Making the most of rodent tumour systems in cancer drug discovery

Classic in vivo cancer models: three examples of mouse models used in experimental therapeutics

Transplantable animal tumors have been associated with the discovery of most clinically active anticancer agents. They are still useful today in conducting detailed evaluations of new candidate anticancer drugs. Three protocols relating to transplantable experimental tumors are described in this unit. Included are the intravenously-implanted murine P388 leukemia, the subcutaneously-implanted murine B16 melanoma and two examples of subcutaneously-implanted human tumor xenografts, the LX-1 (lung) and MX-1 (breast) tumors.

Tumor models for efficacy determination

The first in vivo tumor models were developed in the mid-1960s. These models were mouse leukemia models grown as ascites. The growth pattern was like that of bacteria in vivo and therefore it was possible to apply similar mathematics of growth and response to these tumors as had been worked out for bacteria. Since the development of the murine leukemia models, investigators have devoted a large effort to modeling solid tumors in mice. There are now a variety of models including syngeneic mouse tumors and human tumor xenografts grown as s.c. nodules, syngeneic mouse tumors and human tumor xenografts grown in orthotopic sites, models of disseminated disease, "labeled" tumor models that can be visualized using varied technologies, and transgenic tumor models. Each of these types of models has advantages and disadvantages to the "drug hunter" searching for improved treatments.

Orthotopic models of cancer for preclinical drug evaluation: advantages and disadvantages

Considering the enormous effort that has taken place over the years to discover new chemotherapeutic drugs for treating the common cancers, the conventional murine and xenograft test systems used to test efficacy for drug development have identified only a limited number of useful agents that are active clinically at well tolerated doses. In recent years, considerable effort has been made to develop more clinically relevant models by the use of orthotopic transplantation of tumour material in rodents. It has been shown that it is now possible to transplant tumour material from a variety of tumour types into the appropriate anatomical site and often these tumours will metastasise in a similar manner and to similar locations as the same tumour type will in human cancer. As yet, although a body of literature has amassed on the technique itself and its implications for metastasis, there are relatively few laboratories using these test systems in drug development programmes. Nevertheless, given the expertise now being developed and some interesting observations being made on the role of the tumour site on response to therapeutic agents, it is likely that the use of orthotopic systems will strengthen our ability to select the most appropriate molecules for recommended use in clinical studies.

Antitumour potential of a polysaccharide-rich substance from the fruit juice ofMorinda citrifolia (Noni) on sarcoma 180 ascites tumour in mice

An immunomodulatory polysaccharide-rich substance (Noni-ppt) from the fruit juice of Morinda citrifolia has been found to possess both prophylactic and therapeutic potentials against the immunomodulator sensitive Sarcoma 180 tumour system. The antitumour activity of Noni-ppt produced a cure rate of 25%-45% in allogeneic mice and its activity was completely abolished by the concomitant administration of specific inhibitors of macrophages (2-chloroadenosine), T cells (cyclosporine) or natural killer (NK) cells (anti-asialo GM1 antibody). Noni-ppt showed synergistic or additive beneficial effects when combined with a broad spectrum of chemotherapeutic drugs, including cisplatin, adriamycin, mitomycin-C, bleomycin, etoposide, 5- fl uorouracil, vincristine or camptothecin. It was not beneficial when combined with paclitaxel, cytosine arabinoside, or immunosuppressive anticancer drugs such as cyclophosphamide, methotrexate or 6-thioguanine. Noni-ppt also demonstrated beneficial effects when combined with the Th1 cytokine, interferon gamma, but its activity was abolished when combined with Th2 cytokines, interleukin-4 or interleukin-10, thereby suggesting that Noni-ppt induces a Th1 dominant immune status in vivo. The combination of Noni-ppt with imexon, a synthetic immunomodulator, also demonstrated beneficial effects, but not when combined with the MVE-2 copolymer, a high molecular weight immunomodulator. It was also not effective when combined with interleukin-2 or interleukin-12.