Abstract 878: Tumor heterogeneity and lesion-specific response to targeted therapy in colorectal cancer

How genomic heterogeneity associated with acquired resistance to targeted agents affects response to subsequent lines of therapy is unknown. Exposure to therapy may result in selection of sub-clonal cell populations, capable of growing under drug pressures. Therefore, a single-lesion biopsy at disease progression may vastly underrepresent the molecular heterogeneity of resistant tumor clones in an individual patient and may fail to detect the existence of distinct but important resistance mechanisms that could impact clinical response.

We identified a colorectal cancer (CRC) patient in whom multiple tumor biopsies were obtained at resistance following prolonged response to with the anti-EGFR antibody cetuximab. Full-exome sequencing of 1000 cancer genes of both primary tumor and progression biopsy revealed a TP53 mutation in all samples and a novel MEK1 p.K57T mutation in one of the progressing liver biopsy. A mutation at the same MEK1 codon was identified in the cetuximab-resistant HCA46 CRC cell line. Biochemical analysis showed constitutive activation of MEK and ERK despite cetuximab treatment. However, the combination of the MEK inhibitor trametinib with either cetuximab or panitumumab restored sensitivity, suggesting a potential therapeutic strategy to overcome resistance to EGFR blockade caused by this mutation.

Accordingly, the patient was treated with the combination of panitumumab and trametinib. After 3 months, imaging demonstrated a reduction in size of the biopsied liver metastasis harboring the MEK1 mutation, but revealed that some other lesions had progressed. Plasma collected prior to therapy was analyzed by next-generation sequencing confirming the presence of both TP53 and MEK1 variants, but surprisingly unveiling a previously unrecognized KRAS mutation. ddPCR analysis of longitudinal timepoints of ctDNA unveiled that TP53 mutant levels dropped after initiation of therapy, but rose later during treatment in parallel with CEA tumor marker levels. However, MEK1 mutant levels declined sharply, indicating effective suppression of MEK1 mutant clones by panitumumab and trametinib; while KRAS mutant levels rose, indicating outgrowth of a resistant KRAS-mutant clone. Biopsy of a different liver metastasis that progressed despite panitumumab and trametinib revealed the same KRAS mutation identified in ctDNA.

In summary these findings illustrate how distinct acquired resistance mechanisms can arise concomitantly in separate metastases within the same patient, leading to mixed lesion-specific responses to subsequent targeted therapies. Liquid biopsy approaches, in association with single-tumor biopsies, have the potential to detect the presence of simultaneous resistance mechanisms residing in separate metastases in a single patient and to monitor the effects of subsequent targeted therapies.

Citation Format: Mariangela Russo, Giulia Siravegna, Lawrence S. Blaszkowsky, Giorgio Corti, Giovanni Crisafulli, Leanne G. Ahronian, Benedetta Mussolin, Eunice L. Kwak, Michela Buscarino, Luca Lazzari, Emanuele Valtorta, Mauro Truini, Nicholas A. Jessop, Hayley E. Robinson, Theodore S. Hong, Mari Mino-Kenudson, Federica Di Nicolantonio, Ashraf Thabet, Andrea Sartore-Bianchi, Salvatore Siena, A John Iafrate, Ryan B. Corcoran, Alberto Bardelli. Tumor heterogeneity and lesion-specific response to targeted therapy in colorectal cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 878.

Tumor Heterogeneity and Lesion-Specific Response to Targeted Therapy in Colorectal Cancer

How genomic heterogeneity associated with acquired resistance to targeted agents affects response to subsequent therapy is unknown. We studied EGFR blockade in colorectal cancer to assess whether tissue and liquid biopsies can be integrated with radiologic imaging to monitor the impact of individual oncogenic alterations on lesion-specific responses. Biopsy of a patient's progressing liver metastasis following prolonged response to cetuximab revealed a MEK1(K57T) mutation as a novel mechanism of acquired resistance. This lesion regressed upon treatment with panitumumab and the MEK inhibitor trametinib. In circulating tumor DNA (ctDNA), mutant MEK1 levels declined with treatment, but a previously unrecognized KRAS(Q61H) mutation was also identified that increased despite therapy. This same KRAS mutation was later found in a separate nonresponding metastasis. In summary, parallel analyses of tumor biopsies and serial ctDNA monitoring show that lesion-specific radiographic responses to subsequent targeted therapies can be driven by distinct resistance mechanisms arising within separate tumor lesions in the same patient.

