The multigenic nature of human tumours presents a fundamental challenge for cancer drug discovery. Here we use Drosophila to generate 32 multigenic models of colon cancer using patient data from The Cancer Genome Atlas. These models recapitulate key features of human cancer, often as emergent properties of multigenic combinations. Multigenic models such as ras p53 pten apc exhibit emergent resistance to a panel of cancer-relevant drugs. Exploring one drug in detail, we identify a mechanism of resistance for the PI3K pathway inhibitor BEZ235. We use this data to identify a combinatorial therapy that circumvents this resistance through a two-step process of emergent pathway dependence and sensitivity we term ‘induced dependence'. This approach is effective in cultured human tumour cells, xenografts and mouse models of colorectal cancer. These data demonstrate how multigenic animal models that reference cancer genomes can provide an effective approach for developing novel targeted therapies.

Colorectal cancer remains a leading source of cancer mortality worldwide. Initial response is often followed by emergent resistance that is poorly responsive to targeted therapies, reflecting currently undruggable cancer drivers such as KRAS and overall genomic complexity. Here, we report a novel approach to developing a personalized therapy for a patient with treatment-resistant metastatic KRAS-mutant colorectal cancer. An extensive genomic analysis of the tumor’s genomic landscape identified nine key drivers. A transgenic model that altered orthologs of these nine genes in the Drosophila hindgut was developed; a robotics-based screen using this platform identified trametinib plus zoledronate as a candidate treatment combination. Treating the patient led to a significant response: Target and nontarget lesions displayed a strong partial response and remained stable for 11 months. By addressing a disease’s genomic complexity, this personalized approach may provide an alternative treatment option for recalcitrant disease such as KRAS-mutant colorectal cancer.

Wing patterning in Drosophila requires a Bmp activity gradient created by two Bmp ligands, Gbb and Dpp, and two Bmp type I receptors, Sax and Tkv. Gbb provides long-range signaling, while Dpp signals preferentially to cells near its source along the anteroposterior (AP) boundary of the wing disc. How each receptor contributes to the signaling activity of each ligand is not well understood. Here, we show that while Tkv mediates signals from both Dpp and Gbb, Sax exhibits a novel function for a Bmp type I receptor: the ability to both promote and antagonize signaling. Given its high affinity for Gbb, this dual function of Sax impacts the function of Gbb in the Bmp activity gradient more profoundly than does Dpp. We propose that this dual function of Sax is dependent on its receptor partner. When complexed with Tkv, Sax facilitates Bmp signaling, but when alone, Sax fails to signal effectively and sequesters Gbb. Overall, our model proposes that the balance between antagonizing and promoting Bmp signaling varies across the wing pouch, modulating the level and effective range, and, thus, shaping the Bmp activity gradient. This previously unknown mechanism for modulating ligand availability and range raises important questions regarding the function of vertebrate Sax orthologs.KEY WORDS: Bmp signaling, Dpp, Gbb, Tkv, Sax, Bmp type I receptor, Wing imaginal disc, Morphogen Development 133, 3295-3303 (2006Development 133, 3295-3303 ( ) doi:10.1242 Department of Molecular Biology, Cell Biology, and Biochemistry, Brown University, Providence, RI 02912, USA.*Author for correspondence (e-mail: kristi_wharton@brown.edu) Accepted 28 June 2006DEVELOPMENT 3296 expression seen in small sax-null clones (Singer et al., 1997) indicates that Sax must contribute in some way to the mediation of Bmp signals in the wing imaginal disc.Previous experiments suggested that Gbb signaling is primarily mediated by Sax, whereas Dpp is primarily mediated by Tkv, based on the fact that the wing phenotype associated with overexpression of Gbb or Dpp is better suppressed by co-expression of the dominant-negative (DN) receptor, DN-Sax or DN-Tkv, respectively (Haerry et al., 1998). These respective phenotypic suppressions are similar to demonstrated preferred binding affinities, i.e. Dpp and its vertebrate ortholog Bmp2 have high binding affinity for Tkv, and Gbb, or its vertebrate ortholog Bmp7, cannot compete with Bmp2 for Tkv binding (Penton et al., 1994). A similar receptor-ligand binding preference has been observed among the vertebrate orthologs (Yamashita et al., 1995;Nishitoh et al., 1996;Chalaux et al., 1998;Ebisawa et al., 1999;Piek et al., 1999).Curiously, other data do not agree with the proposal that Sax is the primary mediator of Gbb during wing patterning, despite the likelihood that Gbb and Sax interact with high affinity. Primarily, unlike what would be expected of a receptor and its ligand, loss of sax function does not result in a wing phenotype similar to the loss of gbb function (Singer et al., 1997;Khalsa et al., 1998;Ray and W...

