Improved Tumor Radiotherapy by MORF pretargeting

尽管经过了几十年的努力，传统的放射免疫疗法对血液系统肿瘤，尤其是实体肿瘤的疗效仍然微乎其微。因此，治疗这些疾病的替代方法是必要的。可以说，最有吸引力的替代方法之一是预先确定目标。前靶向的临床前研究已经清楚地证明了有效性，早期临床试验正在提供令人鼓舞的结果。这些研究通常涉及生物素和(链)亲和素。不幸的是，(链状)亲和素已被发现具有免疫原性，而内源性生物素已被证明具有干扰作用。另一种方法，涉及双特异性抗体，用抗体和半抗原制备的困难取代了这些困难。双特异性抗体也表现出数量级的低亲和力--这是前靶向的一个重要考虑因素。UMMS的研究人员一直在探索99mTc标记的寡核苷酸，一种DNA化学类似物：肽核酸(PNA)，以及最近用于这一应用的另一种DNA化学类似物：吗啉(Morf)，并在初步研究中表明，用Morf预靶向可能解决上述困难。表面等离子体共振研究表明，18聚体Morf与其Morf补体(CMORF)的结合速率常数与长度相当的DNA的结合速率常数相当，因此与生物素与(Strept)亲和素的结合速率常数相等。我们还发现，放射性标记的Morf在小鼠体内几乎完全通过肾脏表现出快速的清除动力学。此外，当然，不存在内生的Morf问题。用MN-14-cMORF对LS174T荷瘤裸鼠进行99mTC-MAG3-Morf治疗已经取得了很好的效果。本研究将确定99mTc在荷瘤小鼠体内靶向定位的最佳剂量和时机。然后用188Re标记的Morf重现这些情况，再次在肿瘤小鼠身上研究这种方法的治疗潜力。这项合作研究将来自Gene Tools的研究人员和他们对Morf的知识、免疫医学和花园州立癌症中心在治疗前靶向治疗方面的专业知识以及来自UMMS的具有Morf和其他寡聚体的放射性标记和体内使用经验的研究人员聚集在一起。我们相信，这些研究将证实，用Morf进行预靶向治疗可以显著改善目前用常规放射免疫疗法所能达到的治疗效果，并可能优于使用生物素/(链霉亲和素)或双特异性抗体的预靶向方法。

Despite several decades of effort, conventional radioimmunotherapy of hematopoietic and especially solid tumors is still providing marginal results. As such, alternative methods of treating these diseases are needed. Arguably one of the most attractive alternative approaches involves pretargeting. Preclinical studies of pretargeting have clearly demonstrated efficacy and early clinical trials are providing encouraging results. These studies usually involve biotin and (strept)avidin. Unfortunately (strept)avidin has been found to be immunogenic and endogenous biotin has been shown to interfere. Another approach, involving bispecific antibodies, replace these difficulties with difficulties in antibody and hapten preparation. Bispecific antibodies also show orders-of-magnitude lower affinities - an important consideration for pretargeting. Investigators at UMMS have been exploring 99mTc-labeled oligonucleotides, one DNA chemical analogue: peptide nucleic acid (PNA) and, most recently, another DNA chemical analogue: morpholinos (MORF) for this application and have shown in preliminary studies that pretargeting with MORFs may potentially solve the above difficulties. We have shown by surface plasmon resonance that the association rate constant of a 18-mer MORF for its MORF complement (cMORF) is equivalent of that of DNAs of comparable lengths and therefor equivalent to that of biotin for (strept)avidin. We have also found that radiolabeled MORFs show rapid clearance kinetics in mice almost exclusively through the kidneys. Furthermore, there is, of course, no endogenous MORF problem. Excellent results have already been obtained with 99mTc-MAG3-MORF administered to LS174T tumor bearing nude mice following the administration of MN-14-cMORF. This study will establish the optimum conditions of dosage and timing for pretargeted localization of 99mTc in tumored mice. These conditions will then be reproduced using MORF labeled with 188Re to investigate the therapeutic potential of this approach, again in tumored mice. This collaborative investigation brings together researchers from Gene Tools and their knowledge of MORF, from Immunomedics and Garden State Cancer Center with their expertise in therapeutic pretargeting and from UMMS who have experience in the radiolabeling and in vivo uses of MORFs and other oligomers. We are confident that these investigations will confirm that pretargeting with MORF can significantly improve upon the therapy now achievable with conventional radioimmunotherapy and may be superior to pretargeting approaches involving biotin/(strept)avidin or bifspecific antibodies.