SIGNIFICANCE

Molecular heterogeneity ensuing from acquired resistance drives lesion-specific responses to subsequent targeted therapies. Analysis of a single-lesion biopsy is inadequate to guide selection of subsequent targeted therapies. ctDNA profiles allow the detection of concomitant resistance mechanisms residing in separate metastases and assessment of the effect of therapies designed to overcome resistance.

Abstract PR01: Acquisition of resistance to anti-EGFR therapy drives genomic heterogeneity and lesion-specific responses in colorectal cancer

How genomic heterogeneity associated with acquired resistance to targeted agents affects response to subsequent lines of therapy is unknown. Exposure to therapy may result in selection of sub-clonal cell populations, capable of growing under drug pressures. Therefore, a single-lesion biopsy at disease progression may vastly underrepresent the molecular heterogeneity of resistant tumor clones in an individual patient and may fail to detect the existence of distinct but important resistance mechanisms that could impact clinical response. To this aim, we identified a colorectal cancer (CRC) patient in whom multiple tumor biopsies were obtained at resistance following prolonged response to with the anti-EGFR antibody cetuximab and irinotecan therapy. Full-exome sequencing of 1000 cancer genes of both primary tumor and progression biopsy revealed a TP53 mutation in all samples and a novel MAP2K1 p.K57T mutation in one of the progressing liver biopsy. Interestingly, a mutation at the same MAP2K1 codon was identified in the cetuximab-resistant HCA46 CRC cell line. Biochemical analysis of preclinical model showed constitutive activation of MEK and ERK despite cetuximab treatment. Exogenous expression of the same mutant MEK1, but not wild-type MEK1, in an independent RAS-WT CRC cell line, LIM1215, conferred resistance to cetuximab or panitumumab. However, the combination of the MEK inhibitor trametinib with either cetuximab or panitumumab restored sensitivity, suggesting a potential therapeutic strategy to overcome resistance to EGFR blockade caused by this mutation.

Accordingly, the patient was treated with the combination of panitumumab and trametinib. After 3 months, imaging demonstrated a reduction in size of the biopsied liver metastasis harboring the MAP2K1 mutation, but revealed that some other lesions had progressed. Plasma for circulating DNA (ctDNA) analysis was longitudinally collected during combinatorial treatment. Pre-treatment plasma was analyzed using next-generation sequencing (NGS), confirming the presence of both TP53 and MAP2K1 variants, but surprisingly unveiling an additional KRAS mutation. ddPCR analysis of longitudinal timepopints of ctDNA unveiled that TP53 mutant levels dropped after initiation of therapy, but rose later during treatment with concomitantly/in parallel to CEA ones. However, MAP2K1 mutant levels declined, while KRAS mutant ones rose markedly during therapy, indicating outgrowth of a resistant KRAS-mutant clone. Biopsy of a different liver metastasis' segment that progressed despite panitumumab and trametinib revealed the same KRAS mutation identified in ctDNA.

In summary these findings illustrate how individual metastatic lesions can develop distinct resistance mechanisms to targeted agents, leading to striking differences in lesion-specific response to subsequent targeted therapies. As more trials evaluating targeted therapy strategies designed to overcome specific acquired resistance mechanisms enter the clinic, genomic results from single-tumor biopsies should be interpreted with caution. By contrast, liquid biopsy approaches have the potential to detect the presence of simultaneous resistance mechanisms residing in separate metastases in a single patient and to monitor the effects of subsequent targeted therapies.

