From Tumor Suppressors to Oncogenic Dynamics: The 2015 Dr. Paul Janssen Award Symposium

Journal Articles

Cancer genomics and the war on cancer

Bettegowda C, Sausen M, Leary RJ, et al. Detection and quantification of rare mutations with parallel sequencing. Sci Transl Med. 2014;6(224):224ra24.

Jones S, Chen WD, Parmigiani G, et al. Comparative lesion sequencing provides insights into tumor evolution. Proc Natl Acad Sci U S A. 2008;105(11):4283-8.

Kinde I, Wu J, Papadopoulos N, et al. Detection and quantification of rare mutations with massively parallel sequencing. Proc Natl Acad Sci U S A. 2011;108(23):9530-5.

Le DT, Uram JN, Wang H, et al. PD-1 blockade in tumors with mismatch-repair deficiency. New Eng J Med. 2015;372(26):2509-20.

Segal NH, Parsons DW, Peggs KS, et al. Epitope landscape in breast and colorectal cancer. Cancer Res. 2008;68(3):889-92.

Skora AD, Douglas J, Hwang MS, et al. Generation of MANAbodies specific to HLA-restricted epitopes encoded by somatically mutated genes. Proc Natl Acad Sci U S A. 2015;112(32):9967-72.

Tomasettti C, Marchinni L, Nowak M, et al. Only three driver gene mutations are required for the development of lung and colorectal cancers. Proc Natl Acad Sci U S A. 2015;112(1):118-23.

Tomasettti C, Vogelstein B. Cancer etiology. Variation in cancer risk among tissues can be explained by the number of stem cell divisions. Science. 2015;347(6217):78-81.

Topalian SM, Hodi FS, Brahmer JR, et al. Safety, activity, and immune correlates of anti-PD-1 antibody in cancer. N Engl J Med. 2012;366(26):2443-54.

Vogelstein B, Papadopoulos N, Velcullescu VE, et al. Cancer genome landscapes. Science. 2013;339(6127):1546-58.

Waclaw B, Bozic I, Pittman ME, et al. A spatial model predicts that dispersal and cell turnover limit intratumour heterogeneity. Nature. 2015;525(7568):261-4.

Wagle N, Emery C, Berger MF, et al. Dissecting therapeutic resistance to RAF inhibition in melanoma by tumor genomic profiling. J Clin Oncol. 2011;29(22):3085-96.

Engineering T cells: moving beyond leukemia

Davila ML, Riviere I, Wang X, et al. Efficacy and toxicity management of 19-28z CAR T cell therapy in B cell acute lymphoblastic leukemia. Sci Transl Med. 2014;6(224):224ra25.

Deeks SG, Wagner B, Anton PA, et al. A phase II randomized study of HIV-specific T-cell gene therapy in subjects with undetectable plasma viremia on combination antiretroviral therapy. Mol Ther. 2002;5(6):788-97.

Garfall AL, Maus MV, Hwang WT, et al. Chimeric antigen receptor T cells against CD19 for multiple myeloma. N Engl J Med. 2015;373(11):1040-7.

Grupp SA, Kalos M, Barrett D, et al. Chimeric antigen receptor-modified T cells for acute lymphoid leukemia. N Engl J Med. 2013;368(16):1509-18.

Hannahan D, Weinberg RA. The hallmarks of cancer. Cell. 2000;100(1):57-70.

Irving BA, Weiss A. The cytoplasmic domain of the T cell receptor zeta chain is sufficient to couple to receptor-associated signal transduction pathways. Cell. 1991;64(5):891-901.

June CH, Riddell SR, Schumacher TN. Adoptive cellular therapy: a race to the finish line. Sci Transl Med. 2015;7(280):280ps7.

Kalos M, Levine BL, Porter DL, et al. T cells expressing chimeric receptors establish memory and potent antitumor effects in patients with advanced leukemia. Sci Transl Med. 2011;3(95):95ra73.

