Response Category1All Patients2

n=53 (%)Phase 2-eligible subgroup

n=23 (%)Complete response 6 (11.3)3 5 (21.7)Partial response 0 0Stable disease 10 (18.9) 5 (21.7)Progressive disease 37 (69.8) 13 (56.6)Clinical benefit rate (CR+PR+SD ≥ 6 weeks) 16 (30.2) 10 (43.5)Durable response rate (PR or CR ≥ 24 weeks) 6 (11.3) 5 (21.7)Median Duration of Response (months) 35.1+ (9.2 - 44.9) 35.7+ (14.1 – 44.9)

Immunological activation in responding patients with recurrent HGG after treatment with Toca 511 & Toca FC: Results from a phase 1 trialDerek Ostertag1, William Accomando1, Daniel Hogan1, Oscar Diago1, Dawn Gammon1, Ali Haghighi1, Leah Mitchell1, Maria Rodriguez-Aguirre1, Timothy F. Cloughesy2,

Steven N. Kalkanis3, Tom Mikkelsen3, Joseph Landolfi4, Bob Carter5, Clark C. Chen5, Michael A. Vogelbaum6, Harry E. Gruber1, Asha Das1, Douglas J. Jolly1

1Tocagen Inc, 2Univesity of California, Los Angeles, 3Henry Ford Hospital, 4JFK Medical Center, 5University of California, San Diego , 6Cleveland Clinic Foundation

© 2017 Tocagen Inc.

Introduction and Background

• Ph1 ascending dose trial of Toca 511 & Toca FC in rHGG show: • 6 complete responses (IDH1 wt and mutant) are ongoing with a median duration of response >35.1 months

• Durable response (objective response > 24 weeks) rate may be a valuable end point for immunotherapeutics

• Responders do not show a higher DNA mutational burden in tumors compared to tumors from patients that progressed

• Of the two patients at first recurrence with IDH1 tumor mutations, both responded, suggesting an enrichment of durable complete responses in IDH1 mutant patients at first or second recurrence treated with Toca 511 & Toca FC

• In tumors collected before the start of treatment, responders have significantly higher tumor infiltrating T cells compared to patients who did not respond

• PCA of multiplex inflammatory cytokine ELISAs from longitudinal patient blood shows at least 2 panels of cytokines which expression is associated with response to therapy

Conclusions

4405

Research supported by:Many thanks to all of the patients, their families and caregivers and to individuals and groups providing financial support

Clinical Results

REFERENCES:1. Perez, O. D. et al. Design and selection of Toca 511 for clinical use: modified retroviral replicating vector with improved stability and gene expression. Mol Ther, 2012. 20:1689-16982. Ostertag, D., et al. Brain tumor eradication and prolonged survival from intratumoral conversion of 5-fluorocytosine to 5-fluorouracil using a nonlytic retroviral replicating vector. Neuro Oncol, 2012. 14(2): p. 145-593. Hiroka, K., et. al. Retroviral replicating vector-mediated gene therapy achieves long-term control of tumor recurrence and leads to durable anticancer immunity. Neuro Oncol, 2017. 19(7): 918-9294. Mitchell LA et al. Toca 511 gene transfer and treatment with the prodrug, 5-fluorocytosine, promotes durable antitumor immunity in a mouse glioma model. Neuro Oncol, 2017. 19(7): p. 930-939 5. Cloughesy TF. et. al. Phase 1 trial of vocimagene amiretrorepvec and 5-fluorocytosine for recurrent high-grade glioma. Sci Transl Med. 2016 Jun 1;8(341)

FC cycle is every 6 weeks

Complete Response in a Patient with Progressive GBM: PR at 6 Months, CR at 48 Months*, Alive > 52 Months

*Independent Radiology Review, Macdonald criteria

Toca 511 (Vocimagene amiretrorepvec) is an investigational retroviral replicating vector (RRV) that encodes the transgene cytosinedeaminase (CD) not present in human cells1. Toca 511 can be delivered by multiple routes and selectively infects and spreads in tumorcells. Subsequent oral administration of investigational extended-release 5-FC (Toca FC) results in formation of 5-FU within infectedtumor expressing CD2. 5-FU kills cancer cells and Myeloid Derived Suppressor Cells (MDSCs) leading to immune activation against thetumor via a combination of mechanisms. This sequence of events is amplified with multiple cycles of Toca FC. Treatment with Toca 511and Toca FC selectively destroys cancer cells within the body, while leaving healthy cells unharmed.