Citation Format: Giulia Siravegna, Mariangela Russo, Lawrence S. Blaszkowsky, Giorgio Corti, Giovanni Crisafulli, Leanne G. Ahronian, Benedetta Mussolin, Eunice L. Kwak, Michela Buscarino, Luca Lazzari, Emanuele Valtorta, Mauro Truini, Nicholas A. Jessop, Hayley E. Robinson, Theodore S. Hong, Mari Mino-Kenudson, Federica Di Nicolantonio, Ashraf Thabet, Andrea Sartore-Bianchi, Salvatore Siena, John Iafrate, Ryan B. Corcoran, Alberto Bardelli. Acquisition of resistance to anti-EGFR therapy drives genomic heterogeneity and lesion-specific responses in colorectal cancer. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr PR01.

Patient-derived models of acquired resistance can identify effective drug combinations for cancer

Targeted cancer therapies have produced substantial clinical responses, but most tumors develop resistance to these drugs. Here, we describe a pharmacogenomic platform that facilitates rapid discovery of drug combinations that can overcome resistance. We established cell culture models derived from biopsy samples of lung cancer patients whose disease had progressed while on treatment with epidermal growth factor receptor (EGFR) or anaplastic lymphoma kinase (ALK) tyrosine kinase inhibitors and then subjected these cells to genetic analyses and a pharmacological screen. Multiple effective drug combinations were identified. For example, the combination of ALK and MAPK kinase (MEK) inhibitors was active in an ALK-positive resistant tumor that had developed a MAP2K1 activating mutation, and the combination of EGFR and fibroblast growth factor receptor (FGFR) inhibitors was active in an EGFR mutant resistant cancer with a mutation in FGFR3. Combined ALK and SRC (pp60c-src) inhibition was effective in several ALK-driven patient-derived models, a result not predicted by genetic analysis alone. With further refinements, this strategy could help direct therapeutic choices for individual patients.

Anchored multiplex PCR for targeted next-generation sequencing

We describe a rapid target enrichment method for next-generation sequencing, termed anchored multiplex PCR (AMP), that is compatible with low nucleic acid input from formalin-fixed paraffin-embedded (FFPE) specimens. AMP is effective in detecting gene rearrangements (without prior knowledge of the fusion partners), single nucleotide variants, insertions, deletions and copy number changes. Validation of a gene rearrangement panel using 319 FFPE samples showed 100% sensitivity (95% confidence limit: 96.5-100%) and 100% specificity (95% confidence limit: 99.3-100%) compared with reference assays. On the basis of our experience with performing AMP on 986 clinical FFPE samples, we show its potential as both a robust clinical assay and a powerful discovery tool, which we used to identify new therapeutically important gene fusions: ARHGEF2-NTRK1 and CHTOP-NTRK1 in glioblastoma, MSN-ROS1, TRIM4-BRAF, VAMP2-NRG1, TPM3-NTRK1 and RUFY2-RET in lung cancer, FGFR2-CREB5 in cholangiocarcinoma and PPL-NTRK1 in thyroid carcinoma. AMP is a scalable and efficient next-generation sequencing target enrichment method for research and clinical applications.

Interactions between benthic predators and zooplanktonic prey are affected by turbulent waves