Kochenderfer JN, Dudley ME, Kassim SH, et al. Chemotherapy-refractory diffuse large B-cell lymphoma and indolent B-cell malignancies can be effectively treated with autologous T cells expressing an anti-CD19 chimeric antigen receptor. J Clin Oncol. 2015;33(6):540-9.

Maude SL, Frey N, Shaw PA, et al. Chimeric antigen receptor T cells for sustained remissions in leukemia. N Engl J Med. 2014;371(16):1507-17.

Maus MV, Grupp SA, Porter DL, June CH. Antibody-modified T cells: CARs take the front seat for hematologic malignancies. Blood. 2014;123(17):2625-35.

Mitsuyasu RT, Anton PA, Deeks SG, et al. Prolonged survival and tissue trafficking following adoptive transfer of CD4zeta gene-modified autologous CD4(+) and CD8(+) T cells in human immunodeficiency virus-infected subjects. Blood. 2000;96(3):785-93.

Porter DL, Hwang WT, Frey NV, et al. Chimeric antigen receptor T cells persist and induce sustained remissions in relapsed refractory chronic lymphocytic leukemia. Sci Transl Med. 2015;7(303):303ra139.

Porter DL, Levine BL, Kalos M, et al. Chimeric antigen receptor-modified T cells in chronic lymphoid leukemia. N Engl J Med. 2011;365(8):725-33.

Scholler J, Brady TL, Binder-Scholl G, et al. Decade-long safety and function of retroviral-modified chimeric antigen receptor T cells. Sci Transl Med. 2012;4(132):132ra53.

Modular characterization of circulating tumor cells

Haber DA, Velculescu VE. Blood-based analyses of cancer: circulating tumor cells and circulating tumor DNA. Cancer Discov. 2014;4(6):650-61.

Miyamoto DT, Zheng Y, Wittner BS, et al. RNA-Seq of single prostate CTCs implicates noncanonical Wnt signaling in antiandrogen resistance. Science. 2015;349(6254):1351-6.

Ozkumur E, Shah AM, Ciciliano JC, et al. Inertial focusing for tumor antigen-dependent and -independent sorting of rare circulating tumor cells. Sci Transl Med. 2013;5(179):179ra47.

Yu M, Bardia A, Aceto N, et al. Cancer therapy. Ex vivo culture of circulating breast tumor cells for individualized testing of drug susceptibility. Science. 2014;345(6193):216-20.

Yu M, Bardia A, Wittner BS, et al. Circulating breast tumor cells exhibit dynamic changes in epithelial and mesenchymal composition. Science. 2013;339(6119):580-4.

Copper in oncogenic BRAF signaling and tumorogenesis

Brady DC, Crowe MS, Turski ML, et al. Copper is required for oncogenic BRAF signalling and tumorigenesis. Nature. 2014;509(7501):492-6.

Robert C, Karaszewska B, Schachter J, et al. Improved overall survival in melanoma with combined dabrafenib and trametinib. N Eng J Med. 2015;372(1):30-9.

Turski ML, Brady DC, Kim HJ, et al. A novel role for copper in Ras/mitogen-activated protein kinase signaling. Mol Cell Biol. 2012;32(7):1284-95.

KRAS and the path to new medicines

Appels NM, Beijnen JH, Schellens JH. Development of farnesyl transferase inhibitors: a review. Oncologist. 2005;10(8):565-78.

Cox AD, Der CJ. Ras history: the saga continues. Small GTPases. 2010;1(1):2-27.

Kohl NE, Omer CA, Conner MW, et al. Inhibition of farnesyltransferase induces regression of mammary and salivary carcinomas in ras transgenic mice. Nat Med. 1995;1(8):792-7.

Kohl NE, Wilson FR, Mosser SD, et al. Protein farnesyltransferase inhibitors block the growth of ras-dependent tumors in nude mice. Proc Natl Acad Sci U S A. 1994;91(19):9141-5.

