Abstract 2691: A triple combination of fostrox (MIV-818) with immune checkpoint and kinase inhibition shows increased anti-tumor efficacy in vivo

Background: Fostroxacitabine bralpamide (fostrox) is an orally administered liver-targeted troxacitabine-based nucleotide prodrug currently undergoing phase 1/2a clinical trial in advanced hepatocellular carcinoma (HCC), in combination with pembrolizumab or lenvatinib (NCT03781934). In phase 1 monotherapy fostrox has demonstrated proof-of-concept in advanced HCC, intrahepatic cholangiocarcinoma and liver metastasis from gastrointestinal solid tumors. Liver-selective fostrox-induced DNA-damage and tumor cell killing has the potential to enhance the anti-tumor activity in combination with checkpoint blockade, and inhibition of angiogenesis leads to increased levels of the active metabolite of fostrox. We therefore investigated a triple combination of fostrox with anti-PD1 and lenvatinib in nonclinical tumor models in vivo.

Methods: Combinations of fostrox with anti-PD1 and lenvatinib treatment were evaluated in the subcutaneous syngeneic mouse CT26 model1. Groups of 8 mice were randomized using the Matched Distribution method based on tumor size day 1. Treatment was with fostrox (BID days 1-5, p.o.), anti-PD1 (BIW for 3 weeks, i.p.), and lenvatinib (QD for 21 days, p.o.). Tumours were measured three times weekly during the dosing phase, and statistical differences between the treatment groups was analyzed by two-way ANOVA. Pharmacodynamic response to fostrox, induction of DNA-damage (phospo-ser139-H2AX), was assessed by immunohistochemistry (IHC). Tumor infiltrating lymphocytes (TILs) were assessed by IHC evaluating the expression level of CD8, CD4, LAG-3, and PD-L1.

Results: Treatment with the triple combination of fostrox (30mg/kg) plus anti-PD1 (3mg/kg) and lenvatinib (5mg/kg) showed a significantly (p<0.0001) improved anti-tumor efficacy compared with any double combination, fostrox plus anti-PD1, fostrox plus lenvatinib, or anti-PD1 plus lenvatinib, in the CT26 tumor model. A low basal level of DNA damage was observed, which was increased by fostrox treatment. Analysis of CD8, CD4, LAG-3 and PD-L1 expression levels indicated increased TILs.

Conclusions: The triple combination of fostrox with anti-PD1 and lenvatinib showed enhanced efficacy in a nonclinical tumor model, and changes in TILs were consistent with increased immune-mediated anti-tumor activity. The results indicate a potential for increased anti-tumor efficacy using a triple combination of fostrox plus checkpoint inhibition and anti-angiogenic therapy.

1The study was approved by the Institutional Animal Care and Use Committee (IACUC) of CrownBio UK, and conducted in accordance with the regulations of the Association for Assessment and Accreditation of Laboratory Animal Care (AAALAC)

Citation Format: Fredrik G. Oberg, Sujata Bhoi, Malene Jensen, Karin Tunblad, Hans Wallberg. A triple combination of fostrox (MIV-818) with immune checkpoint and kinase inhibition shows increased anti-tumor efficacy in vivo [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2691.

Synthesis of P1'-functionalized macrocyclic transition-state mimicking HIV-1 protease inhibitors encompassing a tertiary alcohol

Seven novel tertiary alcohol containing linear HIV-1 protease inhibitors (PIs), decorated at the para position of the benzyl group in the P1' side with (hetero)aromatic moieties, were synthesized and biologically evaluated. To study the inhibition and antiviral activity effect of P1-P3 macrocyclization, 14- and 15-membered macrocyclic PIs were prepared by ring-closing metathesis of the corresponding linear PIs. The macrocycles were more active than the linear precursors and compound 10f, with a 2-thiazolyl group in the P1' position, was the most potent PI of this new series (Ki 2.2 nM, EC50 0.2 μM). Co-crystallized complexes of both linear and macrocyclic PIs with the HIV-1 protease enzyme were prepared and analyzed.

