Microtubulin binding sites as target for developing anticancer agents

Microtubules (MTs) play important and diverse roles in eukaryotic cells. Their function and biophysical properties have made α−and β−tubulin, the main components of MTs, the subject of intense study. Interfering with normal MT dynamics, for example, by the addition of tubulin ligands, can cause the cell great distress and affect MT stability and functions, including mitosis, cell motion and intracellular organelle transport. It has been shown in the literature that tubulin is an important target molecule for developing anticancer drugs. Tubulin binding molecules have generated considerable interest after the successful introduction of the taxanes into clinical oncology and the widespread use of the vinca alkaloids vincristine and vinblastine. These compounds inhibit cell mitosis by binding to the protein tubulin in the mitotic spindle and preventing polymerization into the MTs. This mode of action is also shared with other natural agents eg colchicine and podophyllotoxin. However various tubulin isotypes have shown resistance to taxanes and other MT agents. Therefore, there is a strong need to design and develop new natural analogs as antimitotic agents to interact with tubulin at sites different from those of vinca alkaloids and taxanes. This minireview provides SAR on several classes of antimitotic agents reported in the literature. The structures and data given are essential to the scientists who are involved in drug design and development in the field of anticancer drugs.

Investigation of structural requirements of anticancer activity at the paclitaxel/tubulin binding site using CoMFA and CoMSIA

CoMFA and CoMSIA analysis were utilized in this investigation to define the important interacting regions in paclitaxel/tubulin binding site and to develop selective paclitaxel-like active compounds. The starting geometry of paclitaxel analogs was taken from the crystal structure of docetaxel. A total of 28 derivatives of paclitaxel were divided into two groups—a training set comprising of 19 compounds and a test set comprising of nine compounds. They were constructed and geometrically optimized using SYBYL v6.6. CoMFA studies provided a good predictability (q2 = 0.699, r2 = 0.991, PC = 6, S.E.E. = 0.343 and F = 185.910). They showed the steric and electrostatic properties as the major interacting forces whilst the lipophilic property contribution was a minor factor for recognition forces of the binding site. These results were in agreement with the experimental data of the binding activities of these compounds. Five fields in CoMSIA analysis (steric, electrostatic, hydrophobic, hydrogen-bond acceptor and donor properties) were considered contributors in the ligand–receptor interactions. The results obtained from the CoMSIA studies were: q2 = 0.535, r2 = 0.983, PC = 5, S.E.E. = 0.452 and F = 127.884. The data obtained from both CoMFA and CoMSIA studies were interpreted with respect to the paclitaxel/tubulin binding site. This intuitively suggested where the most significant anchoring points for binding affinity are located. This information could be used for the development of new compounds having paclitaxel-like activity with new chemical entities to overcome the existing pharmaceutical barriers and the economical problem associated with the synthesis of the paclitaxel analogs. These will boost the wide use of this useful class of compounds, i.e. in brain tumors as the most of the present active compounds have poor blood–brain barrier crossing ratios and also, various tubulin isotypes has shown resistance to taxanes and other antimitotic agents.

Exposição de fibroblastos da cápsula de Tenon normal de portadores de pterígio ao 5-fluorouracil e à mitomicina C

OBJETIVO: Avaliar a atividade proliferativa dos fibroblastos da cápsula de Tenon normal, proveniente de portadores de pterígios primários e recidivados. MÉTODOS: Foi realizado estudo prospectivo, aleatório, avaliando-se fragmentos da cápsula de Tenon normal, removidos de 20 portadores de pterígios primários e 21, recidivados. A taxa de proliferação foi avaliada em fibroblastos de terceira passagem, quando as culturas foram expostas a agentes antimitóticos: mitomicina C e 5-fluorouracil. Os dados obtidos foram submetidos à análise estatística. RESULTADOS: Dentre os 41 espécimes cultivados, apenas 1 de pterígio primário e 2 de recidivado proliferaram. Quando expostos a mitomicina C e ao 5-fluorouracil não houve diferença estatisticamente significativa quanto a inibição de proliferação celular. CONCLUSÃO: Desta forma, in vitro, ambos os antimitóticos estudados têm a mesma eficácia na inibição da proliferação sobre os fibroblastos de cápsulas de Tenon normal.

