{"id":3190,"date":"2026-09-16T07:00:00","date_gmt":"2026-09-16T11:00:00","guid":{"rendered":"https:\/\/www.insilens.com\/?p=3190"},"modified":"2026-09-16T20:40:39","modified_gmt":"2026-09-17T00:40:39","slug":"circle-pharma-raises-92-5-million-for-direct-cyclin-d1-inhibition","status":"publish","type":"post","link":"https:\/\/www.insilens.com\/?p=3190","title":{"rendered":"Circle Pharma Raises $92.5 Million for Direct Cyclin D1 Inhibition"},"content":{"rendered":"

\"\"<\/p>\n

Company<\/strong><\/p>\n

Circle Pharma<\/p>\n

Event Type<\/strong><\/p>\n

Financing (Series E)<\/p>\n

Platform<\/strong><\/p>\n

MXMO Macrocycle Platform — Oral Cyclin D1-Rb Protein-Protein Interaction Inhibitor<\/p>\n

Indication<\/strong><\/p>\n

Estrogen-Receptor-Positive Breast Cancer<\/p>\n

Summary<\/h4>\n

Circle Pharma closed an oversubscribed $92.5 million Series E led by The Column Group, with Nextech Invest, RA Capital Management, Euclidean Capital and a strategic investment from Eli Lilly. The company plans to advance CID-165, an oral macrocyclic inhibitor designed to disrupt the cyclin D1-Rb interaction, into clinical development for estrogen-receptor-positive breast cancer in the first quarter of 2027 and support its broader cyclin program. The financing is strategically meaningful because it funds a direct approach to a long-recognized but difficult protein-protein interaction; it does not validate efficacy, safety, oral exposure or differentiation from CDK4\/6 inhibitors.<\/p>\n

The September 16 announcement identifies a new Series E round of $92.5 million and names the lead and participating investors. Proceeds are allocated to early clinical development of CID-165 and the wider cyclin-targeted macrocycle pipeline. Circle nominated CID-165 in December 2025 and previously guided to an IND submission in late 2026; the new disclosure shifts the expected clinical start to the first quarter of 2027. The company has reported preclinical monotherapy and combination activity in cyclin D1-driven breast-cancer and lymphoma models, plus more than 2,000-fold biochemical selectivity over cyclin D3-Rb binding. Those are sponsor-reported results, not human data. Financing terms, valuation, exact runway and milestone-based use of proceeds were not disclosed.<\/p>\n

Deep Analysis<\/h4>\n

One interpretation is that the round provides sufficient specialist capital to test whether direct cyclin D1 substrate-recognition blockade can become a new therapeutic class. Cyclin D1 is a lineage dependency in many ER-positive breast cancers, and blocking its RxL-mediated interaction with Rb could preserve Rb tumor-suppressor activity without broadly inhibiting CDK4 and CDK6. The named syndicate and Lilly participation support institutional interest, while the planned clinical entry provides a near-term validation point. Against this view, investor participation is not evidence of target engagement or therapeutic margin, and the clinical start is still prospective. A second interpretation is that CID-165 faces the same translational barriers that have limited intracellular macrocycles: oral bioavailability, tumor exposure, protein-binding effects, intracellular concentration, metabolism, and sustained disruption of a dynamic protein-protein interface. Combination activity with endocrine or CDK inhibitors may increase efficacy but also complicate attribution and tolerability.<\/p>\n

Company and Product Background<\/h4>\n

Circle Pharma develops cell-permeable, orally bioavailable macrocycles using its MXMO platform. Its lead program, CID-078, is a cyclin A\/B RxL inhibitor in Phase I testing for advanced solid tumors. CID-165 is the second oncology candidate and is intended to disrupt binding between cyclin D1 and the retinoblastoma tumor suppressor. In ER-positive breast cancer, cyclin D1-CDK4\/6 activity promotes Rb inactivation and cell-cycle progression. Circle’s approach targets the substrate-recognition interface rather than the kinase active site. That distinction is scientifically relevant but remains clinically unproven.<\/p>\n

Signal Extraction<\/h4>\n
    \n
  • This is a positive, high-value financing signal with moderate interpretive confidence. The round is large enough to move a differentiated macrocycle program from candidate nomination into human testing.<\/li>\n
  • Upgrades with:<\/strong> IND clearance, quantified human exposure and pharmacodynamic Rb effects, early activity in molecularly selected tumors and tolerability differentiated from CDK4\/6 inhibition.<\/li>\n
  • Downgrades with:<\/strong> further timeline slippage, limited oral exposure, dose-limiting cytopenias or dependence on combination therapy without clear added benefit.<\/li>\n
  • Falsified if:<\/strong> clinical pharmacokinetics cannot sustain intracellular target engagement or cyclin D1 selectivity fails to translate into a useful therapeutic window.<\/li>\n<\/ul>\n

    InSilens Take<\/h4>\n

    This is a positive, high-value financing signal with moderate interpretive confidence. The round is large enough to move a differentiated macrocycle program from candidate nomination into human testing and extends validation of direct cyclin targeting as an investable modality. The positive direction applies to financing capacity, not clinical performance.<\/p>\n

    Signal Assessment<\/h4>\n

    Signal strength:<\/strong> 4\/5 — a $92.5 million round directly funding a clinical-stage transition for a differentiated macrocycle program. Importance:<\/strong> Positive for financing capacity. Confidence:<\/strong> High on facts (round size, investors, stated use of proceeds and timeline); moderate for preclinical performance since quantitative results are company-reported. Interpretation confidence:<\/strong> Moderate-low, reflecting preclinical stage, undisclosed economics and unresolved exposure, safety and efficacy.<\/p>\n","protected":false},"excerpt":{"rendered":"

    Circle Pharma closed an oversubscribed $92.5 million Series E led by The Column Group, with Nextech Invest, RA Capital Management, Euclidean Capital and a strategic investment from Eli Lilly. The company plans to advance…<\/p>\n","protected":false},"author":1,"featured_media":3210,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1,2],"tags":[52,773,772],"class_list":["post-3190","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-all-categories","category-deals-and-financing","tag-breast-cancer","tag-circle-pharma","tag-cyclin-d1"],"blocksy_meta":[],"_links":{"self":[{"href":"https:\/\/www.insilens.com\/index.php?rest_route=\/wp\/v2\/posts\/3190","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.insilens.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.insilens.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.insilens.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.insilens.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=3190"}],"version-history":[{"count":2,"href":"https:\/\/www.insilens.com\/index.php?rest_route=\/wp\/v2\/posts\/3190\/revisions"}],"predecessor-version":[{"id":3213,"href":"https:\/\/www.insilens.com\/index.php?rest_route=\/wp\/v2\/posts\/3190\/revisions\/3213"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.insilens.com\/index.php?rest_route=\/wp\/v2\/media\/3210"}],"wp:attachment":[{"href":"https:\/\/www.insilens.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=3190"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.insilens.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=3190"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.insilens.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=3190"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}