Efficacy and selectivity of nilotinib on NF1-associated tumors in vitro

Targeted genetic and molecular therapies in neurofibromatosis - A review of present therapeutic options and a glimpse into the future

Neurofibromatosis type 1, the most common phakomatoses, can present with a host of signs and symptoms, usually involving the skin and the peripheral nervous system. It is characterized by a mutation in the neurofibromatosis type 1 gene on chromosome 17q11.2 that codes for the protein neurofibromin. Neurofibromin acts as a tumor suppressor gene by inhibiting rat sarcoma (Ras) activity and its deficiency leads to increased Ras activity, cellular proliferation and tumor formation. This review was conducted to analyze the various targeted therapies at the genetic and molecular level employed to manage the tumors and other clinical presentations associated with neurofibromatosis type 1. Twenty-eight studies of treatment modalities for the conditions associated with neurofibromatosis and which involved either targeted gene therapy or molecular level therapies, including the latest advances, were included in this review. Mitogen-activated protein kinase kinase inhibition, mammalian target of Rapamycin inhibition and Tyrosine kinase inhibition, represent some of the newer treatment options in this category. Although there are a number of trials for providing therapeutic options at the genetic and molecular level for the various physical and psychological morbidities associated with neurofibromatosis type 1, most of them are in the preclinical stage. Increased clinical trials of the molecules and gene therapies could significantly help in managing the various chronic and sometimes, life-threatening conditions associated with neurofibromatosis 1 and these will probably represent the preferred treatment direction of the future.

The promise of signal transduction in genetically driven sarcomas of the nerve

Neurofibromatosis type 1 (NF1) is an autosomal dominant tumor predisposition syndrome. Malignant peripheral nerve sheath tumors (MPNST) are aggressive soft tissue sarcomas arising from peripheral nerve sheaths, and the most commonly lethal feature associated with NF1. The hallmark of NF1 and NF1-related MPNST is the loss of neurofibromin expression. Loss of neurofibromin is considered a tumor-promoting event, and leads to constitutive activation of RAS and its downstream effectors. However, RAS activation alone is not sufficient for MPNST formation, and additional tumor suppressors and signaling pathways have been implicated in tumorigenesis of MPNST. Taking advantage of the rapid development of novel therapeutics targeting key molecular pathways across all cancer types, the best-in-class modulators of these pathways can be assessed in pre-clinical models and translated into clinical trials for patients with MPNST. Here, we describe the genetic changes and molecular pathways that drive MPNST formation and highlight the promise of signal transduction to identify therapies that may treat these tumors more effectively.

Assessing Specificity of Anticancer Drugs In Vitro

A procedure for assessing specificity of anticancer drugs in vitro using cultures containing both tumor and non-tumor cells is demonstrated. The key element is the quantitative determination of a tumor-specific genetic alteration in relation to a universal sequence using a dual-probe digital PCR assay and the subsequent calculation of the proportion of tumor cells. The assay is carried out on a culture containing tumor cells of an established line and spiked-in non-tumor cells. The mixed culture is treated with a test drug at various concentrations. After the treatment, DNA is prepared directly from the survived adhesive cells in wells of 96-well plates using a simple and inexpensive method, and subjected to a dual-probe digital PCR assay for measuring a tumor-specific genetic alteration and a reference universal sequence. In the present demonstration, a heterozygous deletion of the NF1 gene is used as the tumor-specific genetic alteration and a RPP30 gene as the reference gene. Using the ratio NF1/RPP30, the proportion of tumor cells was calculated. Since the dose-dependent change of the proportion of tumor cells provides an in vitro indication for specificity of the drug, this genetic and cell-based in vitro assay will likely have application potential in drug discovery. Furthermore, for personalized cancer-care, this genetic- and cell-based tool may contribute to optimizing adjuvant chemotherapy by means of testing efficacy and specificity of candidate drugs using primary cultures of individual tumors.

A novel genetic- and cell-based tool for assessing the efficacy and toxicity of anticancer drugs in vitro

AIMS

To develop an in vitro tool for assessing the efficacy and toxicity of anticancer drugs using mixed culture containing both tumor and non-tumor cells. Such in vitro tool should have high application potential in drug-screening and personalized cancer care.