Carcinoma espinocelular de conjuntiva com evolução para exenteração: relato de caso

Portador de carcinoma espinocelular da conjuntiva teve a lesão removida, com recorrência em outra localização. O paciente recebeu ciclos de 5-Fluoruracila como tratamento adjuvante à remoção cirúrgica, apresentando evolução desfavorável que chegou à exenteração orbitária. São feitos comentários quanto ao uso de antimitóticos no tratamento destas lesões.

Segurança e efetividade no tratamento do pterígio usando infiltração de 5-fluoruracila no intraoperatório

OBJETIVO: Avaliar a segurança e a efetividade do uso do 5-fluoruracila (5-FU) como tratamento adjuvante do pterígio, aplicado sob a forma de infiltração subconjuntival, no período intraoperatório. MÉTODOS: Foram avaliados prospectivamente 125 indivíduos (125 olhos) portadores de pterígio. Os indivíduos foram operados segundo a técnica de retalho de deslizamento e receberam, ao final do procedimento, injeção subconjuntival de 0,2 mL de 5-FU (25 mg/mL). Foram anotados os dados do paciente como idade, sexo, profissão, características da lesão (primário ou recidivado, tamanho, carnoso ou involutivo) e feito seguimento pós-operatório, aos 7, 21, 60 e 180 dias. Os dados foram submetidos à avaliação estatística. RESULTADOS: Não foram observados casos de complicação decorrente do uso do 5-FU em injeção no intraoperatório do pterígio. A taxa de recidiva geral observada aos 180 dias de pós-operatório foi de 35,8%, sendo de 35,7% para os pterígios primários e de 36,4% para os recidivados. CONCLUSÃO: A aplicação do 5-FU no período intraoperatório sob a forma de infiltração subconjuntival é segura. Entretanto, ainda resulta em altas taxas de recidiva e novos estudos devem ser realizados a fim de conhecer a concentração/dose ideal que permitirá menores chances de recidiva da lesão.

Exposição de culturas de fibroblastos de pterígios primários e recidivados à mitomicina c e ao 5-fluorouracil

Purpose: To evaluate the proliferation of the fibroblasts from primary and recurrent pterygium in culture of cells, after the exposure to mitomycin C and to 5-fluorouracil. Methods: Cultures of fibroblasts from primary and recurrent pterygiuns had been carried through. The cells of the third passage were exposed to mitomycin C 0.4% during 3 minutes and to 5-fluorouracil 25mg/ml that was kept in the nutritional medium. After 3, 6, 12 and 18 days of the exposure, cell countings were made in hemocytometer, in triplicate, with a control not treated with the drugs for each day. The data were submitted to statistical analysis.Results: Mitomicyn C had homogeneous behavior in the primary and recurrent groups, which inhibited the cellular proliferation since the first counting day. However, with 5-fluorouracil, the proliferation inhibition was verified only after the third day of evaluation (in the second counting day) in the recurrent group, and since the first counting day in the primary group. At the end of the experimental period, 5-fluorouracil and mitomycin C were equally efficient in the inhibition of the fibroblasts from primary and recurrent pterygium proliferation. In the controls not exposed, the cell's numbers were increasing during the experimental time.Conclusion: Mitomycin and 5-fluorouracil are equally able to inhibit fibroblasts proliferation from primary and recurrent pterygium Tenon's capsule in cell culture.

Checkpoint mitótico como alvo terapêutico para sensibilizar células cancerígenas a agentes antimitóticos

Dissertação de Mestrado, Oncobiologia – Mecanismos Moleculares do Cancro, Departamento de Ciências Biomédicas e Medicina, Universidade do Algarve, 2015