Ostrem JM, Peters U, Sos ML, et al. K-Ras(G12C) inhibitors allosterically control GTP affinity and effector interactions. Nature. 2013;503(7477):548-51.

Sponsors

This symposium was made possible with support from

Featured Speaker:
Bert Vogelstein, Johns Hopkins University

Highlights

• In any large tumor, mathematical models show, mutations conferring resistance to treatment will eventually arise; thus cancer treatment should begin as early as possible.
• It may be possible to develop antibodies against proteins encoded by cancer genome mutations to use in targeted cancer therapies.
• Immunotherapies may work best for tumors that have especially high numbers of mutations.
• Early cancer detection could be achieved via assays that would identify mutations in free-floating blood and other body fluids.

Introduction

The Dr. Paul Janssen Award for Biomedical Research is presented annually to honor Janssen's legacy in drug development and biomedical research. William N. Hait of Janssen Research & Development introduced this year's awardee, Bert Vogelstein, as an innovator in cancer research who made an early leap to study the molecular basis of the disease not in animal models and cell lines but in human tissue. That work led Vogelstein to propose in 1988 that cancer is caused by the sequential accumulation of mutations in oncogenes and tumor suppressor genes, and the following year, to identify the p53 gene as a tumor suppressor, Hait explained. In 2006 Vogelstein published the first genome-wide association study in breast and colorectal cancers, revealing several new cancer genes, and many landmark studies followed.

The work of Vogelstein and colleagues in the past few decades "formed a paradigm on which much of modern cancer research is based," Hait said. Indeed, when investigators uncover sequence changes in the progression of normal tissue to malignancy, the schematic representation of the mutations found in a cell is often referred to as a Vogelgram. Vogelstein has recently pioneered powerful diagnostics for detecting early and sporadic forms of cancer, championing the need to intercept cancer before it takes hold.

Cancer genomics and the war against cancer

Bert Vogelstein of Johns Hopkins University began his talk with a history of cancer research. In 1971, at a time when researchers knew very little about the disease, President Richard Nixon declared a "war on cancer." Genetic studies have helped scientists get to know the enemy: more than 15 000 tumors have been sequenced and there are more than 2 million known cancer-associated mutations.

In normal adult tissues, cell birth is perfectly counterbalanced by cell death. But in tumors, the ratio is slightly skewed toward cell birth, by approximately 0.5%. That small discrepancy adds up over time, much like compound interest. "That's how tumors become large," Vogelstein said. "Small increases, large periods of time." Most solid tumors carry between 25 and 75 mutations, but only a few of those are driver mutations, controlling cell survival, cell fate, and mutation rate. For example, one type of pancreatic cancer called Pa34 has about 50 mutations, but just four are driver mutations. There are approximately 200 driver genes in the human genome.

By Vogelstein's count, there are 172 unequivocal driver genes in the human genome. Cell-survival genes (green) allow cells to survive in microenvironments containing low levels of glucose, oxygen, and growth factors; cell-fate genes (blue) control whether stem cells differentiate; and genome-maintenance genes (red) regulate the rate at which cells accrue mutations. (Image courtesy of Bert Vogelstein)

What causes these mutations? Vogelstein, along with Johns Hopkins bioinformatician Cristain Tomasetti, recently showed that lifetime number of stem cell divisions is tightly correlated with lifetime risk of cancer. On average three driver-gene mutations are required for the genesis of a solid tumor, two of which occur replicatively; that is, as a result of normal stem cell division. But averages do not mean much in themselves, Vogelstein explained. "The average human being has one breast and one testicle—not so informative," he said. The details of cause are different for each tumor: in lung cancer, for example, most mutations are caused by environmental factors such as smoking and pollution; in pancreatic cancer most mutations are replicative.