Morphogen gradients ensure the specification of different cell fates by dividing initially unpatterned cellular fields into distinct domains of gene expression. It is becoming clear that such gradients are not always simple concentration gradients of a single morphogen; however, the underlying mechanism of generating an activity gradient is poorly understood. Our data indicate that the relative contributions of two BMP ligands, Gbb and Dpp, to patterning the wing imaginal disc along its A/P axis, change as a function of distance from the ligand source. Gbb acts over a long distance to establish BMP target gene boundaries and a variety of cell fates throughout the wing disc, while Dpp functions at a shorter range. On its own, Dpp is not sufficient to mediate the low-threshold responses at the end points of the activity gradient, a function that Gbb fulfills. Given that both ligands signal through the Tkv type I receptor to activate the same downstream effector, Mad, the difference in their effective ranges must reflect an inherent difference in the ligands themselves, influencing how they interact with other molecules. The existence of related ligands with different functional ranges may represent a conserved mechanism used in different species to generate robust long range activity gradients.

Tumours evolve several mechanisms to evade apoptosis, yet many resected carcinomas show significantly elevated caspase activity. Moreover, caspase activity is positively correlated with tumour aggression and adverse patient outcome. These observations indicate that caspases might have a functional role in promoting tumour invasion and metastasis. Using a Drosophila model of invasion, we show that precise effector caspase activity drives cell invasion without initiating apoptosis. Affected cells express the matrix metalloproteinase Mmp1 and invade by activating Jnk. Our results link Jnk and effector caspase signalling during the invasive process and suggest that tumours under apoptotic stresses from treatment, immune surveillance or intrinsic signals might be induced further along the metastatic cascade.

Although pathogenic bacteria are suspected contributors to colorectal cancer progression, cancer-promoting bacteria and their mode of action remain largely unknown. Here we report that sustained infection with the human intestinal colonizer Pseudomonas aeruginosa synergizes with the Ras1 V12 oncogene to induce basal invasion and dissemination of hindgut cells to distant sites. Cross-talk between infection and dissemination requires sustained activation by the bacteria of the Imd-dTab2-dTak1 innate immune pathway, which converges with Ras1 V12 signalling on JNK pathway activation, culminating in extracellular matrix degradation. Hindgut, but not midgut, cells are amenable to this cooperative dissemination, which is progressive and genetically and pharmacologically inhibitable. Thus, Drosophila hindgut provides a valuable system for the study of intestinal malignancies.

Current models of tumor cell invasion propose that oncogenic signaling converges upon key orchestrators of cytoskeletal dynamics, including c-Jun N-terminal kinase (Jnk) and RhoGTPase family members; these signals dynamically direct Actin remodeling proteins (ARPs) to catalyze the cytoskeletal changes required for migration. Src is a key driver of tumor aggression, metastasis and patient mortality. To clarify how Src regulates Actin dynamics to promote invasive migration, we performed a genetic modifier screen in a Drosophila model of invasion. Nine genes linked to Actin dynamics were identified that mediate invasion in situ. We found that ARPs were required for many oncogenic effects of Src including Mmp1 expression and initiation of apoptosis. Surprisingly, they were also regulators of Jnk pathway activity: both Src and the small GTPase Rho1 activated Jnk in a manner dependent on ARPs during invasion. Our results suggest that ARPs are not simply downstream executors of signal transduction pathways. Rather, they participate in a positive feedback network involving canonical oncogenic signaling pathways that promote tumor invasion.

Recent studies show that both cellular and humoral aspects of innate immunity play important roles during tumor progression. These interactions have traditionally been explored in vertebrate model systems. In recent years, Drosophila has emerged as a genetically tractable model system for studying key aspects of tumorigenesis including proliferation, invasion, and metastasis. The absence of adaptive immunity in Drosophila provides a unique opportunity to study the interactions between innate immune system and cancer in different genetic contexts. In this review, I discuss recent advances made by using Drosophila models of cancer to study the role of innate immune pathways Toll/Imd, JNK, and JAK-STAT, microbial infection and inflammation during tumor progression.