Toca 511- optimized RRV expressing CD, a prodrug activator gene

Toca FC- investigational extended-release oral formulation of 5-FC• 5-FC crosses blood-brain barrier and is approved for fungal infections of the brain• CD converts 5-FC to 5-FU within infected cells• GBM cell lines and MDSCs are sensitive to 5-FU• 5-FU inhibits thymidylate synthase, perturbs RNA synthesis, and affect glycosylation of proteins and lipids• 5-FU mediated killing triggers anticancer immunity from within tumor with systemic benefit• 5-FU has a very short half-life so systemic toxicity is not observed

days post challenge

4K. Hiraoka et al, Neuro-Oncology, 2017

Tumor re-challenge study

3Mitchell et al. Neuro-Oncology, 2017

Adoptive transfer study

Naïve mice implanted with tumor cells, then received lymphocytes from naïve or cured mice; examined survival

days post tumor implant

Naïve or cured mice received tumor cells in the flank; examined tumor growth

Toca 511 & 5-FC activates a durable T cell mediated immune response

Optimized CD(cytosine deaminase)

5-FUAnticancer

Drug

5-FC (Toca FC)Antifungal

Prodrug

Structural RRV genesRegulatory genes CD gene Regulatory genes

5-FU has a very short half-life with direct cell killing

localized to cancer microenvironment

Tumor selectivity and replication in cancers cells is driven by:• Defects in the innate immune system of cancer cells• Virus enters some normal cells, but is rapidly eliminated by

innate and acquired immunity• Virus spreads through tumor without triggering immune system• Virus only infects dividing cells

1Based on Macdonald criteria by independent radiology review (IRR) that includes radiologic, corticosteroid and clinical data2Of 56 safety evaluable patients, 53 patients received Toca 511 & Toca FC are efficacy-evaluable and of these 2 were not evaluable for response 3Includes a patient treated with Toca 511 & Toca FC and bevacizumab who had a CR, which began more than 11.2 months after administration of Toca 511. Because responses in the bevacizumab setting typically occur within a few months of treatment, and even then CRs are rare, the response in this patient is more likely consistent with the immunologic mechanism of Toca 511 & Toca FC therapy.+ means that survival and responses are ongoing

Ph1 ascending dose trial of safety and tolerability of Toca 511 & Toca FC in rHGG5

Toca 511 administered into the resection cavity

Eligibility

•GBM or AA •Planned resection ≥ 80%•18-75 yrs old•Single or contiguous tumor •KPS ≥70•Adequate lab values•No prior bevacizumab for recurrence

•Tumor ≤ 5 cm

SURGERY

Toca 511 once From 1.4 X 107 to 4.8 X 109 TU

(half-log increases)

Cyclic Toca FC From 135 to 220 mg/kg/day

Multi-centerAdaptive 3+3 design

Dose EscalationObjective: Safety, tolerability, and MTD

Immune Monitoring: Sustained PD-1+T cells in Patient Samples Who Have Not Progressed

p = 0.351 p = 0.023Wilcoxon Rank Sum Test p = 0.837

TITL

Fra

ctio

n

Increased Clonality and T Cell Infiltrating Lymphocyte (TITL) Fraction in the Tumor- Pre-Toca 511 treatment

• Responders have significantly higher TITL fractions than non-responders• Responders also have a trend towards higher TITL clonality than non-responders (not significant)• no clear trend in TITL diversity• IHC methods to determine spatial orientation of infiltrating T cells in progress

Inflammatory cytokine changes in blood are associated with patient outcomesIdentified by multivariate analysis

Molecular Characterization of patient tumors: low tumor DNA mutation burden

Summary of RNA and DNA sequencing results from patient tumors(left to right) barplot shows the total number of high confidence mutations called by MUSE from exome sequencing data. The next three left columns summarize results from RNA sequencing: molecular subtype (mesenchymal – red, classical – black, neural –green, proneural – blue), and IDH1 R132H/S mutation (orange)). The next four columns show response (CR – green, SD – purple, PD – orange), clinical features, including eligibility for phase II/III trial (Phase 2-eligible subgroup – yellow), tumor grade at study entry as determined by clinical site pathologist (grade IV = grey, grade III = black), number of recurrences (1 or 2 – light brown, >2 – dark brown). Patients are ordered by duration of survival post-resection and Toca 511 treatment. Patients alive at last contact are indicated by light blue bars.

The proportion of cells exhibiting PD-1+ T cell positivity from patient PBMC samples assessed by multicolor flow cytometry in a cohort (13 pts) from whom samples were available. T-cells include all CD3+ lymphocytes, CD3+ CD4+ or CD3+ CD8+ lymphocytes. The “clinical benefit” category including 5 stable disease and 1 complete responders, while the “progressive disease” category includes 7 patients with progressive disease. All patients received the same dose regimen of Toca511 & Toca FC. Patients may have received Lomustine, Bevacizumab, or neither. Boxplots indicate median and interquartile ranges for the given time point. The resultant p-value from a Kruskal-Wallis one-way analysis of variance on ranks, applied to all samples across time points, is displayed at the top of each plot.

Cytokines were measured by multiplex ELISA. Log-transformed values for 30 cytokines were subjected to principal components analysis (PCA), and PCA scores were used in multivariate statistical models to identify putative associations withpatient outcomes, including best clinical response (logistic regression models) and survival (Cox proportional hazards models). A) table showing the top ten cytokine loadings ranked by relative contribution to the principal component (i.e. cytokine signature), B) scatter plots showing PCA scores relative to time since initial 5-FC treatment stratified by best patient response category and including linear regression fit lines for each category, and C) Kaplan-Meier survival curves with patients stratified by maximum component 8 value or minimum component 12 value, and displaying Wald test p-values with and without adjustment for patient age and gender.