Despite the development of several drugs targeting driver mutations, targeted therapy has so far eventually been overcome by tumor resistance in every case. A Harvard University team working with Vogelstein built a mathematical model that explains why. Every cancerous lesion in a patient with metastatic disease contains hundreds to thousands of resistant cells before therapy begins. A treatment might kill almost all of the cells in the metastasis, but the cells that remain will be the ones resistant to the drug, and within about six months those cells will repopulate the tumor. Studies suggest cancer cells do not divide more quickly than normal cells; indeed, this model explains how a normal rate of cell division is sufficient to bring the cancer back. Mutations conferring drug resistance will inevitably arise in any large tumor, the model showed. Such resistance is not seen in mice, which have much smaller tumors that do not contain the number of cells required for these mutations to arise. There is thus a clear need to initiate treatment when tumors are small, using combination therapies in which one therapy does not cause genetic or epigenetic alterations that would make the tumor more resistant to another therapy.

Most therapies targeting driver mutations are small molecules, but Vogelstein's group aims to develop antibodies against proteins encoded by driver genes. The difficulty is that these proteins are located inside the cell, and antibodies recognize proteins on the cell surface. However, these peptides are displayed on the cell surface by immune system molecules when they are degraded, as an infectious agent would be. The researchers are working to design antibodies that recognize peptides from the mutated portion of these proteins. They have developed so-called MANAbodies (antibodies to mutation-associated neo-antigens) against epitopes of common oncogene driver mutations, including KRAS. Preliminary studies show that MANAbodies can bind to or kill cells with high levels of these epitopes. The studies have not yet shown that MANAbodies can bind to or kill cells with the epitope levels usually found in the body, however. Another method under consideration is to develop MANAbodies to carrier mutations, which are more numerous.

Proteins made by mutated driver genes are dismantled intracellularly and presented on the cell surface for recognition by the immune system's major histone compatibility (MHC) class I molecules. Early work suggests that mutagen-associated neo-antigens, or MANAs, can be recognized by antibodies raised against them—MANAbodies. (Image courtesy of Bert Vogelstein)

The frequency of passenger mutations may also have immediate applications in the clinic. Researchers have long wondered why a powerful new immunotherapy—an antibody against an immune-regulating protein called PDCD1 (PD1)—works well for particular types of melanoma and lung cancer but not for other types of cancer. It turns out that the successful treatments had targeted tumor cells with 10–20 times more mutations. Vogelstein's group found that other cancers with high numbers of mutations also responded to the drug. This example shows how cancer genomics is beginning to play a role in guiding the use of immunotherapies.

The group is also designing methods to detect driver mutations in samples of body fluids, so that cancer can be found early and treated preemptively. Vogelstein noted that it takes some 30 years for a normal cell to develop into metastatic cancer, yet today researchers and clinicians can tune in only for the last three—when the cancer becomes clinically obvious. He envisions a future when routine lab tests will check for driver mutations. When sequencing tumor DNA in free-floating blood (not circulating tumor cells), Vogelstein and his colleagues can detect early signs of cancer in about 40%–70% of samples from four types of cancer. Students in his lab have also developed a Pap smear genetic test that can reliably detect endometrial cancer and detect ovarian cancer in about 50% of cases. Other ideas include testing saliva to detect head and neck cancers, testing stool for colorectal and other GI cancers, and testing nipple aspirates for breast cancer. Indeed, Vogelstein said in closing, early detection is the key to conquering cancer, and although research in this area is still underfunded, some drug companies are beginning to prioritize the development of early-detection technologies.

Speakers:
Carl June, University of Pennsylvania
Daniel A. Haber, Massachusetts General Hospital

Highlights

• One immunotherapy approach is to develop antibodies against checkpoint proteins.
• Researchers are trying to adapt T-cell immunotherapies to types of cancer other than leukemia.
• Cancer's heterogeneity increases with its progression, and single-cell analysis of CTCs allows researchers and clinicians to monitor a cancer's evolution.