Design and synthesis of HIV-1 protease inhibitors for a long-acting injectable drug application

The design and synthesis of novel HIV-1 protease inhibitors (PIs) (1-22), which display high potency against HIV-1 wild-type and multi-PI-resistant HIV-mutant clinical isolates, is described. Lead optimization was initiated from compound 1, a Phe-Phe hydroxyethylene peptidomimetic PI, and was directed towards the discovery of new PIs suitable for a long-acting (LA) injectable drug application. Introducing a heterocyclic 6-methoxy-3-pyridinyl or a 6-(dimethylamino)-3-pyridinyl moiety (R(3)) at the para-position of the P1' benzyl fragment generated compounds with antiviral potency in the low single digit nanomolar range. Halogenation or alkylation of the metabolic hot spots on the various aromatic rings resulted in PIs with high stability against degradation in human liver microsomes and low plasma clearance in rats. Replacing the chromanolamine moiety (R(1)) in the P2 protease binding site by a cyclopentanolamine or a cyclohexanolamine derivative provided a series of high clearance PIs (16-22) with EC(50)s on wild-type HIV-1 in the range of 0.8-1.8 nM. PIs 18 and 22, formulated as nanosuspensions, showed gradual but sustained and complete release from the injection site over two months in rats, and were therefore identified as interesting candidates for a LA injectable drug application for treating HIV/AIDS.

Synthesis, X-ray analysis, and biological evaluation of a new class of stereopure lactam-based HIV-1 protease inhibitors

In an effort to identify a new class of druglike HIV-1 protease inhibitors, four different stereopure β-hydroxy γ-lactam-containing inhibitors have been synthesized, biologically evaluated, and cocrystallized. The impact of the tether length of the central spacer (two or three carbons) was also investigated. A compound with a shorter tether and (3R,4S) absolute configuration exhibited high activity with a K_i of 2.1 nM and an EC₅₀ of 0.64 μM. Further optimization by decoration of the P1′ side chain furnished an even more potent HIV-1 protease inhibitor (K_i = 0.8 nM, EC₅₀ = 0.04 μM). According to X-ray analysis, the new class of inhibitors did not fully succeed in forming two symmetric hydrogen bonds to the catalytic aspartates. The crystal structures of the complexes further explain the difference in potency between the shorter inhibitors (two-carbon spacer) and the longer inhibitors (three-carbon spacer).

HIV-1 protease inhibitors with a transition-state mimic comprising a tertiary alcohol: improved antiviral activity in cells

By a small modification in the core structure of the previously reported series of HIV-1 protease inhibitors that encompasses a tertiary alcohol as part of the transition-state mimicking scaffold, up to 56 times more potent compounds were obtained exhibiting EC(50) values down to 3 nM. Three of the inhibitors also displayed excellent activity against selected resistant isolates of HIV-1. The synthesis of 25 new and optically pure HIV-1 protease inhibitors is reported, along with methods for elongation of the inhibitor P1' side chain using microwave-accelerated, palladium-catalyzed cross-coupling reactions, the biological evaluation, and X-ray data obtained from one of the most potent analogues cocrystallized with both the wild type and the L63P, V82T, I84 V mutant of the HIV-1 protease.

Identification of MMP-12 inhibitors by using biosensor-based screening of a fragment library

Small inhibitors of matrix metalloproteinase 12 (MMP-12) have been identified with a biosensor-based screening strategy and a specifically designed fragment library. The interaction between fragments and three variants of the target and a reference protein with an active-site zinc ion was measured continuously by surface plasmon resonance. The developed experimental design overcame the inherent instability of MMP-12 and allowed the identification of fragments that interacted specifically with the active-site of MMP-12 but not with the reference protein. The interaction with MMP-12 for selected compounds were analyzed for concentration dependence and saturability. Compounds interacting distinctly with the target were further evaluated by an activity-based assay, verifying MMP-12 inhibition. Two effective inhibitors were identified, and the compound with highest affinity was confirmed to be a competitive inhibitor with an IC50 of 290 nM and a ligand efficiency of 0.7 kcal/mol heavy atom. This procedure integrates selectivity and binding site identification into the screening procedure and does not require structure determination.

Two-carbon-elongated HIV-1 protease inhibitors with a tertiary-alcohol-containing transition-state mimic

A new generation of HIV-1 protease inhibitors encompassing a tertiary-alcohol-based transition-state mimic has been developed. By elongation of the core structure of recently reported inhibitors with two carbon atoms and by varying the P1' group of the compounds, efficient inhibitors were obtained with Ki down to 2.3 nM and EC50 down to 0.17 microM. Two inhibitor-enzyme X-ray structures are reported.

