Design of an Interferon-Resistant Oncolytic HSV-1 Incorporating Redundant Safety Modalities for Improved Tolerability

Abstract

Development of next-generation oncolytic viruses requires the design of vectors that are potently oncolytic, immunogenic in human tumors, and well tolerated in patients. Starting with a joint-region deleted herpes simplex virus 1 (HSV-1) to create large transgene capability, we retained a single copy of the ICP34.5 gene, introduced mutations in UL37 to inhibit retrograde axonal transport, and inserted cell-type-specific microRNA (miRNA) target cassettes in HSV-1 genes essential for replication or neurovirulence. Ten miRNA candidates highly expressed in normal tissues and with low or absent expression in malignancies were selected from a comprehensive profile of 800 miRNAs with an emphasis on protection of the nervous system. Among the genes essential for viral replication identified using a small interfering RNA (siRNA) screen, we selected ICP4, ICP27, and UL8 for miRNA attenuation where a single miRNA is sufficient to potently attenuate viral replication. Additionally, a neuron-specific miRNA target cassette was introduced to control ICP34.5 expression. This vector is resistant to type I interferon compared to ICP34.5-deleted oncolytic HSVs, and in cancer cell lines, the oncolytic activity of the modified vector is equivalent to its parental virus. In vivo , this vector potently inhibits tumor growth while being well tolerated, even at high intravenous doses, compared to parental wild-type HSV-1.

Immunotherapeutic Efficacy of Retargeted oHSVs Designed for Propagation in an Ad Hoc Cell Line

“…It is present in the oHSV named M032, currently in clinical trial [ 18 , 19 ]. Additional payloads recently engineered in oHSVs include the ligands to co-stimulatory immune receptors, CPI or combinations thereof [ 20 , 21 ].…”

“…Additional strategies to attain cancer specificity and preserve viral virulence include transcriptional retargeting—i.e., placing a critical viral gene under the control of a cancer-specific promoter, post-transcriptional retargeting and combinations thereof [ 39 ]. Examples include the control of the key γ34.5 virulence gene by a hybrid nestin enhancer-HSP68 minimal promoter which ensures expression of the HSV genome specifically in the nestin-positive glioblastoma cells [ 40 ] and the insertion of miRNA target sequences specific for selected tissues (e.g., brain, heart, or liver) to avoid off-tumor expression of key herpesviral proteins like ICP4 (infected cell protein 4), ICP27, UL8, and γ34.5 [ 20 ]. Such approaches have been elegantly reviewed recently [ 23 ] and are beyond the scope of current review.…”

Oncolytic Virotherapy for Cancer: Clinical Experience

“…Furthermore, the virus contains mutations in the UL37 gene that prevent axonal retrograde transport as well as latency, ensuring that virus will not damage neurons. Additionally, ONCR-177 encodes five immune-modulatory transgenes (IL-12, CCL4, FLT3LG, anti-CTLA4 and anti-PD-L1) driven by a dual bi-directional promoter [ 27 ]. ONCR-177 is currently in Phase I trial to determine the maximum tolerated dose and preliminary efficacy as monotherapy and in combination with pembrolizumab (NCT04348916).…”

In Situ Cancer Vaccination and Immunovirotherapy Using Oncolytic HSV

“…A clinical trial evaluating RP3 alone and in combination with anti-PD-1 in patients with solid tumors has recently started (NCT04735978) (Figure 1). ONCR-177 is armed with five human transgenes (hIL12, hFLT3LG (extracellular domain), hCCL4, and antagonists to hPD-1 and hCTLA-4) cloned into ONCR-159, which has normal cell-specific miRNA targets regulating the expression of HSV ICP4, ICP27, UL8, and γ34.5 [172]. mONCR-171 is identical to ONCR-177 except with mouse transgenes [29].…”