Engineering T cells: moving beyond leukemia

Cancer biologists have long known that a tumor must escape immune recognition to thrive, Carl June of the University of Pennsylvania told the audience. But scientists have only recently begun to understand how to overcome immune tolerance. One immunotherapy approach is to develop antibodies against so-called checkpoint proteins, such as PD1, which put the brakes on the T-cell response to tumors. The antibodies reduce immune inhibition and activate the immune system against the tumor. The other approach is adoptive T-cell therapy, in which T cells taken from the patient are therapeutically altered and then reinfused.

June's lab pioneered a version of the second approach, engineering tumor-recognizing receptors called chimeric antigen receptors (CARs) onto patients' T cells. The early success of this experimental therapy has rocked the field. June described his team's most recent work on a CAR called CTL019. He also explored the questions still open about the therapy, such as whether CARs must persist long-term to be effective, how best to engineer CARs, and which types of T cells should be modified.

CARs were initially designed to explore basic T-cell mechanisms some 25 years ago. In 1997 researchers tried to use them to treat HIV. Early efforts to use CARs as cancer therapies failed, and over the last 10–15 years, researchers have focused on making them more potent and specific. June's first CTL019 trial began in 2010 in patients with advanced chronic lymphocytic leukemia (CLL). The trial, lacking funding, was stopped with only three patients enrolled. However, all three patients responded to the therapy, and the ensuing paper attracted support from Novartis, which continues to fund June's work.

An overview of how CAR cells are engineered and infused into patients in CTL019 therapy. (Image courtesy of Carl June)

Genetic markers on CARs allow researchers to track modified T cells to show that each one kills at least 1000 tumor cells. The modified T cells proliferate upon encountering targets, and patients in remission continue to express antibodies against the cancer, making repeat therapeutic administration unnecessary. The 5-year results of the CTL019 phase I study in 14 patients show a 57% response rate in CLL. Response to CAR therapy was unchanged by the presence of mutations that generally confer treatment resistance, June reported. Meanwhile, a study of 30 patients with acute lymphocytic leukemia (ALL) found a 90% response rate. The ALL survival rate at 2 years for existing therapies is 10%. The first ALL patient treated by June's team, who received CTL019 at age 6, is now 10 years old and remains in remission. She was invited to the White House on January 30, 2015, when President Barack Obama and NIH director Francis Collins announced the Precision Medicine Initiative.

In patients in complete remission, CAR cells had initially expanded to include all the T cells in the blood, but then decreased to a frequency of about 0.1%—the level of memory T cells. Malignant cells fell to undetectable levels within approximately 6 months. The major side effect of CAR therapy is cytokine release syndrome, an extremely high fever lasting several days, or in rare cases weeks. It occurs only while patients are responding to the therapy and is probably a result of macrophage activation and innate immunity. The syndrome is more serious in patients with higher tumor burdens, suggesting a benefit for early administration. Other CAR-related toxicities include B-cell aplasia, tumor lysis syndrome, and macrophage activation syndrome.

Three CARs targeting the cell-surface marker CD19 are in commercial development for leukemias and lymphomas. The compounds activate different signaling pathways, use different delivery vectors, and persist for different lengths of time. Preliminary data indicate persistence may be more important in CLL, whereas short-acting CARs may be sufficient in ALL.

Ten ALL patients have so far developed resistance to CTL019, all with CD19-negative leukemia. Nine of those patients' tumors developed splice variants lacking the site that the CAR recognizes; thus there is a need to engineer CARs able to recognize multiple sites. June's group recently launched a pilot trial of a new CAR that targets CD22. The team also recently tested CTL019 in multiple myeloma, which is thought to be CD19-negative. The therapy was successful in one patient, probably through an unknown indirect mechanism. There is clearly much left to learn about CAR therapies, and studies testing different types of adoptive T-cell therapy and different immune system targets are underway.

Modular characterization of circulating tumor cells

Primary tumors or metastatic deposits send cells to circulate through the blood stream, singly or in clusters. The vast majority of the cells will die in circulation but a few take root in tissues and give rise to metastases. Daniel A. Haber of Massachusetts General Hospital explained that diagnosis would be aided immensely if clinicians had tools to find circulating tumor cells (CTCs). But finding one of about 100 CTCs among some 50 billion red blood cells and 50 million white blood cells is difficult.

