 1,4/100.000 son leucemias crónicas. La quimioterapia para el cáncer ha progresado desde su introducción a la práctica clínica y constituye una modalidad terapéutica muy útil en las leucemias. Sin embargo, su uso se ve limitado por la imposibilidad de predecir la respuesta individual, por lo que la elección de la terapia suele ser en base a criterios médicos y de las guías clínicas establecidas. Esta variación inter-individual en la respuesta a un fármaco antineoplásico puede deberse a factores farmacocinéticos y/o farmacodinámicos, relacionados con otros factores genético-metabólicos, que se traducen en variantes polimórficas de las enzimas encargadas de la biotransformación de estos fármacos o receptores. Al respecto, se estima que la genética da cuenta entre un 20 a un 95 por ciento de la variabilidad en la respuesta terapéutica y toxicológica. De todas las drogas conocidas involucradas en reacciones adversas un 80 por ciento son metabolizadas por estas enzimas. Este artículo pretende dar una visión general acerca de la respuesta potencial de los pacientes sometidos a los protocolos quimioterapéuticos establecidos en Chile para las leucemias de acuerdo a sus perfiles genéticos en las enzimas de biotransformación involucradas.

In Chile, the incidence of leukemia is 4.2/100.000 adults a year. Among them, 2.8/100.000 is acute leukemia and 1.4/100.000 chronic leukemia. The chemotherapy for cancer has been improved through the years in clinical practice and it constitutes a very useful therapeutic option in leukemia. However, its use is limited due to uncertain response; therefore, the pharmacotherapy choice is mainly empiric. In this sense the inter-individual differences in response to antineoplastic drugs could be due to pharmacokinetic factors (affecting absorption, distribution, metabolism and excretion) or pharmacodinamics (affecting receptors or another pharmacological target). It is estimated that genetics accounts for 20 to 95 percent of variability in therapeutics and toxicological response to drugs, which are mainly metabolized through polymorphic biotransformation enzymes (80 percent). Therefore, the present review gives a comprehensive study of the probable response of patients to established leukemia chemotherapy treatment in Chile according their genetic profiles on involved metabolizing enzymes.

Erythrocyte enzyme abnormalities in leukemias.

Red cell enzymes were assayed in a total of 67 patient including 24 patients with AML (19 relapse, 5 remission), 16 patients with ALL (10 relapse, 6 remission), 22 patients with CML and 5 patients with blastic CML. Diagnosis of leukemia was based on clinical presentation, peripheral blood smear and bone marrow examination (as per FAB classification). PK activity was significantly high in case of CML and blastic CML (p<0.01). Red cell HK was high in all leukemia subtypes. There was no alteration in red cell G6PD. Notably there was no PK deficiency in AML or G6PD deficiency in ALL. Activities of G6PD and PK could be correlated in cases of CML, AML, (p<0.05) and ALL (p<0.01) i.e. when there was increased activity of G6PD, PK activity also tended to be higher. HK activity showed a positive correlation with PK and G6PD activity in cases of CML (p<0.05), however in acute leukemia there was no such correlation. Alteration of enzyme activities among red cells in leukemia occurred only during relapse. At the time of remission there has been no significant alteration in any of the enzyme activities. It would therefore, appear that enzyme alterations seen in leukemia patients is due to abnormal pluripotent stem cell that has given to a leukemia cell. The fact that enzyme alterations have primarily occurred at the time of relapse would further substantiate that abnormalities of red cell enzymes may be the result of a derivation some circulating red cells from the abnormal pluripotent stem cell. With the recovery of normal stem cells function during remission, enzyme abnormalities tend to become normal.

Role of caspases in apoptosis and disease.

Apoptosis, a genetically governed process of eliminating cells in response to a variety of stimuli provides protection against cancer and viral infections as well as maintains homeostasis. Recent studies using both molecular and cloning approaches, and in vitro systems have identified a class of highly specific proteases, termed caspases, that appear to have an important role in apoptotic execution. Caspases are synthesized as precursor molecules that require processing at specific aspartate residues to produce the active enzyme which in turn leads to the cleavage of various death substrates that lead to morphological changes typical of apoptosis. This review discusses caspases, their inhibitors and regulators. Since cytotoxic drugs used in chemotherapy of leukemia's and solid tumors cause apoptosis in target cells, elucidating the consequences of proteolytic activity occupies a central role for understanding of the molecular mechanism of apoptosis which can help us to use the caspase inhibitors as targets of therapy.

Total leukocyte acid phosphatase and its isoenzymes in patients with leukemia.

Leukocyte acid phosphatase and its isoenzyme composition was studied in leukemic patients to determine the specificity of different isoenzymes in leukemic leukocytes. It was found that leukocyte acid phosphatase content is significantly increased in ALL, AML, and CML patients, while CLL patients had decreased levels of acid phosphatase. The distribution and intensity of leukocyte ACP isoenzymes vary in respective leukemic condition. Thus isoenzyme 'O' was predominant in AML and CML, while isoenzymes 1, 2 and 3 predominated in ALL. The lack of predominance of isoenzyme 3 was a feature in CLL patients. It was concluded that the isoenzyme patterns, though promising, presented inconclusive picture for diagnosis purpose and further studies on immunochemical characteristics of these isoenzymes are warranted to ascertain their cell specificity.