Predators capture prey in complex and variable environments. In the ocean, bottom-dwelling (benthic) organisms are subjected to water currents, waves, and turbulent eddies. For benthic predators that feed on small animals carried in the water (zooplankton), flow not only delivers prey, but can also shape predator-prey interactions. Benthic passive suspension feeders collect prey delivered by movement of ambient water onto capture-surfaces, whereas motile benthic predators, such as burrow-dwelling fish, dart out to catch passing zooplankton. How does the flow of ambient water affect these contrasting modes of predation by benthic zooplanktivores? We studied the effects of turbulent, wavy flow on the encounter, capture, and retention of motile zooplanktonic prey (copepods, Acartia spp.) by passive benthic suspension feeders (sea anemones, Anthopleura elegantissima). Predator-prey interactions were video-recorded in a wave-generating flume under two regimes of oscillating flow with different peak wave velocities and levels of turbulent kinetic energy ("weak" and "strong" waves). Rates of encounter (number of prey passing through a sea anemone's capture zone per time), capture (prey contacting and sticking to tentacles per time), and retention (prey retained on tentacles, without struggling free or washing off, per time) were measured at both strengths of waves. Strong waves enhanced encounter rates both for dead copepods and for actively swimming copepods, but there was so much variability in the behavior of the live prey that the effect of wave strength on encounter rates was not significant. Trapping efficiency (number of prey retained per number encountered) was the same in both flow regimes because, although fewer prey executed maneuvers to escape capture in strong waves, more of the captured prey was washed off the predators' tentacles. Although peak water velocities and turbulence of waves did not affect feeding rates of passive suspension-feeding sea anemones, increases in these aspects of flow have been shown to enhance feeding rates and efficiency of motile benthic fish that lunge out of their burrows to catch zooplankton. Faster, more turbulent flow interferes with the ability of prey to detect predators and execute escape maneuvers, and thus enhances capture rates both for passive suspension-feeding predators and for actively swimming predators. However, prey captured in the mouths of fish are not washed away by ambient flow, whereas prey captured on the tentacles of suspension feeders can be swept off before they are ingested. Therefore, the effects of flowing water on predation on zooplankton by benthic animals depend on the feeding mode of the predator.

CANINE DISTEMPER IN THE RHESUS MONKEY (MACACA MULATTA)

Canine distemper has been transmitted to rhesus monkeys by a variety of methods. The disease is strikingly similar if not identical in its features with distemper in dogs.

THE SPARING EFFECT OF CANINE DISTEMPER ON POLIOMYELITIS IN MACACA MULATTA

1. Rhesus monkeys inoculated with canine distemper are relatively or completely immune to experimental poliomyelitis during the first 2 weeks of the distemper. 2. Monkeys convalescent from distemper are not resistant to experimental poliomyelitis. 3. Two monkeys vaccinated with distemper virus responded to poliomyelitis in a modified manner. 4. Distemper antiserum did not influence the course of experimental poliomyelitis in rhesus monkeys. 5. Equine encephalomyelitis and vaccinia encephalitis showed no sparing effect on the course of experimental poliomyelitis. 6. The concurrence of distemper and poliomyelitis in monkeys seems to represent a new immunity mechanism in the virus field.

Paternal inheritance of the primary sex ratio in a copepod

Uniparentally inherited genetic elements are under strong selection to manipulate sex determination in their host and shift the host sex ratio towards the transmitting sex. For any sex-ratio trait, lineage analysis and quantitative genetics are important tools for characterizing the mode of inheritance (biparental vs. maternal vs. paternal) thereby narrowing the field of possible sex-determining mechanisms (e.g. polygenic, sex chromosomes with meiotic drive, cytoplasmic microorganisms). The primary sex ratio of the harpacticoid copepod, Tigriopus californicus is often male-biased and is highly variable among full sib families. We found that this extra-binomial variation for the primary sex ratio is paternally but not maternally transmitted in T. californicus. Paternal transmission of the primary sex ratio has been well documented in the haplo-diploid hymenoptera but is relatively rare in diplo-diploid organisms. If the sex-ratio trait is paternally transmitted in other closely related harpacticoid copepods it would explain why male biased primary sex ratios are so common in this group.

Surgical complications and long-term outcome in pediatric liver transplantation

BACKGROUND/AIMS

Liver transplantation has been widely accepted for the treatment of children with end-stage liver disease over the last 10 years particularly with the advent of reduced-size liver transplant technique. This study reviewed the perioperative and long-term results in the pediatric program of the Queensland Liver Transplant Service, Brisbane, Australia.

METHODOLOGY

Retrospective analysis was performed in 153 children who received 176 liver grafts between 1985 and 1995, including 109 (62%) reduced-size and 67 (38%) whole liver grafts. Median follow-up period was 5.3 years.

RESULTS

One-, 5-, and 10-year patient and graft survival rates were 82% and 74%, 75% and 63%, and 70% and 60%, respectively. Normal physical and intellectual development was observed in 98% of survivors. There were no significant differences in patient or graft survival rates between transplants using reduced-size and whole liver grafts. Portal vein thrombosis was the most common vascular complication, occurring in 8%. Hepatic artery thrombosis occurred in 7%, including 11% of children less than 1 year old and 8% of those under 10 kg. Biliary complication was found in 16% and posttransplant gastrointestinal perforation in 19%.