"The first challenge is an engineering one—how to find a needle in the haystack," Haber said. He and bioengineer Mehmet Toner developed a microfluidic device called the CTC iChip that uses three steps to siphon blood cells and isolate tumor cells. First, antibodies carrying magnetic beads bind to white blood cells while a size-sorting mechanism removes platelets and red blood cells. Next, inertial forces applied through the walls of the curved channels press the cells into single file. Finally, a magnetic field sorts the beaded white blood cells from CTCs. Haber likened the process to "getting rid of all the hay to find the needle." The chip is now part of an automated prototype system that can sort about 10 milliliters of blood per hour.

The CTC iChip is round because it is produced by a company that makes DVDs. (Image courtesy of Daniel A. Haber)

The researchers can study the isolated CTCs to learn about how cells transition from an epithelial to a mesenchymal fate, taking on the ability to migrate and form metastases. Haber's team used antibody markers and RNA analysis to observe this process over the course of a patient's treatment. Analyses of genome and transcriptome data from CTCs identified upregulated genes and signaling pathways as cancers became invasive in the bloodstream, acquiring the ability to form metastases.

The analyses also revealed that CTCs are highly heterogeneous. In a recently published study, the researchers examined individual CTCs in prostate cancer patients treated with an androgen receptor (AR) inhibitor. As resistance to the treatment developed, androgen receptor mRNA increased in CTCs but not in the primary tumors. CTCs developed different splice variants that could activate ARs. About two-thirds of patients with treatment-resistant prostate cancer had at least one AR gene abnormality, with about 20% of CTCs carrying more than one abnormality.

Patients resistant to the widely used AR inhibitor enzalutamide had upregulated Wnt-5A signaling. In these resistant patients, primary tumor cells again did not express the pathway, suggesting that new pathways are activated as tumor cells become more aggressive. Tumor cells are initially fairly homogenous in pathway dysregulation, but, Haber explained, successful treatments exert evolutionary pressure on the tumor cells, changing the cancer. Therefore, therapies prescribed first may not be appropriate as the disease progresses.

The best way to identify genetic changes leading to drug resistance is to analyze CTCs on a single-cell level. Together with genetic and RNA analyses, CTC culturing would allow clinicians to monitor a cancer's evolution or to test whether a treatment is likely to work. Researchers in Haber's lab cultured breast cancer cells from women with metastatic breast cancer and examined how the cells' genotypes changed over time. Many of the mutations present were not found at the time of diagnosis but would strongly affect the success of estrogen-based therapies. Intervening when these mutations emerge could prolong patients' lives.

Speakers:
Christopher Counter, Duke University School of Medicine
Peter Lebowitz, Janssen Research & Development

Highlights

• Copper chelators may have clinical potential in cancers driven by oncogenic BRAF.
• Recent work has identified novel compounds that inhibit oncogenic KRAS, and Janssen Pharmaceuticals plans to bring these drugs into clinical trials within 5 years.

Copper in oncogenic BRAF signaling and tumorigenesis

The MAP Kinase (MAPK) signaling pathway, which comprises the kinases RAF, MEK, and ERK, is well studied. The pathway mediates signals promoting cell proliferation to the nucleus, and genes in the pathway are known to play a role in cancer. Christopher Counter of Duke University School of Medicine described his group's work to determine how copper dampens the cancer-promoting effects of MAPK-pathway mutations.

In flies, activating MAPK signaling in the developing eye causes a phenotype called rough eye—a disruption of normal cellular organization. Recent work led by Dennis Thiele at Duke University showed that reducing the levels of copper transporter 1 (CTR1)—the primary means of copper transport into cells—suppressed this phenotype. The researchers also found that MEK is the copper-sensitive link in the chain.

