CYP2B6 gene polymorphisms Relations * 4, * 5 CYP2B6, CYP2B6 * 9 ALDH1A1, GSTM1 and GSTT1 With Hematologic Toxicity Cyclophosphamide On Breast Cancer and Non-Hodgkin's Lymphoma
ABSTRACT: Cancer is a malignant disease that has a high mortality rate. Globocan 2012 showed there were 14.1 million new cases of cancer; 8.2 million deaths from cancer and 32.6 million patients living with cancer (within 5 years of diagnosis) worldwide. Breast cancer is in the top rank of malignancy on women while non-Hodgkin lymphoma cancer is in the 8th on men and the 12th of all cases – with the total of 385,741. Chemotherapy is the standard therapy for non-Hodgkin lymphoma cancer and breast cancer, either as adjuvant therapy or as main therapy for advanced cancer cases. The characteristics of anti-cancer medicine that is unspecific and could damage normal cells other than the cancer cells cause toxicity of some medications to certain individuals. The efficacy and toxicity of anti-cancer medicine vary between individuals so that clinicians and pharmacists need to monitor the drug response to maximize the medications for the patients. Cyclophosphamide is one of anti-cancer medicine in the alkylating agent class, used in the chemotherapy regimen of several cancer cases – solid tumor and blood malignancy. Breast cancer and non-Hodgkin lymphoma cancer are types of cancer that use cyclophosphamide as one of the medication regimen. Medication with cyclophosphamide could cause side effects such as anemia, leukopenia, and thrombocytopenia, toxicity on reproduction system, and based on several researches – secondary cancer. There are some enzymes having roles in cyclophosphamide activation and elimination in order to work as cytotoxic compounds. Those enzymes have various big polymorphic forms. The activation of cyclophosphamide to the active form of 4-hydroxy cyclophosphamide is dominated by CYP2B6 and CYP2C9 enzymes. Cyclophosphamide resistance could be related to the increase of aldophosphamide and phosphoramide mustard’s conjugation by gluthathione S transferase. Through a minor route, cyclophosphamide could be formed into inactive metabolite: 4-hydroxycyclophosphamide change into 4-oxo cyclophosphamide and aldophosphamide change into carboxyphosphamide. The last route is decided by aldehyde dehydrogenase enzyme. This research was done in Dharmais cancer hospital with a cohort research design to see the polymorphism of main enzymes having roles in cyclophosphamide metabolism and elimination, and it was related to the hematological toxicity occurred to the patients after the chemotherapy treatments with regimen containing cyclophosphamide. The inclusion criteria of this research were: patients of breast cancer and non-Hodgkin lymphoma cancer who had received chemotherapy treatments with regimen containing cyclophosphamide; adults (above 18 years old), patients were not having decreased kidney and liver functions; the hemoglobin, leukocytes and thrombocytes levels were normal before chemotherapy; and having reports of blood function monitor (hemoglobin, leukocytes and thrombocytes) after chemotherapy. There were 144 patients consisting 122 females and 22 males, with 110 cases of breast cancer and 34 cases of non-Hodgkin lymphoma cancer recruited in this research. After being explained and requested written approvals afterwards, the patients had their blood drawn for checking the genes of drug-metabolizing enzyme. The test result from the laboratory to monitor hematological toxicity was then recorded and the degree of severity could be seen based on Common Toxicity Criteria-Eastern Cooperative Oncology Group (CTC-ECOG) year 2007. The efficacy monitor was just done to the breast cancer patients, considering the response to breast cancer therapy could be done in the third cycle. The median age of the research subjects is 49, and the average is 48.69. Sixty-two (43.4%) and eighty-one (56.6%) subjects had GSTT1 null and nonnull genotype; and one-hundred-twelve (77.9%) and thirty (21.1%) subjects had GSTM1 null and non-null genotype. From those two types of gluthatione enzymes, there were fifty-seven (39.5%) subjects with double null genotype. Mutated ALDH1A1 was found only in one subject and the AT heterozygous form in seventyseven subjects. The allele frequency distributions of T and A were 27.45% and 72.55% respectively. The form of polymorphic enzyme CYP2B6*9 in G516T TT base was found in fifty-seven (35%) subjects – mutations, in G516T GG thirty-four (20.8%) subjects, and G516T GT heterozygous form in seventy-two (44.2%). The allele frequency distributions of T and G in CYP2B6*9 were 57.1% and 42.9%. The form of polymorphic enzyme CYP2B6*4 in A785G GG base was found in forty-nine (34.0%) subjects – mutations, in A785G AA twenty-seven (18.8%) subjects, and A785G AG heterozygous form in sixty-eight (47.2%). The allele frequency distributions of G and A were 57.6 % and 42.4%. Sixty-nine (42.3%) subjects had mutations either in the CYP2B6*4 or CYP2B6*9. The condition is called polymorph CYP2B6*6. Hardy-Weinberg Equilibrium occurred in CYP2B6*9 and CYP2B6*4 genes with p = 0.964 and 0.971. Meanwhile, in ALDH1A1 there was no equilibrium; there was a significant difference between the numbers of observed and predicted alleles (p = 0.002). There was no significant relationship between the mutation of GSTT1, GSTM1, ALDH1A1, CYP2B6*9, CYP2B6*4, and CYP2B6*6 genes and gender (p=0.80; 0.78; 1.00; 0.94; 1.00; 0.54; 0.81). There was no significant relationship between age, stage of disease, mutation of GSTT1, GSTM1,ALDH1A1, CYP2B6*9, CYP2B6*4, CYP2B6*6 genes, and number of mutant genes with the risk of leukopenia (p=0.56; 0.59; 0.58; 0.27; 0.39; 0.79; 0.24; 0.34; 0.24). Even though there was no significant relationship, there was a tendency for subjects above 40 years old, subjects with advanced stage of disease and subjects with mutations of GSTT1, GSTM1, ALDH1A1, CYP2B6*9, CYP2B6*4, CYP2B6*6 genes, and subjects having mutant genes above three to have higher risk of leukopenia. There was no significant relationship between age, stage of disease, mutation of GSTT1, GSTM1,ALDH1A1, CYP2B6*9, CYP2B6*4, CYP2B6*6 genes, and number of mutant genes with the risk of thrombocytopenia (p=1.00; 0.49; 0.50; 0.68; 0.51; 0.21; 0.10; 0.17; 0.06). Even though there was no significant relationship, there was a tendency for subjects above 40 years old, subjects with mutations of GSTT1, GSTM1, ALDH1A1, CYP2B6*4, CYP2B6*6 genes, and subjects having mutant genes above three to have higher risk of thrombocytopenia. Nevertheless, advanced stage of disease and mutation of CYP2B6*9 gene had less risk to develop thrombocytopenia. There was no significant relationship between age, stage of disease, mutation of GSTT1, GSTM1,ALDH1A1, CYP2B6*9, CYP2B6*4, CYP2B6*6 genes, and number of mutant genes with the risk of thrombocytopenia (p=0.74; 0.27; 0.54; 0.17; 0.52; 0.51; 0.32; 0.58; 0.47). Even though there was no significant relationship, there was a tendency for subjects above 40 years old, subjects with advanced stage of disease, subjects with mutations of ALDH1A1, CYP2B6*4, CYP2B6*6 genes to have higher risk of hemoglobinemia. . Nevertheless, mutation of GSTT1, GSTM1, CYP2B6*9 genes and having mutant genes above three had less risk to develop hemoglobinemia. It is the observation merely on the subject group with breast cancer cases that has data of the therapy response. The advanced stage of disease had 11.67 times higher risk to therapy failure, with p=0.00. The variation of metabolizing enzyme genes had no significant relationship with the therapy response; however, subjects with mutation of GSTT1, GSTM1, ALDH1A1, CYP2B6*9, CYP2B6*4, CYP2B6*6 genes and having mutant genes above three had higher risk to therapy failure