Novel potent macrocyclic inhibitors of the hepatitis C virus NS3 protease: Use of cyclopentane and cyclopentene P2-motifs

Several highly potent novel HCV NS3 protease inhibitors have been developed from two inhibitor series containing either a P2 trisubstituted macrocyclic cyclopentane- or a P2 cyclopentene dicarboxylic acid moiety as surrogates for the widely used N-acyl-(4R)-hydroxyproline in the P2 position. These inhibitors were optimized for anti HCV activities through examination of different ring sizes in the macrocyclic systems and further by exploring the effect of P4 substituent removal on potency. The target molecules were synthesized from readily available starting materials, furnishing the inhibitor compounds in good overall yields. It was found that the 14-membered ring system was the most potent in these two series and that the corresponding 13-, 15-, and 16-membered macrocyclic rings delivered less potent inhibitors. Moreover, the corresponding P1 acylsulfonamides had superior potencies over the corresponding P1 carboxylic acids. It is noteworthy that it has been possible to develop highly potent HCV protease inhibitors that altogether lack the P4 substituent. Thus the most potent inhibitor described in this work, inhibitor 20, displays a K(i) value of 0.41 nM and an EC(50) value of 9 nM in the subgenomic HCV replicon cell model on genotype 1b. To the best of our knowledge this is the first example described in the literature of a HCV protease inhibitor displaying high potency in the replicon assay and lacking the P4 substituent, a finding which should facilitate the development of orally active small molecule inhibitors against the HCV protease.

Variations of the P2 group in HIV-1 protease inhibitors containing a tertiary alcohol in the transition-state mimicking scaffold

A short synthetic protocol leading to HIV-1 protease inhibitors with a tertiary alcohol based transition-state mimicking unit and different P2 side chains has been developed.

Microwave-accelerated synthesis of P1'-extended HIV-1 protease inhibitors encompassing a tertiary alcohol in the transition-state mimicking scaffold

Two series of P1'-extended HIV-1 protease inhibitors comprising a tertiary alcohol in the transition-state mimic exhibiting Ki values ranging from 2.1 to 93 nM have been synthesized. Microwave-accelerated palladium-catalyzed cross-couplings were utilized to rapidly optimize the P1' side chain. High cellular antiviral potencies were encountered when the P1' benzyl group was elongated with a 3- or 4-pyridyl substituent (EC50 = 0.18-0.22 microM). X-ray crystallographic data were obtained for three inhibitors cocrystallized with the enzyme.

A new class of HIV-1 protease inhibitors containing a tertiary alcohol in the transition-state mimicking scaffold

Novel HIV-1 protease inhibitors encompassing a tertiary alcohol as part of the transition-state mimicking unit have been synthesized. Variation of the P1'-P3' residues and alteration of the tertiary alcohol absolute stereochemistry afforded 10 inhibitors. High potencies for the compounds with (S)-configuration at the carbon carrying the tertiary hydroxyl group were achieved with Ki values down to 2.4 nM. X-ray crystallographic data for a representative compound in complex with HIV-1 protease are presented.

Skin circulation in the nipple after reduction mammaplasty by upper and lower glandular resections

Avascular necrosis of the nipple is a serious complication of reduction mammaplasty with nipple transposition. A study was undertaken to measure the skin circulation in the nipple before, during and after this operation. In 14 patients undergoing a reduction mammaplasty according to the method of Strömbeck, the skin circulation was measured in 25 breasts with laser doppler flowmetry (LDF) and fluorescein flowmetry (FF). LDF showed that the skin circulation increased after de-epithelialization to 204.4 +/- 31.0% of the preoperative value (100%) (mean +/- SEM, p less than 0.01). After the upper and lower glandular resection the circulation was reduced to 90.7 +/- 12.3% of the preoperative value. The division of the lateral pedicle did not affect the circulation. After the skin had been sutured, the circulation was 71.5 +/- 9.1% of the preoperative value (p less than 0.01). One to four days postoperatively the circulation was 100.3 +/- 13.2% of the preoperative value. At FF uniform fluorescence was observed in the nipple postoperatively in all patients but two, in whom avascular necrosis later developed. Our results thus show that the circulation in the nipple after reduction mammaplasty by the Strömbeck method is adequate and that it is safe to divide the lateral dermal pedicle.

The thermal emission from the skin and the vascularity of the breasts in normal and scoliotic girls

The vascularity of the breasts was examined by thermographic and diaphanographic methods in normal and scoliotic girls. The thermal emission from the skin registered with an AGA Thermovision 750 camera (Stockholm, Sweden) on black and white Polaroid film was evaluated visually by 10 independent observers. No significant differences between the thermal images of the left and the right breast were found in the control or scoliotic groups or in girls with a right convex thoracic curve, nor was there any significant difference between the groups in this respect. Image analysis of diaphanograms of the breasts using the GOP 300 system showed a significantly greater vascularity of the left breast than of the right, both in the scoliotic series as a whole and in the subgroup with a right convex thoracic curve, but not for the reference group. The vascularity of the left breast but not of the right one was significantly greater for the girls with a right convex thoracic curve than for the control group. The results of the diaphanographic study confirm earlier observations and together provide substantial evidence that unilateral stimulation of rib growth due to a greater vascularity of the left breast and the underlying costosternal junctions might be one initiating factor in the development of right convex thoracic idiopathic scoliosis in adolescent girls.