Counter's group set out to test the effects of copper on cancers driven by mutations in BRAF, a known oncogene. Deleting the CTR1 gene in a mouse model of lung cancer with oncogenic BRAF caused MAPK signaling and tumor burden to decrease. These animals also survived longer than those with the CTR1 gene. The researchers hypothesized that loss of CTR1 expression made oncogenic BRAF unable to transmit its pro-tumor signal, because MEK requires copper to function.

Deleting the CTR1 gene in a mouse model of lung cancer driven by oncogenic BRAF caused a 7-fold reduction in the number of lung tumors (right) compared to mice with normal CTR1 levels (left). (Image courtesy of Christopher Counter)

To study copper's clinical potential in cancer treatment, Counter turned to a rare condition called Wilson's disease, which is characterized by very high copper levels. It is treated with daily oral doses of copper chelators—chemicals that capture copper and remove it from the body, and which have an excellent safety profile. The newest of these molecules, tetrathiomolybdate (TM), had previously been tested in cancer patients.

Counter's team found that TM reduced the transformed growth of tumor cells driven by oncogenic BRAF. Cells with mutations in other oncogenes did not respond. Studying the compound further, the group provided preliminary evidence that TM had a therapeutic benefit in a mouse model of BRAF-driven metastatic melanoma. Specifically, mice with tumor lesions were treated with the BRAF inhibitor vemurafenib (which is used as a front-line therapy in melanoma), with daily oral TM, or with a combination of the two drugs. Both drugs increased survival, but the combination was more potent than either drug alone.

The group has recently registered a phase I trial that will test this combination in humans. A MEK inhibitor called trametinib is already used in cancer therapy, but combining the BRAF and MEK inhibitors with a copper chelator could provide an additional benefit. The group is also exploring whether copper chelators are effective against other types of cancer.

KRAS and the path to new medicines

There are many hurdles in the drug discovery pipeline, explained Peter Lebowitz of Janssen Research & Development; success often depends not only on innovation but also on perseverance. He described Janssen's efforts to develop an inhibitor of RAS-family oncogenes, which have been notoriously difficult to target therapeutically. Lebowitz reported that Janssen expects to have its first direct RAS inhibitor in proof-of-concept trials within 5 years.

The discovery of RAS as an oncogene was made 1982. Researchers transfected DNA from the T24 bladder tumor cell line into fibroblasts, which subsequently transformed into cancerous cells, and identified oncogenic HRAS (a RAS isoform) as the transforming element. RAS has since been found to be mutated in many cancers, including in colorectal and pancreatic cancers, in 20% of lung cancers, and in some melanomas. KRAS is the dominant mutated isoform of RAS in human tumors.

RAS is a GTP-binding protein that acts as a molecular switch, with an "on" state that promotes cell proliferation. Oncogenic mutations lock the protein into this "on" position; thus RAS would seem to be an ideal drug target. But structural studies failed to find clear druggable regions of the protein. A cysteine on one end of the molecule is central to its function, and a chemical tag on the cysteine brings the molecule to the cell membrane, where it accomplishes its signaling task. Companies developed compounds that interfered with this chemical tag, but the approach, which worked in preclinical transgenic HRAS mouse models, failed in clinical trials. "The biology was more complex than we thought," Lebowitz said. The KRAS isoform has an additional mechanism for bringing the molecule to the cytoplasm that made tag interference ineffective. Other efforts to block KRAS action also fizzled.

In 2013 Kevan Shokat at the University of California, San Francisco, identified compounds that bind to KRAS in a region of the protein that is commonly mutated in cancer. In general terms, these compounds trap the oncogenic protein permanently in its "off" position. The compounds also seem to prevent KRAS from interacting with other proteins it regulates. Janssen is partnering with Araxes Pharma, a company Shokat established to develop the compounds, and has had early success with several compounds that Lebowitz hopes will be carried into clinical trials.