METHODS

Fibroblasts were spiked as non-tumor cells into tumor cells of an established line. The mixed culture was treated with a test drug at various concentrations. After the treatment, DNA was prepared directly from the survived adhesive cells in the wells of the 96-well plates using a simple and inexpensive method, and subjected to digital PCR for measuring relative copy numbers of a target gene NF1 to that of a reference gene RPP30. The NF1 gene is known to be heterozygously deleted in these tumor cells while the RPP30 gene has two copies in both tumor and non-tumor cells. Using the NF1/ RPP30 ratios resulting from the dual digital PCR assay, the proportions of tumor cells were calculated for each drug concentration.

RESULTS

Digital PCR confirmed that the tumor cells have only one copy of the NF1 gene while the non-tumor fibroblasts have two copies. By contrast, both types of cells have two copies of the reference gene RPP30. Using the ratio of the two genes, we successfully calculated the proportion of tumor cells which decreased as the dose of the test drug increased up to a certain concentration, indicating that the drug is more effective for the tumor cells than for the non-tumor cells in this dose-range. At the highest dose, we observed a slight increase in the proportion of tumor cells, likely reflecting the toxic effect of the drug on both tumor and non-tumor cells.

CONCLUSION

This pilot study demonstrated the feasibility of a genetic- and cell-based tool for testing efficacy and toxicity of anticancer drugs in vitro. The promising results suggest that additional efforts are merited, for further development since such a tool will likely have high application potential (1) in drug discovery where it enables simultaneously assessing therapeutic effect on target cells and toxic effect on non-target cells, and (2) in personalized adjuvant chemotherapy where multiple drugs can be tested in primary cultures derived from surgically removed tumor.

Preclinical assessment of the anticancer drug response of plexiform neurofibroma tissue using primary cultures

BACKGROUND AND PURPOSE

Individualized drug testing for tumors using a strategy analogous to antibiotic tests for infectious diseases would be highly desirable for personalized and individualized cancer care.

METHODS

Primary cultures containing tumor and nontumor stromal cells were utilized in a novel strategy to test drug responses with respect to both efficacy and specificity. The strategy tested in this pilot study was implemented using four primary cultures derived from plexiform neurofibromas. Responses to two cytotoxic drugs (nilotinib and imatinib) were measured by following dose-dependent changes in the proportions of tumor and nontumor cells, determined by staining them with cell-type-specific antibodies. The viability of the cultured cells and the cytotoxic effect of the drugs were also measured using proliferation and cytotoxicity assays.

RESULTS

The total number of cells decreased after the drug treatment, in accordance with the observed reduction in proliferation and increased cytotoxic effect upon incubation with the two anticancer drugs. The proportions of Schwann cells and fibroblasts changed dose-dependently, although the patterns of change varied between the tumor samples (from different sources) and between the two drugs. The highly variable in vitro drug responses probably reflect the large variations in the responses of tumors to therapies between individual patients in vivo.

CONCLUSIONS

These preliminary results suggest that the concept of assessing in vitro drug responses using primary cultures is feasible, but demands the extensive further development of an application for preclinical drug selection and drug discovery.

Nilotinib is more potent than imatinib for treating plexiform neurofibroma in vitro and in vivo

Plexiform neurofibromas (PNFs) are benign nerve sheath tumors mostly associated with neurofibromatosis type 1. They often extend through multiple layers of tissue and therefore cannot be treated satisfactorily by surgery. Nilotinib is a tyrosine kinase inhibitor used to treat leukemia, with advantages over the prototype imatinib in terms of potency and selectivity towards BCR-ABL, and the DDR, PDGFR, and KIT receptor kinases. In this study, we compared efficacies of the two drugs on cultured cells of PNF in vitro and on xenografted tumor fragments on sciatic nerve of athymic nude mice. Xenografts were monitored weekly using a high resolution ultrasound measurement. Treatment with nilotinib at a daily dose of 100 mg/kg for four weeks led to a reduction of the graft sizes_std by 68_±7% in the 8 treated mice, significantly more than the 33_±8% reduction in the 8 untreated mice (P<0.05) and the 47_±15% in the 7 mice treated with imatinib (P<0.05). The peak plasma nilotinib concentration 6.6_±1.1 µM is within the pharmacological range of clinical application. Imatinib, but not nilotinib significantly hindered body weight increase of the mice and elevated cytotoxicity of mouse spleen cells (P<0.05). Our results suggest that nilotinib may be more potent than imatinib for treating PNFs and may also be better tolerated. Imatinib seems to have some off-target effect in elevating immunity.