Overcoming Radioresistance: Small Molecule Radiosensitisers and Hypoxia-activated Prodrugs.

The role of hypoxia in radiation resistance is well established and many approaches to overcome hypoxia in tumours have been explored, with variable success. Two small molecule strategies for targeting hypoxia have dominated preclinical and clinical efforts. One approach has been the use of electron-affinic nitroheterocycles as oxygen-mimetic sensitisers. These agents are best exemplified by the 5-nitroimidazole nimorazole, which has limited use in conjunction with radiotherapy in head and neck squamous cell carcinoma. The second approach seeks to leverage tumour hypoxia as a tumour-specific address for hypoxia-activated prodrugs. These prodrugs are selectively activated by reductases under hypoxia to release cytotoxins, which in some instances may diffuse to kill surrounding oxic tumour tissue. A number of these hypoxia-activated prodrugs have been examined in clinical trial and the merits and shortcomings of recent examples are discussed. There has been an evolution from delivering DNA-interactive cytotoxins to molecularly targeted agents. Efforts to implement these strategies clinically continue today, but success has been elusive. Several issues have been identified that compromised these clinical campaigns. A failure to consider the extravascular transport and the micropharmacokinetic properties of the prodrugs has reduced efficacy. One key element for these 'targeted' approaches is the need to co-develop biomarkers to identify appropriate patients. Hypoxia-activated prodrugs require biomarkers for hypoxia, but also for appropriate activating reductases in tumours, as well as markers of intrinsic sensitivity to the released drug. The field is still evolving and changes in radiation delivery and the impact of immune-oncology will provide fertile ground for future innovation.

Effects of aminoacids on the autooxidation of 3,5-di-tert-butylcatechol in the presence of surface-active copper(II) complexes.

The rate of autooxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) in the presence of micelles formed from mixing equal concentrations of [Cu(C(12)-tmed)Br(2)] (where C(12)-tmed is N,N,N'-trimethyl-N'-dodecylethylenediamine) and several amino acids has been investigated. It was found that the rate in air-saturated solution is very much dependent on pH, which affects the availability of copper(II) coordination site for the catechol and the degree of micellization. At a given pH, the rates in [Cu(C(12)-tmed)Br(2)] micellar media are greatly enhanced in the presence sodium halide.

Oogenesis, fertilisation and early embryonic development in rats. I: Dose-dependent effects of pregnant mare serum gonadotrophins.

Five hundred and eight mature female Wistar rats divided into 35 different groups were stimulated with pregnant mare serum gonadotrophins (PMSG) (0, 5, 10, 20 & 40 IU) at the late diestrus stage to induce multiple follicular development. No chorionic gonadotrophin (CG) was used for ovulation induction. The quality of oocytes and their in vitro fertilisability, quality of Day 2-embryos, viability of pregnancy and status of fetuses on Day 14 of gestation and status of embryos retrieved on Day 2, 3, 4 and 5 of pregnancy in different subgroups of rats were examined. Results showed that more oocytes and embryos fertilised in in vivo were retrieved from rats supraphysiologically stimulated with 20 IU of PMSG. However, concurrent with the larger number, higher proportions of abnormal oocytes and embryos were found. High doses of PMSG caused lower in vitro fertilisability of oocytes and greater degrees of embryonic degeneration. Although, the number of oocytes and Day 2-embryos were higher in the 20PMGS dose group, the pregnancy rate was significantly reduced to 27%. In the 40PMSG group no viable pregnancy was noted. Most embryo demise occurred by day 3-5 of pregnancy, probably within the oviducts and before the implantation stage. In rats supraphysiologically stimulated with 20 and 40 IU of PMSG, the number of morphologically normal looking embryos was greatly reduced by Day 3-5 of pregnancy. In the 40PMSG group, there were no embryos retrieved by Day 4 and 5.(ABSTRACT TRUNCATED AT 250 WORDS)

Oogenesis, fertilisation and early embryonic development in rats. II: Dose-dependent effects of human chorionic gonadotrophin.

A total of 950 female Wistar rats in 81 groups were involved in this study. Different groups of rats were stimulated with PMSG (0, 10 & 20 IU) at diestrus followed, 48-52 hr later, by different doses of HCG (0, 10, 20, 30 & 40) for ovulation induction. The dose-dependent effects of HCG, either with or without the use of PMSG for stimulation of multiple follicular development, on the quality of oocytes and their in vitro fertilisability, quality of Day 2-embryos, viability of pregnancy and status of embryos retrieved on Day 2, 3, 4 or 5 of pregnancy in different subgroups of rats were examined. Results showed that more oocytes and embryos fertilised in vivo were retrieved from rats supraphysiologically stimulated with 20 IU of PMSG. The addition of HCG did not increase the number of ovulated oocytes or Day-2 embryos. In other words, the number of oocytes or embryos produced is dependent on the dose of PMSG administered during diestrus rather than on the dose of HCG given for ovulation induction. Hence, no increase in the amount of HCG is required to effectively ovulate bigger cohort of preovulatory follicles in supraphysiologically stimulated rats. As was shown earlier, in vitro and in vivo fertilisation rates were reduced when higher doses of PMSG were used. Similarly, these rates were reduced when increasing doses of HCG were used in rats not previously stimulated with PMSG. When higher doses of HCG were used in rats stimulated earlier with PMSG (10 and 20 IU), the in vitro but not the in vivo fertilisation rates were further reduced.(ABSTRACT TRUNCATED AT 250 WORDS)

Fetal limb allograft transplants in young rabbits.

The behavior and growth pattern of a transplanted fetal allograft limb in young rabbits were studied. No previous similar studies have been reported in the English literature. Ninety-four fetuses of four-weeks gestation were obtained through hysterectomy. The left hind limb of the fetus was dissected and disarticulated at the hip joint, preserving the long pedicle consisting of the inferior vena cava and abdominal aorta. The skin was stripped and nails were removed from the fetal limb prior to transplantation into a subcutaneous pouch on the medial aspect of the right thigh of a six-week old rabbit. The aorta and the inferior vena cava of the fetus were anastomosed to the femoral vessels of a recipient young rabbit, using the operating microscope. The rabbits were radiographed at fortnightly intervals to assess growth in the transplanted fetal limb. The rabbits were divided into three experimental groups: Group 1 (n = 26)--vascularized fetal allograft; Group 2 (n = 6)--non-vascularized fetal allograft; Group 3 (n = 5)--vascularized fetal allograft with Cyclosporin A. Preliminary results in Group 1 showed growth in the vascularized fetal limb allograft, with a maximum accelerated growth in the first four weeks. All Group 2 non-vascularized fetal allografts showed no growth. Group 3 showed an increased and accelerated limb growth in the first six weeks of transplant. The results demonstrated that vascularized fetal allograft has the potential for low-grade immunogenicity and of growth at the initial stage, especially with adjunctive immunosuppressive therapy.

Experimental transplantation of limbs.

This article is a brief review of experimental and clinical studies on replantation and transplantation of the whole limbs. Special reference is given to our preliminary study of the foetal limb allograft in young rabbits. The results showed that the vascularised foetal limb allografts of the group with Cyclosporine A (CsA) treatment increased in longitudinal growth in their first 6 weeks of transplantation as compared to the group without CsA treatment. Transplantation of foetal tissue has yielded new possibilities in the treatment of congenital and traumatic limb defects in human in the future. The utility of foetal limb tissues brings us a step closer towards the long road of limb transplantation.