Lebowitz also described Janssen's partnership with Aduro Biotech to pursue an immunological approach to killing cancer cells. Aduro has engineered a strain of Listeria that can carry tumor-cell antigens to dendritic cells, thereby eliciting a potent immune response. This approach is being tested in pancreatic cancer patients and has yielded promising phase II results.

KRAS inhibitors developed in partnership with Araxes Pharma kill cells carrying oncogenic KRAS at a concentration of about 2 micromolar (G12C+, blue) but do not affect normal KRAS (non-G12C, grey). (Image courtesy of Peter Lebowitz)

Moderator:
Brooke Grindlinger, The New York Academy of Sciences

Panel discussion

The panel session began with each panelist discussing how cancer research and therapy might look in the future. Vogelstein described the biggest gaps in the pipeline currently as prevention and detection. Therapeutic research is certainly important; but if detected early enough, most cancers could be cured with existing therapeutics—appropriately timed surgery and drugs. Such a shift in treatment focus has precedent: deaths from cardiovascular disease have decreased by 75% in the last 50 years, not because of improvements in treatment but because of a focus on prevention and diagnostics.

Therapies and diagnostics are inseparable, Vogelstein explained; the earlier a cancer is detected, the more likely a durable remission will be. In an ideal future, most tumors will be diagnosed early enough to be easily treatable. Meanwhile, treatment for more advanced cancer will be potent enough to be administered once in an outpatient setting and will include a combination of targeted and/or immunotherapies, each designed so as not to cause resistance to the others.

Haber pointed out that the current paradigm of oncology care is aimed at treating metastatic disease. Physicians are much less adept at interpreting diagnostic tests of early-stage cancer and determining when such tumors need treatment. In the future, he said, very aggressive screening in the primary care setting will be key, as will a wider arsenal of 20 to 30 potent therapeutic choices, rather than one or two.

Lebowitz added that some cancers, such as multiple myeloma, have premalignant states; indeed, some 15% of people over 65 years old carry premalignant cells that could become leukemias or lymphomas. The ability to identify such premalignancies—and to determine the risk that a premalignancy in any given person will become malignant in the next year—is at the top of his wish list, along with potent drugs that would preemptively eliminate the disease.

June noted that in his area, immuno-oncology, the main challenge is to develop technology to better standardize the manufacture, storage, and delivery of the CAR therapy he and others are developing. Also needed, because many cancer patients are elderly, is research into why the immune system loses potency as we age, and how to maintain its strength. Such work could improve the efficacy of immune-based therapies.

In response to a question about whether regulatory bodies such as the U.S. Food and Drug Administration and the European Medicines Agency need to adapt to keep up with the changing face of cancer treatment, Lebowitz said that regulators have done a good job keeping pace with the science, moving quickly on important new drugs and on the challenges presented by drug combinations and biomarkers. Haber noted, however, that diagnostics—which are becoming more complex and expensive—may pose challenges for regulators and payors. "You're asking the employer or insurance company ... to pay to prevent cancer in someone who might develop it 10 years from now when they work for another company."

An audience member asked panelists to comment on so-called basket studies, particularly the National Cancer Institute MATCH Trial, in which patients are treated not on the basis of where in the body the cancer originated but on the basis of of its molecular signature. Lebowitz explained that these trials have established a framework for testing drugs made by different companies within a single trial. He added, however, that after such trials get a positive signal for efficacy, they should immediately move into the final stages of testing to get a definitive answer.

To what extent will early detection improve the efficacy of cancer therapies?

What types of techniques are most promising for early detection?

Will new technologies be able to detect whether a person with premalignant markers or very early-stage cancer is at high or low risk of developing the disease?

Why do T-cell receptor therapies work so well for some patients but not for others?

Why do immune-based therapies in general work better for some cancer types than for others? Will it be possible to broaden their base of efficacy?

Can T-cell receptor therapies be applied to cancer types other than leukemias?

Can circulating tumor cells be analyzed to determine whether a therapy will be effective?

How do the economics and insurance landscape of cancer care need to change to prioritize diagnostics and early detection?