Breast carcinoma and benign breast lesions. Diaphanography and quantitative evaluation using the computer-controlled image scanner OSIRIS

A total of 110 diaphanograms from women with breast carcinoma and 154 diaphanograms from women with benign breast disorders were quantitatively evaluated using the OSIRIS image scanner. Optical density values in the green and red spectral bands were recorded. The malignant and the benign groups, were statistically evaluated using linear discriminant analysis. Correct classification was obtained in 73.5 per cent of women with breast carcinoma and in 84.6 per cent of women with benign breast disorders. Visual interpretation of the findings alone classified 84.5 per cent of the malignant lesions correctly and 90.8 per cent of the benign lesions correctly. Quantitative evaluation combined with visual interpretation improved the accuracy of classification of breast carcinoma (91.8%), but not of benign breast disorders, which was about the same (83.8%).

Physical interpretation of diaphanograms using the computer-controlled image scanner OSIRIS

Experiments have shown that the light recorded in diaphanography covers approximately the wavelength region of 645 to 900 nm. No significant change in image quality was noted by changing the camera distance between 10 and 25 cm and the light source aperture between 5 and 30 mm. Experiments using polarising filters indicated that the breast is optically isotropic; therefore the results cannot be improved by using polarising filters. In a comparison of various films. Kodak Ektachrome Infrared Film gave the best results. No degradation or variation in image quality was observed when different batches were compared or when the exposed film was stored for 3 weeks before processing. The exposure level is a critical factor and a series of 3 images is needed for optimum evaluation of diaphanograms. The experiments indicate that diaphanography gives consistent results.

Diaphanography in various breast disorders. Clinical and experimental observations

Diaphanograms of various breast disorders were obtained and investigations were made concerning the ways in which changes in skin temperature, fine needle aspiration biopsy and surgery as well as anti-oestrogen treatment affect the findings. A lowering of the skin temperature made it impossible to detect some of the vessels in the breast and more difficult to interpret the diaphanograms. Cooling of the breast should therefore be avoided in diaphanography. Mastitis, haemorrhage after fine needle aspiration biopsy or an induced haemorrhagic cyst will result in the appearance of a shadow on the diaphanogram suggestive of malignancy. The shadow of a haemorrhagic cyst disappeared immediately after the cyst was emptied and diminished gradually in the other cases. Thus the nature of the breast disorder may be determined by diaphanography if it is repeated at short intervals. Fine needle aspiration biopsy may yield false positive findings and should therefore not be made until diaphanography has been performed.

Diaphanography in benign breast disorders. Correlation with clinical examination, mammography, cytology and histology

Histologically classified benign breast disorder was present in 163 breast of 158 symptomatic women. The results of diaphanography (DPG) were correlated with those obtained by clinical examination (CE), mammography (M) and cytology (C). A tumour was palpable in 108 cases (66.3%). A false positive diagnosis, i.e. possibly malignant, probably malignant or malignant was made in 15 cases (9.2%) with DPG, and in 33 cases (20.2%) with M. Use of both M and DPG reduced the number of false positives to 1.8 per cent. In 8 cases (4.9%) false positive diagnosis was made with C. During a mean observation time of 58.5 months (range 44-72 months, one case of breast carcinoma was diagnosed.

Diaphanography in breast carcinoma. Correlation with clinical examination, mammography, cytology and histology

Histologically classified carcinoma was present in 110 breasts of 108 symptomatic women. The results of diaphanography (DPG) were correlated with those obtained by clinical examination (CE), mammography (M) and cytology (C). A tumour was palpable in 87 cases (79.1%). A false negative diagnosis was made in 17 cases (15.5%) using DPG, in 13 cases (11.8%) using M and in 15 cases (13.6%) using C, but in 12 of the latter cases (10.9%) the specimen was not representative. The validity of the findings using DPG and M was also analysed. The calculations were based on the results obtained from the present investigation and from a study of diaphanography in 163 cases of benign breast disorders. For DPG the sensitivity was 85 per cent, the specificity 91 per cent, the positive predictive value 86 per cent and the negative predictive value 90 per cent. For M the sensitivity was 86 per cent, the specificity 80 per cent, the positive predictive value 75 per cent and the negative predictive value 91 per cent. The specificity for diaphanography was significantly different from mammography (p less than 0.05). The use of both M and DPG reduced the number of false negatives from 11.8 per cent to 5.5 per cent. In conclusion, DPG has been demonstrated to be a useful adjunct to CE and M.