CONCLUSIONS

Liver transplantation has the potential to cure and allow development in children with end-stage liver disease.

Stable expression of the human kinin B1 receptor in Chinese hamster ovary cells. Characterization of ligand binding and effector pathways

To delineate ligand binding and functional characteristics of the human B1 kinin receptor, a stable clone of Chinese hamster ovary cells expressing a single class of binding sites for [3H]des-Arg10-lysylbradykinin with a Kd of 0.3 nM and a Bmax of 38 fmol/mg protein ( approximately 40,000 receptors/cell) was isolated. Studies with peptide analogs showed that a lysine residue at position 1 (based on the lysylbradykinin sequence) of ligands was essential for high affinity binding to the human B1 receptor. In marked contrast to cloned Chinese hamster ovary cells expressing the human kinin B2 receptor, which internalized approximately 80% of the ligand within 5 min upon exposure to 2 nM [3H]bradykinin, exposure of cells expressing the B1 receptor to 1 nM [3H]des-Arg10-lysylbradykinin resulted in minimal ligand internalization. Stimulation of the B1 receptor led to inositol phosphate generation and transient increases in intracellular calcium, confirming coupling to phospholipase C, while immunoprecipitation of photoaffinity-labeled G-proteins from membranes indicated specific coupling of the receptor to Galphaq/11 and Galphai1,2. The B1, unlike the B2, receptor does not desensitize (as demonstrated by continuous phosphoinositide hydrolysis), enhancing the potential role of this receptor during inflammatory events.

Neuroleptic-induced striatal dopamine receptor supersensitivity in mice: relationship to dose and drug

Clozapine and molindone administered to mice for 21 days did not elevate the density of striatal 3H-spiperone binding sites at doses clinically equivalent to 1.5 mg/kg haloperidol, which elevated binding by 29%. Thioridazine (25 mg/kg) elevated binding by 25%. It appears that clinically equivalent doses of clozapine and molindone have reduced ability to induce striatal D-2 dopamine receptor supersensitivity. These data are discussed in relationship to in vitro potencies and toxicity. The dose-response relationship of chronic haloperidol treatment and specific striatal 3H-spiperone binding was complex, i.e., binding was elevated at all doses, but the dose-response curve was concave upward. These data suggest that supersensitization is a complex interactive phenomenon comprised of elevation of striatal D-2 dopamine receptor density and other compensatory mechanisms.

Self-induced orbital emphysema as a presenting sign of Munchausen's syndrome

A bizarre case of severe, debilitating pneumo-orbit resulting in proptosis, blindness, and eventual exenteration of the right eye and threatening the same fate for the left eye was worked up painstakingly for over 10 years before a final diagnosis of Munchausen's syndrome was uncovered. Five days after the diagnosis was made and appropriate management was instituted the severely proptotic left eye had returned to normal and the patient was discharged for out-patient psychiatric follow-up. A discussion of the differential diagnosis of pneumo-orbit is presented and Munchausen's syndrome, the final diagnosis in this case, is discussed from both an historical and psychiatric perspective.

Maxillary sinus development in patients with cleft palates as compared to those with normal palates

Maxillary sinusitis appears to be more prevalent in the cleft palate population than in the normal population. The increase in sinusitis may be due to the fact that the maxillary sinus develops differently embryonically in cleft palate patients than in those patients with normal palates. A double blind study was done by measuring the maxillary sinus cephalometric x-rays in cleft palate patients and then comparing them to patients with normally developed palates. The groups studied were 3 months to 20 years of age. It was concluded that in each of these groups there was no significant difference in size, shape, or rate of development of the maxillary sinus in cleft palate patients compared to the normal population. It is probable that the increased incidence of maxillary sinusitis in cleft palate patients is due mainly to the open palate with constant contamination of the nasal mucosa by food pushed into the nares and sinus ostia, resulting in maxillary sinusitis.